In this article we will discuss about:- 1. Meaning of Boiler 2. Historical Development of the Boiler 3. Classification 4. Essentials 5. Introduction to IBR or Regulations for Chimney (with Reference to IBR/MSNC Bombay) 6. Boiler Calculations.
Contents:
- Meaning of Boiler
- Historical Development of the Boiler
- Classification of Boilers
- Essentials of a Good Boiler
- Introduction to IBR or Regulations for Chimney (with Reference to IBR/MSNC Bombay)
- Boiler Calculations
1. Meaning of Boiler:
Amongst a number of power plants fulfilling the power requirements of the world, major share is contributed by thermal power plants. As this type of power plants use steam as the working fluid, the generator of the steam can be said to be heart of it.
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The steam generator is also known as ‘Boiler’.
The steam produced in the boiler is used in the industries for different purposes viz.:
1. For generation of electrical energy as in power plants.
2. For generating mechanical energy in steam turbines.
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3. For process heating purpose as heating of ground nuts in Oil Mills.
4. For sizing and bleaching in textile industries.
Normally a boiler produces steam at high pressure. This steam is first used to drive turbines for generating power. Then the steam exhausted from turbines, which is at lower pressure, is used for process heating purpose.
A typical boiler has two different parts known as pressure part and combustion chamber. Pressure part is closed vessel, strongly fabricated out of steel, this contains water in it. The combustion chamber is constructed around pressure part with the help of fire bricks. The fuel undergoes combustion in this combustion chamber producing high temperature gases.
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These gases are also known as flue gases, hot furnace gases, or products of combustion. When flue gases come in contact with the water container, they give their heat to water, causing generation of steam. Afterwards flue gases are exhausted high into the atmosphere through the chimney.
2. Historical Development of the Boiler:
As we know boiler is steam generator, or it is a closed vessel in which water is heated and converted into steam. The boiler was initially developed in the very first century by Mr. Hero of Alexandria. However it was too small and it was used as toy only.
Consider a tea kettle on stove or burner, which has water or tea boiling in it, we can see that steam spreads as it leaves the spout. If the spout is closed by means of a cork, after some time the cork will be blown off.
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This shows that the steam generated in a closed vessel keeps on the developing pressure. Such steam at high pressure is utilised to do work in expanding in a steam engine.
At the beginning a small closed vessel was used to generate steam by the application of heat. At the beginning the quantity of steam generated and subsequently used in an engine was not sufficient. Therefore larger vessel called Boilers was developed for giving a sufficient quantity of steam at the required pressure. The pressure was maintained constant in the boiler by opening the outlet valve such that the steam generated is the same as the steam supplied to the engine.
At the initial stages boilers used were of the fire tube type or tank boilers.
In our everyday life we used to have hot water for bathing purpose a device similar to a tank boiler but on a very smaller scale.
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Taking into consideration the safety, the development of simple boiler took place over the years. Till the 17th century, there was no much development in the boiler design and manufacturing. Mr. Denis Papin of France designed and developed the first boiler with safety valve in 1679 A.D.
The major developments took place after 1769 A.D., when James Watt of Scotland developed the practical steam engine.
Afterwards taking into consideration the quantity of steam generated with respect to time, water tube boilers were developed. Subsequently high pressure boilers and supercritical boilers for power generation were developed.
The steam generated in the boilers is utilised for 2-purposes viz:
(i) Power Generation:
The boilers generating steam for power generation purposes are bigger in size, generate steam at high pressure and this high pressure steam is first expanded in the turbines for generating power. Then the exhausted steam is utlised for process heating purpose.
(ii) Process Heating Purpose:
For example – heating of the oil seeds in the oil mills before they are being crushed.
3. Types and Classification of Boilers:
Boilers are mainly classified according to the following factors:
1. By the Relative Position of Flue Gases and Water (or Tube Contents):
(a) Fire Tube:
In this case flue gasses flow through the tubes, which are surrounded by the water which is to be evaporated. Example – Lancashire, Cornish, Cochran, Locomotive, Simple vertical, Scotch marine boiler, etc.
(b) Water Tube:
In this case water flows through the tubes and hot gases heat the tubes from outside e.g., Babcock Wilcox, Stirling Boiler, etc.
2. By the Method of Firing:
(a) Internally Fired:
In this case the furnace is located inside the boiler shell as in case of Lancashire boiler.
(b) Externally Fired:
The furnace is located outside the boiler shell as in case of Babcock Wilcox boiler.
3. According to Pressure of Steam:
(a) Low Pressure Boiler:
Boilers which can develop pressures below 80 bar are known as low pressure boilers e.g., Lancashire, Cochran, Cornish etc.
(b) High Pressure Boilers:
Boilers which can develop pressures above 80 bar are known as high pressure boilers e.g., Babcock, Lamount, Velox, Benson etc.
4. Nature of Draught:
Draught is the pressure difference, which is necessary to draw the sufficient quantity of it for combustion.
It is of following types:
(a) Natural Draught:
In this case the draught is produced by mean of chimney only. The amount of draught directly depends upon the height of chimney.
(b) Artificial Draught:
Artificial draught is produced by means of fans.
(i) Induced Draught:
Induced Draught is produced by sucking the flue gases from chamber. It is obtained by providing a fan between the boiler and the chimney. This fan is known as I.D. fan.
