Boilers 2 [Compatibility Mode]

8/6/2019 Boilers 2 [Compatibility Mode]

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QassimQassim UniversityUniversity

acu y o ng neer ngacu y o ng neer ng

Boilers In SteamBoilers In Steamnts

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Power PlantsPower PlantsrPla

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Prof. Dr.Prof. Dr. GamalGamal I.I. SultanSultan470470o

weowe

MansouraMansoura UniversityUniversity

Faculty of EngineeringFaculty of EngineeringMM

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Email:Email: [email protected]@mans.edu.eg && [email protected]@qec.edu.sa

www.ener efficienc asia.or

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UNEPUNEP 20062006


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Assessment of a boiler

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Energy efficiency opportunities

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470470o

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MM

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Economizer

Convective

b

Super heater

d

heater

c=1

ce

Steam toturbine

a

FWPQadd

3


4/40

Exhaust gases

Cold AirBlowerAir Heater to Air

Economizer

Hot Well

ConvectiveEvaporator

SuperheaterSuper heated

Steam

Radiant

Evaporator

4Benson BoilerBenson Boiler


5/40

5

ea a e o evapora onea a e o evapora on

sections.sections.


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Super

heater

Economizer

riser

er H

w

nco

dHeat

Adde

6Drum type water tube boilerDrum type water tube boiler


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1. Boilernt

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2. Boiler blow down

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.

470470oweowe

MMalal

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. o er per ormance

Causes of poor boiler performancents

nts

-Poor combustion

-Heat transfer surface foulingrPla

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-Poor operation and maintenance-Deteriorating fuel and water quality4

70470oweowe

Heat balance: identify heat lossesMMa

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Boiler efficiency: determine deviationher

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Heat Balancents

nts

how energy is transformed from fuel into useful

energy, heat and lossesrPla

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StochiometricExcess Air

Un burnt470470oweowe

FUEL INPUTFUEL INPUTSTEAM

OUTPUT

Stack Gas

MMalal

her

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9Ash and Un-burnt

parts of Fuel in Ash

Blow

Down

Convection

& Radiation


10/40

Balancing total energy entering a boiler againstnts

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e energy a eaves e o er n eren orms

Heat loss due to dry flue gas12.7 %

rPla

rPla

Heat loss due to steam in fuel gas8.1 %

100100..00 %%470470o

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Heat loss due to moisture in fuel

Heat loss due to moisture in air

0.3 %

FuelFuelMMa

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Heat loss due to unburnts in residue2.4 %

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10

Heat in Steam

unaccounted loss

.

73.8


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Heat Balance

nts

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oa : mprove energy e c ency y re uc ng

avoidablelossesrPla

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Avoidable losses include:

-470470o

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,

temperature)

-

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- Blow down lossesher

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- on ensa e osses

- Convection and radiation


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Assessment of a BoilerAssessment of a Boiler

Boiler EfficiencyThermal efficiency: % of (heat) energy input that is

effectively useful in the generated steamn

ts

n

ts

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CALCULATION

EE4747

PowPow

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1) DIRECT METHOD: 2) INDIRECT METHOD:

The energy gain of theThe

The

12

different between lossesand energy input

working fluid (water and steam)

is compared with the energycontent of the boiler fuel.


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Assessment of a BoilerAssessment of a Boiler

Boiler Efficiency: Direct Method

Boiler efficiency () = Heat Input x 100 Q x (hg hf) x 100=n

ts

n

ts

rPl

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hg -the enthalpy of saturated steam in kcal/kg of steamhf-the enthalpy of feed water in kcal/kg of water

EE4747

PowPow

Parameters to be monitored:

- Quantity of steam generated per hour (Q) in kg/hr

-

MM

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- The working pressure (in kg/cm2(g)) and superheat

temperature (oC), if anyThe

The

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-

- Type of fuel and gross calorific value of the fuel (GCV) inkcal/kg of fuel


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Boiler Efficiency: Direct Method

nts

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Advantages Quick evaluationr

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Few parameters for computation Few monitoring instruments

470

470

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benchmark figuresMMa

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No explanation of low efficiency

Various losses not calculatedher

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o er c ency: n rec e o

nts

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Efficiency of boiler () = 100 (i+ii+iii+iv+v+vi+vii)

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Principle lossesPrinciple losses:i) Dry flue gas4

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470

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ii) Evaporation of water formed due to H2 in fuel

iii) Evaporation of moisture in fuel

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iv) Moisture present in combustion air

v) Unburnt fuel in fly ashher

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vi) Unburnt fuel in bottom ash

vii) Radiation and other unaccounted losses


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o er c ency: n rec e o

Required calculation datants

nts

Ultimate analysis of fuel (H2, O2, S, C, moisture

content, ash content)rPla

rPla

% oxygen or CO2 in the flue gas

Fuel as tem erature in C Tf470

470

owe

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Ambient temperature in C (Ta) and humidity

of air in kg/kg of dry air

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GCV of fuel in kcal/kg

% combustible in ash in case of solid fuelsher

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16GCV of ash in kcal/kg (in case of solid fuels)


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Boiler Efficiency: Indirect Method

nts

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Advantages Com lete mass and ener balance for eachr

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individual stream Makes it easier to identify options to improve47

0

470

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Disadvanta es

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Time consuming Requires lab facilities for analysish

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. o er ow own

nts

nts

on ro s o a sso ve so s n e

water that is boiled

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Conductivity measured as indication of TDS470

470

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Calculation of quantity blow down required:MMalal

Blow down (%) =Feed water TDS x % Make up water

Maximum Permissible TDS in Boiler waterher

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Boiler Blow Down

nts

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IntermittentrPla

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Manually operated valve reduces TDS Large short-term increases in feed water4

