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2.Boilers

SyllabusBoilers: Types, combustion in boilers,

performances evaluation, analysis of losses, feed

water treatment, blow down, energy conservationopportunities.

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Boiler

Pressure Vessel

Heat generated byCombustion of Fuel

Heat transferred to

water and steam isgenerated

When water

becomes steam-Volume increasesalmost 1600 times-

safety is vital

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Fuels used in Boiler

Solid Liquid Gaseous AgroWaste

Coal HSD N.Gas Baggase

Lignite LDO Bio Gas Pith

Fur.Oil Rice Husk

LSHS Paddy

Coconut shell

Groundnut shell

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Boiler Systems

Water treatment

system

Feed water systemSteam System

Blow down system

Fuel supply system

Air Supply system

Flue gas system

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Boiler Components and Auxiliaries

Boiler Components Burner/Nozzle

Combustion Space

Convection region

Superheated zone

Shell Tubes(Water/Fire)

Auxiliaries Pumps

Fans

Chimney

Instruments& Controls

Fuel Storage, handling Water treatment plant

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Typical Boiler Specification

Boiler make and year : Nestler 1982

MCR rating : 6 TPH (F & A 100oC)

Type of Boiler : 3 Pass Fire tube, dry

back economic boiler

Design Steam Pressure/ : 10.5 Kg/cm2 150 PSIG

Safety valve

Operating Pressure : 110-130 PSIG

Fuel used : Furnace oil

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Boiler Heating Surfaces

Heating surface enable transfer of heat from fuel to water

Expressed in square metres

Radiant Heating Surfaces (Direct or Primary)

All water-backed surfaces that are directly exposed to the

radiant heat of the combustion flame.

Convection Heating Surfaces ( Indirect or Secondary)

Water-backed surfaces exposed only to hot combustion gases.

Extended Heating Surfaces Surface of economizers and superheaters .

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Boiler Types and Classifications

Fire Tube Boiler

Water Tube Boiler

Packaged boiler

Chain grate or traveling

grate stoker boiler Spreader stoker boiler

Pulverised fuel boiler Fluidised Bed boiler

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Fire Tube Boiler Hot gas through tubes and boiler

feed water in shell side convertedinto steam

Used for small steam capacities( upto 25 tons/hr and 18 kg/cm2

Tubes submerged in water

Used for small industrial units Low Capital Cost

Efficiency high (82%)

Accepts wide & loadfluctuations

Steam pressure variation is less(Large volume of water)

Packaged BoilerFigure 2.2 Fire tube boiler

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Water Tube Boiler

Water flow through tubes

Tubes surrounded by hot gas

Steam capacities range from4.5- 120 t/hr

Calls for very stringent water

quality Used for Power Plants

Characteristics

High Capacity Boiler Used for high pressure steam

Demands more controls

High Capital Cost

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Packaged Boiler

Package boilers are generally

of shell type with fire tube

design

High heat release rate in small

combustion space

More number of passes-so moreheat transfer

Large number of small

diameter tubes leading to goodconvective heat transfer.

Higher thermal efficiency

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Chain-Grate or Traveling-Grate

Stoker Boiler

Coal is fed on one end of a

moving chain grate

Coal burns and ash drops offat other end

Coal must be uniform in sizeas large lumps will not burnout completely

Coal grate controls rate ofcoal feed into furnace bycontrolling the thickness of

the fuel bed.

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Spreader Stoker Boiler

Uses principles of bothsuspension and grate

burning

Coal fed continuously overburning coal bed

Coal fines burn insuspension and larger coalpieces burn on grate

Good flexibility to meetchanging steam loadrequirements

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Pulverized Fuel Boiler

Coal is pulverised by crushing, impaction and attrition (rubbing) to a fine powder(

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Pulverized coal fired Boiler

Advantages Ability to burn all ranks of coal from anthracitic to

lignite

Permits combination firing (i.e. use of coal, oil and

gas in same burner).

