2020-10-29T05:57:11Zhttp://edoc.mpg.de/ac_p_oai.ploai:edoc.mpg.de:137982004-03-1819:89
Yield effects in single and coupled nonlinear thermokinetic reaction systems
Zeyer, K. P.
Mangold, M.
Shah, S.
Kienle, A.
Gilles, E. D.
expertsonly
coupling; thermokinetic systems; oscillations; yield; optimization
The influence of nonlinear dynamic effects on yield is considered for consecutive-parallel reaction schemes in a single phase CSTR. In the first part, the behavior of a single uncoupled reactor is investigated. Emphasis is on the reaction dynamics and the yield of the intermediate ethanal using continuation and optimization techniques. We characterize regions of periodic, complex periodic, and chaotic oscillations. The chaotic region is reached by type III intermittency. In all cases, the global optimum yield of the intermediate is a steady state, which is unstable or stable due to the location of the stability boundary. It is found that autonomous periodic operation is only locally better than steady state operation. In the second part, different types of mass and energy coupling between two reactors are studied. The results obtained for a simple consecutive parallel reaction scheme are validated by a more detailed model of the ethanol oxidation by hydrogen peroxide under iron(III) catalysis, which can be described by an extended consecutive-parallel reaction scheme. Analogies are found with respect to the dynamics and the yield of the intermediate.
2002
Article
http://edoc.mpg.de/13798
urn:ISSN:0942-9352
Zeitschrift für Physikalische Chemie-International Journal of Research in Physical Chemistry & Chemical Physics, v.216, 403-433 (2002)
en
oai:edoc.mpg.de:138012012-03-2819:89
A numerical bifurcation analysis of nonlinear oscillations in crystallization processes
Pathath, P. K.
Kienle, A.
expertsonly
crystallization; modeling; population balance; bifurcation; stability; nonlinear dynamics
The main aim of this work is the theoretical prediction and analysis of the nonlinear behavior of crystallization processes. As a first step towards the theoretical analysis a fairly simple population balance model including fines dissolution and classified product removal has been considered. By means of numerical bifurcation and stability analysis, regions in the parameter space of the operating conditions and the physical properties with periodic behavior have been predicted. Due to the simplicity of the underlying model the results are only of qualitative nature. Future work will focus on a quantitative prediction of the nonlinear behavior with more detailed models and an experimental verification.
2002
Article
http://edoc.mpg.de/13801
urn:ISSN:0009-2509
Chemical Engineering Science, v.57, 4391-4399 (2002)
en
oai:edoc.mpg.de:138092004-03-1719:89
Improving simulated moving bed processes by cyclic modulation of the feed concentration
Schramm, H.
Kaspereit, M.
Kienle, A.
Seidel-Morgenstern, A.
expertsonly
A new mode of operation for simulated moving bed chromatographic processes is presented. While conventional SMB processes are operated with constant feed concentration, a modulation of the feed concentration during the switching cycles is introduced in the new mode of operation. Thereby the performance compared to the conventional SMB process is improved significantly. The productivity and the product concentration is increased. Simultaneously, the solvent consumption is decreased.
2002
Article
http://edoc.mpg.de/13809
urn:ISSN:0930-7516
Chemical Engineering & Technology, v.25, 1151-1155 (2002)
en
oai:edoc.mpg.de:138102012-04-2319:89
Stochastic resonance in a thermokinetic reaction system
Zeyer, K. P.
Münster, A. F.
Gilles, E. D.
expertsonly
We present numerical simulations of the counterintuitive effect of stochastic resonance in a model of a thermokinetic chemical oscillator. Small periodic perturbations are amplified by stochastic or deterministically chaotic parameter fluctuations giving way to large temperature oscillations. Stochastic resonance is characterized by various means, among them Fourier transforms, probability distribution functions and interspike histograms.
2002
Article
http://edoc.mpg.de/13810
Physical Chemistry Chemical Physics, v.4, 5988-5994 (2002)
en
oai:edoc.mpg.de:138112004-07-2619:89
Particulate processes: a special issue of chemical engineering science
Gilles, E. D.
Kienle, A.
expertsonly
2002
Article
http://edoc.mpg.de/13811
urn:ISSN:0009-2509
Chemical Engineering Science, v.57, 4255-4255 (2002)
en
oai:edoc.mpg.de:138172007-10-2619:89
Steady-state multiplicity in bioreactors : bifurcation analysis of cybernetic models
Namjoshi, A.
Kienle, A.
Ramkrishna, D.
expertsonly
cybernetic modeling; multiplicity; bifurcation analysis; mammalian bioreactors
Biological systems have an additional level of complexity compared to other chemical systems because of the effects of metabolic regulation, a defining feature of biosystems. Metabolic regulation in the form of control of enzyme synthesis and activity leads to non-linear behavior in bioreactors. Mathematical models that take into account these control mechanisms can be very successful in capturing the peculiarities of bioreactors such as multiple steady states and periodic phenomena. Cybemetic models model the expression and activation of enzymes by the use of cybernetic control variables and have been used to explain multiplicities in hybridoma reactors. In particular Namjoshi et al. (Biotechnol. BioEng. (2002), accepted) have been able to predict the transition from batch and fed batch to continuous culture in hybridoma experiments (Biotechnol. BioEng. 67(l) (2000) 25). The resulting multiple steady states vary widely in cell mass and waste metabolites. The model captures this multiplicity and its bifurcation analysis his revealed additional steady-state branches, three unstable and one stable. The stability of the additional steady state (steady state 4) was confirmed by dynamic simulations using fed-batch strategy prior to initiation of continuous operation. Steady state 4, in view of its close proximity to steady state 3, appears to have little practical significance. The likelihood of additional steady states that may be significantly different can, however not be ignored. Thus, it seems possible to envisage other states of metabolic activity, displaying alternative flux distributions that could lead to steady states notably different from those already determined. Calculation of the most singular point of the system herein is rendered difficult by both its size and possession of non-differentiable variables. The bifurcation analysis reveals the steady-state behavior under a range of operating conditions and can be used to plan optimum bioreactor operation.
2003
Article
http://edoc.mpg.de/13817
urn:ISSN:0009-2509
Chemical Engineering Science, v.58, 793-800 (2003)
en
oai:edoc.mpg.de:349242003-07-3019:89oai:edoc.mpg.de:350012004-02-1719:89
Nonlinear dynamics and control of reactive distillation processes
Kienle, A.
expertsonly
In some cases reactive distillation is very economical compared to a conventional process design, where reaction and separation are carried out in different processing units. Typical examples are esterification and etherification processes. Consequently, there has been a lot of interest in this type of integrated process during the last years. Emphasis has been on steady state modeling, on development of new processes and on process design. Still, comparably little work has been done on dynamics and control of reactive distillation processes, although these processes can sometimes show an intricate nonlinear dynamic behavior including multiplicities and instabilities. Reliable prediction and understanding of these phenomena is a necessary prerequisite for better process design and control. The objective of this contribution is to give an overview of the present knowledge on dynamics and control of reactive distillation processes with emphasis on the authors work in this field. The outline of the contribution is the following: First, focus is on open loop dynamics of reactive distillation processes involving-multiplicities, self-sustained oscillations and spatio temporal pattern formation also termed as nonlinear wave propagation. Different sources for nonlinear behaviour are systematically identified and implications for process operation and process control are discussed. The second part is concerned with control of continuously operated reactive distillation columns. Emphasis is on inferential control schemes, where the desired product purities are inferred from temperature measurements.
Czech Society for Chemical Engineering (CSCHI)
2002
Conference-Paper
http://edoc.mpg.de/35001
urn:ISBN:80-86059-33-2
Novosad, J.: 15th International Congress of Chemical and Process Engineering CHISA 2002, Czech Society for Chemical Engineering (CSCHI) (2002)
oai:edoc.mpg.de:350132004-02-1719:89
Steady state multiplicity in bioreactors: bifurcation analysis of cybernetic models
Namjoshi, A.
Kienle, A.
Ramkrishna, D.
expertsonly
Biological systems have an additional level of complexity compared to other chemical systems because of the effects of metabolic regulation. Such regulation in the form of control of enzyme synthesis and activity leads to nonlinear behavior in bioreactors. Mathematical models that take into account these control mechanisms can be very successful in capturing the peculiarities of bioreactors such as multiple steady states and periodic phenomena. Cybernetic models, which are extremely suitable for this task model expression and activation of enzymes by the use of cybernetic control variables and have been used to explain multiplicities in hybridoma reactors. In particular, the cybernetic model of Namjoshi et al. (2002) has been able to predict the transition from batch and fed-batch to continuous culture in hybridoma experiments of Europa et al. The multiple steady states that result, vary widely in the concentration of cell mass and waste metabolites. The model captures the multiplicity of steady states for the hybridoma reactors. The bifurcation analysis of such models reveals the steady state behavior under a range of operating conditions and can be used to plan bioreactor operation to get the desired staedy states for maximum productivity.
2002
Conference-Paper
http://edoc.mpg.de/35013
17th Symposium on Chemical Reaction Engineering ISCRE 17 (2002)
oai:edoc.mpg.de:350152004-06-3019:89
Dynamic plantwide modelling, flowsheet simulation and nonlinear analysis of an industrial production plant
Waschler, R.
Kienle, A.
Anoprienko, A.
Osipova, T.
expertsonly
A detailed dynamic model of the Monsanto process for the production of acetic acid is presented. The nonlinear behaviour of the process is investigated and implications different control structures have on its dynamic behaviour are pointed out.
2002
Conference-Paper
http://edoc.mpg.de/35015
Grievink, J.; van Schijndel, J.: European Symposium on Computer Aided Process Engineering - 12 - ESCAPE-12, 583-588 (2002)
oai:edoc.mpg.de:350182004-09-0619:89
Nonlinear Analysis of gPROMS Models Using DIVA as via a CAPE ESO interface
Mangold, M.
Mohl, K. D.
Grüner, S.
Kienle, A.
Gilles, E. D.
expertsonly
The CAPE ESO interface of the process simulator gPROMS is used to pass model information to numerical methods contained in the simulation environment DIVA. By the interface, algorithms for the continuation of stable and unstable steady states and periodic solutions can be applied directly to gPROMS models. The use of the interface is illustrated by a detailed nonlinear model of an industrial distillation column.
2002
Conference-Paper
http://edoc.mpg.de/35018
urn:ISBN:0-444-51109-1
Grievink, J.; van Schijndel, J.: European Symposium on Computer Aided Process Engineering - 12, 919-924 (2002)
oai:edoc.mpg.de:629892004-02-1319:89
Nonlinear behaviour of an ideal reactor separator network with mass recycle
Pushpavanam, S.
Kienle, A.
expertsonly
In this work the nonlinear behavior of a coupled reactor-separator network is analyzed using singularity and bifurcation theory. The reactor is modeled as a CSTR, which sustains an exothermic first order reaction. The separator is modeled as a flash process. The effluent from the reactor is fed to the separator. The reactant rich stream (assumed to be the bottoms) from the separator isrecycled back to the reactor. Focus is on pure mass recycle, as the two units are decoupled energetically via heat exchangers. Two different modes of operation are considered. These are compared with each other and with the well known stand alone reactor with a first order exothermic reaction. For the first mode of operation, the feed rate is fixed and for the second the recycle rate is fixed. In practice, these different modes of operation can be achieved by a suitable control strategy. It is shown that the behavior crucially depends on the mode of operation. Fixing the feed rate can lead to severe operational problems including monotonic and oscillatory unstable steady statesover a wide range of operating conditions. Further, parameterregions are identified, where no steady state exists at all. On the other hand when the recycle rate is fixed the coupled system admits at least one stable steady state solution for a fixed set of operating conditions.
2001
Article
http://edoc.mpg.de/62989
Chemical Engineering Science, v.56, 2837-2849 (2001)
oai:edoc.mpg.de:629902005-06-0619:89
Method of Lines within the Simulation Environment DIVA for Chemical Processes
Köhler, R.
Mohl, K. D.
Schramm, H.
Zeitz, M.
Kienle, A.
Mangold, M.
Stein, E.
Gilles, E. D.
expertsonly
In chemical engineering, detailed process modeling, simulation, nonlinear analysis, and optimization of single process units as well as integrated production plants are issues of growing importance. As a software tool addressing these issues, the simulation environment DIVA is introduced. DIVA comprises tools for process modeling, preprocessing and code generation of simulation models. Furthermore, its simulation kernel contains several advanced methods for simulation, parameter continuation, and dynamic optimization which can be applied to the same process model. These numerical methods require a model description in form of differential algebraic equations (DAE). However, many models of chemical processes derived from first principles lead to partial differential equations (PDE) for distributed parametersystems, to integro partial differential equations (IPDE) for population balances of dispersed phases, and to DAE for lumped parameter systems. In order to transform the PDE and IPDE models into the required DAE model formulation, DIVA employs the "Method-of-Lines" (MOL) approach for one space coordinate. The wide variety of distributed parameter models of chemical processes requires on one hand conventional discretization methods like, e.g.,finite-difference schemes, and on the other hand more sophisticated methods to obtain reliable results in an acceptable computation time. Another approach of so called high-resolution methods uses adaptive approximation polynomials. High-resolution methods are developed forhyperbolic conservation laws with steep moving fronts. Examples areessentially-non-oscillatory (ENO) schemes or the robust upwindkappa-interpolation scheme. In order to support the user of the simulation environment diva, the symbolic preprocessing tool SYPPROT for MOL discretization is developed by means of the computer-algebra-system MATHEMATICA. This tool provides different discretization schemes to transform PDE, IPDE and the related boundary conditions on 1–dimensional spatialdomains into DAE. Discretization options concern fixed spatial grids and moving gridsbased on an equidistribution principle. The toolbox architecture of SYPPROT allows fast testing of various discretization schemes without redefinition of the model equations. This is regarded as an im portant feature to minimize the overall effort for modeling and simulation. A further characteristic that is key to theeasy exchange of discretization schemes is the separation between mode lequations and MOL parameter definitions by means of the mathematica datastructure (MDS).
