30-08-2014, 11:09 AM
SEMESTER INDUSTRIAL TRAINING REPORT
ON
BENEFIT ANALYSIS
OF
NON-DESTRUCTIVE TESTING
IN BOILERS
COMPLETED AT
CHEEMA BOILERS LTD.
SUBMITTED BY
Rahul sharma
100441130750
DEPARTMENT OF MECHANICAL ENGINEERING
KHALSA COLLEGE OF ENGINEERING & TECHNOLOGY
AMRITSAR
MAY, 2014
ACKNOWLEDGEMENT
The authors are highly grateful to Dr. Amarpal Singh, Principal, Khalsa College of Engineering & Technology, Amritsar, for providing this opportunity to carry out the Semester Industrial Training at CHEEMA BOILERS LTD.
The constant guidance and encouragement received from Er. Jaspreet Singh Deo T&P, KCET Amritsar has been of great help in carrying out the project work and is acknowledged with reverential thanks.
The authors would like to express a deep sense of gratitude and thanks profusely to Mr.Harjinder Singh Cheema Director/CEO of Company. Without the wise counsel and able guidance, it would have been impossible to complete the report in this manner.
The help rendered by supervisor Er. SAHIL SHARMA for experimentation is greatly acknowledged.
The author expresses gratitude to other faculty members of MECHANICAL ENGINEERING department of KCET for their intellectual support throughout the course of this work.
Finally, the authors are indebted to all whosoever have contributed in this report work and friendly stay at CHEEMA BOILERS LTD.
Name of Student
Rahul Sharma
INDEX
CHAPTER NO. TITLE PAGE NO.
· INTRODUCTION TO COMPANY 6
· CBL CERTIFICATION 7
1. INTRODUCTION TO BOILERS 8
1.1. Classification of boilers 10
1.1.1. Fire tube boilers 10
1.1.2. Water tube boilers 11
2. PRODUCT DETAIL OF CHEEMA BOILERS 12
2.1. Fluidized bed combustion(FBC) boiler 12
2.2. Atmospheric fluidized bed combustion(AFBC) boiler 12
2.3. Pressurized fluidized bed combustion(PFBC) boiler 13
2.4. Atmospheric circulating fluidized bed combustion(CFBC) boiler 13
2.5. Stoker fired boiler 14
2.6. Spreader stoker boiler 14
3. VARIOUS PARTS OF BOILERS MANUFACTURED AT CHEEMA 19
BOILERS
3.1. Economizer 19
3.2. Super heater 20
3.3. Air pre-heater 21
3.4. Electrostatic Precipitator 23
3.5. C-cyclones 24
3.6. Fans & blowers 26
4. INTRODUCTION TO NON DESTRUCTIVE TESTING 30
4.1. Beginning of Non Destructive Evaluation 30
5. ULTRASONIC TESTING 31
5.1. History of ultrasonics 31
5.2. Present stage of ultrasonics 32
5.3. Basic principle of ultrasonic testing 33
5.4. Wave propagation 35
5.5. Sound propagation in elastic materials 38
5.6. Reflection & Transmission coefficient 43
5.7. Equipments & Transducers 44
5.8. Couplants 49
5.9. Calibration methods 50
5.10. Crack tip diffraction 54
5.11. Data presentation 56
6. DYE PENETRATION TESTING 61
6.1. Introduction & history of Dye Penetration Inspection/Liquid Penetration 61
Inspection
6.2. Basic steps of Liquid Penetration Inspection 62
6.3. Common uses of liquid penetration inspection 64
6.4. Emulsifier 65
6.5. System performance check 66
6.6. Nature of defect 67
6.7. Health & Safety precautions 68
7. MAGNETIC PARTICLE TESTING 70
7.1. Introduction to Magnetic particle Inspection 70
7.2. Basic principle of Magnetic Particle Inspection 70
7.3. Portable magnetizing equipments 72
7.4. Magnetic field Indicator 75
7.5. Suspension Liquids 77
7.6. Dry particle inspection 77
7.7. Wet suspension inspection 78
7.8. Inspection using magnetic rubber 79
8. NON DESTRUCTIVE TESTING FOR BOILERS 80
CONCLUSION 82
REFERENCE 83
INTRODUCTION TO COMPANY
Leader in Manufacturing Process Steam & Power Generation Equipment Cheema Boilers Limited, popularly known as CBL is a trusted name in the field of Indian Boiler Industry. It is known for its commitment, competence and compliance. CBL was established in the year 1999 to provide complete solution to steam generation needs. The company's origin in the boiler industry goes back to founding of it's sister concern Cheema Engineering Services (P) Limited engaged in manufacturing of Steam Boilers, Pollution Control equipment, Fluidized Bed Conversion and energy saving devices since 1991.