Disadvantages

High power consumption for pulverizing

More maintenance, flyash erosion problems andhigher pollution complicate unit operation

i i i

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Fluidized bed boiler

Sand (dolomite and limestone particles) supported on afine mesh

Evenly distributed hot air is passed upward through the

sand bed Sand in a fluidized state is heated to the ignition

temperature of the coal

Coal is fed continuously onto hot air agitated sand bed:veloctiy maintained to keep them in suspension

Coal burns rapidly and the bed attains a uniform

temperature. Boiler tubes are immersed in the fluidised bed

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Fluidized bed boiler

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Fluidized-bed boiler

Advantages : Reduced furnace volume and size

High rates of heat transfer between combustion

gases and boiler tubes

Lower NOx emissions

Combustion temperature < 850o

C Possible use of low sulphur coal

Limestone (CaCO3

) and dolomite (MgCO3

) reactwith SO2 to form calcium and magnesium sulfides

Higher combustion efficiency

Multi fuel firing

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Impediments to Energy Efficient

operation

Excess Air in flue gas Presence of Combustibles (C,CO) in flue gas

High flue gas temperature High steam pressure (More than process need)

High /low Oil pre heat temperature

Boiler Blow Down water loss

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Typical Excess Air Requirements

Fuel Optimum %

Excess Air

Optimum %

O2in flue Gas

FBC (coal) 20 - 25 4.0 - 4.5

PF (Coal) 20 - 30 4.0 - 5.0Stoker Firing 25 - 40 4.5 - 6.5

Oil firing 5 - 15 1.0 - 3.0

N.Gas 5 - 10 1.0 2 0

Black Liquor 5 - 10 1.0 - 2.0

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Performance Evaluation ofBoilers

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Possible Reasons for Unsatisfactory

Boiler Performance

Passage of Time

Poor combustion

Heat transfer Fouling

Poor Operation and Maintenance

Poor Fuel Quality

Poor Water Quality

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Need for Boiler Performance Testing

Efficiency testing helps to improve

performanceHelps to find out how far the boiler

efficiency has drifted away from the bestefficiency.

Any observed abnormal deviations could be

investigated further to pinpoint the problem

area for necessary corrective action.

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Boiler Efficiency Evaluation Method

Indirect Method

Efficiency =

Energy Input Losses

Also called as Heat Loss

Method.

Involves Measurement of

Temperature, Pressure,

Fuel consumption rate and

Flue gas analysis,

More accurate result

Direct Method

Efficiency =

Energy gained by Steam

Energy content of fuel

Measurement of only steam

flow rate & Fuel

consumption Approximate Result

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Direct Method

BoilerFuel Input 100%

Steam

utput

Flue

Gas

O

Efficiency =

Heat in Steam x 100

Heat in Fuel

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Type of boiler: Coal fired Boiler

Heat input data

Qty of coal consumed (Input) :1.6 TPH

GCV of coal : 4000 K.Cal/kg

Heat output data

Qty of steam gen (output) : 8 TPH

Steam pr/temp : 10 kg/cm2(g)/ 180 0C

Enthalpy of steam(sat) at 10 kg/cm2(g) pressure

:665 K.Cal/kg

Feed water temperature : 850 C

Enthalpy of feed water : 85 K.Cal/kg

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Calculation

Boiler efficiency (): = Q x (H h) x 100( q x GCV)

Where Q = Quantity of steam generated per hour (kg/hr)

q = Quantity of fuel used per hour (kg/hr)GCV = Gross calorific value of the fuel (kcal/kg)H = Enthalpy of saturated steam (kcal/kg)h = Enthalpy of feed water (kcal/kg)

Boiler efficiency (

) = 8 TPH x1000Kg/Tx (66585) 1001.6 TPH x 1000Kg/T x 4000

= 72.5%

Evaporation Ratio = 8 Tonne of steam1.6 Ton of coal

= 5

I di t M th d

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Indirect Method

Boiler Flue gas

Steam Output

Efficiency = 100 (1+2+3+4+5+6+7+8)

CO2,H2O,SO2,N2,O2,CO,Ash

C,H,S,

moisture,ash

Air- N2,O2

Fuel Input, 100%

1. Dry Flue gas loss2. H2 loss

3. Moisture in fuel4. Moisture in air

5. CO loss

7. Fly ash loss

6. Surface loss

8. Bottom ash loss

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Format sheet for boiler efficiency testing

Date: Boiler Code No.

Time Ambient air Fuel Feed water Steam Flue gas analysis Surface

Temp

of

boiler,oC

Dry

bulb

Temp,oC

Wet

Bulb

Temp,oC

Flow

Rate,

Kg/hr

TempoC

Flow

rate,

m3/hr

TempoC

Flow

rate,

m3/hr

Pressure

Kg / cm2

TempoC

O2%

CO2%

CO

%

Temp0C

1.

2.

3.

4.

5.

6.7.

8.

