Shale oil and gas reserves are abundant
enough to meet the growing
demand for energy, but the exploitation of organic-rich shale with
low maturity is still a challenging work due to its high kerogen content.
As both a heat carrier and an organic solvent, supercritical water
has been found to be an excellent working medium for hydrogen production
by biomass or coal gasification. This study is an initial attempt
to determine the candidacy of organic-rich shale as a feedstock for
hydrogen-rich gas generation by supercritical water gasification.
The effects of temperature (500–700 °C), pressure (22–28
MPa), time (0–12 h), water/shale mass ratio (1:1–10:1),
and shale particle size (5–150 mesh) were investigated in a
batch reactor. The results showed that the gas products were mainly
consisted of hydrogen, carbon dioxide, and methane, which were produced
by the reactions of steam reforming, water–gas shift, methanation,
and carbonate hydrolysis. The abundant inorganic minerals in the shale,
especially carbonate, could act as the catalyst for gasification reactions
and contribute a lot to carbon dioxide formation. It was found that
temperature and time were dominant factors to gas yield and selectivity.
Increasing the temperature promoted the endothermic reactions of steam
reforming and pyrolysis and accelerated the water–gas shift
reaction. Pressure increase has a less negative but negligible effect
on gasification. The carbon gasification efficiency and hydrogen selectivity
all first increased and then stabilized when the reaction time was
prolonged, and the water–shale mass ratio was increased and
(or) the shale particle size was decreased. Overall, the suggested
conditions were a temperature of 700 °C, a pressure of 22.1 MPa,
a water/shale mass ratio of 5:1, a time of 4 h, and the particle size
range of 10–20 mesh.
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