Magneto hydro dynamic system

1. Prepared by
Prof. Vijay Patel
1PROF. V.C.PATEL
MAGNETO HYDRO DYNAMICS
(MHD) GENERATION

2. Content
o Introduction
o Need of MHDs
o Principle Of MHD Power Generation
o Types of MHD System
o Open Cycle MHD System
o Closed Cycle MHD System
o Difference between
Open Cycle and Closed Cycle MHD System
o Advantages & Disadvantages OF MHD System
o Applications & Conclusion 2PROF. V.C.PATEL

3. Introduction
The Magneto hydrodynamic (MHD) generator is a device that
converts thermal energy of a fuel into electrical energy.
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.
3PROF. V.C.PATEL

4.  Concept given by Michael Faraday in 1832 for the first time.
 MHD System widely used in advanced countries.
 Under construction in INDIA.
4PROF. V.C.PATEL

5. Need of MHDs
At present a plenty of energy is needed to sustain
industrial and agricultural production , and the existing
conventional energy sources like coal, oil, uranium etc are not
adequate to meet the ever increasing energy demands.
Consequently, efforts have been made for harnessing energy
from several non-conventional energy sources like Magneto
Hydro Dynamics (MHD) System.
5PROF. V.C.PATEL

6. 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.
6PROF. V.C.PATEL

7. Lorentz Force on the charged particle (vector),
F = Q (v × B)
where,
F = force acting on the particle.
v = velocity of the particle (vector)
Q = charge of the particle (scalar)
B = magnetic field (vector)
7PROF. V.C.PATEL

8. 8PROF. V.C.PATEL

9. 9
Construction
S
N
combustio
n
Chamber
VIonized Gas
Working
fluid
Water
cooler
Thermal resistance
sealing Magnet
Stream
out
Load
output
Nozzle
Electrod
e
Inlet
 MHD generator consist of a Combustion chamber and generator
chamber.
 The fluid conductor is passed into the combustion
chamber where they are ionized at very high temperature.
 There is a nozzle through which the ionized gas pass into the
generator chamber.
 The generator chamber consist of powerful magnet and a number
of oppositely located electrode pair is inserted in the channel to
conduct the electrical current generated to an external load.
 Both combustion chamber and generator chamber are surrounded
by a heat resistance material and water cooler.PROF. V.C.PATEL

10. S
N
combustio
n
Chamber
V
Ionized Gas
Working
fluid
Water
cooler
Thermal resistance
sealing Magnet
Stream
out
Load
output
Nozzle
Electrod
e
Inlet
Working
 The gaseous (fluid) conductor is passed into the combustion
chamber through inlet.
 By using a fuel like oil (or) natural gas (or) coal, the fluid
conductor is heated to a plasma state and hence it is ionized.
 The temperature in the combustion chamber is around 2000°K to
2400°K.
 The heat generated in the combustion chamber removes the
outermost electrons in the fluid conductor.
 Therefore, the gas particle acquires the charge.
 The charged gas particles with high velocity enters into the
generator chamber via nozzle.
 The positive and negative charge moves to corresponding
electrodes (anode and Cathode) and constitute the current.
 In generator chamber, based principles of Faraday’s law, the high
velocity ionized conducting gas particles experience the magnetic
filed at right angles to their motion of direction and hence the
potential (current) is produced.
The direction of current (Potential) is perpendicular to both the
direction of moving gas particle and to the magnetic field.
90°
90°
Potential (E)
Ionized gas (Q)
Magnetic field (B)
The diagram shows the direction of
charged particle, magnetic field and the
current produced.
All three field are perpendicular to each
other. 10PROF. V.C.PATEL

11. 11
 The electrodes are connected to an external circuit to get a
load output.
 The current produced in the MHD generator are direct current
(DC).
 This DC current can be converted into alternative current
(AC) using an inverter attached with the external circuit.
 In MHD generator, the seeding materials such as potassium and
cesium are used to reduce the ionization temperature.
 These seeds are mixed with fuel material such as natural gas and
coal.
 The overall efficiency of MHD generators are about 50 to 60 %.
 The electrode are made generally using high temperature ceramic
materials such as carbides (SiC,ZrC,MbC), bromides (ZrB2, TiB2,
LaB2) and silicides (WS and MOSi2 ).PROF. V.C.PATEL

12. Comparison between a Turbo generator
and a MHD generator
 A turbo generator is the
combination of a turbine
directly connected to an electric
generator for the generation of
electric power.
 The MHD (Magneto Hydro
Dynamic) generator transforms
thermal energy and kinetic energy
directly into electricity.
12PROF. V.C.PATEL

13. Types of MHD System
1. Open cycle System:
The working fluid is used on the once through basis.
2. Closed cycle System:
The working fluid is continuously recirculated.
I. Seeded inert gas systems
II. Liquid metal systems
13PROF. V.C.PATEL

