Computational-Fluid-Dynamics-Based Evaluation and Optimization of an Entrained-Flow Gasifier Potential for Coal Hydrogasification

Abstract

To evaluate and optimize a developed two-stage entrained flow bed gasifier when it is used for the coal hydrogasification (CHG) process, a series of comprehensive three-dimensional numerical simulations designed with the orthogonal method are carried out. The effects of different operating conditions, including the reaction pressure p, H2/coal mass ratio Rh/c, and O2/H2 mass ratio Ro/h on the fields and the evolution histories of the gasification parameters as well as the carbon conversion rate (CCR), the CH4 mole fraction (MMF), and the cold gas efficiency (CGE) are analyzed, and meaningful conclusions are obtained. The hydrogasifier proposed in this work performs well. Counter flow can be detected in the gasifier and is beneficial for char conversion. The gas temperature and MMF increase with the height of the gasifier, while the hydrogen mole fraction (HMF) decreases. The water mole fraction (WMF) increases with the height of the gasifier if the gasification temperature is high; otherwise, it will decreases slightly. The distribution of CH4 in the top zone of the reductor tends to be homogeneous with the increase of Ro/h. Ranked in descending order, the effect degrees of the operating conditions on CCR, MMF, and CGE are Ro/h > p > Rh/c, p > Rh/c > Ro/h, and Rh/c > Ro/h = p, respectively. The optimum combinations of the operating conditions for CCR, MMF, and CGE are p = 7 MPa, Rh/c = 0.7, and Ro/h = 1.5; p = 7 MPa, Rh/c = 0.3, and Ro/h = 1.5; and p = 3 MPa (p = 5 MPa), Rh/c = 0.7, and Ro/h = 1.25, respectively. After comprehensive analyses, a synthetically optimal combination of the operating condition is proposed. With this condition, CCR can reach 96.78%, MMF can reach 17.42%, and CGE can reach 76.4%.