COMSATS University Islamabad – Abbottabad Campus
Department of Electrical & Computer Engineering
POWER GENERATION
ASSIGNMENT NO 3
NAME:
JAWAD UR REHMAN
REGISTRATION NO:
FA18-EPE-028
SECTION:
EPE-7A
SUBMITTED TO:
SIR SIFAT SHAH
MAGNETO HYDRO DYNAMIC GENERATOR
1. INTRODUCTION:
The MHD generator or dynamo transforms thermal energy or kinetic energy directly into
electricity. MHD generators are different from traditional electric generators in that they
can operate at high temperatures without moving parts. The exhaust of a plasma MHD
generator is a flame, still able to heat the boilers of a steam power plant. In the 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, which can be extracted by placing electrodes in suitable position in the stream.
A magneto-hydrodynamic (MHD) generator, similar to a regular generator, generates
electricity by means of revolving a conductor over a magnetic field; where instead of
copper a hot conductive plasma is used as the moving conductor. MHD power generation
has also been studied as a method for extracting electrical power from nuclear reactors
and also from more conventional fuel combustion systems.
2. DIAGRAM:
3. STRUCTURE:
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EXPANSION NOZZLE- The expansion nozzle reduces the gas pressure and
consequently increases the plasma speed (Bernoulli's Law) through the generator
duct to increase the power output. Unfortunately, at the same time, the pressure
drop causes the plasma temperature to fall (Gay-Lussac's Law) which also
increases the plasma resistance, so a compromise between Bernoulli and GayLussac must be found. The exhaust heat from the working fluid is used to drive a
compressor to increase the fuel combustion rate but much of the heat will be
wasted unless it can be used in another process.
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THE PLASMA- The prime MHD system requirement is creating and managing
the conducting gas plasma since the system depends on the plasma having a high
electrical conductivity. The plasma can be likened to the fourth state of matter
after the solid, liquid and gaseous states, in which the atoms or molecules are
stripped of their electrons leaving positively charged ions. Suitable working fluids
are gases derived from combustion, noble gases, and alkali metal vapors.
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FUEL - The material used in the construction of MHD plants must have
temperature resistance. Also, medium inside the MHD duct is very corrosive,
therefore, highly corrosion resistant materials are used in its construction. The
insulating materials used for duct walls are magnesium oxide, strontium zirconate.
Electrodes are made of tungsten of carbon.
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COMBUSTION- In this the fuel-combustion products at temperatures over
2000°C, achieved by preheating the combustion air, are seeded with potassium
carbonate and passed through a magneto hydro dynamic duct. The waste gases are
then used to heat a conventional steam cycle. The magneto hydro dynamic
process is therefore a topping unit increasing the overall efficiency of power
generation to about 45% and potentially over 50%.
4. WORKING PRINCIPLE:
The working principle of MHD generator is based on Faraday’s Law. It states that when a
conductor is moved in a magnetic field an EMF is induced in the conductor. In an MHD
system, hot gases act as the conductor.
When gases are heated to sufficient temperature by burning of fuel, one or more of the
valence electrons are displaced from their orbit in which they are spinning. Thus, the
neutral atoms are split into the positive and negative ion. These ions are the electrical
conductors. After that, ionized gases are moved in a duct known as the MHD duct at very
high velocity. This movement of gas ions in the MHD duct in which strong magnetic
field is applied leads to the electromagnetic induction and an EMF is induced in the pair
of electrodes. The electrodes are connected to the external circuit and they deliver current
to the external load.
5. MATHEMATICAL FORMULATION:
The power produced by an MHD generator is DC. For transmission purposes, DC is
converted in AC.
P = LƱVB2/ρ
Where,
L = length of duct
Ʊ = electrical conductivity of gas
V = velocity of gas
B = Magnetic field density
ρ = density of gas.
Practically, ionization temperature of gases in pure form is very high. Handling of these
high temperatures is very difficult. To overcome this problem, the gas is seeded with a
small quantity of alkaline metals like sodium and potassium. This drops the ionization
temperature of gases considerably. To increase the overall efficiency of the system MHD
system is used in conjunction with steam power plants. Initially, when temperatures of
gases are high, the energy of gases is used in the MHD system for direct conversion into
electricity. After this, when the temperature of gases falls to a low value, the hot gases are
used for steam generation. This steam is used to generate electrical power in a
conventional steam power plant.
6. APPLICATIONS:
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It converts heat energy directly into electrical energy and hence conversion
efficiency is high.
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Although the costs cannot be predicted very accurately, yet it has been reported
that the capital costs of MHD plants will be competitive with those of
conventional steam plants.
Because of higher efficiency, the overall generation cost of an MHD plant will be
less. It has been estimated that the overall generation cost in an MHD plant would
be about 20% less than in conventional steam plants.
The higher efficiency means better fuel utilization. The reduced fuel consumption
would offer additional economic and social benefits and would also lead to the
conservation of energy resources.
The more efficient heat utilization would decrease the amount of heat discharged
to the environment and the cooling water requirements would also be lower.
The research studies have shown that the use of precipitator not only recovers the
seed material but also effectively traps most other pollution agents.
It has no moving parts.
On and OFF time is very low.
It is a pollution free system.
The size of MHD power plants is small as compared to conventional power plants
for same power output.
The cost of power generation per unit is less.
The operational and maintenance costs are low.
The efficiency of MHD plants is 50% whereas the efficiency of most efficient
conventional power plants is about 40%.
It can work on any type of fuel.