Magneto hydrodynamic power generation:
Power generation through magneto hydrodynamic generation was introduced in 1832 first time by Michel Faraday. In which electrical energy is produced by converting heat into electrical energy. Magneto means magnet and hydro means working fluid by the combination of these two the Magneto Hydro Dynamic Power Generation MHD system will work. In the Magneto Hydro Dynamic Power Generation system the kinetic energy of the electrical conducting material flows in the presence of magnetic field dynamics directly into the electrical energy.
Principle of Magneto hydrodynamic power generation:
The basic idea of the Magneto Hydro Dynamic Power Generation is simple if we have some kind of a channel and if we allow a very hot gas through it, hot gas in the sense plasma that means the bulk of the gas is ionized the electrons have been stripped off, so we have essentially electrons and ions flowing and if we have magnetic field in the direction perpendicular to direction of the conductor. The electrons will be deflected by the magnetic field. The ions will also be deflected by the magnetic field in opposite direction so if we put electrodes in the two sides then some voltage will be induced in these two electrodes and if we have connect some external circuit a current will flow so this is essential idea of the magneto hydro dynamic power generator. Because of the magnetic field there is a charge separation and that charge separation is collected by electrodes and that is what allows the current to flow through an external circuit. The essential idea of the Magneto Hydro Dynamic Power Generation is where we have a fuel which is either a liquid fuel or a gaseous fuel that will be burnt creating a very high temperature and that high temperature gas will be right in the beginning allowed to flow through this kind of a channel. That means that it passes at high speed thus extracting power that is contained in that gas and then after the power is generated a part of the energy is extracted. The rest of the energy still contains a lot of energy that goes through and that is then further extracted by a conventional thermal power plant. That means this MHD cycles becomes conjunction with the conventional steam based thermal power plant becomes what is known as a combined cycle power plant where the MHD is the topping cycle and the Rankine cycle is the bottom. Toping in the sense that where it is high temperature that is when the topping part of the energy is extracted and when it goes out this relatively lower temperature that is when the bottoming part is effective. But there is something more to it. Firstly how we can raise the temperature simply by burning a gas. That means these kinds of systems are considered where there is availability of natural gas and those places will be very effective Magneto Hydro Dynamic Power Generation. It is also considered to use coal in the sense that coal can also be converted into gas. Gasification of coal and then coal can be burnt. So if we are considering that kind of cycle then coal can also be used as a fuel. But essentially we have to some kind of a clean gaseous fuel as a fuel. But still the temperature that is attained here is not sufficient to ionize most of the gas. So there is something additional put in and in order to increase the level of ionization either cesium or potassium is injected. That means a bit of cesium and potassium is injected into the gas this is called seeding that potassium immediately gets ionized and that adds to the overall level of ionization of the material. That means the free electrons that are free to move in this plasma is principally contributed by the seed. So even of the temperature is not all that high, if it is sufficient to ionize the seed that is sufficient. There would be the electrons and ions. Ions would be for example the cesium or potassium ions that will contain its mass. Each of this ion mass will be for exceeding the mass of electron many times about 25 to 1000 times. As a result the bulk of the transport they are in equal in numbers the number of electrons assuming that one is stripped off from one, would be in equal numbers or in some cases electrons will be larger in number provided larger number is stripped off from each ion. So we are considering the actual the bending of the path and then finally reaching that electrode right and the bending of the path will obviously depend on the mass of that ion or electron taking part in the activity. If it is heavy then it will have a larger probability of just going through. If it is light it will bend and take part in this activity. So then this leads us to conclude that bulk of the current that is generated due to electrons though theoretically both take part. Ultimately the activity that happens here is due to electrons. So let consider motion of the electrons in a bit more detail. The structure of the Magneto Hydro Dynamic Power Generation would be something like that MHD consists of chamber in which we have the injection of air and fuel takes place. So this is the combustion chamber, from the chamber it will be sort of going out like a nozzle and the electrodes will be on the two sides of the nozzle and the magnetic field will be perpendicular to it and when it goes out of the nozzle then it is that only in this part the energy is generated and after that it goes to normal boiler in which we have boiler drum there will be water walls and finally there will be superheated section before it take place. Part of the energy is extracted at a higher efficiency through the MHD. When the electron moves in the Magneto Hydro Dynamic in which magnetic field is perpendicular to it the direction, the force can be find by using left hand rule. It will feel a force downward as a result the motion of the electron will be deflected and it will move in helical path. So if the component of the velocity in the direction of B is present it will move in helical path. There could also be electric field because we have also pair of electrodes being in two different voltages will face electric field also. It will drift in the direction of the electric field. It will move in circle if there is no electric field. In the presence of both electric field and magnetic field its motion will be the combination of both. So first we will consider if there is only magnetic field and the component of the velocity is only the direction orthogonal to B. Second we will consider if there is a component of the velocity in the direction of B and third we will consider what will happen if there is an additional electric field. As there is large number of electrons and ions in that gas so we cannot really say that electron will go just like that because it will collide. So ultimately the electrons will transverse a path that will go through various collisions. The acceleration will be centripetal acceleration:
The force that will act on the electron will be centripetal force which is:
e(V x B)= mv2/r
Then we will have to multiply with the number Z representing how many of the electronic charge is there in ion.
