04-03-2010, 12:40 PM
DESIGN OF BOILER STACK
Chimney, which form the last component of a system using a flue gas such as feoiler, IC engines, play a vital role in maintaining efficiency, draft, etc, of a system and also in minimizing the atmospheric pollution.
The boiler plant of HOCL had used LSHS (low Sulphur heavy stock) as a fuel. Recently they changed the fuel to LSFO (low Sulphur furnace oil). As a combined effect of increased corrosion rate and natural calamities the stack had undergone failure. As per the Kerala State Pollution Control Board the height of stack is not enough to avoid the atmospheric pollution. So they decide to construct a new stack for the boiler. As per their desire we decided to do the design of the boiler stack as our project.
The project deals with design considerations of boiler stack as per standard procedures outlined in IS 6533-1971 and the norms of Kerala State Pollution Control Board.
In the project work relevant section of codes related to stack are studied. Detailed stoichiometry workout to identify the flue gas emission rate is done.
The study of various principles outlined in the code for design of stack involves design of holding down bolts, base plate, foundation etc.
The design is checked against earthquake, Stability, Sliding and found that the aesign is safe against these factors.
The dynamic analysis is carried out to ensure the safety of the design. Finally it involves a CAD drawing of the designed stack.
ANISH .S HARIKRISHNA MENON .A PRASANTH M.U ROBY JOY
1.1 ABOUT HOCL
HOCL Kochi unit at Ambalamugal , 15 km away from Ernakulam city was commissioned m the year 1987 to manufacture Phenol and Acetone . The installed capacity is 40000 TPA of Phenol and 24640 Acetone. A new project was commissioned in the year 1997 to manufacture Hydrogen Peroxide with an installed capacity of 5225 TPA.
HOCL is a recipient of various Awards since its inception including system certificate of Quality management and environment Management. The technology for Phenol and Acetone is based on UOP, USA which provides the state of art technology in a single package. The hydrogen Peroxide is manufactured in HOCL applying KRUPP-Uhde (german) technology. PHENOL
Phenol is a versatile industrial organic chemical. The largest end use of phenol is in phenol-formaldehyde resins used in wood additives as well as moulding and laminating resins, paints, varnishes and enamels.
Phenol which is also referred to as carbolic acid or monohydroxibenzene is used to produce a wide variety of chemical intermediates, including phenolic resins this phenol a caprolactum, alkyl phenols,adpic acid,plasticizers, etc.
Phenol is also used in the manufacture of preservatives, disinfectants, lubricating oils herbicides insecticides, pharmaceuticals etc
Acetone is an important commercial solvent and raw material with wide usage in the chemical explosives and lacquer industiy it is commonly used as a solvent for cellulose acetate, nitro cellulose, celluloid, cellulose ether, chlorinated rubber various resins facts and oils and absorbent for acetylene gas. It is being increasingly used in the synthesis of a number of chemicals such as diacetone alcohol, methyl methacrylate and certain resins, pharamacuticals and perfumes HYDROGEN PEROXIDE 50% WAV
Hydrogen peroxide 50% w/w is an eco friendly product from HOCL Kochi unit with wide application in paper and textile industry for bleaching purpose as a substitute for hazardous chlorine. It is also used in electronic and metallurgical industries, effluent treatment plants, sewage treatment and for removal of toxic pollutants from industrial gas streams.
1.2 PROPOSED PROJECT
The boiler plant of HOCL had a steel stack which had a height of 39metres( As per IS 6533-1971). The fuel used was LSHS (low Sulphur heavy stock) with a Sulphur content of 1.5%. After modification of the boiler they changed the fuel to LSFO (low Sulphur furnace oil) with a Sulphur content of 4% using the same stack. With increase of Sulphur content the corrosion rate had increased and along with the natural calamities the stack had undergone failure. So they reworked it .But as per the Kerala State Pollution Control Board the height of stack depends on S02 content in flue gas. While using LSFO the Sulphur content is 120Kg/Hr. And as per the Kerala State Pollution Control Board the height of stack must be 14 x (120)3. This is equal to 58.56, approximately 60mm. So they decide to construct a new stack for the boiler
As per their desire we decided to do the design of the boiler stack as our project. The project includes
1. Collect the required data for the boiler stack design
2. Study of the design procedures
3. Stoichiometry calculations
4. Design calculations
5. Checking the result obtained
6. Dynamic analysis
7. Preparations of drawings
1.3 ABOUT BOILER
HOCL Ambalamughal has 2 X 20.8 TPA Walchand Nagar Industries make boiler, it was Commissioned in the year of 1983- 84 .
The boiler were originally designed for coal on traveling grate as the main fuel with heavy oil as warm up/ support / alternate fuel. Coal fire has been discontinued for the past few many years and the boiler are operating with oil as the only fuel, There were problem like kingering on the burners / furnace floor , frequent chocking of burner tips.
The main parameter of the boiler after revamp is
> Boiler make - Walchand nagar make with 2 burner
> Maximum continuous rating (100% MCR) -24.25TPA Steam pressure at main steam stop valve outlet- 20Kg/cm
> Steam temperature- 214Ã‚Â°C
> Feed water temperature at economizer inlet- 145Ã‚Â°C
> Fuel fired-LSFO
> Construction type - Bi drum type
Bank TIÃ‚Â±M-72G HÃ‚Â«
/ Si<k He*Ã‚Â±r /
' frnit Header
Fig 1.1 Line diagram of boiler
1.4 STEEL CHIMNEY
Chimney, which form the last component of a system using a flue gas such as boiler, play a vital role in maintaining efficiency, draft, etc, of a system and also in minimizing the atmospheric pollution.
The design and construction of chimney have changed considerably with the advancement of technology. For example it has now become customary to provide single chimney for a number of units and reduced flue gas temperature for increased efficiency. This in turn has created the problem of differential expansion when one or more units are shut down and for the chimney insulation so that the gas temperature does not drop below the dew point.
Steel chimneys are also known as steel stacks .The steel chimneys are made of steel plates and supported on foundation. The steel chimneys are used to escape and disperse the flue gases to such a height that the gases do not contaminate surrounding atmosphere. The cross sectional area of the steel chimney is kept large enough to allow the passage of burnt gases. The cross sectional area of the steel chimney depends on the type and quantity of fuel to be used in a plant. The cross sectional area of the steel chimney depends on the type and quantity of fuel used in the plant. The height of the steel chimney is kept to provide the required draught. The draught is defined as the difference between the absolute gas pressure at any point in the depth or steel chimney and the ambient atmospheric pressure. The draught depends on the height of the steel chimney above sea level, the type of fuel to be burnt, the type of furnace and the temperature of the burnt gases. When the gases in a steel chimney are heated, then the gases expand .The hot gases occupy larger volume than before. The weight of gases per cubic meter becomes less. For the purpose of the structural design of the steel chimney, the height and diameter of chimney at the top are known data.
