History of Gasification
The first substantial rise in gasification use occurred in the 1970s and then again in the 1980s in response to the rise in energy prices which made lower cost, less desirable feed stocks attractive economic alternatives to increasingly expensive petroleum and natural gas. During the 1990s, gasification enjoyed even more robust growth, with worldwide capacity increasing by almost 50% during the decade.
The reason for this long-term and continuing growth is clear: modern gasifiers have the ability to convert low value feed stocks into higher value products – chemicals, fuels, and electricity – while meeting the most demanding environmental standards for air emissions, solids, water use, and CO2 removal from the product gas.
Many of the leading gasification technology suppliers and all of their gasification processes to date has been focused on gasifying refinery products and large commercial or power generation use with an “oxygen-blown” system. Oxygen-blown gasification requires supplying a stream of compressed oxygen or oxygen enriched air to the gasification reactor. The oxygen required by this process is produced by a cryogenic oxygen plant commonly called an air separation unit (ASU). Because of the requirement for an ASU and the higher temperatures and pressures at which oxygen-blown systems operate, these gasifiers require costly compressors and utilize substantial power. The auxiliary power requirement of the ASU accounts for the largest internal power operating cost of an IGCC facility utilizing an oxygen-blown gasifier. The result is that an oxygen-blown gasifier can only be used when “economies of scale” exist that allow the higher capital costs for the additional equipment to be recovered over a large volume of Syngas produced.
EPIC uses the alternative to oxygen-blown gasification, “air-blown” gasification, which eliminates the need for the ASU. The air-blown gasifier produces a lower Btu Syngas compared to the oxygen-blown system, (+/- 300 Btu per cubic foot of gas for the oxygen-blown compared to +/- 200 Btu for the air-blown system). However, the air-blown system has a lower capital cost and is less complex to operate. As a result, an air-blown gasifier is more economical for small to mid-sized Syngas users.
If the Syngas is used to produce electricity, it is typically used as a fuel in an IGCC power generation configuration. The combined cycle system has two basic components: a high efficiency combustion turbine, widely used in power generation today, which burns the clean Syngas to produce electricity, and a heat recovery steam generator (HRSG) which converts exhaust heat from the gas turbine into steam to produce additional electricity from traditional high efficiency steam turbines.
Syngas can also be processed using commercially available technologies to produce a wide range of products including fuels, chemicals, and fertilizer, and industrial gases. Some facilities have the capability to produce both power and other Syngas products, depending on the plant’s configuration as well as site specific technical and market conditions.