CHIMNEYPP32

8/8/2019 CHIMNEYPP32

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A REPORT REQUIREMENT IN

INDUSTRIAL POWERPLANT ENGINEERINGMEIP412-412D / A3


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Romans used tubesinside the walls to drawsmoke out of bakeries

Central Europefireplaces withcylindrical masonrychimneys were used asearly as the 11th century

Real chimneys appearedonly in Northern Europein the 12th century


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The first industrialchimneys were built in

the mid-17th century

Industrial chimneysbecame common in

the late 18th century


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To produce the draftnecessary to cause theair to flow into the

furnace and dischargethe products ofcombustion to theatmosphere

To deliver the productsof combustion and flyash to a high altitude


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The chimney is part of asteam-generating boiler

Its evolution is closely linkedto increases in the power of

the steam engine

The chimneys of ThomasNewcomens steam enginewere incorporated into thewalls of the engine house

Free-standing industrialchimneys that appeared inthe early 19th century wererelated to the changes inboiler design associated withJames Watts "double-powered" engines


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The invention of fan-assistedforced draft (draught) in theearly 20th century removedthe industrial chimney'soriginal function

Building materials changedfrom stone and brick to steeland later reinforced concrete

The height of the industrial

chimney was determined bythe need to dispersecombustion flue gases tocomply with governmentalair pollution controlregulations


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The height and diameterof the stack.

The desired amount ofexcess combustion airneeded to assure completecombustion.

The temperature of theflue gases leaving thecombustion zone.


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The frictional resistance to theflow of the flue gases throughthe chimney or stack, whichwill vary with the materialsused to construct the chimneyor stack.

The heat loss from the fluegases as they flow through the

chimney or stack. The local atmospheric

pressure of the ambient air,which is determined by thelocal elevation above sea level.


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HEIGHT

Draft Pressure

Density of air

Density of flue gases

where H = height of the chimney

P = barometric pressureRa=gas constant of air

Rg=gas constant of flue gas

Ta=absolute temperature of air

Tg=(T1+T2)/2


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DIAMETER

Where: Qg = volume flow of flue gases

Qg =

mg = mass of flue gas

Vel = actual velocity of flue gas in m/s


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For the actual velocity:

where:cv = velocity coefficient, 0.40 usual assumption

Vt = theoretical velocity of flue gas in m/s

Value of R for any gas:


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By mass balance in the furnace:

where:ma = mass of airmf= mass of fuelmash = mass of ash (usually expressed as percentage of mf)mg = mass of gas


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A coal fired steam boiler uses 3,000 kg coal

per hour. Air required for combustion is 15.5

kg per kg of coal at barometric pressure of98.2 kPa. The flue gas has a temperature of

285C and an average molecular weight of 30.Assuming an ash loss of 11% and allowable

gas velocity of 7.5 m/s, find the diameter ofthe chimney.(April 1981)


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Given: Mass of fuel = 3000 kg coal/hourAir required = 15.5 kg air/kg coal

Barometric Pressure = 98.2 kPaFlue gas temperature = 285 CAverage molecular weight = 30Assuming ash loss = 11%

Allowable Gas Velocity = 7.5 m/s

Required: Diameter of the chimney


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Solution:

solving for Q:

the gas constant R:

amount of air required:


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By mass balance:


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from:


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let D = diameter of chimney

thus;


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2.52 kg of coal per second are consumed by asteam boiler plant and produced 18.54 kg ofdry flue gas per kg of coal fired. The air

temperature outside is 32C, the averagetemperature of the flue gases entering thechimney is 343C and the average temperatureof the flue gases in the chimney is 260C. Thegage fluid specific volume is 1.005x10-3 m3 /kgand a theoretical draft of 2.286 cm of water atthe chimney base is needed when thebarometric pressure 101.3 kPa. Find thediameter of chimney in meters.(April 1987)


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Given: 2.52 kgcoal/sec18.54 kg dry flue gas / kg of coal firedOutside air temperature = 32 CAve. temp of flue gases = 260 CGage fluid spec. vol. = 1.005x10-3 m3/kgTheoretical draft = 2.286 cm H2OBarometric Pressure = 101.325 kPa

Required: diameter of the chimney in meters


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Solution:

Flow gases have higher molecular weight than air; assume


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solving for draft and velocity:


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For the velocity of the flue gases considering a velocitycoefficient of 0.40:

for the velocity of the flue gases considering a velocity coefficient of 0.40


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Solving for the diameter:


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A power plant is situated at an altitude having

an ambient air at 96.53 kPa and 23.88C. Flue

gases at rate of 5 kg/s enter the stack at200C and leaves at 160C. The flow gases

gravimetric analysis are 18% CO2, 7% O2 , and75% N

2

. Calculate the diameter of the stack in

meters for a driving pressure of 0.20 kPa.(Note: the actual velocity is 40% of the

theoretical velocity)(April 1990)


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Given: Air Pressure = 96.53 kPaAir Temperature = 23.88 CFlue Gases flow rate = 5 kg/s