The steel chimney is made cylindrical in shape. The lower portion of steel chimney is widened or flared, in order to provide a large base and greater stability. The widened section of the chimney at the base reduces the unit stresses in the steel at the base of the chimney. The loads acting on the steel chimney are transferred to the foundation easily by widened section. The conical base is provided generally.
The steel chimney is designed and constructed conforming to code of practice for design and construction of steel chimneys IS: 6533-1971
1.5 CLASSIFICATION OF STEEL CHIMNEY
The steel chimneys are of two types:
1. Self-supporting steel chimneys.
2. Guyed steel chimneys.
1. Self-supporting steel chimneys:
/////J///////777 Fig .1.2 Self supported chimney
When the lateral forces (wind or seismic forces) are transmitted to the foundation by the cantilever action of the chimney, then the chimney is known as self-supporting chimney. The self-supporting chimney together with the foundation remains stable under all working conditions without any additional support. The self-supporting chimneys are made up to 10-meter diameter and from 50 meter to 100 meters in height. 2. Guyed steel chimneys:
Fig 1.3 Guyed chimney
In high steel chimneys, the mild steel wire ropes or guys are attached to transmit the lateral forces such steel chimneys are known as guyed steel chimneys. In guyed steel chimneys, all the externally applied loads (wind, seismic force etc.) are not totally carried by the chimney shell. These attached guys or stays ensure the stability of the guyed steel chimney. These steel chimneys may be provided with one, two or three sets of guys. In each set of the guys, three or four or sometimes six wires are attached to the collars. When one set of the guy is used, then the guys are attached to a collar at one-third or one fourth of the height from the top. When more than one set of guys are used, then these are used at various heights.
A particular type of steel chimney is selected depending on the advantage and disadvantages with reference to economy. A choice between self-supporting and guyed steel chimney is made by considering some of the important factors. Number of units, type of equipments and the type of fuel to be used are considered. The mode of operation of the equipment shall also be considered.
Access Hooks- Fitting welded to a chimney to permit the attachment of steeplejack equipment. lAnchor for Guy- The foundation for fixing of guy.
Base Gussets- usually triangular or trapezoidal fins of steel fixed to the shell of the chimney and to the base plate.
Base Plate- A horizontal plate fixed to the base of the chimney
Chimney- The arrangements by which flue gases are lead into the atmosphere for dispersion. Cleaning Door- A door, normally at the base of the chimney to permit the removal of flue dust and/ or to provide access.
Cope Band- A steel flat or angle attached to the top of the chimney around its perimeter to prevent distortion and to provide additional strength at this area.
Cowl- A conical or dished cap attached to the top of the chimney around its perimeter to prevent
distortion and to provide additional area to this area.
Cowl stays-Steel stays, which connect the cowl to the top of the chimney.
Cravat- An up stands fixed to the roof or roof plate to prevent water entering the building.
Draft- The difference between absolute gas pressure at any point in the duct or chimney shell and
the atmospheric pressure.
Draft losses- The pressure losses caused by friction and other consideration between any points in the chimney shell or ducts.
Flare- The bottom portion of the chimney in the form of truncated cone. Gallery- The platform around the shaft for observation and maintenance.
Guy band- A steel band fitted around the outside of a chimney with lugs for the attachment of guy wires.
Guyed chimney- A chimney in which all externally applied loads (wind, seismic force, etc) are not totally carried by the chimney shell and for which guys or stays are provided to ensure stability.
Guy or stay- Arrangement for supporting the chimney shaft. Height- The height of the chimney top from datum.
Height of the steel shaft- The height between the top of foundation and top of chimney, Holding down bolts- Bolts built into a concrete foundation, brick base or supporting frame work. Inlet- A circular or rectangular opening in the side of a chimney, to permit the entry of exhaust gases from connecting flue.
Joining flange- A steel flat or angle fitted to each end of a chimney sections to enable sections to be connected together.
Nominal chimney diameter- Internal diameter at the top most opening of the steel shell.
Roof plate- A plate which follows the contour of the roof round the chimney where it passes
through the roof. It is also known as flashing around the chimney.
Self supporting chimneys- A chimney which together with the foundation will remain stable under all working conditions without any additional support. Stack- Normally the straight portion of the chimney.
Weather hood- A truncated cone designed to shed rain water clear of the cravat and prevent its entry into the building.
2.1 SELECTION OF CHIMNEY
Factors to be considered while considered while choosing chimneys are as follows:
1. Characteristics of the equipments for which chimneys are designed that is, type,
number of units, etc;
2. Type of fuel used;
3. In the case of boilers, surface area, output efficiency, draft required, etc;
4. Mode of operation;
5. Temperature of the flue gas before entering the chimney and its likely variation;
6. Composition of the flue gas -its specific weight, quantity of dust data about
aggressiveness of the gases. These factors decide the type of lining.
7. Local statutory regulations, relating to height, dispersion of ash, provision for earthing, aviation warning lamps, health etc; and
8. The mode of erection of chimney
2.2 SITE INFORMATION
Ã‚Â£)esign wind velocity 45m/s
Design wind pressure
Height from ground level
Risk coefficient Ki=l Terrain category = 1 Topography K3 =1 Seismic Factor As per IS 1893
Seismic zone factor 0.15 to 0 .2
2.3 LOAD CONSIDERATION
1. Dead load
2. Wind load
3. Seismic load
2.4 CHIMNEY PARAMETERS
1. Basic dimensions
A self supporting chimney of height 40 meter and above shall be provided with a flare of one -third the height of the chimney, at the base to achieve better stability.
The minimum outside diameter of unlined chimney shell at the top is kept I/20th of height of the cylindrical portion of chimney and for lined chimneys it is kept at l/25th of the cylindrical portion.
The minimum outside diameter of flared chimney shell is kept at 1.6 times the outside diameter of chimney shell at top.
