A sequential modular simulation (SMS) approach was used to simulate hydrodynamics and detailed kinetics of a fluidized-bed biomass gasifier in Aspen Plus. The kinetics of tar cracking reactions was taken into account in the simulation. The effects of operating conditions including temperature, equivalence ratio (ER), and steam-to-biomass ratio (SBR) on the composition and the lower heating value (LHV) of the effluent gas were studied and compared with experimental data. The model predictions well agreed with the experimental data. The increase of the bed temperature significantly decreased the tar content and increased the hydrogen content of the product gas. At ER = 0.3, the increase of the temperature from 973 K to 1123 K resulted in the increase of H 2 molar concentration in the product gas from 7.6% to 11.3% and CO molar concentration from 13.1% to 17.0%. At a temperature of 1073 K, the optimum ER value was 0.3 and the increase in ER from 0.2 to up to 0.3 increased the amount of fuel gases but further increases in ER shifted the system kinetics toward the combustion regime. At 1073 K and ER = 0.3, with an increase in SBR from 0 to 1.0, H 2 and CO 2 concentrations increased from 9.3% and 13.3% to 10.8% and 14.7%, respectively, and CO concentration decreased from 15.8% to 12.9%. The analysis showed the SMS model with four stages gives the most satisfactory predictions, via comparison with the experimental data.

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A spectral radiation-transport model was integrated with a three dimensional computational fluid dynamics model to simulate the hydrodynamics and light transfer in open raceway ponds (ORPs). The predicted threedimensional velocity and light intensity agreed well with measured values collected on a lab-scale ORP. However, there was a slight difference in the predicted velocity profiles using two different types of boundaries for the paddlewheel, i.e., the moving zone boundary and inlet velocity boundary, with R 2 values between the predicted and measured velocities of 0.

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A sequential modular hydrodynamic model integrated with detailed reaction kinetics (SMHM-RK) was developed and validated to predict tar and syngas components produced by the steam gasification of biomass in a fluidized bed gasifier. The simulations showed that the prediction accuracy is sensitive to both models for hydrodynamics and reaction kinetics. The simulations showed that the tar composition predicted by the SMHM-RK was more close to the measured values than those predicted by the well-mixed hydrodynamic model integrated with the same reaction kinetics (WMHM-RK). The predictions showed that the total tar decreased, but the polycyclic aromatic tar compounds increased with the increase in gasification temperature. There was an optimum steam-to-biomass ratio (SBR) for minimizing tar formation. The simulations found that the contents of total tar and heavy tar compounds decreased by increasing the SBR from 0.3 to 0.9, and then increased by further increasing the SBR. The injection of a small amount of oxygen in steam gasification cannot reduce tar formation. The injection of oxygen in steam gasification changed the reaction pathways of naphthalene to produce more naphthalene in the syngas. The de-volatilization rate affects pyrolytic volatile compositions and subsequent tar formation. Therefore, biomass devolatilization and homogeneous gas reactions should be solved simultaneously to accurately predict the syngas and tar composition.