Producing Liquid Fuels from Coal
Two basic approaches to convert coal to a liquid fuel:
- Direct Liquefaction calls for breaking coal down in a solvent at elevated temperature and pressure, followed by interaction with hydrogen gas and a catalyst.
- Indirect Liquefaction involves first gasifying coal and then making synthetic fuels from this “syngas.”
Using modern technology, indirect liquefaction produces environmentally compatible zero-sulfur liquid fuels that are cleaner than required under today’s emissions laws and regulations.
Basically, a CTL plant consists of three main processes:
- Syngas Production: this process converts a solid, liquid or gas feedstock (usually natural gas) into hydrogen and carbon monoxide.
- Fischer-Tropsch (F-T) Synthesis: it is the heart of the process. The syngas is converted into liquid hydrocarbons, through a catalytic reaction using cobalt as catalyst. The syngas reacts with the cobalt, joining together simpler hydrocarbon chains contained in the gas, to create a longer liquid hydrocarbon chain (syncrude).
- Refining: the liquid hydrocarbon is then filtered and refined to produce the end product fuels: LPG, Naphtha, Jet fuel and Diesel.
Established Technologies Improved by R&D
- Coal-to-liquid fuel technologies are well-established and have been improved by 30 years of U.S. government research and development efforts, directly and through industry partnerships, into innovative processes ready for widespread commercialization in the 21st century.
- Technology has come a long way since the first coal-derived liquid fuel (a synthetic crude oil) was produced through direct liquefaction in the early 1900s. In 1925, Franz Fischer and Hans Tropsch used an indirect liquefaction process, which still bears their name, to produce excellent transportation fuels. Germany had 25 liquefaction plants that, at their peak in
1944, produced more than 124,000 barrels daily and met 90 percent of the nation’s needs.
In the 1950s, South Africa, through its SASOL Co., developed a commercial coal liquids industry to produce transportation fuels (gasoline and diesel) using synthesis gas produced by the gasification of coal. Modern research has further developed this technology, and
SASOL has produced more than 700 million barrels of synthetic fuels from coal since the early 1980s. About 85 percent of the coal consumed in South Africa is used as synfuels feedstock or to produce electricity.
Advantages of Coal-to-Liquid Fuels
- For Many countries, it improves national and economic security by lessening dependence on foreign oil and substituting plentiful, domestic coal.
- Produces very high quality fuels. The end products are essentially free of sulphur, olefins, metals, alcohols and aromatics. CTL liquid fuels are superior to conventional refinery fuels.
- Coal is far more plentiful than oil and significant reserves exist in more countries
- Products produced can be marketed through existing channels and used in existing vehicles.
The conversion of any feedstock to liquid fuels is an energy intensive one. Emissions across the entire process have to be considered. The coal to liquids process is more CO2 intensive than conventional oil refining and although there are options for preventing or mitigating these emissions this is a very big drawback.
The conversion of any feedstock to provide an alternative fuel requires sizeable upfront
investment and all alternatives are more costly to build than a conventional oil refinery.
The cost of building a conversion facility varies according to location, but recent work suggests that CTL plants are one of the most cost effective of the alternative fuels, particularly when overall operating costs and the low cost of coal are considered. CTL capital investment costs range around $50,000-$70,000 per barrel of daily capacity.
- World Coal Organisation
- National Mining Association
- The Coal-To-Liquids Coalition
- COAL: LIQUID FUELS Report