magneto hydro dynamics seminar by vipul

7/31/2019 Magneto Hydro Dynamics Seminar by Vipul

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IntroductionIt is well known that man had always been trying to fined

Something new to achieve a new aims 80% of total electricity

produced in the

world is hydral while remaining 20% is produced from nuclear,

thermal, solar,Geothermal energy and from magneto hydro dynamic power

generation.

MHD power generation is a new system of

electric power

generation which is said to be of high efficiency and low

pollution. In advanced

Countries MHD generator are widely used but in developing

countries like India

it is still under construction. This construction work is in

progress at

Tiruchirapalli in Tamilnadu unders joint efforts of BARC

(Bhabha Atomic

Research Centre), BHEL, Associated cement corporation and

Russiantechnologists.

As its name implies, magneto-hydro-dynamic (MHD) is

concerned with the flow of conducting fluid in presence of

magnetic and


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electric field. This fluid may be gas at elevated temperature or

liquid metal like

sodium or potassium. A MHD generator is a device for

converting heat energyof fuel directly into electric energy without a conventional

electric generator.

The basic difference between conventional generator and MHD

generator is in

the nature of conductor.


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Principle of MHD power generation

The principle of MHD generation is simple, discovered by

faraday when an electric conductor moves across a magnetic field, aemf. Is

induced in it, which produced an electric current. This is the principle of

the

conventional generator also, where the conductors consists of copper

strips. In

MHD generator the solid conductors are replaced by a gaseous

conductor; i.e.

an ionized gas. If such gas is passed at high velocity through a powerfulmagnetic field, i.e. suppose we have a charged particle (having charge q)

moving at a high velocity V towards right and a perpendicular

magnetic field

is applied. A magnetic force F acts on the charged particle. Show in

fig. A

Positively charged particles as forced upward and negatively charged

particle

is forced downward.

The positive ions would be accelerated towards the upperplate P, and negative ions would be accelerated towards the plate P2 . If

the P1

and P2 are externally connected through a resistance, a current would

flow

through the resistance. Thus gas energy directly converted into electrical

energy. This is the principle of MHD generator. A MHD conversion is

known as

direct energy conversion because it produced electricity directly fromheat

source without the necessity of the additional stage of steam generation

as in

a steam power plant.


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Lorentz forceLorentz force law describes the effect of a charge particle moving in a

constant magnetic field.

F=Q.(V x B)


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MHD systems

There are two types of systems.1.open cycle system

2.closed cycle system

In open cycle system the working fluid after generatingelectrical energy is discharged to the atmosphere through a stack. In a

closed

cycle system the working fluid is recycled to the heat sources and thus

used

again and again. The operation of MHD generator directly on

combustion

products in an open cycle system. In open cycle system working fluid is

air. Inclosed cycle system helium or argon is used as the working fluid.


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An elementary open cycle MHD system is shown in fig. The

MHD generator resembles a rocket engine surrounded by a

magnet the coal is burnt to produce hot gas. The hot gas is then

seeded with a small amount of an ionized alkali metal (cesium or

potassium) to increase the electrical conductivities of gas. The

gas expand through the generator surrounded by powerful

magnet. During the motion of gas the positive and negative ions

move to the electrodes and constitute an electric current. The

rejected gas passes through an air heater for preheating the inlet

air. The seed material is recovered for successive use. Thenitrogen and sulphor are removing for pollution controlled and

then gasses are discharged to the atmosphere. The above cycle is

not suitable for commercial use. The exhaust gases of MHD unit

are still at a sufficiently hot temperature it is possible to use for

additional power generation in a steam turbine alternator unit.

This is increase the efficiency of process. Such cycle is known as

hybrid MHD-steam plant cycle. Figure shows hybrid MHD steam

cycle, coal is processed and burnt in the combustor at hightemperature (2750 to 3000 K) and pressure (7 to 15 at

atmosphere) with preheated air to form the plasma. The plasma is

then seeded with small fraction (1%) of an alkali metal

(potassium) introduced usually as a carbonate powder or solution.


