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Showing posts with label Generation. Show all posts
Showing posts with label Generation. Show all posts

Monday, December 23, 2019

December 23, 2019

MHD Generation or Magneto Hydro Dynamic Power Generation

MHD Generation or Magneto Hydro Dynamic Power Generation

The MHD generation or, also known as magneto hydrodynamic power generation is a direct energy conversion system which converts the heat energy directly into electrical energy, without any intermediate mechanical energy conversion, as opposed to the case in all other power generating plants. Therefore, in this process, substantial fuel economy can be achieved due to the elimination of the link process of producing mechanical energy and then again converting it to electrical energy.

History of MHD Generation

The concept of MHD power generation was introduced for the very first time by Michael Faraday in the year 1832 in his Bakerian lecture to the Royal Society. He in fact carried out an experiment at the Waterloo Bridge in Great Britain for measuring the current, from the flow of the river Thames in earth’s magnetic field.
This experiment in a way outlined the basic concept behind MHD generation over the years then, several research work had been conducted on this topic, and later in August 13, 1940 this concept of magneto hydro dynamic power generation, was imbibed as the most widely accepted process for the conversion of heat energy directly into electrical energy without a mechanical sub-link.

Principle of MHD Generation

The principal of MHD power generation is very simple and is based on Faraday's law of electromagnetic induction, which states that when a conductor and a magnetic field moves relative to each other, then voltage is induced in the conductor, which results in flow of current  acrossthe terminals.
As the name implies, the magneto hydro dynamics generator shown in the figure below, is concerned with the flow of a conducting fluid in the presence of magnetic and electric fields. In conventional generator or alternator, the conductor consists of copper windings or stripswhile in an MHD generator the hot ionized gas or conducting fluid replaces the solid conductor.
A pressurized, electrically conducting fluid flows through a transverse magnetic field in a channel or duct. Pair of electrodes are located on the channel walls at right angle to the magnetic field and connected through an external circuit to deliver power to a load connected to it. Electrodes in the MHD generator perform the same function as brushes in a conventional DC generator. The MHD generator develops DC power and the conversion to AC is done using an inverter.
The power generated per unit length by MHD generator is approximately given by,

Where, u is the fluid velocity, B is the magnetic flux density, σ is the Electrical conductivity of conducting fluid and P is the density of the fluid.It is evident from the equation above, that for the higher power density of an MHD generator there must be a strong magnetic field of 4-5 tesla and high flow velocity of conducting fluid besides adequate conductivity.

MHD Cycles and Working Fluids

The MHD cycles can be of two types, namely
  1. Open Cycle MHD.
  2. Closed Cycle MHD.
The detailed account of the types of MHD cycles and the working fluids used, are given below.

Open Cycle MHD System

In open cycle MHD system, atmospheric air at very high temperature and pressure is passed through the strong magnetic field. Coal is first processed and burnet in the combustor at a high temperature of about 2700oC and pressure about 12 ATP with pre-heated air from the plasma. Then a seeding material such as potassium carbonate is injected to the plasma to increase the electrical conductivity. The resulting mixture having an electrical conductivity of about 10 Siemens/m is expanded through a nozzle, so as to have a high velocity and then passed through the magnetic field of MHD generator. During the expansion of the gas at high temperature, the positive and negative ions move to the electrodes and thus constitute an electric current. The gas is then made to exhaust through the generator. Since the same air cannot be reused again hence it forms an open cycle and thus is named as open cycle MHD.

Closed Cycle MHD System

As the name suggests the working fluid in a closed cycle MHD is circulated in a closed loop. Hence, in this case inert gas or liquid metal is used as the working fluid to transfer the heat. The liquid metal has typically the advantage of high electrical conductivity, hence the heat provided by the combustion material need not be too high. Contrary to the open loop system there is no inlet and outlet for the atmospheric air. Hence, the process is simplified to a great extent, as the same fluid is circulated time and again for effective heat transfer.

Advantages of MHD Generation

The advantages of MHD generation over the other conventional methods of generation are given below.
  1. Here only working fluid is circulated, and there are no moving mechanical parts. This reduces the mechanical losses to nil and makes the operation more dependable.
  2. The temperature of working fluid is maintained by the walls of MHD.
  3. It has the ability to reach full power level almost directly.
  4. The price of MHD generators is much lower than conventional generators.
  5. MHD has very high efficiency, which is higher than most of the other conventional or non-conventional method of generation.
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December 23, 2019

Power Plants and Types of Power Plant

Power Plants and Types of Power Plant


What is Power Plant?

A power plant or a power generating station, is basically an industrial location that is utilized for the generation and distribution of electric power in mass scale, usually in the order of several 1000 Watts. These are generally located at the sub-urban regions or several kilometers away from the cities or the load centers, because of its requisites like huge land and water demand, along with several operating constraints like the waste disposal etc.
For this reason, a power generating station has to not only take care of efficient generation but also the fact that the power is transmitted efficiently over the entire distance and that’s why, the transformer switch yard to regulate transmission voltage also becomes an integral part of the power plant.
At the center of it, however, nearly all power generating stations has an AC generator or an alternator, which is basically a rotating machine that is equipped to convert energy from the mechanical domain (rotating turbine) into electrical domain by creating relative motion between magnetic field and the conductor.

