aph presentation.pptx

8/10/2019 aph PRESENTATION.pptx

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DESIGN OF AIR PRE HEATEAND ECONOMIZER

Submitted byJ.SHANMUKA VENKATA GOPICHAND (101FA08133)L.SURYA TEJA (101FA08141)

Under the guidance of(Internal)

N.B.PRAKASH TIRUVEEDULA

ASSISTANT PROFESSOR

VIGNAN UNIVERSITY

Under the guidance of(Exter

Mr. SREEKANTH JAB

GM AND PROJECT EN

HARTEX RUBBER PVT


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CONTENTS1. Process of Air pre-heater

2. Economizer

3. Boiler basics

4. Heat Exchangers

5. Cross Flow & Compact Heat Exchangers

6. Design Calculation of Economizer7. Design Calculation of Air pre-heater

8. Boiler Efficiency

9. Heat Balance sheet

10. Conclusion


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Process of Air pre-heater

An air pre-heater (APH) is a general term to describe any device designed to hbefore another process (for example, combustion in a boiler) with the primaryincreasing the thermal efficiency of the process.

There are two types of air pre-heaters for use in steam generators in thermal postations: One is a tubular type built into the boiler flue gas ducting, and the othregenerative air pre-heater.

Ambient air is forced by a fan through ducting at one end of the pre-heater tubother end the heated air from inside of the tubes emerges into another set of duwhich carries it to the boiler furnace for combustion


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There are two types of regenerative air pre-heaters: the rotating-plate regeneraheaters (RAPH) and the stationary-plate regenerative air pre-heaters.

Rotating-plate regenerative air pre-heater
http://en.wikipedia.org/wiki/File:Ljungstr%C3%B6m_regenerative_heat_exchanger.jpghttp://en.wikipedia.org/wiki/File:Rotating_Air_Preheater.PNG


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The rotating-plate design (RAPH) consists of a central rotating-plate element iwithin a casing that is divided into two (bi-sectortype), three (tri-sector type) (quad-sector type) sectors containing seals around the element.

In stationary-plate regenerative air pre-heaters the heating plate elements are a

in a casing, but the heating plate elements are stationary rather than rotating.
http://en.wikipedia.org/wiki/File:Stationary_Plate_Air_Preheater.png


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Economizer

Economizers are mechanical devices intended to reduce energyconsumption, or to perform another useful function such as prehefluid.

Economizer performs a key function in providing high overall bothermal efficiency by recovering low level energy from the flue git is exhausted to the atmosphere.

Economizer recovers the energy by heating the boiler feed water.


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It scavenge the waste heat from thermal exhaust flue gases by passingexhaust effluent through heat transfer surfaces to transfer some of thewaste heat to a process media.

It Efficiency is in direct relationship to equipment design and stack gavelocities.

Velocity increases through the stack as firing rate increases, which resin a decrease in contact time with the economizer heating surfaces


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BOILER BASICS

The hot water or steam under pressure is then usable for transferring the heat frequirements of process industries or for power generation.

During the combustion process, oxygen reacts with carbon, hydrogen and othein the fuel to produce a flame and hot combustion gases.

As these gases are drawn through the boiler, they cool as heat is transferred to

The main components in a boiler system are boiler feed water heaters, deaerat

pump, economizer, super heater, Attemperators, condenser and condensate pum


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Heat Exchangers

Heat Exchangers are classified according to their function and geometry:

Function:

Recuperative: two fluids separated by a solid wall

Evaporative: enthalpy of evaporation of one fluid is used to heat or cool the othe

Regenerative: use a third material which stores/releases heat

Geometry: 1. Double Tube 2. Shell and Tube

3. Cross-flow Heat Exchangers 4. Compact Heat Exchangers


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Heat Exchangers

The heat transfer rate for most heat exchangers can be calculated using the LM(Log Mean Temperature Difference), if the inlet (T1) and outlet (T2) temperatuknown:

U = Overall heat transfer coefficient [ W/m2-oC ]

A = Effective heat transfer surface area [ m2 ]

F = Geometry correction factor

= Log mean temperature difference

F

TT

TTT

12

12

/ln

TAUQ

T


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Cross flow and compact heat exchangers

Cross-flow and compact heat exchangers are used where space is limited. Themaximize the heat transfer surface area.

Commonly used in gas (air) heating applications.

The heat transfer is influenced by whether the fluids are unmixed (i.e. confinechannel) or mixed (i.e. not confined, hence free to contact several different heasurfaces).

In a cross-flow heat exchanger the direction of fluids are perpendicular to each


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Compact heat exchangers

In Compact heat exchangers, the heat transfer rate is directly related to press

Advantages:

very small

Ideal for transferring heat to / from fluids with very low conductivity or whtransfer must be done in very small spaces

Disadvantages:

high manufacturing costs

very heavy

Extremely high pressure losses.


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DESIGN OF ECONOMIZER

ASSUMPTION:

The properties are remains constant under steady state conditions and neglectsurrounding losses. Kinetic and potential energies are neglected.

