Effect of syngas recirculation in the pyrolysis zone on the rice husk gasification process using the downdraft reactor

Abstract

As one of the world's largest rice producers, Indonesia has an abundance of rice husk as a byproduct of rice milling. Rice husks were utilized to examine downdraft gasification with syngas recirculation system. This study attempts to produce better syngas than conventional downdraft gasifier. With an equivalency ratio of 0.20, syngas was recirculated into the reactor in the pyrolysis zone with valve openings at 25%, 50%, and 75%. This study determined the syngas recycling ratio that maximizes H2 and CO gas and decreases tar. Increasing the syngas recirculation valve (25%, 50%, and 75%) accelerates flame propagation and pyrolysis zone temperature. Syngas study showed no recirculation condition produces the maximum CO2 and CH4. Different recirculation valve openings little affect CO and CH4 gas composition. The H2 gas composition demonstrates that valve openings significantly change H2 gas generation and that the peak was at 50% syngas recirculation. Tar content decreased to 30% and 35% at 50% and 75% valve openings. Based on H2/CO comparison and tar concentration, 50% opening syngas recirculation became the optimum case.