In our very first issue in Sept. 1973 we wrote about "An Orphan Called MHD"¾magnetohydrodynamics, a way to generate electricity from coal or other fuels without the intermediary of steam, in fact, without any moving parts at all: The only thing that moves is a jet of gas at a high temperature.
Michael Faraday (1791 - 1867) himself suggested the method, but only today is technology getting close to the materials of the required mechanical, thermal, and electrical strengths. Faraday's Law says that a voltage (electrical pressure) is induced in a conductor when the conductor is moved through a magnetic field (anyway, that's close enough to what it really says). In all of our present large-scale generators of electricity the conductors are copper coils, and the moving is done by machines converting heat (or the energy of falling water) to motion.
Now what makes a conductor a conductor are the free electrons (unattached to atoms) in it. Metals are particularly rich in such free electrons, but hot gases have them too, particularly when they are "seeded" with materials to increase their conductivity, such as potassium. If a jet of such a hot, ionized gas (a "plasma") is forced at high velocity through a "channel" (a tapered tube with rectangular cross-section) in a strong magnetic field directed perpendicular to the flow, a voltage can be tapped off electrodes in the walls of the channel at right angles to both the flow and the magnetic field.
There is thus no steam, nor any moving parts. Moreover, the exiting gas is still hot enough to drive a gas turbine, so that the overall efficiency of the two generators in series is 50% or more¾some 10% above that of the most efficient steam plants.
(The most efficient fossil-fired plants reach about 41%, the most efficient¾non-breeding¾nuclear plants about 39%.)
The main obstacles¾as so often in engineering¾used to be the materials (contradictory requirements for thermal and electrical conductivity, see AtE Jan. 77) and the superconducting magnets producing a sufficiently intense magnetic field.
The leading MHD research in the US is done by AVCO Everett Research Labs in Massachusetts, which at our last report had logged 95 hours' operation at 200 kW in 1976. Longer runs were not possible then because of thermal stresses at 5000 degrees F and coal-slagging (clogging up the channel walls). In August of last year, however, AVCO made a run of 250 hours, and in January of this year, a successful run of 500 hours was made.
Meanwhile, Argonne National Lab in Illinois built a 40-ton superconducting magnet capable of producing an intense magnetic field for an MHD generator of 250 MW capacity followed by a conventional 300 MW steam turbine generator powered by the exiting hot gases. Construction of the plant was begun this year; it should go on line in 1985.
Where?
In Ryazan, on the Oka River, some 125 miles southeast of Moscow. "The most significant event in Soviet-American scientific cooperation since the Apollo-Soyuz space flight," gushed an enraptured DoE spokesman.
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Vol. 7, No. 3
Newsletter: Access to Energy Newsletter Archive Volume: Volume 7 Issue/No.: Vol. 7, No. 3 Date: November 01, 1979 02:52 PM Title: Hairshirts or energy?
Copyright © 2004 - Access to Energy Newsletter Archive
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