Example: Boiler Efficiency Calculation

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Example: Boiler Efficiency Calculation

Fuel firing rate = 5599.17 kg/hr

Steam generation rate = 21937.5 kg/hr

Steam pressure = 43 kg/cm2(g)

Steam temperature = 377 oC

Feed water temperature = 96 oC

%CO2in Flue gas = 14

%CO in flue gas = 0.55

Average flue gas temperature = 190o

C

Ambient temperature = 31 oC

Humidity in ambient air = 0.0204 kg / kg dry air

Surface temperature of boiler = 70 oC

Wind velocity around the boiler = 3.5 m/s

Total surface area of boiler = 90 m2

GCV of Bottom ash = 800 Kcal/kg

Fuel Analysis (in %)

Ash content in fuel = 8.63

Moisture in coal = 31.6

Carbon content = 41.65

Hydrogen content = 2.0413

Nitrogen content = 1.6

Oxygen content = 14.48

GCV of Coal = 3501 Kcal/kg

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Theoretical (stochiometric) air fuel ratio and excess

air supplied are to be determined first for computingthe boiler losses.

Conversion formula for proximate analysis to ultimate analysis

%C = 0.97C+ 0.7(VM+0.1A) - M(0.6-0.01M)

%H2 = 0.036C + 0.086 (VM -0.1xA) - 0.0035M2(1-0.02M)

%N2 = 2.10 -0.020 VM

where C = % of fixed carbon

A = % of ash

VM = % of volatile matter

M = % of moisture

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Theoretical air required for complete

combustion

a) Theoretical air required for

combustion

= [(11.43 x C) + [{34.5 x (H2 O

2/8)} + (4.32 x S)] /

100 kg/kg of fuel. [from fuel analysis]

b) Excess Air supplied (EA) = (O2x 100) / (21 O2) [from flue gas analysis]

(or )

=7900 x [ (CO2)t ( CO2)a]

[from flue gas analysis]

CO2x [ 100 (CO2)t]

c) Actual mass of air supplied/kg of fuel (AAS)

= {1 + EA/100} x theoretical air

1 Heat loss due to dry flue gas

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1. Heat loss due to dry flue gas

L1 =

m x cpx (Tf Ta)

x 100

GCV of fuel

L1 = % Heat loss due to dry flue gas

m = Mass of dry flue gas in kg

= Combustion products from fuel ( CO2,SO2) and in this H2O should not

be considered + Nitrogen in fuel + Nitrogen in the actual mass of air

we are supplying

Cp = Specific heat of flue gas in kcal/kg/oC

Tf = Flue gas temperature inoC

Ta = Ambient temperature inoC

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2. Heat loss due to evaporation of water

formed due to H2 in fuel (%)

L2 =9 x H2 x{584 + Cp(Tf Ta)} x 100

GCV of fuel

WhereH2 = % Of hydrogen present in fuel on 1 kg basis

Es = Enthalpy of steam

Ef = Enthalpy of feed water

3. Heat loss due to moisture present in fuel

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L3 =

M x {584 + Cp( Tf Ta)}

X 100 GCV of fuel

where

M = % moisture in fuel in 1 kg basis

Tf = Flue gas temperature in oC

Ta = Ambient temperature inoC

4. Heat loss due to moisture present in air

L4 =

AAS x humidity x Cpx (Tf Ta) x 100

GCV of fuel

where

AAS = Actual mass of air supplied per Kg of fuel

Tf = Flue gas temperature in

o

CTa = Ambient temperature inoC

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5. Heat loss due to incomplete combustion:

L5 =

%CO x %C 5744

x x 100

% CO + % CO2 GCV of fuel

L5 = % Heat loss due to partial conversion of C to CO

CO = Volume of CO in flue gas leaving economizer (%)

CO2 = Actual Volume of CO2in flue gas (%)C = Carbon content Kg / Kg of fuel

or

When CO is obtained in ppm during the flue gas analysis

Hco = Mco x 5654CO formation (Mco) = CO (in ppm) x 10

-6x Mfx 28

Mf = Fuel consumption in kg/hr

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6. Heat loss due to radiation and convection:

L6 = 0.548 x [ (Ts/ 55.55)4 (Ta/ 55.55)

4] + 1.957 x (Ts Ta)1.25 x sq.rt o

[(196.85 Vm+ 68.9) / 68.9]

where

L6 = Radiation loss in W/m2

Vm = Wind velocity in m/s

Ts = Surface temperature (oK)

Ta = Ambient temperature (oK)

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7. Heat loss due to unburnt in fly ash (%).

