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MAGNETO HYDRO DYNAMIC POWER GENERATION

ABSTRACT

The electricity requirements of the world including India are increasing at

alarming rate and the power demand has been running ahead of supply. It is also now

widely recognized that the fossil fuels and other conventional resources, presently

being used for generation of electrical energy, may not be either sufficient or suitable

to keep pace with ever increasing demand of the electrical energy of the world.

Also generation of electrical power by coal based steam power plants or

nuclear power plants causes pollution. The recent severe energy crisis has forced the

world to develop new and alternative methods of power generation. MAGNETO

HYDRO DYNAMIC (MHD) power generation is a new unique method of power

generation.

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i

CONTENTS

Chapter No. TITLE Page No.

LIST OF FIGURES iiiLIST OF TABLE iv

1 INTRODUCTION

1.1. Introduction 1

1.2. Experimental Developments 2

1.3. Necessity of MHD system 4

2 MHD POWER GENERATION

2.1. Principle of MHD power generation 5

2.2. Electrode configuration of MHD 8

3 MHD SYSTEM 9

3.1. Open cycle MHD system 10

3.2. Hybrid MHD steam part open cycle system 11

3.3. Closed cycle MHD system 13

4 MERITS AND DEMERITS

4.1. Advantages of MHD system 15

4.2. Disadvantages of MHD system 16

5 ACHIEVEMENTS 17

6 PROBLEMS ENCOUNTERED IN

DESIGN OF MHD18

7 APPLICATIONS 19

8 CONCLUSION

REFERENCES 20

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GEC EEE(dept) Page ii

LIST OF FIGURES

Figure No TITLE Page No.

1.2.1 MHD Lab at UCLA 3

2.1 Principle Of MHD Generator 5

2.2 Flemings Right Hand Rule 6

2.3 TurbogeneratorAnd MHD Generator 6

2.2.1 Segmented Electrode Configuration 8

2.2.2 Continuous Electrode Configuration 8

2.2.3 Hall Generation 8

3.1 Open Cycle MHD System 10

3.2 Hybrid MHD-Stream Part Open Cycle 11

3.2(A) Open Cycle MHD Plant Coupled With a Stream Plant 12

3.3 Closed Cycle MHD Generator 13

LIST OF TABLE

Table No TITLE Page No.

1. Comparison Between Open CycleSystem And Closed Cycle System 9

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GEC EEE(dept) Page 1

CHAPTER 1

INTRODUCTION

1.1INTRODUCTION

MHD (Magneto Hydro Dynamics) Systemis a new system of electric

powergeneration which is said to be of high efficiency and low pollution. As

its name implies, magneto-hydro-dynamics (MHD) isconcerned with the flow

of conducting fluid in presence of magnetic andelectric field. This fluid may

be gas at elevated temperature or liquid metal likesodium or potassium. The

working fluid here is called plasma.

A MHD generator is a device for converting heat energy of

fuel directly into electric energy without a conventional electric

generator.The basic difference between a conventional generator and a

MHD generator is inthe nature of conductor. MHD converter system is a

heat engine whose efficiency , like all heat engines , is increased by

supplying the heat at the highest practical temperature and rejecting it

at the lowest practical temperature. MHD power generation looks the

most promising of the direct conversion techniques for the large scale

production of electric power.

In advancedcountries MHD generators are widely used but in

developing countries like Indiait is still under construction. This construction

work is in progress atTiruchirapalli in Tamilnadu under joint efforts of

BARC (Bhabha AtomicResearch Centre), BHEL, Associated Cement

Corporation and Russiantechnologists.

1.2. EXPERIMENTAL DEVELOPMENTS

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In the early part of the nineteenth century Michael Faraday (1832) conducted

MHD experiments using the brackish water of the river Thames flowing through the

Earth's magnetic field. He described the conversion process in MHD in 1893.

However the actual utilisation of this concept remained unthinkable.