It's visionary Mr. Harjinder Singh Cheema, currently CBL Managing Director along with his three brothers, now CBL Directors started this company with Boiler services and very soon CBL moved to manufacturing of full-fledged Process Boilers. Presently company is manufacturing all types of boiler to meet the requirement of process and power industry.
CBL has got its own manufacturing facilities at Kurali 25 kms from Chandigarh, near Ropar and Corporate Office at Mohali, (Chandigarh).
In last 8 years of operation, the company has established its name in Boiler Industry with internal core competency in Engineering, Manufacturing and Project commissioning. A dedicated and multi-skilled manpower has taken this company to a new height of business excellence. Its operation facilities, technology, manpower competency and customer base are expanding every year, which has resulted in doubling the company's turnover year over year. Company has already drawn an ambitious short and long term plan to meet growing demand of energy in India and abroad.CBL is already exporting to Asian and European countries.
CBL has sizeable manufacturing facilities that produce 'A' grade quality goods. The Company has extensive experience in the manufacturing of boilers and boiler house auxiliaries. Producing through three plants, located one at Nalagarh (HP) and two plants at Kurali (near Chandigarh), CBL supplies the nation the cost-effective power solutions.
The Nalagarh plant produces process boilers while the Kurali Unit-I produce power boiler parts like boiler drums, headers and larger process boilers. The Kurali Unit-II manufactures tubular products for power boilers and boiler auxiliaries like ESP, Fans and Air Pre-Heaters etc.
The CBL plants are well equipped with destructive and non-destructive testing, and work with proven quality management systems like ISO Type equation here. 9001:2000 and ASME code stamp.
CBL CERTIFICATION:
ISO 9001, ISO 14001, OHSAS 18001. It implies
· Passport for International Market.
· Professional Image.
· Increased customer confidence.
· Improved quality cut in costs owing to rejection control
· Clarity of responsibility and authority.
· Better and Defined system.
· Consistent Quality.
· Improved Cycle Time.
ASME Certification:
Cheema Boilers has received ASME (American Society of Mechanical Engineers) Certification for "U" & "S" stamps. It implies
· Complete traceability of raw materials
· All design meets the A.S.M.E. code
· All pressure vessel tests is witnessed by an A.S.M.E. third party
· Unsurpassed quality assurance
· Quality Manager and an Authorized Inspector actually travel with each project through all phases of the work
Final inspection where units are hydrostatically tested at 1.5 times the working pressure
CHAPTER 1. INTRODUCTION OF BOILERS
A steam generator or boiler is, usually, a closed vessel made of steel. Its function is to transfer the heat produced by the combustion of fuel to water, the ultimately to generate the steam. The steam produced may be supplied.
1. To an external combustion engine
2. At low pressure for industrial process work in cotton mills, sugar factories, breweries etc.
3. For producing hot water, which can be used for heating installation at much lower pressure
A boiler is an enclosed vessel that provides a means for combustion heat to be transferred to water until it becomes heated water or steam. The hot water or steam under pressure is then usable for transferring the heat to a process. Water is a useful and inexpensive medium for transferring heat to a process. When water at atmospheric pressure is boiled into steam its volume increases about 1,600 times, producing a force that is almost as explosive as gunpowder. This causes the boiler to be an equipment that must be treated with utmost care.
The boiler system comprises of: a feed water system, steam system and fuel system. The feed water system provides water to the boiler and regulates it automatically to meet the steam demand. Various valves provide access for maintenance and repair. The steam system collects and controls the steam produced in the boiler. Steam is directed through a piping system to the point of use. Throughout the system, steam pressure is regulated using valves and checked with steam pressure gauges. The fuel system includes all equipment used to provide fuel to generate the necessary heat. The equipment required in the fuel system depends on the type of fuel used in the system.
