Magneto Hydrodynamic Generation (MHD)

Magnetohydrodynamic is the branch of science which deals with the study of physics background of conducting plasma.The electrical energy is obtained from high temperature conducting plasma, highly intense magnetic field.

MHD Generator

Suppose  charge particle "q" moves with a velocity of "v" right angle to the magnetic field, it means two plates p as shown, then magnetic force is given by,

If this charged particle q is replaced by a mass of ionized gas with same velocity v then positive ions accelerates toward upper plate and negative ions to the lower plate.

If this plates are connected externally through resistance  then current start flowing through resistance thus electrical power is generated by extracting the mechanical power of ionized gas.

This is the principle of Magnetohydrodynamic generation called direct form of generation  from heat without the necessity of any accessories as in Steam Power Plant.

Working principle of Magnetohydrodynamic Generation

There are two types of cycle in Magnetohydrodynamic generation:

1. Open cycle MHD generation
2. Closed cycle MHD generation.

1. Open Cycle MHD generation

Open Cycle MHD Generation

In above figure you can see that open cycle MHD generation consisting of a MHD generator resembles shape of a  rocket engine. Coal or natural gas is burned into combustor to produce hot gases. The hot gases is then seeded with alkaline metals ( cesium or potassium ) to increase electrical conductivity of of the gas. This gas then enters into a MHD generator which is rocket engine shaped in which gas expands and electrical power is generated by accelerating gas ions towards electrode and strong magnet. 

          Air preheater is used to preheat the air which is used as input hot air to the combustor. Later on seed material is recovered from the gas and next on Nitrogen and Sulphur is extracted from the gas to avoid air pollution and then flue gases are exhausted to the atmosphere with the help of stack. The output of MHD generator which is surrounded by the huge magnet is in the form of DC and then that DC is converted into AC with the help of inverter.

2. Closed Cycle MHD generation         

         

Closed Cycle MHD Generation

• HX1& HX2 - Heat exchanger 1 & 2
• S.T. - Steam Turbine
• CP - Compressor Product
• P - Removal of Nitrogen and Sulphur
• CS - Cessium injection

          Closed cycle MHD generation consist of three distinct part but interlocked with each other. In figure, at very left side heating loop in which air, coal and steam is used to be converted into gasifier form at a temperature of 520℃ and this heated gas is then fed to the combustor in which Argon gas is heated. The combustor product passes through the air preheater which preheats the air and then fed as input to the combustor. After air preheater removal of Nitrogen and Sulphur from the flue gases to decrease the air pollution and then this gas is exhausted to the atmosphere through stack.

         Heated Argon gas is fed to the MHD generator which resembles rocket engine shape surrounded by the huge magnet.

         During the expansion of the Argon gas into MHD generator, conversion of mechanical energy into electrical energy take place and then converted into 3Ø AC with the help of inverter. The speed of the gas is slowed down with the help of diffuser and then heat of the gas is utilized in heat exchanger 2 and water get get converted into steam. Steam is partially used to drive compressor and partially used to generate electrical power with the help of alternator. The Argon gas is recycled and fed back to heat exchanger 1 through the compressor and intercooler.