Numerical investigation of coal-sawdust co-firing in a Carolina-type boiler: Power derating and emission analysis

• Iterative CFD predicts power derating during sawdust co-firing. • Higher sawdust ratios reduce combustion chamber temperatures. • Up to 50% sawdust maintains stable velocity distribution in the boiler. • Sawdust co-firing reduces CO 2 , NOx, and SOx emission intensities. • Bottom injection minimizes CO emissions during sawdust co-firing. Indonesia’s commitment to achieving net-zero emissions by 2060 requires a fundamental transition in energy production and consumption. Biomass, particularly sawdust, which is abundantly available in Indonesia, is a viable renewable energy source that can support the energy transition in the country. This work employs computational fluid dynamics (CFD) to explore the co-firing of coal and sawdust in a 600 MW Carolina-type boiler, with the outlet economizer temperature set to a constant and excess O 2 set to 2–4 %. The results show a significant power derating phenomenon when co-firing sawdust with coal, which is not solely determined by the decrease of fuel calorific value supplied to the boiler. Despite sawdust’s gross calorific value being about half that of coal, a 75 % co-firing of sawdust leads to a 50 % power output derating from 600 to 300 MW, a rate disproportionately higher than the calorific value difference suggests. Various factors, including higher water and hydrogen content in the mixed fuel, reduced heat transfer rates of radiation and convection, and changes in heat absorption efficiency in the combustion chamber, contribute to a 6 % decrease in boiler efficiency at 75 % co-firing. The study also observes a reduction in SO x (67 %) and NO x (50 %) emission and CO 2 intensity (65 %) during co-firing with 75 % sawdust. However, the research identifies limitations in the co-firing process through CFD simulations, necessitating further optimization for enhanced combustion efficiency and efficacy. This study underscores the potential of integrating biomass like sawdust into existing coal-fired power plants, contributing to Indonesia’s energy transition while highlighting areas for future improvement.