The water supplied to the boiler that is converted into steam is called feed water. The two sources of feed water are: (1) Condensate or condensed steam returned from the processes and (2) Makeup water (treated raw water) which must come from outside the boiler room and plant processes. For higher boiler efficiencies, an economizer preheats the feed water using the waste heat in the flue gas.
Fig 1.1 schematic diagram of boiler room
1.1. CLASSIFICATION OF BOILER
Boilers are classified in the following ways:-
The boilers are broadly classified into two categories according to contents of tubes.
1. fire tube
2. water tube
1.1.1. FIRE TUBE BOILER
Afire-tube boileris a type ofboiler in which hot gases from a fire pass through one or more tubes running through a sealed container of water. Theheatof the gases is transferred through the walls of the tubes bythermal conduction, heating the water and ultimately creatingsteam.
The fire-tube boiler developed as the third of the four major historical types of boilers: low-pressure tank or "haystack" boilers,flued boilerswith one or two large flues, fire-tube boilers with many small tubes, and high-pressurewater-tube boilers. Their advantage over flued boilers with a single large flue is that the many small tubes offer far greater heating surface area for the same overall boiler volume. The general construction is as a tank of water penetrated by tubes that carry the hotflue gasesfrom the fire. The tank is usuallycylindricalfor the most part—being the strongest practical shape for apressurized container and this cylindrical tank may be either horizontal or vertical.
This type of boiler was used on virtually allsteam locomotivesin the horizontal "locomotive" form. This has a cylindrical barrel containing the fire tubes, but also has an extension at one end to house the "firebox". This firebox has an open base to provide a large grate area and often extends beyond the cylindrical barrel to form a rectangular or tapered enclosure. The horizontal fire-tube boiler is also typical of marine applications, using theScotch boiler.Vertical boilershave also been built of the multiple fire-tube type, although these are comparatively rare: most vertical boilers were either flued, or with cross water-tubes.
1.1.2. WATER TUBE BOILER
Awater tube boiler(also spelled water-tube and water tube) is a type ofboilerin which water circulates in tubes heated externally by the fire. Fuel is burned inside thefurnace, creating hot gas which heats water in the steam-generating tubes. In smaller boilers, additional generating tubes are separate in the furnace, while larger utility boilers rely on the water-filled tubes that make up the walls of the furnace to generatesteam.
The heated water then rises into thesteam drum. Here, saturated steam is drawn off the top of the drum. In some services, the steam will reenter the furnace through asuper heaterto become superheated. Superheated steam is defined as steam that is heated above the boiling point at a given pressure. Superheated steam is a dry gas and therefore used to drive turbines, since water droplets can severely damage turbine blades.
Cool water at the bottom of the steam drum returns to the feed water drum via large-bore 'down comer tubes', where it pre-heats the feed water supply. (In large utility boilers, the feed water is supplied to the steam drum and the down comers supply water to the bottom of the water walls). To increase economy of the boiler, exhaust gases are also used to pre-heat the air blown into the furnace and warm the feed water supply. Such water tube boilers inthermal power stationare also calledsteam generating units.
The olderfire-tube boilerdesign – in which the water surrounds the heat source and the gases from combustion pass through tubes through the water space – is a much weaker structure and is rarely used for pressures above 350psi (2.4MPa). A significant advantage of the water tube boiler is that there is less chance of a catastrophic failure: there is not a large volume of water in the boiler nor are there large mechanical elements subject to failure.