(ii) Forced Draught:
Forced draught is produced by forcing the air into the combustion chamber with the help of a fan, known as F.D. fan.
(iii) Balanced Draught:
Balanced draught is produced by means of I.D. fan and F.D. fan.
5. Method of Circulation of Water:
(a) Natural Circulation:
In which the circulation of water is due to gravity.
(b) Forced Circulation:
In which the circulation of water is obtained by a centrifugal pump.
6. By the Use:
(a) Land type – Boilers used with stationary plants.
(b) Marine type
(c) Locomotive boilers
7. By the Design of Flue Gas Passages:
The flue gas may follow a single pass, return pass or multipass.
8. By the Number of Drums:
There are 2 types-
(a) Single dram
(b) Multi-drum boilers.
9. According to Energy Source (Fuel) Used:
The heat energy may be derived from –
(a) Combustion of fossil fuels such as coal, wood, oil or natural gas etc.
(b) Electric or Nuclear energy.
(c) Hot waste gases of other chemical reactions.
10. According to the Material of Construction of the Boiler Shell:
(a) Steel Boilers:
Power boilers are generally fabricated out of steel plates.
(b) C.I. Boilers:
Generally low pressure boilers are, sometimes built out of castings.
4. Essentials of a Good Boiler:
1. With minimum fuel consumption, the boiler should be capable of generating steam at the required quality.
2. It should be light and occupy less space.
3. It should be capable of quick starting.
4. The initial cost, installation cost and maintenance cost of the boiler should be minimum.
5. The different parts of the boiler should be easily approachable for repairs.
6. The boiler should have minimum number of joints and those too should be away from direct flames.
7. There should be no deposition of mud and other deposits on the inner surface of the boiler drum.
8. Boiler should conform to safety regulations, laid down in Boiler act [Indian Boiler Regulations (IBR) Act].
5. Introduction to IBR or Regulations for Chimney (with Reference to IBR/MSNC Bombay):
To keep control on boiler accidents, Indian Government after independence made following rules and regulations, which the boiler should conform.
They are as under:
1. A plan of the boiler house and chimney is to be approved by the chief inspector of Indian Boiler Regulations (IBR)/Maharashtra Chief Inspector of Nuisance Commission (MSNC)—Bombay.
2. Chimney fabrication drawings are to be approved before fabrication.
3. A plan of 1m = 1cm in blue print showing the exact position of furnace, flues, chimney, duly certified by the chartered engineer/owner should be submitted.
4. Substantial structure certificate for the chimney stating that the chimney in self supported/supported by wire ropes and with stands a wind load of 207 kg/m2 is to be submitted (Note this should be certified by the chartered engineer).
5. Chimney height minimum required as per IBR/MSNC is 100 feet that i.e., 30.48 m from the firing floor of the boiler.
6. An undertaking for the height of chimney is to be submitted by the owner to MSNC.
7. An undertaking for the use of specific fuel is to be submitted by the owner.
8. No objection certificate (NOC) is to be obtained from Air Force Deptt.
9. Smoke generated should conform to Bombay Smoke Nuisance Act 1912.
10. Chimney should be dry painted, (i.e., Red and white strips of equal width in total 7 strips are to be painted)
11. Anti-collision lights are to be fitted, for sighting in the night and poor visibility.
12. Following details are to be submitted –
(a) Height of own factory building/boiler house.
(b) Height of tallest building within a radius of 300 m around ground level.
(c) Capacity of boiler.
(d) Working pressure
(e) Type of fuel
(f) Quantity of fuel/hour
(g) Type of chimney self-supported/supported by wire ropes
(h) Material of construction.
6. Boiler Calculations:
In case of boilers it is very important to find,
(a) Heat transfer required to form steam. We have studied steam generation process,
(b) Energy Received from Fuel:
(c) Boiler Thermal Efficiency:
It is the ratio of the energy received by the steam to the energy supplied by the fuel to produce steam.
Thus, Boiler Thermal Efficiency;
(d) Boiler Performance:
The main function of the boiler is to produce steam from feed water, with the use of heat liberated by the combustion of fuel. It is to be noted the number of kg of water evaporated per hour is not an exact measure of the performance of the boiler. Since different boilers may be operating at different at different conditions, so their comparison may be made on the basis of some reference condition known as Equivalent of Evaporation.
Equivalent of Evaporation from and at 100°C:
“The evaporation which would be obtained if the feed water were supplied at 100°C and converted into dry and saturated steam at 100°C, at standard atmospheric pressure, is known as equivalent of evaporation from and at 100°C”.
Evaporative Capacity:
“It is defined as the amount of water and water evaporated into steam per hour”. The evaporative capacity may be expressed in kg/hr or kg/kg, of fuel or kg/hr-m2 of heating surface area.
Actual Evaporation:
It is defined as the amount of water evaporated into steam, at actual working conditions, per kg of fuel burnt.
Energy Balance:
Energy released due to the combustion of fuel will be utilised for various purposes and is tabulated in heat balance sheet.
Note – In order to reduce radiation losses, Asbestos lagging is to be provided on the exposed boiler surface and is to be painted by a black paint.
All the above items may be expressed in the balance sheet as follows:
