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Abstract: In a recent paper a segregated stochastic model was proposed for influenza virus replication in vaccine production processes [Sidorenko, Y., Schulze-Horsel, J., Voigt, A., Reichl, U., Kienle, A., 2008. Stochastic population balance modeling of influenza virus replication in vaccine production processes. Chemical Engineering Science 63, 157–169]. The model used a simple segregated, unstructured approach for the description of the virus replication. In particular, effects arising from limited internal cellular resources and detailed cell physiology were not taken into account. The degree of infection—corresponding to the number of virus equivalents per cell—was used as the only internal coordinate. The model was successful in describing the integral dynamics of the process, however, revealed some discrepancies with respect to the “internal dynamics” of the virus replication. Therefore, in a second step, a much more detailed description of the virus replication process is considered in this paper. Again, cell physiology is described in terms of global growth and death events. Limitations of the intracellular resources are not taken into account. It is shown that this type of model does not contribute significantly to an improvement of the prediction of the internal dynamics. Hence, it is concluded that limited intracellular resources or a detailed description of the cell physiology is required for a more realistic modeling of virus replication dynamics. [Copyright &y& Elsevier]

Horizontal stirred bed reactors for polypropylene production have a typical axial powder mixing pattern which is unique for polyolefin gas-phase reactors. The polymer, although adhering to the catalyst particles, has a shorter mean residence time and a broader residence time distribution than the catalyst. Both polymer and catalyst residence time distributions, strongly depend on the temporal catalyst activity profile. The powder mixing pattern in a horizontal stirred bed reactor results from two transport effects: the continuously increasing powder net flow in the downstream direction caused by the particle growth, and the simultaneous stirring flows with equal intensity in the up- and downstream directions. Both together lead to a residence time distribution of the reacting catalyst particles between fully backmixed and plug flow. A modelling approach is proposed which describes the axial flow contributions of stirring and polymerisation separately, and which is more accurate and flexible than simple cells-in-series models used in most papers so far. For large-scale reactors, residence time distributions are predicted from experimental pulse–response curves obtained in a miniaturised mixing model without reaction. Residence time distributions equivalent to “three to five” well-mixed reactors in a series reported in the literature are experimentally accessible only with difficulties under polymerising conditions. With the modelling approach proposed in this paper, the “reacting” RTD can be calculated on the basis of the cold-flow experimental data. We compare the proposed modelling concept with simple cells-in-series models by simulating catalyst yields, particle size distributions and catalyst transitions using two model catalysts with different activity profiles. The selection of the right modelling approach has indeed a significant influence on the simulation results, especially if the throughput or the axial velocity profile is changing and the catalyst is not deactivating. [Copyright &y& Elsevier]

Abstract: In the first paper of this series, it has been demonstrated that the capital investment and operating cost can frequently be reduced substantially through seeking further internal heat integration between the reaction operation and separation operation for a reactive distillation column involving reactions with highly thermal effect. In this paper, the dynamics and operation of the resultant reactive distillation system is to be examined, with special emphasis focused on the dynamic effect of the supplementary internal heat integration. It has been found that seeking further internal heat integration can sometimes improve process dynamics and lessen difficulties in process operation. This outcome stems from the refined relationship between the reaction operation and separation operation involved and is of great significance in tightening process design for a reactive distillation column containing reactions with highly thermal effect. It should, however, be pointed out that seeking further internal heat integration might also confine severely the flexibility of the resultant reactive distillation column due to the reduction of mass transfer driving forces. When encountering a sharp increase in the product specification that is more relevant to the supplementary internal heat integration, the process might show deteriorated dynamic performance and can even converge to an undesirable steady state where the economical advantages of the supplementary internal heat integration are lost totally. Therefore, some effective measures to increase the redundancy of the resultant process design have to be taken to deal with the side-effect during process development. [Copyright &y& Elsevier]

Abstract: Process optimisation and optimal control of batch and continuous drum granulation processes are studied in this paper. The main focus of the current research has been: (i) construction of optimisation and control relevant, population balance models through the incorporation of moisture content, drum rotation rate and bed depth into the coalescence kernels; (ii) investigation of optimal operational conditions using constrained optimisation techniques; (iii) development of optimal control algorithms based on discretized population balance equations; and (iv) comprehensive simulation studies on optimal control of both batch and continuous granulation processes. The objective of steady state optimisation is to minimise the recycle rate with minimum cost for continuous processes. It has been identified that the drum rotation-rate, bed depth (material charge), and moisture content of solids are practical decision (design) parameters for system optimisation. The objective for the optimal control of batch granulation processes is to maximize the mass of product-sized particles with minimum time and binder consumption. The objective for the optimal control of the continuous process is to drive the process from one steady state to another in a minimum time with minimum binder consumption, which is also known as the state-driving problem. It has been known for some time that the binder spray-rate is the most effective control (manipulative) variable. Although other possible manipulative variables, such as feed flow-rate and additional powder flow-rate have been investigated in the complete research project, only the single input problem with the binder spray rate as the manipulative variable is addressed in the paper to demonstrate the methodology. It can be shown from simulation results that the proposed models are suitable for control and optimisation studies, and the optimisation algorithms connected with either steady state or dynamic models are successful for the determination of optimal operational conditions and dynamic trajectories with good convergence properties. [Copyright &y& Elsevier]