CHAPTER 2. PRODUCT DETAILS OF CHEEMA BOILERS:
Various types of boilers manufactured at cheema boilers limited are:
2.1. Fluidized Bed Combustion (FBC) Boiler
Fluidized bed combustion (FBC) has emerged as a viable alternative and has significant advantages over a conventional firing system and offers multiple benefits – compact boiler design, fuel flexibility, higher combustion efficiency and reduced emission of noxious pollutants such as SOx and NOx. The fuels burnt in these boilers include coal, washery rejects, rice husk, bagasse & other agricultural wastes. The fluidized bed boilers have a wide capacity range- 0.5 T/hr to over 100 T/hr. When an evenly distributed air or gas is passed upward through a finely divided bed of solid particles such as sand supported on a fine mesh, the particles are undisturbed at low velocity. As air velocity is gradually increased, a stage is reached when the individual particles are suspended in the air stream – the bed is called “fluidized”. With further increase in air velocity, there is bubble formation, vigorous turbulence, rapid mixing and formation of dense defined bed surface. The bed of solid particles exhibits the properties of a boiling liquid and assumes the appearance of a fluid – “bubbling fluidized
bed”. If sand particles in a fluidized state are heated to the ignition temperatures of coal, and coal is injected continuously into the bed, the coal will burn rapidly and the bed attains a uniform temperature. The fluidized bed combustion (FBC) takes place at about 840OC to 950OC. Since this temperature is much below the ash fusion temperature, melting of ash and associated problems are avoided. The lower combustion temperature is achieved because of high coefficient of heat transfer due to rapid mixing in the fluidized bed and effective extraction of heat from the bed through in-bed heat transfer tubes and walls of the bed. The gas velocity is maintained between minimum fluidization velocity and particle entrainment velocity. This ensures stable operation of the bed and avoids particle entrainment in the gas stream.
2.2. Atmospheric Fluidized Bed Combustion (AFBC) Boiler
Most operational boiler of this type is of the Atmospheric Fluidized Bed Combustion. (AFBC). This involves little more than adding a fluidized bed combustor to a conventional shell boiler. Such systems have similarly being installed in conjunction with conventional water tube boiler. Coal is crushed to a size of 1 – 10 mm depending on the rank of coal, type of fuel fed to the combustion chamber. The atmospheric air, which acts as both the fluidization and combustion air, is delivered at a pressure, after being preheated by the exhaust fuel gases. The in-bed tubes carrying water generally act as the evaporator. The gaseous products of combustion pass over the super heater sections of the boiler flowing past the economizer, the dust collectors and the air pre-heater before being exhausted to atmosphere.
2.3. Pressurized Fluidized Bed Combustion (PFBC) Boiler
ON
BENEFIT ANALYSIS
OF
NON-DESTRUCTIVE TESTING
IN BOILERS
COMPLETED AT
CHEEMA BOILERS LTD.
SUBMITTED BY
Rahul sharma
100441130750
DEPARTMENT OF MECHANICAL ENGINEERING
KHALSA COLLEGE OF ENGINEERING & TECHNOLOGY
AMRITSAR
MAY, 2014
ACKNOWLEDGEMENT
The authors are highly grateful to Dr. Amarpal Singh, Principal, Khalsa College of Engineering & Technology, Amritsar, for providing this opportunity to carry out the Semester Industrial Training at CHEEMA BOILERS LTD.
The constant guidance and encouragement received from Er. Jaspreet Singh Deo T&P, KCET Amritsar has been of great help in carrying out the project work and is acknowledged with reverential thanks.
The authors would like to express a deep sense of gratitude and thanks profusely to Mr.Harjinder Singh Cheema Director/CEO of Company. Without the wise counsel and able guidance, it would have been impossible to complete the report in this manner.
The help rendered by supervisor Er. SAHIL SHARMA for experimentation is greatly acknowledged.
The author expresses gratitude to other faculty members of MECHANICAL ENGINEERING department of KCET for their intellectual support throughout the course of this work.
Finally, the authors are indebted to all whosoever have contributed in this report work and friendly stay at CHEEMA BOILERS LTD.
Name of Student
Rahul Sharma
INDEX
CHAPTER NO. TITLE PAGE NO.
