Determination of Energy and Exergy of Syngas Produced from Air-steam Gasification of Wheat Straw in a Dual Distributer Fluidized Bed Gasifier
Yaning Zhang *
School of Energy Science and Engineering, Harbin Institute of Technology, Harbin, China and Department of Process Engineering and Applied Science, Faculty of Engineering, Dalhousie University, Halifax, Nova Scotia, Canada.
Abdel Ghaly
Department of Process Engineering and Applied Science, Faculty of Engineering, Dalhousie University, Halifax, Nova Scotia, Canada.
Sammy S. Sadaka
Department of Biological and Agricultural Engineering, Division of Agriculture, University of Arkansas - AR, USA.
Bingxi Li
School of Energy Science and Engineering, Harbin Institute of Technology, Harbin, China.
*Author to whom correspondence should be addressed.
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.
Keywords: Energy, exergy, syngas, air, steam, gasification, wheat straw, fluidization velocity, biomass ratio, seam flow