The epoxy-polymerization process can be better understood by investigating the underlying optimization problem involving a number of conflicting objectives and more than 20 decision parameters. A combination of minimization or maximization of objectives, such as the number average molecular weight, polydispersity index and reaction time, are considered in this paper. The first two objectives are related to the properties of a polymer, whereas the third objective is related to productivity of the polymerization process. The decision variables are addition quantities of various reactants, e.g. the amount of addition for bisphenol-A (a monomer), sodium hydroxide and epichlorohydrin at different time steps (modeled in a semi-batch operation), whereas the satisfaction of all species balance equations is treated as constraints. A multi-objective evolutionary algorithm (the elitist non-dominated sorting genetic algorithm or NSGA-II) is used to obtain a set of non-dominated solutions in a single simulation run. The results show a substantial improvement (with about 300% more productivity) over the benchmark condition (reported by performing a one-time addition of reactants in the beginning in a batch process). Importantly, this study brings out a salient aspect of using an evolutionary approach to multi-objective problem solving. The availability of multiple optimal trade-off solutions allows a process engineer to have salient information about the polymerization process. Changes in the distribution of various polymer species in the course of polymerization process as observed among various Pareto-optimal solutions are identified and explained for this purpose. Such information provide important information about optimal operating conditions corresponding to different trade-offs among objectives, which are otherwise difficult to obtain. The systematic approach of starting from the two-objective problems to capture the essential features of interesting optimal operating conditions to finally solving the three-objective problem associated with the epoxy-polymerization problem in discovering the optimal trade-off interactions should motivate further such studies on other chemical process optimization problems. Overall, this paper demonstrates how fundamental optimization principles can be used systematically and reliably to find optimum operating conditions for complex chemical process operations. [Copyright &y& Elsevier]

Computer-based simulations of a reverse-flow reactor should be carried out till the attainment of the so-called cyclic steady state. Usually this state is achieved by the method of direct dynamic simulations. In the paper of Unger et al. (Comput. Chem. Eng. 21 (1997) 5167.) special approaches, making use of various minimization algorithms based most often on Newton algorithms, are proposed. In the present paper one deals with a comparison and an appraisal of these methods, applied to the reverse-flow catalytic combustion of methane that occurs in coal-mine ventilation air. [Copyright &y& Elsevier]

The release of active principles from microencapsulated drugs has been studied and treated extensively in the literature. However, only empirical or semiempirical models have been proposed. Often, such models are not able to describe correctly the articulated behavior of the release phenomenon. This paper, based on a first principles approach, defines a fully theoretical model of the release process within the human body.The key point of this work is the penetration theory that describes the experimental evidence of release dependency from square root of time.In addition, the paper deals with the observed lead-lag time characterizing the release dynamics of active principle that diffuses towards the external solution. A detailed analysis of the transport phenomena involved, focuses the attention on the diffusive mechanism, which is strictly related to the existing affinity between active principle and polymer coating. Finally, the good agreement between experimental release data, for different active principles, and corresponding simulated curves allows the proposed model to be considered of real value for predictive design purposes. [Copyright &y& Elsevier]

Abstract: This paper presents numerical study of co- and counter-flow arrangements for catalytic plate reactors (CPR). CH4 steam reforming coupled with CH4 oxidation is simulated using detailed surface reaction mechanisms. Effect of inlet velocities to the reforming channel, oxidation channel, and material properties of the plate on the resulting plate temperature and CH4 conversions is studied. The simulation results agree very well with an industrial scale reformer unit and calculations are further carried out to evaluate the number of CPRs and stacks required to replace and industrial unit. [Copyright &y& Elsevier]

Abstract: This paper presents a new methodology for the optimal process and control design of dynamic systems under uncertainty. Robust feasibility and stability analyses are incorporated within the proposed methodology to ensure process dynamic operability and asymptotic stability. These analyses are formulated as convex mathematical problems; thus, the present approach is computationally attractive since it does not require the solution of an MINLP to evaluate dynamic feasibility and stability as it has been proposed by recent dynamic optimization-based methodologies. A norm-bounded metric based on Structured Singular Value (SSV) analysis is employed to estimate the worst-case deviation in the process constraints in the presence of critical realizations in the disturbances. The robust stability test is based on Lyapunov theory and guarantees process asymptotic stability. Accordingly, the optimal process and control design alternative obtained by the method proposed here is dynamically feasible and asymptotically stable since it accommodates the most critical realizations in the disturbances. A ternary distillation system featuring a rigorous tray-by tray process model is used to illustrate the application of the proposed method. [Copyright &y& Elsevier]

Abstract: This paper demonstrates the experimental validation and mechanistic analysis of the continuous cross-flow atomic layer deposition (ALD) reactor model developed in the first article of this series (Holmqvist et al., in press). A general nonlinear parameter estimation problem was formulated to identify the kinetic parameters involved in the developed ALD gas–surface reaction mechanism, governing ZnO film growth, from ex situ film thickness measurements. The presented methodology for comprehensive model assessment considers the statistical uncertainty of least-squares estimates and its ultimate impact on the model predicted response. Joint inference regions were determined to assess the significance of parameter estimates and results indicate that all estimates involved in the precursor half-reactions were adequately determined. The reparameterization of the Arrhenius equation effectively decreased the characteristically high correlations between Arrhenius parameters, leading to improvement in precision of individual parameter estimates. Model predictions of the spatially dependent film thickness profile with narrow confidence band were in good agreement with both calibration and validation experimental data, respectively, under a wide range of operating conditions. The subsequent extensive theoretical analysis exhibits that the experimentally validated model successfully reproduces the detailed process dynamics revealed by in situ quartz crystal microbalance and quadrupole mass spectroscopy diagnostics, and thereby provides a supplementary analysis tool. Finally, the univariate sensitivity analysis revealed the mechanistic dependence of all the measured process operating parameters on the spatially dependent film thickness profile, resolved at the level of a single pulse sequence. Hence, the presented model-based framework serves as a means to guide future research efforts in the field of ALD process optimization. [Copyright &y& Elsevier]

