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MHD-PPT

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MHD-PPT

  1. 1. SAURAV LAHOTI Department of EEE DSCE, BENGALURU-78. GUIDE: P. USHA MHD GENERATORS
  2. 2.  NEED FOR MHD  INTRODUCTION  PRINCIPLE  HALL EFFECT  ELECTRODE CONFIGURATION FOR VARIOUS MHD GENERATOR  VARIOUS SYSTEMS  ADVANTAGES  CONCLUSION  REFERENCE
  3. 3. 0 0.5 1 1.5 2 2.5 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 Metric tons of Carbon dioxide per capita
  4. 4.  Magneto hydro dynamic (MHD) principle is applied for generating power from coal fired or reactor power plants.    MHD generator plant does not require any turbine and does not have any generator shaft. In a MHD generator the thermal energy in plasma (hot ionized gas) is directly converted to electrical energy (without intermediate conversion to mechanical shaft energy).  
  5. 5.  The field of MHD was initiated by  Hannes Alfvén , for which he received the  Nobel Prize in Physics in 1970 Hannes Alfvén
  6. 6.  When an electric conductor moves across a magnetic field, a voltage is induced in it which produces an electric current.  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.  The principle can be explained as follows: An electric conductor moving through a magnetic field experiences a retarding force as well as an induced electric field and current.
  7. 7.  This effect is a result of FARADAYS LAWS OF ELECTRO MAGNETIC INDUCTION  The induced EMF is given by Eind = u x B where u = velocity of the conductor. B = magnetic field intensity.  The induced current is given by, Iind = C x Eind where C = electric conductivity
  8. 8. The disturbance of lines of current flow in conducting path is due to the application of magnetic field leading to an electric potential gradient transverse to direction of current flow.     The field Ē gets influenced by Hall Effect as follows:- Electrons moving in field E constitute flow of current. This current flow is through the strong magnetic field B & hence produces another gradient ε cause by Hall Effect.   Field ε is in transverse direction to field E. The direction of electron field is governed by electron angular frequency & electron mean free time and hall parameters. Due to Hall Effect and resulting, the path of electrons departs from original field caused by MHD such that the direction becomes inclined to E.   HALL EFFECTHALL EFFECT
  9. 9. HALL EFFECTHALL EFFECT
  10. 10. There are three possible arrangements of providing electrodes in MHD generators to counter Hall effect. Segmented electrode configuration: The electrode segments are separated by insulator segments, so there will be no current flowing in the direction. The electric field vector has a component both along the channel and across the channel.
  11. 11. Continuous electrode configuration: In this case the electric field is across the channel only, but the current has components along the channel as well as across it. In this case the hall angle is minimized and thus losses are reduced. Hall electrode: In this case the electrodes wrap up the channel all the way in segment. The electric field becomes parallel to the channel axis. Due to this reason there cannot be any potential difference across the channel.
  12. 12. The MHD systems are broadly classified into following types.  OPEN CYCLE SYSTEM  CLOSED CYCLE SYSTEM  LIQUID METAL SYSTEM
  13. 13. Fossil fuel (coal) is burnt to very high temperature in the furnace to very high temperature to achieve ionized gas. The electrical conductivity of the plasma is increased by seeding the gas by addition of potassium or cesium. High conductivity plasma is accelerated through the MHD tunnel convergent-divergent portion of the nozzle shaped tunnel.
  14. 14. The pressure ratio (P1/P2) from high pressure side to low pressure side to nozzle throat is so high and angle of divergence of tunnel is such that very high gas velocity is achieved in divergent portion. Conductive gas passes through the magnetic field B of the MHD generator. The MHD generator delivers DC electric power through its electrode system. Heat from hot exhaust gases can be recovered further in the heat recovery chamber. Heat is supplied to heat exchanger to produce steam for steam turbine which drives auxiliary generator.
  15. 15. CLOSED CYCLE SYSTEMCLOSED CYCLE SYSTEM
  16. 16.  Two general types of closed cycle MHD generators are being investigated.  Electrical conductivity is maintained in the working fluid by ionization of a seeded material, as in open cycle system.  A liquid metal provides the conductivity.  The carrier is usually a chemical inert gas, all through a liquid carrier is 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 heat exchanger. Hence the heat sources and the working fluid are independent. The working fluid is helium or argon with cesium seeding.
  17. 17. Two working fluids are used, one for liquid metal & the other for inert gases. Liquid metal is heated by coal fired plant or nuclear reactor plant. Heating by liquid metal causes the expansion of inert gases. The mixture of inert gas & liquid metal is passed through MHD tunnel. The gas expanding in the tunnel gets accelerated & increases the velocity of the mixture. The liquid metal acts as a moving conductor in the tunnel. After passing through the MHD generator, the two fluids are separated again. The liquid metal is reheated. The gas is cooled & recompressed. Both the working fluids are re-circulated again.
  18. 18.  The conversion efficiency of a MHD system can be around 50% much higher compared to the most efficient steam plants. Still higher efficiencies are expected in future, around 60 – 65 %, with the improvements in experience 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 fuel plants.
  19. 19.  Although the cost cannot be predicted very accurately, yet it has been reported that capital costs of MHD plants will be competitive to conventional steam plants.  It has been estimated that the overall operational costs in a plant would be about 20% less than conventional steam plants.  Direct conversion of heat into electricity permits to eliminate the turbine (compared with a gas turbine power plant) or both the boiler and the turbine (compared with a steam power plant) elimination reduces losses of energy.  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.  It is possible to use MHD for peak power generations and emergency service. It has been estimated that MHD equipment for such duties is simpler, has capability of generating in large units and has the ability to make rapid start to full load.
  20. 20. CONCLUSIONCONCLUSION In the MHD generator the advantage of having no moving parts allows to work at higher temperatures than a conventional energy conversion. It is possible to work with temperature around 3000K, and a these temperature the maximum theoretical efficiency would be near 90%. In the section of near future MHD power generation system the plant efficiency can be increased by increasing the working temperature. Also, in order to reduce CO2 emission, use nuclear power with high efficiency
  21. 21. REFERENCEREFERENCE ELECTRICAL POWER SYSTEMS- Dr. S.L. UPPAL, Prof. S. RAO NON-CONVENTIONAL ENERGY SOURCES- G.D. RAI GOOGLE INTERNATIONAL JOURNAL OF SCIENTIFIC AND RESEARCH PUBLICATIONS, VOLUME 3, ISSUE 6, JUNE 2013

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