Multi-scope decarbonization and environmental impacts evaluation for biomass fuels co-firing CHP units in China

Co-firing of waste biomass as low-carbon fuels in combined heat and power (CHP) units is an indispensable energy supply technology providing regional electricity and heat, especially in industrial parks, that can combat climate change and support the achievement of Sustainable Development Goals (SDGs) in China. In this study, we proposed a life cycle material-energy-carbon integrated GHG accounting framework for CHP units converting waste to energy with co-firing of sludge and biomass pellets, including supply and value chains. This framework enables the prediction of multi-scope GHG emissions and environmental impacts associated with co-firing based on the properties of biomass fuels. It facilitates the selection of suitable biomass fuels according to decarbonization or reduced environmental impact objectives. When considering CO₂ emissions alone, co-firing with sludge appears to be a beneficial option due to the economic gains from waste disposal. However, this also leads to increased GHG emissions unless avoided emissions from original disposal are considered, thus highlighting the need to expand the regulatory framework pertaining to GHG emissions that recognizes non-CO₂ GHG emissions. Additionally, the practice of co-firing biomass fuels presents a complex interplay between enhanced decarbonization effects but potentially more significant environmental impacts when the co-firing ratio increases, highlighting the trade-offs between enhanced decarbonization and environmental challenges. Leveraging this framework, our study evaluated the national decarbonization potential through the deployment of CHP units with sludge or biomass co-firing across various provinces, indicating that biomass pellets co-firing could lead to more substantial GHG emission reduction.