Why liquefied coal (CTL) and natural gas (GTL) can’t replace oil
Preface. Here are just a few of the reasons why we aren’t likely to convert enough coal to diesel to matter as oil decines (see Chapter 11 Liquefied Coal: There Goes the Neighborhood, the Water, and the Air for more details on this in When Trucks Stop Running: Energy and the Future of Transportation)
It is not likely much coal will be converted to diesel, because if all global coal production were converted to liquid coal, perhaps 17 million barrels a day (Mb/d) could be produced. That amounts to 22 % of current world oil production. If more efficient liquefaction technologies came along, and coal now used to generate electricity and make cement, steel, aluminum, paper, and chemicals were all diverted to make liquid fuels, as much as 54 Mb/d could be made. But roughly 17 Mb/d is more likely because diverting most or all of the coal from other uses to make CTL is not realistic. After all, we do need cement and steel to build the CTL coal liquefaction plants, roads, and the trucks and pipelines to transport the CTL itself.
In the U.S. coal production could be doubled to make CTL, but that might cut reserve life in half. In the U.S., there may be 63 years of reserves at current rates of production, but only 31.5 years if we doubled coal production.
The thermal efficiency of liquefaction is roughly 50–60 %; hence, only half the coal energy used in liquefaction will come out as the energy available in the CTL fuel. And there may be other losses. An inconvenient truth about coal is that it is a dirty fuel. If carbon capture and sequestration were to be required, 40 % of the remaining energy in a liquid coal power plant would be consumed.
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