Abstract: Nonstandard finite differences (NSFD) schemes can improve the accuracy and reduce computational costs of traditional finite-difference schemes. However, the development of these schemes is based on analytical solutions and ad hoc rules. In this paper, we derive a NSFD scheme based on Green's function formulations for reaction–diffusion–convection systems. The formulation of the NSFD scheme is divided into three stages. In the first one, the domain of the original boundary value problem is decomposed into N subdomains. In the second stage, for each subdomain, integral formulations based on Green's functions are derived for each subdomain. Finally, the resulting integrals are approximated by means of quadrature rules. The proposed NSFD scheme based on Green's function formulation incorporates, in a natural way, the effects of boundary nodes in the discretization approximation (i.e., avoiding the use of heuristic rules), it also exhibits global approximation orders of and leads to smaller approximation errors with respect to standard FD schemes. Numerical simulations on a catalytic particle model and a benchmark tubular reactor model are used for illustrating the accuracy and performance of the proposed NSFD scheme as compared to standard finite differences schemes. [Copyright &y& Elsevier]

Abstract: This paper presents the analytical and numerical investigations of two established models for simulating liquid chromatographic processes namely the equilibrium dispersive and lumped kinetic models. The models are analyzed using Dirichlet and Robin boundary conditions. The Laplace transformation is applied to solve these models analytically for single component adsorption under linear conditions. Statistical moments of step responses are calculated and compared with the numerical predictions for both types of boundary conditions. The discontinuous Galerkin finite element method is proposed to numerically approximate the more general lumped kinetic model. The scheme achieves high order accuracy on coarse grids, resolves sharp discontinuities, and avoids numerical diffusion and dispersion. For validation, the results of the suggested method are compared with some flux-limiting finite volume schemes available in the literature. A good agreement of the numerical and analytical solutions for simplified cases verifies the robustness and accuracy of the proposed method. The method is also capable to solve chromatographic models also for non-linear and competitive adsorption equilibrium isotherms. [Copyright &y& Elsevier]

Abstract: Sorption enhanced methane reforming (SER), employing a CaO-based solid as a high temperature CO2 sorbent, is generally considered to be a promising route for H2 production. In this paper we present a dynamic pseudo-homogeneous model to describe the operation of a packed bed reactor in which the SER reaction is carried out under adiabatic conditions. This reactor can be implemented according to several process schemes, including a novel Ca/Cu looping process for hydrogen generation with inherent CO2 capture. The proposed SER model is based on the well-established principles of gas–solid contact and heat transfer in fixed-bed reactors and on the kinetic expressions published in the literature that describe the main reactions involved in the process. The resulting model describes the transient performance of the SER reaction and confirms the theoretical viability of this critical reaction stage in a large scale H2 production facility. It is demonstrated that the SER process can yield a CH4 conversion and H2 purity of up to 85% and 95%, respectively, under operating conditions of 923K, 3.5MPa, a steam/carbon ratio of 5 and a space velocity of 3.5kg/m2 s. [Copyright &y& Elsevier]

Abstract: The dynamic optimisation and optimal control of innovative cyclic chemical processes are challenging because these problems involve apart from temporal periodicity constraints often also Partial Differential Equation (PDE) models and multiple objectives. To allow a fast and efficient generation of the Pareto set, this paper presents a deterministic approach that integrates accurate scalarisation methods for multi-objective optimisation as Normal Boundary Intersection (NBI) and (Enhanced) Normalised Normal Constraint (E)NNC, with a fast direct multiple shooting approach for optimal control. The feasibility of the proposed approach is presented for a reverse flow reactor involving conflicting conversion and energy objectives. In addition, advantages of the NBI and (E)NNC methods over the classic Weighted Sum of the individual objectives have been illustrated. [Copyright &y& Elsevier]

Abstract: This paper considers a new approach of improving the efficiency of adsorption–catalytic removal of volatile organic compounds (VOCs) from waste gases based on the use of a combined structured fixed bed consisting of a coarse-grained adsorbent–catalyst and a microfiber catalyst. Numerical mathematical modeling showed that during high-temperature oxidative regeneration of the adsorbent–catalyst, the microfiber catalyst (∼0.01mm in diameter) is heated much faster than large pellets (∼2–20mm in diameter) of the adsorbent–catalyst due to the significantly higher external specific surface area (∼500–5000 times greater). This allows one to efficiently oxidize unoxidized VOCs desorbed from the surface of the adsorbent–catalyst, thus minimizing the desorption losses and significantly increasing the degree of gas purification (up to 99%). [Copyright &y& Elsevier]

Abstract: This paper presents a rigorous dynamic rate based model suitable for simulation of distillation of mixtures in packed columns. The model equations are described in detail considering structure exploitation at simulation level in order to alleviate the large number of states involved in the model description. Moreover, this kind of model may leads to differential-algebraic equations with a differentiation index higher than one. Here this issue is analyzed and a differentiation-index reduction procedure based on the incidence of model states in the Jacobian and the properties of the model dynamics is proposed. This procedure allows for a simplified index-1 model with a reduced stiffness so that dynamic simulation can be performed with off-the-shelf solvers. [Copyright &y& Elsevier]

Abstract: The scope of the paper is the analysis of the possibility of increasing conversion in different types of systems based on continuous stirred tank reactors. A numerical model of the cascade with constant direction of material flow is tested, a model of changes of direction flow and a relaxation model. The analysis is conducted by means of parametric continuation method and numerical simulation, with the designation of bifurcation diagrams and time series. An essential impact of the relaxation method on the increase of the conversion degree is indicated. [Copyright &y& Elsevier]

