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Solution cum Scheme of Evaluation

IV/IV B.Tech (Regular) Degree Examination

ME 423 Power Plant Engineering

Mechanical Engineering

March, 2017

Prepared by

P.Umamaheswarrao

Assistant Professor

Department of Mechanical Engineering

Bapatla Engineering College

Bapatla-522102

Mob: 9440871256

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1. 12x 1M=12 M

a) Hydrograph is defined as a graph showing discharge (Runoff) of flowing water with respect to

time for a specified time. The time period for discharge hydrograph may be hour, day, week or

month. The discharge may be m3/sec, or day-second-metre.

b) Surge tank (or surge chamber) is a device introduced within a hydropower water conveyance

system having a rather long pressure conduit to absorb the excess pressure rise in case of a

sudden valve closure. It also acts as a small storage from which water may be supplied in case of

a sudden valve opening of the turbine. In case of a sudden opening of turbine valve, there are

chances of penstock collapse due to a negative pressure generation. If there is no surge tank.

c) The method of increasing the air capacity of an engine is known as supercharging.

The device used to increase the air density is known as supercharger.

(or)

Supercharging is a process of increasing the pressure of air supplied to an internal combustion

engine.

d) Remove heat from the water discharged from the condenser so that the water can be

discharged to the river or recirculated and reused.

A cooling tower is a heat rejection device that rejects waste heat to the atmosphere through the

cooling of a water stream to a lower temperature. Cooling towers may either use the evaporation

of water to remove process heat and cool the working fluid to near the wet-bulb air temperature

or, in the case of closed circuit dry cooling towers, rely solely on air to cool the working fluid to

near the dry-bulb air temperature.

e) Coal and ash Circuit

Air and gas circuit

Feed water and steam circuit

Cooling water circuit

f) 1. Mechanical dust collectors

i) Wet type (Scrubbers)

a) Spray type

b) Packed type

c) Impingement type

ii) Dry type

a) Gravitational separators

b) Cyclone separators

2. Electrical dust collectors

a) Rod type

b) Plate type

g) Tariffs (or) energy rates are the different methods of charging the consumers for the

consumption of electricity.

Objectives

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1. Recovery of cost of capital investment in generating equipment, transmission and distribution

system

2. Recovery of the cost of operation, supplies and maintenance of the equipment

3. Recovery of the cost of material, equipment, billing and collection cost as well as for

miscellaneous services.

h) It is defined as the ratio of energy produced in a given time to the maximum possible energy

that could have been produced during the actual number of hours the plant was in operation

i) 1. Cost of land, buildings

2. Cost of equipments, transmission and distribution lines

3. Interest on loan, insurance, taxes

j)

Principle of Tidal power generation:

Tide or wave is periodic rise and fall of water level of the sea. Tides occur due to the attraction

of sea water by the moon. Tides contain large amount of potential energy which is used for

power generation. When the water is above the mean sea level, it is called flood tide. When

water level is below the mean level it is called ebb tide.

Working of Tidal power generation:

The arrangement of this system is shown in image. The ocean tides rise and fall and water can be

stored during the rise period and it can be discharged during fall. A dam is constructed separating

the tidal basin from the sea and a difference in water level is obtained between the basin and sea.

During high tide period, water flows from the sea into the tidal basin through the water turbine.

The height of tide is above the tidal basin. Hence the turbine unit operates and generates power,

as it is directly coupled to a generator.

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During low tide period, water flows from tidal basin to sea, as the water level in the basin is

more than that of the tide in the sea. During this period also, the flowing water rotates the turbine

and generates power.

The generation of power stops only when sea level and the tidal basin level are equal. For the

generation of power economically using this source of energy requires some minimum tide

height and suitable site. Kislaya power plants in France are the only examples of this type of

power plant

k)

A fuel cell is a device that converts the chemical energy from a fuel into electricity through a

chemical reaction with oxygen or another oxidizing agent.

(or)

A Fuel Cell is an electrochemical device that combines hydrogen and oxygen to produce

electricity, with water and heat as its by-product.

Advantages

1. High conversion efficiency

2. It can be installed near the user

3. Most fuel cells operate silently, compared to internal combustion engines. They are therefore

ideally suited for use within buildings such as hospitals.

4. Fuel cells can eliminate pollution caused by burning fossil fuels; for hydrogen fuelled fuel

cells, the only by-product at point of use is water.

5. No need of large volumes of cooling water

l) The thermoelectric effect is the direct conversion of temperature differences to electric

voltage and vice versa.