The first successful power generation experiment, developed by Richard

Rosa in 1959, generated 10 kW with a timber walled channel on the AVCO "Mark 1"

facility in Boston, Massachusetts. This success and the possibility of cheap MHD

power led in the 1960s to national programs in Britain, the Soviet Union, The

Netherlands, France, Germany, Poland, Italy, India, Australia and Israel.In1965 the

AVCO "Mark 5" generator successfully generated 32 MW over a one minute run

using alcohol at 45 kg/sec fired with oxygen. AVCO later developed a sophisticated

coal fired MHD channel for a 2,000 hour test program and demonstrated technical

feasibility under the most stringent conditions.

In1972in Moscow, a large experimental facility, the "U-25," used a 250 MW

natural gas combustor and generated 20 MW. The Soviets have been using very

successfully mobile, pulsed MHD generators throughout the Soviet Union, for

seismic studies.

MHD programs in the United States are concentrated in two major facilities.

A "Component Development and Integration Facility" is located in Butte, Montana,

and a "Coal Fired Flow Facility" at the University of Tennessee to studies coal fired

MHD, slag processing, seed handling and downstream systems.

MHD Lab at UCLA

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:

Fig:1.2.1 MHD Lab at UCLA

Less effort has been applied to closed-cycle liquid-metal and plasma MHD systems

since these systems are at a lower state of development than is the coal-fired open-

cycle plasma MHD system and appear to be more expensive and less efficient than

open-cycle plasma MHD.

JUPITER 2 MHD Heat Transfer Exp. inUCLA FLIHY Electrolyte Loop

BOB magnet

QTOR maand LM

loop

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1.3.NECESSITY OF MHD SYSTEM

It is a well known fact that at present a plenty of energy is needed to

sustain industrial and agricultural production, and the existing conventional

energy sources like coal, oil, uranium etc are not adequate to meet the ever

increasing energy demands. Consequently, scientists and engineers in

exploring the possibilities of harnessing energy from several non-

conventional energy sources have made sincere and untiring efforts. Magneto

Hydro Dynamics(MHD) Generator is one of those energy sources. Today

80% of total electricity produced in the world is hydel, while remaining 20%

is produced from nuclear, thermal, solar, geothermal energy and from

magneto hydro dynamic power generation.

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CHAPTER 2

MHD POWER GENERATION

2.1 PRINCIPLE OF MHD POWER GENERATION

The principle of MHD generation is simple, based on Faradays law o f

electromagnetic induction,i.e., when an electric conductor moves across a

magnetic field, a emf is induced in it, which produces an electric current.

The conductor need not be a solid- it may be a gas or liquid. This is the

principle of the conventional generator also, where the conductors consists

of copper strips. Ina MHD generator the solid conductors are replaced by a

gaseous conductori.e.an ionized gas.

If such gas is passed at high velocity through a powerful or strong magnetic

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 (Lorentz Force)F acts on the charged particle.

As shown in the figure below the positive ions would be accelerated towards

the upper plate P1(cathode) and negative ions would be accelerated towards

the lower plate P2(anode) . If the P1and P2areexternally connected through a

resistance, a current would flow through the resistance. Thus gas energy is

directly converted into electrical energy. This is the principle of MHD

generator.

Fig .2.1-principle of MHD generator

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Lorentz Force Law:

F = q(v B)

where,

F = force of the acting(charged) particle v = velocity of the particle (vector) q= charge of the particle (scalar) B = magnetic field (vector)

Fig.2.2-flemings right hand rule

The vector F is perpendicular to both v and B according to Right

Hand Rule. Summarizing the above explanation we can say that in aMHD system the kinetic energy of the working fluid is converted to

electric energy.

The figure given below shows a comparison between a turbo generator

and a MHD generator.

fig.2.3-turbogenerator and MHD generator

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qj

TkT

t

TCp

2

2)(V

)( BVEj

Here, in turbo generator, the conductor moving inside the

magnetic field is solid, while in MHD generator the conductor moving

inside the magnetic field is in gaseous state.

But both of them are working on the same principle, doing thesame work, giving the same output. However, the efficiency of both of

them varies, as mhd generator gives much better and more output than

the turbo generator, hence it is more efficient.

MHD EQUATIONS

Navier-Stokes equations with the Lorentz force

(2.1)

Continuity

(2.2)

Energy equation with the Joule heating

(2.3)

Amperes law

(2.4)

Faradays law

(2.5)

Ohms law*

(2.6)

Eqns.(2-6) are usually grouped together to give either a vector

induction equation or a scalar equation for electric potential.

