Determination of Energy and Exergy of Syngas Produced from Air-steam Gasification of Wheat Straw in a Dual Distributer Fluidized Bed Gasifier

Abstract

The energy and exergy of syngas produced from air-steam gasification of wheat straw in a dual-distributor fluidized bed gasifier under different operating conditions were evaluated. Three fluidization velocities (0.35, 0.40 and 0.45 m/s), 3 steam flow rates (0.20, 0.25 and 0.30 kg/min) and 3 biomass: steam ratios (3.00, 4.00 and 5.00 kg/kg) were investigated. The energy values of CO, H2, N2, CO2, CH4, C2H4 and C2H6 varied within the ranges of 1627.09-4646.60, 1543.30-2896.11, 274.75-1742.86, 82.03-574.24, 3225.39-4931.40, 1493.35-3777.44 and 892.74-2319.72 kJ/kg fuel, respectively. The overall energy distribution was (CH4 & CO & C2H4 & H2)>C2H6>(N2 & CO2). The results showed that when the fluidization velocity (FV) was increased from 0.35 m/s to 0.45 m/s (28.57%), the total energy of syngas increased by 1.16-28.59% depending on the steam flow rate (SFR} and biomass: steam ratio (B:S) used. Increasing the SFR from 0.20 kg/min to 0.30 kg/min (50.00%) decreased the total energy of syngas by 27.23-62.35% depending on the FV and B:S used. Increasing the B:S from 3.00 kg/kg to 5.00 kg/kg (66.67%) decreased the total energy of syngas by 11.86-37.33% depending on the FV and SFR used. The exergy values of CO, H2, N2, CO2, CH4, C2H4 and C2H6 were in the ranges of 1486.70-4224.40, 1183.82-2209.00, 60.26-677.26, 54.02-452.97, 2913.74-4448.38, 1404.76-3541.76 and 833.00-2156.42 kJ/kg fuel, respectively. The overall exergy distribution was (CH4 & CO)>(C2H4 & H2 & C2H6)>(N2 &CO2). When the FV was increased from 0.35 to 0.45 m/s(28.57%), the total exergy of syngas increased by 1.45-26.93% depending on the SFR and B:S used. Increasing the SFR from 0.20 kg/min to 0.30 kg/min (50.00%) decreased the total exergy of syngas by 26.78-63.26% depending on the FV and B:S used. Increasing the B:S from 3.00 kg/kg to 5.00 kg/kg (66.67%) decreased the total exergy of syngas by 10.32-36.07% depending on the FV and SFR used. The effect of SFR on the total energy and total exergy of syngas was the highest, followed by B:S and FV. The highest energy (20004.54 kJ/kg fuel) and exergy (16886.06 kJ/kg fuel) of syngas were obtained at the FV of 0.45 m/s, the SFR of 0.20 kg/min and the B:S of 3.00 kg/kg.