A thermoelectric device creates voltage when there is a different temperature on each side.

Conversely, when a voltage is applied to it, it creates a temperature difference. At the atomic

scale, an applied temperature gradient causes charge carriers in the material to diffuse from the

hot side to the cold side.

2. a) Run-off is the total amount of water flowing into a stream. 1M

Factors influencing Run off 3M

1. Rainfall pattern

The runoff is more if the rainfall is heavy. The runoff increases more rapidly with

increase in rainfall because the time allowed for evaporation and percolation losses is small when

the intensity of rainfall is high. If the duration of the rainfall is more, the runoff will also be

prolonged because the soil tends to become saturated and lowers the rate of seepage and humid

atmosphere slows evaporation.

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2. Character of catchment area

The topography, shape, its vegetal cover and nature of the surface and sub-surface geology

have great influence upon the runoff characteristics of the catchment area. The steep and rocky

surface gives more runoff.

3. Shape and size of the catchment area

Large catchment area gives more runoff.

4. Vegetation

The nature and extent of vegetation including crops determine the transpiration and

interception losses. Vegetation, particularly of forest, has considerable effect upon the runoff. It

consumes a proportion of the rain fall, causes interception losses and provides physical

obstruction for runoff.

5. Geology of the area

The geology of the catchment area is of fundamental importance in the consideration of

runoff. Rocky area gives higher runoff than softy or sandy area.

6. Weather conditions

Low temperature, high relative humidity and low winds give high runoffs because the

evaporation losses increase with the increase in temperature, decrease in relative humidity and

increase in wind velocity. Water absorbed by the hot earth is also more which reduces the runoff.

Measurement methods of Run off 2M

Rational Method

Tracer method

Velocity -area method with current-meter

Velocity -area method using the dipping bar or “Tauchstab nach Jens“

Bucket method

Float method

Bucket method

If one finds a spot where it is possible to capture all the water from the stream flow (for example

at a spillway), using a stop watch and a bucket one can collect the volume of water delivered by

the stream during a precisely known period, and then measure this volume to finally calculate the

discharge.

Velocity-area method with current-meter

Principle:

Discharge is obtained by calculating the integral of the stream velocity over the cross-section

area of the flow A, where is measured perpendicular to the cross-section:

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The velocity can be measured in discrete intervals along the cross-section by means of a

current-meter. A current-meter consists of a small propeller mounted on a pole that is connected

to a device which measures the frequency of the propeller rotation. This information can be

converted into a stream velocity using the provided look-up tables, which were established

during calibration experiments.

If we assume a purely laminar flow, the theory of fluid mechanics states that the stream velocity

is expected to vary vertically following a parabolic function because of the zero velocity (no-slip

condition) at the bottom of the stream bed. In case of a turbulent flow, we would get a

logarithmic function. For this reason, velocity should ideally be measured at several depths for

each interval along the river cross-section. Alternatively, a single measurement is best taken at

40% of the local depth, which is generally the depth with the mean velocity.

Errors in the measurements can be introduced by random occurrences of turbulent eddies during

the establishment of the profile, by changes in water height or width of the stream. During the

experiment you should also take care to estimate the uncertainty of your measurements.

2. b) 6M

i) The mean discharge for the given data =

80+50+40+20+0+100+150+200+250+120+100+80/12

= 1160/12 = 96.67 millions of m3/month

ii) It is necessary to find lengths of time during which certain flows are available to obtain the

flow duration curve.

Discharge in millions of

m3/month

Total number of months

during which flow is available

% of Time

0 12 100

20 11 91.8

40 10 83.4

50 9 75

80 8 66.6

100 6 50

120 4 33.3

150 3 25

200 2 16.65

220 1 8.3

Power available in MW = mgh 1

-------- x ηa x ------ 1000 1000

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= 96.67x106x9.81 1000x100 1

-------------------- x -------------- x 0.8 x ----

30x24x3600 1000 1000

= 29.26 MW

3. a) Line Diagram of Diesel Engine Power Plant 5M

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1. Engine: This is the main component of the plant which develops required power. The engine is directly

coupled to the generator.

2. Air-filter and super charger:

The function of the air filter is to remove the dust from the air which is taken by the engine.

The function of the supercharger is to increase the pressure of the air supplied to the engine to

increase the power of the engine. The superchargers are generally driven by the engines.

3. Exhaust system:

This includes the silencers and connecting ducts. The temperature of the exhaust gases is

sufficiently high; therefore, the heat of the exhaust gases many times is used for heating the oil or

air supplied to the engine.