14. Coal
Processor
Coal
 The fuel used maybe oil through an oil tank or gasified coal
through a coal gasification plant.
Open Cycle System
14PROF. V.C.PATEL

15.  The fuel (coal, oil or natural gas) is burnt in the combustor or
combustion chamber.
 The hot gases from combustor is then seeded with a small amount
of ionized alkali metal (cesium or potassium) to increase the electrical
conductivity of the gas.
 The seed material, generally potassium carbonate is injected into
the combustion chamber, the potassium is then ionized by the hot
combustion gases at temperature of roughly 2300 °c to 2700 °c.
Coal
Processor
Coal
Combustor
Compressed Air
Open Cycle System
15PROF. V.C.PATEL

16.  To attain such high temperatures, the compressed air is used to
burn the coal in the combustion chamber, must be adequate to at least
1100’c. A lower preheat temperature would be adequate if the air is
enriched in oxygen. An alternative is used to compress oxygen alone
for combustion of fuel, little or no preheating is then required. The
additional cost of oxygen might be balanced by saving on the
preheater.
Coal
Processor
Coal
Combustor
Compressed Air
Open Cycle System
16PROF. V.C.PATEL

17.  The hot pressurized working fluid living in the combustor flows
through a convergent divergent nozzle. In passing through the
nozzle, the random motion energy of the molecules in the hot gas is
largely converted into directed, mass of energy. Thus , the gas
emerges from the nozzle and enters the MHD generator unit at a high
velocity.
Coal
Processor
Coal
Combustor
Compressed Air
Open Cycle System
Magnet
Magnet
MHD
Generator
Seeding
17PROF. V.C.PATEL

18.  The arrangement of the electrode connection is determined by the
need to reduce the losses arising from the Hall effect. By this
effect, the magnetic field acts on the MHD-generated current and
produces a voltage in flow direction of the working fluid.
Coal
Processor
Coal
Combustor
Compressed Air
Open Cycle System
Magnet
Magnet
MHD
Generator
Seeding
The MHD generator is a
divergent channel made of a
heat resistant alloy with
external water cooling. The
hot gas expands through the
rocket like generator
surrounded by powerful
magnet. During motion of the
gas the +ve and –ve ions
move to the electrodes and
constitute an electric current.
Inverter AC Power
DC
Supply
18PROF. V.C.PATEL

19. Coal
Processor
Combustor
Magnet
AirPreheater
OR
Regenerator
Inverter
Magnet
MHD
Generator
Coal
Compressed Air
Seeding
AC Power
DC
Supply Exhaust
Gases
Open Cycle System
 The larger residual heat available from the hot discharge working
gas can then be utilized in several ways. For example it converse to
preheat the combustion air by way of a heat exchanger similar to the
regenerator in a gas turbine.
19PROF. V.C.PATEL

20. Open Cycle System
Coal
Processor
Combustor Purifiers
Magnet
AirPreheater
OR
Regenerator
Inverter
Seed
Recovery
Apparatus
Magnet
MHD
Generator
S
t
a
c
k
Coal
Compressed Air
Seeding
AC Power
DC
Supply Exhaust
Gases
Sulphur &
Nitrogen
Flue
Gases
 The seed material is recovered for successive use in seed recovery
apparatus. Prior to the discharge of the working gas (as flue gas ) from
the steam boiler to the atmosphere the fly ash from the coal fuel must
be removed. However , instead of discharging fly ash , as is usually
done, it may have to be treated for the recovery of the seed material
which is mixed with flu ash.
 Unless the sulphur in the coal has been removed , the original
potassium carbonate seed will have been converted into potassium
sulphate.
 The removal of residual sulphur by the potassium carbonate seed
eliminates need for desulphurization of the flue gas, but nitrogen
oxides are not removed. When oxygen alone is used for combustion
of the coal , the problem of nitrogen oxide formation does not arise.
 However, if nitrogen is present, the nitrogen oxide content of the
combustion gases will be high because of the required high temp. of
the working fluid. Consequently a controlled combustion procedure is
used to reduced the nitrogen oxide level in the discharge flue gas. The
air supplied to the combustion chamber is not sufficient to permit the
complete combustion therefore additional air is supplied.
 The lower combustion temp. is accompanied by a decrease in the
nitrogen oxide concentration.
20PROF. V.C.PATEL

21.  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.
Closed Cycle System
21PROF. V.C.PATEL

22. Closed Cycle System( Seeded Inert Gas )
 In a closed cycle system the carrier gas operates in the form of
Brayton cycle. In a closed cycle system the gas is compressed and
heat is supplied by the source, at essentially constant pressure, the
compressed gas then expands in the MHD generator, and its pressure
and temperature fall. After leaving this generator heat is removed
from the gas by a cooler, this is the heat rejection stage of the cycle.
Finally the gas is recompressed and returned for reheating.
22PROF. V.C.PATEL

