Hydrogen rich producer gas generation from coal Co-gasification with dual biomass feedstock in a downdraft fixed bed gasifier: Experimental study and RSM optimization

The increasing global demand for energy, driven by population growth, highlights the need for sustainable and efficient energy conversion technologies. Gasification has emerged as a promising approach for converting low-grade coal into valuable gaseous products. In this study, the co-gasification of coal with cashew nut shells (CNS) and pigeon pea stalks (PPS) was experimentally investigated using a 50 kW th downdraft fixed-bed gasifier. The system was operated under varying conditions to evaluate the quality and performance of producer gas from individual feedstock and their blends. Among the tested cases, the coal and CNS blend showed the best performance, producing 6.42 vol% CO 2 , 8.29 vol% CO, 4.03 vol% CH 4 , and 15.79 vol% H 2 , with a lower heating value of 4.67 MJ/Nm 3 and a maximum cold gas efficiency of 73.43%. Response Surface Methodology (RSM) was applied using Design-Expert software to model and optimize the process. The effects of temperature (600 to 1000 °C) and equivalence ratio (0.20 to 0.42) were analysed in detail. The results indicate that higher temperatures enhance hydrogen production and overall gas quality, while increasing ER promotes oxidation and reduces combustible gas components. Further optimization using the desirability function identified optimal conditions at a temperature of 875.779 °C and an ER of 0.29, with 15.51 vol% H 2 and a desirability of 0.881.