A prototype 3 kW solar gasifier that operates in continuous mode to produce a mixture of hydrogen and carbon monoxide (synthesis gas) was operated at 1200 K in a high flux solar simulator with record breaking efficiency for steam gasification of cellulose. A unique aspect of the gasifier is the use of a molten alkali salt as heat transfer media and chemical catalyst. To identify an appropriate salt composition, we assess the physical solubility and chemical reactions of product and reactant species over a range of oxidizer stoichiometry. For near-stoichiometric steam oxidation, a carbonate blend of 38.6% mol Li2CO3, 29.7% Na2CO3, and 22.9% K2CO3 with 8.7% mol alkali metal hydroxide salts, including 6.1% LiOH, 1.5% KOH, and 1.1% NaOH ensures equilibrium of the salt exposed to steam gasification products and no excess production of CO2. The product is syngas with a hydrogen and carbon monoxide ratio of 1:1. Feedstock carbon conversion is 78%, and the reactor thermal efficiency is 40%. Assuming that unconverted carbon is recycled, the projected efficiency is 44%. The efficiency exceeds that previously reported for CO2 gasification due to an improved feed system.
Bibliographical noteFunding Information:
The authors acknowledge the funding received from the Minnesota Institute on the Environment. We thank Fletcher Carlson, Jesse Fosheim, and Samantha Kopping for their help monitoring the experiments in the solar simulator and Nathaniel Lewin for his work on the feedstock injector redesign.
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