23. Combustor
MHD
Generator
Diffuser
Air
Preheater
Inverter
STST
Compresso
r with
Intercooler
Gasifier
Air,
Steam &
Coal
2HE
AC3Φ
1HE
Argon
Compressor
Generator
To
Stack
CondenserFeed
Water ST = Steam Turbine
HE = Heat Exchanger
Magnet
 The complete system has three distinct but interlocking loops.
1.On the left is the external heating loop (Open).
2.In the center is the MHD loop (Closed).
3.On the right is the steam loop (Closed).
Closed Cycle System( Seeded Inert Gas )
23PROF. V.C.PATEL

24. Combustor
Air
Preheater
Gasifier
Air,
Steam &
Coal
1HE
To
Stack
 In the First loop, Coal is gasified and burnt in the combustor.
 The flue gas are passed through primary heat exchanger, Air
Preheater and air purifier for removal of nitrogen and sulphur, and
then discharged to the atmosphere.
Closed Cycle System( Seeded Inert Gas )
24PROF. V.C.PATEL

25.  In the primary Heat Exchanger 1, Heat from the flue gases is
transferred to a carrier gas Argon/helium (Working Fluid) of the
MHD cycle. The problem of extracting the seed material from fly ash
does not arise due to the combustion system is separated from the
working fluid
Combustor
MHD
Generator
Diffuser
Air
Preheater
Inverter
STST
Compressor
with
Intercooler
Gasifier
Air,
Steam &
Coal
2HE
AC3Φ
1HE
Argon
Compressor
Generator
To
Stack
CondenserFeed
Water ST = Steam Turbine
HE = Heat Exchanger
Magnet
Closed Cycle System( Seeded Inert Gas )
25PROF. V.C.PATEL

26. Combustor
MHD
Generator
Diffuser
Air
Preheater
Inverter
STST
Compressor
with
Intercooler
Gasifier
Air,
Steam &
Coal
2HE
AC3Φ
1HE
Argon
Compressor
Generator
To
Stack
CondenserFeed
Water ST = Steam Turbine
HE = Heat Exchanger
Magnet
 The loop in the centre is the MHD loop. In this loop, a seeded
insert gas is compressed and then heated in a primary heat exchanger.
A small quantity of the seed material is then added to make up for the
loss of seed through leakage. The seed, cesium metal, is more
expensive than potassium but attains adequate conductivity at a
relatively lower temp. of 1900 ºC.
Closed Cycle System( Seeded Inert Gas )
26PROF. V.C.PATEL

27. As little make up seed is required due to closed loop operation an
expensive but better seed material may be advisable. The lower temp.
Operation also permits wide choice of material for various
equipments. However, operation at lower temp. Also reduces the
thermal efficiency of the cycle. The DC output available from the
MHD generator is inverted to obtain grid quality AC.
Combustor
MHD
Generator
Diffuser
Air
Preheater
Inverter
STST
Compressor
with
Intercooler
Gasifier
Air,
Steam &
Coal
2HE
AC3Φ
1HE
Argon
Compressor
Generator
To
Stack
CondenserFeed
Water ST = Steam Turbine
HE = Heat Exchanger
Magnet
Closed Cycle System( Seeded Inert Gas )
27PROF. V.C.PATEL

28. Combustor
MHD
Generator
Diffuser
Air
Preheater
Inverter
STST
Compressor
with
Intercooler
Gasifier
Air,
Steam &
Coal
2HE
AC3Φ
1HE
Argon
Compressor
Generator
To
Stack
CondenserFeed
Water ST = Steam Turbine
HE = Heat Exchanger
Magnet
 The loop in the right side is the steam loop. The working fluid is
slowed down in the diffuser to a low subsonic speed for further
recovery of the heat of working fluid.
Closed Cycle System( Seeded Inert Gas )
28PROF. V.C.PATEL

29.  Then hot fluid (argon/helium) enters a secondary heat exchanger,
which serves as a waste heat boiler to generate steam.
Combustor
MHD
Generator
Diffuser
Air
Preheater
Inverter
STST
Compressor
with
Intercooler
Gasifier
Air,
Steam &
Coal
2HE
AC3Φ
1HE
Argon
Compressor
Generator
To
Stack
CondenserFeed
Water ST = Steam Turbine
HE = Heat Exchanger
Magnet
Closed Cycle System( Seeded Inert Gas )
29PROF. V.C.PATEL