4. Fuel system:

It includes the storage tank, fuel pump, fuel transfer pump, strainers and heater. The fuel is

supplied to the engines according to the load on the plant.

5. Cooling system: This system includes water circulating pumps, cooling towers or spray ponds and water filtration

plant. The purpose of cooling system is to carry the heat from the engine cylinder to keep the

temperature of the cylinder in safe range and extend its life.

6. Lubrication system: It includes the oil pumps, oil tanks, filters, coolers and connecting pipes. The function of the

lubrication system is to reduce the friction of moving parts and reduce the wear and tear of the

engine parts.

7. Starting system: This includes compressed air tanks. The function of this system is to start the engine from cold

by supplying the compressed air.

8. Governing system:

The function of the governing system is to maintain the speed of the engine constant

irrespective of load on the plant. This is done generally by varying fuel supply to the engine

according to load

Fuel Injection system 1M

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A single pump supplies high pressure fuel to header, a relief valve holds the pressure constant.

The control wedge adjusts the lift of mechanically operated valve to set amount and time of

injection.

3. b) Various methods to improve Thermal efficiency of Gas Turbine Power plant

a) Intercooling 2M

b) Reheating 2M

c) Regeneration 2M

Intercooling

A compressor utilizes the major percentage of the power developed by the gas turbine. The work

required by the compressor can be reduced by compressing the air in two stages and

incorporating a intercooler between two.

Reheating

The output of gas turbine can be improved by expanding the gases in two stages with a reheater

between the two.

The H.P Turbine drives the compressor and the L.P Turbine provides useful power output.

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Regeneration

The exhaust gases from the Turbine carry a large quantity of heat with them since their

temperature is far above the ambient temperature.

They can be used to heat air coming from the compressor there by reducing the mass of fuel

supplied in the combustion chamber.

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4. a) Unit and Central System 4M

Advantages of unit system 1M

1. It is simple in layout and cheaper than central system

2. The coal transportation system is simple

3. It allows direct control of combustion from the pulveriser

4. The maintenance charges are less as spares required are less

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Advantages of Central or Bin system 1M

1. The central system is flexible and changes can be made to accommodate quick changes in

demand

2. There is greater degree of flexibility as the quantity of fuel and air can be separately controlled

3. Burners can be operated independently of the operation of coal preparation

4. b) La Mont Boiler 5M

Advantages: 1M

1. It can high pressure boiler.

2. It is flexible in design.

3. This boiler can reassemble in natural circulation boiler.

4. It can easily start.

5. It has high steam generation capacity of about 50 ton/ hour.

6. This boiler has higher heat transfer rate.

5. a) Advantages 1M

1. It is clean, dustless and totally enclosed

2. Its ash carrying capacity is considerably large therefore it is more suitable for large thermal

power plants

3. It can discharge the ash at a considerable distance (1000m) from the power plant

4. It can also be used to handle a stream of molten ash

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Low pressure hydraulic ash handling system 2M

High pressure hydraulic ash handling system 3M

5. b) Draught 1M

Principle of Forced and Induced Draught 3M

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Draught is defined as a small pressure difference required between the fuel bed (furnace) and

outside air to maintain constant flow of air and to discharge the gases through chimney to the

atmosphere. Draught can be obtained by chimney, fan, steam jet (or) -air jet (or) combination of

these.

Classification of Draught 1M Draught is classified as

1. Natural draught

2. Artificial draught

The artificial draught is further classified as

(a) Steam jet draught

(b) Mechanical draught

(c) Induced draught

(d) Forced draught

Why balanced draught is preferred over forced or induced draught 1M

In the induced draught system, when the furnace is opened for firing, the cold air enters

the furnace and dilute the combustion. In the forced draught system, when the furnace is opened

for firing, the high pressure air will try to blow out suddenly and furnace may stop. Hence the

furnace cannot be opened for firing or inspection in both, systems. Balanced draught, which is a

combination of induced and forced draught, is used to overcome the above stated difficulties.

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6. a) Pressurised water Reactor 4M

Working In a typical design concept of a commercial PWR, the following process occurs:

The core inside the reactor vessel creates heat.

Pressurized water in the primary coolant loop carries the heat to the steam generator.

Inside the steam generator, heat from the primary coolant loop vaporizes the water in a

secondary loop, producing steam.

The steamline directs the steam to the main turbine, causing it to turn the turbine

generator, which produces electricity.