L7 = Total ash collected / Kg of fuel burnt x G.C.V of fly ash x 100

GCV of fuel

8. Heat loss due to unburnt in bottom ash (%)

L8 =

Total ash collected per Kg of fuel burnt x G.C.V of bottom ash x 100

GCV of fuel

Boiler Heat Balance:

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Boiler Heat Balance:Input/Output Parameter Kcal / Kg of

fuel%

Heat Input in fuel = 100

Various Heat losses in boiler

1. Dry flue gas loss =

2. Loss due to hydrogen in fuel

3. Loss due to moisture in fuel =

4. Loss due to moisture in air =5. Partial combustion of C to CO =

6. Surface heat losses =

7. Loss due to Unburnt in fly ash =

8. Loss due to Unburnt in bottomash

=

Total Losses =

Boiler efficiency= 100 (1+2+3+4+5+6+7+8)

Boiler Efficiency = 100 % all losses in boiler

Measurements required for thermal energy

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Audit in Boiler

Fuel flow, steam/water flow

Temp & Pressure of steam

Temperature of water inlet / outlet t of economizer

Draught

CO2, O2, CO , Temperature from Flue Gas

Surface Temp & Ambient Temp

Heat flux, Kcal/m2 hr. Surface Area, m2

Size & dimension of boiler

Heat content of fuel

Amount of blow down

Test Procedure

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Plan / inform the concerned dept. Calibrate all the Instrument

Ensure fuel and water availability

Test at maximum steam load condition

Conduct 8 hrs minimum (1/2 or 1 hr frequently)

Check that water level in drum is same at start & endof test

Check that gas sampling point is proper

Ensure No blow down during test

Why give Boiler Blow Down ?

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Why give Boiler Blow Down ?

1 Issue of Safety

2 Issue of Energy Efficiency

When water evaporates

Dissolved solids gets concentrated

Solids precipitates

Coating of tubes

Reduces the heat transfer rate

Recommended TDS levels for various boilers

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eco e ded S eve s o v ous bo e s

2000 (in feed water)Coil boiler and steam generator6.

3000Package and economic boiler5.

3000-3500High pressure water tube boiler with super

heater

4.

2000-3000Low pressure water tube boiler3.

5000Smoke and water tube boiler2.

10,000Lanchashire1.

Maximum TDS (ppm)Boiler Type

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Continuous Blow down lossSteam 10 T/hr

TDS(T) =0

TDS (C) =3500 ppm Allowable)TDS(S) in feed water

100 ppm

Blow down(B)=100 / (3500-100)

=(100/3400)x100

=2.9 %=3%

B=SX100/(C-S)

Blowdown %= TDS in FWx100

TDSin Boiler - TDS in FWBlow down flow rate=3%x 10,000kg/hr=300kg/hr

Purpose of Boiler Water

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p

Treatment To reduce blow down losses from boiler

To reduce formation of scale

To reduce corrosion of boiler components

To reduce water carryover in steam

The presence of boiler water salts in condensate

from steam traps in process plant or deposits inprocess equipment indicate carryover from the

boiler.

Scale Formation

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Scale Formation

Most feed water components are soluble

However under heat and pressure, they come out ofsolution as

Particulate solids

Crystallized forms

Amorphous particles

When solubility of a specific component in water isexceeded, scale or deposits develop.

Large amounts of deposits throughout the boiler couldreduce the heat transfer enough to reduce the boilerefficiency significantly

External Water Treatment

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To remove Suspended solids,

Dissolved solids (Ca and Mg ions which area major cause of scale formation) and

Dissolved gases (O2

and CO2).

External Water Treatment Techniques

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q

Precipitation processes, in which chemicals are added to

precipitate Ca and Mg as compounds of low solubility.The

lime-soda process is typical of this class

(other precipitating agents- caustic soda and sodium phosphate)

Ion-exchange progresses, in which the hardness is removed as

the water passes through bed of natural zeolite or synthetic resin

and without the formation of any precipitate. Ion exchange

processes can be used for almost total demineralization.

Deaeration, in which gases are expelled by preheating the

water before entering the boiler system.

Filtration, to remove suspended solids

Internal Water Treatment

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Addition of various additives into the boiler feed water,

which have specific effects.

Additives include sodium sulphite or hydrazine for oxygen

removal, antifoams and pH control agents.

