Theoretical and experimental investigation of ash-related problems during coal co-firing with different types of biomass in a pulverized coal-fired boiler

Biomass waste can be utilized as a mixed co-firing fuel in power plants to reduce net carbon emissions. However, understanding the characteristics of biomass and its blend before being applied to actual power plants is required. Adding biomass to the existing power plant fuel may cause problems such as slagging and fouling due to ash deposits, affecting the plant's lifetime and operational and maintenance costs. This study comprehensively investigated the slagging and fouling potential when co-firing coal with four types of biomasses by combining theoretical calculations and experimental methods. The experimental method included combustion tests and a series of ash investigations, such as probe observation, scanning electron microscopy–energy dispersive X-ray spectroscopy, and X-ray diffraction. The results show that co-firing of coal with 25% of either palm oil empty fruit bunch–frond or wood chip yields a similar performance concerning combustion characteristics, gas emissions, ash deposits, and ash mineralogy. The addition of 25% rice husk needs consideration of soft scratches on the surface probe and the amount of ash deposit. The results also suggest that a co-firing with less than 25% solid recovered fuel needs further investigation to mitigate the slagging and fouling tendency. Finally, these findings are important for clarifying several types of biomasses as potential co-firing fuels for pulverized coal-fired power plants.