Engineering study of coal co-firing based on biomass mixture and slagging-fouling control in the steam power plant

Coal combustion intensifies carbon emissions, contributing to global warming. This study explores co-firing coal with biomass sources—rice husks, sawdust, and cocopeat—and examines the role of calcium carbonate (CaCO₃) in reducing slagging. The research was conducted in three stages: (1) laboratory-scale analysis for raw material characterization, (2) prototype-scale combustion testing for efficiency and emissions, and (3) full-scale evaluation in a coal-fired power plant. Laboratory tests identified a 50% rice husk (RH) – 50% sawdust (SW) mixture as optimal, with a calorific value of 15,788.324 kJ/kg and a low alkali index (0.11). Prototype testing showed that emissions remained within regulatory limits, and CaCO₃ addition effectively reduced SO₂, NOₓ, and CO emissions while increasing SO₃ and SiO₂ retention in bottom ash, mitigating slagging risks. However, CaCO₃ exhibited limited and inconsistent effectiveness, making it unsuitable for large-scale application. Full-scale trials demonstrated that co-firing improved boiler efficiency (83.46% with 5% biomass – 95% coal co-firing vs. 83.65% with 100% coal), with stable power output (396–400 MW) and a fuel consumption of 0.6 kg/kWh. Sawdust contributed to combustion stability due to its lower porosity, while rice husks enhanced airflow, accelerating combustion. Slagging and fouling indices indicated a high slagging potential (category 6) for sawdust and cocopeat, but mixed biomass variables exhibited reduced slagging risk (category 5). Cocopeat had the highest sodium fouling and slagging indices (1.41, 1.54, 1.56), making it unsuitable for co-firing. Community involvement in biomass procurement engaged 266 stakeholders, though seasonal limitations required external sourcing. Additionally, training programs in organic fertilizer production were implemented to support biomass sustainability. Overall, this study demonstrates that biomass–coal co-firing represents a viable pathway for cleaner energy production that simultaneously provides economic and environmental benefits.