PRESENTATION ON STEAM BOILERS

WHAT IS A BOILER?WHAT IS A BOILER?

A boiler is usually a closed vessel made of steel. Its function is to A boiler is usually a closed vessel made of steel. Its function is to transfer the heat produced by the combustion of fuel to water and transfer the heat produced by the combustion of fuel to water and ultimately to generate steam.ultimately to generate steam.open vessels, generating steam at atmospheric pressure are not open vessels, generating steam at atmospheric pressure are not considered to be boiler.considered to be boiler.

The steam produced may be supplied toThe steam produced may be supplied to• • power generationpower generation • • heatingheating

space heatingspace heatinghot water supplyhot water supply

• • industrial processesindustrial processes sugar millssugar millschemical industrieschemical industries

Essential of a good boilersEssential of a good boilers1. The boiler should be capable of generating steam at the required1. The boiler should be capable of generating steam at the required pressure and of the required quality quickly and with minimum fuelpressure and of the required quality quickly and with minimum fuel consumption.consumption.2. The initial cost, installation cost and the maintenance cost of the 2. The initial cost, installation cost and the maintenance cost of the boilerboiler should not be too high.should not be too high.3. The boiler should be light in weight, should need the least amount 3. The boiler should be light in weight, should need the least amount ofof brick work construction and should occupy small floor area.brick work construction and should occupy small floor area.4. The boiler should meet the fluctuating demands or steam supply 4. The boiler should meet the fluctuating demands or steam supply without being overheatedwithout being overheated5. The different parts of the boiler should be easily approachable for 5. The different parts of the boiler should be easily approachable for repairs.repairs.6. There should be no deposition of mud and other foreign particles on 6. There should be no deposition of mud and other foreign particles on thethe heated surfacesheated surfaces7. The boiler should conform to the safety regulations as laid down in 7. The boiler should conform to the safety regulations as laid down in the "Boilers Act“.the "Boilers Act“.

CLASSIFICATION OF BOILERSCLASSIFICATION OF BOILERS

Relative position of hot gas and waterRelative position of hot gas and water

Fire tube boiler Fire tube boiler Hot gasses pass through the tubes that surrounded by water. Horizontal return Hot gasses pass through the tubes that surrounded by water. Horizontal return tubular, vertical tubular, Lancashire, Cochran, Cornish, locomotive fire box, etc.tubular, vertical tubular, Lancashire, Cochran, Cornish, locomotive fire box, etc.

Water tube boilerWater tube boilerThe tubes contain water and the hot gases flow outside Babcock and Wilcox, The tubes contain water and the hot gases flow outside Babcock and Wilcox, Lamont boiler Wilcox, boiler, la-boiler, Benson boiler and Loffler boiler.Lamont boiler Wilcox, boiler, la-boiler, Benson boiler and Loffler boiler.

Method of firingMethod of firing

• • Internally fired boilerInternally fired boiler Lancashire, Locomotive, and ScotchLancashire, Locomotive, and Scotch

• • Externally fired boilerExternally fired boiler Babcock and WilcoxBabcock and Wilcox

Pressure of steamPressure of steam

• • High pressure (>80 kg/cm2)High pressure (>80 kg/cm2) Babcock and Wilcox Lamont etcBabcock and Wilcox Lamont etc • • Low pressure (<80 kg/cm2)Low pressure (<80 kg/cm2)

Cochran, Cornish, Lancashire and LocomotiveCochran, Cornish, Lancashire and Locomotive

According to the axis of shaftAccording to the axis of shaft

• Vertical tubularVertical tubular• Horizontal tubularHorizontal tubular

Method of circulation of waterMethod of circulation of water

• Natural circulationNatural circulation• Forced circulationForced circulation

Nature of service to be performedNature of service to be performed

• • Land boilersLand boilers• • Portable boilerPortable boiler• • Mobile boilersMobile boilers

Heat sourceHeat source

• • Combustion of solid, liquid, or Combustion of solid, liquid, or gasgas

• • Electrical or nuclear energyElectrical or nuclear energy• • Hot waste gases of other Hot waste gases of other

chemical chemical reactions reactions

Fire Tube BoilersFire Tube Boilers

A fire tube boiler is a type of boiler in which hot gases pass through one or A fire tube boiler is a type of boiler in which hot gases pass through one or more tubes running through a sealed container of water. The heat energy more tubes running through a sealed container of water. The heat energy from the gases passes through the sides of the tubes by thermal from the gases passes through the sides of the tubes by thermal conduction, heating the water and ultimately creating steam.conduction, heating the water and ultimately creating steam.

