Study on the Co-combustion characteristics and synergistic effect of semi-coke and dust coal produced from biomass briquette in fluidized bed gasification

Biomass briquette semi-coke (BFSC) is one of the byproducts of biomass gasification. It is difficult to reuse due to its inadequate carbonization, unsatisfactory pore structure, and surface properties. Co-combustion of BFSC with coal-fired boilers can be a cost-effective usage of biomass gasification semi-coke while also improving dust coal's combustion characteristics. However, research on the optimal blending ratio, co-combustion properties, and synergistic effects of BFSC and dust coal is lacking. This study conducted experimental and theoretical research on the co-combustion and reaction kinetic characteristics of BFSC and dust coal with a 0.3 MW pilot experimental system. The findings indicate that during co-combustion, sawdust semi-coke (SC), eucalyptus bark semi-coke (EBC), rice husk semi-coke (RHC), and corn straw semi-coke (CSC) exhibit favorable synergistic effects. At a 25 % blending ratio, the corresponding synergistic parameter indexes (SPIs) were 1.313, 1.053, 1.001, and 1.042. Adding EBC and SC may significantly promote the combustion of dust coal and make it enter the combustion stage sooner, improving combustion stability. When 25 % RHC or CSC is co-combusted, the activation energy predicted by the kinetic control equations is 17 kJ/mol and 5 kJ/mol lower than theoretical values, with a relative error of less than 3 %. The annual EBC output from a 1-ton biomass boiler may replace roughly 706 tons of normal coal, lowering CO2 emissions by approximately 634 tons and producing a direct economic gain of $33300. Therefore, BFSC is a low-carbon and low-cost coal boiler fuel with great potential for large-scale industrial applications.