Abstract: In this paper, the regulation problem of convection governed dynamical processes described by linear distributed parameter models with position-independent inputs is addressed by combining the method of characteristics (MC) and the Malek-Zavarei and Jamshidi theorem. In this approach, the MC is used to transform the first order partial differential equations model of such processes into a set of time-delayed ordinary differential equations whose elements are used to generate certain matrices that satisfy linear matrix inequalities that render the proportional integral (PI) control parameters that guarantee the process stability. The performance of the proposed PI controller is tested via numerical simulations in the temperature regulation of a linear heat exchanger and compared to a tightly tuned classical PI controller. The application of the proposed controller is extended to regulate the outlet concentration in a nonlinear non-isothermal plug flow reactor. It is shown that the proposed controller is able to handle the infinite dimensional nature of the process model yielding smooth and unsaturated responses around the predetermined set-point trajectory in the face of load changes, time varying boundary conditions and set-point changes. [Copyright &y& Elsevier]

Abstract: In this paper a smoothed particle hydrodynamics (SPH) method is proposed for solving the two-fluid model of dense particle–fluid fluidizations. The particle–fluid two-phase flow fields are represented with two types of SPH particles, where the interactions between particles of the same type constitute the inner-phase stress while those between particles of different types result in the drag force. Two typical fluidization systems, namely the liquid–solid sedimentation and single-orifice gas–solid bubbling fluidization, are simulated with this approach, showing good agreement with experimental data. [Copyright &y& Elsevier]

Abstract: In this paper an extension of the proper orthogonal decomposition to a multi-parameter domain is proposed. The method produces a low-order model after three consequent steps: construction of an optimal basis functions set with respect to model error; computing the model coefficients with the Galerkin approach; calibration of the coefficients to minimize the model error. As a particular example the 2D square cylinder wake flow is used to show the potential of the extended method for different laminar flow regimes. The proposed method shows good interpolation properties of the reduced model with respect to the defined range of Reynolds numbers. [ABSTRACT FROM AUTHOR]

Abstract: Preparative chromatography is a widely used unit operation in downstream processing. A major step for its implementation is the choice of the process concept. The most popular concept is batch chromatography (BC), which is easy to implement. But also the more complex simulated moving bed chromatography (SMBC) has reached a high significance over the last years. Between these two concepts, closed loop recycling (CLRC) and steady state recycling chromatography (SSRC) promise higher performance than BC and less complexity than SMBC. This paper will analyze the advantages and disadvantages of CLRC and SSRC compared to the both BC and SMBC. These four chromatographic concepts for different separation tasks are compared by dynamic process simulation. Therefore, six isotherms for two component systems are generated and three different feed compositions are regarded. For each case, all mentioned process concepts are optimized and compared with regard to performance. The results show that CLRC and SSRC can be a good choice, especially for difficult separations. [ABSTRACT FROM AUTHOR]

Abstract: In this preliminary paper, the dynamic responses of bioethanol fermentors to sinusoidal periodic perturbations of the feed concentration have been investigated. It is shown that the steady state autonomous model of the unforced fermentor can be reduced analytically to a cubic polynomial. This analytical form enables to implement the global bifurcation analysis to divide the parameter space into regions with different number of steady state solutions; moreover, the discriminant of the cubic polynomial is used for the analysis of the nature of the number of the steady state solutions. The bifurcation analysis shows that the locus of the fold points is equivalent to the locus of the discriminant of the cubic polynomial in the (D, C so ) plane. It has been shown that the periodic operation of the autonomous fermentor gives higher average ethanol concentration than the corresponding unstable steady state. The investigation reveals that the centre of forcing has significant effect on the dynamic response of the periodically forced fermentors. Chaotic behavior is developed when the centre of forcing is relatively close to a homoclinic infinite period orbit, while quasi-periodicity is developed when the centre of forcing is in the neighborhood of a Hopf bifurcation point. The system shows interesting phase planes at certain forcing amplitudes. It has been shown that within the parameters range studied the best policy for production of bioethanol is to operate the forced fermentors in the frequency locking regions at small forcing amplitudes. [Copyright &y& Elsevier]

Abstract: In this paper a design method was formulated to deal with robustness and performance specifications for any MIMO linear controller. The controller tuning procedure was expressed as an optimization problem in which novel time-domain integrals of the weighted squared error and weighted squared control signals, with initial state zero and inputs not necessarily defined over the Lebesgue normed space , were minimized. The control robustness is achieved by constraining the minimization such that the maximum complex/real ratio of the closed-loop control system eigenvalues was lower than one. The proposed tuning method was applied in the design of linear controllers with PID structure for a CSTR with disturbance noise and a nonlinear CSTR with control signal saturations, both reported in literature. The results show that the proposed control systems surpass the performance and robustness characteristics of the controllers designed with other reported methods. [Copyright &y& Elsevier]

Abstract: Possible hindering effects of impurities on the crystal growth were shown to take place because of the adsorption of impurity species on the crystal surface. Transient features of this adsorption were observed, such that the growth of a given crystal does not depend on supersaturation only, but also on the time a given particle spent in contact with impurities present in the mother liquor. Meanwhile, few kinetic models describe the effect of impurities on the growth of crystals in solution, and published models are usually derived from data obtained, thanks to specific experiments based on the evaluation of the growth rate of single crystals. Such models are obviously questionable because, in the industrial practice, distributed properties of crystals are actually involved. Considering the “time of contamination” of particles as a new internal variable is thus made necessary. This is the reason why a specific PBE resolution algorithm is presented in this paper. The numerical scheme for the resolution of PBEs is based on the method of characteristics and shown to allow fast and accurate simulation of transient features of the crystal size distribution in the particular case when the growth or nucleation rates are assumed to exhibit unsteady-state dynamics. The algorithm is finally used to simulate the isothermal desupersaturation crystallization of citric acid in water. [Copyright &y& Elsevier]

Abstract: The simulated moving bed (SMB) is a continuous chromatography process for separation of chemical mixtures. It has been used in large-scale industrial production of cheap specialty products like sugar separation, as well as small-scale production of high value products like enantiomer separation in the pharmaceutical industry. Physical models can be employed in control of SMB processes, but it can be difficult to obtain accurate physical parameters. Empirical models do away with the need to obtain parameters, but without physical representation, they may not be suitable for control applications. In this research paper, wave propagation is linked with the empirical model to enhance the physical constraint on designing SMB. However, there is an interaction between the zonal wave velocities and process outputs; thus, control strategies based on the partial least squares (PLS) are proposed in this work. PLS decoupling of the system to achieve pairs of SISO (single input single output) in the subspace is useful because the conventional SISO can be directly applied to the control design. The use of wave propagation allows the application of the constraints in Zones II and III based on the shifting of the wave fronts. Two modes of control are proposed: cycle to cycle and within cycle. The performance of these control strategies is assessed by implementation on a virtual eight-column SMB unit for set-point tracking and disturbance rejection. [Copyright &y& Elsevier]

Abstract: In the present paper freely sedimenting n-butanol droplets in water are simulated by means of computational fluid dynamics. The finite-element and the extended finite-element methods were implemented and evaluated. The level-set function is used for capturing the interface movement. The three-dimensional nonstationary simulations included the stages of droplet acceleration, deformation, and stability in terms of shape and velocity. The influence of the grid resolution, the computational domain walls, and the droplet initial velocity was investigated and quantified. The droplet diameters that were studied spanned the region of spherical, deformed, and oscillating droplets. The simulation results were compared to experiments and empirical models in terms of droplet shape, oscillation behavior and terminal velocity, showing good agreement. The extended finite-element method was found to provide simulation results in better accordance to the experiments and empirical models than the conventional finite-element method. [Copyright &y& Elsevier]

Abstract: When several rival mathematical models are proposed for one and the same process, experimental design techniques are available to design optimal discriminatory experiments. Because these techniques are model-based, it is important that the model predictions are not too uncertain. Therefore, model discrimination may become more efficient and effective if this uncertainty is reduced first. This can be achieved by performing experiments designed to increase the accuracy of the parameter estimates and, thus, the model predictions. However, performing such an additional experiment for each rival model may undermine the overall goal of optimal experimental design, which is to minimize the experimental effort. This paper deals with the design of a so-called compromise experiment, which is an experiment that is not optimal for each of the rival models, but sufficiently informative to improve the overall accuracy of the parameters of all rival models. For this purpose, the problem is approached as a multi-objective optimization problem and the ideal point method is proposed to design the compromise experiment. This method searches for the experiment that is as close as possible to the optimal experiments of the individual rival models. The method is applied to a case study where nine rival models are competing to describe the kinetics of an enzymatic reaction, and the obtained results show that the ideal method is capable of designing a compromise experiment. [Copyright &y& Elsevier]

Abstract: A systematic approach for on-the-fly mechanism reduction is proposed in this paper. The approach consists of element flux analysis and dynamic generation of reduced mechanisms during reactive flow computation. At each time step of the computation, a reduced mechanism is generated based on local conditions and no previous information or analysis is necessary. The approach is demonstrated in a plug-flow reactor (PFR) model and a pairwise mixing stirred reactor (PMSR) model. A detailed n-pentane oxidation mechanism with 385 species and 1895 elementary reactions and a primary reference fuel (PRF) mechanism with 1034 species and 4236 reactions are used to illustrate the proposed approach. Auto-ignition delay, temperature, and species composition profile predicted by the on-the-fly reduction scheme agree with the detailed simulation and experimental results over a wide range of temperatures and equivalence ratios. [Copyright &y& Elsevier]

Abstract: The numerical solution of a hyperbolic or a convection-dominated parabolic partial differential equation is challenging due to the large local gradients that are present in the solution. A possible method to track the sharp fronts that are associated with large gradients is to adapt the grid and this can be done dynamically or statically, i.e. at discrete points of time during the simulation. In this paper, a novel approach that is based on combining the high-order WENO scheme with a static moving grid method is presented. The proposed algorithm is tested on the viscid Burgers’ equation, the linear advection equation and the population balance equation that describes particle growth in emulsion polymerization. Enhancements in the performance are observed in all case studies when compared with the conventional WENO scheme on a uniform grid making it a promising alternative when dealing with similar problems. [Copyright &y& Elsevier]

Abstract: The use of the monolith as an adsorptive reactor (MAR) is proposed as a viable and novel alternative for VOC disposal. The MAR combines adsorptive separation and catalytic combustion of the VOC in a single reactor unit and is thought to make effective utilisation of energy due to efficient heat integration. Theoretical studies on the feasibility and application of the adsorptive reactor concept for VOC oxidation is presented in this paper. Thus unlike previous work, present studies focus on an exothermic reaction system and the ability of the MAR to control thermal runaway. A two dimensional mathematical model accounting for non isothermal adsorption and reaction, mass transfer limited adsorption kinetics and non linear (Tóth) adsorption equilibria, has been developed. The process is operated cyclically in two steps: adsorption and desorption/reaction. The VOC is fed into the reactor in the adsorption step and captured to produce a pure carrier gas effluent. Concentration and thermal swing is induced in the second step by means of an air feed. The most outstanding feature of the MAR is its ability to prevent thermal runaway whilst maintaining a high VOC conversion. Simulation results indicate that the careful selection of step times for adsorption and desorption, feed temperatures and inlet velocities lead to stability and energy requirements which outperform equivalent conventional designs. The MAR is thermally more stable due to the controlled release of the reactant from the adsorbed phase into the reaction zone, and also the heat integration of endothermic desorption and exothermic reaction. [Copyright &y& Elsevier]

Abstract: This paper reviews the importance of temperature gradient induced moisture diffusion in powder beds. Redistribution of moisture by this mechanism is important for a wide variety of products, especially those which are crystalline in nature. Moisture transfer in these products can result in very high local water activity and lead to microbial spoilage and caking problems. A conceptual model was developed for heat and moisture transfer due to the application of thermal gradients across a one-dimensional powder bed. The validity of the key assumptions in the model formulation were demonstrated and a mathematical model was derived and solved numerically. The model was validated against experimental data collected using crystalline lactose powders as a working example. [Copyright &y& Elsevier]

Abstract: Butene isomers are obtained in the refinery as by-products of the steam cracking of naphtha and light gas oil. The isomers contain a large fraction of butadiene. Butadiene is separated from this fraction by extractive distillation to produce a raffinate stream. However, the raffinate stream contains traces of butadiene (up to approximately 1%). For this stream to be used for isooctane production via the dimerization of isobutene and the hydrogenation of isooctene in a catalytic distillation column, the butadiene present in this stream should be removed, as it would otherwise poison the dimerization catalyst. The butadiene present in this stream may be removed by selective hydrogenation. This paper describes a kinetic study of the liquid-phase selective hydrogenation of 1,3-butadiene present in a mixture with isobutene using a catalyst in a semi-batch reactor. Experimental results revealed that was highly selective for the hydrogenation of butadiene in the presence of isobutene. The catalyst did not show any appreciable deactivation. Hydrogenation of butadiene produced 1- and 2-butenes and -butane. A very detailed reactor model, incorporating internal diffusion inside the catalyst particles was developed to interpret the experimental results. A kinetic model for the selective hydrogenation on the catalyst was developed by using simplified versions of the Langmuir–Hinshelwood mechanism. The estimated model parameters described the experimental data accurately. The hydrogenation reaction was found to be severely limited by the diffusion rate of hydrogen in the catalyst particle. [Copyright &y& Elsevier]

Abstract: In this paper a dynamic simulator of the fluid catalytic cracking (FCC) pilot plant, operating in the Chemical Process Engineering Research Institute (CPERI, Thessaloniki, Greece), is presented. The operation of the pilot plant permits the execution of case studies for monitoring of the dynamic responses of the unit, by imposing substantial step changes in a number of the manipulated variables. The comparison between the dynamic behavior of the unit and that predicted by the simulator arise useful conclusions on both the similarities of the pilot plant to commercial units, along with the ability of the simulator to depict the main dynamic characteristics of the integrated system. The simulator predicts the feed conversion, coke yield and heat of catalytic reactions in the FCC riser on the basis of semi-empirical models developed in CPERI and simulates the regenerator according to the two-phase theory of fluidization, with a dilute phase model taking account of postcombustion reactions. The riser and regenerator temperature, the stripper and regenerator pressure drop and the composition of the regenerator flue gas are measured on line and are used for verification of the ability of the simulator to predict the dynamic transients between steady states in both open- and closed-loop unit operation. All the available process variables such as the reaction conversion, the coke yield, the carbon on regenerated catalyst and the catalyst circulation rate are used for the validation of the steady-state performance of the simulator. The comparison between the dynamic responses of the model and those of the pilot plant to step changes in the feed rate and preheat temperature reveals the ability of the simulator to accurately depict the complex pilot process dynamics in both open- and closed-loop operation. The dynamic simulator can serve as the basis for the development of a model-based control structure for the pilot plant, alongside its use as a tool for off-line process optimization studies. [Copyright &y& Elsevier]

Abstract: The aim of this study is to obtain a model that can simulate the performance of an industrial fluid catalytic cracking (FCC) unit in steady and dynamic state, and which will subsequently be used in studies of control and real time optimisation. In this paper, a dynamic model for a R2R type FCC unit is presented. The model includes the riser, the stripper/disengager, the regeneration system and the catalyst transport lines. Mass, energy and pressure balances are performed for each of these sections. Simulation results for steady state are presented and compared qualitatively to those obtained from previous FCC models. The dynamic behaviour of the system is explored through two perturbations in open loop, one on the fresh feed flow rate and one on the air flow rate to the first regenerator. The results illustrate the consistency of the model and are in agreement with what has been observed in studies available in the open literature. [Copyright &y& Elsevier]

Abstract: This paper presents a systematic numerical investigation of airflow during compression in a simplified tablet press geometry. Air entrainment during tablet compression has been cited as the cause of manufacturing defects and quality problems. The effects of tablet punch profile, speed and punch to die wall clearance on airflow in the system are investigated. Conditions under which air entrainment in the tablet formulation are likely to occur have been identified, and are found to correspond with punch concavity. For a flat profile punch, the effects of punch speed and punch to die wall clearance are shown to be of minor importance. [Copyright &y& Elsevier]

Abstract: To design cyclic separation processes by adsorption, such as pressure swing adsorption (PSA) processes, one has to simulate the start-up time in order to determine the cyclic steady state (CSS), which can be very time-consuming. A fast way to estimate the CSS reached by a PSA process is proposed by —assuming equivalency between the PSA system and a continuous countercurrent flow system (CCF). The CCF model is improved in the present paper, taking into account the gaseous phase located in a column when the system switches from a constant pressure step to another step. By performing a parametric study, the limits of the CCF model are tested. It is shown that this model can quantitatively predict the purities and recoveries obtained at CSS for kinetically controlled separation by comparison with a detailed model of PSA. It is also shown that the CCF model can also give a good approximation of the dynamic behavior of the PSA process. Finally, the simulation of dry air separation is proposed. [Copyright &y& Elsevier]

Abstract: The laser Doppler anemometer (LDA) and conductivity probes were used for measuring the local hydrodynamic performances such as gas holdup and liquid velocity in a lab-scale gas–liquid–TiO2 nanoparticles three-phase bubble column. Effects of operating parameters on the local gas holdup and liquid velocity were investigated systematically. Experimental results showed that local averaged axial liquid velocity and local averaged gas holdup increased with increasing superficial gas velocity but decreased with increasing TiO2 nanoparticles loading and the axial distance from the bottom of the bubble column. A three-dimensional computational fluid dynamic (CFD) model was developed in this paper to simulate the structure of gas–liquid–TiO2 nanoparticles three-phase flow in the bubble column. The time-averaged and time-dependent predictions were compared with experimental data for model validation. A successful prediction of instantaneous local gas holdup, gas velocity, and liquid velocity were also presented. [Copyright &y& Elsevier]

Abstract: In this paper, the dynamic behavior and control of the low pressure methanol synthesis fixed bed reactor have been investigated. For simulation purpose, a heterogeneous one-dimensional model has been developed. First, the reactor simulation is carried out under steady-state condition and the effects of several parameters such as shell temperature, feed composition (especially CO2 concentration) and recycle ratio on the methanol productivity and reactor temperature profile are investigated. Using the steady state model and a trained feedforward neural network that calculates the effectiveness factor, an optimizer which maximizes the reactor yield has been developed. Through the dynamic simulation, the system open loop response has been obtained and the process dynamic is approximated by a simple model. This model is used for the PID controller tuning and the performances of fixed and adaptive PID controllers are compared for load rejection and set point tracking. Finally the proposed optimizer is coupled with a controller for online optimization and hot spot temperature protection. [Copyright &y& Elsevier]

Abstract: Granulation is one of the fundamental operations in particulate processing and has a very ancient history and widespread use. Much fundamental particle science has occurred in the last two decades to help understand the underlying phenomena. Yet, until recently the development of granulation systems was mostly based on popular practice. The use of process systems approaches to the integrated understanding of these operations is providing improved insight into the complex nature of the processes. Improved mathematical representations, new solution techniques and the application of the models to industrial processes are yielding better designs, improved optimisation and tighter control of these systems. The parallel development of advanced instrumentation and the use of inferential approaches provide real-time access to system parameters necessary for improvements in operation. The use of advanced models to help develop real-time plant diagnostic systems provides further evidence of the utility of process system approaches to granulation processes. This paper highlights some of those aspects of granulation. [Copyright &y& Elsevier]

Abstract: The numerical solution of non-stationary convection-dominated partial differential equations (PDEs), as for example encountered in the simulation of reverse flow reactors, can be a computationally quite demanding task because of the prevailing steep concentration and temperature gradients. The computational effort can be greatly reduced with higher-order discretisation schemes for the convection terms and with an automatic, local grid adaptation. In this paper, WENO schemes (e.g. Advanced Numerical Approximations of Nonlinear Hyperbolic Equations, Lecture Notes in Mathematics, vol. 1697, Springer, Berlin, 1998, pp. 325–432) are used for the convection terms and a local grid adaptation technique is presented that uses the smoothness indicators and interpolation polynomials of the WENO schemes. It is shown that the number of grid cells required to accurately capture steep gradients can be greatly reduced with this grid adaptation technique. Finally, the capabilities of the numerical algorithm is demonstrated for the simulation of a reverse flow reactor. [Copyright &y& Elsevier]

Abstract: An experimental and theoretical study of forced unsteady-state operation of trickle-bed reactors in comparison to the steady-state operation is the subject of this paper. It is well known that changes in the control variables influence the regime and the performance of trickle-bed reactors. In this study as one example for a forced periodic operation of a trickle-bed reactor an unsteady-state technique was used in which the catalyst bed is contacted periodically with different liquid flow rates. The unsteady-state operation was considered as square-waves cycling liquid flow rate at the reactor inlet. The hydrogenation of alpha-methylstyrene to cumene: CH(CH)=CH+ HHCH(CH) over a Palladium-catalyst (0.7% Pd/-AlO) was selected as a model reaction. The experimental results of the alpha-methylstyrene hydrogenation in a laboratory-scale trickle-bed reactor showed, that the reactor performance can be significantly improved by feed liquid flow modulation. The simulation studies demonstrate that the liquid flow variation has a strong influence on the liquid hold-up oscillation and on the catalyst wetting efficiency. Consequently the time average alpha-methylstyrene conversion will be increased, because the mass transfer resistance between the phases (gas–liquid, gas–solid and liquid–solid) affect the overall reaction rate and consequently the conversion will be improved. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

The temperature at the surface of a human body is strongly related to heat generation in underlying tissue, and its perfusion by blood. The phenomena of heat generation and dissipation unfold the thermo-regulatory control of a human body. Excursions of body temperatures from “normal” have long been considered as evidence of ill health or abnormal physiological states. In this paper, a noninvasive technique is presented to determine the peripheral rates of heat generation and blood flow in a human limb from its recorded skin surface temperature. The technique involves an analysis based on calculus-of-variation, and features the well-known circadian cycle of mammalian body temperature. The method can readily be adapted to different body parts given appropriate heat transfer models. Further, the method may confirm or contribute to greater reliability of medical diagnosis of individuals for whom recorded skin surface temperatures are available. The technique is demonstrated for a set of skin surface temperature data. [Copyright &y& Elsevier]

The paper is devoted to the dynamic behavior and stability of gas–liquid stirred reactor taking into account the temperature influence on gas solubility. Since the rate of gas–liquid processes is very sensitive to concentration of gas reactant dissolved in liquid, even weak fluctuations of temperature can significantly influence on process pass. There are two cases of temperature influence on gas solubility are possible: (1) the solubility decreases with increasing temperature; (2) the solubility grows with increasing temperature. The first case is typical for majority of gases. The second case occurs more rarely but has a great practical importance. It takes place, for example, for the hydrogenation of many compounds in organic solvents (such as benzene, toluene, isopropyl alcohol and others). A model of gas–liquid process has been developed to demonstrate the stability of gas–liquid reactor. It has been shown that the gas solubility behavior has an influence on the form of heat production curve and therefore on the multiplicity of the steady states. The areas of multiplicity and limit cycles were found and the phenomenon of hysteresis in the reactor was shown. A criterion to determine whether the multiplicity is possible under the given conditions was found. By means of an analysis of a mathematical model the stability of steady states of the reactor was studied. [Copyright &y& Elsevier]