BjgVVV

V

11

)(

2

pt

0 V

)/10257.1104:(67

0

1mHvacuum

Bj

EB

t

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2.2.ELECTRODE CONFIGURATION OF MHD GENERATOR

There are three possible arrangements of providing electrodes for MHD

generators.

1. Segmented electrode configuration:

The electrode segments are separated by insulator segments so there will be

no current flowing in the direction. The electric field vector has a component both

along the channel and across the channel.

Fig .2.2.1-segmented electrode configuration

2. Continuous electrode configuration:

In this case the electric field is across the channel only; but here current has

components along the channel as well as across it. In this case the hall angle is

minimized and thus the losses are reduced.

Fig.2.2.2- continuous electrode configuration

3.Hall generator:

In this case the electrodes wrap up the channel all the way in segment. The

electric field becomes parallel to the channel axis. Due to this reason there cannot be

any potential difference across the channel.

Fig .2.2.3.hall generation

CHAPTER 3

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MHD SYSTEM

The MHD System is broadly classified into:

(1)Open cycle System

(2)Closed cycle System

(i)Seeded inert gas systems

(ii) Liquid metal systems

Table.1.comparison between open cycle system and closed cycle system

Open Cycle System Closed Cycle System

(1) Here the working fluid aftergenerating electrical energy is

discharged to the atmosphere

through a stack.

(1) Here the working fluid is recycled tothe heat sources and thus can be

usedagain and again.

(2) The operation of MHD generator is

done directly on combustion

products (like coal, oil, natural

gas(hot gases thus formed are

seeded with small amount of an

ionized alkali metal like cesium orpotassium))in an open cycle system.

(2)Inclosed cycle system helium or

argon(with cesium seeding) is

used as the working fluid.

(3) Temperature requirement here is very

high, i.e., about 2300C to 2700C.(3)Here the temperature requirement is

comparatively less, i.e., about 530C.

(4)The open-cycle MHD system involvesrelatively-complex high-risk technology,

primarily because of the required high

temperatures.

(4) The closed-cycle MHD system involvescomparatively-simple low-risk

technology, primarily because of

comparatively lower working

temperatures.

(5) As per the latest research anddevelopmental work, its efficiency is

found to be more.

(5) Till now no significant developmentshave occurred in this system, and its

efficiency appears to becomparatively less.

(6) They are less costly (6) They are quite expensive.

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3.1.OPEN CYCLEMHD SYSTEM

An elementary open cycle MHD system, is shown in the figure below:

The MHD generator resembles a rocket engine surrounded by a

magnet. Here the fuel (such as coal,oil,natural gas) is burnt in the

combustion chamber(combustor) to produce hot gases. The air required for

combustion is from the air preheater. The hot gases produced are then

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

to increase conductivity of the gas. The ionization of potassium (generally

potassium carbonate is used as seed material) takes place due to gases

produced at temperatures of about 2300 C to 2700C by combustion. The

hot pressurized working fluid so produced leaves the combustion chamber

and passes through a convergent-divergent nozzle.The gases comes out of the

nozzle at high velocity and then enter the MHD generator.The gases

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 (direct current). By using an inverter this direct

current can be converted into alternating current. The rejected gas passes

through an air heater for preheating the inlet air. The seed material is

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recovered in seed recovery for successive use. The nitrogen and sulphur are

removed for pollution control and then the gases are discharged into the

atmosphere.

The above cycle is not suitable for commercial use. The exhaust gases of

MHD unit are still at a sufficiently hot temperature and it is possible to use

them for additional power generation in a steam turbine alternator unit. This

increases the efficiency of the process. Such cycle is known as Hybrid

MHD-Steam Plant Cycle.

3.2.HYBRID MHDSTEAM PART OPEN CYCLE SYSTEM

Fig3.2.Hybrid MHD steam part open cycle system

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The above figure shows hybrid MHD steam cycle.Here coal is processedand

burnt in the combustor at high temperature (2750 to 3000 K) andpressure

(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. The

resulting mixture having anelectricalconductivityof 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 change it to ac before thepower can be fed to an

electric grid.

