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MAGNETO HYDRO DYNAMIC POWER GENERATION (MHD)

complete guide on mhd generator

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MAGNETO HYDRO DYNAMIC

POWER GENERATION (MHD)

CONTENTS INTRODUCTION HISTORY INTRODUCTION PRINCIPLE CONSTRUCTION WORKING COMPONENTS TYPES ADVANTAGES DISADVANTAGES APPLICATIONS CONCLUSION

INTRODUCTION Magneto hydro dynamics (MHD) (magneto fluid dynamics or hydro magnetics) is the 

academic discipline which studies the dynamics of electrically conducting fluids. Examples of such fluids include plasmas, liquid metals, and salt water.

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

This is a device that transforms thermal energy and kinetic energy into electricity.

MHD power generation provides a way of generating electricity directly from a fast moving stream of ionised gases at high temperatures without the need for any moving mechanical parts - no turbines and no rotary generators

In advanced countries MHD generators are widely used but in developing countries like INDIA, it is still under construction, this construction work in in progress at TRICHI in TAMIL NADU, under the joint efforts of BARC (Bhabha atomic research center), Associated cement corporation (ACC) and Russian technologists.

HISTORY The field of MHD was initiated by Hannes Alfvén , for which he received the 

Nobel Prize in Physics in 1970. Michael Faraday in 1832 carried out an experiment at the Waterloo Bridge in Great

Britain for measuring the current, from the flow of the river Thames in earth's magnetic field.

1920s and ’30s, Bela Karlovitz, a Hungarian-born engineer, first proposed a gaseous MHD system

In 1938 Bela Karlovitz and Hungarian engineer D. Halász set up an experimental MHD facility at the Westinghouse Electric Corporation research laboratories and by 1946 had shown that, through seeding the working gas, small amounts of electric power could be extracted

In 1959 the American engineer Richard J. Rosa operated the first truly successful MHD generator, producing about 10 kilowatts of electric power.

By 1963 the Avco Research Laboratory, under the direction of the American physicist Arthur R. Kantrowitz, had constructed and operated a 33-megawatt MHD generator

PRINCIPLE MHD power generation process is governed by M.Faradays law of Electromagnetic

Induction. (i.e. when the conductor moves through a magnetic field, it generates an electric field perpendicular to the magnetic field & direction of conductor). The flow of the conducting plasma through a magnetic field at high velocity causes a voltage to be generated across the electrodes, perpendicular to both the plasma flow and the magnetic field according to Flemings Right Hand Rule .

The Lorentz Force Law describes the effects of a charged particle moving in a constant magnetic field. The simplest form of this law is given by the vector equation:

F = Q * ( v * B )where F is the force acting on the particle. v is the velocity of the particle Q is the charge of the particle B is the magnetic field.

PRINCIPLE

MHD generator resembles the rocket engine surrounded by enormous magnet. It has no moving parts & the actual conductors are replaced by ionized gas (plasma) The magnets used can be electromagnets or superconducting magnets Superconducting magnets are used in the larger MHD generators to eliminate one of the large parasitic

losses. As shown in figure the electrodes are placed parallel & opposite to each other. It is made to operate at very

high temperature, without moving parts.

Because of the high temperatures, the non- conducting walls of the channel must be constructed from an exceedingly heat-resistant substance such as yttrium oxide or zirconium dioxide to retard oxidation.

CONSTRUCTION

CONSTRUCTION In conventional generator or alternator, the conductor consists of copper windings or strips while in an

MHD generator the hot ionized gas or conducting fluid replaces the solid conductor. A pressurized, electrically conducting fluid flows through a transverse magnetic channel walls field in a

channel or duct. Pair of electrodes are located on the at right angle to the magnetic field and connected through an external

circuit to deliver power to a load connected to it. Electrodes in the MHD generator perform the same function as brushes in a conventional DC generator.

The MHD generator develops DC power and the conversion to AC is done using an inverter. The MHD system constitutes a heat engine, involving an expansion of the gas from high to low pressure

in a manner similar to that employed in a conventional gas turbogenerator . In the turbogenerator, the gas interacts with blade surfaces to drive the turbine and the attached electric generator.

WORKING

It is the generation of electric power utilizing the high temperature conducting plasma (stream of high temp working fluid) moving through an intense magnetic field.

It converts the heat energy of fuel (thermal energy) directly into electrical energy The fuel is burnt in the presence of compressed air in combustion chamber. During combustion seeding materials are added to increase the ionization & this ionized gas (plasma) is

made to expand through a nozzle into the generator. Magnetic field, a current is generated & it can be extracted by placing electrodes in a suitable stream. This

generated EMF is DC

WORKINGIonization of GAS: Various methods for ionizing the gas are available, all of which depend on imparting sufficient energy to

the gas. The ionization can be produced by thermal or nuclear means. Materials such as Potassium carbonate or Cesium are often added in small amounts, typically about 1% of

the total mass flow to increase the ionization and improve the conductivity, particularly combustion of gas plasma.

