Assessment of Fuel Feed Ratio and Emissions for Coal and Biomass Co-Firing in the Circulating Fluidized Bed Boiler

Global warming and reduced reliance on fossil fuels for electricity generation have prompted many nations to pursue sustainable energy alternatives. Singapore's future carbon tax pricing will subsequently increase in coming years; from 2019 to 2023, the initial carbon pricing scheme is set at S$5/tCO2e and scheduled to increase by S$25/tCO2e in 2024. The CFB boiler in Tembusu Multi-Utilities Complex consumed coal fuel in co-firing with biomass, contributing to higher carbon emission than biomass fuel. The study aims to reduce coal consumption by increasing the feed flow of palm kernel shells and woodchips fuel by improving the fuel feed ratio in coal-biomass co-firing use in the CFB boiler. The study highly safeguards the boiler's safe operating limits and reliability; the as-built and design specifications of the boiler are identified and reviewed before the adjustment test. The study assessed the effects of fuel feed ratio adjustment on the boiler's critical parameters, and no significant impact was observed. The revised 59:41 fuel feed ratio is obtained, compared to the original 80:20 design ratio. The emissions have shown promising results in reducing the following pollutants: SO2 by 65.33%, NOx by 5.59%, Mercury by 19.98%, CO by 36.74%, and opacity by 3.83%, while CO2, dust, and excess %O2 were maintained. The fly ash and bed ash physical properties are also improved and beneficial for both fly ash collectors and bed ash recycling life. The boiler efficiency increased by + 0.79% as the revised mixed fuel specific heat input and other heat credits increased.