· INTRODUCTION TO COMPANY 6
· CBL CERTIFICATION 7
1. INTRODUCTION TO BOILERS 8
1.1. Classification of boilers 10
1.1.1. Fire tube boilers 10
1.1.2. Water tube boilers 11
2. PRODUCT DETAIL OF CHEEMA BOILERS 12
2.1. Fluidized bed combustion(FBC) boiler 12
2.2. Atmospheric fluidized bed combustion(AFBC) boiler 12
2.3. Pressurized fluidized bed combustion(PFBC) boiler 13
2.4. Atmospheric circulating fluidized bed combustion(CFBC) boiler 13
2.5. Stoker fired boiler 14
2.6. Spreader stoker boiler 14
3. VARIOUS PARTS OF BOILERS MANUFACTURED AT CHEEMA 19
BOILERS
3.1. Economizer 19
3.2. Super heater 20
3.3. Air pre-heater 21
3.4. Electrostatic Precipitator 23
3.5. C-cyclones 24
3.6. Fans & blowers 26
4. INTRODUCTION TO NON DESTRUCTIVE TESTING 30
4.1. Beginning of Non Destructive Evaluation 30
5. ULTRASONIC TESTING 31
5.1. History of ultrasonics 31
5.2. Present stage of ultrasonics 32
5.3. Basic principle of ultrasonic testing 33
5.4. Wave propagation 35
5.5. Sound propagation in elastic materials 38
5.6. Reflection & Transmission coefficient 43
5.7. Equipments & Transducers 44
5.8. Couplants 49
5.9. Calibration methods 50
5.10. Crack tip diffraction 54
5.11. Data presentation 56
6. DYE PENETRATION TESTING 61
6.1. Introduction & history of Dye Penetration Inspection/Liquid Penetration 61
Inspection
6.2. Basic steps of Liquid Penetration Inspection 62
6.3. Common uses of liquid penetration inspection 64
6.4. Emulsifier 65
6.5. System performance check 66
6.6. Nature of defect 67
6.7. Health & Safety precautions 68
7. MAGNETIC PARTICLE TESTING 70
7.1. Introduction to Magnetic particle Inspection 70
7.2. Basic principle of Magnetic Particle Inspection 70
7.3. Portable magnetizing equipments 72
7.4. Magnetic field Indicator 75
7.5. Suspension Liquids 77
7.6. Dry particle inspection 77
7.7. Wet suspension inspection 78
7.8. Inspection using magnetic rubber 79
8. NON DESTRUCTIVE TESTING FOR BOILERS 80
CONCLUSION 82
REFERENCE 83
INTRODUCTION TO COMPANY
Leader in Manufacturing Process Steam & Power Generation Equipment Cheema Boilers Limited, popularly known as CBL is a trusted name in the field of Indian Boiler Industry. It is known for its commitment, competence and compliance. CBL was established in the year 1999 to provide complete solution to steam generation needs. The company's origin in the boiler industry goes back to founding of it's sister concern Cheema Engineering Services (P) Limited engaged in manufacturing of Steam Boilers, Pollution Control equipment, Fluidized Bed Conversion and energy saving devices since 1991.
It's visionary Mr. Harjinder Singh Cheema, currently CBL Managing Director along with his three brothers, now CBL Directors started this company with Boiler services and very soon CBL moved to manufacturing of full-fledged Process Boilers. Presently company is manufacturing all types of boiler to meet the requirement of process and power industry.
CBL has got its own manufacturing facilities at Kurali 25 kms from Chandigarh, near Ropar and Corporate Office at Mohali, (Chandigarh).
In last 8 years of operation, the company has established its name in Boiler Industry with internal core competency in Engineering, Manufacturing and Project commissioning. A dedicated and multi-skilled manpower has taken this company to a new height of business excellence. Its operation facilities, technology, manpower competency and customer base are expanding every year, which has resulted in doubling the company's turnover year over year. Company has already drawn an ambitious short and long term plan to meet growing demand of energy in India and abroad.CBL is already exporting to Asian and European countries.
CBL has sizeable manufacturing facilities that produce 'A' grade quality goods. The Company has extensive experience in the manufacturing of boilers and boiler house auxiliaries. Producing through three plants, located one at Nalagarh (HP) and two plants at Kurali (near Chandigarh), CBL supplies the nation the cost-effective power solutions.
The Nalagarh plant produces process boilers while the Kurali Unit-I produce power boiler parts like boiler drums, headers and larger process boilers. The Kurali Unit-II manufactures tubular products for power boilers and boiler auxiliaries like ESP, Fans and Air Pre-Heaters etc.
The CBL plants are well equipped with destructive and non-destructive testing, and work with proven quality management systems like ISO Type equation here. 9001:2000 and ASME code stamp.