Chemical engineers are turning to multiscale modelling to extend traditional modelling approaches into new application areas and to achieve higher levels of detail and accuracy. There is, however, little advice available on the best strategy to use in constructing a multiscale model. This paper presents a starting point for the systematic analysis of multiscale models by defining several integrating frameworks for linking models at different scales. It briefly explores how the nature of the information flow between the models at the different scales is influenced by the choice of framework, and presents some restrictions on model—framework compatibility. The concepts are illustrated with reference to the modelling of a catalytic packed bed reactor. [Copyright &y& Elsevier]

The Discrete Element Method (DEM) is becoming widely used to simulate particle flows. It is a versatile and powerful tool. Its main limitation, the CPU time required, is becoming less critical with the development of computer technology. Most DEM simulations consider spherical particles in three dimension (3D) or circles in 2D. Several researchers are developing models of non-circular particles in 2D, but there are few applications of DEM to non-spherical particles in 3D granular flow. This paper proposes a technique of sphere intersection for particle description that is applied here in 2D and 3D. It then describes a known technique of sphero-cylinders in 3D and applies it to small-scale simulations of discharge of frictionless particles, modelling contact normal forces, from a hopper. Aspect ratio for these particles is shown to have a negligible effect on discharge rate. Simulations in 2D showed that the disc-shaped particles discharged 40% faster than the circular particles. Program code tests are described to check the complex model of rotational dynamics for non-spherical particles in 3D. [Copyright &y& Elsevier]

This paper studies the residence time behaviour and concentration distribution in a simplified rhomboidal DMFC anode flow bed by 3D numerical flow simulations and by experimental measurements. The rhomboidal DMFC anode flow bed and the applied volume flow are discussed with regard to data given in the literature. Simulations with CFX, based on Finite Volume Method, and MooNMD, based on Finite Element Method, show strongly similar results and the reliability of the computed residence time distributions (RTD) is proved by showing that they depend only slightly on parameters of the numerical schemes applied. The realisation of the RTD and concentration distribution measurements are described. Experimentally obtained RTD results are in good agreement with the numerical simulations. Also, the experimentally obtained concentration distribution inside the anode flow bed is very similar to the computed distribution. By analysing the RTDs and concentration distributions, the obtained results provided evidence of weaknesses of the flow bed design. [Copyright &y& Elsevier]

Despite its wide applications, fluidization is not understood enough to satisfy our technical or academic interests. Cascading simulation approaches on different scales, with small-scale approaches provide constitutional correlations to larger scale approaches, is considered a practical way toward this direction. However, by physically reproducing many macro-scale phenomena in fluid flow and fluidization on micro-scales even below the traditional continuum limit, pseudo-particle modeling (PPM, Ge and Li (Proceedings of the Fifth International Conference on Circulating Fluidized Bed, Beijing, China, Science Press, Beijing, 1996) has suggested the possibility of a more straightforward and penetrating way. In this paper, traditional approaches are reviewed first and then PPM is discussed in full length and validated further. We demonstrate that it has maintained all necessities on the molecular level for comprehensive flow description, and the reproduced phenomena, such as bubbling, clustering and radial heterogeneity, have reflected the fundamental mechanism of their macro-scale counterparts despite the vast scale difference. With this digital miniature, every detail of the flow can be traced non-intrusively until the lowest level in classic physics and experiment with flexible parameters, which provides a unique tool for theoretical study and engineering predictions. Therefore, PPM is at least a useful complement, if not substitute, to traditional approaches. [Copyright &y& Elsevier]

The influence of perturbations in the exhaust gas composition on the operation of three-way catalytic converters (3WCC) has been the subject of many research works. This paper aims to investigate the effect of such transients on the light-off temperature of a commercial 3WCC, by using a dynamic mathematical model for 3WCC simulation. This modeling approach embodies a comprehensive oxygen storage and release submodel into an existing 3WCC quasi-steady model. The dynamic model developed is validated against previously published experimental data, which imply that the presence of transients in the exhaust gas results in an improved low-temperature catalyst performance. Having validated the model, the improved light-off performance is investigated, and attributed primarily to exhaust gas stoichiometry and secondarily to the heat released in the catalyst by the oxidation reactions (self-acceleration). Finally, a parametric study is performed to assess the influence of different patterns of transient exhaust gas composition. The results obtained show that lean composition of the exhaust gas is more favorable during the light-off phase, while frequency and amplitude of the composition oscillation play only a minimal role. This investigation encourages further application of mathematical modeling in areas like lambda control strategy optimization, which were beyond the scope of earlier 3WCC models. [Copyright &y& Elsevier]

Cascade control is commonly used in the operation of chemical processes to reject disturbances that have a rapid effect on a secondary measured state, before the primary measured variable is affected. In this paper, we develop a state estimation-based model predictive control approach that has the same general philosophy of cascade control (taking advantage of secondary measurements to aid disturbance rejection), with the additional advantage of the constraint handling capability of model predictive control (MPC). State estimation is achieved by using a Kalman filter and appending modeled disturbances as augmented states to the original system model. The example application is an open-loop unstable jacketed exothermic chemical reactor, where the jacket temperature is used as a secondary measurement in order to infer disturbances in jacket feed temperature and/or reactor feed flow rate. The MPC-based cascade strategy yields significantly better performance than classical cascade control when operating close to constraints on the jacket flow rate. [Copyright &y& Elsevier]