Magneto Hydro Dyanamic Power Generation

8/13/2019 Magneto Hydro Dyanamic Power Generation

1/28


2/28

INTRODUCTION

PRINCIPLE

VARIOUS SYSTEMSADVANTAGESDISADVANTAGES

ITS FUTURE PROSPECTS


3/28

Eighty percent of total electricity is produced in the world,is hydral,while remaining 20% is produced from nuclear,thermal,solar,geothermal energy & from magnatohydrodynamic(mhd) generators. The field of MHD was initiated

by Hannes Alfvn, for which he got the Nobel Prize in 1970.MHD power generation is a new system of electric powergeneration which is said to be of high efficiency and lowpollution. In advanced countries MHD generators are widely

used but in developing countries like India it is still underConstruction. This construction work in progress intrichi,in tamilnadu,under joint efforts of BARC(Bhaba AtomicResearch Centre), Associate cement corporation(ACC)& Russian technologists


4/28

An MHD generatorsconverting heat energy of a fuel directly

into electrical energy without conventional electric generator.

In this system, an MHD converter system is a heat engine,in which heat is taken up at a higher temperature is partly

converted into use full work and the remainder is rejected ata lower temperature.Like all heat engines, the thermalefficiency of an MHD converter is increased by supplying theheat at the highest practical temperature and rejecting it atthe lowest practical temperature.


5/28

When an electric conductor moves across a magnetic field a voltage isInduced in it which produces an electric current.

This is the principle of theconventional generatorwhere theConductors consists of copper strips.

In MHD generator the solid conductors are replaced by gaseous conductor;an ionized gas. If such a gas is passed at a high velocity through a powerfulmagnetic field, a current is generated and extracted by placing electrode in asuitable position in the steam.

The principle can be explained as follows. An electric conductor movingthrough a magnetic field experiences a retarding force as well as an inducedelectric field and current.


6/28


7/28

The effect is a result of faradays law of electromagnetic induction

The induced emf is given by

Where,u=velocity of the conductorB=Magnetic field intensity

The induced current is given by,

Where,

=electric conductivity

The retarding force on the conductor is Lorentz force given by


8/28

The electromagnetic is the principle not limited to solid conductors .

The movement of a conducting fluid through a magnetic field can alsogenerate electrical energy.

When a fluid is used for the energy conversion technique, it is calledthe MAGNATO HYDRODYNAMIC(MHD) ,energy conversion.

If the flow directionis right angles to the magnetic field direction ,

an electromotive force (or electric voltage) is induced in the rightdirection at right angles to bothto both flow & field direction, asshown in the next slide.


9/28


10/28


11/28

The conducting fluid is forced between the plates with a kinetic energy& pressure differential sufficient to overcome the magnetic induction

Force Find.The end view drawing illustrates the construction of the flow of channel.

An ionized gas is employed as a conducting fluid.

Ionization is produced either by thermal means i.e. by an elevatedtemperature or by seeding with substance like cesium or potassium

vapours which ionize at relatively low temperatures.

The atoms of seed element split off electrons. The presence of the negativelycharged electrons make the carrier gas an electrical conductor.


12/28

Thus the MHD systems can be classified broadlyas follows:

1) Open cycle system

2)Close cycle system

a)Seeded inert gas systemb) Liquid metal system


13/28

Fuel use may be oil through an oil tank or gasified coalthrough a coalgasification plant.

The fuel(coal , oil or natural gas ) is burnt in the combustor,combustion

chamber.

The hot gases from combustor is then seeded with a small amountof an ionized alkali metal(cesiumor potassium) to increase the electricalconductivity of the gas.

The seed material , generally potassium carbonate is injected in to thecombustion chamber , the potassium is then ionized by the hot combustiongases at temperature roughly (2300-2700 c)


14/28


15/28

To attain such high temperature ,the compressed air used to burn the coalin the combustion chamber ,must be adequate at least 1100c.A lower pre-

heat temperature would be adequate if the air where enriched in oxygen.An alternative is use to compressed oxygen alone for combustion of fuel,little or no preheating is then required. The additional cost of the oxygenmight be balanced by saving on the preheater.

The hot pressurized working fluid living the combustor flows throughthe convergent divergent nozzle. In passing through the nozzle , therandom motion energy of the molecules in the hot gas is largely convertedinto directed, mass of energy. Thus the gas emerges from the nozzle and

enters the MHD generator units at a high velocity.


16/28

The MHD generator is divergent channel made of heat resistant alloywith external water cooling . The hot gas expands through the rocketlike generator surrounded by powerful magnet. During motion of thegas the +ve & -ve ions move to the electrode and constitute an electriccurrent .