The unused steam is exhausted to the condenser, where it is condensed into water. The resulting

water is pumped out of the condenser with a series of pumps, reheated, and pumped back to the

steam generator. The reactor's core contains fuel assemblies that are cooled by water circulated

using electrically powered pumps. These pumps and other operating systems in the plant receive

their power from the electrical grid. If offsite power is lost, emergency cooling water is supplied

by other pumps, which can be powered by onsite diesel generators. Other safety systems, such as

the containment cooling system, also need electric power. PWRs contain between 150-200 fuel

assemblies.

Advantages 1M

1. PWR reactors are very stable due to their tendency to produce less power as temperatures

increase; this makes the reactor easier to operate from a stability standpoint.

2. PWR reactors can be operated with a core containing less fissile material. This significantly

reduces the chance that the reactor will run out of control and makes PWR designs relatively safe

from critical accidents.

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3. PWR reactors can use ordinary water as coolant, moderator hence less expensive and easily

available.

4. PWR turbine cycle loop is separate from the primary loop, so the water in the secondary loop

is not contaminated by radioactive materials.

5. A small number of control rods are required.

Disadvantages 1M

1. The coolant water must be highly pressurized to remain liquid at high temperatures. This

requires high strength piping and a heavy pressure vessel and hence increases construction costs.

2. Most pressurized water reactors cannot be refueled while operating. This decreases the

availability of the reactor - it has to go offline for comparably long periods of time (some weeks).

3. Natural uranium is only 0.7% Uranium-235, the isotope necessary for thermal reactors.

This makes it necessary to enrich the uranium fuel, which increases the costs of fuel

production. If heavy water is used it is possible to operate the reactor with natural uranium, but

the production of heavy water requires large amounts of energy and is hence expensive.

6. b) Load Curve 2M

i) Energy generated= Area under the load curve

= 20x6+50x4+60x2+40x4+80x4+70x2+40x2

= 120+200+120+160+320+140+80

= 1140 Mw-hrs

Average load = 1140/24= 47.5 MW

Load Factor = Average load/Max Demand= 47.5/80= 0.594 2M

ii) If the load above 60 MW is supplied by a stand by unit of 20 MW capacity, the energy

generated

= 20x4+10x2 = 80+20 = 100MW-hrs

Time during which stand by unit remains in operation = 6 hours

Average load = 100/6 = 16.7 MW

Load factor = Average load/Peak load = 16.7/20 = 0.835 2M

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7. a)

Nuclear power plant 2M

Capital cost = 6000x100x103

= Rs 60x107

Interest = Rs (10/100) x 60x107

Annual fixed cost (Interest +Depreciation) = 2 x (10/100) x 60x107

= Rs 12x107

Energy generated per year = Avg.load x 8760

= Load factor x Max. Demand x 8760

= 0.4 x 100x 103 x 8760 = 35.04 x 10

7 KWh

Running cost/KWh = operating cost/ KWh + Transmission and distribution cost/ KWh

= 12+0.24=12.24 Paise

Overall cost / KWh = Running cost/KWh + Fixed cost

= 12.24+ (12x 107/35.04 x 10

7) x 100

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= 46.48 Paise

Hydro plant 2M

Capital cost = 4320x100x103 = 43.2 x10

7

Depreciation = (8/100) x 43.2x 107 = 3.456 x10

7

Interest = (10/100) x 43.2x 107 = 4.32 x 10

7

Annual fixed cost (Interest +Depreciation) = 3.456 x107+4.32 x 10

7= 7.776 x 10

7

Running cost/KWh = 6+ 0.96 = 6.96 Paise

Overall cost / KWh = Running cost/KWh + Fixed cost

= 6.96 + (7.776 x 107/35.04 x 10

7) x 100

= 29.15 Paise

Steam plant 2M

Capital cost = 2160x100x103 = 21.6 x10

7

Interest = (12/100) x 21.6x 107 = 2.592 x 10

7

Depreciation = (12/100) x 21.6x 107 = 2.592 x 10

7

Annual fixed cost (Interest +Depreciation) = 2.592 x 107+2.592 x 10

7 = 5.184x 10

7

Running cost/KWh = 18+0.24= 18.24 Paise

Overall cost / KWh = Running cost/KWh + Fixed cost

= 18.24 + (5.184x 107/35.04 x 10

7) x 100

= 33.03 Paise

Therefore, overall cost/KWh is minimum in case of hydro power plant.