The resulting overall DAE are written in symbolic form as an inputfile for the DIVA code generator, which automatically generates the DIVA simulation files representing a process unit model in the modellibrary. In the following section 13.2 the architecture of the simulation environment DIVA is presented. This architecture consists of four layers, i.e.the DIVA simulation kernel, the code generator, the symbolic preprocessing tool SYPPROT, and the process modeling tool PROMOT. The MOL discretization of PDE and IPDE as the main preprocessing feature is the focus of Section 13.3. Standard discretizationschemes like finite-difference and finite volume schemes as well as adaptive approaches like high-resolution methods and an equidistribution principle based moving grid method are explained for distributed parameter models with one space coordinate. The application of these discretization methods within the symbolic preprocessing tool SYPPROT follows in Section 13.4, where the PDE and IPDE model representation as well as the implemented MOL discretization capabilities are described.
Chapmann and Hall
2001
InBook
http://edoc.mpg.de/62990
urn:ISBN:1-58488-231-X
Adaptive Method of Lines, 371-406 (2001)
oai:edoc.mpg.de:630572004-02-1319:89
New Control Strategies for Moving Bed Chromatographic Processes
Schramm, H.
Grüner, S.
Kienle, A.
expertsonly
Two different control strategies for Moving Bed chromatographic processes are developed and applied to True as well as Simulated Moving Bed processes. The first method represents an inferential control scheme with simple PI controllers. No mathematical model is required. Good control performance is obtained for processes with constant feed compositions and fluctuating flow rates. For processes with fluctuating feed composition and flow rates, a second, model based control scheme is proposed. It is based on nonlinear wave theoryand guarantees minimal solvent consumption and maximal feed throughput for any desired product purity without long winded optimization calculations.
2001
Conference-Paper
http://edoc.mpg.de/63057
Proceedings of the 3rd European Congress of Chemical Engineering (ECCE) (2001)
oai:edoc.mpg.de:630712004-09-0619:89
Nonlinear inferential control of an autonomous periodic fixed-bed reactor
Hua, X.
Mangold, M.
Kienle, A.
Gilles, E. D.
expertsonly
This paper deals with the control of an autonomous periodic fixed-bed reactor, which is called circulation loop reactor (CLR). This process can be described by a distributed parameter system with sustained oscillations. The state variables at some positions of such a process, e.g. the conversion at the reactor exit, may be required to vary in a smooth fashion, which in general is a difficult task due to the process’s inherent complex behavior. Here, a straight forward control strategy of the CLR based on direct exit concentration regulation is presented. A relay feedback controller is found to be effective for achieving overall conversion while using relatively small external heating. In order to implement the control scheme without online concentration measurement, a nonlinear inferential control concept is adopted. A newly-developed nonlinear distributed parameter observer is used to infer the exit concentration from the temperature measurements at only a few positions. Moreover, an approach based on integrating a disturbance estimator is presented for improving the performance of the observer in the case of unmeasured inlet concentration. It is found that there exist simple determinate relations between the inlet variables or the model parameters and the maximum amplitude or the period of the oscillatory temperature at an axial position for the considered cases. By employing the oscillatory feature of the CLR, a method of estimating the inlet concentration is proposed, and a parameter estimation method based on the least square technique is given to update offline model parameters. It is shown that substantial benefits could be realized using the proposed nonlinear inferential control scheme for the CLR because it can provide excellent disturbance rejection capabilities and strong robustness.
1998
Article
http://edoc.mpg.de/63071
Journal of Process Control, v.8, 239-250 (1998)
oai:edoc.mpg.de:632952004-07-2319:89
Real-time optimization for large scale processes: Nonlinear model predictive control of a high purity distillation column
Diehl, M.
Uslu, I.
Findeisen, R.
Schwarzkopf, S.
Allgöwer, F.
Bock, H. G.
Bürner, T.
Gilles, E. D.
Kienle, A.
Schlöder, J. P.
expertsonly
The purpose of this paper is an experimental proof-of-concept of the application of NMPC for large scale systems using specialized dynamic optimization strategies. For this aim we investigate the application of modern, computationally effcient NMPC schemes and real-time optimization techniques to a nontrivial process control example, namely the control of a high purity binary distillation column. All necessary steps are discussed, from formulation of a DAE model with 164 states up to the final application to the experimental apparatus. Especially an effcient real-time optimization scheme based on the direct multiple shooting method is introduced. It is characterized by an initial value embedding strategy, that allows to immediately respond to disturbances, and real-time iterations, that dovetail the optimization iterations with the real process development. Using this scheme, sampling times of 10 seconds are feasible on a standard PC. This shows that an efficient NMPC scheme based on large scale DAE models is feasible for the real-time control of a pilot scale distillation column.
Springer-Verlag
2001
InBook
http://edoc.mpg.de/63295
urn:ISBN:3-540-42459-8
Online Optimization of Large Scale Systems, 363-383 (2001)
oai:edoc.mpg.de:651322004-02-2619:89
Dynamic behavior of a counter-current fixed-bed reactor with sustained oscillations
Mangold, M.
Klose, F.
Gilles, E. D.
expertsonly
Travelling reaction zones have proven to be energetically advantageous for weakly exothermic reactions. In this contribution, a new coupled system of catalytic fixed-bed reactors is presented, which uzilizes travelling reaction waves created by autonomous periodic oscillations. The system consists of two parallel fixed beds with inlets for gaseous reactants at opposite ends. Thermal recoupling is established by heat exchangers which connect the ends of the two beds. So far, several variants of the system with co-current and counter-current heat exchange have been studied in dynamic simulation as well as by nonlinear analysis. The investigations reveal a complex dynamic behaviour. In a far range of operation conditions, two types of autonomous oscillations are found to coexist.
Elsevier
2000
Conference-Paper
http://edoc.mpg.de/65132
urn:ISBN:0-444-50520-2
Pierucci, S.: European Symposium on Computer Aided Process Engineering - 10 : ESCAPE-10, Elsevier, 205-210 (2000)
oai:edoc.mpg.de:651412004-04-0519:89
Catalysts from waste materials
Klose, F.
Scholz, P.
Kreisel, G.
Ondruschka, B.
Kneise, R.
Knopf, U.
expertsonly
Wastes containing transition metal compounds can be used as a resource to manufacture catalysts, for instance for the deep oxidation of hydrocarbons. If the starting waste material meets some requirements with regard to amounts and dispersion of metal and organic compounds, the catalyst is produced using a simple combination of mechanical and thermal treatment. The procedure does not require any additional fine chemicals. Such catalyst granulates are highly active and, thus they are comparable to commercially available catalysts. The granulates reach surfaces of more than 100 m(2)/g. Their porous structure can be stable up to 600 degrees C and is based on a carbon framework. A detailed report about the influence of different parameters of the manufacturing process on the properties of the final products is given.
2000
Article
http://edoc.mpg.de/65141
Applied Catalysis B: Environmental, v.28, 209-221 (2000)
oai:edoc.mpg.de:651512008-05-3019:89
Separation using coupled reactive distillation columns
Stein, E.
Kienle, A.
Sundmacher, K.
expertsonly
A case study is presented on separating isobutene form a mixture of hydrocarbons, with the clean-fuel additive, MTBE, as an intermediate product.
2000
Article
http://edoc.mpg.de/65151
Chemical Engineering, v.107, 68-72 (2000)
oai:edoc.mpg.de:651522004-02-2619:89
Nonlinear model reduction for nonreactive and reactive distillation processes using nonlinear wave propagation theory
Kienle, A.
expertsonly
A uniform approach to nonlinear model reduction for nonreactive as well as reactive distillation processes with fast reversible chemical reactions in the liquid phase is presented. The approach is based on spatio-temporal pattern formation phenomena in distillation processes also termed as nonlinear wave propagation. Focus is on ideal and moderately nonideal mixtures.
2000
Conference-Paper
http://edoc.mpg.de/65152
Ministery of Education: Third Symposium on Process Control, 72-78 (2000)
oai:edoc.mpg.de:651612004-02-2619:89
Application of the process modeling tool PROMOT to the modeling of metabolic networks
Ginkel, M.
Kremling, A.
Tränkle, F.
Gilles, E. D.
Zeitz, M.
expertsonly
ARGESIM
2000
Conference-Paper
http://edoc.mpg.de/65161
urn:ISBN:3-901608-15-X
Troch, I.; Breitenecker, F.: Proceedings 3rd MATHMOD, IMACS Symposium on Mathematical Modelling, ARGESIM, 525-528 (2000)
oai:edoc.mpg.de:664282004-03-0219:89
Nonlinear computation using DIVA - methods and applications
Mangold, M.
Kienle, A.
Mohl, K. D.
Gilles, E. D.
expertsonly
Methods for 1-parameter continuation and stability analysis of periodic solutions as well as 2-parameter continuation of Hopf and limit bifurcation points have been added to the dynamic flowsheet simulation environment sc Diva. They are specially tailored for large sparse systems of differential algebraic equations with arbitrary structural properties usually arising in dynamic flowsheet simulation of chemical processes and plants. The application of these methods combined with the other capabilities of such an integrated tool for nonlinear system analysis is demonstrated for two different types of processes. The first is the so-called circulation loop reactor, which has been used for catalytic combustion of waste air. Through periodic operation of the reactor, abatement of small amounts of volatile organic compounds (VOCs) in the waste air is possible auto-thermally or with minimum supply of energy. Control strategies are studied for extending the region of desired periodic operating points, when the amount of VOCs is too small for autonomous periodic operation. The second application is concerned with the nonlinear dynamic behaviour of reactive distillation processes for the production of fuel ethers MTBE and TAME. In particular, the existence of multiple steady states is analyzed for the practical important case, when pre-reaction is carried out prior to the reactive distillation column. Further these results are compared to the case without pre-reaction and a physical interpretation is given.
2000
Article
http://edoc.mpg.de/66428
Chemical Engineering Science, v.55, 441-454 (2000)
oai:edoc.mpg.de:664292004-03-0119:89
Low-order dynamic models for ideal multicomponent distillation processes using nonlinear wave propagation theory
Kienle, A.
expertsonly
A new approach to the development of low-order dynamic models for multicomponent distillation processes is presented. This approach makes direct use of well known spatio-temporal pattern formation phenomena also termed as nonlinear wave propagation. It takes into account the typical features of multicomponent systems, i.e. coexistence of different constant pattern waves within a single section of a distillation column and the resulting wave interactions. In a first step, constant molar holdups and flow rates, constant pressure and constant relative volatilities are assumed. Under these conditions a rigorous analytical treatment is possible and a comparably simple but sound and robust method for nonlinear model reduction is developed. The approach applies to packed as well as staged columns provided the number of column stages is sudfficiently large. Application is demonstrated for two different distillation processes with a three and a five component mixture, respectively. It is shown that the dynamic behaviour of the low-order modelis in good agreement with corresponding reference model for a large set of operating conditions. Finally, extensions of the present approach to processes with variable molar flow rates as well as variable volatilities are discussed.
2000
Article
http://edoc.mpg.de/66429
Chemical Engineering Science, v.55, 1817-1828 (2000)
oai:edoc.mpg.de:1119802004-03-0519:89
Object-oriented modeling of distillation processes
Tränkle, F.
Kienle, A.
Mohl, K. D.
Zeitz, M.
Gilles, E. D.
expertsonly
The process modeling tool PROMOT supports the object-oriented and equation-based modeling of chemical processes for the process simulation environment DIVA. This contribution demonstrates the modeling methodology of PROMOT and the advantages of object-oriented modeling by looking at the design of a knowledge base containing reusable modeling entities for modeling (reactive) distillation processes.
1999
Article
http://edoc.mpg.de/111980
Computers and Chemical Engineering, v.23, S743-S746 (1999)
en
oai:edoc.mpg.de:1119902004-06-3019:89
Optimization of a reactor network for ethylene glycol synthesis : an algorithmic approach
Stein, E.
Kienle, A.
Esparta, A. R.
Mohl, K. D.
Gilles, E. D.
expertsonly
This contribution is concerned with reactor network synthesis for the production of ethylene glycol by hydration of ethylene oxide, which is an industrially relevant process. This reaction is not only very fast and strongly exothermic but also higher glycols are formed as by products. Starting point of the study is a general reactor network serving as a superstructure. The system consists of two different kinds of units: a reaction-condensation unit with chemical reaction in the liquid phase and simultaneous vaporization as well as condensation, and different mixer/splitters. Usually, reactor network synthesis is concerned with rather simple isothermal reactions in homogeneous liquid or gasphase. Instead, here a rigorous
non-isothermal two-phase model with a liquid and a vapor phase is developed. Chemical reaction and mass separation by vaporization is included. In principle, the synthesis problem is solved on the phase level [4]. This approach allows the combination of the unit operations reaction and separation in various ways. In particular, the resulting superstructure includes two processes, which have been treated previously. The first is the conventional process for the production of ethylene glycol which consists of a reactor followed by a separation sequence with a water recycle [6]. The second is a reactive distillation column recently proposed in [3]. The latter is also used to validate the reactor network model. Moreover, completely new two-phase reactor separator structures are synthesized. Recently, Mehta and Kokossis presented a similar approach for the synthesis of novel reactor designs [5]. The general superstructure is optimized by means of NLP techniques in the optimization tool GAMS [1]. Starting with a detailed examination of a single reaction-condensation unit a better understanding of the physical and chemical processes is obtained with emphasis on interaction between chemical reaction and separation. In the next step a network containing two reaction-condensation units is investigated. It turns out that the principle of the conventional process, spatial separation of reaction and mass separation, is an optimal structure. Finally, networks with up to eleven reaction-condensation units are considered, corresponding to the reactive distillation column presented by Ciric and coworkers [3]. Completely new structures for the production of ethylene glycolare synthesized and compared with the structure of the column with respect to the energy costs. It turns out that the structure equivalent to the column represents a local optimum for the isobaric network considered here in a first step. Further improvements can be achieved by the feeding strategy and by varying the pressure from unit to unit. However, due to the strongly nonlinear reactor network model and its enormous number of degrees of freedom no claims of globality of optima found can be made. To overcome these limitations of local optimizers and to find new structures for ethylene glycol synthesis to chastic optimization algorithms are considered [2]. [1] A. Brooke, D. Kendrick and A. Meeraus: GAMS A user’s guide, release 2.25. The Scientific Press, San Francisco, 1992. [2] M.F. Cardoso, R.L. Salcedo, S.F. de Azevedo and D. Barbosa: A simulated an nealing approach to the solution of MINLP problems. Comp. Chem. Engng, 21(12):1349-1364, 1997. [3] A.R. Ciric and D. Gu: Synthesis of nonequilibrium reactive distillation processes by MINLP optimization. AIChE Journal, 40:1479-1487, 1994. [4] E.D. Gilles: Network theory for chemical processes. Chem. Engng. Technol., 21(2):121-132, 1998. [5] V.L. Mehta and A. Kokossis: Development of novel multiphase reactors using a systematic design framework. Comp. Chem. Engng, 21, Suppl.:S325-S330, 1997. [6] Ullmann’s encyclopedia of industrial chemistry, Vol. A 10, Chap. Ethylene Glycol. VCH Verlagsgesellschaft mbH, Weinheim, 1990.
