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 ]

8

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

10

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

11

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]

13

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