Performance evaluation of downdraft gasifiers under various conditions

This research studied the effect of biomass types and moisture content on the performance of a downdraft gasifier. Sawdust, woodchip and bean chaff were used as test samples at three moisture contents (10, 20 and 30% w.b) which was determined with oven drying method and Pascal's manometric tube was prepared to measure the quantity of methane, hydrogen sulfide, carbon dioxide and carbon monoxide in the syngas. The gas obtained at 10% moisture content for the three biomass after gasification was analyzed and compared to standard values. Ash content, gasification time and temperature were measured using standard methods. The ash contents at 10, 20 and 30% moisture contents for wood chips, sawdust and bean chaff were 0.210, 0.457, 0.750kg, 0.202, 0.290, 0.651kg and 0.295, 0.228, 0.394kg respectively. The gas samples were taken at 10% moisture for analysis because it produced the lowest ash content. Gas produced at 10% moisture content showed that methane, CO2 and H2S contents for wood chips; sawdust and bean chaff were 60.85, 27.50, 0.44%; 62.33, 23.77, 0.87% and 63.94, 18.91, 0.58% respectively. The values of CO was insignificant. The moisture content of the biomass significantly (p < 0.05) affected the values of ash content, gasification time and temperature but the effects of biomass types were not significant. Ash content and gasification time increased with increase in moisture level with the least value of 0.210 kg and 61 minutes at 10% moisture content respectively. The gasification temperature decreased as moisture level increased and vice versa. Increase in moisture level increased the ash content and gasification time. The higher the gasification temperature, the lower the time. Gasifier efficiency was also affected by moisture content and biomass types. The best gasifier efficiency was observed at 10% moisture content with 60, 57 and 75% for sawdust, woodchips and bean chaff respectively.