High oil prices have drawn attention not only to biofuels, but also to a range of other liquid fuel alternatives. Large investments are being made in developing more difficult-to-access conventional oil resources located in remote areas or deeper waters, unconventional sources, such as oil sands and heavy crude oil, and the conversion of coal to oil. According to the US Department of Energy, while world oil production is expected to increase 30 percent by 2030, production from unconventional fossil fuels will increase even faster. One alternative source of energy is converting coal to oil, which is of particular interest to economies with abundant coal resources, such as South Africa, China, and the United States.
What is coal liquefaction?
The coal-to-liquids technology has been well-established for many decades. It was originally invented in Germany in the 1920s and developed there and in the US in the 1930s. During World War II Germany used to produce up to 600,000 barrels a day of petrol and avgas. There are two different methods for converting coal into liquid fuels:
Direct liquefaction works by dissolving the coal in a solvent at high temperature and pressure. This process is highly efficient, but the liquid products require further refining to achieve high grade fuel characteristics.
Indirect liquefaction gasifies the coal to form a ‘syngas’ (a mixture of hydrogen and carbon monoxide). The syngas is then condensed over a catalyst – the ‘Fischer-Tropsch’ process – to produce high quality, ultra-clean products.
Benefits of coal liquefaction
The coal liquefaction process has the added benefit of a wide range of by-products such as petrochemicals, waxes, feedstocks for plastics manufacture, and fuel gas. Moreover, coal-derived fuels are sulphur-free, low in particulates, and low in nitrogen oxides.The coal-to-liquid technology has been greatly improved in South Africa, especially during the years of Apartheid when there was a great national need to reduce dependence on foreign oil. Today, there are three large coil-to-liquid plants, operating in South Africa, converting coal into 150,000 barrels a day (equal to the output of a medium-sized oilfield). Consequently, unlike the rest of the developed world, South Africa does not need to worry about the oil-supply shock, as it supplies about 40% of its oil needs with the domestic coal-to-liquids technology.
South Africa’s success with the development and production of coal-to liquid has lead the US and China to take note and follow suite. The US has the world’s largest coal deposits, with 268 billion tons of recoverable reserves. At a standard conversion rate of two barrels of synthetic fuels from one ton of coal, US reserves are equivalent to 20 times the nation’s current crude oil reserves. Yet, the US it continues to import 60% of its oil requirements, 27% of which come from OPEC. Researchers estimate that it would take 70-100 coal-to-liquid plants in the US to replace all the oil currently being imported from OPEC. The average per-barrel production cost would be about $48, including the cost of carbon dioxide removal. China is also building its own coal-to-liquid plants and is less constrained by environmental concerns and regulations than the US.
Challenges of the coal-to-liquids technology
One of the most significant challenges related to the coal liquefaction process is the negative impact on the environment with its high production of carbon dioxide, known to be one of the causes of global warming. Efficient and effective carbon dioxide removal is a key consideration, since a standard coal -to- liquid plant produces about 2.5-times the carbon dioxide than a standard refinery puts out. At this point the technology is not effective enough to deal with the excessive greenhouse gas emissions.
An analysis by the US Department of Energy has found that liquid fuels from coal, even with carbon capture and storage employed, still produce at least 20% more carbon dioxide than petrol and diesel made from oil. Another problem is that the energy-intensive conversion plants also require massive amounts of cooling water to stop them overheating. Overall, while it is evident that coal-to-liquid production has the potential to significantly reduce our national and global dependence on oil, a lot more funding needs to be invested to make these technologies more environmentally safe, if they are to take the place of oil in the future.