The thickness of lining varies from 10cm to 25cm depending on the temperature of flue
12. Allowable stresses
In order to control buckling in steel chimneys the compressive stress caused by the combination | of extreme fiber stresses due to bending and direct load should not exceed the values given in table for steels conforming to IS: 226 and IS: 2062.TABLE 2.1 ALLOWABLE STRESS IN BENDING FOR CIRCULAR STEEL CHIMNEY
ALLOWABLE STRESS IN AXIAL COMPRESSION FOR CIRCULAR STEEL CHIMNEY
Allowable stress in N/mm
100 & less
125 150 175 200 225 250 300 350 400 450 500 550
125.00 125.00 125.00 125.00 125.00 125.00 125.00 124.00 107.00 92.80 85.80 78.30 71.80
110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 300 350
125.00 125.00 125.00 125.00 125.00 125.00 125.00 116.00 103.50 90.60 78.60 68.00 58.90 51.30 45.00 39.70 35.30 31.50 28.40 25.50 23.20 21.10 19.20 17.60 16.20 15.00 10.60 7.72
125.00 125.00 125.00
125.00 125.00 125.00 125.00 125.00 125.00
125.00 125.00 125.00 125.00 124.00
71.80 68.00 58.90 51.30 45.00 39.70 35.30 31.30 28.40 25.50 23.20 21.10 19.20 17.60 16.20 15.00 10.60 7.72
Note : *For ratio of d/t and h1/k in the zone above zig zag, the stress from the top line may read
:**For ratio of d/t and h1/k in the zone below zig zag, the stress from the coloumn headed '100 and less' may be read :*** Above values of the stresses have been converted in SI units from those given in MKS unit
2.5 STEEL PLATES FOR CHIMNEY
The width of steel plates required for the steel chimney varies from 0.9m to 2.5m. The steel plates of 1.50m widths are most commonly used .The thickness of steel plate should not be less than 6mm. The thickness of steel plates in the two upper sections of the chimney should not be less than 8mm to resist more corrosion likely at the top of the chimney. The thickness of steel plates in the flared portion should not be less than the thickness at the lowest section of the cylindrical portion. The steel plates are available in thickness of 5,6,10,12,14,16,18,20,22,25,28,32,36,40,45,50,56and 63mm. For the ease in construction, the upper diameter of plates forming the side of chimney is kept less than the lower diameter. Each course fits telescopic over the lower course.
The steel plates are sheared or planed to proper bevel for caulking. The steel plates of chimney are caulked from the inner side of chimney. The caulking is done with a round nosed caulking tool.
The steel plates (or all steel works) are painted in order to avoid corrosion. One coat of approved paint is applied before leaving the shop. Two coats of approved paint are applied both inside and outside after the chimney is erected. The paint applied should be heat resistant. Graphite or carbon paint or other tried heat resistant paint may be applied. The painting should never be done in wet or freezing weather. The thickness shall not be less than 6mm. The corrosion resistant steel plates may be used in the chimney. Copper bearing steel plates may be used for self-supporting steel chimneys.
The thickness of steel chimney obtained from stress calculations and deflection consideration shall be increased by permitting an allowance for corrosion determined from the consideration of the design life of the chimney and aggressiveness of the flue gases. The allowance for corrosion permitted is decided depending upon the expected amount of internal corrosion of
steel plates. For 10 years of design life, the corrosion allowance for non-copper bearing quality of steel for slight, normal and exceptional internal corrosion is 2mm, 3mm and 5mm, respectively.
In case the design life for the steel chimney is 20years, then this allowance for said quality of steel and amount of internal corrosion is 4mm, 5mm and 8mm respectively. The copper bearing quality of steel is used when it is essential. The quality of steel needs less corrosion allowance as compared to that of non- copper bearing quality of steel.
However the minimum thickness of shell of a chimney shall not be less than 6mm.
2.6 CORROSION ALLOWANCE FOR STEEL CHIMNEY
The thickness of shell obtained from calculations and deflection consideration shall be increased by an amount determined from the considerations of the design life of the chimney and aggressiveness of flue gases. The corrosion allowance for the design life of 10 and 20 years are given in table 2.1
Amount of internal Corrosion allowance Tc for design Life
con-osion/ epicted 1 OYears 20Years
Non copper Copper Non copper Copper
bearing bearing bearing bearing
quality quality quality quality
Slight (for example, lined or insulated) 2mm - 4mm 2mm
Normal (for example unprotected for coal fired 3mm 2mm 5mm 3mm
Exceptional (for example unprotected for oil fired) 5mm 3mm 8mm 5mm
2.7 LINING FOR CHIMNEY
The guyed steel chimneys are usually unlined. The self-supporting chimneys are usually unlined. Sometimes, the self-supporting chimneys are also left unlined. The unlined chimneys
have also given excellent service. In general practice, the self-supporting chimneys are all made with lining. The steel chimneys are lined in order to protect the chimneys from heat, to act as a protecting cover and thus reduce the corrosion on the steel plates, and to maintain the temperature Ã‚Â¦of the flue gases.
The fire brick, common brick, solid grade diatomaceous (mole earth) bricks, acid resisting bricks, moler concrete, refractory concrete are the various material used for lining. The material |used for lining should be capable of withstanding high temperature up to 2000Ã‚Â°F.The lining is required from below the breach opening to the height, where the heat of gas does not damage the chimney. The height of lining should not be less than lOtimes the diameter or one- third height above the breach opening. The lining may be done from the base to the top of chimney. The self-supporting chimneys are usually lined throughout the full height of chimney. LINING MATERIALS
The brief description of lining made of different materials, construction and maintenance of lining is as follows.
1. Fire bricks: In order to suit the dimensions of the steel chimneys, the firebricks are made in radial forms. The Alumina content between 28 and 32 percent in firebricks is satisfactory for most of the applications. These bricks are set in the mortar. The mortar is made from ground clay or any other suitable heat resistant cement. The firebrick lining acts as a protective lining. It reduces the corrosion. It also protects the chimney up to a temperature of 1200Ã‚Â°C. The firebricks have high density. As such this type of lining is not suitable in maintaining the temperature of flue gases. Its strength and hard surface give necessary protection to the steel chimney from abrasion. When the steel chimneys are to discharge flue gases having a temperature higher than 1200Ã‚Â°C temperature, then the special duty lining shall be used.
2. Insulating refractory bricks: Three different grades of these bricks are available to suit temperatures of 850Ã‚Â°C and 1500Ã‚Â°C respectively.
3. Solid grade diatomaceous (molar earth) bricks: These bricks are made to suit diameter of chimney and to suit thickness as needed by the designer. These bricks are set in mortar. The mortar is made from the brick material ground to powder with the addition of Portland or alumina cement depending on the temperature of flue gases. The lining provided with these bricks give necessary protection from heat and also maintains the temperature of flue gases. These bricks provide protective cover depending upon the nature of flue gases. These bricks are used temperature of 150-800Ã‚Â°C.
4. Acid resisting: When the flue gases are highly acidic and have a temperature below 150Ã‚Â°C, then the lining is made from the acidic resisting bricks. These bricks are set in acidic resisting cement. This type of lining is not suitable to resist short fluctuations in temperature.
