8/6/2019 Boilers 2 [Compatibility Mode]
1/40
QassimQassim UniversityUniversity
acu y o ng neer ngacu y o ng neer ng
Boilers In SteamBoilers In Steamnts
nt
s
Power PlantsPower PlantsrPla
rPla
Prof. Dr.Prof. Dr. GamalGamal I.I. SultanSultan470470o
weowe
MansouraMansoura UniversityUniversity
Faculty of EngineeringFaculty of EngineeringMM
a
l
a
l
Email:Email: [email protected]@mans.edu.eg && [email protected]@qec.edu.sa
www.ener efficienc asia.or
her
her
1
UNEPUNEP 20062006
8/6/2019 Boilers 2 [Compatibility Mode]
2/40
Assessment of a boiler
nt
s
nt
s
Energy efficiency opportunities
rPla
rPla
470470o
weowe
MM
a
l
a
l
her
her
2
8/6/2019 Boilers 2 [Compatibility Mode]
3/40
Economizer
Convective
b
Super heater
d
heater
c=1
ce
Steam toturbine
a
FWPQadd
3
8/6/2019 Boilers 2 [Compatibility Mode]
4/40
Exhaust gases
Cold AirBlowerAir Heater to Air
Economizer
Hot Well
ConvectiveEvaporator
SuperheaterSuper heated
Steam
Radiant
Evaporator
4Benson BoilerBenson Boiler
8/6/2019 Boilers 2 [Compatibility Mode]
5/40
5
ea a e o evapora onea a e o evapora on
sections.sections.
8/6/2019 Boilers 2 [Compatibility Mode]
6/40
Super
heater
Economizer
riser
er H
w
nco
dHeat
Adde
6Drum type water tube boilerDrum type water tube boiler
8/6/2019 Boilers 2 [Compatibility Mode]
7/40
1. Boilernt
s
nt
s
2. Boiler blow down
rPla
rPla
.
470470oweowe
MMalal
her
her
7
8/6/2019 Boilers 2 [Compatibility Mode]
8/40
. o er per ormance
Causes of poor boiler performancents
nts
-Poor combustion
-Heat transfer surface foulingrPla
rPla
-Poor operation and maintenance-Deteriorating fuel and water quality4
70470oweowe
Heat balance: identify heat lossesMMa
lal
Boiler efficiency: determine deviationher
her
8
8/6/2019 Boilers 2 [Compatibility Mode]
9/40
Heat Balancents
nts
how energy is transformed from fuel into useful
energy, heat and lossesrPla
rPla
StochiometricExcess Air
Un burnt470470oweowe
FUEL INPUTFUEL INPUTSTEAM
OUTPUT
Stack Gas
MMalal
her
her
9Ash and Un-burnt
parts of Fuel in Ash
Blow
Down
Convection
& Radiation
8/6/2019 Boilers 2 [Compatibility Mode]
10/40
Balancing total energy entering a boiler againstnts
nts
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
weowe
Heat loss due to moisture in fuel
Heat loss due to moisture in air
0.3 %
FuelFuelMMa
lal
Heat loss due to unburnts in residue2.4 %
her
her
10
Heat in Steam
unaccounted loss
.
73.8
8/6/2019 Boilers 2 [Compatibility Mode]
11/40
Heat Balance
nts
nts
oa : mprove energy e c ency y re uc ng
avoidablelossesrPla
rPla
Avoidable losses include:
-470470o
weowe
,
temperature)
-
MMalal
- Blow down lossesher
her
11
- on ensa e osses
- Convection and radiation
8/6/2019 Boilers 2 [Compatibility Mode]
12/40
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
rPl
rPl
CALCULATION
EE4747
PowPow
MM
m
al
m
al
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.
