Biomass Gasification in Supercritical Water

Abstract

Biomass feedstocks, including corn- and potato-starch gels, wood sawdust suspended in a cornstarch gel, and potato wastes, were delivered to three different tubular flow reactors by means of a “cement” pump. When rapidly heated to temperatures above 650 °C at pressures above the critical pressure of water (22 MPa), the organic content of these feedstocks vaporized. A packed bed of carbon within the reactor catalyzed the gasification of these organic vapors in the water; consequently, the water effluent of the reactor was clean. The gas was composed of hydrogen, carbon dioxide, methane, carbon monoxide, and traces of ethane. Its composition was strongly influenced by the peak temperature of the reactor and the condition of the reactor's wall. Extraordinary yields (>2 L/g) of gas with a high content of hydrogen (57 mol %) were realized at the highest temperatures employed in this work. Irrespective of the reactor geometry and method of heating, all three reactors plugged after 1−2 h of use with feedstocks that contained 15 wt % organic material. Lower loadings of organics lengthened the time before plugging occurred. The plug resulted from accumulations of ash and small amounts of char formed by coking reactions involving the biomass vapors. A method for removing plugs from the reactor was developed and employed during an 8-h gasification run involving potato wastes. Extensive corrosion of each reactor's inner wall occurred during these tests. Nickel and other metals were leached from the reactor and deposited in the carbon catalyst. Nickel alloy tubes are not suitable for use in this application.

SunCHem: an integrated process for the hydrothermal production of methane from microalgae and CO2 mitigation

“…Typical catalyst supports, e.g., silica and γ-alumina, cannot be used, as they will be severely degraded under the harsh conditions of the supercritical water. During the last 15 years, new catalyst formulations have been developed that use combinations of stable metals such as ruthenium (Ru), or nickel (Ni) bimetallics, and stable supports such as titania, zirconia, or carbon (Elliott et al 2006;Antal et al 2000;Waldner et al 2007;Peterson et al 2008;Vogel 2009). …”

Environmental Impacts of Hydrogen Production by Hydrothermal Gasification of a Real Biowaste

“…Morimoto et al [13] of Kyoto University studied hydrothermal gasification process of brown coal. Antal et al [14] reported the gasification of cornstarch and wood dust. Yoshida et al [15] studied supercritical water gasification of cellulose, hemi-cellulose, and lignin.…”

Cogeneration of renewable energy from biomass (utilization of municipal solid waste as electricity production: gasification method)

“…Longer residence time can improve gasification thoroughness, but there is also an inverse relationship between temperature and reaction completeness, dropping from a few minutes below 600°C to a few seconds above 600°C. The optimal temperature threshold for SCWG (i.e., 600°C) has been shown on the lower side of the conversion range for higher concentration biomass in the absence of a catalyst [23][24][25][26]. From the viewpoint of thermodynamics, biomass can be gasified completely in SCW with a product formation of H 2 and CO 2 , but adequate reaction time was required to complete the gasification process.…”