Biomass feedstocks, including corn- and potato-starch gels, wood sawdust su
spended in a cornstarch gel, and potato wastes, were delivered to three dif
ferent tubular flow reactors by means of a "cement" pump. When rapidly heat
ed to temperatures above 650 degreesC at pressures above the critical press
ure of water (22 MPa), the organic content of these feedstocks vaporized. A
packed bed of carbon within the reactor catalyzed the gasification of thes
e organic vapors in the water; consequently, the water effluent of the reac
tor was clean. The gas was composed of hydrogen, carbon dioxide, methane, c
arbon monoxide, and traces of ethane. Its composition was strongly influenc
ed 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 hydroge
n (57 mol %) were realized at the highest temperatures employed in this wor
k. Irrespective of the reactor geometry and method of heating, all three re
actors plugged after 1-2 h of use with feedstocks that contained 15 wt % or
ganic material. Lower loadings of organics lengthened the time before plugg
ing 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 rea
ctor's inner wall occurred during these tests. Nickel and other metals were
leached from the reactor and deposited in the carbon catalyst. Nickel allo
y tubes are not suitable for use in this application.