Magneto hydro Dynamic(MHD) Generator 1

Presented By: Umair Farooq 2010-EE-10 Electrical Engineering Department BZU MULTAN

3 Introduction Lorentz force law Faraday’s law Principle, construction and working of Magneto hydrodynamic generator (MHD) Different configrations Advantages, disadvantages and applications

4 What is MHD generator??? The Magneto hydrodynamic (MHD) generator is a device that converts thermal energy of a fuel into electrical energy.

5 The Lorentz force law is the basis for the Magnetohydrodynamic generator The lorentz force law states that the charged particle expreinec a force when is moving in the electromagnetic field. This force can be explained as F= Q (v xB) Where, F is the force acting on charged particl. Q is the charge of the particle V is the velocity of particle B is the magnetic induction 2.Lorentz force law

6 3.Fraday’s law When a charged partcile moving in a magnetic field, it expreience the retarding foce as well as produce voltage. This is the basis of Faraday’s law. S N V Output current Hot gaseous conductor

7 The meaning of M agneto H ydro D ynamics

8 4.Principle, construction and working of Magneto hydrodynamic generator (MHD) Principle The principle of Magnetohydrodynamic generator is based on Lorenz 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.

PH 0101 Unit-5 Lecture -59

10 Construction: MHD generator consist of a Combustion chamber and generator chamber. The fluid conductor is passed into the combustion chamber where they are ionized at very high temperature. There is a nozzle through which the ionized gas pass into the generator chamber. The generator chamber consist of powerful magnet and a number of oppositely located electrode pair is inserted in the channel to conduct the electrical current generated to an external load. Both combustion chamber and generator chamber are surrounded by a heat resistance material and water cooler

11 Construction S NS N combustion Chamber V Ionized Gas Working fluid Water cooler Thermal resistance sealing Magnet Stream out Load output Nozzle Electrode Inlet

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13 Working 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°C to 2400°C. 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 expansion nozzle reduces the gas pressure and consequently increases the plasma speed (Bernoulli's Law) through the generator duct to increase the power output. Unfortunately, at the same time, the pressure drop causes the plasma temperature to fall (Gay-Lussac's Law) which also increases the plasma resistance, so a compromise between Bernoulli and Gay-Lussac must be found.Bernoulli's LawGay-Lussac's Law The exhaust heat from the working fluid is used to drive a compressor to increase the fuel combustion rate but much of the heat will be wasted unless it can be used in another process. 14

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16 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.

17 90° Potential (E) Ionized gas (Q) Magnetic field (B) The diagram shows the direction of charged particle, magnetic field and the currentproduced All three field are perpendicular to each other

18 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.

19 The electrode are made generally using high temperature ceramic materials such as carbides (SiC, ZrC, MbC), bromides (ZrB 2, TiB 2, LaB 2 ) and silicides (WS and MOSi 2 ).

VARIOUS MHD SYSTEMS The MHD systems are broadly classified into two types. OPEN CYCLE SYSTEM CLOSED CYCLE SYSTEM o Seeded inert gas system o Liquid metal system

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OPEN CYCLE SYSTEM

Close Cycle System (SEEDED INERT GAS SYSTEM)

Efficiency: Typical efficiencies of MHD generators are around 10 to 20 percent mainly due to the heat lost through the high temperature exhaust. This limits the MHD's potential applications as a stand alone device but they were originally designed to be used in combination with other energy converters in hybrid applications where the output gases (flames) are used as the energy source to raise steam in a steam turbine plant. Total plant efficiencies of 65% could be possible in such arrangements. 24

25 Advantages 1.The on and off time is about second. 2.There are no moving parts, it is very reliable to use. 3.The MHD generator has high thermal efficiency 4.It is a direct conversion device. 5.They have a better fuel utilization 6.It can produce large amount of power 7.The size of the pant is small 8.It has been estimated that the overall operational costs in a plant would be about 20% less than conventional steam plants 5.Advantages, disadvantages and applications

26 Disadvantages 1.They need high pure superconductor. 2.Working temperature is very high as about 2000°C to 2400°C. 3.The loss of power if very high 4.The components get high corrosion due to high working temperature.

27 Application The MHD generators are used to power submarines and aircrafts. Electrical power production for domestic applications They are used in a pulsed detonation rocket engine (PDRE) for space application They can be used as power plants in industry.

References: Hugo K. Messerle, "Magnetohydrodynamic Power Generation", 1994, John Wiley, Chichester, Part of the UNESCO Energy Engineering Series (This is the source of the historical and generator design information). Shioda, S. "Results of Feasibility Studies on Closed- Cycle MHD Power Plants", Proc. Plasma Tech. Conf., 1991, Sydney, Australia, pp. 189–200. R.J. Rosa, "Magnetohydrodynamic Energy Conversion", 1987, Hemisphere Publishing, Washington D.C. G.J. Womac, "MHD Power Generation", 1969, Chapman and Hall, London. 28