Coal power with a d spells cash

3 June 2003

The two biggest-rival solid fuels must surely be coal and nuclear. The latter is often accused, unfairly, of presenting insoluble waste-disposal problems. But the former does, in this respect of waste disposal at least, have one decided and well-documented lead over its competitor.

Coal-fired power stations generate about 37 per cent of humankind's electricity, and many of them burn their fuel more efficiently by taking it in as coal powder. Pulverised or not, up to a fifth of coal is nonetheless incombustible, so a 2000 MWe station can turn out a megaton of ash in a year. Pulverised coal ash is mostly fine powder ­ 'fly ash' ­ carried out in furnace exit gases, but some coarser stuff comes out of the furnace bottom. Both forms are recovered and can be put to good use. The byproducts made from pulverised fuel ash (pfa) often sell for more money than the ash would cost to dispose of as waste.

None of this is news to you, I know. Pfa byproducts have been going into an increasing number of markets for many years, serving more industries than I have room to name. (Let me just mention cenospheres, though, because I think them the cutest pfa byproduct. These particles are just amazingly light and strong hollow glass balls filled with CO gas. They are splendid for foundry-patternmaking, filling plastic and paint, foam-stuffing glass-fibre sandwich panels, doing their bit in fire-resistant boarding and so on: and they make exceedingly good putty.)

What may surprise you, as I admit it did me, is the extent and completeness with which the ash can be magicked from waste-product into commercial byproduct. I have seen a 'best practice' brochure, issued by a UK government department, that describes how far the art has been advanced at a 2000 MWe coal-fired station at Didcot, England. But, according to this brochure, the remarkable progress continues. The suggested goal of yet further development ­ both of products and of markets ­ at Didcot is one hundred per cent utilisation. That's right, the lot. The other big-time solid fuel will surely never compete with that, over such a variety of product lines: will it?

Nuclear engineers who want to know what they are up against, and any other power engineers who need to know the state of the art of ash utilisation in pf stations, could do worse than try tapping Didcot for information. The address is Innogy plc, Didcot Power Station, Didcot, Oxfordshire OX11 7HA, United Kingdom.

History (almost) repeats itself

Funny how the old stagers are coming back. During last century's seventies, when politically engineered energy crises began to be big global business, a hunt followed for 'alternatives' to oil and other fossil fuels. The energies of winds, tides, sea waves, falling and flowing water, solar radiation, hot geological strata, submarine currents and other phenomena ­ already at times exploited in one small way or another, perhaps since antiquity ­ became popular candidates for restoration to use, in modern guise, to such modern ends as power generation.

Some truly imaginative, not to say fanciful, ideas were enthusiastically aired. They included towers to trap winds and turn them into turbine-driving internal tornadoes, ponds filled with cunningly layered saline water to collect solar heat, photovoltaically carpeted deserts, volcano-tapping power stations and, of course, even if incognito, some perpetual motion machines.

Gradually the political imperatives have given way to environmental ones concerning pollution, the depletion of natural resources, sustainability and climate change. Some of those twentieth-century 'alternative energy' ideas, put into cold storage after research, are being revived because the imperatives have been revised. I rather like two that have made comebacks lately. One is the turbogenerator-driving 'solar chimney' for sunny undeveloped territory (MPS, August 2002). The other is the drawing of geothermal energy from deep and dry subterranean rock to raise steam in power stations (MPS, October 2002). These have whetted my appetite for more.

Maybe even as I write, an ingenious mind is being applied to re-opening the studies of a researcher who is on record as having 'been eight years upon a project for extracting sun-beams out of cucumbers, which were to be put into vials hermetically sealed, and let out to warm the air in raw inclement summers'. The reporter who wrote those words was the author of Gulliver's Travels, namely Jonathan Swift, who flourished in 1667-1745. Of course in those days there were not many people who knew that you could use sun-beams without cucumbers to make electricity.

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