Newsletter: 4th Quarter 2007
Coal for oil — new possibilities
As the world's populations continue to expand on their use of cars, planes and oil in general the search for new possibilities has lead to coal. In the United States alone the counties population used 18 million barrels of oil a day, that was in 2002, in 2006 their oil consumption has raised by 3.5 million barrels a day. This does not take into account growing wealth and increased car ownership in Asians countries. The latest answer to oil shortages and prices is coal liquefaction, technology that has been around since the 1920's and turns a profit when oil is more than $40 a barrel.
Research and development into coal liquefaction technology has primarily been driven by the price and depletion of crude oil. In countries such as South Africa large-scale application of coal liquefaction technology has been occurring since the 1980s. The driving force here however has been a lack of oil, embargos and ample coal reserves. In the 1980s up to 60% of transportation fuel requirements have been met from coal.
Source: Cleaner Coal Technology Program; Department of Trade & Industry: UK
Source: Cleaner Coal Technology Program; Department of Trade & Industry: UK
Coal can be used to produce liquid fuels by removing carbon or adding hydrogen. The first approach is called carbonisation or pyrolysis and the second is known as liquefaction. There are many processes in adding hydrogen to the organic structure of coal, all of which are closely related in terms of their underlying chemistry. Common features used in the various types of technology include the dissolution of coal in a solvent at high temperature and pressure, followed by hydro-cracking of the dissolved coal with H2. The overall efficiency range for is 60% to 70% liquid yields by weight of the dry mineral matter. After the initial conversion of coal to liquid further refining is required for transportation use, this can be achieved by utilising standard petroleum industry techniques.
Coal liquefaction processes can be divided into two main groups, this depends on whether the initial dissolution of the coal is separated from the conversion of the dissolved coal into distillable products.
- A single stage coal liquefaction process gives distillates via one primary reactor. This process may include an integrated on-line hydro-treating reactor, and upgrades the primary distillates without directly increasing the overall conversion.
- A two stage coal liquefaction process is designed to give distillate products via two reactors or reactor trains in series. The first stage is coal dissolution. The heavy coal liquids produced are hydro-treated in the second stage in the presence of a high-activity catalyst to produce additional distillate.
Single stage processes have been used since World War II such as the Kohleoel process below. Two stage processes have been developed since oil price rises of the early 1970s, this includes the Catalytic Two-stage Liquefaction Process (see diagrams).