CBL CERTIFICATION:
ISO 9001, ISO 14001, OHSAS 18001. It implies
· Passport for International Market.
· Professional Image.
· Increased customer confidence.
· Improved quality cut in costs owing to rejection control
· Clarity of responsibility and authority.
· Better and Defined system.
· Consistent Quality.
· Improved Cycle Time.
ASME Certification:
Cheema Boilers has received ASME (American Society of Mechanical Engineers) Certification for "U" & "S" stamps. It implies
· Complete traceability of raw materials
· All design meets the A.S.M.E. code
· All pressure vessel tests is witnessed by an A.S.M.E. third party
· Unsurpassed quality assurance
· Quality Manager and an Authorized Inspector actually travel with each project through all phases of the work
Final inspection where units are hydrostatically tested at 1.5 times the working pressure
CHAPTER 1. INTRODUCTION OF BOILERS
A steam generator or boiler is, usually, a closed vessel made of steel. Its function is to transfer the heat produced by the combustion of fuel to water, the ultimately to generate the steam. The steam produced may be supplied.
1. To an external combustion engine
2. At low pressure for industrial process work in cotton mills, sugar factories, breweries etc.
3. For producing hot water, which can be used for heating installation at much lower pressure
A boiler is an enclosed vessel that provides a means for combustion heat to be transferred to water until it becomes heated water or steam. The hot water or steam under pressure is then usable for transferring the heat to a process. Water is a useful and inexpensive medium for transferring heat to a process. When water at atmospheric pressure is boiled into steam its volume increases about 1,600 times, producing a force that is almost as explosive as gunpowder. This causes the boiler to be an equipment that must be treated with utmost care.
The boiler system comprises of: a feed water system, steam system and fuel system. The feed water system provides water to the boiler and regulates it automatically to meet the steam demand. Various valves provide access for maintenance and repair. The steam system collects and controls the steam produced in the boiler. Steam is directed through a piping system to the point of use. Throughout the system, steam pressure is regulated using valves and checked with steam pressure gauges. The fuel system includes all equipment used to provide fuel to generate the necessary heat. The equipment required in the fuel system depends on the type of fuel used in the system.
The water supplied to the boiler that is converted into steam is called feed water. The two sources of feed water are: (1) Condensate or condensed steam returned from the processes and (2) Makeup water (treated raw water) which must come from outside the boiler room and plant processes. For higher boiler efficiencies, an economizer preheats the feed water using the waste heat in the flue gas.
Fig 1.1 schematic diagram of boiler room
1.1. CLASSIFICATION OF BOILER
Boilers are classified in the following ways:-
The boilers are broadly classified into two categories according to contents of tubes.
1. fire tube
2. water tube
1.1.1. FIRE TUBE BOILER
Afire-tube boileris a type ofboiler in which hot gases from a fire pass through one or more tubes running through a sealed container of water. Theheatof the gases is transferred through the walls of the tubes bythermal conduction, heating the water and ultimately creatingsteam.
The fire-tube boiler developed as the third of the four major historical types of boilers: low-pressure tank or "haystack" boilers,flued boilerswith one or two large flues, fire-tube boilers with many small tubes, and high-pressurewater-tube boilers. Their advantage over flued boilers with a single large flue is that the many small tubes offer far greater heating surface area for the same overall boiler volume. The general construction is as a tank of water penetrated by tubes that carry the hotflue gasesfrom the fire. The tank is usuallycylindricalfor the most part—being the strongest practical shape for apressurized container and this cylindrical tank may be either horizontal or vertical.
This type of boiler was used on virtually allsteam locomotivesin the horizontal "locomotive" form. This has a cylindrical barrel containing the fire tubes, but also has an extension at one end to house the "firebox". This firebox has an open base to provide a large grate area and often extends beyond the cylindrical barrel to form a rectangular or tapered enclosure. The horizontal fire-tube boiler is also typical of marine applications, using theScotch boiler.Vertical boilershave also been built of the multiple fire-tube type, although these are comparatively rare: most vertical boilers were either flued, or with cross water-tubes.