5. Moler concrete: The aggregate for molar concrete is made from molar earth bricks in appropriate grading and mixed withy alumina cement. The moler concrete may be precasted to shapes needed, casted in situ or gunited. In no case, the thickness of monolithic lining shall be less than 50mm. A minimum cover of 25mm shall be provided to anchorage where the corrosive conditions exist. This lining protects the chimney from heat and maintains the temperature of the gases. This lining provides protective covering in temperature range of 150Ã‚Â° to 980Ã‚Â° C depending upon the type of flue gases.
6. Refractory concrete: This type of lining may be casted in situ or gunited. This lining is similar to fire brick lining in its use and fulfills the similar requirements. The aggregate for this type of concrete is made from fire bricks or insulating refractory bricks of appropriate gradings. This
' lining is used to line the chimneys less than lm in diameter with brick.
7. Sand and cement mixture: This is useful a s lining by gunning for low temperature range, normally below 150 Ã‚Â°C .
2.8 MISCELLANEOUS COMPONENTS
In addition to structural parts like base plates, base gussets and holding down bolts of stacks, other miscellaneous items are needed for the proper functions, maintenance and safety of stacks. These are as follows
1. Breech openings
2. Baffle plates
3. Clean out doors
5. Steps and ladders %. Warning lamps
7. Lightening conductors 1. Breech openings
These are openings in the shell of the stack for the entrance of the flue gas. They are usually 20% larger than the internal cross sectional area of the chimney. The minimum width of the opening should not exceed 2/3 of the diameter. The reinforcement at the vertical sides should be greater than the material removed, in the ratio of the diameter to the long chord normal to the face opening. The same amount of reinforcement may be provided at the top and bottom of the opening. The opening is provided above the conical base for self-supporting stacks, in order to avoid placement of reinforcement in the conical base.
Two breach opening at Three breach opemng
Fig 2.1 Breach Openings
Where there are two or more breach openings in the shell, baffle plates are provided to properly direct the gases from each flue of the chimney, to prevent them from interfering with the operation of other flues. The baffle plates should extent from below the bottom of the breach opening to the top of breach opening so that the flue gases come together when they are moving in parallel lines The facing of firebrick is provided to prevent steel from hot gases. 3. Clean out doors
Clean out doors of size 2200* 1200mm are generally provided at the base of the stack, though the minimum size being 500*800mm.
III III III . Jll
III :=lll III
ST IFF ME RS
HINGE Fig 2.2 Clean out door
Galleries of width 800mm, with handrails of height lm, are provided around the chimney for erection and service of the lamps, earthing, inspection etc.
5. Steps and ladders
Steps are welded to the shell at a spacing of 300mm, the width being 150mm.The projection of a step is kept at 250mm.Inside the chimney if the steps are supported by lining their minimum thickness is 200mm.If the diameter of the stack is more than 3m, a second raw of steps should be welded to the shell. The spacing between the raw is usually kept at 380mm and the second raw is staggered.
Fig 2.3 Ladder
6. Warning lamps
Fig 2.4 Location of warning lamps on the chimney
Suitable warning lamps depending on the height of the chimney should be provided at specified points. Two numbers must always be provided, diametrically opposite to each other.
Position of lamp
Height of lamp in m for chimney height
32.0 56.0 63.0 70.0 80.0 90.0 100.0 110.0 30.50 54.50 61.0 68.50 78.50 88.50 98.50 108.00 27.0 31.50 33.50 38.50 43.50 48.50 73.50
p. Lightning conductors
Chimney should be provided with a lightning protection arrangement in the form of suitable metal connection, well grounded to prevent damage from lightning discharges.
It is essential that both lined and unlined chimney should be inspected periodically and necessary maintenance work carried out to ensure the designed life of chimney. 1. Unlined chimney
Unlined steel chimney should be inspected by a competent person annually to check the thickness of the shell. This could be done by ultrasonic testing or by any other suitable approved methods to ensure that the shell thickness is not less than that required from design considerations. Wherever the thickness is found insufficient it should be compensated by new plates.
The exterior surface should also be inspected by and maintained by painting. In the case of large diameter chimneys the inside may be inspected by the use of painters trolley or cradle scaffolding. For chimney of diameter exceeding 3m at the top, two such painters trolley shall be provided. (2.Lined chimney
Lined chimney should be inspected every alternate year in a manner similar to that described for the unlined chimney. In addition to that the conditions of the lining or the insulation should be Ã‚Â¦checked in order to ensure that it serve the purpose for which it is provided.
In the case of chimney with riveted or bolted construction the angle flanges should be inspected so as to remove any accumulation of rust between them as this will over load the rivet/bolt in tension and cause failure and also the rivet heads on the interior should be inspected to ensure that they are not corroded to a dangerous limits leading to damage or failure
In the case guyed, chimneys, the guy wires and fittings should be inspected annually to ensure the safety of the wires. The guy wires should be cleaned, greased and re-tensioned to the designed condition.
The earthing connection and connections to the warning lamps should also be inspected and maintained in good conditions so that they are functionally efficient. Ã‚Â»he typical figure of a painters trolley is shown below.
Fig 2.5 Details of painters trolley
2.10 ASH DISPOSAL General
Fig 2.6 Ash removal system for chimney
In any coal/oil fired boiler a particular percentage of ash which escapes along with the flue gas will be precipitated, due to change in direction of flue, at the bottom of the chimney. This will require periodical disposal depending upon the quantity of ash. For small boilers, quantity will be very small and this will not require elaborate arrangements while for medium and higher capacity boilers the quantity will be considerable and will require separate arrangements for disposing the ash.
lAsh disposal system
In case of bigger boilers, where the quantity is more, a separate arrangement has to be provided and usually this will be a hopper at the bottom of the chimney and just below breach openings left for flue connections.
In the case of small boilers, the ash may be disposed by providing a hopper on the foundation. This consist of a hopper with a gate at the bottom which when a particular weight or volume of ash is collected, will automatically open and discharge the ash in to the pit at the bottom. This ash can be disposed of by mechanical or pneumatic or hydraulic systems, depending on the system adopted for the disposal of the ash from the combustion chamber.
In the case of a mechanical system a conveyer will be provided in the pit ,so that the ash can be removed and loaded in the trucks outside.
In the pneumatic system ash will be removed by ejector or sucking by compressed air and discharged in to the main ash disposal system.
In the case of hydraulic system, enough quantity of water will flush into the main ash disposal system.
Assume density as 1 kg /m3.
The fuel used in boiler stack is LSFO (Low Sulphur furnace oil).The composition of the furnace oil includes:
Carbon : 85.49%
Hydrogen : 10.41%
Sulphur : 4.0 %
Ash -m o/Å¾
The fuel is supplied at a rate of 1500kg/hr
REACTIONS INVOLVED 1. CARBON
The main reactions involved with carbon are:
C + 02 -+C02 (1)
2C + 02^2CO (2.1)
2 CO +02 - 2C02 (2.2)
On combining the reactions 2.1, 2.2 we get
2C+ 202^ 2C02 (3)
Therefore the total reaction is:
3C + 302- 3C02 (1+3)
From the above equation it is seen that the ratio of C, 02 and C02 1:1:1, that
1 kmole of C reacts with lKmole of 02 to give 1 kmole of C02.
