Chang-Bock Chung

Dynamic modeling and simulation of a fluidized catalytic cracking process. Part I: Process modeling

The purpose of this study is to develop a detailed dynamic model of a typical FCC unit that consists of the reactor, regenerator, and catalyst transfer lines. A distributed parameter model is presented for the reactor riser to predict the distributions of the catalyst and gas-phase velocities, the molar concentrations of 4-lump species, and the temperatures. The regenerator is also modeled in such detail that the two-regime, two-phase behavior of typical fluidized beds can be accounted for. An efficient model solver was constructed on the basis of a modular approach in which the model equations are grouped into 12 modules each corresponding to a specific part of the unit and type of equations. The dynamic model is implemented in Part II of this paper for extensive simulation study on FCC processes.

Dynamic modeling and simulation of a fluidized catalytic cracking process. Part II: Property estimation and simulation

Abstract A dynamic simulator was developed which implements the detailed dynamic model for an FCC process and the model solver presented in Part I of this paper. The simulator incorporates the correlation equations developed in this study for the thermodynamic properties and transport parameters contained in our model. First, the simulator was validated by comparing the overall steady-state behavior of the system with those in the literature. Then, base case steady-state profiles were obtained for major process variables in the reactor riser and regenerator of an industrial scale FCC unit. Next, the issue of multiple steady states in FCC operations was addressed and confirmed by investigating the sensitivity of our model to initial conditions. Finally, the dynamic responses to step changes in three major process inputs were presented and discussed with an emphasis on the interaction between the reactor and regenerator dynamics.

Modeling of a fluidized catalytic cracking process

Abstract The purpose of this study is to develop a detailed dynamic model of a typical fluidized cracking (FCC) unit that consists of the reactor, regenerator, catalyst transport lines, and several auxialiary units (pre-heater, catalyst cooler, and blowers). Hydrodynamic descriptions for the crucial parts of the unit are incorporated into the model. Special attention has been paid to the reactor riser to predict the velocity distributions of the catalyst and gas phases, the molar concentrations of 10-lump species, and the temperature profile by utilizing momentum, mass, and energy balances. The regenerator is modeled in such detial that the two-regime (dense bed and freeboard), two-phase (emulsion and bubble) behavior of typical fluidized beds can be described. The models for cylcones, valves, and several auxiliary units of the FCC unit are also applied to investigate their dynamic effects on the overall systems. The resulting model equations are grouped into 14 molecules each of which corresponds to a specific part of the unit and type of equations, and then an efficient iterative scheme is employed for convergence of all the modules. The model solver is constructed on the basis of a modular approach and then implemented by a Fortran code. Finally, to validate the developed simulator, the steady-state simulation results are compared with those in the literature and the dynamic responses of the process are predicted and analyzed.

Optimal cure steps for product quality in a tire curing process

Numerical algorithms and computer programs have been developed to determine optimal cure steps in a tire curing process. A dynamic constrained optimization problem was formulated with the following ingredients: (1) an objective function that measures product quality in terms of final state of cure and temperature history at selected points in a tire; (2) constraints that consist of a process model and temperature limits imposed on cure media; (3) B-splines representation of a time-varying profile of cure media temperature. The optimization problem was solved using the complex algorithm along with a finite element model solver. Numerical simulations were carried out to demonstrate the procedure of determining optimal cure steps for a truck/bus radial tire.

Eco-friendly synthesis of zeolite A from synthesis cakes prepared by removing the liquid phase of aged synthesis mixtures

Zeolite A can be synthesized through hydrothermal reaction of a synthesis cake prepared by removing the liquid phase from a synthesis mixture. The volume and weight of the synthesis cake prepared using a filter press were about one-eighth and one-fourth those of the mixture, respectively. This implies that the reactor volume and energy input required for the hydrothermal reaction can be reduced by the same respective factors, allowing the eco-friendly synthesis of zeolites.

Sensitivity behavior analysis in distributed parameter estimation

This paper is concerned with sensitivity analysis for the distributed parameter estimation problem arising in the modeling process for fluid flow in underground porous media. An efficient algorithm was constructed using variational calculus techniques for the evaluation of sensitivity gradient curves which describe variations of system outputs resulting from variations of a spatially-varying parameter in nonlinear partial differential equations. For a test problem of estimating transmissivity of a one-dimensional ideal gas reservoir, sensitivity behavior was analyzed under various reservoir conditions, and the results were applied to devising a parameter discretization scheme which will yield improved parameter estimates.

Effect of gas diffusion layer compression on the polarization curves of a polymer electrolyte membrane fuel cell: Analysis using a polarization curve-fitting model

The effect of gas diffusion layer (GDL) compression on the polarization curves of a polymer electrolyte membrane fuel cell was analyzed using a polarization curve-fitting model. The polarization curves measured at four different GDL compression ratios were fitted with the model and were decomposed into an open circuit voltage and three over-voltages resulting from activation, ohmic, and mass-transport losses, respectively. The model fitting was excellent enough to use the model in the subsequent analysis of the GDL compression effect. The relationship between the over-voltages and the compression ratio was investigated by analyzing the estimated model parameters, and an optimal compression ratio was determined for the fuel cell. The proposed analysis method based on the polarization curve-fitting model can be applied to identifying quantitative differences of polarization curves under various operating conditions and designs for fuel cells.

Fine control of particle size by seeding and ageing under agitation in the synthesis of analcime zeolite

The size of analcime particles produced through hydrothermal reactions of alkaline synthesis mixtures was finely controlled by seeding and ageing under agitation. Adding acid-treated analcime seeds to the synthesis mixture followed by ageing in an agitated vessel facilitated further nucleation, which resulted in the formation of fine analcime particles with an extremely narrow size distribution. The size of analcime particles could be controlled in the range of 0.5-5.0 µm with a standard deviation of less than 0.1 µm by varying the amount and type of the acid-treated seeds, the ageing time, and the agitation speed.

Monte Carlo Simulations of Colloidal Particle Coagulation and Breakup under Turbulent Shear

Both a Monte Carlo model and an algorithm were presented to simulate the particle coagulation and breakup phenomena taking place in a colloidal solution under turbulent fluid shear. The model is represented by the probability density functions that describe the stochastic coagulation and breakup phenomena taking place among numerous particles. From a dimensional analysis of the model two dimensionless groups,Kc andKb, were derived that represent the relative intensity of the coagulation and breakup phenomena. In order to overcome the memory problem in saving the sizes of a large number of particles, the model was converted to a form suitable for carrying out a sectional mass balance. Detailed simulation steps were presented and applied to acrylonitrile-butadiene-styrene (ABS) latex coagulation. Numerical simulations revealed that the steady state particle size distribution does not depend on the initial distributions but on theKc/Kb ratio. Setting the operation variables to increase the ratio was found to shift the particle size distribution toward larger particles.

Estimation of a state-dependent model parameter

A numerical algorithm was developed which estimates a state-dependent model parameter on the basis of transient state observation data. The algorithm was presented for the problem of estimating the temperature dependence of thermal diffusivity in a one-dimensional heat equation. The estimation problem was converted into a finite dimensional optimization problem by the least-squares formulation and B-splines representation of the parameter. Numerical experiments were performed using simulated observation data as well as the actual observation data obtained in a heat conduction experiment on rubber compound layers. The performance of the algorithm was discussed in relation to the effect of the parameter representation scheme, the quality and quantity of the data.