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The resulting mixture having an electrically conductivity of about

10 ohm/m is expanded through a nozzle to increase its velocity

and then passed through the high magnetic field (5 to 7 teslas) of

the MHD generator. Electrodes channel provided electric contact

between flow and external load. The power o/p is dc and it is

necessary to use to change it to ac before the power can be fed

to an electric grid. The gas coming out of MHD generator is stillsufficiently hot and is used to raise steam, which generates

additional energy in a steam in a steam turbine alternator unit. A

part of this steam is also used in a steam turbine which driver a

compressor for compressing air for the MHD cycle. The seed

material is recovered from the gas the harmful emissions

(sulphur) are also removed from gas before it is discharged to

atmosphere through a stack. For efficient practical realization a

MHD system must have following features:1) Air superheating arrangement to heat the gas to around 2500

C so that the

electrical conductivity gas is increased.

2) The combustion chamber must have low heat losses

3) A management to add a low ionization potential seed material

to the gas to

increase, its conductivity.

4) A water cooled but electrically insulating expanding dust with

long life electrodes.

5) A magnet capable of producing high magnetic flux density.


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6) Seed recovery apparatus necessary for both environmental and

economics

reasons.


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The closed cycle inert gas MHD system was conceived 1965. The

main disadvantages of the open cycle system is very high MHD

Power Generation temperature requirement and a very

chemically active flow could be removed, by closed cycle MHD

system. As the name suggests the working fluid in closed cycle, is

circulated in a closed loop. The working fluid is helium or argon

with cesium seeding. Figure show a closed cycle MHD system.


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The complete system has three distinct but interlocking loops. On

the left is the external heating loop, coal is gasified and the gas

having a high heat value of about 5.35 MJ/kg and temperature of

about 530C is burnt in a combustor to produce heat. In the heat

exchanger HX, this heat is transferred to argon the working fluidof MHD cycle. The combustion products after passing through the

air preheater (to recover a part of the heat of combustion

product) and purifiers (To remove harmful emissions) and

discharged to atmosphere. The loop in the centre is the MHD loop.

The hot argon gas is seeded with cesium and passed through

MHD generator. The dc power output of MHD generator is

converted to A.C. by the inverter and is then feed into the grid.

The loop shown on the right hand side in fig is the steam loop forfurther recovering the heat of the working fluid and converting

this heat into electrical energy. The fluid passes through the heat

exchanges HX2 where it imparts its heat to water which gets

converted to steam. This steam is used partly for during a turbine

which runs the compressor partly for turbine driver an alternator.

The output of the alternator is also to the grid. The working fluid

goes back to the heat exchanges HX) after passing through

compressor and intercooler. A closed system can provide more

useful power conversion at lower temperatures (around 1900o K

as compared to 2500o K for open cycle system).

11.


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The MHD generator or dynamo transfer thermal energy orkinetic energy directly into electricity.

MHD generators are different from traditional electric

generators in that they can operate at high temperatures

without moving parts

A simple magnetohydrodynamic generator consists of a gas

nozzle. The gas nozzle is a combustion chamber that injects

a pulse of gas into the channel/duct. The walls of the

channel act as an electrode. The induced electric current is

fed to the load by an external circuit that supplies thegeneratedelectricityto the desired destination. The MHD

generators can be constructed in various designs like the

Faraday generator, Hall generator and disc generator.

Faraday generator was the first designed MHD generator. It

was made by Michael Faraday in 1831. The Faraday

generator used copper disks and a horse-shoe magnet to

generate electricity.
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Under high pressure condition, an electrically conducting

gas is produced by burning afossil fuel. Most of the MHD

systems use coal ornatural gasas fossil fuel. However,

inert gases like argon andheliumare also used in some

MHD systems. The gas is passed through a nozzle at a high

speed of 1000 to 2000 meter per second. The

magnetohydrodynamic generators do not create electric

charge, it is inherent in the ionized fluid or gases. Tounderstand it better, think of a water pump that allows the

water to pass through but it is not the source of water.

