Numerical investigation on oxy-combustion characteristics of a 200 MW_e tangentially fired boiler

摘要

In recent years, oxy-fuel combustion in coal-fired plants has become one of the most promising technologies for carbon capture and storage (CCS). Compared with air-fired combustion, high concentrations of CO_2 and H_2O in the flue gas cause a remarkable change in the pulverized coal combustion and heat transfer characteristics in furnace. In this study, improved models for the gas radiative properties and chemical reaction mechanisms were incorporated into the computational fluid dynamics (CFD) code to simulate a 200 MW_e tangentially fired utility boiler, which is expected to operate at full load under both conventional air-fired and oxy-fuel combustion. Different flue gas recycle patterns: dry recycle and wet recycle, were also investigated. The results indicate that, stable combustion is achieved by a compatible burner design in both air-fired and oxy-fuel combustion. In the oxy-fuel combustion, the flue gas peak temperature and wall heat flux decrease and high CO concentration appears in the burner region, resulted from higher heat capacity of CO_2 and chemical effect of CO_2 (Liu et al., 2003, Glarborg and Bentzen, 2008). Based on the comparison of the wet recycle and dry recycle, it shows the wet recycle has more advantages than dry recycle. This study indicates a slight increase in total heat transfer, when the oxygen concentration in oxidant increases from 23% to 29%, consistent with the results of Vattenfall and Callide pilot scale oxy-combustion plant. Thus, compared with air-fired combustion, the full load of a boiler may decrease by 5-10% under oxy-fuel combustion.