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what is it? Converting coal to a liquid fuel is known as coal liquefaction and can be done in two ways; direct liquification, where the coal is dissolved at high temperature and pressure and then refined; and indirect liquification, where it is ‘gasified’ to form a ‘syngas’ (a mixture of hydrogen and carbon monoxide), which is then condensed to make a liquid fuel. Both processes require large amounts of energy.
Coalandgas to Liquids ( Synthetic Liquid Fuels)
TURNING COAL OR NATURAL GAS INTO LIQUID FUELS. PROCESS WASTES A LOT OF ENERGY AND HAS SERIOUS CONSEQUENCES FOR WATER RESOURCES AND CLIMATE CHANGE.
Converting gas to liquids (GTL) can also be done using two methods, via direct conversion, or indirectly by converting first to syngas then using the Fisher-Tropsh process. The Fischer-Tropsch process was invented in the 1920s by two German chemists. The process was used to produce liquid fuel from coal during the Second World War as Germany lacked access to sufficient crude oil. The advent of cheap oil led to the technology being largely abandoned. Several direct conversion processes have been developed but have proven uneconomical. So far only indirect methods have been commercialised.1 Coal to liquids (CTL) technology was re-invigorated in the 1950s in South Africa when the country was isolated during apartheid, and it remains the only country with significant commercial CTL operations. However, as most transport infrastructure around the world is dependent on liquid fuels (particularly cars and planes), and with conventional oil reserves slowly running low, there is huge demand for alternative liquid fuels. Converting coal and gas to liquid fuels also means some countries can use their own resources for transportation fuel instead of being dependent on foreign imports. Another attractive feature of synthetic liquid fuels from coal and gas is that they can be used to create various chemicals traditionally made from crude oil.
Coal can also be converted to gas (coal gasification) using a process which is also very energy inefficient. This can be carried out underground, which results in serious greenhouse gas emissions, groundwater pollution, and other environmental problems (see Underground Coal Gasification factsheet for more information) Note that GTL technologies are different from Liquefied Natural Gas (LNG). LNG is where natural gas is cooled and pressurised so it condenses into a liquid. It needs to be maintained at the correct temperatures and pressure in order to remain in liquid form. The processes for making and transporting LNG also use large amounts of energy.