Emission characteristics of co-combustion of a low calorie and high-sulfur-lignite coal and woodchips in a circulating fluidized bed combustor: Part 2. Effect of secondary air and its location

In this study, co-combustion of woodchips and Bursa-Orhaneli lignite was carried out in a circulating fluidized bed combustor, 6 m long and 108 mm inside diameter. Co-combustion of lignite and woodchips was performed in order to investigate the effect of secondary air ratio (SAR) on the flue gas emissions. The woodchips content of the fuel mixture was 30% and 50% by wt. Secondary air (SA) was supplied to the combustor from five different locations along the combustor and at several SARs. During the combustion experiments, CO2, CO, O-2, NO, and SO2 emissions in the flue gas were continuously measured and recorded by ABB-AO 2000 flue gas analyzer. Increasing SAR lowered the recirculation rate which was followed by an increase in temperature of the dense phase and a decrease in the temperature of the dilute phase in the combustor. CO emissions were increased for the co-combustion of 30% by wt. woodchips and lignite, and for SAR greater than 15%. Increasing SAR caused cyclone outlet temperature to decrease and this indirectly increased the CO emissions. NO emission decreased with increasing SAR. It was observed that the location of SA given into the combustor had a distinctive effect on NO emission especially for SA higher than 15% for the co-combustion of 30% by wt. woodchips with lignite coal. NO emissions increased with the increase in woodchips share in fuel mixture. While SO2 emissions increased with SAR in all cases for the co-combustion of 30% by wt. woodchips, they did not change too much with SAR up to 20% for the co-combustion of 50% by wt. woodchips with coal. (C) 2014 Elsevier Ltd. All rights reserved.