CONTENTS1. What is MHD ? 2. Need of MHDs3. Principle Of MHD Power Generation4. Types of MHD SYSTEM5. Open Cycle MHD System6. Closed Cycle MHD System7. Advantages OF MHD System8. Disadvantages of MHD System9. Applications
HEEE WITHOUT A CONVENTIONAL GENERATOR DIRECT CONVERSION FOR LARGE POWER GENERATION ENERGY IS GENERATED DUE TO THE MOVEMENT OF CONDUCTING FLUID INSIDE A MAGNETIC FIELD η > 50%
NEED OF MHDS 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, efforts have been made for harnessing energy from several non-conventional energy sources like Magneto Hydro Dynamics(MHD) System.
HISTORY• In 1932, Michael Faraday, demonstrated the experiments
that there is an electromagnetic induction in a current carrying conductor moving the earth magnetic field.
• In 1938, U.S scientist Bela Karlovitz is the first one developed the Magneto hydrodynamic generator.
• In India, the MHD generator program is undergoing in Thiruchirappalli in collaboration with Bharat heavy electrical limited (BHEL).
PRINCIPLE OF MHD POWER GENERATION
1.Faraday’s law of electromagnetic induction : When an electric conductor moves across a magnetic field, an emf is induced in it, which produces an electric current .
2.Lorentz Force Charged particle experience a force when is moving in the
electromagnetic field. This force can be explained as
F = q.(v × B) where,• v = velocity of the particle (vector)• q= charge of the particle (scalar)• B = magnetic field (vector)
Principle, construction and working of Magneto hydrodynamic generator (MHD)
PrincipleThe principle of Magneto hydrodynamic generator is
based on Lorentz law and faraday's law.
In this system, the hot ionized gaseous conductor (working fluid) is passed into the high magnetic field and thereby the current is produced. By placing suitable electrodes (Anode and cathode) inside the chamber, the output load is taken through the external circuit.
Water coolerThermal resistance sealing Magnet
• The gaseous (fluid) conductor is passed into the combustion chamber through inlet.
• By using a fuel like oil (or) natural gas (or) coal, the fluid conductor is heated to a plasma state and hence it is ionized.
• The temperature in the combustion chamber is around 2000°K to 2400°K.
• The heat generated in the combustion chamber removes the outermost electrons in the fluid conductor.
• Therefore, the gas particle acquires the charge
• The charged gas particles with high velocity enters into the generator chamber via nozzle.
• The positive and negative charge moves to corresponding electrodes (anode and Cathode) and constitute the current.
• In generator chamber, based principles of Faraday’s law, the high velocity ionized conducting gas particles experience the magnetic filed at right angles to their motion of direction and hence the potential (current) is produced.
• The direction of current (Potential) is perpendicular to both the direction of moving gas particle and to the magnetic field.
• The electrodes are connected to an external circuit to get a load output.
• The current produced in the MHD generator are direct current (DC)
• This DC current can be converted into alternative current (AC) using an inverter attached with the external circuit.
• In MHD generator, the seeding materials such as potassium and cesium are used to reduce the ionization temperature.
• These seeds are mixed with fuel material such as natural gas and coal.
• The electrode are made generally using high temperature ceramic materials such as carbides (SiC, ZrC, MbC), bromides (ZrB2, TiB2, LaB2) and silicates (WS and MOSi2 ).
TYPES OF MHD SYSTEMS
(1) Open cycle System(2) Closed cycle System (i)Seeded inert gas systems (ii) Liquid metal systems
OPEN CYCLE MHD SYSTEM
CLOSED CYCLE MHD SYSTEM
DIFFERENCE BETWEEN OPEN CYCLE AND CLOSED CYCLE SYSTEM
Open Cycle System Working fluid after generating
electrical energy is discharged to the atmosphere through a stack .
Operation of MHD generator is done directly on combustion products .
Temperature requirement : 2300˚C to 2700˚C.
Closed Cycle System Working fluid is recycled to
the heat sources and thus is used again.
Helium or argon(with cesium seeding) is used as the working fluid.
Temperature requirement : about 530˚C.
ADVANTAGESConversion efficiency of about 50% .Less fuel consumption.Large amount of pollution free power generated .Ability to reach full power level as soon as started. Plant size is considerably smaller than conventional fossil
fuel plants .Less overall operational cost.No moving parts, so more reliable . Suitable for peak power generation and emergency service
DISADVANTAGES Suffers from reverse flow (short circuits) of electrons through
the conducting fluids around the ends of the magnetic field.
Needs very large magnets and this is a major expense.
High friction and heat transfer losses.
High operating temperature.
Coal used as fuel poses problem of molten ash which may short circuit the electrodes. Hence, oil or natural gas are much better fuels for MHDs. Restriction on use of fuel makes the operation more expensive.