Oxy-combustion characteristics as a function of oxygen concentration and biomass co-firing ratio in a 0.1 MWth circulating fluidized bed combustion test-rig

摘要

Oxy-combustion with a circulating fluidized bed (Oxy-CFBC) can facilitate the separation of high CO_2 concentration and reduce emissions by biomass co-firing. This study investigated Oxy-CFBC characteristics such as temperature, solid hold-up, flue gas concentrations including CO_2, pollutant emissions (SO_2, NO, and CO), combustion efficiency and ash properties (slagging, fouling index) with increasing input oxygen levels (21-29 vol%), and biomass co-firing ratios (50, 70, and 100 wt% with domestic wood pellet). The possibility of bio-energy carbon capture and storage for negative CO_2 emission was also evaluated using a 0.1 MWth, Oxy-CFBC test-rig. The results show that combustion stably achieved with at least 90 vol% CO_2 in the flue gas. Compared to air-firing, oxy-firing (with 24 vol% oxygen) reduced pollutant emissions to 29.4% NO, 31.9% SO_2 and 18.5% CO. Increasing the biomass co-firing from 50 to 100 wt% decreased the NO, SO_2 and CO content from 19.2 mg/MJ to 16.1 mg/MJ, 92.8 mg/MJ to 25.0 mg/ MJ, and 7.5 mg/MJ to 5.5 mg/MJ, respectively. In contrast to blends of sub-bituminous coal and lignite, negative CO_2 emission (approximately -647 g/kW_(th)) was predicted for oxy-combustion only biomass.