A three-dimensional CFD (computational fluid dynamics) steady-state model was established to simulate biomass gasification in a circulating fluidized-bed (CFB) reactor. The standard k−ε turbulence model was coupled with the kinetic theory of granular flow to simulate the hydrodynamics in the gasifier. The kinetics of homogeneous and heterogeneous reactions were studied and integrated with the equations of continuity, motion, and energy to describe the distributions of velocity, temperature, and concentration. The simulation results were compared to experimental data. The impacts of turbulence models, radiation model, water−gas shift (WGS) reaction, and equivalence ratio (ER) were investigated to present a reliable understanding of biomass gasification in a CFB reactor.

An industrial Ethanol Amine (EA) production plant was simulated and optimized. Due to lack of accurate reaction rate information, the first step involved obtaining reliable kinetic data from the SRI (Stanford Research Institute) industrial database and calculation using error minimization method. In the next step, by implementing the obtained reaction kinetics the whole plant was simulated using Hysys software. Simulation results were compared with the SRI data and showed that there is acceptable agreement between simulation and the measured industrial data. In the next step of study by applying the gradient search (GS) optimization technique the plant was optimized using: feeding ammonia to ethylene oxide (EO) molar ratio, water flow rate in the feed stream, and reactor temperature as optimization variables. Employing process profit as objective function the optimal operating conditions were found to be: ammonia to EO ratio of 5 (mol/mol), water flow rate of 52.59 kg mol/hr and reactor temperature of 85 o C.

A three-dimensional unsteady-state CFD (computational fluid dynamics) model is built to simulate biomass gasification in a circulating fluidized bed. The RNG (renormalization group) k-epsilon turbulence model is coupled with the enhanced wall treatment to describe the hydrodynamic regime of the gas-particle system. The conservation of momentum, mass, and energy equations are integrated with reaction kinetics to simulate chemical reactions in the gasifier. The impact of product distribution coefficient, θ, for char combustion on the CFD biomass gasification model is examined in nine cases. According to the simulation results, the coefficient of θ has a minor effect on the predictions of outlet gas compositions. However, it is found that the value of θ can influence the profile of gasifier temperature, and the peak temperature regions from the cases assigning 0.50 to the coefficient appear faster than those from the models using higher values of θ.

Two modeling approaches, the scaling-law and CFD (Computational Fluid Dynamics) approaches, are presented in this paper. To save on experimental cost of the pilot plant, the scaling-law approach as a low-computational-cost method was adopted and a small scale column operating under ambient temperature and pressure was built. A series of laboratory tests and computer simulations were carried out to evaluate the hydrodynamic characteristics of a pilot fluidized-bed biomass gasifier. In the small scale column solids were fluidized. The pressure and other hydrodynamic properties were monitored for the validation of the scaling-law application. In addition to the scaling-law modeling method, the CFD approach was presented to simulate the gas-particle system in the small column. 2D CFD models were developed to simulate the hydrodynamic regime. The simulation results were validated with the experimental data from the small column. It was proved that the CFD model was able to accurately predict the hydrodynamics of the small column. The outcomes of this research present both the scaling law with the lower computational cost and the CFD modeling as a more robust method to suit various needs for the design of fluidized-bed gasifiers.

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