| 1. |
- Galbe, Mats, et al.
(författare)
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Simulation of ethanol production processes based on enzymatic hydrolysis of woody biomass
- 1994
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Ingår i: Computers & Chemical Engineering. - : Elsevier BV. - 1873-4375 .- 0098-1354. ; 18:Suppl. 1, s. 687-691
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Tidskriftsartikel (refereegranskat)abstract
- The process simulator ASPEN PLUS was used for simulation of an ethanol production process based on enzymatic hydrolysis of lignocellulosic materials. Various process configurations were studied to increase the overall yield of ethanol and to reduce the energy consumption in the process. An increased utilization of the pentosan fraction was achieved by a complex recycling of streams in the process. This increased the total overall yield from 56% to 70%. Internal recycling of an ethamol containing stream increased the ethanol concentration in the distillation feed from 2.6 to 7.1 wt% which decreased the energy consumption in the distillation from 8 to 2 MW. The recycling will however result in increased concentrations of byproducts and inhibitors which requires future investigation of how these new conditions will affect the performance in the hydrolysis and fermentation steps.
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| 2. |
- Karlsson, Hans, et al.
(författare)
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A Simple Approximation of the Error Function
- 1980
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Ingår i: Computers & Chemical Engineering. - : Elsevier BV. - 1873-4375 .- 0098-1354. ; 4:1, s. 67-68
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Tidskriftsartikel (refereegranskat)
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| 3. |
- Liu, Yunda, et al.
(författare)
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An activity-coefficient model for electrolyte systems
- 1989
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Ingår i: Computers & Chemical Engineering. - : Elsevier BV. - 0098-1354. ; 13:4-5, s. 405-410
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Tidskriftsartikel (refereegranskat)abstract
- The activity-coefficient model proposed by Liu and Prausnitz is extended in this study to represent the non-idealities of multi-component electrolyte systems. Two modifications have been made. Based on binary information only, the model has been applied to the prediction of mean ionic activity coefficients of aqueous systems with two electrolytes. The predicted values agree well with experimental data.
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| 4. |
- Björk, Kaj-Mikael, et al.
(författare)
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Some convexifications in global optimization of problems containing signomial terms
- 2003
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Ingår i: Computers and Chemical Engineering. - : Elsevier. - 0098-1354 .- 1873-4375. ; 27:5, s. 669-679
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Tidskriftsartikel (refereegranskat)abstract
- It is often possible to use different convexification techniques with different transformations in global optimization. In 'Optimization Eng. (submitted for publication)', a new global optimization technique based on convexifying signomial terms is presented. The technique is based on the solution of a sequence of convexified approximate subproblems. The choice of transformation functions is clearly essential. It is not enough to use convexifications that will result in convex and underestimating problems, if an effective optimization approach is wanted. The transformations should be such that they make the resulting problems convex but at the same time do not change the problem more than necessary. It will be shown in this article that for certain problems the choice of transformations has a clear influence on the efficiency of the proposed optimization approach. Using other transformations than what is proposed in 'Optimization Eng. (submitted for publication)' will, in some examples, give solution times that are shorter by an order of magnitude. The concept of power convex functions (Generalized Concavity Optimization Econ. (1981) 153) will be used as a measure of the quality of the transformations. In this paper, the new transformation functions are also shown to be very successful in a heat exchanger network synthesis application. © 2002 Elsevier Science Ltd. All rights reserved.
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| 5. |
- Gruhn, Günter, et al.
(författare)
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Development of an object-oriented simulation system for complex solids processes
- 1997
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Ingår i: Computers and Chemical Engineering. - 0098-1354 .- 1873-4375. ; 21, s. S187-S192
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Tidskriftsartikel (refereegranskat)abstract
- This contribution focuses on the development of SolidSim, an object-oriented, sequential-modular simulator adopted to the special requirements of steady-state solids processes. The conceptual design of the program system and implementational issues concerning process streams and unit operation models are outlined. Results from first test runs for different solids processes are presented.
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| 6. |
- Hanke, Michael, et al.
