Endhaned H2 gas production from wood chip air/steam gasification by using heat recovery in a downdraft gasifier

Abstract

The purpose of this study is to increase the concentration of hydrogen gas in the process of biomass gasification with self-produced steam by using waste sensible heat of producer gas from a fixed bed downdraft gasifier. The system produces the thermal power of 50 kWth. The temperature of reactor is fixed at 920oC, and biomass consumption is at 14 kg/h. The flow rate of producer gas flowing through the heat exchanger is 32 m3/h. The sensible heat of the producer gas is 2.04 kWth. The producer gas temperatures at both inlet and outlet of heat exchanger are 350oC and 170oC, respectively. The small shell and tube heat exchanger having a heating surface area of 0.068 m2 (approximately) produces 2.6 kg/h of steam at 120oC and 1.2 bar. The effectiveness of the heat exchanger is 0.92. In this study, the air/steam mixture is used as the gasifying agents flowing into the oxidation zone of the downdraft gasifier. To conclude, it has been found that the producer gas resulting from the air-steam gasification contains 19% hydrogen, which is 8% higher in hydrogen concentration than the gas product resulting from the air gasification. Furthermore, the heating value of the producer gas resulting from the air-steam gasification is 4.70-5.30 MJ/Nm3, which is 26% higher heating value than the producer gas resulting from the air gasification. The equivalent ratio, ER, is 0.45.