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energy efficiency boiler and turbine thermal power plant
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1SP. ENTROPY,S
SP. E
NT
HA
LP
Y,
H
2
Need of efficiency & performance monitoring :
• High cost of installation of new power plantRs. 3.5 to 4 Crore /MW installation
+Rs. 1.5 to 2 Crore /MW for T&D
• Increased plant performance leads to increased plant availability and vice versa
• Maximising generation with minimum generation cost
For increasing station performance main areas :
• Planned Maintenance Loss• Thermal Efficiency Factors• Plant Load factor• Forced outages• Plant Availability Factor• Optimising terminal conditions of the unit
MS parameters
Rejection Parameters
3
Areas of concentration for increasing Efficiency :
• Heat rate of Turbine• Boiler Efficiency• DM water Make-up• Specific Oil Consumption• Excess air • Condenser Back Pressure
4
Basic Concepts of Efficiency :
• Overall Station Efficiency = Output Input
Energy Sent Out (KW) Fuel Burnt (Kg) * Calorific Value of Fuel=
• Rankine Cycle
ENTROPY,S
TE
MP
ER
AT
UR
E,
T
Boiler Efficiency ((Steam Supplied in Kgs * Total heat in superheated steam) - Total heat of feed water))
Fuel Burnt (Kg) * Calorific Value of Fuel (Kcal/Kg)
=
4
3
2
1
=B
Ms*h3-Mf*h1
Mc * C.V.* 100
5
Heat Balance Diagram Showing Losses :
0
100P
ER
CE
NT
AG
E HE
AT
IN
PU
T
BOILER LOSSES10 - 13 %
CONDENSER LOSSES45 - 49 %
GENERATOR LOSS2 - 4 %
USEFUL HEAT OUTPUT34 - 39 %
6
Weight of Air required for Combustion :
(i) Carbon C + O2 = CO2
12 + 32 = 44
1 + 8/3 = 11/3 O2 = 8/3 C --------- (a)
Oxygen required = 8/3 times wt. Of Carbon
(ii) Hydrogen 2H2 + O2 = 2H2O
4 + 32 = 36
1 + 8 = 9 O2 = 8H -----------(b)
Oxygen required = 8 times the wt. Of Hydrogen
7
Weight of Air required for Combustion : contd...
(iii) Sulphur S + O2 = SO2
32 + 32 = 64
1 + 1 = 2 O2 = 1 S --------- (c)
Oxygen required = Same as wt. of Sulphur(iv) Combining formula (a), (b) & (c)
Oxygen required / gm of fuel = 8/3 C + 8H + S ------- (d)(v) Assuming all the Oxygen in the fuel will combine with
Hydrogen in the fuel the actual amount of Hydrogen requiring air is (H - O/8)
(vi) Oxygen in gm/gm of fuel = 8/3C + 8(H - O/8) + S
Air in gm / gm of fuel = 4.31[ 8/3C + 8(H-O/8) + S ]
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Excess Air requirement :
Optimum Excess air = 20 % of Stoichiometric (perfect) air for combustion
PERCENTAGE EXCESS AIR
PE
RC
EN
TA
GE
HE
AT
L
OSS
20
10
40 60 80 100
20
30
40
MINIMUM LOSS
EXCESS AIR FOR MINIMUM LOSS0
0
9
Boiler Efficiency :
Direct method
Boiler Efficiency =
( Enthalpy of Steam - Enthalpy of Feed water)* Steam flow
Fuel Burnt (Kg) * Calorific Value of Fuel
Indirect or losses method
Boiler Efficiency = 100 % - Total Loss in Percentage
Boiler Losses
• Dry Flue Gas Loss• Wet Flue Gas Loss
• Due to moisture in fuel• Due to Hydrogen in fuel
• Unburnt Carbon Loss
• Rejection Loss in Ash• Radiation Loss• Unaccounted Loss
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Boiler Efficiency :
L1 = DRY FLUE GAS LOSS = {100 * Qa * Cpg * (Tg – Ta)} (Wg * GCV)
Qa = TOTAL AIR FLOW IN Kg/Hr
Tg = FLUE GAS TEMP. AT ESP OUTLET K
Tr = REFERENCE AMBIENT TEMP. IN K
Wg = COAL FLOW RATE IN Kg/Hr
Cpg = SPECIFIC HEAT OF FLUE GAS = 0.246 Kcal
GCV = GROSS CALORIFIC VALUE OF FED COAL IN Kcal /Kg
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Boiler Efficiency :
L2 = LOSS DUE TO MOISTURE IN FUEL = {100* M* Wg* ( hg - ha)} Wg * GCV
hg = SP. ENTHALPY OF VAPOUR AT AIRHEATER OUTLET IN Kcal/Kg(FOR AIR)
ha = SP. ENTHALPY OF WATER AT AIRHEATER INLET IN Kcal/Kg (FOR AIR)
M = MOISTURE CONTENT IN FED COAL IN % OF WEIGHT
L3 = LOSS DUE TO HYDROGEN IN FUEL = {9 * 100* H* Wg* ( hg - ha)} Wg * GCV
H = HYDROGEN CONTENT IN FED COAL IN % OF WEIGHT
12
Boiler Efficiency :