The gas coming out of MHD generator is still sufficiently hot andis used to

raise steam, which generates additional energy in a steam in asteam turbine

alternator unit. A part of this steam is also used in a steamturbine which driver a

compressor for compressing air for the MHD cycle. Theseed material is recovered

from the gas the harmful emissions (sulphur) arealso removed from gas before it is

discharged to atmosphere through a stack.

Fig .3.2(a)-open cycle MHD plant coupled with a stream plant

The above figure shows an open cycle MHD plant coupled with a

Steam plant, which increases the efficiency of steam plant having a

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maximum conversion efficiency of about 40% by 10 20% , thus making the

overall efficiency of the plant 60% .

For efficient practical realization a MHD system must have following features:

1) Air superheating arrangement to heat the gas to around 2500 C sothat the

electrical conductivity of the 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, itsconductivity.

4) A water-cooled but electrically insulating expanding dust with long life electrodes.

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

6)Seed recovery apparatus necessary for both environmental and economical reasons.

3.3. CLOSEDCYCLE MHD SYSTEM

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

disadvantages of the open cycle system is very high temperature requirement and

a very chemically active flow which could be removed by closed cycle

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

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

cesium seeding.

The given above figure shows a closed cycle MHD system. 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 about5.35 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 fluid of MHD cycle.The combustion products after passing

through the airpreheater (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 gasis seeded

with cesium and passed through MHD generator. The dc poweroutput of

MHD generator is converted to A.C. by the inverter and is then feedinto the

grid.

The loop shown on the right hand side in the figure is the steamloop

for further recovering the heat of the working fluid and converting thisheatinto electrical energy. The fluid passes through the heat exchanges

HX2where it imparts its heat to water which gets converted to steam. This

steam isused partly for during a turbine which runs the compressor partly

for turbine driver an alternator. The output of the alternator is also

connected to the grid. The working fluid goes back to the heat exchanger

and exchanges HX after passing through compressor and intercooler.

A closed system can provide more useful power conversion at lower

temperatures (around 1900 K as compared to 2500K for open cycle system).

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CHAPTER 4

MERITS AND DEMERITS

4.1. ADVANTAGES OFMHD SYSTEM

MHD generation offers several advantages as compared to other methods

of electric generation. They are as follows:

1.The conversion efficiency of a MHD system can be about 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.

6. The more efficient heat utilization would decreases the amount of heat

discharged to environment and the cooling water requirements would also be

lower.

7.The higher efficiency means better fuel utilization. The reduced fuel

consumption would offer additional economic and social benefits.

8. The Closed cycle system produces power free of pollution.

9. The size of plant is considerably smaller than conventional fossil

fuel plants.

10.It is suitable for peak power generation and emergency

service.Since high temperatures are involved, operational efficiency is high

4.2. DISADVANTAGES OF MHD SYSTEM

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Even after having a number of advantages, MHD System has its own

disadvantages that prohibits its commercialization. The disadvantages of

MHD System are enlisted below:

1) MHD Systems suffer from the reverse flow (short circuits) ofelectrons through the conducting fluids around the ends of the

magnetic field.

This loss can be reduced by:

(i) increasing aspect ratio (L/d) of the generator.

(ii) by permitting the magnetic field poles to extend beyond the

end of electrodes.

(iii) by using insulated vanes in the fluid ducts

2) There will be high friction losses and heat transfer losses. Thefriction loss may be as high as 12% input.

3) The MHD system operates at a very high temperature to obtainhigh electrical conductivity. But the electrodes must be relatively

at low temperatures and hence the gas in the vicinity of the

electrodes is cooler. This increases the resistivity of the gas

near the electrodes and hence there will be a very large voltage

drop across the gas film. By adding the seed material, the

resistivity can be reduced.

4) The MHD system needs very large magnets and this is a majorexpense.

5) Coal,when used as a fuel, poses the problem of molten ash

which may short circuit the electrodes. Hence, oil or natural gas

are considered to be much better fuels for this system.