7. b) Thermal Pollution 2M

Thermal pollution is defined as sudden increase or decrease in temperature of a natural body of

water which may be ocean, lake, river or pond by human influence. This normally occurs when a

plant or facility takes in water from a natural resource and puts it back with an altered

temperature. Usually, these facilities use it as a cooling method for their machinery or to help

better produce their products.

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Sources of Thermal Pollution:

The following sources contribute to thermal pollution.

Nuclear power plants

Coal fired plants

Industrial effluents

Nuclear power plants

Nuclear power plants including drainage from hospitals, research institutions, nuclear

experiments and explosions, discharge a lot of heat that is not utilized along with traces of toxic

radio nuclides into nearby water streams. Emissions from nuclear reactors and processing

installations are also responsible for increasing the temperatures of water bodies. The operations

of power reactors and nuclear fuel processing units constitutes the major contributor of heat in

the aquatic environment. Heated effluents from power plants are discharged at 10 C higher than the receiving waters that affects the aquatic flora and fauna.

Coal-fired power plants

Coal fired power plants constitute a major source of thermal pollution. The condenser coils in

such plants are cooled with water from nearby lakes or rivers. The resulting heated water is

discharged into streams thereby raising the water temperature by 15C. Heated effluent decreases

the dissolved content of water resulting in death of fish and other aquatic organisms. The sudden

fluctuation of temperature also leads to "thermal shock" killing aquatic life that have become

acclimatized to living in a steady temperature.

Industrial effluents

Industries like textile, paper, pulp and sugar manufacturing release huge amounts of cooling

water along with effluents into nearby natural water bodies. The waters polluted by sudden and

heavy organic loads result in severe drop in levels of dissolved oxygen leading to death of several aquatic organisms.

Solid waste pollution 2M

Solid wastes are any discarded or abandoned materials. Solid wastes can be solid, liquid, semi-

solid or containerized gaseous material.

Causes of solid waste pollution

Causes of solid waste pollution are pollutants from households, industrial units, manufacturing

units, commercial establishments, landfills, hospitals and medical clinics. The pollutants from

these places may be in the form of non-biodegradable matter or non-compostable degradable

matter.

Trash collected from households often takes the form of plastic bags and organic waste. Solid

feces flowing out of homes and into sewers pollute underground water. Commercial

establishments also pile up a lot of such waste matter. Industrial units involved in manufacturing

produce toxic solid waste, such as slag, from the industrial process of obtaining metals from their

ores.

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Hospitals and clinics also produce waste in the form of disposable syringes, used test tubes,

plastic bags used for collecting blood, cotton swabs and used bandages. Such solid waste needs

careful handling and disposal. The soil becomes polluted with dangerous medical waste when

such matter is disposed of directly into landfills.

Solid waste is usually dumped in landfills. Landfills are large pits in the ground that act as

garbage disposal places. The biodegradable matter in landfills becomes a part of the soil

gradually. The toxic non-biodegradable and non-compostable matter poses a health hazard as it

does not decompose but mixes with the soil and the underground water.

Industrial incinerators are used to burn trash on a large scale. They cause pollution by emitting

greenhouse gases while burning solid waste.

Methods to control Pollution 2M

1. Preventive Technique

It includes use of devices for removal of pollutants from exhaust gases e.g. Scrubbers, dry and

wet collectors, filters, Electro Static Precipitator.

Building of higher stake facility for discharging of pollution into air.

2. Effluents control

Substitution of raw materials causing more pollution with that of less pollution causing materials.

Use of non conventional fuels like Gobar gas, Bio gas, CNG and LPG must be prepared and

encouraged

Venturi Scrubbers

• Venturi scrubbers use a liquid stream to remove solid particles.

• In the venturi scrubber, gas laden with particulate matter passes through a short tube with

flared ends and a constricted middle.

• This constriction causes the gas stream to speed up when the pressure is increased.

Venturi Scrubber

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• The difference in velocity and pressure resulting from the constriction causes the particles

and water to mix and combine.

• The reduced velocity at the expanded section of the throat allows the droplets of water

containing the particles to drop out of the gas stream.

• Venturi scrubbers are effective in removing small particles, with removal efficiencies of

up to 99 percent.

• One drawback of this device, however, is the production of wastewater.

Electrostatic Precipitators (ESPs)

An ESP is a particle control device that uses electrical forces to move the particles out of the

flowing gas stream and onto collector plates.

The ESP places electrical charges on the particles, causing them to be attracted to oppositely

charged metal plates located in the precipitator

• The particles are removed from the plates by "rapping" and collected in a hopper located

below the unit.

