Science: Gas in the Generator

Electric-power production is a conservative business; it makes electricity just as it did more than a century ago—by driving copper wires through magnetic fields. That is all that happens in the huge, spinning generators of a power station. The rest of the massive apparatus—furnaces, boilers, turbines, condensers, etc. —is only to make the generators spin. Last week Avco Corp. described an infant invention that may grow into a wholly different and more efficient way to generate electricity.

Avco’s apparatus, called a magneto-hydrodynamic (MHD) electric generator, works on the principle that any conductor of electricity that is moved through a magnetic field will generate in itself a current of electricity. This applies not only to copper wires (as in conventional generators), but to gases, which become conductors when they are made so hot that some of their atoms separate (ionize) into electrically charged particles. If forced through a magnetic field, a stream of ionized gas causes an electrical current to flow across it. This principle has been known for years, and many efforts have been made to apply it practically, but the trick is not easy. The gas must be so hot (at least 4,000° F.) that it destroys many structural materials. Another problem is the poor conductivity of most gases.

Through a Cone. After ten years of study, Avco scientists built a laboratory model MHD that produces 10 kw. of 55-volt electricity. This is hardly enough to run a gadget-filled kitchen, but ten big U.S. power companies have now joined with Avco to help develop MHD generators big enough to supply commercial power. A major advantage: an MHD generator has no primary moving parts, with the exception of those in the relatively simple compressor.

Avco is working on two MHD generators. One of them will burn coal in a stream of compressed, preheated air. While passing through the flame, the air gets hotter, expands and rushes out of the furnace at high speed. A small amount of potassium chloride fed into it increases its ionization and makes it a better electrical conductor. Then the stream shoots into a hollow cone made of a heat-resisting, nonconducting material (see diagram). Electrical coils outside the cone create a strong magnetic field. As the gas speeds through, a powerful current of electricity flows across it and is collected by two electrodes inside the cone.

From Nose Cones. Most of the electricity generated by the system comes from the electrodes, but waste heat can be harnessed to drive a conventional turbogenerator, adding importantly to the system’s efficiency. Overall, Avco scientists estimate that a 450,000-kw. coal-fired MHD generator will produce electricity with the sensational thermal efficiency of 55%. The best that conventional plants can do is 40%.

Even more exciting is the possibility of using the MHD system with a nuclear reactor. In this case the gas will probably be argon or helium, laced with cesium to make it more conductive. It will circulate through the reactor, then through the generator and back to the reactor again. This system will have to wait for the development of high-temperature reactor cores, but Project Rover, the Atomic Energy Commission’s nuclear-rocket program, has shown that the prospects of this are promising.

Avco started its study of magnetohydrodynamics (the behavior of “plasmas” of ionized particles) to help make better nose cones for long-range missiles. “It was very pleasant,” says Dr. Arthur Kantrowitz, head of Avco’s Everett, Mass. laboratory, “to get something of peaceful value out of military research.”