Gasification and Liquefaction
Gasification and liquefaction is a proven process for converting coal into market-competitive substitutes for petroleum products. These technologies have been used successfully in other parts of the world for more than 50 years.
An early form of coal gasification called 'town gas' was used in the 1800s to light America's largest cities, but was replaced when large natural gas reserves were developed. In the 1970s, when the supply of natural gas seemed to be declining, coal gasification regained its popularity only to lose it when large quantities of natural gas once again became available. Rising natural gas and crude oil prices have renewed the interest in this technology. Today over one hundred gasification facilities are in operation worldwide with more under development.
The Fischer-Tropsch liquefaction technology, originally developed in the 1920s by German researchers Franz Fischer and Hans Tropsch, was used during World War II in Germany and Japan to produce alternative fuels. By 1944, 25 plants were producing a total of 124,000 barrels per day.
In the 1940s, the U.S. Congress appropriated $100 million in the Synthetic Liquid Fuels Act for studying coal-to-liquids technology and, by 1953, Fischer-Tropsch process test plants produced up to 5,000 barrels per day of gasoline. That same year, the U.S. abandoned its research about the time that the South African government began investing heavily in Fischer-Tropsch infrastructure. Isolated due to its Apartheid policies, South Africa embraced the Fischer-Tropsch process in order to meet its energy needs. Today, South Africa uses indigenous coal to meet nearly 30 percent of its gasoline and diesel needs.
The technology for methanol-to-gasoline was developed for use by ExxonMobil in New Zealand during the 1980s and can produce commercial volumes of transportation fuels.
The gasification process converts any carbon-containing material into a synthesis gas composed mainly of carbon monoxide and hydrogen. The gas is used as a basic chemical building block for a large number of uses in the petrochemical and refining industries, or used to produce electricity or steam. Gasification adds value to low or negative value feedstocks by converting them to marketable fuels and products.
Gasification technologies vary in many aspects but share certain general production characteristics. Typical raw materials used in gasification are coal, petroleum based materials (crude oil, high sulfur fuel oil, petroleum coke, and other refinery residuals), gases, or materials that would otherwise be disposed of as waste. The feedstock is prepared and fed to the gasifier in either dry or slurried form. The feedstock reacts in the gasifier with steam and oxygen at high temperature and pressure in a reducing (oxygen starved) atmosphere. This produces the synthesis gas, or syngas, made up primarily of carbon monoxide and hydrogen (more than 85% by volume) and smaller quantities of carbon dioxide and methane.
The high temperature in the gasifier converts the inorganic materials in the feedstock (such as ash and metals) into a vitrified material resembling coarse sand. The vitrified material, generally referred to as slag, is inert and has a variety of uses in the construction and building industries. A cleaning process then removes the sulfur, CO2 and other trace elements, leaving a mixture of hydrogen and carbon monoxide.
In the conversion process, the cleaned syngas is passed through a chemical reactor loaded with a catalyst. The reaction generates chemicals and heat. In addition to a wide variety of liquids, including methanol, diesel, naphtha, kerosene, butane, propane, gasoline and jet fuel that are very low in sulfur and aromatics, conversion facilities can produce electricity and a number of other useful products.
The residual syngas, along with heat from the gasification and chemical reactions, is used to generate power for facility operations. In some cases, the electricity is available for export to wholesale power customers.
Marketable byproducts of the conversion process include chemicals and ash. CO2 removed in cleaning the syngas is used in enhanced oil recovery (EOR) to significantly increase production from mature oil fields. The sale of byproducts from conversion can substantially enhance the economics of a facility while reducing waste.