30.  This steam is partly utilized to a drive a turbine generator and for
driving a turbine which runs the argon/helium compressor.
Combustor
MHD
Generator
Diffuser
Air
Preheater
Inverter
STST
Compressor
with
Intercooler
Gasifier
Air,
Steam &
Coal
2HE
AC3Φ
1HE
Argon
Compressor
Generator
To
Stack
CondenserFeed
Water ST = Steam Turbine
HE = Heat Exchanger
Magnet
Closed Cycle System( Seeded Inert Gas )
30PROF. V.C.PATEL

31.  The output of the generator is also fed to the main grid. The
working fluid is returned back to the primary heat exchanger after
passing through compressor.
Combustor
MHD
Generator
Diffuser
Air
Preheater
Inverter
STST
Compressor
with
Intercooler
Gasifier
Air,
Steam &
Coal
2HE
AC3Φ
1HE
Argon
Compressor
Generator
To
Stack
CondenserFeed
Water ST = Steam Turbine
HE = Heat Exchanger
Magnet
Closed Cycle System( Seeded Inert Gas )
31PROF. V.C.PATEL

32. Closed Cycle System ( Liquid Metal )
 When a liquid metal provides the electrical conductivity, it is
called a liquid metal MHD system.
 An inert gas is a convenient carrier.
32PROF. V.C.PATEL

33. Drift
Tube or
Mixer
Nuclear
reactor
Magnet
MHD
Generator
To Conventional
Steam Cycle
Nozzle
Liquid
Metal
Boiler Or
Heat
Exchanger
Metal
Vapour
AC Supply
Closed Cycle System ( Liquid Metal )
 The carrier gas is pressurized and heated by passage through a heat
exchanger within combustion chamber. The hot gas is then
incorporated into the liquid metal usually hot sodium to form the
working fluid. The latter then consists of gas bubbles uniformly
dispersed in an approximately equal volume of liquid sodium. 33PROF. V.C.PATEL

34.  The working fluid is introduced into the MHD generator through a
nozzle in the usual ways. The carrier gas then provides the
required high direct velocity of the electrical conductor.
Drift
Tube or
Mixer
Nuclear
reactor
Magnet
MHD
Generator
To Conventional
Steam Cycle
Nozzle
Liquid
Metal
Boiler Or
Heat
Exchanger
Metal
Vapour
AC Supply
Closed Cycle System ( Liquid Metal )
34PROF. V.C.PATEL

35.  After passage through the generator, the liquid metal is separated
from the carrier gas. Part of the heat exchanger to produce steam for
operating a turbine generator. Finally the carrier gas is cooled,
compressed and returned to the combustion chamber for reheating
and mixing with the recovered liquid metal.
Drift
Tube or
Mixer
Nuclear
reactor
Magnet
MHD
Generator
To Conventional
Steam Cycle
Nozzle
Liquid
Metal
Boiler Or
Heat
Exchanger
Metal
Vapour
AC Supply
Closed Cycle System ( Liquid Metal )
 The working fluid temperature is usually around 800’c as the
boiling point of sodium even under moderate pressure is below 900’c.
At lower operating temp, the other MHD conversion systems may be
advantageous from the material standpoint, but the maximum thermal
efficiency is lower.
 A possible compromise might be to use liquid lithium, with a
boiling point near 1300’c as the electrical conductor lithium is
much more expensive than sodium, but losses in a closed
system are less.
35PROF. V.C.PATEL

36. Open Cycle System Closed Cycle System
 Working fluid after generating
electrical energy is discharged to
the atmosphere through a
stack.
 Working fluid is recycled to
the heat sources and thus is used
again.
 Operation of MHD generator
is done directly on combustion
products.
 Helium or argon(with cesium
seeding) is used as the working
fluid.
 Temperature requirement:
2300˚Cto 2700˚C.
 Temperature requirement :
about 530˚C.
 More developed.  Less developed.
Difference Between Open Cycle And
Closed Cycle System
36PROF. V.C.PATEL

37. Advantages of MHD System
 Conversion efficiency of about 50%.
 Less fuel consumption.
 Large amount of pollution free power generated .
 Ability to reach full power level as soon as started.
 Plant size is considerably smaller than conventional fossil fuel
plants .
 Less overall generation cost.
 No moving parts, so more reliable . 37PROF. V.C.PATEL

38. Disadvantages of MHD System
 Suffers from reverse flow (short circuits) of electrons through
the conducting fluids around the ends of the magnetic field.
 Needs very large magnets and this is a major expense.
 High friction and heat transfer losses.
 High operating temperature.
 Coal used as fuel poses problem of molten ash which may
short circuit the electrodes. Hence, oil or natural gas are
much better fuels for MHDs. Restriction on use of fuel
makes the operation more expensive.
38PROF. V.C.PATEL

39. Applications
 Power generation in space craft.
 Hypersonic wind tunnel experiments.
 Defense application.
39PROF. V.C.PATEL

40. MHD Design Problems and Developments
40PROF. V.C.PATEL

41. THANK YOU !!
41PROF. V.C.PATEL