Unlike Europe, where coal-fired power is about twice as expensive as nuclear, the two are comparable in the US, and with the astronomical costs imposed on nuclear power by political and judicial means, we must surely be approaching the time when coal-fired power becomes the cheaper type; this has, in fact, already happened in some parts of the country.
Nevertheless, coal has two economic drawbacks: high labor intensity and transportation problems. The latter are mainly problems of the railroads, which would find it difficult to compete with energy transported via grids and pipelines even if they were not overregulated by the government and milked to death by the unions.
It is therefore not surprising that intensive research to ship coal by pipeline is being carried out
¾see our previous reports on pneumatic and slurry pipelines [AtE Feb 82]. The railroads, judging by the ferocious resistance their lobbies are putting up in Washington, apparently consider pipelines superior to their own mode of transportation, an opinion shared by most other experts.However, slurry lines are not without disadvantages, one being the loss of water in places that sometimes cannot afford it, another the inconvenience and energy loss in separating the coal from water at the destination (usually by centrifuge). But the latter drawback can be eliminated by simply foregoing separation and burning the slurry, or Coal Water Mixture (CWM), as is.
You do not, of course, burn the water; on the contrary, you lose 3% to 5% of the coats thermal energy in the ("latent") heat required to change the water from liquid to vapor; but this and other costs may well be worth the advantage of transportation by pipepline almost directly into the boiler.
CWM's contain from 50% to 70% coal (occasionally more); the rest is water, often with chemical additives to improve (lower) the viscosity of the mix and to prevent the coal settling out of the slurry.
Research on burning CWM's has been going on for some two decades in the USSR and in Germany. In the Soviet Union, coal fields are abundant, but the coal must be transported over vast distances by a rickety railroad system that has never been far from the verge of collapse since the October Revolution. German projects, too, were successful, but were abandoned in the late 1960's, for there was little point in competing with oil at $2 a barrel.
US research, now carried out mainly by the Pittsburgh Energy Technology Center, is not aimed at systems optimizing CWM burning as is Russian and earlier German research: it is aimed at retrofitting existing oil-burning boilers for CWM. Test programs are now being run on oil-designed firetube and watertube boilers.
CWM burning degrades the performance of boilers
¾for example, the efficiency of burning the fuel drops from 99.8% for oil to the lower 80's, and the boiler efficiency from 82.9% to the upper 60's. Nevertheless, this may well be a price worth paying for converting oil-fired plants to coal¾a program that in spite of various government incentives has had remarkably little success. Besides, the present data come from small-scale experiments, and there seems to be good reason to hope that for larger volumes of watertube boilers there will be little degradation in performance.[More: "Why coal slurries stir worldwide interest" by Bergman, Kirkland and George, Coal Mining and Processing, Oct. 1982, pp.34-41.]
|
Vol. 10, No. 4
Newsletter: Access to Energy Newsletter Archive Volume: Issues Issue/No.: Vol. 10, No. 4 Date: November 23, 2004 03:36 PM Title: Put not your trust in princes (Psalm 143:3)
Copyright © 2004 - Access to Energy Newsletter Archive
|