MHD power generation

MagnetohydrodynamicThermal to Electric Conversion

Session 2016-2017Department of Electrical Engineering

University College of Engineering, RTU (Kota)Guided By:-

Dr. Dhreeaj palwalia(Professor and Head)Department of Electrical Engg

Submitted By:-

Abhishek Dosaya13/003

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Abhishek Dosaya 13/003

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

For the conventional power plants thermal energy is converted in to kinetic energy which is then converted into electrical energy. For MHD, thermal energy is directly converted to electrical energy, hence know as direct energy conversion system.

Magnetohydrodynamics power generation technology is the production of electrical power utilizing a high temperature conducting plasma moving through an intense magnetic field.

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What is MHD


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

This is the principle of the conventional generator where the conductors consist of copper strips.

In MHD generator, the solid conductors are replaced by a gaseous conductor, an ionized gas. If such a gas is passed at a high velocity through a powerful magnetic field, a current is generated and can be extracted by placing electrodes in suitable position in the stream

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How it Works


PRINCIPLE OF MHD POWER GENERATION

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Related equationsPotential Difference is obtained by-

U=V. B. dWhere V= Average speed of plasma B= Magnetic flux density d= Distance between the electrodesPower generated by MHD generator-

Where electrical conductivity of fluid , u= fluid velocity p= Density of fluidPressure difference is created to force the gas. 4


Ionization Method- Thermal ionization WORKING FLUID- Gases from the combustor, ionized by

intense temperature. A lower preheat temperature would be adequate if the air is enriched in oxygen.

Conductivity of gases is too low at a temperature of 5000F to deal this difficulty seeded material like cesium, potassium nitrate, or potassium carbonate is added to reduce the temperature to 2000-3000F for adequate conductivity .

Used as hybrid MHD-steam plant cycle to increase the efficiency.

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OPEN CYCLE MHD SYSTEM


OPEN CYCLE MHD SYSTEM

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Features of Open cycle MHD for efficient system Management of seed material. Combustion chamber must have low heat losses. Compressed air enriched in oxygen is used to

reduce the preheater cost.

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Closed Cycle MHD system

In a Closed Cycle MHD, Working gas is not mixed with combustor material. Gases like helium argon is heated by the regenerative heat exchanger. Hence the heat sources and the working fluid are independent.

The working fluid is helium or argon with cesium seeding Major advantage of closed cycle MHD are simple

operation and do not require seed processing facility. inert gas or liquid metal is used to transfer the heat. The

liquid metal has typically the advantage of high electrical conductivity; hence the heat provided by the combustion material does not required too high.

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Abhishek Dosaya 13/003 10


Seeder inert gas system Working fluid-inert gas like helium or argon. The complete system has three distinct but interlocking

loops- On the left is the external heating loop. Coal is gasified and the gas is burnt in the combustor to provide heat. In the primary heat exchanger, this heat is transferred to a carrier gas argon or helium of the MHD cycle. The combustion products after passing through the air preheated and purifier are discharged to atmosphere. Because the combustion system is separate from the

working fluid, so also are the ash and flue gases. Hence the problem of extracting the seed material from fly ash does not arise.

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Liquid metal system

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The liquid metal has typically the advantage of high electrical conductivity; hence the heat provided by the combustion material does not required too high.

Working fluid-liquid lithium, liquid sodium and carrier gas like helium or argon gas with cesium seeding.

Carrier gas provide high direct velocity to the liquid metal.

Carrier gas works as thermodynamic electric fluid.

Liquid metal works as electrodynamics fluid.12

Liquid metal system


Generator DesignsFARADAY GENERATOR:-

This type of generator consists of a non-conductive wedge-shaped pipe or tube. When ionized plasma (conductive fluid) flows through the tube in the presence of an intense magnetic field than current is induced, which can be extracted by placing electrodes on the sides of wedged shaped pipe or tube at 90-degree of magnetic field.

The main practical issue with faraday generator is differential voltages and currents in the fluid short through the electrodes on the sides of the tube.

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Faraday generator

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HALL GENERATOR

In faraday generator, the issue is reduce the faraday current due to Hall effect(Hall current).

In Hall generator first electrode of one wall and last electrode of opposite wall is connected, which reduce the hall effect.

Another concept to reduce the Hall current is segmented Faraday generator.

