Chemical Equilibrium Model and Prediction for Coal Hydrogasification

Abstract

Abstract Researches on coal hydrogasification (CHG) which is the core component of the zero emission coal (ZEC) system are rarely reported and the characteristics of CHG have not been well understood. A chemical equilibrium model (CEM) for coal hydrogasification is proposed in this work to study the effects of different reaction conditions on the CHG characteristics. The results from the model are then validated against literature available experimental data and the model is proved reliable. After the validation, sensitivity analysis on the CHG process is done and meaningful results are obtained. Increasing the reaction pressure (p) and H2/coal mass ratio (R) or decreasing the reaction temperature (T) can enhance the hydrogasification reactions. The carbon conversion rate begins to decrease at 800 K and 1,250 K for operation pressures of 0.1 MPa and 7 MPa, respectively. Remarkable effects on the gasification characteristics are found when p is lower than 1 MPa. At 7 MPa and 1,000 K, carbon is entirely converted when R is 0.25 and the maximum CH4 mole fraction is reached. In the case that T is variable, carbon will be all converted at 7 MPa when R is about 0.5. Carbon will never be all converted at 0.1 MPa no matter how high R is. Mole fraction of CH4 will decrease with R both at the pressures of 7 MPa and 0.1 MPa.