The arrangement of the electrode connection is determined by the needto reduce loss arising from the Hall effect. By this effect the magnetic field,acts on the MHD generated current and produces a voltage in flow direction

of the working fluid rather than at right angles to it.


17/28

Two general type of closed cycle MHD generators are beinginvestigated.

1) Electrical thermal conductivity is maintain in theworking fluid by

Ionization of a seed material, as in open cycle system.

2) A liquid metal provides the conductivity.

The carrier is usually a chemical inert gas, all through a liquid carrieris been used with a liquid metal conductor. The working fluid is circulated

in a closed loop and is heated by the combustion gases using a heatexchanger .Hence the heat sources & the working fluid are independent.The working fluid is helium or argonwith cesium seeding.


18/28


19/28

In a closed cycle system the carrier gas operates in a form of Brayton cycle.In a closed system the gas is compressed & the heat is supplied by the source,

At essentially constant pressure, the compressed gas then expand in the MHDgenerator & its pressure & temperature fall. After leaving the generator,heat

is removed from the gas by a cooler, this is the heat rejection stage of the cycle.Finally the gas is recompressed & return for reheating.

The complete system has three distinct but interlocking loops. On theleft it is external heating loop. Coal is gasified & the gas burn in a combustor

to provide heat. In the primary heat exchanger , the heat is transferred in toa carrier gas argon or helium of the MHD cycle. The combustion pressureafter passing through the air preheater & purifier are discharge to the atmo-sphere.


20/28

Because the combustion system is separate from the working fluid,so also are the ash & the flue gases, hence the problem of extracting

the seed material from the fly ash does not arise. Then the fuel gases are usedto preheat the combustion air & then treated for fly ash and SO2 removal,if necessary prior to discharge through a stack to the atmosphere.

The loop in the centre is MHD loop. The hot argon gas is seeding withcesium& resulting working fluid is passed through the MHDgenerator at high speed. The dc power out of MHD generator is convertedin ac by the inverter & is then fed into the grid.


21/28

When a liquid metal provides the electrical conductivity, an inert gas isconvenient carrier.

The carrier gas is pressurized & heated by passage through a heat

exchanger with an combustion chamber. The hot gas is then incorporatedinto the liquid metal usually hot sodium to form the working fluid. Thelatterthen consists of gas bubbles uniformly dispersed in an approximately equal

volume of liquid sodium.

The working fluid is introduced into the MHD generator through a nozzlein usual ways; the carrier gas then provides the required high direct velocityof the electrical conductor.


22/28


23/28

After passage through the generator, the liquid metal is separated from thecarrier gases. Part of the heat remaining in the gas is transferred into water

in a heat exchanger to produce steam for operating a turbine generator .Finally the carrier gas is cooled, compressed & returned to the combustionchamber for reheating & mixing with recovered liquid metal. The workingfluid temp is usually around 800 c as the boiling point of sodium; even undermoderate pressure is below 900c.

The lower operating temp then in other MHD conversion systems may beadvantageous for the material stand point, but the max thermal efficiencyis lower. A possible compromise might be to use liquid lithium, with a boilingpoint near 1300c as the electrical conductor lithium is much more expensive

then sodium, but losses in a closed system may be small.


24/28

1) The conversion efficiency of a MHD system can be around 50 percentAs compared to less than 40 percent for the most efficient steam plants.Still higher thermal efficiencies (60-65%)are expected in future, with theImprovements in experience & technology.

2)Large amount of power is generated

3)It has no moving parts, so more reliable.

4)The closed systems produces power free pollution.

5)It has ability to produces power free of pollution

6)The size of the plant is considerably smaller than conventional fossil fuel plants


25/28

7)Although the cost cannot be predicted very accurately, yet it has beenreported that capital costs of MHD plants will be competitive with thoseof conventional steam plants.

8)It has been estimated that over hall operational ,cost in an MHDplant would be about 20% less than the conventional steam plants.

9) Direct conversion of heat in to electricity permits to eliminate the gasturbine(compared with a gas turbine power plant) or both the boiler & theturbine (compared with a still power plant). This elimination reduces losses

of energy .10)These system permits better fuel utilization .The reduced fuel consumption

would offer additional economic & special benefits and also lead toconservation of energy sources.

11)It is possible to utilize MHD for peak power generation & emergencyservices(up to 100 years per year) It has been estimated the MHDequipments for such duties is simpler , has the capability of generatingin large units & has the ability to make rapid start to full load.


26/28

1) Heavy losses in the power electrode in MHD power

plant.2) The material used in the MHD power plant doesnt

withstand in high temperatures.


27/28


28/28

Magneto Hydro Dyanamic Power Generation

Documents

Transcript of Magneto Hydro Dyanamic Power Generation