• TOPIC : MegnatoHydrodDynamicGenerationPresented To: Sir Engr. Jabbar BaigGroup Members1. Zain-Ul-Abedin (09-EE-03)2. Muhammad Usman (09-EE-12)3. Qamar-Uz-Zaman (09-EE-19)4. Moon Shahzad (09-EE-29)5. Bilal Nazir (09-EE-30)
The word magneto hydro dynamics (MHD) isderived from magneto meaning magnetic field,and hydro meaning liquid, and dynamicsmeaning movement. An MHD generator is a device for converting heatenergy of a fuel directly into electrical energy withoutconventional electric generator Examples of such fluids include plasmas, liquidmetals, and salt water. The field of MHD wasinitiated by Hannes Alfven , for which hereceived the nobel Prize in Physics in 1970
In MHD generator, the solid conductorsare replaced by a gaseous conductor,an ionized gas. If such a gas is passedat a high velocity through a powerfulmagnetic field, a current is generatedand can be extracted by placingelectrodes in suitable position in thestream. An electric conductor moving through amagnetic field experiences a retardingforce as well as an induced electric fieldand current.
• The electro magnetic induction principle is not limited tosolid conductors. The movement of a conducting fluidthrough a magnetic field can also generate electricalenergy.• When a fluid is used for the energy conversion technique,it is called MAGNETO HYDRO DYNAMIC (MHD), energyconversion.• The flow direction is right angles to the magnetic fieldsdirection. An electromotive force (or electric voltage) isinduced in the direction at right angles to both flow andfield directions, as shown in the next slide.
• The conducting flow fluid is forced between the plates with akinetic energy and pressure differential sufficient to over come themagnetic induction force Find.• The end view drawing illustrates the construction of the flowchannel.• An ionized gas is employed as the conducting fluid.• Ionization is produced either by thermal means I.e. by anelevated temperature or by seeding with substance like cesium orpotassium vapors which ionizes at relatively low temperatures.• The atoms of seed element split off electrons. The presence ofthe negatively charged electrons makes the gas an electricalconductor.
• The fuel used maybe oil through an oil tank or gasifiedcoal through a coal gasification plant.• The fuel (coal, oil or natural gas) is burnt in thecombustor or combustion chamber.• The hot gases from combustor is then seeded with asmall amount of ionized alkali metal (cesium orpotassium) to increase the electrical conductivity of thegas.• The seed material, generally potassium carbonate isinjected into the combustion chamber, the potassium isthen ionized by the hot combustion gases at temperatureof roughly 2300’ c to 2700’c.
• To attain such high temperatures, the compressed air isused to burn the coal in the combustion chamber, mustbe adequate to at least 1100’c. A lower preheattemperature would be adequate if the air is enriched inoxygen. An alternative is used to compress oxygen alonefor combustion of fuel, little or no preheating is thenrequired. The additional cost of oxygen might bebalanced by saving on the preheater.• The hot pressurized working fluid living in the combustorflows through a convergent divergent nozzle. In passingthrough the nozzle, the random motion energy of themolecules in the hot gas is largely converted intodirected, mass of energy. Thus , the gas emerges fromthe nozzle and enters the MHD generator unit at a high
• Two general types of closed cycle MHD generators arebeing investigated.• Electrical conductivity is maintained in the working fluidby ionization of a seeded material, as in open cyclesystem.• A liquid metal provides the conductivity.• The carrier is usually a chemical inert gas, all through aliquid carrier is been used with a liquid metal conductor.The working fluid is circulated in a closed loop and isheated by the combustion gases using a heat exchanger.Hence the heat sources and the working fluid areindependent. The working fluid is helium or argon with
• In a closed cycle system the carrier gas operates in theform of Brayton cycle. In a closed cycle system the gas iscompressed and heat is supplied by the source, atessentially constant pressure, the compressed gas thenexpands in the MHD generator, and its pressure andtemperature fall. After leaving this generator heat isremoved from the gas by a cooler, this is the heatrejection stage of the cycle. Finally the gas isrecompressed and returned for reheating.• The complete system has three distinct but interlockingloops. On the left is the external heating loop. Coal isgasified and the gas is burnt in the combustor to provideheat. In the primary heat exchanger, this heat istransferred to a carrier gas argon or helium of the MHDcycle. The combustion products after passing through theair preheated and purifier are discharged to atmosphere.
• When a liquid metal provides the electrical conductivity,it is called a liquid metal MHD system.• An inert gas is a convenient carrier• The carrier gas is pressurized and heated by passagethrough a heat exchanger within combustion chamber.The hot gas is then incorporated into the liquid metalusually hot sodium to form the working fluid. The latterthen consists of gas bubbles uniformly dispersed in anapproximately equal volume of liquid sodium.• The working fluid is introduced into the MHD generatorthrough a nozzle in the usual ways. The carrier gasthen provides the required high direct velocity of theelectrical conductor.
• The conversion efficiency of a MHD system can be around 50% muchhigher compared to the most efficient steam plants. Still higher efficienciesare expected in future, around 60 – 65 %, with the improvements inexperience and technology.• Large amount of power is generated.• It has no moving parts, so more reliable.• The closed cycle system produces power, free of pollution.• It has ability to reach the full power level as soon as started.• The size if the plant is considerably smaller than conventional fossil fuelplants.
• Although the cost cannot be predicted very accurately,yet it has been reported that capital costs of MHDplants will be competitive to conventional steam plants.• It has been estimated that the overall operational costsin a plant would be about 20% less than conventionalsteam plants.• Direct conversion of heat into electricity permits toeliminate the turbine (compared with a gas turbinepower plant) or both the boiler and the turbine(compared with a steam power plant) eliminationreduces losses of energy.
• It is estimated that by 2020, almost 70 % of the totalelectricity generated in the world will be from MHDgenerators.• Research and development is widely being done on MHDby different countries of the world.Nations involved:• USA• Former USSR• Japan• India• China• Yugoslavia• Australia• Italy• Poland
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