(författare)
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Simulated annealing for the optimization of batch distillation processes
- 2000
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Ingår i: Computers and Chemical Engineering. - 0098-1354 .- 1873-4375. ; 24:1, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- Batch distillation processes are widely used in the chemical industry. In this work, we consider the optimization of such processes by simulated annealing. Although this method is stochastically in nature, it has two well-known advantages: it can be readily connected to highly sophisticated simulation codes and it converges towards a global optimum. According to the characteristics of batch distillation operation we propose to use a two-step computation approach. A feasible strategy (admissible control) will be searched for in the first step and it will be optimized in the second step. The approach has been applied to a model of a pilot batch distillation plant. These results show the potential of the method for developing optimal operation strategies for batch chemical processes;
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| 7. |
- Liu, Yi, et al.
(författare)
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On the use of reduced order models in bifurcation analysis of distributed parameter systems
- 2004
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Ingår i: Computers and Chemical Engineering. - 0098-1354 .- 1873-4375. ; 28:1-2, s. 161-169
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Tidskriftsartikel (refereegranskat)abstract
- Bifurcation theory provides a powerful tool for analyzing the nonlinear dynamic behavior of process systems. However, although the theory in principle applies to lumped as well as distributed parameter processes, it is in practice necessary to reduce the order of distributed (partial differential equations, PDE) models prior to application of the theory. As shown in this paper, simply applying some ad hoc discretization method such as finite differences or finite elements, can result in spurious bifurcations and erroneous predictions of stability. To enable detection of such anomalities, and to aid in the selection of a proper model order, we propose a method for estimating the error introduced by the model reduction. Apart from simply providing a label of confidence in the results of the bifurcation analysis, the estimated error can be used to improve the quality of the reduced order model. For this purpose we propose a method based on dynamically moving the discretization mesh such as to minimize the discretization error. The proposed method is based on principles from feedback control, and is both very simple and highly robust compared with existing so-called moving mesh methods. As an application we consider bifurcation analysis of a heat-integrated fixed-bed reactor.
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| 8. |
- Schmidt, H., et al.
(författare)
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Selecting control configurations for performance with independent design
- 2003
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Ingår i: Computers and Chemical Engineering. - 0098-1354 .- 1873-4375. ; 27:1, s. 101-109
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Tidskriftsartikel (refereegranskat)abstract
- An important task in the design of decentralized control systems for multivariable plants is the choice of the structure of interconnections between manipulated variables and controlled outputs, i.e. the control configuration. Most tools available for this task, such as the RGA, address mainly the stability properties of the overall system. In this paper we focus on performance, and consider in particular the problem of selecting control structures that enable a desired performance to be achieved through independent tuning of the subsystems. We show that, for this task, the common assumption of perfect control within the bandwidths of the subsystems is a poor one. Based on this, a new measure of interactions, the decentralized relative gain (dRG), is proposed. Finally, it is stressed that the effect of interactions on the magnitude as well as on the phase lag of the subsystems should be considered when selecting control configurations for performance.
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| 9. |
- Toebermann, J.-Christian, et al.
(författare)
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Block-oriented process simulation of solids processes
- 2000
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Ingår i: Computers and Chemical Engineering. - 0098-1354 .- 1873-4375. ; 23:11-12, s. 1773-1782
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Tidskriftsartikel (refereegranskat)abstract
- A block-oriented process simulation system has been developed for solids processing applications. The specific requirements which have to be fulfilled for the description of processes with particulate solids are outlined and their implications for design and implementation of a simulator are discussed. The prototype simulator SolidSim is presented and its features are demonstrated by soil-washing and gravel processing applications.
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| 10. |
- Billeter, J., et al.
(författare)
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On decoupling rate processes in chemical reaction systems – Methods and applications
- 2018
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Ingår i: Computers and Chemical Engineering. - : Elsevier BV. - 0098-1354 .- 1873-4375. ; 114, s. 296-305
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Tidskriftsartikel (refereegranskat)abstract
- Models of chemical reaction systems can be complex as they need to include information regarding the reactions and the mass and heat transfers. The commonly used state variables, namely, concentrations and temperatures, express the interplay between many phenomena. As a consequence, each state variable is affected by several rate processes. On the other hand, it is well known that it is possible to partition the state space into a reaction invariant subspace and its orthogonal complement using a linear transformation involving the reaction stoichiometry. This paper uses a more sophisticated linear transformation to partition the state space into various subspaces, each one linked to a single rate process such as a particular reaction, mass transfer or heat transfer. The implications of this partitioning are discussed with respect to several applications related to data reconciliation, state and rate estimation, modeling, identification, control and optimization of reaction systems.
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