• The removal efficiencies for ESPs are highly variable; however, for very small particles

alone, the removal efficiency is about 99 percent.

• Electrostatic precipitators are not only used in utility applications but also other industries

(for other exhaust gas particles) such as cement (dust), pulp & paper (salt cake & lime

dust), petrochemicals (sulfuric acid mist), and steel (dust & fumes).

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8. a) Horizontal Axis Wind Turbine 3M

Advantages of Horizontal Axis Wind Turbine

1. Tall tower allows placement on uneven land or in offshore locations

2. Tall tower allows access to strong wind

3. Ability to warp blades, which gives the turbine blades the best angle of attack

Disadvantages

1. The tall towers and long blades are hard to transport from one place to another and they need a

special installation procedure.

2.

VERTICAL AXIS WIND TURBINE 3M

Vertical axis wind turbines have the main rotor shaft running vertically. The tower

construction is simple here because the generator and gear box can be placed at the bottom, near

the ground.

Vertical axis wind turbine can be classified into two types

1. Darrieus type

2. Savonius type

Darrieus type rotor

This wind mill needs much less surface area. It is shaped like an egg beater and has two

or three blades shaped like aero foils.

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Savonius type rotor

Savonius turbine is S-shaped if viewed from top. This turbine turns relatively slow, but

yields high torque. It is used for grinding grains and for pumping water.

Advantages of vertical Axis wind turbines

They can produce electricity in any wind direction

Strong supporting tower in not needed because generator, gearbox and other components

are placed on the ground

Low production cost as compared to horizontal axis wind turbine

As there is no need of pointing turbine in wind direction to be efficient so yaw drive and

pitch mechanism is not needed

Disadvantages

As only one blade of wind turbine work at a time so efficiency is very low

They need a initial push to start, this action use few of its own produce electricity

When compared to horizontal axis wind turbine they are very less efficient with respect

to them. This is because they have an additional drag when their blades rotate.

They have relative high vibration because the air flow near the ground creates turbulent

flow

8. b) OTEC system 1M

Ocean Thermal Energy Conversion (OTEC) is a process that can produce electricity by using the

temperature difference between deep cold ocean water and warm tropical surface waters. OTEC

plants pump large quantities of deep cold seawater and surface seawater to run a power cycle and

produce electricity. OTEC is firm power (24/7), a clean energy source, environmentally

sustainable and capable of providing massive levels of energy.

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OTEC open cycle 3M

OTEC closed cycle 2M

9. a) Solar Pond Power Plant 4M

Working 2M

The sun is the largest source of renewable energy and this energy is abundantly available in all

parts of the earth. It is in fact one of the best alternatives to the non-renewable sources of energy.

One way to tap solar energy is through the use of solar ponds. Solar ponds are large-scale energy

collectors with integral heat storage for supplying thermal energy. It can be use for various

applications, such as process heating, water desalination, refrigeration, drying and power

generation.

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The solar pond works on a very simple principle. It is well-known that water or air is heated they

become lighter and rise upward e.g. a hot air balloon. Similarly, in an ordinary pond, the sun’s

rays heat the water and the heated water from within the pond rises and reaches the top but loses

the heat into the atmosphere. The net result is that the pond water remains at the atmospheric

temperature. The solar pond restricts this tendency by dissolving salt in the bottom layer of the

pond making it too heavy to rise.

A solar pond has three zones. The top zone is the surface zone, or UCZ (Upper Convective

Zone), which is at atmospheric temperature and has little salt content. The bottom zone is very

hot, 70°– 85° C, and is very salty. It is this zone that collects and stores solar energy in the form

of heat, and is, therefore, known as the storage zone or LCZ (Lower Convective Zone).

Separating these two zones is the important gradient zone or NCZ (Non-Convective Zone). Here

the salt content increases as depth increases, thereby creating a salinity or density gradient. If we

consider a particular layer in this zone, water of that layer cannot rise, as the layer of water above

has less salt content and is, therefore, lighter. Similarly, the water from this layer cannot fall as

the water layer below has a higher salt content and is, therefore, heavier. This gradient zone acts

as a transparent insulator permitting sunlight to reach the bottom zone but also entrapping it

there. The trapped (solar) energy is then withdrawn from the pond in the form of hot brine from

the storage zone.

9. b) 1M

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

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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.

Principle of MHD Generation

The principle 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

across the terminals. As the name implies, the magneto hydro dynamics generator 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 strips while 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.

Closed cycle MHD system 5M