Magneto Hydro Dynamic (MHD) system is a non- conventional source of energy which is based upon Faraday’s Law of Electromagnetic Induction, which states that energy is generated due to the movement of an electric conductor inside a magnetic field.
Principle of MHD Power Generation
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
Principle & Operation
The basic principle of operation is based on Faraday’s law of electro magnetic induction, which states an e.m.f. is induced in a conductor moving in magnetic field. The conductor may be a soild, liquid or a gaseous one.
The study of the dynamics of an electrically conducting fluid interacting with a magnetic field, is called magneto hydro dynamics.
In this method, gases at about 2500°C are passed through the MHD duct across which a strong magnetic field has been applied. Since the gases are hot, and partly ionized they form an electrically conducting conductor moving in the magnetic field. An e.m.f. (directcurrent) is thus induced, which can be collected at suitable electrodes.
Electrically conduction gas is called Plasma
Lorentz Force on the charged particle
F = q(v × B)
v = velocity of the particle
q= charge of the particle
B = magnetic field
Comparison between a Turbo generator and a MHD generator
In Turbogenerator steam, gas or some force moves the turbine i.e mechanical energy changes to electrical energy to generate current however; ionized gas in magnetic field cause energy production in MHD. No energy form change thus gives good output with least wastage.
Steam turbine converts steam energy into mechanical energy, which drives a generator. This way, the mechanical energy is converted into electric energy. The repeated conversion of various forms of energy involves losses and, hence, the overall efficiency of thermal power plant decreases. The typical range of efficiency of thermal plants is 37 to 40%
The direct conversion of heat to electricity would enable the industry to use the fuel resources more efficiently. MHD generation is one form of energy technology, wherein direct conversion of heat into electric energy has been devised
An ionized gas is used as conducting medium in the MHD generator. The gas can be made electrically conducting when it is maintained at least at a temperature of 2000°C. This fact does not allow MHD generation from being used in the entire temperature range from 3000 K to 300 K. It is therefore, thought beneficial that MHD generators be used in conjunction with steam operated thermal plants utilising the heat of the gas leaving the MHD ducts. The combined operation of MHD generators alongwith the conventional thermal plant, will raise the overall efficiency to nearly 60%, thereby lot of saving in the fuel cost will result.
Electrically conducting fluids
*electrical conductivity (1/Ohm´m), shows ability of liquid to interact with
a magnetic field
Types of MHD
The hot gas is first passed through the MHD generator (a process known as topping) and then on to the turbogenerator of a conventional steam plant (the bottoming phase). An MHD power plant employing such an arrangement is known as an open-cycle, or once-through, system.
MHD can also be used with solar concentrator, nuclear reactor etc
Advantages & Disadvantages of MHD Systems