Thermodynamic Analysis for Gasification of Thailand Rice Husk with Air, Steam, and Mixed Air/Steam for Hydrogen-Rich Gas Production

Thermodynamic analysis of gasification with air, steam, and mixed air-steam was performed over rice husk to determine the optimum conditions (i.e., equivalence ratio (ER), steam to biomass ratio (SBR) and operating temperature) that can maximize the yield of hydrogen production with low energy consumption. It was found that for air gasification, H2 production is always less than CO production and considerably decreased with increasing ER. For steam gasification, the simulation revealed that H2 production is greater than CO, particularly at high SBR and low temperature; furthermore, H2 yield increased steadily with increasing temperature and SBR until reaching SBR of 3.5-4.0, then the effect of steam on H2 yield becomes less pronounced. As for the mixed steam/air gasification, H2 production yield increased with increasing SBR, but decreased dramatically with increasing ER (up to 0.4). Among these three operations, the highest H2 production yield can be achieved from the steam gasification with SBR of 4.0. Nevertheless, by considering the system efficiency, the combined air-steam gasification provided significant higher hydrogen production efficiency than the other two operations. The optimum condition for combined air-steam gasification can be achieved at 900°C with ER of 0.1 and SBR of 2.5, which provided the efficiency up to 66.5 percent.