This invention relates to generating electricity. More particularly, it relates to magnetohydrodynamics systems which utilize a liquid metal moving by gravity through a magnetic field to generate electricity.
The most common method of generating electricity is by rotating conductors in a magnetic field. This method results in an induced electromotive force or EMF. Large high-speed turbines are utilized in power plants to generate electricity using this method. In order to turn a heavy turbine it is necessary to use large mechanical forces. Pressure generated by steam, which is normally formed by heating water with burning coal or nuclear energy is the preferred force. In some cases hydro power from dams is used to turn the turbines. However because of the conversions of heat energy to mechanical energy and the mechanical energy to electrical energy as well as because of a large number of precision moving parts the above-referenced types of electricity generation are very expensive.
Recently another type of EMF generator has been developed which is referred to as liquid metal magnetohydrodynamics (MHD) system. In a MHD plant high speed turbines are not utilized nor is super hot high pressure steam utilized. A reservoir of liquid metal, such as wood's alloy, is maintained just above the melting temperature of the metal. The reservoir is in an elevated position. A vertically oriented tube carries the liquid metal from the reservoir by gravity past a magnetic field with electrodes being attached to the tube within the magnetic field. As the liquid metal passes through the magnetic field electromotive force is generated across the electrodes due to the movement of the liquid metal. One of the great advantages of using MHD is that metals may be used having low melting points, e.g. below 212.degree. F., therefore low grade waste heat made be used.
Once the liquid metal has passed the magnetic field it must be pumped back up to the reservoir via a lift tube. The technical problem of moving the liquid metal back into the reservoir has been dealt with what is believed to be only limited success by Professor Herman Banover of Ben Gurion University of Israel and Dr. Michael Pertrick of the Argon National Laboratory in Chicago. Basically the Banover and Pertrick solution which is outlined in an article by John Free, Titled "Now: Liquid metal MHD" appearing in the July 1985 issue of Popular Science, is to inject air vapor into the lift tube return path forming a large number of bubbles each acting as a small air piston to push the liquid metal into the elevated reservoir. It has been found that this method of moving the liquid metal into the reservoir has several drawbacks. First of all it takes a great amount of vapor to move the liquid up the lift tube, i.e. approximately five volumes of vapor for one volume of molten material. Furthermore the system is very inefficient because the liquid metal is normally very dense. Also since Banover and Pertrick must minimize the slip between the bubbles and the liquid metal they must choose metals having certain specific surface tensions. Therefore the choice of metal alloys become very limited. It is believed that the alloys chosen by Banover and Pertrick contain mercury which is very expensive and potentially dangerous to the environment.