In conventional power generation, fuel such as oil or coal is burned. The burning fuel heats boilers to produce steam. The steam is used to drive turbo-alternators. The MHD process generates electricity without requiring a boiler or a turbine.
MHD generation works on the principle that when a conductor cuts a magnetic field, a current flows through the conductor. In MHD generation the conductor is an ionized gas. Small amounts of metal are added to the gas to improve its conductivity. This is called seeding the gas. The seeded gas is the pumped at a high temperature and pressure through a strong magnetic field. The electrons in the gas are collected at an electrode. This movement of electrons constitutes a current flow.
Two methods of MHD generation can be used : the open cycle and the closed cycle. In the open cycle method the hot gas is discharged. In the closed cycle method it is recirculated.
The open cycle method uses gas from burning coal or oil. The gas is seeded and then passed through a magnetic field to generate current. The seeding elements are recovered and the gas can then be used to drive a turbine before being allowed to escape.
The closed cycle method uses an inert gas, such as helium, which is heated indirectly. The gas is circulated continually through the MHD generator.
MHD generation is still in its early stages but already an efficiency rate of 60% has been reached. This compares with a maximum of 40% from conventional power station.
