Effects of Reactor Wall Properties, Operating Conditions and Challenges for SCWG of Real Wet Biomass

Abstract

Hydrogen is considered the cleanest fuel as it does not create any pollution during combustion. However, hydrogen is not readily available in nature as a primary energy source, but a secondary energy generated from the primary energy sources via various conversion processes. Supercritical water gasification (SCWG) process in contrast to the conventional gasification process does not require biomass drying, and rather it uses the moisture and external water in the reaction. Much research has been performed on SCWG of various types of biomass for hydrogen production, where numerous reactors made from different materials were used. Various operating conditions were also widely studied, such as catalysts, temperature, pressure, feed concentration etc. Researchers have tried quartz reactors to avoid corrosion of metallic reactors due to the supercritical water, but the overall performance was not satisfactory as the total gas yield and H2 yield were less compared to any metallic reactor. Using catalysts improved the overall gas and hydrogen yield but the common challenge is the supported catalysts becoming deactivated over a longer operating time. Temperature has the most prominent and positive effect on H2 yields, while pressure does not have any significant effect rather it has complex effects on the process. A higher concentration of the feed increases CO2 production, and a lower concentration increases H2 and CH4 yields. Moreover, the major challenge of SCWG is feeding real biomass into the reactor. Most of researchers used model biomass or fractions of biomass (such as cellulose or lignin) for conversion. Little literature work was reported on SCWG of real biomass in continuous flow reactors, mostly in batch reactors. Therefore, this chapter aims to discuss about the effects of the reactor wall properties, operating parameters on supercritical water gasification of real wet biomasses and the associated operating challenges.