The Carbon present in the fuel = 1500 * 85.49 / 100 = 1282.35 kg / hr. Number of moles of carbon = 1282.35/ 12 = 106.86 kmole. Therefore C02 produced = 106.86 * 44 =4701.84 kg/hr.
The reaction in which hydrogen is involved is:
2H2 + 02 -Ã‚Â» 2 H2 O. H2 present in the fuel = 1500* 10.41/ 100 =156.15 kg / hr. Number of moles of hydrogen = 156.15 / 2 = 78.075 kmole.
2 kmoles of H2 gives 2Kmoles of H 20 or the ratio is 1: 1, 78.075 kmole of H2 GIVES 78.075 kmole of H 20 Therefore H 20 produced = 78.075 * 18 = 1405.35 kg/ hr.
The reaction in which sulphur is involved is:
S + 02 -Ã‚Â» S02 Sulphur present in the fuel = 4 *1500/ 100= 60 kg / hr.
Number of moles of sulphur = 60/ 32 = 1.875
1 kmole of S gives 1 kmole of 02 and 1 kmole of S02. Therefore S02 produced = 1.875 * 64 = 120 kg / hr. 4. OXYGEN Requirement
From the equation: C + 02~> C02 106.86 kmole of C requires 106.86 kmole of 02, So the 02 required = 106.86 * 32 = 3419.52 kg / hr From the equation: 2H 2+ O 2_>2H2 O
2 kmole of H2 requires 1 kmole of 02.
So the 02 required = 78.075 *32/ 2=1249.2 kg / hr. From the equation: S + 02 -Ã‚Â» S02 02 required = 1.875 * 32 = 60 kg /hr.
Therefore the total 02 required = 3419.52 + 1249.2 +60 = 4728.72 kg /hr.
Now an additional supply of 02 up to 4% is also supplied, so
02 supplied = 4* 4728.72/ 100= 4917.86 kg / hr.
Take 79 % of air contains N2 and remaining 21% is 02.
N2 supplied = 4917.86* (79/21) =18500 kg/hr.
So, Air supplied = 18500 + 4917.86 = 23418. 38 kg/hr.
02 unreacted = 4917.86- 4728.72= 189.14 kg/hr.
N2 present in the flue gases = 18500.52 kg/hr.
The following are the quantity of flue gases: l.C02 : 4701.95 kg/hr 2. H2 0 : 1405.35 kg/hr
3. S02 : 120 kg /hr
4. 02 (unreacted): 189.14 kg /hr 5.N2: 18500.52 kg/hr
Therefore, the total flue gas output = 24916.96 kg / hr
For change over purpose additional 300 kg/hr will supply. Then the total fuel supply becomes 1800 kg/hr. Then the flue gas emission become 30000 m3 /hr. So the internal diameter is designed for maximum flue gas emission.
3.2 DESIGN FORMULAE
3.2.1.THE FORCES ACTING ON THE STEEL CHIMNEY:
The various forces acting on the self supporting steel chimney are as follows. 1 .Self weight of the steel chimney
2. Weight of lining
3. Wind pressure
4. Seismic forces
1. Self weight of the chimney:
The self weight of the steel chimney Ws acts vertically. Consider a horizontal section XX. The
thickness of the steel plates above the section XX may be assumed constant. The weight of the
chimney is given by,
Ws = Ds*3.14*d*t*h.
Ds = Unit weight of steel=78.5 kN/m3
d = Diameter of chimney in m
t =Thickness of steel plates in m
h = Height of steel chimney above the section XX in m.
The compressive stress in the steel plates at the section XX due to the self-weight of the chimney is given by,
Fst = Ws/(3.14*d*t) = 0.0785*hN/mm2 (3.1)
2. Weight of lining:
The weight of the lining in the steel chimney, WL, also acts vertically. The thickness of concrete
lining maybe assumed as lOOmm.The weight of lining,
WL = Dc*3.14*d*(0.1)*h
Dc =Unit weight of concrete lining=20KN/m
WL = (2*3.14*d*h)kN
The compressive stress in the steel plates at the section XX, due to the weight of lining EH =WL /(3.14*d*t)=(2*3.14*d*h)/(3.14*d*t)
=0.002(h/f) N/mm2 (3.2)
3. Wind pressure:
The wind pressure act horizontally. The wind pressure on a structure depends on the shape of the structure, the width of the structure, the height of the structure, the location of the structure, and the climatic condition. The wind pressure per unit area increases with the height of the structure above the ground level. In order to simplify the design, the steel chimney is divided in to number of segment of equal height. The height of each segment may be kept 10m.The intensity of wind pressure over each segment may be assumed as uniform. The wind pressure on the flared portion may be found by using average diameter. The wind pressure may be assumed to act at the mid height of each segment and as also in the flared portion. It has also been practice to take uniform wind pressure over the height of chimney. The wind pressure, P = K*p i * (proj ected area)
Shape factor. It accounted for the shape of structure. The shape factor for cylindrical
portion is 0.7.
- Intensity of wind pressure.
=Outer diameter of the chimney.
In addition to the wind effect the over turning effect due to wind pressure, the wind has also aerodynamic effect. The aerodynamic effect of the wind has not been taken into consideration for design of steel chimney.
4. Seismic forces:
The seismic forces also act horizontally. The seismic forces act on structure, when the structures are located in the seismic area.
The following the load combination for the calculation of stress at any point of steel chimney are considered:
(i)Dead load +Wind load +Temperature effect.
(ii) Dead load +Earthquake (seismic) load +Temperature effect.
The effect of temperature is considered only when the temperature of the flue gas is more than 250Ã‚Â° C. Only one effect is considered for the design of the structure out of the two forces.
3.2.2. DIAMETER OF THE CHIMNEY:
The inside diameter of the chimney is calculated as follows:
d= / ((4*q)/ (IT *k*v))
Quantity of flue gas in m3/s
the theoretical velocity of gas in m/s = V (gH (Tg/Ta-1))
Height of the chimney in m
acceleration due to gravity in m/s2,
k = a constant = actual velocity/ theoretical velocity, and this may be taken as 0.6.
However, the diameter shall be so chosen that the velocity will not exceed, under any circumstances, 30m/s.
The most optimum range for velocity will be 15 to 20 m/s. 3.2.3 HEIGHT OF THE CHIMNEY:
The height of the chimney may be calculated by the following formula, as per the Kerala state pollution control board.