The energy source harnessed to turn the generator shaft varies widely, and is chiefly dependent on the type of fuel used.

Types of Power Station

A power plant can be of several types depending mainly on the type of fuel used. Since for the purpose of bulk power generation , only thermal, nuclear and hydro power comes handy, therefore a power generating station can be broadly classified in the 3 above mentioned types. Let us have a look in these types of power stations in details.

Thermal Power Station

A thermal power station or a coal fired thermal power plant is by far, the most conventional method of generating electric power with reasonably high efficiency. It uses coal as the primary fuel to boil the water available to super heated for driving the steam turbine. The steam turbine is then mechanically coupled to an alternator rotor, the rotation of which results in the generation of electric power. Generally in India, bituminous coal or brown coal are used as fuel of boiler which has volatile content ranging from 8 to 33% and ash content 5 to 16 %. To enhance the thermal efficiency of the plant, the coal is used in the boiler in its pulverized form.
In coal fired thermal power plant, steam is obtained in very high pressure inside the steam boiler by burning the pulverized coal. This steam is then super heated in the super heater to extreme high temperature. This super heated steam is then allowed to enter into the turbine, as the turbine blades are rotated by the pressure of the steam.
The turbine is mechanically coupled with alternator in a way that its rotor will rotate with the rotation of turbine blades. After entering into the turbine, the steam pressure suddenly falls leading to corresponding increase in the steam volume. After having imparted energy into the turbine rotors, the steam is made to pass out of the turbine blades into the steam condenser of turbine. In the condenser, cold water at ambient temperature is circulated with the help of pump which leads to the condensation of the low pressure wet steam.
Then this condensed water is further supplied to low pressure water heater where the low pressure steam increases the temperature of this feed water, it is again heated in high pressure. This outlines the basic working methodology of a thermal power plant.

Advantages of Thermal Power Plants

  • Fuel used i.e coal is quite cheaper.
  • Initial cost is less as compared to other generating stations.
  • It requires less space as compared to hydro-electric power stations.

Disadvantages of Thermal Power Plants

  • It pollutes atmosphere due to production of smoke and fumes.
  • Running cost of the power plant is more than hydro electric plant.

Nuclear Power Station

The nuclear power generating station are similar to the thermal stations in more ways than one. However, the exception here is that, radioactive elements like uranium and thorium are used as the primary fuel in place of coal. Also in a Nuclear station the furnace and the boiler are replaced by the nuclear power and the heat exchanger tubes.
For the process of nuclear power generation, the radioactive fuels are made to undergo fission reaction within the nuclear reactors. The fission reaction, propagates like a controlled chain reaction and is accompanied by unprecedented amount of energy produced, which is manifested in the form of heat. This heat is then transferred to the water present in the heat exchanger tubes. As a result, super heated steam at very high temperature is produced. Once the process of steam formation is accomplished, the remaining process is exactly similar to a thermal power plant, as this steam will further drive the turbine blades to generate electricity.

Hydro-Electric Power Station

In Hydro-electric plants the energy of the falling water is utilized to drive the turbine which in turn runs the generator to produce electricity. Rain falling upon the earth’s surface has potential energy relative to the oceans towards which it flows. This energy is converted to shaft work where the water falls through an appreciable vertical distance. The hydraulic power is therefore a naturally available renewable energy given by the eqn:
P = gρ QH
Where, g = acceleration due to gravity = 9.81 m/sec 2
ρ = density of water = 1000 kg/m3
H = height of fall of water.
This power is utilized for rotating the alternator shaft, to convert it to equivalent electrical energy.
An important point to be noted is that, the hydro-electric plants are of much lower capacity compared to their thermal or nuclear counterpart. For this reason hydro plants are generally used in scheduling with thermal stations, to serve the load during peak hours. They in a way assist the thermal or the nuclear plant to deliver power efficiently during periods of peak hours.

Advantages of Hydro Electric Power Station

  • It requires no fuel, water is used for generation of electrical energy.
  • It is neat and clean energy generation.
  • Construction is simple, less maintenance is required.
  • It helps in irrigation and flood control also.

Disadvantages Hydro Electric Power Station

  • It involves high capital cost due to dam construction.
  • Availability of water depends upon weather conditions.
  • It requires high transmission cost as the plant is located in hilly areas.

Types of Power Generation

As mentioned above, depending on the type of fuel used, the power generating stations as well as the types of power generation are classified. Therefore the 3 major classifications for power production in reasonably large scale are :-
  1. Thermal power generation .
  2. Nuclear power generation .
  3. Hydro electric power generation .
Apart from these major types of power generations, we can resort to small scale generation techniques as well, to serve the discrete demands. These are often referred to as the alternative methods or non conventional energy of power generation and can be classified as :-
  1. Solar power generation. (making use of the available solar energy)
  2. Geo-thermal power generation. (Energy available in the Earth’s crust)
  3. Tidal power generation.
  4. Wind Power generation (energy available from the wind turbines)
These alternative sources of generation has been given due importance in the last few decades owing to the depleting amount of the natural fuels available to us. In the centuries to come, a stage might be reached when several countries across the globe would run out of their entire reserve for fossil fuels. The only way forward would then lie in the mercy of these alternative sources of energy which might play an instrumental role in shaping the energy supplies of the future. For this reason these might rightfully be referred as the energy of the future.
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