Entering Stack Temperature = 200 CLeaving Stack Temperature = 160 CDriving Pressure = 0.20 kPaFlow Gases Gravimetric Analysis

(Note: Actual Velocity is 40% of the theoretical velocity)

Required:d

iameter of the stack in meters


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Solution:The molecular weight and gas constant of theflue gas:


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Average temperature of flue gas ; Tg


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solving for the volume flow rate, Q

thus;


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A steam generator with economizer and air

heater has an overall draft loss of 21.78 cm

water. If the stack gases are at 177C and ifthe atmosphere is at 101.3 kPa and 26C,

what theoretical height of stack in meters isneeded when no draft fans are used? Assume

that the gas constant for the flue gases is thesame as that for air.(April 1995)


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Given: Overall draft loss = 21.78 cmH2OStack gases temperature = 177C

Pressure = 101.325 kPaTemperature = 26C

Required: theoretical height of stack in meters

(Note: assume that the gas constant for the fluegases is the same as that for air)


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Solution:

solving for the total draft, hw

solving for the densities of air and gas


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solving for the densities of air and gas


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then;


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If the actual draft required for a furnace is

6.239 cm of water and the frictional losses in

the stack are 15% of theoretical draft,calculate the required stack height in meters.

Assume that the flue gas have an averagetemperature of 149 C and molecular weight

of 30. Assume air temperature of 21C.(October 1995)


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Given: draft = 6.329 cmH2Ofriction losses = 15%

average temperature = 149 Cmolecular weight = 30air temperature = 21 C

Required: height of the chimney in meters


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Solution:

Solving for total draft, hw :

Solving for the densities of air and gas:


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Substitute the values to solve for the height:


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A steam boiler plant consumes 9,000 kg of coalper hour and produce 20 kg of dry flue gases perkg of coal fired. Outside air temperature is 32C,

average temperature of flue gas entering thechimney is 343C, and average temperature ofthe dry flue gas in the chimney is 260C. Thegage fluid density is 994.78 m3 /kg and atheoretical draft of 2.286 cm of H2O at thechimney base is needed when the barometricpressure is 760 mm Hg. determine the height ofthe chimney in meters.(April 1998)


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Given: 9000 kg coal/hour20 kg flue gases/kg coal firedOutside air temperature = 32 C

Average temperature of flue gas enteringthe chimney = 343 CAverage temperature of dry flue gas in thechimney = 260 CGage fluid density = 994.78 m3 /kg

Theoretical draft = 2.286 cmH2oBarometric pressure = 760 mmHg

Required: height of the chimney in meters


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Solution:

solving for the draft head, hw


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Solving for the densities of air and gas:


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then;


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The over-all draft loss of steam generating

unit is 400 mm water. Air enters at 101.325

kPa, 26C and the average flue gastemperature is found to be 250C. if no draft

fans are to be installed, what is the height ofthe chimney? Assume Rg = 0.277 kJ/kg-K.


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Given: over-all draft loss of steam = 400 mmH2OAir pressure entering = 101.325 kPaAir temperature entering = 26CAverage flue gas temperature = 250CRg=0.277 KJ/kg-K

Required: height of the chimney


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Solution:

solving for the total draft, hw

solving for densities of air and gas


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then;


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A 15 kg gas enters a chimney at 19 m/s. if the

temperature and pressure of a gas are 26C

and 100 kPa respectively, what is thediameter of chimney?

Use R = 0.287 kJ/kg-K.


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Given: m = 15 kg gasVel = 19 m/sTemperature = 26CPressure = 100 kPaR = 0.287 KJ/Kg-K

Required : diameter of chimney


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Solution:

solving for Q,

then by substituting the values;


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thus;


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A steam power plant, 5 kg of coal is consumedper second and it was later found that 25kg ofdry flue gas is produced per kg of coal fired. Air

enters at 25C. The average temperature of theflue gas entering the chimney is 350C and theaverage temperature of the flue gas inside thechimney is 250C. A theoretical draft of 5 cm ofwater at the base of the chimney is needed. The

gage fluid specific volume is 0.0025 m3/kg. If themolecular weight of the gas is 30, calculate theheight of the chimney.


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Given: 5 kg coal/s25 kg flue gas/kg coal25C air temperature250C average temperature of flue gas5 cmH2O theoretical draft0.0025 m3/kg gage fluid specific volume

30 molecular weight

Required: height of the chimney


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Solution:

solving for da and dg:


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then substituting the values;


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What is the height of the chimney if the

driving pressure is 30Pa and the gas and air

densities are 1 kg/m3

and 1.5 kg/m3

respectively?


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Given: driving pressure = 30 Pa

Gas density = 1 kg/m3

Air density = 1.5 kg/m3

Required: height of chimney


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Solution:

substituting the values;


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END OF REPORT


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GROUP 1Leader: Bagadiong, Carol M.Members: Andres, Michael . ; Arrastia, Paolo ; Banquicio, Bienvenido ;

Binallia, Paolo R. ; Bonifacio, Harold F. ; Consulta, Billy

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