H = Height of the chimney, and Q = Quantity of Sulphur emission in kg/hr. 3.2.4 STRESS IN CHIMNEY SHELL:
The total stress in any particular section of the chimney is,
fc = (G/A) + (M/Z)
(As per IS 6533-1971)
fc =total stress in N/mm2 (compression),
G = Weight of the part of the chimney above the section in N,
area of steel at the particular section, : bending moment at the section in N mm, modulus of section under consideration in mm3
3.2.5 HOLDING DOWN BOLTS:
The maximum force in one bolt Pi is,
Pi = (4Mb/n.D,)-(Ws/n) (3.7)
(As per IS 6533-1971)
Mb = bending moment at base of the chimney,
n = number of bolts,
Di = diameter of bolt ring,
Ws=weight of steel stack. 3.2.6 BASE PLATE: (i) Forces in base plate
Compressive force per unit length of plate, circumferentially,
= (4Mb/ n.D2) + (Ws+W,/ n.D,) (3.8)
(As per IS 6533-1971)
Ws = weight of steel stack, W] = weight of lining,
D = diameter of shell,
D] = diameter of bolt ring, and
Mb = bending moment at the base of the chimney.
(ii) The thickness of the base plate should be calculated from,
tb = 0.866*b*V(Fp/Fbc) (3.9)
(As per IS 6533-1971)
Fp = allowable bearing stress on the foundation Fbc = allowable bending compressive stress.
The Foundation of the chimney depends on soil characteristics; availability of space and the amount of overturning. The following types of foundations are generally adopted, (i) Raft foundation
(a) Full raft (circular slab)
(b) Annular raft (ii)Pile foundation
(iii) Truncated cone foundation
(iv) Hyperbloid foundation
The maximum soil pressure is determined from the following procedure (a) Find e - M0/W
(b) Compute e/Df and F = W/A
© Find K5 and Fmax
(d) Check K5/D>=0.6 and e/D<=0.255
(As perlS 6533-1971)
Df= Diameter of the footing M0=over turning moment
W= Total weight of the stack A=Area of circular footing Fmax - maximum unit bearing pressure including overturning moment. 3.3 DESIGN CALCULATIONS
Inside Diameter of the steel stack d = V ((4*30000)/ (3.14*0.6*15)) (As per IS 6533-1971)
Total fuel consumption in kg/hr is 1500. But there are two boilers. So for change over purpose the fuel consumption become 1800 kg/h.
When this fuel burning the amount of S02 is 120 kg/h
So the height of steel stack = 14. (120)A0.3
~ 60m (by Kerala state pollution control board)
Intensity of wind pressure
= 1.6 kN/m2
Flared portion height = H/3
= 60/3 = 20m
So the out side diameter of steel stack D = (d + (2*T) + (2*tm))
= 1.1+(2*0.1)+ (2*.006) = 1.30m
d = inside diameter of the steel stack in m
T = thickness of lining in m
tm = minimum thickness of steel shell in m
Bottom diameter of the steel shell
= (5/3)*D ==(5/3)* 1.30 = 2.09m ~ 2.10m
(as per IS:6533-1971)
From Table 2.1,
Corrosion allowance for oil fired boiler and 20 years life,
= 5 mm (as per IS 6533-1971)
OVERTURNING MOMENT DUE TO WIND LOAD:
To make the calculations easier divide whole section in to 6 parts (10 m each, Fig 3.1)
Shape factor for round section of the chimney shell, S = 0.7 (as per IS 6533-1971)
V7777777777Z Fig 3.1 Sections of stack
Over turning moment at XiXi,
pi hj= S *Wind load*Projected area*hl = 0.7*1.73*1.3*10*5 =78.55 kNm
S = Shape factor Pi = Wind load at part 1 h| = point of application of the wind load
Pi h, = .7*1.73*1.3*10*15 p2h2= 0.7*1.67*1.3*10*5
Total = 312.08 kNm
3. At X3X3:
p, hi = 0.7*1.73*1.3*10*25 p2 h2 = 0.7*1.67*1.3*10*15 p3 h3= 0.7*1.6*1.3*10*5
Total =694.255 kNm
pi hi =0.7*1.73*1.3*10*35 p2 h2 =0.7*1.67*1.3*10*25 p3 h 3=0.7*1.6*1.3*10*15 p4h4=0.7* 1.54*1.3*10*5
Total =1219.295 kNm
5. At X5X5:
Pi h, =0.7*1.73*1.3*10*45 p2h2 = 0.7*1.67*1.3*10*35 p3h3 = 0.7*1.6*1.3*10*25 p4 114 = 0.7*1.54*1.3*10*15 p5h5 =0.7*1.46*1.5*10*5
Total =1887.905 kNm
p, h, =0.7*1.73*1.3*10*55 p2h2 = 0.7*1.67*1.3*10*45 p5 h3 = 0.7*1.6*1.3*10*35 p4h4 = 0.7*1.54*1.3*10*25 p5h5 = 0.7*1.46*1.5*10*15 p6h6= 0.7*1.28*1.9*10*5 Total= 2715.135 kNm
STRESS CALCULATION Part 1:
Minimum thickness of the shell, t = D/500
= 2.66 mm ~ 3mm
Corrosion allowance = 5 mm
D/t =1300/3 = 433.33 He Ik =10000/ (0.707* 1.3) = 21.96 (He = L for bending stress and for compressive stress He = 2L in the case of circular steel chimneys)
From table 2.1:
Allowance tensile stress, F,
From table 2.2:
Allowable compressive stress, F,
Stress due to moment, Fmo
Stress due to chimney weight, Fst
Stress due to chimney lining, Fy,
Maximum tensile stress, Ft
Maximum compressive stress, Fc
= 92.8 N/mm2
= 4M/ (3.14*D2*f) =78.7/ (250*3..14* 1.32* 0.003) = 19.77 kN/mm2 = 0.079*h = 0.79 N/mm2 = 0.002*h/t =.002*10/.003 = 6.66N/mm2 = 19.77-0.79= 18.98 N/mm2 = 19.77+0.79+6.66 = 27.22 N/mm2
Ft < Fta and Fc < Fca. So design is safe.
10-5 = 5mm
From table 2.1:
From table 2.2:
= 125 N/mm' = 47.04 N/mm2
Fst F,i Ft Fc
= 1.58 N/mm2 = 8 N/mm2 = 45.46 N/mm2 =56.62 N/mm2
Ft < Ffa and Fc < Fca.
So design is safe..