DESIGN ANALYSIS:

Heat Transfer,

Q = m x c x t

Where m = mass of fluid in kg

C = specific heat of water in kj/kg oc

t= temperature difference


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Here m = 1800 kg/h

= 5 kg/sec

Specific heat of water is 4.18 kj/kg oc

Temperature difference, t= (70oc - 40oc) = 30oc

Q = 5 x 4.18 x 30oc

Q = 627 kW

Heat loosing fluid

Qc = m x c x t

= 16 x 1.005 x (200160)

= 643.2 kw.


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In Counter flow

LMTD = ((Th1Tc2)- (Th2Tc1)) / ln ((Th1Tc2 ) - ( Th2Tc1 ))

= ((200-70)(160-40)) / ln ((200-70)/ (160-40))

= (130-120) / ln (130/120)

= 10 / ln (1.083)

= 10 / 0.0797

LMTD = 125.47oc


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Actually this economizer is a cross flow economizer so, the LMTD equation b

(LMTD)cross= F X (LMTD)counter

Here F = correction factor

It is calculated by using graphical method by using dimension parameters P, Z

P= (Tc2-Tc1)/(Th1-Tc2)

P= (70-40)/ (200-70)

P= 0.2307


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Z= (Th1

-Th2

)/(Tc2

-Tc1

)

Z= (200-160)/ (70-40)

Z= 1.33

From this values we get F = 0.98 (from graphically,pgno:31)

So we have multiplied the counter flow LMTD with correction factor F

get LMTD of cross flow

(LMTD) cross = F X (LMTD) counter

= 0.98 x 125.47

= 122.96oc


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From heat transfer equation we calculate the area of economizer as follows

Q = UA Tmx F

Here F = Correction factor F = 0.98

A = Area of Economizer

A = (627 x 1000) / (850 x 125.4 x 0.98)

A = 6.01 m2

U = 850 w / m2oc (from tables)


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From Average velocity in the tube and discharge we Calculate total flow area

m = A u

Here m = mass of water

A = Tube flow area

U = velocity of flow = 0.2 m/sec

A = 5 / (1000 x 0.2)

A = 0.025 m2


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The above area is equal to actual crosssectional area of tube

0.025 =n x /4 x d2

0.025 = n x 3.14 x (0.025)2/ 4

n= 50

From Equation 1 the area is 17.47 m2

Then the total surface area in 2 tube pass is given below

2ndL = 6.01

L = 6.01/(2 x 0.025 x 3.14 x 50)

L = 76 mtrs


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Each tube = 2.2 mtrs

No. of passes = 2

No. of tubes = 50


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DESIGN OF AIR PRE HEATER

ASSUMPTIONS: The properties are remains constant under steady state conneglect surrounding losses. Kinetic and potential energies are neglected.

DESIGN ANALYSIS:

Heat Transfer,

Q = m x c x t

Where m = mass flow rate

C = specific heat of air in kJ/kg oc

C = 1.005

t= temperature difference in oc


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Here m = 5 kg/sec

Specific heat of water is 4.18 kJ/kg oc

Temperature difference, t= (110oc - 50oc) = 60oc

Q = 5 x 1.005 x 60oc

Q = 301.5 kw

Heat loosing of fluid Q = m x c x t

= 5 x 1.005 x (270-200)

= 351.75 kw


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LMTD = ((Th1Tc2 ) - ( Th2Tc1 )) / ln((Th1Tc2 )- ( Th2Tc1 ))

= ((270-110)(200-50))/ln ((270-110)/(200-50))

= (160-150)/ln (160/150)

LMTD = 156.46 oc

Actually this Air pre-heater is a cross flow Air pre-heater so the LMTD equati

Becomes,


Here F = correction factor


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It is calculated by using graphical method by using dimension parameters P, Z from graph,

P= (Tc2-Tc1)/(Th1-Tc2)

P= (110-50)/(270-110)

P= 60/160

P=0.375

Z = (Th1-Th2)/(Tc2-Tc1)

Z = (270-200)/(110-50)

Z = 70/60

Z = 1.16

From this values we get F = 0.94 (from graphically)


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So we have multiplied the counter flow LMTD with correction factor F, the

LMTD of cross flow


= 0.94 x 156.46

= 147.07oc

Q = UA Tmx F

Where U = overall heat transfer coefficient

A = Area of Air Pre heater

F = correction factor

U = 50 w / m2oc (As per standard tables)


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From Average velocity in the tube and discharge we Calculate total flow ar

Here correction factor F = 0.94

A = q / U Tmx F

= (301.5X 1000) / (50 x 0.94 x 156.4)

= 43.015m2

m = Au

Here m = mass flow rate kg/sec

A = Tube flow area m2

U = velocity of flow = 0.2 m/sec

= 1.5 kg / m3


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From continuity equation

Q = A1 X V1

5 / 1000 = 3.14 X (0.04)2X V1

V1 = 3.98 m/sec

m = Au

A= m/( x V1)

A=5/(1.5 x 3.98 ) = 0.83 m2

A = 0.83 m2


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The above area is equal to actual cross sectional area of tube

0.83 m2= n X /4 X d2

n = 658 tubes

Length of tube for two passes

ndL= 43.015m2

L = 43.015 / (658 x 3.14 x 0.04)

L = 0.52m

No. of tubes = 658

No. of passes = 2, Length = 0.52m


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BOILER EFFICIENCY Now we calculate the boiler efficiency of thermax boiler.