1999
Article
http://edoc.mpg.de/111990
Computers and Chemical Engineering, v.23, S903-S906 (1999)
en
oai:edoc.mpg.de:1119942004-03-1119:89
Dynamic optimization of multicomponent distillation processes
Stein, E.
Kienle, A.
Gilles, E. D.
expertsonly
Increasing quality requirements and decreasing production periods demand the real-time optimization of simple units as well as of wholeplants in the process industry. In this work a multicomponent distillation process as the most widespread separation technique in process industries is considered. The system consists of two coupled distillation columns with additional pumps, valves, controllers, condensers and one reboiler. The side column needs no reboiler, since it is fed by a vaporside-withdrawal of the main column. Hence, this configuration requires only little energy but is comparably difficult to operate. After a sudden change of the composition in the liquid feed to the main column, optimal trajectories for the input variables have to be computed in limited time in order to guarantee the desired product specifications. The optimization of a rigorous model of the distillation system with a standard SQP algorithm results in an unacceptably high computation time [3]. In principle, there are two complementary possibilities to reduce the computational effort. First, efficient special tailored algorithms like a multiple shooting approach could be used [2]. Second, the model size and complexity could be reduced. Emphasis in this contribution is on the second option. It turns out that a reduction of the rigorous model by means of simplifying assumptions is not sufficient. A further reduction of the system order beyond those model simplifications is needed. For this purpose, a new model reduction approach for multicomponent systems is used based on nonlinear wave propagation theory [1]. As the order of the system can be dramatically reduced in comparison with the simplest rigorous model, the real-time optimization of the input variables becomes possible. In this contribution, the real-time requirements for the process described above are considered. Afterwards, an overview is given over possible model formulations for distillation processes including different rigorous models and the wave model. The potential of these models with respect to dynamic optimization computations is discussed. Finally, computational results for the different models are given and compared. [1] A. Kienle: Reduced models for multicomponent separation processes using nonlinear wave propagation theory. In CHISA’98, paper 109, Praha, Czech Republic, August 23 - 28, 1998. [2] D.B. Leineweber and A.C. Ströder: Parameter estimation and optimal control for dynamic chemical processes. In Keil, Mackens, Voss and Werther (Eds.): Scientific Computing in Chemical Engineering, Springer-Verlag, Berlin, 1996.[3] C.P. Majer: Erweiterung einer Simulationsumgebung für verfahrentechnische Prozesse zur Parameterschätzung, Versuchsplannung und Trajektorienoptimierung. VDI Fortschritt-Berichte Nr. 3/538, VDI-Verlag, Düsseldorf, 1998.
Springer
1999
InBook
http://edoc.mpg.de/111994
urn:ISBN:3-540-65851-3
Scientific Computing in Chemical Engineering II, 362-369 (1999)
en
oai:edoc.mpg.de:1120192005-11-0819:89
Synthese einer Anfahrregelung für eine Destillationskolonne auf der Grundlage einer ereignisdiskreten Approximation der kontinuierlichen Dynamik
Klein, E.
Raisch, J.
Kienle, A.
Wehlan, H.
expertsonly
Der Beitrag beschreibt die Synthese einer ereignisdiskreten Regelung für den Anfahrvorgang einer Destillationskolonne. Der Ansatz basiert auf Methoden der hybriden und ereignisdiskreten Systemtheorie: Im ersten Schritt erfolgt die ereignisdiskrete Modellierung des Prozesses durch Approximation eines detaillierten kontinuierlichen Prozeßmodells; die resultierende ereignisdiskrete Beschreibung ist ein endlicher Moore-Automat. Der Entwurf der Regelung erfolgt dann als formaler Syntheseschritt auf der Grundlage des abstrakten Automatenmodells. Kennzeichen der Vorgehensweise ist, dass das Verhalten des Automaten per Konstruktion eine übermenge des Verhaltens des detaillierten Prozemodells ist. Aus diesem Grund garantiert die entworfene Regelung die Erfülllung der Spezifikation auch für das kontinuierliche Prozeßmodell.
TU Braunschweig
1999
Conference-Paper
http://edoc.mpg.de/112019
E. Schnieder: EKA - 6. Fachtagung Entwicklung und Betrieb komplexer Automatisierungssyteme, TU Braunschweig, 447-464 (1999)
de
oai:edoc.mpg.de:1120222004-03-0819:89
Low-order dynamic models for two coupled distillation columns
Kienle, A.
Stein, E.
Rehm, A.
Kloppenburg, E.
expertsonly
Nonlinear low-order models are developed for two coupled distillation columns separating a ternary mixture of methanol, ethanol and 1-propanol. The approach is based on well-known spatio temporal pattern formation phenomena in distillation processes also termed as nonlinear wave propagation. In a first step, the energy balance is neglected assuming constant molar flow rates in each column section. Further, constant molar holdups are assumed. In a second step, the wave approach is extended for columns with variable flow rates and constant volumetric holdups. It is shown that these assumptions are more realistic for the process considered here. In both cases the low-order models are in good agreement with the corresponding reference models with constant and variable flow rates, respectively. Further, the reduction of the system order is considerable in both cases.
rubicon
1999
Conference-Paper
http://edoc.mpg.de/112022
Proceedings of the 5th European Control Conference ECC`99, rubicon (1999)
en
oai:edoc.mpg.de:1120242004-03-1219:89
Modeling and simulation of a chemical reactor for the production of acetic acid : II. Two-phase model
Kienle, A.
Pfisterer, F.
Waschler, R.
Sviatnyi, S.
Gilles, E. D.
Anoprienko, A.
Osipova, T.
expertsonly
A two-phase model of a reactor for the production of acetic acid is presented and simulation results are compared to results obtained for a one-phase model described in a previous study. It is shown that the new model yields significant improvements in describing both the nonlinear steady state and the dynamic transient behaviour as can be seen from comparisons with measured data from the real plant.
Donetsk State Technical University
1999
Conference-Paper
http://edoc.mpg.de/112024
Informatics, Cybernetics and Computer Science (ICCS-98), Donetsk State Technical University, 15-23 (1999)
en
oai:edoc.mpg.de:1149222004-03-2319:89
Periodicity and chaos in chemiluminescence : the ruthenium-catalyzed Belousov-Zhabotinsky reaction
Zeyer, K. P.
Schneider, F. W.
expertsonly
We investigate the chemiluminescence of the homogeneous Belousov-Zhabotinsky (BZ) reaction catalyzed by tris(2,2’-bipyridine)ruthenium(II)([Ru(bpy)3]2+) in a continuous-flow stirred tank reactor where the chemiluminescence originates from the electronically excited Ru(bpy)3]2+ catalyst. At high flow-rates, Farey-ordered as well as complex burst-like states are observed in the pure ruthenium-catalyzed reaction which we investigated using five different concentration sets. We also characterized the chemiluminescent behavior when both Ru2+ and Ce3+ were present at four different mole fractions. Under conditions of low Ru2+concentrations, we observed two chaotic chemiluminescent states which are reached by a period-adding and a period-doublingroute, respectively. Model calculations with the reaction scheme of Gao and Foersterling were performed with semiquantitative agreement with our experimental observations.
1998
Article
http://edoc.mpg.de/114922
Journal of Physical Chemistry A, v.102, 9702-9709 (1998)
en
oai:edoc.mpg.de:1149262004-03-2319:89
Optimization of a reactor network for ethylene glycol synthesis
Stein, E.
Kienle, A.
Esparta, R.
Mohl, K. D.
Gilles, E. D.
expertsonly
This contribution is concerned with the energy optimal process design for ethylene glycol synthesis which is an industrially relevant process. A systematical approach is developed based on the optimization of a general network model. A rigorous non-isothermal model for different network constituents is derived. These constituents are a two-phase reactor condenser element and several mixer/splitters with which the elements are connected to form the network superstructure. As one special case the resulting superstructure includes a process scheme commonly used in industries where reaction and separation are carried out in different devices. A second special case is a reactive distillation column recently proposed in literature. The general reactor network model is optimized by nonlinear programming (NLP) methods in order to obtain an energy minimal network configuration.
1998
Conference-Paper
http://edoc.mpg.de/114926
Preprints CHISA'98 (1998)
en
oai:edoc.mpg.de:1167652004-04-1319:89
Nonlinear computation using DIVA : methods and applications
Mangold, M.
Kienle, A.
Gilles, E. D.
Mohl, K. D.
expertsonly
Methods for the 1-parameter continuation and stability analysis of periodic solutions as well as 2-parameter continuation of Hopf and limit bifurcation points have been added to the dynamic flowsheet simulation environment (sc Diva). They are specially tailored for large sparse systems of differential algebraic equations with arbitrary structural properties usually arising in dynamic flowsheet simulation of chemical processes and plants. The application of these methods combined with the other capabilities of such an integrated tool for nonlinear system analysis is demonstrated for two different types of processes. The first is the so-called circulation loop reactor which has been used for catalytic combustion of waste air. Through periodic operation of the reactor abatement of small amounts of volatile organic compounds (VOCs) in the waste air is possible autothermally or with minimum supply of energy. Control strategies are studied for extending the region of desired periodic operating points, when the amount of VOCs is too small for autonomous periodic operation. The second application is concerned with the nonlinear dynamic behaviour of reactive distillation processes for the production of fuel ethers MTBE and TAME. In particular, the existence of multiple steady states is analyzed for the practical important case, when pre-reaction is carried out prior to the reactive distillation column. Further these results are compared to the case without pre-reaction and a physical interpretation is given.
1998
Conference-Paper
http://edoc.mpg.de/116765
Preprints CHISA '98 (1998)
en
oai:edoc.mpg.de:1167712005-11-0819:89
Synthesizing a supervisory control scheme for the start-up procedure of a distillation column : an approach based on approximating continuous dynamics by DES models
Klein, E.
Kienle, A.
Raisch, J.
expertsonly
This paper addresses the problem of synthesizing a supervisory control scheme for the start-up procedure of a distillation column. We use techniques from the areas of hybrid and discrete event systems theory to solve the problem: First, the detailed plant model is approximated by an automaton. Then, a discrete control scheme is generated for the abstract (automaton) model. By construction, the automaton behaviour covers the detailed model behaviour. Hence, the controller not only forces the abstraction but also the underlying detailed plant model to obey the specifications.
Pergamon Pr.
1998
Conference-Paper
http://edoc.mpg.de/116771
Koussoulas, N. T.; Groumpos, P.: Large Scale Systems : theory and Applications : a proceedings volume, Pergamon Pr., 716-721 (1998)
en
oai:edoc.mpg.de:1167722004-04-0819:89
Reduced models for multicomponent separation processes using nonlinear wave propagation theory
Kienle, A.
expertsonly
A new model reduction approach for multicomponent separation processes is presented. This approach makes directly use of well-known spatio temporal pattern formation also termed as nonlinear wave propagation. It takes into account the typical features of multicomponent systems, i.e. coexistence of different constant pattern waves within a single section of a separation column and the resulting wave interactions. It is shown that the approach is comparably simple but sound and robust. The reduced model is purely predictive, i.e. all parameter scan be calculated from basic physical properties such as separation factors and operating conditions. It applies to spatially continuous as well as staged separation processes, provided the number of column stages is sufficiently large. Application is demonstrated for multicomponent distillation processes. It is shown that the dynamic behaviour of the reduced model is in good agreement with the detailed reference for a large set of operating conditions.
1998
Conference-Paper
http://edoc.mpg.de/116772
Preprints CHISA´98 (1998)
en
oai:edoc.mpg.de:1236602005-06-2719:89
A comparison of different models for the prediction of nonlinear oscillations in ammonium sulfate crystallization
Pathath, P. K.
Kienle, A.
expertsonly
Crystallization processes involve different kinetic processes such as nucleation of crystals, their subsequent growth and breakage. The rate equations of these kinetic processes are typically nonlinear and may give rise to complex nonlinear behavior including self sustained oscillations. These instabilities in turn lead to poor product quality and should therefore be avoided. A reliable prediction and thorough understanding of potential sources for instability is not only of scientific interest but also an important issue for better design and control of crystallization processes. In this contribution focus is on ammonium sulfate crystallization. This system has been studied intensively in the past and can be viewed as a standard test system for crystallization processes. Focus is on crystallizers with fines dissolution and classified product removal. Using methods from numerical bifurcation analysis we investigate, how stability in such a system depends on the various operational parameters, like cut sizes and recycle rates of fines dissolution and product classification. Theoretical predictions of three different population models are compared with each other: (i) a model with simple kinetics and ideal fines classification as introduced in [1], (ii) a model with complex kinetics involving breakage due to attrition and ideal fines classification as introduced in [2], and (iii) a model with simple kinetics and nonideal fines classification as introduced in [3]. It is found that predictions of the instability regions with models (i) and (ii) are rather close. In contrast to this the nonideal fines classification can change stability rather drastically. Hence, at least for the stability analysis, a detailed model of the classification seems to be more important than a detailed model of the population kinetics. References: [1] P. Pathath and A. Kienle. Chem. Engng. Sci. 57 (2002), 4391-4399. [2] A. Gerstlauer, S. Motz, A. Mitrovic and E.D. Gilles. Chem. Engng. Sci. 57, 4311-4328. [3] A. Mitrovic. PhD Thesis, University Stuttgart, VDI Fortschrittsberichte Nr. 3/749, VDI-Verlag, Düsseldorf.
2003
Conference-Paper
http://edoc.mpg.de/123660
Proc. 4th European Congress of Chemical Engineering, ECCE -4 (2003)
en
oai:edoc.mpg.de:1244802004-05-2819:89
Entwicklung einer Bibliothek dynamischer Membranreaktormodelle mit Hilfe des Modellierungswerkzeugs ProMoT
Mangold, M.
Ginkel, M.