1.1.2. WATER TUBE BOILER
Awater tube boiler(also spelled water-tube and water tube) is a type ofboilerin which water circulates in tubes heated externally by the fire. Fuel is burned inside thefurnace, creating hot gas which heats water in the steam-generating tubes. In smaller boilers, additional generating tubes are separate in the furnace, while larger utility boilers rely on the water-filled tubes that make up the walls of the furnace to generatesteam.
The heated water then rises into thesteam drum. Here, saturated steam is drawn off the top of the drum. In some services, the steam will reenter the furnace through asuper heaterto become superheated. Superheated steam is defined as steam that is heated above the boiling point at a given pressure. Superheated steam is a dry gas and therefore used to drive turbines, since water droplets can severely damage turbine blades.
Cool water at the bottom of the steam drum returns to the feed water drum via large-bore 'down comer tubes', where it pre-heats the feed water supply. (In large utility boilers, the feed water is supplied to the steam drum and the down comers supply water to the bottom of the water walls). To increase economy of the boiler, exhaust gases are also used to pre-heat the air blown into the furnace and warm the feed water supply. Such water tube boilers inthermal power stationare also calledsteam generating units.
The olderfire-tube boilerdesign – in which the water surrounds the heat source and the gases from combustion pass through tubes through the water space – is a much weaker structure and is rarely used for pressures above 350psi (2.4MPa). A significant advantage of the water tube boiler is that there is less chance of a catastrophic failure: there is not a large volume of water in the boiler nor are there large mechanical elements subject to failure.
CHAPTER 2. PRODUCT DETAILS OF CHEEMA BOILERS:
Various types of boilers manufactured at cheema boilers limited are:
2.1. Fluidized Bed Combustion (FBC) Boiler
Fluidized bed combustion (FBC) has emerged as a viable alternative and has significant advantages over a conventional firing system and offers multiple benefits – compact boiler design, fuel flexibility, higher combustion efficiency and reduced emission of noxious pollutants such as SOx and NOx. The fuels burnt in these boilers include coal, washery rejects, rice husk, bagasse & other agricultural wastes. The fluidized bed boilers have a wide capacity range- 0.5 T/hr to over 100 T/hr. When an evenly distributed air or gas is passed upward through a finely divided bed of solid particles such as sand supported on a fine mesh, the particles are undisturbed at low velocity. As air velocity is gradually increased, a stage is reached when the individual particles are suspended in the air stream – the bed is called “fluidized”. With further increase in air velocity, there is bubble formation, vigorous turbulence, rapid mixing and formation of dense defined bed surface. The bed of solid particles exhibits the properties of a boiling liquid and assumes the appearance of a fluid – “bubbling fluidized
bed”. If sand particles in a fluidized state are heated to the ignition temperatures of coal, and coal is injected continuously into the bed, the coal will burn rapidly and the bed attains a uniform temperature. The fluidized bed combustion (FBC) takes place at about 840OC to 950OC. Since this temperature is much below the ash fusion temperature, melting of ash and associated problems are avoided. The lower combustion temperature is achieved because of high coefficient of heat transfer due to rapid mixing in the fluidized bed and effective extraction of heat from the bed through in-bed heat transfer tubes and walls of the bed. The gas velocity is maintained between minimum fluidization velocity and particle entrainment velocity. This ensures stable operation of the bed and avoids particle entrainment in the gas stream.
2.2. Atmospheric Fluidized Bed Combustion (AFBC) Boiler
Most operational boiler of this type is of the Atmospheric Fluidized Bed Combustion. (AFBC). This involves little more than adding a fluidized bed combustor to a conventional shell boiler. Such systems have similarly being installed in conjunction with conventional water tube boiler. Coal is crushed to a size of 1 – 10 mm depending on the rank of coal, type of fuel fed to the combustion chamber. The atmospheric air, which acts as both the fluidization and combustion air, is delivered at a pressure, after being preheated by the exhaust fuel gases. The in-bed tubes carrying water generally act as the evaporator. The gaseous products of combustion pass over the super heater sections of the boiler flowing past the economizer, the dust collectors and the air pre-heater before being exhausted to atmosphere.
2.3. Pressurized Fluidized Bed Combustion (PFBC) Boiler