Conductivity of the fluid can be increased by adopting

various methods. If the fluid is an inert gas, then suitable

amounts of potassium carbonate can be added.

The gas enters the channel or duct where a strong magnetic

field is applied with the help of superconductingmagnets.

The magnetic intensity or magnetic field strength of the

magnetic field inside the channel is usually between 3 to 5

Tesla. As the gas passes through the channel, an

electromotive force is experienced by it. How does this

force arise? According to the Faraday's law ofelectromagnetic induction current/voltage (EMF) is

induced in a coil/wire whenever there is a change in the

magnetic flux linked with the coil. Here, the electromagnets

are stationary but the conductor fluid is moving constantly.
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A 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 themagnetic field

The main practical problem of a Faraday generator is that

differential voltages

Currents in the fluid short through the electrodes on the

sides of the duct

The most powerful waste is from the Hall effect current


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The normal scheme is to place arrays of short, verticalelectrodes on the sides of the duct.

The first and last electrodes in the duct power the load

Each 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.


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A disc generator has fluid flowing between the center of a

disc, and a duct wrapped around the edge. The magnetic

excitation field is made by a pair of circular Helmholtz

coils above and below the disc

The Faraday currents flow in a perfect dead short around

the periphery of the disk

The Hall effect currents flow between ring electrodes near

the center and ring electrodes near the peripheryAnother significant advantage of this design is that the

magnet is more efficient.


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The commercial use of MHD concept has not been possiblebecause numerous technological advancements are needed prior

to commercialization of MHD systems. Most of these are related

to material problem created by the simultaneous presence of

high

temperature and a highly corrosive and abrasive environment.

The MHD channel operates extreme conditions of temperature,

magnetic and electric fields. Search is on for better insulator and

electrode materials which can with stand the electrical, thermal,mechanical and thermo-chemical stresses and corrosion.

MHD generation offers several advantages as compared to other

methods of electric generation.

1) The conversion efficiency of a MHD system can be 50% as

compared to less than 40 percent for the most efficient steam

plants.

2) Large amount of power is generated.3) It has no moving parts, so more reliable.

4) It has ability to reach the full power level as soon as started.

5) Because of higher efficiency, the overall generation cost of an

MHD plant will be less.


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6) The more efficient heat utilization would efficient heat

utilization would

decreases the amount of heat discharged to environment and thecooling

water requirements would also be lower.

7) The higher efficiency means better fuel utilization. The

reduce

fuel

consumption would offer additional economic and social

benefits.

8) The Closed cycle system produces power free of pollution.Following table show the pollutant emission of an MUD plant

and

a

conventional steam plant.

Pollutant emission m tons per day based on use of coal having-3

percent

sulphur contents.


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1.) Power generation in space craft.

2.) Hypersonic wind tunnel experiments.

3.) Defense application.

4.) Astrophysics


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With the increased industrial and agricultural activities, powerdemand is also highly increased. In the country is sure to fall

short of the energy demand by the first decade of next century.

This means an additional capacity of power is required next 10

year. The answer to this is in non conventional energy. The

MHD

power generation is in advanced stage today and closer to

commercial utilization significant progress has been made in

development of all critical component and sub systemtechnologies coal burning MHD combined steam power plant

promise significant economic and environmental advantages

compared to other coal burning power generate technologies. It

will not be long before the technological problem of MHD

generate are overcome and MHD power generation transform

itself from nonconventional to conventional energy sources.


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Non-Conventional energy source : G.D. Rai

Electrical Power System : Dr. Inamdar

Generation Distribution & Utilization of Electrical Energy :

C.L.Wadwa

www.wikipedia.org

magneto hydro dynamics seminar by vipul

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