Gilles, E. D.
expertsonly
Eine Modellbibliothek für örtlich verteilte Membranreaktormodelle wird vorgestellt. Die Struktur der Bibliothek orientiert sich an einem allgemeinen Strukturierungskonzept für verfahrenstechnische Modelle. Die Bausteine der Modellbibliothek lassen sich daher auch für die Modellierung verwandter Prozesse wie Festbettreaktoren, Adsorptionskolonnen oder Brennstoffzellen verwenden. Die Bibliothek ist im Modellierungswerkzeug ProMoT implementiert.
SCS Publishing House
2003
Conference-Paper
http://edoc.mpg.de/124480
Hohmann, R.: Simulationstechnik : 17 Symposium in Magdeburg, September 2003, SCS Publishing House, 161-166 (2003)
de
oai:edoc.mpg.de:1244892004-05-2719:89
Nonlinear model reduction of a dynamic two-dimensional molten carbonate fuel cell model
Mangold, M.
Sheng, M.
expertsonly
A reduced nonlinear model of a planar molten carbonate fuell cell is presented. The model is derived from a spatially distributed dynamic model of the cell by applying the Karhunen Loeve Galerkin procedure. The reduced model is of considerably lower order than the original one and requires much less computation time. The comparison between the two models shows that the reduced model can describe the dynamic of the temperature field with sufficient accuracy and has good extrapolation qualities with respect to changes in the model parameters. The usefulness of the reduced model for process control purposes is demonstrated by applying it in the framework of a state and parameter estimator.
2003
Conference-Paper
http://edoc.mpg.de/124489
Proc. AIChE 2003 Annual Meeting (2003)
en
oai:edoc.mpg.de:1245222005-11-0819:89
Time optimal control of a batch reactor using Pontryagin's Maximum Principle
Gromov, D.
Mishra, B. V.
Raisch, J.
Kienle, A.
expertsonly
Time optimal control of a batch reactor is a dynamic optimisation (DO) problem. In chemical engineering, the popular trend of solving this problem involves transformation of the DO problem to a non-linear programming (NLP) problem using a suitable time discretisation scheme. This approach, however, may imply a number of difficulties, ranging from problem size to failure in locating the global optimum. These difficulties may be overcome by using approaches that are more analytical in nature. This paper presents the application of one such approach, the Pontryagin maximum principle (PMP), to the time optimal control problem of a batch reactor.
2003
Conference-Paper
http://edoc.mpg.de/124522
SPC2003 : International Symposium on Process Control, 16-21 (2003)
en
oai:edoc.mpg.de:1245282004-06-0219:89
Nonlinear analysis of reactor separator systems involving an evaporatively cooled reactor
Waschler, R.
Zeyer, K. P.
Kienle, A.
expertsonly
The focus of this contribution is on the nonlinear analysis of a model reactor separator system. The first order reaction A to B is carried out in an adiabatic, evaporatively cooled reactor. The vapor leaving the reactor is completely recycled after total condensation in an overhead condenser. The liquid reaction mixture is separated in a flash separator, with the liquid being recycled to the reactor. For the case of a temperature-controlled flash, the control strategy relying on perfect reactor level control via manipulation of the reactor effluent stream is investigated. The existence of multiple steady states for this configuration is demonstrated, and stability issues are discussed. In particular, it is shown that the behavior of this integrated system with non-isothermal reactor is qualitatively different from both the corresponding system with isothermal operation of the reactor, and also from the behavior of the standalone evaporatively cooled reactor.
2003
Conference-Paper
http://edoc.mpg.de/124528
Proc. AIChE Annual Meeting (2003)
en
oai:edoc.mpg.de:1245342005-11-0819:89
Short-term scheduling of chemical processes : an overall optimisation approach
Mishra, B. V.
Mayer, E.
Raisch, J.
Kienle, A.
expertsonly
The production-scheduling problem has gained considerable importance over the last decade, especially for batch processes due to their inherent flexibility. It is a well-known fact that a good production schedule has a significant impact on the process economics. Extensive research has been done in this area and several elegant approaches have been proposed so far. Most of the approaches reported in the literature till now are based on standard production recipes, i.e. the recipes are standardised either empirically or via single batch optimisation and the information obtained thereby is used for the scheduling problem formulation. However, standardisation of recipes removes degrees of freedom from the system, and due to this scheduling formulations based on standardised recipes result only in suboptimal solutions. This paper presents an overall optimisation approach for the short-term scheduling of batch processes. In the proposed approach, the process dynamics are incorporated within the scheduling formulation rather than being standardised offline. This restores the additional degrees of freedom of the system and can therefore yield a better solution. The proposed formulation is based on a continuous time representation and results in an infinite dimensional mixed integer dynamic optimisation (MIDO) problem. Appropriate discretisation of the control and the state variable profiles transforms this infinite dimensional MIDO problem to a finite dimensional mixed integer non-linear programming (MINLP) problem, which can be approached using conventional MINLP solvers. The effectiveness of the proposed formulation is illustrated with the help of simple examples. The results are compared with the existing scheduling formulations to demonstrate that the proposed approach clearly outweighs the standard recipe approaches.
2003
Conference-Paper
http://edoc.mpg.de/124534
4th European Congress of Chemical Engineering (ECCE) (2003)
en
oai:edoc.mpg.de:1247842004-06-0319:89
Nonlinear behavior of reactor separator networks : influence of separator control structure
Zeyer, K.-P.
Pushpavanam, S.
Kienle, A.
expertsonly
Chemical process plants are primarily made up of two basic units, i.e. reactors and separators. In a typical plant fresh reactants are partially converted to products in a reactor and the mixture of reactants and products is then transferred to a separator unit for purification. For economic reasons unreacted material or expensive catalysts must be recycled back to the reactor unit. We investigate the dynamic behavior of a coupled reactor separator system. The upstream reactor is modeled as a continuous flow stirred tank reactor (CSTR) and the downstream separator as a binary one-step distillation unit (flash). The outflow of the CSTR is used as the input of the flash unit. Coupling arises due to the recycle of the liquid stream (the bottoms) of the separator to the reactor. The CSTR is operated under isothermal and ideally mixed conditions. A simple first order reaction A to B is studied. The flash is nonreactive and the mixture of A and B is assumed to be homogeneous and ideal. In particular, three different types of isobaric flash control strategies are considered: a) fixed flash temperature, b) fixed flash heating rate (including an adiabatic flash), and c) fixed flash vapor flow rate. For each of these flash operation modes we discuss three different flow control strategies for the CSTR: a) fresh feed flow controlled, b) reactor effluent flow controlled, and c) both of these flow controlled (variable CSTR holdup). We can show that the individual units always possess unique, stable and feasible steady states. Surprisingly, even for this very simple model system, more complex dynamics involving infeasibility, multiple steady states and stable oscillations can be observed in many cases as soon as the recycle is closed. It is shown that the behavior crucially depends on the flow control as well as on the flash control strategy. Stability criteria are derived and instabilities are systematically identified to predict the conditions for possible pitfalls a practicing engineer may encounter in operation of this type of reactor separator system, which is a basic unit in many industrial plants.
2003
Conference-Paper
http://edoc.mpg.de/124784
4th European Congress of Chemical Engineering; Vol. 8, Topic 9 (2003)
en
oai:edoc.mpg.de:1247872004-06-0419:89
Effect of delay on the stability of a coupled reactor-separator system
Balasubramanian, P.
Kosuri, M. R.
Pushpavanam, S.
Kienle, A.
expertsonly
2003
Article
http://edoc.mpg.de/124787
Industrial & Engineering Chemistry Research, v.42, 3758-3764 (2003)
en
oai:edoc.mpg.de:1247882004-05-2619:89
Improved operation of simulated moving bed processes through cyclic modulation of feed flow and feed concentration
Schramm, H.
Kienle, A.
Kaspereit, M.
Seidel-Morgenstern, A.
expertsonly
Recently, different strategies for improving simulated moving bed (SMB) chromatographic separation processes have been proposed, including a modulation of the feed flow and the feed concentration during the tacts. In this contribution these two different strategies are applied to a benchmark problem and are compared with each other. Physical explanations of the improvements obtained compared with the conventional operation mode are given in terms of moving concentration fronts. Practical aspects for the implementation of the different strategies are also discussed.
2003
Article
http://edoc.mpg.de/124788
Chemical Engineering Science, v.58, 5217-5227 (2003)
en
oai:edoc.mpg.de:1247982004-07-0619:89
Dynamic simulation of a tubular reactor for the production of low density polyethylene
Häfele, M.
Kienle, A.
Boll, M.
Schwibach, M.
Mähling, F.-O.
Schmidt, C.-U.
expertsonly
Low density polyethylene is one of the most produced polymers in the world. In mass production there are two ways of synthesizing it, either in an autoclave or in a tubular reactor. In both types reaction takes place at very high pressures. It is started by the addition of initiators, which decompose into radicals selectively with respect to reaction temperature. The radicals start the chain growth by forming longer radicals. The chain length which determines the characteristic properties of the polymer is controlled by a component which bonds radicals. The chain growth releases very much energy so that heat removal is one main issue in this process. Due to the exothermic behavior initiator is not only added at the beginning of, but also at some discrete additional points along the tube. The outlet of the tube is fed into two subsequent flashes, separating the product from the unreacted monomer. The monomer is recycled and again fed in the process. In this work we will present a detailed dynamical model for such a production plant comprising the tubular reactor, the compressors, the separating units and the recycle. The partial differential equation are transformed into an ODE system using adaptive method of lines. Simulation results show good agreement with given data. By means of the simulation model dynamic transient behaviour of the plant is investigated for some characteristic disturbances, i.e. load or grade changes. It is shown that the sensitivity with respect to these disturbances crucially depends on the basic control structures.
2003
Conference-Paper
http://edoc.mpg.de/124798
4th European Congress of Chemical Engineering (2003)
en
oai:edoc.mpg.de:1248082004-07-0619:89
DIVAGUI : the graphical user interface for the simulation environment DIVA
Chebotarov, M.
Ginkel, M.
Häfele, M.
Mangold, M.
Gilles, E. D.
Kienle, A.
Svjatnyj, V.
expertsonly
SCS Publishing House
2003
Conference-Paper
http://edoc.mpg.de/124808
Hohmann, R.: Simulationstechnik : 17 Symposium in Magdeburg, September 2003, SCS Publishing House, 155-160 (2003)
en
oai:edoc.mpg.de:1248202004-05-2619:89
Simulated moving bed process with cyclic modulation of the feed concentration
Schramm, H.
Kaspereit, M.
Kienle, A.
Seidel-Morgenstern, A.
expertsonly
The improvement of the simulated moving bed (SMB) process based on the introduction of a cyclic modulation of the feed concentration is described. It is demonstrated that such a feed concentration gradient during the shifting cycle can improve the performance significantly. The productivity and the product concentrations can be increased while simultaneously the solvent consumption can be decreased compared to the conventional SMB process with constant feed parameters.
2003
Article
http://edoc.mpg.de/124820
Journal of Chromatography A, v.1006, 77-86 (2003)
en
oai:edoc.mpg.de:1248222004-05-2619:89
Optimal operation of simulated moving bed chromatographic processes by means of simple feedback control
Schramm, H.
Grüner, S.
Kienle, A.
expertsonly
In this contribution, simple methods are presented for controlling a simulated moving bed chromatographic process with standard PI controllers. A first method represents a simple and model-free inferential controlscheme which was motivated from common distillation column control. The SMB unit is equipped with UV measurements. The UV signals in the four separation zones of the unit are fixed by four corresponding PI controllers calculating the ratio of liquid and solid flow in the respective separation zone. In order to be able to adjust the product purity a second, model-based control scheme is proposed. It makes use of the nonlinear wave propagation phenomena in the apparatus. The controlled chromatographic unit is automatically working with minimum solvent consumption and maximum feed throughput without any numerical optimization calculations. This control algorithm can therefore also be applied for fast optimization of SMB processes.
2003
Article
http://edoc.mpg.de/124822
Journal of Chromatography A, v.1006, 3-13 (2003)
en
oai:edoc.mpg.de:1248252004-05-2619:89
Nonlinear behavior of reactor-separator networks : influence of separator control structure
Zeyer, K.-P.
Pushpavanam, S.
Kienle, A.
expertsonly
In this paper we analyze the behavior of a coupled reactor separator system with reactant recycle. The reactor is represented by a CSTR and the separator is represented by a flash unit. The reactor is operated isothermally and sustains a first order reaction A goes to B. The individual units always possess a unique, stable and feasible steady state. Surprisingly, even for the simple model system considered here, more complex patterns of behavior – involving infeasibility, multiple steady states and limit cycles – can be observed, when the recycle is closed. It is shown that the behavior crucially depends on the flow and the flash control strategy. Stability criteria are derived for different flow and flash control strategies. They depend on the operating conditions and on the basic physico-chemical properties of the mixture. Potential sources for instability are systematically identified and illustrated.
2003
Article
http://edoc.mpg.de/124825
Industrial & Engineering Chemistry Research, v.42, 3294-3303 (2003)
en
oai:edoc.mpg.de:1250602004-05-2819:89
Flexible Modellierung grosschemischer Anlagen mit dem Modellierungswerkzeug ProMoT
Waschler, R.
Angeles-Palacios, O.
Ginkel, M.
Kienle, A.
expertsonly
SCS Publishing House
2003
Conference-Paper
http://edoc.mpg.de/125060
Hohmann, R.: Simulationstechnik : 17 Symposium in Magdeburg, September 2003, SCS Publishing House, 173-178 (2003)
de
oai:edoc.mpg.de:1250632004-07-0219:89
Nonlinear control of a reactive distillation column
Grüner, S.
Mohl, K. D.
Kienle, A.
Gilles, E. D.
Fernholz, G.
Friedrich, M.
expertsonly
Control of reactive distillation columns is a challenging task due to the complex dynamics arising from the coupling of reaction and separation. In this paper, asymptotically exact input/output-linearization is applied in simulation studies to an industrial reactive distillation column which is operated by Bayer AG. The resulting control law is rather general and can be easily adopted for other reactive distillation columns. This control scheme requires knowledge of the complete state of the process and therefore an observer is designed. Asymptotically exact input/output-linearization inherits robust stability from a robust observer. It is intuitively argued that the proposed observer is robust w.r.t. both model structure and parameter errors. In order to compensate for steady state observer offsets an outer control loop with simple PI-controlers is implemented. Simulation studies evidence that in comparison with a well-tuned linear controller the nonlinear controler shows superior performance with respect to setpoint changes and disturbances, even in the presence of unknown input delays.
