Gasification

If one approach to reducing carbon emissions is to utilize a fuel with less carbon and more hydrogen, gasification offers one pathway to reaching that goal. Gasification evolved as a solution to a developing energy challenge reached at the turn of the nineteenth century. Early gasifier designs—in the late 1800s—capitalized on the abundance of low cost fuels (coal) to provide a combustible gas for illumination. District gas distribution systems were common in major urban centers, in an era prior to wide scale availability of electricity. By the beginning of the twentieth century, thousands of gasifiers dotted the landscape in Europe and North America. Electrification quickly assumed the role of providing illumination and the availability of natural gas would mark the end of this phase of gasification for residential and commercial applications.

A century later, gasification would find new applications based on a completely different set of requirements—decreasing quality of the feedstock and increasing demand of more refined products. Today's gasifiers produce syn-gas (a mixture of CO and H2) primarily for the production of chemicals (the Great Plains gasification complex produces synthetic natural gas from low rank lignite coal). Beginning in 1980s, there were several attempts to match gasification technology (a process that could use cheap but low quality fuels) to gas turbine technology (a process that was not dependent on fuel properties like octane and Cetane ratings) and operating at higher efficiency. The combination could be a win-win since carbon could be extracted just after the gasification step supplemented with a water-gas-shift reaction. The techno-economic challenges of gas separation (carbon dioxide from fuel gases, and oxygen from the atmosphere) saddled the technology with additional complexity and high costs. Today, there are a handful of gasifiers operating as Integrated Gasification Combined Cycle (IGCC) and many of these were heavily subsidized in an attempt to build momentum toward commercialization.

The largest application of gasification technology is in the production of syngas to manufacture chemicals. For power generation, engineers still struggle with designs that will minimize the cost and complexity without sacrificing reliability. A lignite burning plant described earlier can reach over 41% thermal efficiency; the IGCC reaches 40% without including the parasitic loads to capture CO2. However, if gasification is one-step in the path forward, what might that highway look like? Economically, gasification has a viable future for the production of commodities (like ammonia and liquid fuels), or Polygeneration (commodities like fuel in addition to electricity or steam). The idea of a "CO2 capture ready" facility might look more like a chemical plant making SNG or Fischer-Tropsch liquids (where in both cases the CO2 must be chemically separated in such facilities prior to the chemical production step).

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