Water–gas shift modeling in coal gasification in an entrained-flow gasifier – Part 2: Gasification application

Abstract

Water–gas-shift (WGS) reaction is one of the major reactions in the industrial gasification process. Using an adequate WGS reaction rate is vital to predicting correctly syngas composition in a gasification process. In Part 1, three different WGS reaction rates from Jones, Wade, Sato were modified to match the experimental data of raw syngas undergoing water quench process. It is not clear if these calibrated WGS reaction rates are adequate in a gasification process. Hence, the objective of this study in Part 2 is to apply both the three original published WGS rates and the calibrated rates derived in Part 1 to simulate experiments performed in the Japanese CRIEPI research gasifier. The CFD model incorporates 3-D Navier–Stokes equations and nine species transport equations with seven global gasification reactions (three heterogeneous and four homogeneous,) and a two-step thermal cracking model for volatiles. The Chemical Percolation Devolatilization (CPD) model is used for the devolatilization process. Similar to the result in Part 1 for water quench process, the result in this study further shows that the three originally published rates cannot be directly applied to the simulation of coal gasification process, due to different temperature and pressure range. Even the modified rates obtained from a water quench process in Part 1 also appear faster in the gasification process. The pre-exponential rate constant value (A) of each reaction rate is therefore further slowed down, while the activation energy is kept the same as the original value to match the experimental data. The results show that all three WGS reaction rates can be modified to match the experimental data reasonably well. The exit temperature can be matched within 2% (20K). The mole fractions of CO and H2O can be matched fairly well within 4 percentage points (or 10%); however, the simulated H2 mole fractions are always 7–9 percentage points higher than the experimental data. It needs to be emphasized that the calibrated WGS reaction rates in this study can only be applied in the range of water quench and gasification operating conditions for which they have been validated.