2003
Article
http://edoc.mpg.de/125063
Control Engineering Practice, v.11, 915-925 (2003)
en
oai:edoc.mpg.de:1250642004-10-0719:89
Esterification of acetic acid with butanol in the presence of ion-exchange resins as catalysts
Gangadwala, J.
Mankar, S.
Mahajani, S.
Stein, E.
Kienle, A.
expertsonly
The esterification of acetic acid with n-butanol was studied in the presence of ion-exchange resin catalysts such as Amberlyst-15 to determine the intrinsic reaction kinetics. The effect of various parameters such as temperature, mole ratio, catalyst loading, and particle size was studied. Kinetic modeling was performed to obtain the parameters related to intrinsic kinetics. Pseudohomogeneous, Eley-Rideal, Langmuir-Hinshelwood-Hougen-Watson (LHHW), and modified LHHW models were developed. The kinetics for the side-reaction etherification was also investigated. The rate expressions would be useful in the simulation studies for reactive distillation. The experimental data generated for the reaction under total reflux were validated successfully using the developed rate equation and estimated values of kinetic parameters.
2003
Article
http://edoc.mpg.de/125064
Industrial and Engineering Chemistry Research, v.42, 2146-2155 (2003)
en
oai:edoc.mpg.de:1250662004-06-0419:89
Multiple steady states in two-phase reactors under boiling conditions
Waschler, R.
Pushpavanam, S.
Kienle, A.
expertsonly
In this paper, we analyze the nonlinear behavior of two–phase reactors under boiling conditions. First we focus on a simple nth-order reaction of the form A -> B, which allows a rigorous analytical treatment. Three necessary conditions for the existence of multiple steady states have been identified: the reactant A has to be the light–boiling component, the difference in boiling point temperatures between the reactant A and the product B has to be sufficiently large, and the order of the reaction has to be less than some physical parameter alpha. This parameter alpha can be interpreted as a measure for the phase–equilibrium–driven self–inhibition of the reaction mechanism. Thus, we have found an elegant explanation for the occurrence of multiplicities. Analytical and therefore general quantitative criteria identifying the regions of multiplicity for the model system are presented. Practical relevance of our results is demonstrated by means of two examples, the Monsanto process for the production of acetic acid and the ethylene glycol reactive distillation system.
2003
Article
http://edoc.mpg.de/125066
Chemical Engineering Science, v.58, 2203-2214 (2003)
en
oai:edoc.mpg.de:1250742004-06-0719:89
Verbesserter Betrieb von Simulated Moving Bed-Prozessen durch zyklische Modulation der Feedkonzentration
Schramm, H.
Kaspereit, M.
Kienle, A.
Seidel-Morgenstern, A.
expertsonly
In diesem Beitrag wird eine neue Betriebsweise für SMB Prozesse vorgestellt. Durch eine zyklische Variation der Feedkonzentration (ModiCon) während des Schaltintervalls kann die Produktivität signifikant gesteigert und der spezifische Lösemittelverbrauch wesentlich verringert werden.
2003
Article
http://edoc.mpg.de/125074
Chemie-Ingenieur-Technik, v.75, 379-383 (2003)
de
oai:edoc.mpg.de:1250782004-07-0219:89
Application of the Process Modeling Tool ProMoT to large-scale chemical engineering processes
Waschler, R.
Angeles-Palacios, O.
Ginkel, M.
Kienle, A.
expertsonly
The application of the process modeling tool ProMoT to large-scale chemical engineering processes is presented. Particular emphasis is on the flexibility of the tool in terms of creating flowsheet alternatives - a prerequisite for efficient plant design and control structure selection. The main concepts in this respect are the bottom-up development of an object-oriented knowledge base for the simplified implementation of submodels on the level of process units, the efficient aggregation on the flowsheet level, and the flexibility to effectively perform top-down refinements for problem-specific applications. All concepts are illustrated on the basis of an industrial scale process.
2003
Conference-Paper
http://edoc.mpg.de/125078
urn:ISBN:3-901608-24-9
Proceedings 4rd MATHMOD, IMACS Symposium on Mathematical Modelling : February 5 - 7, 2003 ; Vol. 2: Full Papers CD, 1113-1121 (2003)
en
oai:edoc.mpg.de:1250802004-06-0219:89
Nonlinear dynamics and control of reactive distillation processes
Kienle, A.
Marquardt, W.
expertsonly
Wiley-VCH
2003
InBook
http://edoc.mpg.de/125080
urn:ISBN:3-527-30579-3
Reactive distillation : status and future directions, 241-281 (2003)
en
oai:edoc.mpg.de:1250812012-03-2819:89
Nonlinear oscillations in ammonium sulphate crystallization : a comparison of different model predictions
Pathath, P. K.
Kienle, A.
expertsonly
In this paper, the focus is on nonlinear oscillations of ammonium sulfate crystallization. This system has been studied intensively in the past and can be viewed as a standard test system for crystallization processes. The focus is on crystallizers with fines dissolution and classified product removal. Using methods from numerical bifurcation analysis, we investigate how stability in such a system depends on the various operational parameters, like cut sizes and recycle rates of fines dissolution and product classification. Theoretical predictions of three different population models are compared with each other: (i) a model with simple kinetics and ideal fines classification, (ii) a model with complex kinetics involving breakage due to attrition and ideal fines classification, and (iii) a model with simple kinetics and nonideal fines classification. It is found that predictions of the instability regions with models i and ii are rather close. In contrast, the nonideal fines classification can change the stability rather drastically.
2003
Article
http://edoc.mpg.de/125081
Industrial and Engineering Chemistry Research, v.42, 6949-6955 (2003)
en
oai:edoc.mpg.de:1738692004-07-0819:89
Dynamical simulation of a plant for the production of low density polythylene
Häfele, M.
Kienle, A.
Boll, M.
Mähling, F. O.
Schmidt, C.-U.
Schwibach., M.
expertsonly
Hochdruck-Polyethylen ist ein sehr weit verbreiteter Kunststoff, der in Rohrreaktoren produziert werden kann. Die Reaktion setzt sehr viel Reaktionswärme frei, die abgeführt werden muss. Deshalb sind derartige Reaktoren zum einen meist sehr lang, zum anderen werden die Initiatoren, welche die Reaktion in Gang setzen, an mehreren Stellen über den Reaktor verteilt zudosiert. Das Modell der Anlage besteht aus dem Rohrreaktor, drei Verdichtern, zwei Trennstufen und den Rückführungen, durch welche das in den Separatoren abgetrennte, nicht umgesetzte Edukt in den Prozess erneut eingespeist wird. Der Rohrreaktor wird zur Modellierung in 16 Module aufgeteilt, wobei jedes dieser Module aus 35 partiellen DGL’s besteht. Zur Simulation werden diese mittels einer adaptiven Linienmethode in gewöhnliche DGL’s umgewandelt [1]. Adaptiv heißt dabei, dass nicht die Anzahl der Gitterpunkte, sondern ihr Abstand variabel ist. Die Längenverteilung der Polymermolekülketten, die ausschlaggebend für die physikalischen Eigenschaften des produzierten Kunststoffes ist, wird mit Hilfe ihrer statistischen Momente erfasst. Aus diesen Momenten lassen sich beispielsweise die mittlere Kettenlänge oder die Breite der Kettenlängenverteilung berechnen. Außerdem werden in dem Modell die Lang- und Kurzkettenverzweigungen sowie die Bildung von Doppelbindungen berücksichtigt. Diese Größen sind ebenfalls ausschlaggebend für die Eigenschaften des Kunststoffes. Der Reaktor zeigt ein ausgeprägtes nichtlineares dynamisches Verhalten, das durch wandernde Temperatur- und Konzentrationsfronten gekennzeichnet ist und das im Rahmen des Beitrages illustriert wird. Langfristig soll das oben genannte Modell als Grundlage zur Entwicklung neuer Prozessführungskonzepte dienen. Literatur [1] A. Vande Wouwer, Ph. Saucez, and W. E. Schiesser, editors. Adaptive Methodof Lines. Mathematics/Chemical Engineering. Chapman & Hall/CRC, 2001
SCS Publishing House
2003
Conference-Paper
http://edoc.mpg.de/173869
Hohmann, R.: Simulationstechnik : 17. Symposium in Magdeburg, September 2003, SCS Publishing House, 179-184 (2003)
de
oai:edoc.mpg.de:1738732004-07-0819:89
Production of butyl acetate by catalytic distillation : reaction kinetics and process design studies
Gangadwala, J.
Kienle, A.
Stein, E.
Mahajani, S.
expertsonly
This paper studies reactive distillation for the synthesis of n-butyl acetate from n-butanol esterification with acetic acid over Amberlyst -15. This study is carried out to influence the unwanted side product dibutylether formation, produced by butanol dehydration. First of all, activity based intrinsic reaction kinetics for the main reaction (esterification) and the side reaction (etherification) have been developed. Effect of various parameters such as temperature, mole ratio, catalyst loading and catalyst particle size was studied. The intrinsic kinetic parameters related to Pseudohomogeneous (PH), Eley-Rideal (RE), Langmuir Hinshelwood Hougen Watson (LHHW), and modified LHHW (ML) models were developed. Good agreement between the model predictions and experimental data were obtained. For the main reaction RE model or modified LHHW model and for the side reaction LHHW model are appropriate representations of intrinsic kinetics. The developed rate expression were then used for the simulation based design of reactive distillation column for the production of butyl acetate with the goal of eliminating the side product formation and achieving high purity of desired product butyl acetate. A simple equilibrium stage, steadystate reactive distillation column model was developed and validated using expeimental data from the literature. The following column configurations are invesigated: (a) column with non - reactive rectifying section and reactive stripping section (b) column with non - reactive rectifying section, non - reactive stripping section and reactive middle section; and (c) conventional distillation column with pump around reactor. For each configuration, effect of design parameters such as, reboiler heat duty, catalyst loading, catalyst section length and location, and feed stage location were investigated with the objective to achieve desired goal.
2003
Conference-Paper
http://edoc.mpg.de/173873
ISMR3 - CCRE18 : joint research symposium of the 3rd International Symposium on Multifunctional Reactors and the 18th Colloquia on Chemical Reaction Engineering, 191-194 (2003)
en
oai:edoc.mpg.de:1926492005-02-1619:89
Equilibrium theory and nonlinear waves for reactive distillation columns and chromatographic reactors
Grüner, S.
Kienle, A.
expertsonly
A general framework for analyzing and understanding the dynamics of reactive separation processes is developed. The theory is based on the assumption of simultaneous phase and reaction equilibrium. It makes use of transformed concentration variables, which were first introduced by Doherty and co-workers for the steady state design of reactive distillation processes (Proc. Roy. Soc. London A 413 (1987a) 459). It is shown that these transformed variables can be directly generalized to the dynamic problem considered here. Further, they can also be applied to other reactive separation processes like fixed bed as well as countercurrent chromatographic reactors, for example. They provide profound insight into the dynamic behavior of these processes and reveal bounds of feasible operation caused by reactive azeotropy. It is shown that reactive azeotropy, which is well-known phenomenon in reactive distillation (Proc. Roy. Soc. London A 413 (1987b) 443) may also rise under very similar conditions in other reactive separation processes like chromatographic reactors for example.
2004
Article
http://edoc.mpg.de/192649
Chemical Engineering Science, v.59, 901-918 (2004)
en
oai:edoc.mpg.de:1949322005-06-2719:89
Verbesserung der Trennleistung von Simulated Moving Bed-Prozessen durch zyklische Modulation der Feedkonzentration
Schramm, H.
Kaspereit, M.
Kienle, A.
Seidel-Morgenstern, A.
expertsonly
Im Konferenzbeitrag wird eine neuartige und im Vergleich einfache Betriebsweise mit zyklischer Modulation der Feedkonzentration vorgestellt (ModiCon). Der Einfluss dieser Modulation auf die Trennleistung von SMB-Prozessen wird anhand von theoretischen und experimentellen Daten analysiert. Die Methode ermöglicht eine signifikante Steigerung der Produktivität und eine gleichzeitige Senkung des Lösemittelverbrauchs für nichtlineare Trennungen. Alternativ hierzu kann auch die Produktreinheit gesteigert werden.
2003
Conference-Paper
http://edoc.mpg.de/194932
Proc. GVC annual meeting, 1170-1171 (2003)
de
oai:edoc.mpg.de:1991182004-10-0219:89
Nonlinear model reduction of a two-dimensional MCFC model with internal reforming
Mangold, M.
Sheng, M.
expertsonly
A reduced nonlinear model of a planar molten carbonate fuel cell is presented. The model is derived from a spatially distributed dynamic model of the cell by applying the Karhunen Loève Galerkin procedure. The reduced model is of considerably lower order than the original one and requires much less computation time. The comparison between the two models shows that the reduced model can describe the dynamics of the temperature field with sufficient accuracy and has good extrapolation qualities with respect to changes in the model parameters.
2004
Article
http://edoc.mpg.de/199118
Fuel Cells : from Fundamentals to Systems, v.4, 68-77 (2004)
en
oai:edoc.mpg.de:2076212005-02-0719:89
Effect of Conversion-Dependent Viscosity on the Nonlinear Behavior of a Reactor with Fixed Pressure Drop
Krishna, M. V.
Pushpavanam, S.
Kienle, A.
expertsonly
Polymerization reactions are characterized by changes in physical properties, such as viscosity, as the reaction proceeds. The effect of a conversion-dependent viscosity on the nonlinear behavior of polymerization reactor is investigated in this paper. This involves considering the coupling between the momentum balance, mass balance, and energy balance of the reactor. It is shown that, when the viscosity increases with the conversion steady-state multiplicity can occur when the pressure drop across the reactor is fixed. The different steady-states have different inlet flow rates and exit conversions. Two models of ideal continuous reactors, i.e., CSTR and PFR, are investigated. We analyze these reactors considering operation under a constant pressure drop. Our results indicate that multiple steady states can occur in systems such as polymerization reactors where viscosity significantly increases with conversion in the reactor. We show even an isothermal reactor can exhibit multiple steady states. The physical source, i.e., the positive-feedback effect, that causes this multiplicity is identified. The applicability of the predicted results is illustrated for a case study of the manufacture of low-density polyethylene. We postulate that operation of a reactor with a fixed pressure drop leads to decoupling of the reactor from a downstream separator in a coupled reactor-separator network. This can hence form a desirable control strategy for operating coupled systems.