Recommended boiler water limits

Parameter Upto 20 Kg/cm2 21 - 40 Kg/cm2 41 - 60 Kg/cm2

TDS 3000-3500 1500-2000 500-750

Total iron dissolved solids ppm 500 200 150

Specific electrical conductivity at250C (mho)

1000 400 300

Phosphate residual ppm 20-40 20-40 15-25

pH at 250C 10-10.5 10-10.5 9.8-10.2

Silica (max) ppm 25 15 10

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Conventional Phosphate treatment

Provides conditions for formation ofcalcium and magnesium precipitates

Neutralization of acid contaminants such as

organic acids Maintaining residual of phosphate and

hydroxide alkalinity in boiler feed water

PO4 in range 20-40 ppm

Hydroxide alkalinity in range 300-500 ppm

Deaeration

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Deaeration

Certain gas such as CO2 and O2 normally present in water

combine with water to form carbonic acid

CO2+O2+H2O H2CO3

Carbonic acid corrodes metal, forms scales on tubes,

reduces heat transfer and reduces life of equipment

Mechanical deaeration involves heating of feed water

using steam to reduce CO2 and O2 concentration

To reduce CO2 and O2 levels further, sodium sulfite or

hydrazine or amines are used Chemical deareation

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2.7 EnergyConservation

Opportunities

1 High Stack Temperature

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1. High Stack Temperature

Stack temperatures > 200C indicates

potential for recovery of waste heat

Indicate scaling of heat transfer/recovery

equipment Urgency of taking an early shut down for water

/ flue side cleaning.

2. Feed Water Preheating using

Economiser

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Economiser

For older shell boiler, with

flue gas exit temperature of

260

o

C, Economizer could beused to reduce it to 200oC

Every 6oC rise in feed water

Temperature equals 1%

improvement in Efficiency

Condensing economizer

(NaturalGas) Flue gas

reduction up to 65oC

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3. Combustion Air Preheat

Combustion air preheating is an alternative

to feedwater heating.

In order to improve thermal efficiency by

1%, the combustion air temperature must beraised by 20oC or Flue gas temperature islowered by 22oC.

Most gas and oil burners used in a boiler plantare not designed for high air preheattemperatures.

4A. Incomplete Combustion Oil & Gas

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Leads to efficiency loss

May arise from a shortage of air or surplus of fuel or

poor distribution of fuel. In case of oil fired system, CO or smoke with normal or

high excess air indicates burner system problem

In gas fired systems, CO with normal or high excess air

may point to burner system problems.

Another frequent cause is poor mixing of fuel and air atthe burner - Poor oil fires may arise from improper

viscosity, worn tips, carbonization on tips and

deterioration of diffusers or spinner plates.

4B. Incomplete Combustion

Coal Firing

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Coal Firing

Loss occurs as grit carry-over or carbon-in-ash (2%

loss).

In chain grate stokers, large lumps will not burn outcompletely, while small pieces and fines may block the

air passage, thus causing poor air distribution.

In sprinkler stokers, stoker grate condition, fuel

distributors, wind box air regulation can affect carbon

loss. Increase in the fines in pulverized coal also increases

carbon loss.

5. Action Plan: Control excess air

for every 1% reduction in excess air 0 6% rise in efficiency

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for every 1% reduction in excess air, 0.6% rise in efficiency.

The optimum excess air level varies with furnace design, type of burner,

fuel and process variables.. Install oxygen trim system

Excess air levels for different fuels

Fuel Type of Furnace or Burners Excess Air

(% by wt)

Completely water-cooled furnace for slag-tap or dry-ash removal

15-20Pulverised coal

Partially water-cooled furnace for dry-ashremoval

15-40

Spreader stoker 30-60

Water-cooler vibrating-grate stokers 30-60

Chain-grate and traveling-gate stokers 15-50

Coal

Underfeed stoker 20-50Fuel oil Oil burners, register type 5-10

Multi-fuel burners and flat-flame 10-30

Wood Dutch over (10-23% through grates) and

Hofft type

20-25

Bagasse All furnaces 25-35

Black liquor Recovery furnaces for draft and soda-pulping processes

5-7

6. Radiation and Convection Heat Loss

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Surfaces heat loss to the surroundings depends uponthe surface area and the difference in temperaturebetween the surface and the surroundings.

This heat loss from the boiler shell is normally a fixedenergy loss, irrespective of the boiler output.

With modern boiler designs, this may represent only1.5% on the gross calorific value at full rating, butwill increase to around 6%, if the boiler operates at

only 25 percent output. Repairing or augmenting insulation can reduce heat

loss through boiler walls

7. Blowdown Heat Loss

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Uncontrolled blowdown is very wasteful 10% blowdown in 15 kg/cm2 boiler can result in 3% efficiency

loss.