8/6/2019 Boilers 2 [Compatibility Mode]
13/40
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
rPl
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
m
al
m
al
- The working pressure (in kg/cm2(g)) and superheat
temperature (oC), if anyThe
The
13
-
- Type of fuel and gross calorific value of the fuel (GCV) inkcal/kg of fuel
8/6/2019 Boilers 2 [Compatibility Mode]
14/40
Boiler Efficiency: Direct Method
nts
nts
Advantages Quick evaluationr
Pla
rPla
Few parameters for computation Few monitoring instruments
470
470
oweowe
benchmark figuresMMa
lal
No explanation of low efficiency
Various losses not calculatedher
her
14
8/6/2019 Boilers 2 [Compatibility Mode]
15/40
o er c ency: n rec e o
nts
nts
Efficiency of boiler () = 100 (i+ii+iii+iv+v+vi+vii)
rPla
rPla
Principle lossesPrinciple losses:i) Dry flue gas4
70
470
oweowe
ii) Evaporation of water formed due to H2 in fuel
iii) Evaporation of moisture in fuel
MMalal
iv) Moisture present in combustion air
v) Unburnt fuel in fly ashher
her
15
vi) Unburnt fuel in bottom ash
vii) Radiation and other unaccounted losses
8/6/2019 Boilers 2 [Compatibility Mode]
16/40
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
owe
Ambient temperature in C (Ta) and humidity
of air in kg/kg of dry air
MMalal
GCV of fuel in kcal/kg
% combustible in ash in case of solid fuelsher
her
16GCV of ash in kcal/kg (in case of solid fuels)
8/6/2019 Boilers 2 [Compatibility Mode]
17/40
Boiler Efficiency: Indirect Method
nts
nts
Advantages Com lete mass and ener balance for eachr
Pla
rPla
individual stream Makes it easier to identify options to improve47
0
470
owe
owe
Disadvanta es
MMalal
Time consuming Requires lab facilities for analysish
er
her
17
8/6/2019 Boilers 2 [Compatibility Mode]
18/40
. o er ow own
nts
nts
on ro s o a sso ve so s n e
water that is boiled
rPla
rPla
Conductivity measured as indication of TDS470
470
owe
owe
Calculation of quantity blow down required:MMalal
Blow down (%) =Feed water TDS x % Make up water
Maximum Permissible TDS in Boiler waterher
her
18
8/6/2019 Boilers 2 [Compatibility Mode]
19/40
Boiler Blow Down
nts
nts
IntermittentrPla
rPla
Manually operated valve reduces TDS Large short-term increases in feed water4
70
470
owe
owe
Continuous
MMalal
Ensures constant TDS and steam purity Heat lost can be recovered -h
er
her
19
8/6/2019 Boilers 2 [Compatibility Mode]
20/40
Boiler Blow Down
nts
nts
Lower retreatment costsrPla
rPla
Less make-up water consumption470
470
owe
owe
Reduced maintenance downtimeMMa
lal
Lower consum tion of treatmenther
her
20chemicals
8/6/2019 Boilers 2 [Compatibility Mode]
21/40
3. Boiler Feed Water Treatment
nts
nts
Quality of steam depend on water
treatment to controlrPla
rPla
Steam purity Deposits4
70
470
owe
owe
Corrosion
Efficient heat transfer onl if boiler
MMalal
water is free from deposit-forming
solidsher
her
21
8/6/2019 Boilers 2 [Compatibility Mode]
22/40
8/6/2019 Boilers 2 [Compatibility Mode]
23/40
nts
nts
Chemicals added to boiler to prevent scalerPla
rPla
Different chemicals for different water types
Conditions:470
470
owe
owe
Feed water is low in hardness saltsMMalal
,
Small water quantities treatedher
her
23
Internal treatment alone not recommended
8/6/2019 Boilers 2 [Compatibility Mode]
24/40
nts
nts
Removal of suspended/dissolved solids and
rPla
rPla
Pre-treatment: sedimentation and settling4
70
470
owe
owe
rs rea men s age: remova o sa s
ProcessesMMalal
a) Ion exchange
b) Demineralizationher
her
24
c) De-aeration
d) Reverse osmoses
8/6/2019 Boilers 2 [Compatibility Mode]
25/40
-
x
nts
nts
Water passes through bed of natural zeolite ofsynthetic resin to remove hardnessr
Pla
rPla
Base exchange: calcium (Ca) and magnesium(Mg) replaced with sodium (Na) ions
470
470
owe
owe
Does not reduce TDS, blow down quantity andalkalinityMMa
lal
em nera za on
Complete removal of saltsher
her
25
Cations in raw water replaced with hydrogenions
8/6/2019 Boilers 2 [Compatibility Mode]
26/40
External Water Treatment
nts
nts
-
Dissolved corrosive ases O2 CO2rPla
rPla
expelled by preheating the feed water4
70
470
owe
owe
Mechanical de-aeration:used prior to additionMMa
lal
o c em ca oxygen scavangers
Chemical de-aeration:removes trace oxygenher
her
26
8/6/2019 Boilers 2 [Compatibility Mode]
27/40
x erna a er rea menx erna a er rea men
Ventnts
nts
Boiler Feed WaterSpray Nozzles
rPla
rPla
Steam
Scrubber Section
(Trays)470
470
owe
owe
Stora e
MMalal
Section
her
her
27
De-aerated Boiler
Feed Water
8/6/2019 Boilers 2 [Compatibility Mode]
28/40
8/6/2019 Boilers 2 [Compatibility Mode]
29/40
x erna a er rea men
-nts
nts
Removal of trace oxygen with scavenger
rPla
rPla
o um su p e:
Reacts with oxygen: sodium sulphate470
470
owe
owe
Increases TDS: increased blow down
H drazine
MMalal
Reacts with oxygen: nitrogen + waterher
her
29
boilers
8/6/2019 Boilers 2 [Compatibility Mode]
30/40
External Water Treatment
nts
nts
v
OsmosisrPla
rPla
Solutions of differing concentrations47
0
470
owe
owe
-
Water moves to the higher concentrationMMalal
Reversed osmosis
her
her
30
Water moves in reversed direction
8/6/2019 Boilers 2 [Compatibility Mode]
31/40
External water treatment
nts
nts
vPressure
rPla
rPla
470
470
owe
owe
Fresh WaterFeed
WaterMMa
lal
Concentrated
Solution
Water FlowConcentrateFlowh
er
her
31
UNEPUNEP 20062006Semi Permeable
Membrane
8/6/2019 Boilers 2 [Compatibility Mode]
32/40
.
