Exergy Analysis of a Biomass Co-Firing Based Pulverized Coal Power Generation System

Results are reported of an exergy analysis of a biomass co-firing-based power generation system. A simulation is performed for a typical pulverized coal-fired steam cycle system by considering four biomass fuels (chicken litter, refuse derived fuel, rice husk, and sawdust) and two coals (bituminous coal and lignite) to investigate the effect of biomass co-firing on the system performance. Inlet and outlet exergy flows, exergy losses, and exergy efficiencies of the boiler and the plant are determined for various fuel combinations and the two cases considered at different co-firing conditions. The results show that the exergy efficiencies of both the boiler and the overall plant decrease with increasing biomass content in the fuel blend. The greatest decrease in exergy efficiency occurs for sawdust blends, while exergy efficiency decreases the least for chicken litter blends at all co-firing ratios and for both cases considered. For case 1 (fixed fuel flow rate), the plant exergy efficiency decreases from 33.82% to 32.94% and 33.39%, respectively, for the blends of bituminous coal/sawdust and bituminous coal/chicken litter, and from 32.22% to 31.54% and 32.03%, respectively, for the blends of lignite/sawdust and lignite/chicken litter when co-firing ratio increases from 0% to 30%. For case 2 (fixed heat input to steam cycle), the plant exergy efficiency declines to 32.50%, 33.05%, 31.45%, and 31.97%, respectively, for the blends of bituminous coal/sawdust, bituminous coal/chicken litter, lignite/sawdust, and lignite/chicken litter when coal flow decreases to 0.7 kg/sec.