90% conductivity can be achieved with a fairly low degree of ionization of only about 1%.

WORKING FLUID:

The Plasma: creating and managing the conducting gas plasma since the system depends on the

plasma having a high electrical conductivity. the fourth state of matter after the solid, liquid and gaseous states, in which the

atoms or molecules are stripped of their electrons leaving positively charged ions. Suitable working fluids are gases derived from combustion, noble gases, and alkali

metal vapours.

The Gas Plasma: To achieve high conductivity, the gas must be ionised by detaching the electrons

from the atoms or molecules leaving the positively charged plasma. The plasma flows through the magnetic field at high speed, in some designs, more

than the speed of sound, the flow of the positively charged particles providing the moving electrical conductor necessary for inducing a current in the external electrical circuit..

Containment: Since the plasma temperature is typically over 1000 °C, the duct containing the

plasma must be constructed from non-conducting materials capable of withstanding these high temperatures

The electrodes must of course be conducting as well as heat resistant

Power Output: The output power is proportional to the cross sectional area and the flow rate of the ionised plasma Output of 30 MW-75 MW is known till date. An MHD generator produces a direct current output which needs an expensive high power

inverter to convert the output into alternating current for connection to the grid The power generated per unit length by MHD generator is approximately given by,

Where ,u is the fluid velocity, B is the magnetic flux density, σ is the electrical conductivity of conducting fluid and P is the density of fluid.

Efficiency: Typical efficiencies of MHD generators are around 20 to 30 percent mainly due to the heat

lost through the high temperature exhaust. Total plant efficiencies of 65% could be possible in combination with other energy plants. Like all heat engines, the thermal efficiency of an MHD converter is increased by supplying

the heat at the highest practical temperature and rejecting it at the lowest practical temperature.

Experience: Demonstration plants with capacities of 50 MW or more have been built in several countries

but MHD generators are expensive Typical use could be in peak shaving applications but they are less efficient than

combined-cycle gas turbines which means there are very few installations and MHD is currently not considered for mainstream commercial power generation.

TYPES OF MHD POWER GENERATION

BASED ON CYCLE

Open cycle MHD Closed cycle MHD

Seeded inert gas system Liquid metal system

OPEN CYCLE MHD

Temperature in OC MHD is about 2500oC

Working fluid-potassium seed combustion product.

DC Superconducting magnets of 4~6Tesla are used.

Here exhaust gases are left out to atmosphere & the capacity of these plants are about 100MW.

OPEN CYCLE MHD

CLOSED CYCLE MHD

•Working fluid-cesium seeded helium

•. Temperature of CC MHD plants is very less compared to OC MHD plants. It’s about 1400oC.

•DC Superconducting magnets of 4~6Tesla are used. •Here exhaust gases are again recycled & the capacities of these plants are more than 200MW

CLOSED CYCLE MHD

Seeded inert gas system

Liquid metal system

ADVANTAGES In MHD the thermal pollution of water is eliminated. (Clean Energy System) It contribute greatly to the

solution of serious air and thermal pollution faced by steam plants. Use of MHD plant operating in conjunction with a gas turbine power plant might not require to reject any

heat to cooling water.

These are less complicated than the conventional generators, having simple technology.

There are no moving parts in generator which reduces the energy loss.

These plants have the potential to raise the conversion efficiency up to 55-60%. Since conductivity of plasma is very high (can be treated as infinity).

It is applicable with all kind of heat source like nuclear, thermal, thermonuclear plants etc. Extensive use of MHD can help in better fuel utilization.

Direct conversion of heat into electricity permits to eliminate the turbine (compared with a gas turbine power plant) or both the boiler and the turbine (compared with a steam power plant) elimination reduces losses of energy.

DISADVANTAGES The construction of superconducting magnets for small MHD plants of more than 1kW electrical capacity

is only on the drawing board.

Difficulties may arise from the exposure of metal surface to the intense heat of the generator and form the corrosion of metals and electrodes.

Construction of generator is uneconomical due to its high cost.

Construction of Heat resistant and non conducting ducts of generator & large superconducting magnets is difficult.

MHD without superconducting magnets is less efficient when compared with combined gas cycle turbine.

APPLICATIONS Power generation in space craft.

Hypersonic wind tunnel experiments.

Defense application

CONCLUSION

Improvement in corrosion science & superconducting magnets can make rapid commercialization possible.

Saving billions of dollars towards fuel prospects of much better fuel utilization.

It can therefore be claimed that the development of MHD for electric utility power generation is an objective of national significance.

The practical efficiency of this type of power generation will not be less than 60%. Hence it will be most significant in upcoming decade

REFERENCES Journel of Yoshihiro OKUNO Department of

Energy Sciences Tokyo Institute of Technology http://www.britannica.com/technology/

magnetohydrodynamic-power-generator https://en.wikipedia.org/wiki/

Magnetohydrodynamic_generator

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