Japanese researchers have found a way to burn lignite cleanly, and could potentially make scrubbing filters on power plants unnecessary.
Researchers at the Japan Chemical Innovation Institute and the National Institute of Materials and Chemical Research have combined supercritical steam at 600°C and 300 atmospheres with sodium hydroxide, and hydrogen peroxide as an oxidiser. These were burnt with lignite in a closed pressure chamber. When the coal had been burnt, the mixture was pumped out and the liquids and gases separated.
The nitrogen from the lignite formed ammonia rather than NOx. By varying the temperature of the supercritical steam, the researchers were able to vary the amount of ammonia produced. The carbon was completely oxidised to CO2 rather than forming toxic CO. The sodium hydroxide neutralised sulphuric or nitric acid. Only 1 per cent of the sulphur ended up as SO2 or SO3.
There is a problem. A way has to be found to introduce a large amount of combustible material into a pressurised chamber.
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