Types of Fire Tube BoilerTypes of Fire Tube Boiler• • Cochran boilerCochran boiler• • Lancashire boilerLancashire boiler• • Scotch marine boilerScotch marine boiler• • Locomotive boiler etcLocomotive boiler etc

Fig.: Schematic Diagram of a Fire Tube Boiler

Cochran BoilerCochran Boiler• • VerticalVertical• • Multi tubularMulti tubular• • Internally firedInternally fired• • Natural circulationNatural circulation• • Favorable in smallFavorable in small PlantsPlants• • Coal or oil burntCoal or oil burnt

Fire Tube Fire Tube BoilerBoiler

Water Tube BoilerWater Tube Boiler

A water tube boiler is a type of boiler in which water circulates in tubes heatedA water tube boiler is a type of boiler in which water circulates in tubes heatedexternally by the hot gases / flue gases. Water tube boilers are used for high-externally by the hot gases / flue gases. Water tube boilers are used for high-pressure boilers. Fuel is burned inside the furnace, creating hot gas which heatspressure boilers. Fuel is burned inside the furnace, creating hot gas which heatsup water in the steam generating tubes.up water in the steam generating tubes.

Types of water tube boilerTypes of water tube boiler

• • Babcock & Wilcox boiler,Babcock & Wilcox boiler,• • Sterling boiler etc.Sterling boiler etc.

Fig.: Schematic Diagram of a Water Tube Boiler

Water Tube BoilerWater Tube BoilerBabcock & Wilcox boilerBabcock & Wilcox boiler

ComparisonComparisonFire Tube BoilerFire Tube Boiler Water Tube BoilerWater Tube BoilerThe hot gases from the furnace The hot gases from the furnace passpassthrough the tubes which are through the tubes which are surrounded by water in the shellsurrounded by water in the shell

The water circulates inside the The water circulates inside the tubes which are surrounded by tubes which are surrounded by hot gases from the furnacehot gases from the furnace

It cannot handle high pressureIt cannot handle high pressure It is a high pressure boilerIt is a high pressure boilerThe rate of generation of steam is The rate of generation of steam is relatively lowrelatively low

The rate of generation of steam is The rate of generation of steam is highhigh

Overall efficiency is up to 75%Overall efficiency is up to 75% Overall efficiency is up to 90%Overall efficiency is up to 90%It is not preferable for fluctuating It is not preferable for fluctuating loads for a longer time periodloads for a longer time period

It is preferred for widely It is preferred for widely fluctuating loadsfluctuating loads

The operating cost is lessThe operating cost is less The operating cost is highThe operating cost is highThe bursting chances are less but The bursting chances are less but bursting produces greater risk to bursting produces greater risk to the damage of the propertythe damage of the property

The bursting chances are higher The bursting chances are higher butbutbursting doesn’t produce any bursting doesn’t produce any destruction to the whole boilerdestruction to the whole boiler

It is generally used for supplying It is generally used for supplying steam on a small scale and is not steam on a small scale and is not suitable for large power plantssuitable for large power plants

It is used for large power plantsIt is used for large power plants

Boiler MountingsBoiler Mountings

Mountings are required for proper and safe functioning of theMountings are required for proper and safe functioning of theboiler which are generally mounted over the boiler shell.boiler which are generally mounted over the boiler shell.

Water Level IndicatorWater Level Indicator Pressure gaugePressure gauge Safety valvesSafety valves Steam stop valveSteam stop valve Blow off cockBlow off cockFusible plugFusible plug Feed Check valveFeed Check valve

Boiler AccessoriesBoiler Accessories

Accessories are used for efficient running of the Accessories are used for efficient running of the boilerboiler

• • Super heaterSuper heater• • EconomizerEconomizer• • Air preheatedAir preheated

Super heaterSuper heater

EconomizEconomizerer

Fig.: Air Preheater

Air PreheaterAir Preheater

Boiler CapacityBoiler Capacity

• • Evaporation or equivalent evaporation per hour may be Evaporation or equivalent evaporation per hour may be takentaken as a measure of boiler capacity. It is generally measured as a measure of boiler capacity. It is generally measured inin tons or kg per hour.tons or kg per hour.

Boiler EfficiencyBoiler EfficiencyEfficiency of a boiler may be defined as the ratio of heat utilized forEfficiency of a boiler may be defined as the ratio of heat utilized forthe generation of steam to heat supplied due to the burning of fuel.the generation of steam to heat supplied due to the burning of fuel.

Boiler efficiency,Boiler efficiency,

ms be the mass of steam evaporated in a given timems be the mass of steam evaporated in a given time

mf be the mass of fuel burnt at the same timemf be the mass of fuel burnt at the same time

HV be the heating value of fuel per unit massHV be the heating value of fuel per unit mass

h be the enthalpy per unit mass of steamh be the enthalpy per unit mass of steam

h0 be the enthalpy of feed waterh0 be the enthalpy of feed water

ms (h-ho ) mf*HV

Energy utilize Energy supplied

=η =

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