Liquified Coal
(and other Synthetic Fuel)

Coal can be liquified to create synthetic diesel fuel using two different processes, direct coal liquification and indirect coal liquification. Direct coal liquification requires higher quality coal and is a more efficient conversion process, but the technology is still in the pilot plant stage. The indirect conversion process, called the Fischer-Tropsch process, has been used to produce synthetic diesel fuel since the 1920s, and can be used to liquify natural gas and biomass in addition to coal. The resulting fuels—commonly referred to as CTL ("coal to liquid"), GTL ("gas to liquid") or BTL ("biomass to liquid")—are usable in any diesel engine either in pure form or blended with conventional diesel fuel.

These fuels have zero sulfur, high cetane and low aromatic levels, which makes them extremely clean burning. Coal to liquid conversion is profitable when petroleum prices are $40 or above and coal costs betweenv $1 and $2 per million BTU. CTL can also be combined with other energy generation processes in order to produce electricity, steam, chemicals, and fuel simultaneously. Although the United States has vast coal resources, commerical production plants do not exist in the United States today. However, coal-based aviation fuels are under development for military use, and successful use of liquified coal in that context may spur further commercial development of coal based fuels. Gas to liquid is economically viable when oil prices per barrel are $25 or above and natural gas prices range from $.50 to $1.00 per million BTU. The GTL process can also co-generate other energy sources. There are no active GTL plants in the United States today, although several plants are under consideration. Biomass to liquid fuels are competitive when oil prices are above the $80 per barrel range. Currently the United States does not convert biomass to synthetic diesel fuel using the Fischer-Tropsch process.

Visual source: http://www.eia.doe.gov/oiaf/aeo/issues.html

The Fischer-Tropsch Process: First, the feedstocks are converted into gas, called syngas. Then, the syngas is fed into reactors and converted to paraffin wax, hydrocracked to produce hydrocarbons, and finally reacted with catalysts to produce fuel and other synthetic petroleum products.

Sources:

• Energy Information Administration Annual Energy Outlook 2006
• The Auto Alliance
• Compare chemical and physical properties of all alternative fuels
• Compare practical differences between alternative fuels