MHD Power Generation Introduction •Shortage of conventional Energy Sources.

•Non Conventional Sources of Energy.

•Geothermal Energy

•Tidal Energy

•Solar Energy

•MHD Energy

•Works on nature of plasma

•Potential proposed by Arthur Kantrowitz in 1959

•Faraday and MHD

•Avco-Everett Research Lab. & it’s development.

Simplified Constructional figure

Simplified MHD generator•Faraday’s law of electromag. Induction

•Temp. effects with & without seeding.

•Hall effect•P=(1/4)*(sigma)*(V*B)2

•Power Densities:

10-500 MW/ cubic cm.

•Field Req. 4.5-6 Teslas Partially cooled hafnia and thoria - As insulator.

Doped Zirconia - As electrode.

Potassium / Cesium - As seeding elements.

Inconel - Heat resistant alloy from which ducts are made.

Advantages of MHD system•The efficiency of MHD power plant with steam power plant will be equal to 50% ,while the efficiency of best working steam power plant is 40%.•Very high output power density(10-500 MW/cubic cm.)•No moving part; so more reliable.•The closed cycle MHD produce pollution free power.•It has ability to reach at full power level as soon as started.•The size of the plant is considerably smaller than conventional fuel plats.•Direct conversion of heat in to electricity permits to eliminate the gas turbine . This elimination reduces losses of energy.

Problems in designing•Temperature without seeding == 4000-5000 K.

•Without seeding == 3000 K still pauses a problem.

•Attack by ‘seeds’ on insulating material.

•Combustion gases may cause Erosion of Electrodes.

•Slag & seed recovery is somewhat difficult.

•Economy of stand alone MHD is low.

Liquid *, 1/Ohmm

Weak electrolytes 10-4 to 10-2

Strong electrolytesWater+25% NaCl (20C)Pure H2SO4 (20C)

101 to 102

21.6 73.6

Molten salts (FLiNaBe, FLiBe at 500C ) ~ 150

Liquid metalsMercury (20C)

106 to 107

1.0106

Abdou Lecture 4 7

*, electrical conductivity (1/Ohmm), shows ability of liquid to interact with a magnetic field

MHD Power generation Kshitij 2002

•According to the faraday law of electromagnetic induction, Here the magnetic field is perpendicular direction to the channel axis & when the plasma is flowing, the emf is generated; which is perpendicular to both plasma flow & magnetic field

• So, here the electric field vector has a component both along the channel & across the channel

•Here the loads are connected to each separate electrode pair & the electrode segment are separated by insulator segments.

Segmented faraday Gen.

Hall type Generator•When the faraday current is produced, the hall current is also produced in the perpendicular direction to the faraday current.

•In this type of generator; each electrode pair is short circuited out side the generator & load is

Connected between the electrodes at the two ends of MHD generator to get only hall EMF.

• Due to this action the electric field becomes parallel to the channel axis.so that there can’t be any potential difference across the channel.

•This generator is the best alternative of linear type hall generator, it avoids the problem which occurs in linear type hall generator like use of super conducting magnets.

•It has advantage that, it has continuous & radial flow of plasma.

•Here the faraday current is short circuited & only the hall current is flowing & we get Hall emf between the center & the Outer periphery of the disk.

Disk Type Generator

Open Cycle MHD Generator

Fuel+Seed

MHD

Generator HP LP

C.C.

Gas in

Electromagnet

Air preheaterSeed Recovery

CondensorCompressor

Air inOutput to grid

Invertor

Boiler Super Heater Reheater

To Atm.

Conventional Steam Power Plant

MHD

GeneratorFast

Breeder

Reactor

Pump

Pump

Condensor

SeperatorInvertor

Nozzle

Closed cycle MHD Generator

Types of working fluids used

•Gaseous Fluids•Chemically inert gases with oxygen are used•Plasma State can be achieved by heating up to 3000 K •These need to be ionized by seeding.

•Liquid Fluids•Includes Liquefied metals as their thermal conductivity is nearly 10e6 times that of plasma.

•Research is in progress on this type fluid using power plant. •Alkali metals like Potassium used as working fluids.

Summary:

Mhd is gaining ground in many parts of the world. Much stress on R&D in many scientifically advanced countries. However it is yet to make a major impact in India, where the pre-capita consumption is abysmally low, And there is an urgent need of the day to increase power supply cheaply, pollution free & fast.