This Loss varies may vary between 1% and 6% depending on anumber of factors: Total Dissolved Solids (TDS) allowable in the boiler water

Quality of the make-up water, which depends mainly on the type of water

treatment installed (e.g. base exchange softener or Demineralisation) Amount of uncontaminated condensate returned to boiler house

Boiler load variations.

Correct checking and maintenance of feedwater and boiler water quality,

maximising condensate return and smoothing load swings

Automatic blowdown controls can be installed that sense andrespond to boiler water conductivity and pH.

Waste heat recovery system can be added to produce flash steamfrom hot blowdown

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Blowdown Heat Recovery Efficiency Improvement - Up

to 2% Installing a heat exchanger in

the blowdown line allows this

waste heat to be used in

preheating makeup and feed

water.

Most suitable for continuous

blowdown operations

8. Reduction of Scaling and Soot Losses

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g

Soot buildup on tubes side or Scale on water side

Acts as an insulator against heat transfer

Elevates stack temperature and heat loss 1% efficiency loss with 4.4 4oC increase ion stack temperature

Indicated by high exit gas temperatures at normal excess air

level Water side deposits require review of water treatment

procedures and tube cleaning

It is time to clean soot deposits when flue gas temperature rise20oC above temperature for newly cleaned boiler

Check and record stack temperature regularly

Scaling Facts and Figures

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0.25 mm thick air film offers the same resistance to

heat transfer as a 330mm thick copper wall

A 3mm thick soot deposition on the heat transfer

surface can cause in fuel consumption to the tune of

2.5% A 1mm thick scale (deposit) on the water side

could increase fuel consumption by 5 to 8%

Cleaning

Incorrect water treatment, poor combustion and poor cleaning

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Incorrect water treatment, poor combustion and poor cleaning

schedules can easily reduce overall thermal efficiency by 2%. However, the additional cost of maintenance and cleaning must

be taken into consideration when assessing savings.

Cleanliness of Boilers

48Savings, Toe

10481000Annual losses, Toe

8884Annual Consumption, Toe

3030Air temperature, deg C

1212CO2 ,%

300220Flue gas temperature, deg C

6 months after cleaningClean BoilerFuel oil

-

Solution: brushing gas tubes of the boiler each month

9. Reduction of Boiler Steam Pressure

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Lower steam pressure gives a lower saturated steam

temperature and without stack heat recovery, a similar reduction

in the temperature of the flue gas temperature results. Potential

1 to 2% improvement.

Steam is generated at pressures normally dictated by the highest

pressure / temperature requirements for a particular process. In

some cases, the process does not operate all the time, and there

are periods when the boiler pressure could be reduced.

Adverse effects, such as an increase in water carryover from the

boiler owing to pressure reduction, may negate any potential

saving. Pressure should be reduced in stages, and no more than

a 20 percent reduction should be considered.

10. Variable Speed Control for Fans,

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Blowers and Pumps

Combustion air control is normally done by

opening or closing dampers at forced and induceddraft fans.

Dampers are simple means to control butinaccurate Gives poor control at top and bottom

of operating range

If the load characteristic of the boiler is variable,the possibility of replacing the dampers by a VSD

should be evaluated.

11. Effect of Boiler Loading on Efficiency

As the steam load falls the mass flow rate of the flue gases

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As the steam load falls, the mass flow rate of the flue gases

through the tubes also falls This reduction in flue gas flow for same heat transfer area reduces

exit flue gas temperatures, and marginally reduces sensible heat

loss. Below half load, most combustion appliances need more excess

air to burn the fuel completely and increases the sensible heat loss.

13. Boiler Replacement

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Consider replacement

If the existing boiler is old and inefficient

Not capable of firing cheaper substitution fuel Over or under-sized for present requirements

Replacement options

Long-term fuel availability Company growth plans

Financial and engineering factors

Since boiler plants traditionally have a useful life of well over25 years, replacement must be carefully studied.

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END

Boiler Efficiency Improvement by damper control

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Thermax Boiler

6 TPH

10.75 Kg/cm2

Coconut shell

fired Dust

Collector

9 %

Economiser

Hopper

Coconut shell

crusher

Primary Air

FanSecondary Air

Fan14 %

Damper

Induced Draft

Fan

Fuel Savings due to Boiler Efficiency

Improvement

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By damper control O2 in flue gas brought

down from 14 to 9 %

Correspondingly excess air came down

from 200 to 75 % Savings in coconut shell consumption 5 %

Annual Savings Rs. 3.44 Lakhs