The engine reformer : syngas production in engines using spark-ignition and metallic foam catalysts

Abstract

An experimental study was performed to assess the feasibility of performing methane (CH4) partial oxidation (POX) in two internal combustion engines: one equipped to perform spark-ignition (the "spark-ignited engine"), and the other containing a catalyst in the engine cylinder (the "catalytic engine"). The exhaust gases were rich in hydrogen- (H 2) and carbon monoxide- (CO), and could be used as synthesis gas ("syngas") for the synthesis of liquid fuels such as methanol. Conventional syngas production techniques are only economical on a large scale and cannot be transported to hard-to-reach gas sources, where gas-to-liquids (GTL) would have the biggest impact on the transportability of that gas. Engines could be deployed at these locations to produce syngas on a small scale and at low cost, as they benefit from the economies of mass production that have been achieved through advanced manufacturing techniques. We call this type of engine an "engine reformer". This thesis contrasts the results of performing methane POX in two different engine reformers, using atmospheric air as the oxidizer. One of four cylinders in a Yanmar 4TNV84T marine diesel generator was converted to ignite methane POX mixtures using a spark plug. Intake temperatures > 350 °C were required to minimize misfire. Exhaust H2 to CO ratios of 1.4 were achieved with methane-air equivalence ratios (0m) up to 2.0, while ratios of > 2.0 were achieved with hydrocarbon-air equivalence ratios (PHc) up to 2.8 with the assistance of hydrogen (H 2) and ethane (C 2H6). High equivalence ratios °PHC > 2.2 showed reduced CH4 conversion efficiency, therefore PHC = 2.2 (with H2 produced a good tradeoff between syngas quality and CH4 conversion. A single-cylinder Lister-Petter TRl diesel generator was used to perform methane POX using a palladium (Pd) washcoat catalyst deposited on a Fecralloy® disk. With > 150 °C intake temperatures, exhaust H2 to CO ratios of 1.0 were achieved with methane-air equivalence ratios (PM = 4.0 with varying amounts of CO2 to simultaneously perform methane dry reforming. Spark-ignition appeared to provide higher reliability, though tests will continue to be performed on the catalytic engine to optimize performance. A larger engine of a similar design to the spark-ignited Yanmar will be deployed at a demonstration plant in North Carolina to produce syngas at higher flow rates, and will be integrated with a liquids synthesis reactor to produce methanol.