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Gujarat Power Engineering & Research Institute

Power Plant Engineering

Prepared By:-1)Patel Pranav V.(131040119042)2) Patel Jigar B. (131040119032)

Guided By:-Dr. Vijay K. Matawala

Prepared By P. Vijaykumar Patel

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High Pressure BoilersThe steam Generating Unit

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Rankine Cycle

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Purpose of Boilers:-• For generating power in steam engines or steam turbines.• In textile industries for sizing and bleaching.• For heating the buildings in cold weather and for producing

hot water for hot water supply.• In the Process industry like sugar, Fertilizers, Paper.• Marine applications.• Locomotives (it is now a day obsolete).

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Boiler Classification The boilers are classified based on the various criteria :• Based on the contents of fluid :- - Fire tube Boilers - Water Tube Boilers• Based on applications:- - Utility Boilers - Industrial Boilers - Marine Boilers - Locomotive Boilers• Based on Axis :- - Horizontal Boilers - Vertical Boilers

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Continue...• Based on the fuel :-

- Coal - Wood - Gas - Diesel

• Based on the Pressure:-- High Pressure Boilers (P > 80 bar).- Medium Pressure Boilers (30 < P < 80 bar).- Low Pressure Boilers (P < 30 bar).

• Based on Circulation of Water:-- Natural Circulation- Forced Circulation

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Circulation in boiler:

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Why the High Pressure Boiler ? • Where 30 bar pressure & steam rate of 30 tones/hour is

required the fire tube boilers are preferred due to lower cost.• In the power plant it is necessary to produce the steam at

high pressure , high rate and high efficiency.• For the steam of 30 bar pressure & steam rate of 30

tones/hour is required then the water tube boilers are preferred.

• Modern high pressure boilers are generate stem at the rate of 30 to 650 tones/hour and pressure upto 225 bar and temp. of around 5500 C.

• To reduce the drum size.

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Advantages of High pressure Boilers• Due to forced circulation of water, evaporative capacity of the

boiler is increased and size of drum is reduced.• Due to high velocity of water, chances of scale formation is

reduced.• Due to uniform heating there is less chances of overheating.• High Temp. and Pressure increases the plant efficiency.• The steam can be raised quickly to meet the variable load.• It is using modified draught system which leads to reduction

in the pollution.

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Different High Pressure Boilers• La-Mont Boiler• Benson Boiler• Velox Boiler• Loffler Boiler• Schmidt-Hartmann Boiler• Supercritical Boiler• Supercharged Boiler• fluidized bed combustion Boiler

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La-Mont Boiler

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Specifications• Pressure 120 bar .• Temperature up to 5000 C or above.• Steam production rate : 45 to 50 tones/hour.

Difficulties• The deposition of salt and sediments on the inner surfaces of

the water tubes ,which reduces the heat transfer rate.• There also formation of bubbling at the inner surfaces of

water tubes.

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Benson Boiler

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Specifications• It was discovered based on the argument of “If the pressure

of boiler is raised to the critical pressure of (225 bar), the steam and water have same density .”

• So, The danger of bubble formation can be easily eliminate.• Temperature high up to 6500 C .• Pressure 225 bar.• Steam production rate : 150 tones/hour.• Once through boiler.

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Advantages• It does not require drum it leads to the overall weight up to

20% and also reduction in cost also.• At the overload it can be operated economically by changing

pressure and temperature.• There is no problem of bubbling.• High steam generation rate. So, used for steam power plant.

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Disadvantages• Salt deposition.• Sediment on the inner surface of tube.• Danger of over heating.

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Loeffler Boiler

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Specification• Forced circulation.• Pressure 100 bar.• Steam production rate : 100 tones/hour.

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Working• The steam circulating pump draws saturated steam from

evaporative drum.• The steam passes through radiant and convective

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Schmidt-Hartmann Boiler

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Supercritical Boiler

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Continue...• The most recent method to produce economical electric

power is by the use of supercritical boiler in the power plant.• In the supercritical boiler working under the pressure above

critical pressure (221.2 bar), so the enthalpy of evaporation is becomes zero. And at the temperature of 3740 C. and the problems of bubbling is solved.

• The once through boiler is only type suited to supercritical boiler.

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Advantages• Heat transfer rates are very high.• There is no drum, so it weight is reduced.• There is no two phase mixture. So, there is erosion and

corrosion is minimised.

Disadvantages• The high pressure and temperature restrict the use of it.• The impurities remains in tubes after evaporation of water and blocks the flow passages.

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Supercharged Boiler

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• When the combustion is carried out under high pressure in the combustion chamber by supplying the compressed air then rate of heat transfer is increased and heating surfaces required is reduced.

• The high pressure & temperature exhaust gases from combustion chamber are used to run the turbine. The work of turbine is used to run compressor.

Continue...

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Advantages• It requires the 20 to 30 % less heat transfer area.• Rapid start is possible in this boiler.• The part of turbine output can be used to run another

auxiliary of boiler.

Note:- it requires tight passage for high pressure gas.

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Fluidized bed combustion Boiler• Fluidized bed combustion (FBC) is a combustion technology

used to burn solid fuels.• In its most basic form, fuel particles are suspended in a hot,

bubbling fluidity bed of ash and other particulate materials (sand, limestone etc.) through which jets of air are blown to provide the oxygen required for combustion or gasification.

• The resultant fast and intimate mixing of gas and solids promotes rapid heat transfer and chemical reactions within the bed.

• FBC plants are capable of burning a variety of low-grade solid fuels, including most types of coal and woody biomass, at high efficiency and without the necessity for expensive fuel preparation (e.g., pulverising).

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Principle of FBC

FLUE GASES

AIR IN

FEED WATER IN

DISTRIBUTOR PLATE

COAL + DOLOMITE

STEAM OUT

ASH

EVAPORATOR TUBE

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Principle of FBC

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Advantages• High thermal efficiency.• Short commissioning and erection period. • Efficient operation at temperatures down to 150° C ( i.e. well

below the ash fusion temperature).• Reduced coal crushing etc. (pulverised coal is not a necessity

here).• The system can respond rapidly to changes in load demand,

due to quick establishment of thermal equilibrium between air and fuel particles in the bed.

• The operation of fluidized bed furnace at lower temperature helps in reducing air pollution.

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Disadvantages• There may be problem in distribution of coal and dolomite.• The direct contact of flue gases and tubes may erosion.• High pressure air is required.

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Types of FBC• Atmospheric FBC

- Classical FBC- Circulation FBC

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Classical FBC

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Advantages• Production of NOx is temperature depended as in FBC

temperature is less than other combustion processes Hence it results in low production of NOx.

• Lower production of SOx because SO2, SO3 etc. are captured by limestone.

• FBC has 10 times more heat transfer then other combustion processes because of burning particle, hence it has a high combustion efficiency.

• FBC has a lower combustion temperature of 750 °C whereas an ordinary boiler operates at 850 °C.

• Less area is required for FBC due to high coefficient of convective heat transfer.

• Low air pollution.

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Circulation FBC

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Circulation FBC

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Continue...

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Advantages• Increase in bed residence time.• High lateral turbulence.• Effective burning.• Comparative low pollution.• Easy removal of Ash.