70

470

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Continuous

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Ensures constant TDS and steam purity Heat lost can be recovered -h

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Boiler Blow Down

nts

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Lower retreatment costsrPla

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Less make-up water consumption470

470

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Reduced maintenance downtimeMMa

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Lower consum tion of treatmenther

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20chemicals


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3. Boiler Feed Water Treatment

nts

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Quality of steam depend on water

treatment to controlrPla

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Steam purity Deposits4

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470

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Corrosion

Efficient heat transfer onl if boiler

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water is free from deposit-forming

solidsher

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nts

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Chemicals added to boiler to prevent scalerPla

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Different chemicals for different water types

Conditions:470

470

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Feed water is low in hardness saltsMMalal

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Small water quantities treatedher

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Internal treatment alone not recommended


24/40

nts

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Removal of suspended/dissolved solids and

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Pre-treatment: sedimentation and settling4

70

470

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rs rea men s age: remova o sa s

ProcessesMMalal

a) Ion exchange

b) Demineralizationher

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c) De-aeration

d) Reverse osmoses


25/40

-

x

nts

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Water passes through bed of natural zeolite ofsynthetic resin to remove hardnessr

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Base exchange: calcium (Ca) and magnesium(Mg) replaced with sodium (Na) ions

470

470

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Does not reduce TDS, blow down quantity andalkalinityMMa

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em nera za on

Complete removal of saltsher

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Cations in raw water replaced with hydrogenions


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External Water Treatment

nts

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-

Dissolved corrosive ases O2 CO2rPla

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expelled by preheating the feed water4

70

470

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Mechanical de-aeration:used prior to additionMMa

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o c em ca oxygen scavangers

Chemical de-aeration:removes trace oxygenher

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x erna a er rea menx erna a er rea men

Ventnts

nts

Boiler Feed WaterSpray Nozzles

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Steam

Scrubber Section

(Trays)470

470

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owe

Stora e

MMalal

Section

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De-aerated Boiler

Feed Water


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x erna a er rea men

-nts

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Removal of trace oxygen with scavenger

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o um su p e:

Reacts with oxygen: sodium sulphate470

470

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Increases TDS: increased blow down

H drazine

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Reacts with oxygen: nitrogen + waterher

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boilers


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External Water Treatment

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v

OsmosisrPla

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Solutions of differing concentrations47

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470

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-

Water moves to the higher concentrationMMalal

Reversed osmosis

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Water moves in reversed direction


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External water treatment

nts

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vPressure

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470

470

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Fresh WaterFeed

WaterMMa

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Concentrated

Solution

Water FlowConcentrateFlowh

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UNEPUNEP 20062006Semi Permeable

Membrane


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.

2. Feed water preheating using economizers

3. Combustion air pre-heatingnts

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4. Incomplete combustion minimization

5. Excess air controlrPla

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7. Automatic blow down control47

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470

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9. Reduction of boiler steam pressure

10. Variable speed control

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11. Controlling boiler loading

12. Proper boiler schedulingher

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.


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. ac empera ure on ro

nts

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If >200C then recover waste heat

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2. Feed Water PreheatingEconomizers4

70

470

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Potential to recover heat from 200 300 oC flue

ases leavin a modern 3- ass shell boiler

MMalal

3. Combustion Air Preheatingher

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If combustion air raised by 20C = 1% improve

thermal efficiency


34/40

4. Minimize Incomplete Combustion

nts

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Smoke, high CO levels in exit flue gas

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auses:

Air shortage, fuel surplus, poor fuel distribution470

470

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Poor mixing of fuel and air

Oil-fired boiler:

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Improper viscosity, worn tops, cabonization on

dips, deterioration of diffusers or spinner platesher

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34 Coal-fired boiler: non-uniform coal size


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Energy Efficiency OpportunitiesEnergy Efficiency Opportunities

5. Excess Air Control

Optimum excess air levels varies

a

nts

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.

Portable or continuous oxygen analyzers00e

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ue g a r req. g ue 2 n ue gas n prac ce

Solid Fuels

Bagasse 3.3 10-12EE4

7

4

7

PoPo

(bituminous)

Lignite

Paddy Husk

.

8.5

4.5

5.7

-

9 -13

14-15

11.13mal

mal

Wood

Liquid Fuels

Furnace Oil 13.8 9-14The

The

35

LSHS 14.1 9-14


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6. Radiation and Convection Heatn

ts

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Fixed heat loss from boiler shell, regardless of

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o er ou pu

Repairing insulation can reduce loss470

470

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MMalal

. Sense and respond to boiler water conductivity

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. ca ng an oo oss e uc on

on

ts

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efficiency loss

=rPla

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9. Reduced Boiler Steam Pressure

.

470

470

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Lower steam pressureMMalal

= ower sa ura e s eam empera ure

= lower flue gas temperatureher

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Steam generation pressure dictated by process


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10. Variable Speed Control for Fans,

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Suited for fans, blowers, pumps

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Should be considered if boiler loads are

variable47

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47

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11. Control Boiler LoadingMMalal

Maximum boiler efficiency: 65-85% of rated load

Significant efficiency loss: < 25% of rated loadher

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12. Proper Boiler Scheduling

O timum efficienc : 65-85% of full loadn

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Few boilers at high loads is more efficient than

large number at low loadsrPla

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13. Boiler Replacement470

47

0

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Financially attractive if existing boiler is

Old and inefficient

MMalal

Not capable of firing cheaper substitution fuel

Over or under-sized for resent re uirementsher

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39 Not designed for ideal loading conditions


40/40

n

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47

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47

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FOR YOUR ATTENTIONFOR YOUR ATTENTIONMMalal

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UNEP GERIAPUNEP GERIAP

Documents

Boilers 2 [Compatibility Mode]