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CHAPTER 5

ACHIEVEMENTS

USSR has constructed a pilot plant of 75MW installed capacity, 25MW isprovided by the MHD generator. The fuel used is natural gas. The plant is

designated as U-25.

A 5-15 MW thermal input pilot plant is being set up in India at Tiruchirapalli.This plant uses fluidized bed combustion.

Besides the use of MHD system for commercial electrical power generation ithas got other special uses. A major effort was made in U.S.A use MHD as the

conversion system in a nuclear electrical system for space craft.

In India also considerable studies have been carried out in this field under theNational Council of Science and Technology (NCST) .

The Department of Science and Technology of government of India hassponsored research and development programmes on coal based MHD power

generation.

MHD conversion has also been considered for ship propulsion, airborneapplications, hypersonic wind tunnel experiments and for many other defence

applications.

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CHAPTER 6

PROBLEMS ENCOUNTERED IN DESIGN OF MHD

1. Sufficient high temperature for thermal ionization can be sustained by refractorymaterials. A more practical method of reducing the required temperature is by

seeding.

2. Seed material potassium attacks insulating materials and make them conducting.

3. Electrode materials are chemically eroded by combustion of gases.

4. The major problem forced by this generator is the economics. Although the

overall thermal efficiency is 60% against 40% for conventional thermal plant,

additional investment in the magnet, generator, duct, compressors, scrubbers, seed

recovery plant and DC to AC converters may increase the plant cost and it may

be much higher than conventional plant.

5. Most of the problems are related to material problems caused by high temperature

and highly corrosive and abrasive environment.

CHAPTER 7

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APPLICATIONS

1.)Power generation in space craft

2.)Hypersonic wind tunnel experiments

3.)Defense application

4.) The Yamoto: Aboat built by Mitsubishi powered solely byMHD propulsion

can travel at upto 15 km/hr.

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CHAPTER 8

CONCLUSION

8.1.CONCLUSION

With the increased industrial and agricultural activities,power demand is also

highly increased. In such situation, 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 in the next 10 years. The answer to this is in

non conventional energy.

The MHD power generation is in advanced stage today and closer tocommercial utilization. Significant progress has been made in development

of all critical components and sub system technologies. Coal burning MHD

combined steam power plant promises significant economic and

environmental advantages compared to other coal burning power generation

technologies. It will not be long before the technological problem of MHD

systems will be overcame and MHD system would transform itself from

non-conventional to conventional energy sources.

8.2.FUTURE WORK

Need For Further Research:

Focussing upon the advantages of a MHD system while considering its

disadvantages, we can conclude that this system needs further developments for

commercialization.

However the commercial use of MHD concept has not been

possible because 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 on

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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.

Future prospects:1.It is estimated that by 2020, almost 70 % of the total electricity generated in the

world will be from MHD generators.

2.Research and development is widely being done on MHD by different countries

of the world.

Nations involved:

USA Former USSR Japan India China Yugoslavia Australia Italy Poland

REFERENCES

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[1]Faraday, M. (1832). "Experimental Researches in Electricity." First Series,Philosophical Transactions of the Royal Society, pp. 125-162.

[2]Messerle, H. K. (1995). Magneto-Hydro-Dynamic Electrical PowerGeneration. Chichester, England: John Wiley & Sons Ltd.

[3]Petrick, M., and Shumyatsky, B. Y. (1978). Open-CycleMagnetohydrodynamic Electrical Power Generation. Argonne, IL: Argonne

National Laboratory.

[4]Rosa, R. J. (1960). "Experimental Magnetohydrodynamic Power Generation."Applied Physics 31:735-36.

[5]Rosa, R. J. (1987). Magnetohydrodynamic Energy Conversion. Washington,DC: Hemisphere Publishing Corp.

[6]Shioda, S. (1991). "Results of Feasibility Studies on Closed Cycle MHDPower Plants." Proceedings Plasma Technology Conference, Sydney,

Australia, pp. 189-200.

[7]Simpson, S. W.; Marty, S. M.; and Messerle, H. K. (1989). "Open-Cycle DiskGenerators: Laboratory Experiments and Predictions for Base-Load

Operation." MHD An International Journal 2(1):57-63.

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