D/t = 260
He/k = 65.94
From table 2.1:
Fta = 140 N/mm2
From table 2.2:
Fca = 125 N/mm2 Fmo = 104.66 N/mm2
Fst =2.35 N/mm2
Fii =12 N/mm2
F, =102.245 N/mm2
Fc =118.925 N/mm2
Ft < Fto and Fc < F, So design is safe.
Minimum thickness = 14-5 = 9mm
D/t = 144.4
He/k = 87.9
Fta =153 N/mm2
From table 2.2:
= 98.97 N/mm-
Ft < F,a and Fc < Fca. So design is safe.
16-5 = 11mm
125 N/mm2 97.1706 N/mm2 3.95 N/mm2
FH =10.4546 N/mm2
F, = 93.22 N/mm2 FC =115.57 N/mm2
F, < Fta and Fc < Fca. So design is safe.
From table 2.1: From table 2.2:
= 18-5= 13 mm
He/k = 192.44
FTA = 153N/mm2
FCA =125 N/mm2
Fmo = 73.7 N/mm2
Fst = 4.74 N/mm2
FH = 10.61 N/mm2
F, = 68.96 N/mm2
FC = 89.05 N/mm2
F, < Fta and Fc < Fca.
So design is safe.
The stress at the flared part is multiplied by 1/ cos 0
Where 0 = half of the flare angle
0 = tan_1((2.1-1.3y2)/2 = 1.145
Hence no change in the stress.
CHECK FOR EARTHQUAKE
Seismic factor as per IS 1893, 1984 with Amendment 1 reaffirmed in 1991.
Seismic zone factor
: 0.15 to 0.2
Average thickness of the steel shell
Weight of steel
= (8+ 10*2+ 14+ 16+ 18)/6= 12.66 = ( 1.3+2. l)/2= 1.7mm = volume * density =3.14*1.7*0.01266*60*79=318.8 kN
Weight of lining
Increase the weight by 5% for sti
Therefore, total weight
Area of cross section of the base
Radius of gyration
= 3.14*1.7*60*0.1*23 = 736.64 kN , platform and ladders etc.
= 1.05*(318.8+736.64) =1108.21 kN = 3.14*2.1*0.018 = 0.1186 m2 = 0.707*2.1 =0.735 mm = 60/0.735 = 81.63
Values of CT and Cv
Ratio K CT Cv
5 14.4 1.02
10 21.2 1.12
15 29.6 1.19
20 38.4 1.25
25 47.2 1.30
30 56.0 1.35
35 65.0 1.39
40 73.8 1.43
45 82.8 1.47
50 or more 1.8k 1.50
From table 3.1 C, = 1.8*h/k =1.8*81.63 = 130
Period of free vibration Tp = C, V (WhH/EAg) (3.10)
Where, Wh = weight of the chimney including stiffness platform and ladders. H = height of the chimney A = area of base E = modulus of elasticity g = acceleration due to gravity
Period of vibration Tp = 130*V (1108.21 * 1000*60000)/ (200* 1000*0.1186* 106*9810 =2.19 s
Fig 3.1 Average acceleration
= 1.5*0.01266*1108.21/1.33 = 15.82 kNm. Which are very small when compared to wind effect.
For design of the base plate the force due to the movement is increased by 25%
So, Force due to moment = 4M\J (3.14D2)
= (4*2715.35*1.25)/ (3.14*2.1)2 = 80kN/m
Similarly force due to gravity is increased by 10%
Force due to gravity = (1108.21*1.1)/(3.14*2.1)
= 184.77 N
Therefore total force, F
Allowable bearing pressure for concrete = 4N/mm
Width of base
Provide a width ~ 300mm
Pressure under the base
= (1164.77*1000)/ (4*1000) = 291.19 mm
= (1164.77* 1000)/(300* 1000) =3.88 N/mm2
Thickness of base plate
0.866*b*V (Fp/Fbc) 0.866*300*V (4/ (0.75*250)) 37.68 mm
Thickness based on 1.77 N/mm pressure
= 37.68*V (1.77/4)
= 25.06 mm ~ 28mm
Use a base plate of 300*28 mm HOLDING DOWN BOLTS
= 1.25*125 N/mm2
Net area of bolt required = 375.65/(1.25*125)
Therefore diameter of the bolt, db = V ((2404.16*4)/3.14)
Selecting bolt M60
Try a circular slab (raft) foundation having diameter 7m (obtained by trial and error
Depth = 2 m
Weight of foundation, Wf = 3.14* 3.52 *2 *25=192 3.25 kN
Weight of chimney and lining
Total weight, Wt
= 736*1.1 = 809.6 kN = 2732.85 kN
Area of foundation, Ar
3.14*3.52 = 38.47 mm2
Direct pressure at foundation Fd = Wt/Af = 2732.85/38.47= 71.04 kN/mm2
For design the total lateral force at base of the chimney is increased by 45% Total lateral force at the base of chimney,
P = (Pi+P2+P3+P4+P5+P6) 1-45, where p is the load at
section at 1,2, 3,4,5,6 resp.
Moment at the base
= (15.74+ 15.197+14.56+14.014+14.7+7.024) 1.45 =131.89kN
= (2715.135*1.45) + (131.89*2) = 4200.7 kNm
= M/W = 4200.7/2732.85 =1.53
So design is safe.
e/ D =1.53/7 = 0.21, which is less than 0.255 ;
0 0.14 0.20 0,25 0.30 â€šÂ¬.35 0.40 0.45 0.50
. â€ e/D Values â€
Fig 3.2 Maximum soil pressure and neutral axis for
From Fig 3.2,
The value of K5 /D From chart 3.2,
=0.73 > 0.6, so design safe.
=3*71.04=213.12 kN/mm2<250 kN/mm2
So design safe.
Check against overturning
Overturning moment, M0 = 4200.7 kNm
Resolving moment, MR = (2732.5-736)*3.5
= 1996.5*3.5 = 6987.75
Factor of safety = MR/M
= 6987.75/4200.7 = 1.66 > 1.5;
So design is safe. CHECK FOR SLIDINGS
Friction coefficient between concrete and soil ~ 0.35
Frictional force = 2732.5*0.35=956.375 > 174.6 KN,
So design is safe.
(a)Stiffhess of the flared chimney ~ 2 times that of the prismatic chimney.
