Numerical simulation of crushed coal pressurized slagging gasification

Abstract

The Crushed Coal Pressurized Slagging Gasification (British Gas-Lurgi, BGL) renders the use of gates obsolete and changes from dry slag discharge to liquid slag discharge, significantly improving the gasification performance. This study aims to reveal the essential structural characteristics of BGL coal gasification to further improve the performance of gasification equipment. We established the thermodynamic equilibrium model, coal gasification dynamics model and Euler multiphase flow model via numerical simulation, and validated these models. The simulation results show that 1) compared with Lurgi coal gasification, the gasification equilibrium temperature increases from 795 ℃ (Lurgi gasifier) to 1 029 ℃, and the decomposition rate of water vapor increases from 32.66 % to 93.12 %. The maximum bed temperature increases from 1 110 ℃ to 1 837 ℃, much higher than the coal ash flow temperature (1 210 ℃). This improves the gasification intensity and ensures liquid slag discharge. 2) BGL coal gasification reaction is mainly completed in the lower part of the furnace, with only a small amount of water vapor participating in the shift reaction. CH4 in the crude gas mainly comes from coal pyrolysis. 3) The fluctuation of bed surge in gasifier enhances heat and mass transfer. 4) Nozzle Jet impacts and squeezes coal char particles, forming an ellipsoidal combustion raceway extending to the central area. This becomes an important functional unit of BGL gasification, realizing primary gas distribution and providing heat for gasification layer and slag pool. 5) The liquid slag in the slag pool whirls up and down, which is beneficial to reduce carbon residue in slag and ensure smooth slag discharge.

Keywords

• coal gasification
• crushed coal slag
• gasification equilibrium temperature
• combustion raceway
• bed structure