Sub-Critical Water Gasification of Biomass for Hydrogen Production – Gasification Efficiency and Hydrogen Selectivity

In this context, sub-critical water gasification of distillery wastewater has been experimentally studied. Biomass can be converted into fuel gas near and beyond critical point of water (e.i. T=274.15 ⁰C and P=22.1 MPa). Distillery wastewater possesses a high level of COD, which makes it a potential source of wet biomass as a proper feed for sub- and supercritical water gasification. In this regard, a 160 mL autoclave was used to investigate the effects of temperature, biomass loading and reaction time on gasification efficiency (GE), carbon gasification efficiency (CGE) and hydrogen selectivity (HS) of gas product. Gaseous product contained mainly hydrogen and carbon dioxide accompanying few amount of methane and carbon monoxide. Results revealed that temperature is the most affecting parameter on GE, CGE and HS. Increasing temperature from 300 to 375 ⁰C at 45 min resulted in considerable rise of HS from 0.05 to 0.95 and CGE from 71% to 98%, respectively. Also, biomass loading had slight negative effect on both GE and CGE. Moreover, reaction time is the second most influencing parameter on gasification efficiencies, especially at low temperatures, but it has a slight decreasing effect on HS. Generally, higher gasification efficiency is achieved at higher temperature and longer reaction time, but at lower biomass loading; while, shorter reaction time and higher temperature favour hydrogen selectivity.