Tp =2.19/2= 1.095 sec
Fr = 1/1.095 = 0.91 cycles/sec
Stronghold critical velocity, Vc
= 5*D*f = 5*1.3*0.91
K, = K3 = 1 K2= 1.15
Design wind velocity
Critical range for resonance Hence there is no resonance effect
Basic wind speed = 39 m/s
= 39*1*1*1.15 = 44.85 -45 m/s
= 0.5 to 0.8 Vd = 22.5 to 36 m/s
= 1.095 Sec > 0.25 Sec
So Dynamic effect is to be considered
di value of d for
Lined chimney Un lined chimney
0 1.20 1.3
.025 1.70 2.5
.05 1.90 3.1
.075 2.10 3.5
.10 2.30 3.75
.125 2.45 4.10
.150 2.60 4.30
.175 2.70 4.50
.200 2.75 4.70
Type of location Height above ground level in metre
Up to 10 20 40 60 100 200 300 and above
A 0.60 0.55 0.48 0.46 0.42 0.38 0.35
1. Type A relates to open location (desert, sea coast, Lake Etc.)
2. Type B relates to outskirt of town having obstacles of light more than 10m.
B 0.83 0.72 0.65 0.60 0.54 0.46 0.40
From table 4.1 Dynamic coefficient From table 4.2
Height coefficient Mass for part 1
Steel: 3.14* 1.3*0.008* 10*78500/9.81 Lining:3.14*(1.3-0.1 )*0.1 * 10*20000/9.81 Total
Mass for part 2 & 3 are same Steel: 3.14*1.3*0.01 * 10*78500/9.81 Lining:3.14*(l. 3-0.1)*0.1*10*20000/9.81 Total
= Tp*Vb/1200= 1.095*39/1200 =0.0355
= 2613.1 kg = 7681.9 kg
Mass for part 4
Steel:3.14*1.3*0.014*10*78500/9.81 =4573.0 kg
Lining:3.14*(1.3-0.1)*0.1*10*20000/9.81 = 7681.95 kg
Total = 12255.0 kg
Mass for part 5
Steel:3.14*1.5*0.016*10*78500/9.81 = 6030.3 kg
Lining:3.14*( 1.5-0.1 )*0.1 * 10*20000/9.81 = 8962.2 kg
Total = 14992.5 kg
Mass for part 6
Steel:3.14* 1.9*0.018* 10*78500/9.81 = 8593.2 kg
Lining:3.14*(1.9-0.1)*0.1*10*20000/9.81 = 11522.9 kg
Total =20116.1 kg
Assume first mode shape is represented by 2nd degree parabola whose ordinates at 55 are unity. So
that the ordinates, y at a distance x is
y = (x/55)2
Assume type of location is B in Table 4.3 The data required is tabulated below
55~ 10295.0 0.6125 ~T~ 15.74
45 10948.0 0.6375 0.669 15.74
35 10948.0 0.6675 0.405 14.56
25 12255.0 0.7025 0.21 14.014
15 15992.5 0.775 0.074 14.7
5 20116.1 0.83 0.00 17.024
Height Mass (kg) p y Pst(kN)
I Yk*Pst*kPk = (9.64 + 6.48 + 3.94 + 2.07 + 0.84) = 22.97
X yk2*Mk=(82.1 +540.4+1795.8 + 4899.8+ 10295.0)= 17613.1
ai a2 a3 a* a5
Pa' P4' Ps'
Dynamic inertia forces
= 10295.0*1.8*0.65*0.0013 = 10948.0*1.8*0.65*0.000869 = 10948.0*1.8*0.65*0.000526 = 12255.0*1.8*0.65*0.000273 = 14992.5*1.8*0.65*0.0000962
M3' =(15.66*5+ 11.14*3 + 6.74)5
W =(15.66*7+ 11.14*5 + 6.74*3 + 3.91)5
= 0.0013 = 0.000869 = 0.000526 = 0.000273 = 0.0000962 = 0.00
Â¢ 15.66kN = 11.14kN = 6.74 kN = 3.91 kN = 1.69 kN = 0.00 kN
= 78.29 kNm =290.57 kNm = 592.245 kNm = 947.18 kNm
M5' =(15.66*9+ 11.14*7 + 6.74*5 + 3.91*3 + 1.69)5 - 1330.13 kNm
\V =(15.66*11 + 11.14*9 + 6.74*7 + 3.91*5 + 1.69*3 + 0)5 = 1721.51 kNm
Check for shell thickness Parti:
t = 8mm
fcmax = 27.22 + (19.77*78.290)/78.7 = 46.88N/mm2 < the allowable stress
t = 10mm
fcmax = 56.62 = (47.07*290.57)/312.08 = 100.44 N/mm2 < the allowable stress
t = 10mm
fcmax = 118.925 + (104.66*592.245)/694.255 = 208.206 N/mm2 < the allowable stress
t = 14mm
fcmax = 114.139 +(102.119*947.185)/1219.295 = 193.468 N/mm2 < the allowable stress Part 5;
t = 16mm
fcmax = 111.57 + (97.17* 1330.130/1887.905 = 180.03 N/mm2 < the allowable stress
fcmax = 89.05 + (73.70* 1721.51)/2715.135 = 135.78 N/mm2 < the allowable stress
So the design is safe
CHAPTER-5 RESULT AND CONCLUSION
The Results obtained from the design of boiler stack are:
> Height of steel stack = 60 m
> Inside diameter at the top = 1.1 m
> Outside diameter at top = 1.3 m
> Outside diameter at the base = 2.1 ra
> Thickness of the steel plate at different sections are
Â¢ Section 1 = 8 mm
Â¢ Section 2=10 mm
Â¢ Section 3 = 10 mm
Â¢ Section 4=14 mm
Â¢ Section 5 = 16 mm
Â¢ Section 6=18 mm
> Base plate dimension is 300*28 mm steel plate
> Holding down bolts M 60 (12 nos.)
> Foundation M20 grade concrete
Â¢ Diameter of the foundation = 7m
Â¢ Depth of foundation = 2 m >. The lining thickness = 100 mm
Â¢ Lining material is Refractory Concrete.
The design considerations of boiler stack subject to various rules and regulations of IS 6533-1971 and Kerala State Pollution Control Board is done. It includes the design considerations of various dimensions of stack, foundation, base plate, holding down bolts.
The design is checked against earthquake, Stability, Sliding and found that the design is safe against these factors.
The dynamic analysis is also done.
Finally the drawings of the designed parts are prepared using Auto Cad software.
The new design is very efficient in maintaining the proper draught and the corrosion rate is also very less. Since the height is designed as per the nonns of Kerala State Pollution Control Board the atmospheric pollution is very less.
DUCT FfiQM * i-BOllE* ^*A\j
ENLARGED VIEW SHOWING CHIMNEY DOOR .AND BOILER DUCTS
DETAIL AT Y
FOR DETAIL CcFIG. 8
A Typical Self Supported Chimney
> Indian Standard Code 6533-197J
> Design of steel structure by M.Raghupathy ; Tata McGraw-Hill publishers
y Design of steel structure Ram Chandra ; Standard publishers
> Stoichiometry by B.I.Bhatt and S.M.Vora ; Tata McGraw-Hill publishers