Technical Performance and Emission Impacts of High- Ratio Woodchip Biomass Co-Firing in a Subcritical Coal-Fired Power Plant

Abstract

This study assesses the technical performance and emission characteristics of high-ratio biomass co-firing at PLTU Anggrek Gorontalo, a2 × 25 MW subcritical coal-fired power plant in Indonesia. The investigation focuses on a 50% woodchip biomass substitution (on a thermal input basis) compared with a conventional 100% coal operation. Full-scale plant trials were conducted under steady-state conditions at 80–90% load to ensure operational consistency. Fuel properties were characterized through proximate and ultimate analyses, as well as higher heating value (HHV) determination. Key operational parameters—including boiler efficiency, steam pressure, temperature, mass flow rate, furnace temperature, and air preheater temperature—were continuously monitored. Stack emissions (CO₂, SO₂, NOₓ, and O₂) were measured to evaluate environmental performance. The results indicate that 50% woodchip co-firing can be implemented without significant derating of plant capacity. Gross electrical output, main steam pressure, temperature, and flow rate remained comparable to baseline coal operation, while furnace and air preheater temperatures stayed within acceptable operating limits. However, gross specific fuel consumption increased from 1.13 to 1.22 kg/kWh despite the blended fuel exhibiting a higher gross calorific value. This suggests an efficiency penalty likely associated with suboptimal combustion dynamics and air–fuel mixing at high biomass fractions. In terms of emissions, a distinct trade-off was observed. NOₓ concentrations decreased significantly under co-firing conditions, indicating improved nitrogen-related emission performance. Conversely, SO₂ concentrations increased relative to pure coal combustion, and CO₂ emissions rose slightly, accompanied by lower excess oxygen levels in the flue gas. Overall, the findings demonstrate that 50% woodchip co-firing is technically feasible in a subcritical coal-fired unit and offers substantial NOₓ mitigation potential. Nevertheless, further combustion optimization, air distribution adjustment, and biomass quality control are necessary to minimize efficiency penalties and manage SO₂ emissions effectively.