2004
Article
http://edoc.mpg.de/207621
Industrial and Engineering Chemistry Research, v.43, 8284-8292 (2004)
en
oai:edoc.mpg.de:2077042005-02-1019:89
Nichtlineare Dynamik in Reaktor-Separator-Systemen
Zeyer, K.-P.
Kulkarni, A. A.
Pushpavanam, S.
Kienle, A.
expertsonly
Chemische Produktionsanlagen bestehen im Wesentlichen aus Reaktions- und Separationsprozessen. In den Reaktionsprozessen werden die zugeführten Ausgangsstoffe teilweise in die gewünschten Produkte umgesetzt. In den nachfolgenden Separationsprozessen werden nicht umgesetzte Ausgangsstoffe von den Produkten abgetrennt und in den Reaktor rezykliert. Derartige Recycles sind einerseits notwendig um den Prozess ökonomisch und ökologisch sinnvoll zu gestalten, andererseits können sie das dynamische Verhalten einer Produktionsanlage negativ beeinflussen und Instabilität sowie erhöhte Sensitivität gegenüber Störungen verursachen. Solche Verhaltensweisen werden im Rahmen des geplanten Beitrages zunächst an zwei typischen industriellen Beispielprozessen illustriert. Dabei handelt es sich um eine Anlage zur Produktion von Essigsäure und eine Anlage zur Herstellung von Hochdruckpolyethylen. Es wird weiter gezeigt, dass sich die beobachteten Phänomene mit Hilfe eines einfachen Modells systematisch untersuchen und verstehen lassen. Bei dem betrachteten Modellsystem handelt es sich um einen idealen Rührkesselreaktor und einen nachgeschalteten einstufigen Flash mit Recycle. Die Dynamik eines solchen Systems hängt ganz entscheidend von der grundlegenden Regelungsstrategie ab. Selbst für den einfachen Fall einer isothermen Reaktion erster Ordnung können infolge des Recycles Instabilitäten und Mehrdeutigkeiten auftreten. Die dynamischen Instabilitäten bleiben sogar im nichtreaktiven Grenzfall erhalten und können im Falle einer nicht vernachlässigten Transportverzögerung im Recycle zu komplexem bi- und multirhythmischem Verhalten führen. Umgekehrt lassen sich mit Hilfe dieser Untersuchungen Regelungsstrategien identifizieren, die immer auf eindeutige und stabile Betriebszustände führen.
2004
Conference-Paper
http://edoc.mpg.de/207704
Chemie-Ingenieur-Technik, v.76, 1313 (2004)
de
oai:edoc.mpg.de:2077992005-03-0819:89
Nonlinear Dynamics in Reactor Separator Systems
Zeyer, K.-P.
Kulkarni, A. A.
Kienle, A.
expertsonly
Industrial process plants are primarily made up of two basic units, i.e. reactors and separators. The reactants are fed to the reactor unit and partially converted to products. The mixture of reactants and products is then transferred to a separator unit. In the separator the unreacted material is separated from the product and recycled back to the reactor (Figs. 1 and 2). However, recycles may introduce complex dynamics involving instability and sensitivity to disturbances. So far a nonlinear exothermic first order reaction [1] and an autocatalytic isothermal reaction [2] have been studied in a continuous flow stirred tank reactor (CSTR) coupled to an isothermal separator represented by a heated flash corresponding to a one-step distillation unit. Recently these studies have been extended to the investigation of an isothermal first order reaction [3]. Although this model system is very simple we found surprisingly complex dynamic phenomena, such as multiplicity (static instability) and autonomous periodic oscillations (dynamic instability). It was shown that the dynamic behavior depends on the flow and the flash control strategy. Especially for the case of fixed reactor inlet flow and constant heating power of the flash we found the most complex behavior involving multiplicity and oscillations. Model system: In the present paper we are focussing on the case of fixed CSTR inlet and constant heating of the flash mentioned above. The system is further simplified by skipping the reaction completely so that the reactor can now be regarded as a simple mixing unit. The whole set-up can therefore be interpreted as a single step distillation unit with recycle. The mixture is assumed to be binary, ideal and homogeneous. All flow rates are based on molar units. The controllers are assumed to be perfect. For recycling we have investigated two different modes i) vapor phase (Fig. 1) and ii) liquid phase (Fig. 2) recycling. In a second step we have introduced a delay time in the recycle which is caused by a transportation lag. Due to the simplicity of the model system an analytical approach is possible. The results are confirmed by model calculations, such like integration and continuation of stationary and oscillatory states, which were performed using the software package DIVA [4].
Results: In the case of vapor recycle we prove static as well as dynamic stability for all operating conditions. The results are confirmed by model calculations. For the case of liquid recycle static stability can be proven. However, dynamic stability can be guaranteed only for DhA > DhB and Tfl < TR, where DhA and DhB are the evaporation enthalpies and Tfl and TR are the temperatures of the flash and the reactor unit, respectively. Here A is assumed to be the heavy boiling component. For the reversed case where A is the light boiling component dynamic stability can be proven only for DhA < DhB and Tfl < TR. For all other cases dynamic instabilities can occur. Examples of stable and unstable periodic oscillations have been found in our model calculations. The oscillations can emerge smoothly at supercritical Hopf bifurcation points or rapidly at subcritical Hopf points. Dynamic instabilities and Hopf bifurcation points can be found for the binary mixtures of water and acetic acid as well as for ethanol and acetic acid. Taking a set of parameters where stable periodic oscillations occur we introduced delay times in the recycle of the liquid phase. For increasing delays the period of the oscillations increases and decreases in a saw-tooth like manner. The individual saw-tooths are overlapping so that different oscillatory states are obtained for increasing and decreasing delay time. Therefore, two or more different stable oscillatory states are coexisting for the same parameter set. Further analysis shows that the coexisting stable oscillatory states are separated by unstable periodic orbits (multirhythmicity). This behavior is analogous to studies of delayed feed back in the isothermal nonlinear minimal bromate oscillator.
2004
Conference-Paper
http://edoc.mpg.de/207799
CHISA 2004 : 16th International Congress of Chemical and Process Engineering (2004)
en
oai:edoc.mpg.de:2078742005-02-0919:89
Development of physical models for the process control of a molten carbonate fuel cell system
Mangold, M.
Sheng, M.
Heidebrecht, P.
Kienle, A.
Sundmacher, K.
expertsonly
The subject of the paper is the development of suitable models for the process design and process control of molten carbonate fuel cell (MCFC) systems. In a first step, a rigorous dynamic, spatially distributed model of an MCFC is derived from first principles. As this model is too complex for most process control purposes, a reduced model is developed in the following. The reduced model is derived from the spatially distributed reference model of the cell by applying the Karhunen–Loève–Galerkin procedure. The reduced model is of considerably lower order than the original one and requires much less computational time. The applicability of the reduced model to process control problems is demonstrated by using it in the framework of a state and parameter estimator.
2004
Article
http://edoc.mpg.de/207874
Chemical Engineering Science, v.59, 4847-4852 (2004)
en
oai:edoc.mpg.de:2079562005-02-1119:89
Nonlinear analysis of current instabilities in high temperature fuel cells
Mangold, M.
Krasnyk, M.
Sundmacher, K.
expertsonly
The conductivity of electrolytes in high temperature fuel cells increases with increasing temperature. It is shown that this property may lead to instabilities, inhomogeneous temperature fields, and hot spots. A simple spatially one-dimensional model of a cell is studied by phase plane analysis and numerical bifurcation analysis. The operation of the cell at constant voltage and at constant current is considered. It is found that in both cases spatial temperature patterns and channels of high current density can form.
2004
Article
http://edoc.mpg.de/207956
Chemical Engineering Science, v.59, 4869-4877 (2004)
en
oai:edoc.mpg.de:2079822005-02-1119:89
Nonlinear model predictive control of multicomponent distillation columns using wave models
Grüner, S.
Schwarzkopf, S.
Disli-Uslu, I.
Kienle, A.
Gilles, E. D.
expertsonly
2004
Conference-Paper
http://edoc.mpg.de/207982
7th International Symposium on Advanced Control of Chemical Processes : preprints; Vol. 1, 231-236 (2004)
en
oai:edoc.mpg.de:2080562012-03-0919:89
Production of Butyl Acetate by Catalytic Distillation : Process Design Studies
Gangadwala, J.
Kienle, A.
Stein, E.
Mahajani, S.
expertsonly
A simulation-based design method is employed to figure out the promising reactive distillation process configuration for the production of butyl acetate. The intrinsic kinetics developed for the esterification and the unwanted side reaction etherification over the Amberlyst-15 catalyst are utilized to evaluate the steady-state performance of different reactive distillation processes. A steady-state column model is developed and compared with experimental data from the literature. With this model, three different column configurations are investigated for the production of butyl acetate with the goal of eliminating the formation of byproduct dibutyl ether and achieving a high purity of the desired product butyl acetate. The following column configurations are explored: (a) a column with a nonreactive rectifying section and a reactive stripping section; (b) a column with a nonreactive rectifying section, a nonreactive stripping section, and a reactive middle section; and (c) a conventional distillation column with a cocurrent pump-around reactor. Configuration c is compared with the side reactor configuration, where the pump-around reactor is coupled to the column in a countercurrent fashion.
2004
Article
http://edoc.mpg.de/208056
Industrial & Engineering Chemistry Research, v.43, 136-143 (2004)
en
oai:edoc.mpg.de:2153312005-11-0219:89
Computer Aided Modeling of Chemical and Biological Systems : Methods, Tools, and Applications
Mangold, M.
Angeles-Palacios, O.
Ginkel, M.
Kremling, A.
Waschler, R.
Kienle, A.
Gilles, E. D.
expertsonly
Computer tools can support and accelerate the development and implementation of first principle models for chemical and biological processes significantly. Several application examples illustrate this in the contribution. Models of a bio-chemical reaction network, of a catalytic fixed bed reactor, and of two chemical production processes are considered. The models are implemented in a structured way in the process modeling tool ProMoT, whose key features are discussed. The structuring of the models is based on a uniform structuring methodology whose main ideas are presented as well.
2005
Article
http://edoc.mpg.de/215331
Industrial & Engineering Chemistry Research, v.44, 2579-2591 (2005)
en
oai:edoc.mpg.de:2173422005-11-0219:89
Steady State Behavior of Coupled Nonlinear Reactor-Separator Systems : Effect of Different Separators
Painuly, A.
Pushpavanam, S.
Kienle, A.
expertsonly
In a typical plant, downstream separators are coupled to upstream reactors through recycle streams. The bifurcation behavior of the coupled system is different from that of the individual units. The bifurcation diagram depicts the dependence of the steady state on an operating parameter. In this work, we analyze the behavior of three different coupled reactor-separator systems. Each system is characterized by a different separator. The three different separator units investigated are a flash unit, a nanofiltration unit, and an ultrafiltration unit. The reactor is modeled as a CSTR sustaining a cubic autocatalytic reaction. The stand-alone reactor can have a maximum of three solutions. The coupled system is investigated for the situation when the fresh feed is flow controlled and the reactor level is maintained constant using the reactor effluent flow stream. It is shown that the coupled reactor-flash system has a maximum of two steady solutions, while the two coupled reactor-membrane separation systems have a maximum of three solutions. Each coupled process is analyzed for two situations: (i) a binary system and (ii) ternary system. The physical cause for the difference in these behaviors is analyzed.
2005
Article
http://edoc.mpg.de/217342
Industrial and Engineering Chemistry Research, v.44, 2165-2173 (2005)
en
oai:edoc.mpg.de:2176562012-03-0919:89
Production of Butyl Acetate by Catalytic Distillation : Theoretical and Experimental Studies
Singh, A.
Hiwale, R.
Mahajani, S. M.
Gudi, R. D.
Gangadwala, J.
Kienle, A.
expertsonly
The esterification reaction of acetic acid with n-butanol in a continuous catalytic distillation system has been studied. The products of esterification reactions viz, water and butyl acetates are separated by distillation during the course of the reaction, to overcome the equilibrium limitations. A 3-m-tall column with reactive and nonreactive zones, packed with a commercial catalytic packing (KATAPAK-S) and noncatalytic wire gauze packing, was used for this purpose. For a feed concentration corresponding to that obtained in a one-stage continuously stirred tank reactor at reaction equilibrium, conversion of ~100% was realized, with selectivity on the order of 99%. Interestingly, in most of the experiments, the bottom stream contained butyl acetate that was almost free of acetic acid. The influence of various operating parameters, such as feed flow rate, feed composition, feed location, and boil-up rate, on the conversion, selectivity, and separation was studied. A dynamic equilibrium stage model was developed and solved to predict the transient and steady-state results. Reasonably good agreement between the experimental and simulation results was realized.
2005
Article
http://edoc.mpg.de/217656
Industrial and Engineering Chemistry Research, v.44, 3042-3052 (2005)
en
oai:edoc.mpg.de:2182982005-11-0219:89
Effect of Delay on the Stability of a Coupled Reactor-Flash System Sustaining an Elementary Non-isothermal Reaction
Balasubramaniam, P.
Pushpavanam, S.
Kienle, A.
Balaraman, K. S.
expertsonly
In this work, we investigate the stability of a continuous stirred tank reactor (CSTR) coupled to an isothermal, isobaric flash. The coupling is through the recycle of the reactant-rich stream from the downstream flash unit to the upstream reactor. We consider the first-order irreversible reaction A -> B occurring non-isothermally in the CSTR. The main focus of this work is to investigate the effect of delay arising as a result of transportation lag from the reactor to the separator on the system stability. In the absence of delay, it has been clearly shown that the coupled system exhibits static and dynamic instability. The effect of delay on the stability of the coupled system is studied for the two classical control strategies: (i) The fresh feed flow rate, F₀, is flow controlled and the reactor effluent flow rate, F, is used to control the molar holdup in the reactor, M_R. (ii) The flow rate, F, is flow controlled, and F₀ is used to control M_R. It is shown that delay induces new regions of dynamic instability. The system switches from instability to stability and vice versa for these two control strategies as the delay is increased.
2005
Article
http://edoc.mpg.de/218298
Industrial and Engineering Chemistry Research, v.44, 3619-3625 (2005)
en
oai:edoc.mpg.de:2200362012-03-2719:89
Short-Term Scheduling of Batch Processes : a Comparative Study of Different Approaches
Mishra, B. V.