2. Feed water preheating using economizers
3. Combustion air pre-heatingnts
nts
4. Incomplete combustion minimization
5. Excess air controlrPla
rPla
.
7. Automatic blow down control47
0
470
owe
owe
9. Reduction of boiler steam pressure
10. Variable speed control
MMalal
11. Controlling boiler loading
12. Proper boiler schedulingher
her
32
.
8/6/2019 Boilers 2 [Compatibility Mode]
33/40
. ac empera ure on ro
nts
nts
If >200C then recover waste heat
rPla
rPla
2. Feed Water PreheatingEconomizers4
70
470
owe
owe
Potential to recover heat from 200 300 oC flue
ases leavin a modern 3- ass shell boiler
MMalal
3. Combustion Air Preheatingher
her
33
If combustion air raised by 20C = 1% improve
thermal efficiency
8/6/2019 Boilers 2 [Compatibility Mode]
34/40
4. Minimize Incomplete Combustion
nts
n
ts
Smoke, high CO levels in exit flue gas
rPla
rPla
auses:
Air shortage, fuel surplus, poor fuel distribution470
470
owe
owe
Poor mixing of fuel and air
Oil-fired boiler:
MMalal
Improper viscosity, worn tops, cabonization on
dips, deterioration of diffusers or spinner platesher
her
34 Coal-fired boiler: non-uniform coal size
8/6/2019 Boilers 2 [Compatibility Mode]
35/40
Energy Efficiency OpportunitiesEnergy Efficiency Opportunities
5. Excess Air Control
Optimum excess air levels varies
a
nts
a
nts
.
Portable or continuous oxygen analyzers00e
rPl
erPl
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
8/6/2019 Boilers 2 [Compatibility Mode]
36/40
6. Radiation and Convection Heatn
ts
n
ts
Fixed heat loss from boiler shell, regardless of
rPla
rPla
o er ou pu
Repairing insulation can reduce loss470
470
owe
owe
MMalal
. Sense and respond to boiler water conductivity
her
her
36
8/6/2019 Boilers 2 [Compatibility Mode]
37/40
. ca ng an oo oss e uc on
on
ts
n
ts
efficiency loss
=rPla
rPla
9. Reduced Boiler Steam Pressure
.
470
470
owe
owe
Lower steam pressureMMalal
= ower sa ura e s eam empera ure
= lower flue gas temperatureher
her
37
Steam generation pressure dictated by process
8/6/2019 Boilers 2 [Compatibility Mode]
38/40
10. Variable Speed Control for Fans,
n
ts
n
ts
Suited for fans, blowers, pumps
rPla
rPla
Should be considered if boiler loads are
variable47
0
47
0
owe
owe
11. Control Boiler LoadingMMalal
Maximum boiler efficiency: 65-85% of rated load
Significant efficiency loss: < 25% of rated loadher
her
38
8/6/2019 Boilers 2 [Compatibility Mode]
39/40
12. Proper Boiler Scheduling
O timum efficienc : 65-85% of full loadn
ts
n
ts
Few boilers at high loads is more efficient than
large number at low loadsrPla
rPla
13. Boiler Replacement470
47
0
owe
owe
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
her
39 Not designed for ideal loading conditions
8/6/2019 Boilers 2 [Compatibility Mode]
40/40
n
ts
n
ts
rPla
rPla
47
0
47
0
owe
owe
FOR YOUR ATTENTIONFOR YOUR ATTENTIONMMalal
her
her
40
UNEP GERIAPUNEP GERIAP