L4 = LOSS DUE TO UNBURNT IN ASH = {100* Wg * U * A * K Wg * GCV
U = WEIGHTED AVERAGE OF UNBURNT CONTENT IN %
A = ASH CONTENT IN FED COAL IN %
K = C. V. OF CARBON BURNT TO CO2 IN Kcal/Kg = 8139
L5 = DUE TO HEAT REJECTED IN ASH = [ 100* Cpg * A * {0.1*(Tba – Ta) + 0.9*(Tg-Ta)}] GCV
Tba = BOTTOM ASHING TEMP. IN K
L6 = RADIATION LOSS = 0.8 (ASSUMED)
L7 = UNACCOUNTD LOSS = 0.647 ( DESIGN FIGURE )
= 100 – [ L1 +L2 +L3 +L4 +L5 +L6 +L7]
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Other parameters affecting Boiler Efficiency :
• CONTROL OF BLOW DOWN AND MAKE UP
• AUXILIARY POWER CONSUMPTION
• OPTIMIZATION OF OIL CONSUMPTION
• AIR HEATER PERFORMANCE AND TRAMP AIR TO BOILER
PERCENTAGE EXCESS AIR
PE
RC
EN
TA
GE
HE
AT
LO
SS
20
10
40 60 80 100
20
30
40
MINIMUM LOSS
HEAT LOSS DUE TO UNBURNT
0
0
HEAT LOSS DUE TO FLUE GAS
HEAT LOSS DUE TO UNBURNT GAS
TOTAL HEAT LOSS
14
HEAT RATE :
TURBINE HEAT RATE = Qs * (Hs - Hf) Eg
Qs = STEAM FLOW AT TURBINE INLET IN KG/HR
Hs = TOTAL HEAT OF STEAM AT TURBINE INLET IN KCAL/KG
Hf = TOTAL HEAT OF FEED WATER AT ECONOMISER INLET IN KCAL/KG
Eg = NET LOAD GENERATED IN KW
TURBINE EFFICIENCY = 860 * 100 HEAT RATE
PLANT HEAT RATE = 860 *100TURBINE EFF. *BOILER EFF.
15
CONDENSER PERFORMANCE :
Volume, m3/kg
Pre
ssu
re, b
ar a
bs.
1
4
2 3 4
8
12
16
00
20
p2
p3
p1
p4
EFFICIENCY = (H1-H2) / H1
= (T1-T2) / T1
DELTA T = CW O/L - CW I/L
TERMINAL TEMP. DIFF. (TTD) = EXH. HOOD - CW O/L
CONDENSER VACUUM = BAROMETRIC PR. - BACK PR.
16
CONDENSER PERFORMANCE :
LIMITATIONS IN REDUCING BACK PRESSURE :
• INCREASED CW PUMPING POWER
• HIGH LEAVING LOSSLEAVING LOSS SQR (VELOCITY) SQR (SP. VOL)
1 / SQR (BACK PRESSURE)
• REDUCED CONDENSATE TEMP.
• WETNESS OF STEAMEVERY 1 % INCREASE IN WETNESS= 1 % DECREASE IN EFFICIENCY OF ASSOCIATED STAGE
17
PUMP PERFORMANCE & MONITORING
Terms used in pumping system :
A : Potential head/geometric head/ static head = head due to height + head due to pressure = H + P/D*g where , H= height of water column P = pressure on the surface of water in the tank D = water density at a particular temp. g = acceleration due to gravity
B : Kinetic head / dynamic head = V2/2*g where , V= velocity of liquid in the pipe line This head is proportional to flow rate(Q).
18
C : Frictional head = 4* f*L*V2 / 2*g*D where , f= pipe surface roughness L= length of pipe V= flow velocity D= inner dia. of pipe g= gravitational constant
E : E : Net positive suction head (NPSH)Net positive suction head (NPSH)NPSH) NPSH) available available = (P - P= (P - Pvv)* 2.31/ sp. Gravity -losses +/- Z)* 2.31/ sp. Gravity -losses +/- Z
Where , P= absolute pressure at liquid surfaceWhere , P= absolute pressure at liquid surface PPvv = vapour pressure of liquid at pumping temp. = vapour pressure of liquid at pumping temp.
Losses = kinetic head + frictional head + Losses = kinetic head + frictional head + entrance lossentrance loss Z= static elevation from liquid level in suction Z= static elevation from liquid level in suction tank to the centre line of the first stage impeller of the pumptank to the centre line of the first stage impeller of the pump
D : Gross total head = potential head + kinetic head + losses
19
Cavitation starts
FLOW RATE Q
NPSH
NPSH) available
NPSH)required
As a general rule the NPSH ) available should be 30% higher than the required NPSH at the operating point.
20
NOTE : If NPSH) available approaches to zero than there will be severe cavitation in the pump.
IMPROVEMENT IN NPSH AVAILABLE OF BFP1:Raise the deaerator height for more static head.2: Incorporate slow speed booster pump to have lower NPSH) required.
3: Keep dp across the suction filter less than 0.5 kg/cm2.
IMPROVEMENT IN NPSH AVAILABLE OF CEP1: Use larger size suction piping with larger radius bend instead of elbows.2: Use long radius suction bell mouths in case of vertical pumps.
21