Mayer, E.
Raisch, J.
Kienle, A.
expertsonly
The approaches to scheduling problem formulation in chemical engineering can be broadly classified into two categories, namely, the standard recipe approach (SRA) and the overall optimization approach (OOA). In the SRA, first the recipes are standardized either empirically or via single-batch optimization (SBO) and then the production scheduling problem is formulated on the basis of these standardized recipes. However, the standardization of recipes removes degrees of freedom from the system, and because of this, the solutions obtained with this approach can be suboptimal, whereas in the OOA, the process dynamics are directly included in the scheduling problem formulation instead of the standardized recipes. This restores the additional degrees of freedom of the system, and therefore this approach can yield a better solution. However, direct inclusion of the process dynamics in the scheduling problem formulation results in a mixed-integer dynamic optimization (MIDO) problem, the solution of which can be a formidable task. The objective of this paper is to illustrate the advantages and disadvantages of the SRA and OOA for short-term scheduling of batch chemical processes with the help of illustrative examples. It is shown that the results crucially depend on the cost structure of the specific application as well as on the objective function employed.
2005
Article
http://edoc.mpg.de/220036
Industrial and Engineering Chemistry Research, v.44, 4022-4034 (2005)
en
oai:edoc.mpg.de:2237372005-11-0719:89
Numerical Analysis of Higher-Order Singularities in Complex Chemical Process Models in ProMoT
Krasnyk, M.
Ginkel, M.
Mangold, M.
Kienle, A.
expertsonly
nonlinear analysis; singularity theory; bifurcation; augmented system
In this contribution, a tool is presented that allows the continuation of singularities of higher codimension also for complex chemical process models. The tool is an extension of the process-modelling tool ProMoT. It allows creating analytically augmented systems for singularity points with currently codimension up to 2. Required higher order directional derivatives up to the third order are obtained analytically via an interface to the computer algebra system Maxima.
Elsevier
2005
Conference-Paper
http://edoc.mpg.de/223737
Puigjaner, L.; Espuña, A.: European Symposium on Computer Aided Process Engineering - 15, Elsevier, 223-228 (2005)
en
oai:edoc.mpg.de:2237512005-11-0719:89
Optimal Process Design for the Synthesis of 2,3-Dimethylbutene-1
Gangadwala, J.
Kienle, A.
Haus, U.-U.
Michaels, D.
Weismantel, R.
expertsonly
Reactive distillation; isomerization; 2,3-dimethylbutenes; optimization; MINLP
This paper is concerned with the computer-aided optimal design of reaction-distillation processes. The production of solvent 2,3-dimethylbutene-1 by isomerization of 2,3-dimethylbutene-2 is considered as an innovative benchmark problem. Possible process candidates are a reactive distillation column, a reactor coupled to a nonreactive distillation column or a reactive reboiler with a nonreactive distillation column on top. Local MINLP optimization indicates that the reactive distillation has the lowest total annualized costs. However, due to the non-convexity of the underlying mathematical problem better solutions for the other process candidates cannot be excluded. For this purpose a new global approach is proposed which is based on discrete optimization of the underlying model equations and which proves globally that reactive distillation is the best option.
Elsevier
2005
Conference-Paper
http://edoc.mpg.de/223751
Puigjaner, L.; Espuña, A.: European Symposium on Computer Aided Process Engineering - 15, Elsevier, 847-852 (2005)
en
oai:edoc.mpg.de:2243602005-11-0719:89
Nonlinear Behaviour of a Low-Density Polyethylene Tubular Reactor-Separator-Recycle System
Häfele, M.
Disli-Uslu, I.
Kienle, A.
Krishna, V. M.
Pushpavanam, S.
Schmidt, C.-U.
expertsonly
polymerisation; tubular reactor; low-density polyethylene (LDPE); nonlinear dynamic model; nonlinear analysis
The aim of this work is to analyse the nonlinear behaviour of a low-density polyethylene reactor-separator-recycle system. A simplified dynamic model is derived based on the detailed model presented in Häfele (2004). A numerical bifurcation and stability analysis is performed to predict the region of stable operation. As a result multiple steady states and oscillatory behaviour were found. The implications of these findings for practical process operation are discussed.
Elsevier
2005
Conference-Paper
http://edoc.mpg.de/224360
Puigjaner, L.; Espuña, A.: European Symposium on Computer Aided Process Engineering - 15, Elsevier, 1423-1428 (2005)
en
oai:edoc.mpg.de:2244952012-04-1219:89
Instabilities in High-Temperature Fuel Cells due to Combined Heat and Charge Transport
Mangold, M.
Krasnyk, M.
Kienle, A.
Sundmacher, K.
expertsonly
Wiley VCH
2005
InBook
http://edoc.mpg.de/224495
urn:ISBN:3-527-30831-8
Integrated Chemical Processes, 69-84 (2005)
en
oai:edoc.mpg.de:2244972012-04-1219:89
Equilibrium Theory and Nonlinear Waves for Reaction Separation Processes
Kienle, A.
Grüner, S.
expertsonly
Wiley VCH
2005
InBook
http://edoc.mpg.de/224497
urn:ISBN:3-527-30831-8
Integrated Chemical Processes, 149-181 (2005)
en
oai:edoc.mpg.de:2301702005-11-0319:89
A theoretical analysis of oscillations and dynamic instabilities in continuous fluidized bed spray granulation
Radichkov, R.
Kienle, A.
Heinrich, S.
Müller, T.
Peglow, M.
Mörl, L.
expertsonly
The main goal of this work is the theoretical prediction and qualitative analysis of the nonlinear behavior of fluidized bed granulation with external classification. First a new population balance model including a mass balance of the fluidized bed unit has been developed. Using methods from nonlinear systems analysis, such as a numerical bifurcation and stability analysis, unstable regions in the parameter space have been predicted. Due to the simplicity of the model the presented results are only qualitative. Future research will concentrate more on a quantitative investigation of the nonlinear process behavior with more detailed models and experimental validation.
2005
Conference-Paper
http://edoc.mpg.de/230170
Proceedings of the 3rd Nordic Drying Conference (2005)
en
oai:edoc.mpg.de:2378522005-11-0219:89
Dynamic simulation of a tubular reactor for the production of low-density polyethylene using adaptive method of lines
Häfele, M.
Kienle, A.
Boll, M.
Schmidt, C.-U.
Schwibach, M.
expertsonly
The dynamic mathematical model of a tubular reactor for the production of low-density polyethylene (LDPE) is introduced and simulation studies of a LDPE plant are presented. The plant consists of the tubular reactor, compressors, heat exchangers and material recycles. The overall model formulation comprises differential, partial differential and algebraic equations. This model formulation is transformed into a DAE system using an adaptive method of lines approach, where the grid points may change their position but their number remains constant. With this technique a solution on a standard PC is possible.
2005
Article
http://edoc.mpg.de/237852
info:doi/10.1016/j.cam.2004.12.033
Journal of Computational and Applied Mathematics, v.183, 288-300 (2005)
en
oai:edoc.mpg.de:2378532009-05-2719:89
Evolution of oxidation states in vanadium-based catalysts under conventional XPS conditions
Suchorski, Y.
Rihko-Struckmann, L.
Klose, F.
Ye, Y.
Alandjiyska, M.
Sundmacher, K.
Weiss, H.
expertsonly
The stability of different vanadium-based catalysts for the selective oxidation of small hydrocarbons under the ultra-high vacuum (UHV) conditions of standard X-ray photoelectron spectroscopy (XPS) was studied by using a multi-purpose surface analysis apparatus which allows time spans of only a few minutes between the sample transfer into vacuum and the first photoelectron spectrum. For vanadium phosphorus oxide catalysts a significant dependence of the average vanadium oxidation state on the time of exposure to the UHV was observed, with a substantial decrease of the V+5/V+4 ratio within only a few minutes. A much less pronounced reduction was found for alumina-supported VOx catalysts. The observed changes are predominantly due to the vacuum environment with a rather minor (if at all)
contribution of the X-ray excitation.
2005
Article
http://edoc.mpg.de/237853
info:doi/10.1016/j.apsusc.2004.11.083
Applied Surface Science, v.249, 231-237 (2005)
en
oai:edoc.mpg.de:2380882006-09-2619:89
Development and experimental investigation of an extended Kalman filter for a molten carbonate fuel cell system
Grötsch, M.
Gundermann, M.
Mangold, M.
Kienle, A.
Sundmacher, K.
expertsonly
Molten carbonate fuel cell; State estimation; Kalman filter
Industrial fuel cell stacks only provide very limited measurement information. To overcome this deficit, a state estimator for a molten carbonate fuel cell system is developed in this contribution. The starting point of the work is a rigorous spatially distributed model of the system. From this model, a reduced model is derived by using a Galerkin method and the Karhunen Loève decomposition technique. An extended Kalman filter with a continuous time simulator part and a discrete time corrector part is designed on the basis of the reduced model. The filter is tested in simulations and experimentally.
2006
Article
http://edoc.mpg.de/238088
info:doi/10.1016/j.jprocont.2006.05.001
Journal of Process Control, v.16, 985-992 (2006)
en
oai:edoc.mpg.de:2380892007-03-1919:89
Modeling and analysis of a plant for the production of low density polyethylene
Häfele, M.
Kienle, A.
Boll, M.
Schmidt, C.-U.
expertsonly
Dynamic model; Simulation; Discretization; Adaptive method of lines; Polymerization; Low density polyethylene; Tubular reactor; Method of moments
In this paper a detailed dynamic mathematical model of a plant for the production of low density polyethylene (LDPE) is derived. Besides the main part, a tubular reactor, the plant comprises compressors, heat exchangers and material recycles. The dynamic model for the overall system consists of differential, partial differential and algebraic equations. For the numerical solution with the simulator DIVA, this system is transformed into a system of differential and algebraic equations. For the transformation an adaptive finite difference scheme is used. With this mathematical model, the influence of the reactor wall and the influence of the material recycles on the plant dynamics is studied. In particular, it is shown that the reactor wall due to its high thermal capacity dominates the time constant of the stand alone reactor. By closing the material recycles the time constant is significantly increased. In addition, the recycles give rise to intricate nonlinear behavior.
2006
Article
http://edoc.mpg.de/238089
info:doi/10.1016/j.compchemeng.2006.05.001
Computers and Chemical Engineering, v.31, 51-65 (2006)
en
oai:edoc.mpg.de:2380902006-03-2919:89
Global Bounds on Optimal Solutions for the Production of 2,3 Dimethylbutene-1
Gangadwala, J.
Kienle, A.
Haus, U. U.
Michaels, D.
Weismantel, R.
expertsonly
This paper is concerned with computer-aided optimal design of combined reaction-distillation processes. The production of solvent 2,3-dimethylbutene-1 by isomerization of 2,3-dimethylbutene-2 is considered as an innovative benchmark problem. Possible process candidates are a reactive distillation column, a reactor coupled to a nonreactive distillation column, or a reactive reboiler with a nonreactive distillation column on top. Suitable mathematical models of the different processes are formulated, and the reaction kinetics of the isomerization over an Amberlyst 15 catalyst is determined. Local mixed-integer nonlinear optimization indicates that reactive distillation has the lowest total annulized costs. However, because of the nonconvexity of the underlying optimization problem, better solutions for the other process candidates cannot be excluded with the local approach. Therefore, a new approach is presented which provides a global lower bound for the second best solution and therefore proves that reactive distillation is the best option. The new approach is based on some suitable polyhedral approximation of the underlying model equations leading to a mixed-integer linear optimization problem.
2006
Article
http://edoc.mpg.de/238090
Industrial and Engineering Chemistry Research, v.45, 2261-2271 (2006)
en
oai:edoc.mpg.de:2380912012-03-0919:89
MINLP optimization of butyl acetate synthesis
Gangadwala, J.
Kienle, A.
expertsonly
Reactive distillation; Side reactor; Optimization; Butyl acetate; Esterification
The synthesis of butyl acetate by catalytic distillation has been studied using MINLP optimization. Two process alternatives are investigated, namely a reactive distillation column (RDC) and side reactors coupled with a non-reactive distillation column (SRC). The comparison is made with preliminary results obtained by a one parameter continuation method [1]. Important insights have been gained for a solution procedure of the optimization models. Significant improvements in the economic benefits have been observed in the optimized designs. For example, in terms of a reboiler heat duty 5% improvement in the RDC and 30% improvement in the SRC is noticed. In addition, a more rigorous optimization in terms of an overall operating and equipment cost is carried out.
2007
Article
http://edoc.mpg.de/238091
Chemical Engineering and Processing, v.46, 107-118 (2007)
en
oai:edoc.mpg.de:2380942007-06-1119:89
Ausbeutesteigerung mittels Membranreaktoren bei Parallel- und Folgereaktionen
Thomas, S.
Klose, F.
Seidel-Morgenstern, A.
expertsonly
Membranreaktoren besitzen das Potenzial, die Selektivität der Bildung eines gewünschten Reaktionsproduktes durch örtlich verteilte Eduktzugabe zu steigern.
In dieser Arbeit wird sowohl theoretisch als auch experimentell die optimale Dosierung gesucht, mit der die Ausbeute eines Zielproduktes maximiert werden kann.
Als Modellreaktion wird die oxidative Dehydrierung von Ethan zu Ethen unter Verwendung eines VOx/γ-Al₂O₃ -Katalysators gewählt.
2005
Article
http://edoc.mpg.de/238094
Chemie-Ingenieur-Technik, v.77, 1901-1909 (2005)
de
oai:edoc.mpg.de:2380952005-11-1719:89
Nichtlineare Dynamik der kontinuierlichen Wirbelschicht-Sprühgranulation
Radichkov, R.
Kienle, A.
Heinrich, S.
Müller, T.
Peglow, M.
Mörl, L.
expertsonly
2005
Conference-Paper
http://edoc.mpg.de/238095
Chemie-Ingenieur-Technik, v.77, 8, 1010-1011 (2005)
de
oai:edoc.mpg.de:2380962006-03-2919:89
Theoretical Investigations of Steady State Multiplicities in Solid Oxide Fuel Cells
Mangold, M.
Krasnyk, M.
