Coal gasification

The term gasification covers the conversion of any carbonaceous material into a gaseous product with a usable calorific value (essentially CO, H ₂ , CH ₄ ). Coal gasification comprises an initial pyrolysis stage followed by partial oxidation producing a synthesis gas (or "syngas") comprising mainly CO and hydrogen in varying contents. The oxidant can be oxygen, air or steam. This technology developed rapidly between 1945 and 1955, before the use of natural gas, and then fluctuated according to the price and availability of oil and gas (see historical overview). Coal gasification can be used to produce a wide variety of products: electricity, chemicals, natural gas substitutes (SNG), transport fuels, and is of considerable interest in today's economic climate (figure 1 ).

Power generation has become a growth market for gasification, which is seen as a means of increasing the environmental acceptability of coal. The idea of using syngas in turbines is not new. As early as 1950, technical problems such as increasing the temperature in turbines were studied; prototypes were built in the USA and Europe, and commercial units have been in operation for some ten years. Major interest in the IGCC (Integrated Gasification Combined Cycle) emerged in 2003, with GE Energy acquiring Texaco technology in the USA and Siemens acquiring Future Energy technology in Europe.

The production of basic CTC (Coal to Chemicals) chemical intermediates is also booming (methanol, DME dimethyl ether, ammonia, olefins). Developments are taking place in the USA and mainly in China.

Coal gasification as a substitute for natural gas remains limited (Dakota unit – Beula), but numerous projects are under consideration in view of the rising price of natural gas.

Finally, indirect coal liquefaction (CTL, Coal To Liquids) for the production of synthetic fuels, via coal gasification followed by Fischer Tropsch synthesis, is attracting renewed interest beyond South Africa, in China as well as in...