Energy question of the week: How can coal be converted into liquid fuel?
When oil becomes scarce, fuel for aircraft and cars will have to be produced from other sources. Since Franz Fischer and Hans Tropsch invented the Fischer-Tropsch process in 1925, synthetic fuels can also be derived indirectly from coal. Countries with large coal deposits, such as South Africa and China, make extensive use of this process. But how does the process work?
The most efficient way to transform solid coal to liquid fuel is to first produce a synthetic gas. This is done by heating coal to above 1000 degrees Celsius. Adding steam and oxygen to the heated coal produces the synthetic gas. Catalyst-induced reactions during this intermediate stage, which is rich in carbon monoxide and hydrogen, produce hydrocarbons that are liquid under normal conditions. Depending on the conditions, the reaction can be used to produce petrol, kerosene, diesel and other substances such as aromatics for the chemical industry.
The history of 'petrol from coal'
In Germany, the Fischer-Tropsch process was of strategic importance to Germany in the 1930s and 40s, since at that time it had almost no access to oil wells but had extensive coal deposits. The trade embargo during South Africa's apartheid era also led to widespread use of the process. China is producing increasing amounts of petrol from its coal deposits as the country's hunger for energy grows. Numerous new plants throughout the country have brought production up to around 40 million tons a year.
Coal is not the only substance suited to such methods of fuel production. Natural gas can also be used, in combination with steam and oxygen, to produce synthetic gas and thus fuel. DLR's Institute of Combustion Technology (Institut für Verbrennungstechnik) in Stuttgart has a team of about 20 researchers working under Institute Head Manfred Aigner to improve current technology. With a focus on aviation, they are endeavouring to improve the quality of synthetic kerosene. "We have around 50 parameters we can manipulate to optimise the process," says Aigner. The aim is to develop an aviation fuel with optimal ignition and combustion qualities, which will maximise performance while minimising emissions.
The future – carbon-neutral biofuels
The Stuttgart team is in great demand internationally. For example, they are working with partners in the EU Alfa-Bird project to develop a plan for alternative fuels. They are also working on collaborative projects with numerous companies, including Shell, Rolls-Royce and the Qatar Science and Technology Park. They certainly won't have a shortage of work for the foreseeable future. After coal and natural gas, biomass is becoming ever more important for liquid fuel production – with the enormous advantage that it is carbon neutral, and does not contribute to the greenhouse effect.
For further information:
DLR Institute for Combustion Technology
The DLR Energy question of the week in 'The future of energy' Year of Science
The Federal Ministry of Education and Research (BMBF) has given the Year of Science 2010 the motto 'The future of energy'. For this reason the science journalist Jan Oliver Löfken will this year answer a question on the subject of energy in his blog each week. Do you have a question about how our energy supply might look in the future? Or do you want to know, for example, how a wave power plant works and how it can efficiently generate electricity? Then send us your question by email. Science journalist Jan Oliver Löfken will investigate the answers and publish them each week in this blog.