Fly Ash Transformation and Fouling Tendency during Co-firing Biomass with Coal

Abstract

The co-firing of coal with biomass is a promising method for reducing net CO2 emissions from existing coalfired power plants. This present study examined the effect of the co-firing of coal with biomass on the produced fly ash and the fouling tendency under condition representative of reheater region of pulverized-coal (PC) boiler. The fouling tests were conducted in a drop-tube furnace by inserting a water-air-cooled deposition probe to the point where the inner furnace temperature was 800-900 °C and probe’s metal temperature was kept at 500 °C. Bituminous coal was mixed with up to 50% (energy basis) of three types of biomass, namely; Palm Kernel Shell (PKS), Japanese cedar (without bark) and bark of cedar respectively. Fouling tendency was evaluated by determining the ash deposition ratio during co-firing tests. The properties of fly ashes and ash deposits for each sample were analyzed in detail by XRF and CCSEM analysis. Compared to coal firing, PKS or bark co-firing significantly increases the fouling tendency, whereas cedar co-firing does not affect the fouling tendency. The increase of minerals with low melting point, particularly Ca-Fe-Al-Si and K/Na-Al-Si, in fly ash accelerated the fouling tendency during co-firing.