Sundmacher, K.
expertsonly
bifurcation analysis; fuel cells; modelling; nonlinear dynamics; SOFC
The nonlinear steady state behaviour of solid oxide fuel cells (SOFCs) is investigated. It is found that the temperature dependence of the electrolyte's conductivity has a very strong influence on the occurrence of multiple steady states, instabilities and the formation of hot spots. Two correlations from literature for the electrolyte's conductivity are studied in a lumped model and in a 1D spatially distributed model of a SOFC. The cases of galvanostatic operation, potentiostatic operation, and operation under a constant ohmic load are considered. The lumped model possesses a unique steady state under galvanostatic operation and up to three steady states under potentiostatic operation or under constant load. In the distributed model, three steady states may coexist under galvanostatic operation and up to five under potentiostatic operation.
2006
Article
http://edoc.mpg.de/238096
Journal of Applied Electrochemistry, v.36, 265-275 (2006)
en
oai:edoc.mpg.de:2380982005-11-0219:89
Shortcut Method for Evaluation and Design of a Hybrid Process for Enantioseparations
Kaspereit, M.
Gedicke, K.
Zahn, V.
Mahoney, A. W.
Seidel-Morgenstern, A.
expertsonly
Hybrid processes for enantioseparations have a considerable potential for reducing investment and operational costs. An example is the combination of simulated moving bed (SMB) chromatography and selective crystallisation. However, the design of integrated processes is a difficult task. A shortcut method is presented that can serve as a tool for design and estimation of the potential of such processes. The approach requires only limited experimental data and thus allows for systematic parameters studies.
The method is based on the determination of the purity-performance characteristic of the SMB process and rigorous application of mass balances. The use of relative mass fluxes allows derivation of simple algebraic expressions for essential process parameters. The significant potential of combining SMB and crystallisation is demonstrated for the example of the separation of mandelic acid enantiomers.
2005
Article
http://edoc.mpg.de/238098
Journal of Chromatography A, v.1092, 43-54 (2005)
en
oai:edoc.mpg.de:2380992006-02-1419:89
Dynamics of Reaction Separation Processes in the Limit of Chemical Equilibrium
Grüner, S.
Mangold, M.
Kienle, A.
expertsonly
reaction separation processes; reactive distillation; chromatographic reactor; membrane reactor; equilibrium theory; nonlinear waves
A new approach for analyzing and understanding the dynamics of combined reaction separation processes with fast chemical reactions was proposed recently. The approach is based on transformed concentration variables which were first introduced by Doherty and co-workers for the steady-state design of reactive distillation processes. Application was demonstrated for reactive distillation processes and fixed bed, as well as moving-bed chromatographic reactors. The focus was on simple reactions of type 2A ⇌ B + C. This approach is further extended and applied to some real fairly complex multireaction systems. Applications to be considered are a reactive enantiomeric separation process in a fixed-bed chromatographic reactor, and an industrial reactive distillation column. Finally, application to membrane reactors is discussed.
2006
Article
http://edoc.mpg.de/238099
info:doi/10.1002/aic.10686
AIChE Journal, v.52, 1010-1026 (2006)
en
oai:edoc.mpg.de:2381002007-03-1919:89
Oxidative Dehydrogenation of Ethane in a Fluidized Bed Membrane Reactor
Ahchieva, D. G.
Peglow, M.
Heinrich, S.
Mörl, L.
Wolff, T.
Klose, F.
expertsonly
2005
Article
http://edoc.mpg.de/238100
urn:ISSN:0926-860X
Applied Catalysis A, v.296, 176-185 (2005)
en
oai:edoc.mpg.de:2381012012-03-0719:89
Object-oriented modelling of large scale chemical engineering processes with ProMoT
Waschler, R.
Angeles-Palacios, O.
Ginkel, M.
Kienle, A.
expertsonly
Object-oriented; Modelling tool; Chemical processes; Model libraries
The application of the process modelling tool ProMoT to large-scale chemical engineering processes is presented. Particular emphasis in on the flexibility of the tool in terms of creating flowsheet alternatives - a prerequisite for efficient plant design and control structure selection. The main concepts in this respect are the bottom-up development of an object-oriented knowledge base for the simplified implementation of submodels on the level of process units, the efficient aggregation on the flowsheet level and the flexibility to effectively perform top-down refinements for problem-specific applications. All concepts are illustrated on the basis of an industrial scale process.
2006
Article
http://edoc.mpg.de/238101
Mathematical and Computer Modelling of Dynamical Systems, v.12, 5-18 (2006)
en
oai:edoc.mpg.de:2381022013-02-0819:89
A numerical bifurcation analysis of continuous fluidized bed spray granulation with external product classification
Radichkov, R.
Müller, T.
Kienle, A.
Heinrich, S.
Peglow, M.
Mörl, L.
expertsonly
Nonlinear oscillations in continuous fluidized bed spray granulation with external product classification are analyzed. Using methods from numerical bifurcation analysis the size and location of the instability regions in the space of the design parameters and the adjustable operating parameters are predicted and discussed. The analysis is based on a new relatively simple population balance model, which is formulated on a mass basis, and provides first qualitive insights into the nonlinear dynamic behavior of continuous fluidized bed spray granulation processes.
Copyright © 2006 Elsevier B.V. All rights reserved. [accessed February 8th 2013]
2006
Article
http://edoc.mpg.de/238102
Chemical Engineering and Processing, v.45, 826-837 (2006)
en
oai:edoc.mpg.de:2381372005-12-1419:89
Analysis of Ester Hydrolysis Reactions in a Chromatographic Reactor Using Equilibrium Theory and a Rate Model
Vu, T. D.
Seidel-Morgenstern, A.
Grüner, S.
Kienle, A.
expertsonly
In this paper, a new methodology for the conceptual design of chromatographic reactors is proposed and illustrated for ester hydrolysis reactions in a fixed-bed chromatographic reactor with a pulse injection of the ester. In the first step, an extended equilibrium theory approach for chromatographic reactors is used to study the feasibility, i.e., to clarify whether total conversion of the reactant and total separation of the products are possible. In the second step, the required column length is calculated using a rate based model, which takes into account the finite reaction kinetics and axial dispersion. Finally, the theoretical predictions are compared with the experimental results.
2005
Article
http://edoc.mpg.de/238137
Industrial & Engineering Chemistry Research, v.44, 9565-9574 (2005)
en
oai:edoc.mpg.de:2411832005-11-0319:89
State estimation of a Molten Carbonate Fuel Cell by an Extended Kalman Filter
Mangold, M.
Grötsch, M.
Sheng, M.
Kienle, A.
expertsonly
Industrial fuel cell stacks only provide very limited measurement information. To overcome this deficit, a state estimator for a molten carbonate fuel cell is developed in this contribution. The starting point of the work is a rigorous spatially distributed model of the system. Due to its complexity, this model is hardly suitable for the design of a state estimator. Therefore, a reduced model is derived by using a Galerkin method and the Karhunen Loève decomposition technique. A low order system of ordinary differential equations and algebraic equations results. The reduced model is used to study the observability of the system for different sensor configurations. An extended Kalman filter with a continuous time simulator part and a discrete time corrector part is designed on the basis of the reduced model. The filter is tested in simulations.
Springer
2005
Conference-Paper
http://edoc.mpg.de/241183
urn:ISBN:3-540-27938-5
Meurer, T.; Graichen, K.; Gilles, E. D.: Control and Observer Design for Nonlinear Finite and Infinite Dimensional Systems, Springer, 93-109 (2005)
en
oai:edoc.mpg.de:2419562012-03-2619:89
Miniaturized Systems for Homogeneously and Heterogeneously Catalyzed Liquid-Phase Esterification Reaction
Kulkarni, A. A.
Zeyer, K. P.
Jacobs, T.
Kienle, A.
expertsonly
A miniaturized-plant concept is presented for the analysis of homogeneous and heterogeneous acid-catalyzed esterification of acetic acid with butanol. The plant configuration includes a micromixer followed by an isothermal microreactor. For the case of homogeneously catalyzed esterification, a long tube of 1.3 mm inner diameter acted as the reaction tube and also helped to achieve longer residence times. The results were found to be consistent with the data from literature obtained with conventional equipment on lab scale, while deviations were seen at long reaction times and high catalyst concentrations. A novel miniaturized fixed-bed reactor (mFBR) was designed for the heterogeneously catalyzed reaction, with Amberlyst-15 as a catalyst. The performance of the mFBR was satisfactory for a very long time, was reproducible, and could be used for continuous synthesis. A change in the residence time and the reactive length can be achieved by changing the total flow rate and the number of reaction plates in the stack, respectively.
2007
Article
http://edoc.mpg.de/241956
Industrial and Engineering Chemistry Research, v.46, 5271-5277 (2007)
en
oai:edoc.mpg.de:2419622006-02-1419:89
Nonlinear Behavior of Coupled Reactor-Separator Systems with Azeotropic Vapor-Liquid Equilibriums (VLEs) : Comparison of Different Control Strategies
Vetukuri, S. R. R.
Pushpavanam, S.
Zeyer, K. P.
Kienle, A.
expertsonly
In this paper we discuss the behavior of a coupled reactor - separator system. The reactor is modeled as a CSTR sustaining an elementary first order reaction and the separator as a single stage flash unit. The coupling occurs via a recycle of the bottoms stream from the downstream separator to the upstream reactor. The emphasis in this paper is on studying the behavior of the coupled system when the VLE of the mixture has an azeotrope. Consequently the bottoms stream can be reactant rich or lean. Different control strategies for the operation of the reactor and separator are discussed. The stability of the steady states is analyzed analytically for each strategy. Physical explanation for the stabilty results are presented. In general, it is found that the recycle lean stream gives rise to instability.
2006
Article
http://edoc.mpg.de/241962
Industrial and Engineering Chemistry Research, v.45, 1019-1028 (2006)
en
oai:edoc.mpg.de:2419642012-03-0219:89
Studies of Homogeneously and Heterogeneously Catalyzed Liquid Phase Reactions in Micro Systems with Application to Esterification
Kulkarni, A. A.
Zeyer, K. P.
Jacobs, T.
Kienle, A.
expertsonly
A microplant concept is introduced for the analysis of homogeneously and heterogeneously catalyzed liquid phase reactions. Esterification of acetic acid with butanol is considered as a benchmark problem. The plant configuration includes a micromixer (SIMMV-2, IMM Mainz, Germany), which mixes the reactants fed at the reaction temperature (200C, 60-800C) followed by the microreactor. For the case of homogeneously catalyzed esterification, a long tube of 1mm inner diameter acted as the reaction tube with reasonable residence time. The results from the experiments for the range of temperature and the different catalyst concentrations were consistent with the published literature. For the case of hererogeneously catalyzed esterification a micro fixed bed reactor ( FBR) was designed by stacking and connecting several reaction plates on which several micro-channels were created through micro-machining. Amberlyst-15 was used a catalyst and filled in the reactor channels (1.43m total length). The pressure drop across the length of the reactor was not very high even in the swollen condition of the catalyst particle. The reactor gave excellent conversion rates at steady state and the performance of the FBR was consistent for very long time (over 42hrs of continuous operation). A change in the residence/reaction time and the reactive length was achieved by changing the total flow rate and the number of reaction plates, respectively. The microplant is flexible in terms of desired residence time, amount of the catalyst, particle size and the flow rates. The FBR developed in this investigation offered the following advantages: (i) the system can be maintained practically isothermal, (ii) due to the very long active life of the catalyst, the reactor needs not to be disassembled frequently, (iii) the mole ratio of the reactants can be modified externally, (iv) the system is suitable for the analysis of the dynamics of this adsorption enhanced reaction. (v) The concept is simple and yet gives flexibility in extending this design for achieving a continuous small-scale production facility.
2006
Conference-Paper
http://edoc.mpg.de/241964
ACHEMA 2006 : 28th International Exhibition-Congress on Chemical Engineering, Environmental Protection and Biotechnology, 48 (2006)
en
oai:edoc.mpg.de:2460892007-03-2019:89
Nonlinear Model Reduction of a Dynamic Two-dimensional Molten Carbonate Fuel Cell Model
Mangold, M.
Sheng, M.
expertsonly
A reduced nonlinear model of a planar molten carbonate fuel cell is presented. The model is derived from a spatially distributed dynamic model of the cell by applying the Karhunen Loeve Galerkin procedure. The reduced model is of considerably lower order than the original one and requires much less computation time. The comparison between the two models shows that the reduced model can describe the dynamic of the temperature field with sufficient accuracy and has good extrapolation qualities with respect to changes in the model parameters.
Springer
2006
InBook
http://edoc.mpg.de/246089
Progress in Industrial Mathematics at ECMI 2004, 262-266 (2006)
en
oai:edoc.mpg.de:2488802006-01-1619:89
Nonlinear Behavior of Reactor-Separator Systems with Azeotropic Mixtures
Krishna, M. V.
Pushpavanam, S.
Kienle, A.
Vetukuri, S. R. R.
expertsonly
In this work, the behavior of a coupled nonlinear reactor-separator system is analyzed. The reactor is modeled as a continuous stirred tank reactor (CSTR) that sustains a first-order reaction of the form A -> B. The separator is modeled as a flash. The effluent from the reactor is fed to the separator. Here, we assume that the liquid stream from the separator is recycled back to the reactor. The primary interest is to investigate the system when the vapor-liquid equilibrium (VLE) has an azeotrope. Under these conditions, the recycle stream can be either reactant-rich or reactant-lean depending on the feed composition to the flash. The focus is on pure mass recycle, as the two units are assumed to be decoupled energetically via heat exchangers. Two different modes of operations are considered. In the first mode of operation, the fresh feed flow rate is fixed. In the second mode of operation, the effluent flow from the reactor is fixed. In practise, these different modes of operation can be achieved using a suitable control strategy. When fresh feed to the network is flow-controlled, there is a region of dynamic instability in the solution branch corresponding to the recycle of the reactant-lean stream. In addition, coexistence of states with the recycle of reactant-rich and reactant-lean streams is possible. Our analysis indicates the presence of large regions of static and dynamic instabilities when the reactant-lean stream is recycled to the reactor and the effluent from the reactor is flow-controlled. Our results imply that the region in which the separator operates is very important in determining the behavior of the coupled system. Consequently, startup of the system is critical when the VLE of the system has an azeotrope.
2006
Article
http://edoc.mpg.de/248880
Industrial Engineering and Chemistry Research, v.45, 212-222 (2006)
en
ResultSet_6NVcOwmvWgP_range_100-199