MHD(Magneto Hydro Dynamics) Power generation tech.

Vipul kumar guptaEN third year0714321053

IntroductionMagneto hydrodynamic (MHD) is the academic

discipline which studies the dynamics of electrically conducting fluids.

The word magneto hydrodynamics (MHD) is derived from magneto- meaning magnetic field, and hydro- meaning liquid, and -dynamics meaning movement.

The MHD generator or dynamo transforms thermal energy or kinetic energy directly into electricity.

MHD generators are different from traditional electric generators in that they can operate at high temperatures without moving parts.

Facts about MHD Hannes Alfven was the first to introduce the term “MAGNETOHYDRODYNAMICS”. He described astrophysical phenomena as an independent scientific discipline.Hannes alfven (1908-1995) winning the Nobel prize in 1970 on his work on magneto hydro dynamics.

Principle of MHD Power Generation

MHD power generation uses the interaction of an electrically conducting fluid with a magnetic field to convert part of the energy of the fluid directly into electricityThe idea of MHD is that magnetic fields can induce currents in a moving conductive fluidWhen a conductive fluid flow through a intense magnetic field .A voltage is induced in it , which produces an electric current

Lorentz forceThe Lorentz Force Law describes the effects of a charged particle moving in a constant magnetic field.

F=Q.(V x B)F is the force acting on the particleQ is the charge of the particleV is the velocity of the particleB is the magnetic field

Types of MHD systems1. Open cycle systems

2. Close cycle systems

Open cycle systems In open cycle systems , the working fluid after generating

electrical energy is discharged to the atmospheres. Coal is burnt to produce hot gas . Hot gas is seeded with a

small amount of an ionized alkali metal to increase the electrical conductivity of the gas.

The gas expand through the generator surrounded by a magnetic field . During the motion of gas the positive and negative ions move to the electrode and constitute an electric current.

Seed material is recovered for successive use. This cycle is not suitable for commercial use . The exhausted

gases are still at a sufficiently hot temp . we can use it for additional power generation at steam turbine alternator

Closed cycle systemAs the name suggest the working fluid in closed

cycle. Working fluid is helium or argon with cesium feeding.

Coal is gasified and a gas having a high heat value and temp of about 530 C is burnt to produce heat.

This heat is transferred to argon , the working fluid of MHD cycle.

The DC power output of MHD generator is converted to ac and is then feed into the grid.

The working fluid is still sufficiently hot and is used to raise steam , which generate additional energy in a steam turbine alternator unit.

MHD system must have following featuresAir superheating arrangement to heat the gas

to around 2500 C so that the electrical conductivity of the gas is increased.

The combustion chamber must have low heat losses.

A management to add a low ionization seed material to the gas to increase it’s conductivity.

A magnet capable of producing high magnetic flux density.

Seed recovery apparatus necessary for both environmental and economic reasons.

MHD GeneratorsThe MHD generator or dynamo transforms

thermal energy or kinetic energy directly into electricity

MHD generators are different from traditional electric generators in that they can operate at high temperatures without moving parts

Types of MHD generatorsFaraday Generator Hall GeneratorDisc Generator

ComparisonTurbo Generator and MHD GeneratorThe basic concept underlying the mechanical and fluid dynamo is same. Fluid dynamo however uses the motion of fluid to generate the current , which generate electrical energey The mechanical dynamo, in contrast, uses the motion of mechanical devices to accomplish this

Faraday GeneratorA simple Faraday generator would consist of

a wedge-shaped pipe or tube of some non-conductive material

When an electrically conductive fluid flows through the tube, in the presence of a significant perpendicular magnetic field, a charge is induced in the field

This charge can be drawn off as electrical power by placing the electrodes on the sides at 90 degree angles to the magnetic field

Faraday Generator

Hall GeneratorThe normal scheme is to place arrays of short, vertical

electrodes on the sides of the duct. The first and last electrodes in the duct power the loadEach other electrode is shorted to an electrode on the

opposite side of the duct.These shorts of the Faraday current induce a powerful

magnetic field within the fluid, but in a chord of a circle at right angles to the Faraday current.

Losses are less than a Faraday generator, and voltages are higher because there is less shorting of the final induced current.

Hall Generator

Advantages of MHD power generation

The conversion efficiency of a MHD system can be 50% as compared to less than 40% for the most efficient steam plant.

It has no moving parts. So more reliable. It has the ability to reach the full power level as soon as

started.The more efficient heat utilization would decrease the

amount of heat discharged to environment.The higher efficiency means better fuel utilization. The

reduce fuel consumption would offer additional economic benefits.

The closed cycle system produces power free of pollution.

Following table shows the pollutant emission of a MHD plant and a conventional steam plant.Pollutant emission in tons per day based on use of coal having 3% sulphur content.

1000 mwc conventional steam plant

1000 mwc MHD plant using coal as a fuel

Particulate matter 33 3

Sulphur oxide 450 3

Nitrogen oxide 80 4

ApplicationPower generation in space crafts.

MHD generators have also been proposed for a number of special situations. In submarines

Hypersonic wind tunnel experiment.

Defense application.

Other uses of MHDThe “Yamoto”: a boat built by Mitsubishi powered

solely by MHD propulsionCan travel at up to 15 km/hr