ZeB = mv/r
The negative sign shows that electron move opposite to the motion of electric field.
Construction of Magneto Hydro Dynamic Power Generation MHD:
MHD consists of a chamber in which we have two poles of magnet one is North Pole and other is South Pole. The two sides are anode and cathode. When these north and South Pole give magnetic field and anode and cathode will attract the respective ions. In an MHD generator, electrically conducting gas such as plasma or ionized gas at a very high temperature is passed at high velocity through this chamber then electric current will generate in this working fluid. The gas will be used as electrical conductor. Electric current will be generating in the gas and the ions will go through respective electrodes and dc power supply will be generated by this manner which will be further converted into ac power supply. MHD has two systems open and close system.
Open Magneto hydrodynamic system:
It consists of the following components:
- Coal processor
- Expansion nozzle
- MHD system
- Air pre-heater
- Seed recovery
- Purifier for nitrogen and Sulphur
- Stack or chimney
The compressor will work for air compression. All the components are connected through pipes. The air pre-heater is connected with the compressor to supply pre heat to the compressor for increasing the efficiency of the MHD system.
Working of the open Magneto Hydro Dynamic MHD system:
The working fluid in open MHD Magneto Hydro Dynamic Power Generation system is air. Coal will come from the coal processor and after burning of coal the combustor will produce hot gases and compressor will supply air to the combustion chamber where air will be heated to about 2000 C and is converted into plasma or ionized gas. Then this plasma or ionized gas is supply to the MHD and the respective ion will go the respective electrodes. By this process electric current generation will takes place and inverter will convert this dc power into ac power. Now the extracted gases will go to the air pre heater, seed recovery, purifier and then to the chimney. Airs pre-heater will pre heat the air. Seed recovery means when give away the extra additive to the gas or increasing the dialectical conductivity of the gas then this additive will be recover by this seed recovery box. Then after this purifier in the gas some polluting agent like nitrogen or sulphur are removed by the purifier and then the gas is pass through the chimney. So this is open MHD system in which air is used as working fluid.
Closed Magneto Hydro Dynamic system:
The closed MHD consists of the following components:
- Coal processor
- Heat exchanger
- Expansion nozzle
- MHD system
- Seed recovery
Working of closed Magneto Hydro Dynamic system:
The working fluid in the closed MHD system is argon or helium gas. Coal processor will process the coal and send to the combustion chamber. The combustion chamber will exchange the heat energy with the heat exchanger and argon will be converted into vapour and this argon or helium gas will be sent to the MHD system and the respective ion will go to the respective electrode which will then send to the inverter or dc power supply. The further process same as in the open MHD system. But the extraction of the heat is also used for the heat exchanger for generating steam and after this turbine will rotate with the help of the steam and generator will create energy. This is another cycle of the close MHD system. Now in this this system argon will be supplied again and again because this is closed MHD system.
The MHD system works on two laws Faraday law and Lorentz force. According to Faraday law “induced emf is produced when conductor moves across magnetic field which will further produce current” here in the MHD the working fluid works as conductor and will pass through the magnetic field. The other is Lorentz force which states that when a particle will move in magnetic field the particle will experience force.
Where v is the velocity of the particle
B is the magnetic field and q is the charge.
MHD technology has quite less environmental burden as compared to other methods of power generation. The efficiency comparison between different power
generation systems clearly indicates the supremacy of MHD generation over the other systems.
Advantages of Magneto Hydro Dynamic Power Generation
The advantages of Magneto Hydro Dynamic power generation over the other power generation are given below:
- Magneto Hydro Dynamic power generation involve only fluid and there are no moving mechanical parts due to which it has no mechanical loss.
- MHD wall will maintain the temperature of the fluid
- The cost of Magneto Hydro Dynamic power generation is less than other generation
- It has the ability to reach full power level almost directly.
- Magneto Hydro Dynamic power generation has very high efficiency.