Fossil fuels produce emissions of carbon dioxide (CO2), sulphur dioxide (SO2), nitrogen oxides (NOx), particulate matter (dust) and other substances such as mercury. The Clean Coal technologies for controlling these emissions are at varying stages of development.
Switch to a cleaner fuel or reduce load to burn less of a ‘dirty’ fuel
Direct coal liquefaction converts coal to a liquid by dissolving coal in a solvent at high temperature and pressure. This process is highly efficient, but the liquid products require further refining by either ‘hydrocracking’ or adding hydrogen over a catalyst to achieve high grade fuel characteristics.
Indirect coal liquefaction first gasifies the coal with steam to form a ‘syngas’, which is a mixture of hydrogen and carbon monoxide. The sulphur is removed from this gas and the mixture adjusted according to the desired product. The syngas is then condensed over a catalyst, in the ‘Fischer-Tropsch’ process, to produce high quality, ultra-clean products.
An array of products can be made via these processes including ultra-clean petroleum and diesel, synthetic waxes, lubricants, and chemical feedstocks. A similar process, using different catalysts, will produce alternative liquid fuels such as methanol and dimethyl ether (DME). Efficiency and productivity can be improved by co-producing liquid fuels, electricity and chemical feedstocks in a process known as polygeneration.
The conversion of a fuel into a usable form such as electricity or gas is an inefficient process. By increasing the efficiency of the conversion process less fuel is required to produce a given amount of electricity and consequently fewer emissions are generated. Some measures apply to the generation of electricity in general, regardless of fuel used, such as: reducing losses during transmission by using superconductive wires or, distributed generation, in which the generators are located near to the load
centres, again reducing transmission and distribution losses.