Sierra Energy selects Oxford Catalysts microchannel FT reactor for California waste-to-liquids commercial demonstration plant
30 July 2012
Sierra Energy has selected microchannel Fischer-Tropsch (FT) reactor technology developed by Velocys, Inc., the US-based subsidiary of the Oxford Catalysts Group, for use in a waste-to-liquids (WTL) commercial demonstration plant to be constructed in northern California by the California-based company Sierra Energy.
The plant, which is partially funded by a $5-million award from the California Energy Commission (CEC), will have a capacity of 25-100 barrels per day (bpd), which will be produced from locally sourced municipal solid waste (MSW). It is expected to begin operating in 2013.
The waste-to-liquids process involves two main operations: production of a synthesis gas (syngas) using a gasifier; followed by FT synthesis. The resulting FT product can then be upgraded via hydrocracking and fractionation to produce a range of liquid hydrocarbon fuels. The fuels produced can be directly substituted for conventional fuels, and are generally of higher quality than those derived by conventional means.
In the commercial demonstration, which will be hosted by SacPort Biofuels, the gasification will be carried out using Sierra Energy’s proprietary FastOx waste gasification process. The FT synthesis will be carried out using Velocys’ microchannel FT reactor technology. Sierra Energy intends to use this commercial demonstration as the basis for the design of a turn-key, waste gasification system called the FastOx Pathfinder.
The FastOx gasifier is a simple derivative of the blast furnace, specifically designed to convert waste; waste is fed into the top of the gasifier while oxygen and steam are injected into the bottom. The injection of oxygen and steam is one of Sierra Energy’s patented innovations. The waste passes through four reaction zones as it descends in the gasifier:
Drying occurs when the hot syngas produced at the bottom of the gasifier rises and passes through the waste in the top zone of the unit, drying the waste as it passes.
Devolatization is where the majority of the organic matter is driven off into syngas.
Partial oxidation occurs when carbon-containing materials in the waste react with the injectors. This reaction creates high temperatures in the range of 4,000 °F, allowing for the thorough conversion of remaining carbon into syngas.
Melting of inorganic compounds results from the high temperatures occurring in the partial oxidation zone. These compounds collect at the bottom of the unit and are continuously removed as inert stone (slag) and recycled metals.
The devolatization step yields many complex compounds including tars; these compounds need to be cleaned up. That's been the historic headache for waste-to-fuel projects. I have to wonder what twist they've come up with this time.
I recall another effort which separated the devolatization and gasification steps. Volatiles were driven off in a low-temperature reactor which produced char; in the gasifier, the gas from devolatization was burned to react the char with steam, also breaking down the complex compounds in the process.
Posted by: Engineer-Poet | 30 July 2012 at 02:26 PM