Experimental and Numerical Investigations on Heat Transfer Characteristics of a 35MW Oxy-fuel Combustion Boiler

Oxy-fuel combustion has different combustion and heat transfer characteristics from those of air-combustion, due to the high concentration of CO2 and H2O in the flue gas. This study investigated the heat transfer characteristics in a 35 MW oxy-combustion large pilot plant. The experimental and numerical investigations are carried out with a sub-bituminous coal. The gas temperature, exhaust emission, and heat transfer are measured in conventional air-combustion and oxy-fuel conditions with wet and dry flue gas recycle. Detailed numerical studies of combustion and heat transfer are performed with a modified radiative property model and global reaction mechanism. The results are in good agreement with the experimental data. The effects of char and ash on radiative heat transfer are investigated. The experimental and numerical results show that although the peak temperature decreases, the heat transfer in membrane-wall and superheater in oxy-fuel combustion is slightly greater than that in air-combustion. The absorption coefficient ratios of particle to gas are approximately 2.5 and 2.4 in air-combustion and oxy-fuel combustion. The particle radiation dominates the radiative heat transfer in the pulverized coal combustion, which has a significant influence on the temperature level and distribution.