Capacity of boiler = 6 tons/hour

Exisisting values

Water temperature (tw) = 35oc

Mass of steam (ms) = 6000kg/hr

Mass of fuel (mf) = 1250 kg/hr Calorific value of husk = 3500 k.cal/kg = 14644.35kj/kg ( 1 joule = 0.239 k

Temperature of steam (ts) = 190oc

Boiler efficiency = ms(hs-hw)/mfx c.v


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Enthalpy of water at 35oc hw=hf+x hfg

(x = 0, i.e., dryness factor, by using steam tables)

hw= 151.5 + 0 x hfg

hw= 151.5 kj/kg

Enthalpy of steam at 190oc

hs=hf+x hfg

hs= 8067 + (0.8 X 1977.5)

hs= 2388.7 kj/kg

Therefore, boiler efficiency = ms (hs-hw) /(mfx c.v) x 100

= 6000(2388.7-151.5)/1250 x 14644.35) x 100

= 0.733 x 100 = 73.3%


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8.1 BOILER EFFICIENCY WITH ECONOMI

Now introducing economizer the temperature of water increases from

now water temperature (tw) = 50oc

And quality of steam increases up to 90 percent

Economizer with boiler efficiency = ms(hs-hw)/mfx c.vx100

enthalpy of water at 50oc (hw) = hf+ x hfg

= 213.7 + 0 x hfg

hw= 213.7 kj/kg


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enthalpy of steam at 190oc (hs) = hf+ x hfg

= 806.7 + (0.9 x 1977.5) (here quality of the s

= 806.7 + 1779.5

= 2586.45 kj/kg

Economizer with boiler effieciency = ms(hs-hw)/mfx c.v x 100

= 6000 (2586.45 - 213.7)/(1250 x 14644

=0.77 x 100

=77%


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8.2 BOILER EFFICIENCY WITH AIR PRE-HEA

Now we are introducing air preheater the husk consumption reduced to 125

1083 kg/hr

Boiler efficiency with air preheater = MS(HSHW)/MFXCVX100

= 6000 (2586.45-213.7)/1083 X14644.35)

= 14236500/15859831.05 X100

= 0.89 X100

Boiler efficiency with air preheater = 89%


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Water consumption per hour = 4250

Specific heat of water = 1

T= T2-T1

= 95OC-85OC

= 10OC

MCPT = 4250 X1 X10 X24 = 1020000 K.CAL

= 291.42857 KJ/KG

Therefore 291.42857 KJ/KGRice husk is saving


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Heat Balance Sheet Pressure of Steam = 14.2 bar

Steam produced = 6000 kg/hour

Coal used = 1250 kg/hour

Moisture in Fuel = 2% of mass

Mass of Dry Fuel gas = 9 kg of fuel

Calorific Value of Fuel = 3500 k.cal

Temperature of gas = 200

0

c Temperature of Boiler room = 280c

Feed water Temperature = 500c

Specific heat of gas = 1.005 kj/kg

Quality of steam = 0.9%


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Heat supplied for the fuel = mfx c.v

H.S = 1 x 3500

= 3500 k.cal

Heat supplied = 3500 k.cal

If moisture is present then heat supplied by 1 kg of fuel = (1- mm) c.v

Where mm is percentage of moisture

= (1-0.02) x 3500

= 3430 k.cal

= 4913.043 kj

Heat utilized in producing Steam = ms/mf(hs-hw) 1

Where hs = hf+ x hfg

= 806.7 + (0.9 x 977.5)

= 2586.45 kg


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hw= hf

hw= 806.7

= 6000/1250 (2586.45 206.7)

= 4.8 x 2379.75

= 11422.8 kj


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1250 1250

1083

950

1000

1050

1100

1150

1200

1250

1300

0

10

20

30

40

50

60

70

80

90

100

1 2 3

fuel consumption ( kg/hr

)

boiler efficiency (%)

Name fuel consumption

( kg/hr )

Boiler efficiency(%)

without airpreheater andeconomizer

1250 73.3

with economizer 1250 77with airpreheater 1083 89


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CONCLUSION

In this course of project it came to learn about the Design of Air pre-heater and

Economizer in boiler.

By using the Air pre-heater and Economizer boiler Efficiency can be increased

Gas flow distribution or heat transfer into the economizer section is improved of guide vanes at inlet of economizer duct.

Analysis of economizer module was carried out to predict the economizer feedoutlet temperature.

The economizer size optimized by reducing the number of tubes of module bythe heat transfer across the module.

By installing the Air pre-heater and Economizer the total husk consumption rareduced and the efficiency of the boiler is also increased to 73% to 89%


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aph presentation.pptx

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