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HALL GENERATOR

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Disk Generator

The disc generator is the most efficient design. This design currently grasps the efficiency and energy

concentration records for MHD generation. A disc generator has plasma (ionized gas) or 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 under the disk

The Faraday currents flow in a perfect dead short around the edge of the disk. The Hall Effect currents flow between ring electrodes near the center and ring electrodes near the edge.

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Disk generator

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Disk generator

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Selection of seed material Seed material has atoms which ionize easily, for

example, cesium, potassium and calcium, and by supplying electrons causes an increase in the electrical conductivity of the gas.

However, it is not possible to raise the electrical conductivity by increasing the concentration of the seed material.

The electrical conductivity carrier gas mixed with appropriate quantity of seed depends upon-

1.Collison profile 2.Molecular weight

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Collision Profile:-The collision profile of a gas stream is defined as a value that is proportional to the probability of collisions of gas atoms with an electron. Since these collisions of gas atoms with the electrons reduce the mobility of the electrons within an electrical field, a high collision profile is synonymous to a low electrical conductivity.

Molecular weight:- The power density is inversely proportional to the molecular

weight of the gas, therefore, in order to attain a high power density it will be advantageous to select a carrier gas with a low molecular weight.

Hence, hydrogen as a carrier gas and potassium as a seed is used

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Plasma Physics EXPERIMENTS ON HIGH TEMPERATURE XENON PLASMA:-

High temperature Xe plasma is generated by shock tunnel. This Xenon Plasma flows into a linear shaped segmented type faraday generator.

The channel width is constant at 20mm,and the height variable.

Variable temperature and variable flux density is applied.

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Effect of inlet total temperature on enthalpy extraction ratio

4000 6000 8000 10000 120000

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10

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XeAr

Inlet total temperature

Eent

halp

hy e

xtra

ctio

n ra

tio

Ar

Xe


Relation between stream-wise length and the power output density

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60 90 120 1500

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40

60

80

100

ArXe

Stream wise length

pow

er o

utpu

t de

nsity


Effect of magnetic flux density on enthalpy extraction ratio

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Result

In this experiment, however, the maximum enthalpy ratio remains only remains only 8%,smaller than the target performance of a CCMHD generator(enthalpy extraction ratio=30%).

High enthalpy extraction ratio should be achieved with a long channel generator or a high magnetic flux density.

For MHD generators to operate with good performance and the reasonable physical dimensions, the electrical conductivity lies 10 semen's per meter of plasma lies must be lie in temperature 1500-28000 F about 1800 K.

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Why Is need of MHD

Conventional Coal Fired Generators achieve a max. efficiency of about 35%.MHD generators have the potential to reach 50%-60% efficiency. utilization of heat.

The MHD process is industrial attractive because of reduced cooling requirements

It has been estimated the overall operational costs of MHD plants would be about 20% less than conventional steam plants.

Use MHD fluid in some nuclear reactors as coolant for Directly MHD electricity generation.

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Why is it not commercialized

Material corrosion problem created by the presence of high temperatures.

Maximum enthalpy ratio remains only 8%, smaller than the target performance (30%) of a CCMHD generator.

Seed material attacks insulating materials and make them conducting.

The gases used as flow media are ionized only to a limited degree because their temperature must be kept within tolerance by the components of the generator.

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Why is it not commercialized

Working temperature is very high as about 2000 k to 3000 k.

Construction of generator is uneconomical due to its high cost.

Selection of carrier gas, channel problem, predominant fuel.

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

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RELATED WORK

The first “commercial” plant will be the U-500 Ryazan Power Station. Construction on site has been initiated, the design of the plant components has been completed and consultation by U.S.S.R. industries on the manufacturing of the components is taking place.

In India , it is still under construction, this construction work in in progress at TRICHI in TAMIL NADU 5MW, under the joint efforts of BARC (Bhabha atomic research center), Associated cement corporation (ACC) and Russian technologists

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Conclusion

These systems permit better fuel utilization. The reduced fuel consumption would offer additional economic and special benefits and would also lead to conservation of energy resources. The MHD power generation is in advanced stage today and closer to commercial utilization significant process has been made in development of all critical component and subsystem technologies coal burning MHD combined steam power plant promise significant economic. Aim will be to increase enthalpy extraction ratio.

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Thank you