Feed water Heating

DMR Panda

UNIT : I 6th July 05

S.No DESCRIPTION UNITS DESIGN TEST DESIGN TEST READINGS:

1 UNIT LOAD MW 200 203 200 2032 FW PRESSURE KSC 190 177.3 190 177.33 FW INLET TEMPERATURE Deg. C 189.33 190.7 212.23 213.94 FW OUTLET TEMPERATURE Deg. C 212.23 213.9 240.08 247.75 SHELL PRESSURE KSC 19.94 20.00 33.88 38.106 EXT STEAM TEMPERATURE Deg. C 473.3 355.87 DRAIN OUTLET TEMP. Deg. C 194.33 195.9 217.23 215.88 DRIP LEVEL mm 218 2669 FW FLOW T/Hr 584 558 584 558

CALCULATIONS:10 SATN. TEMP.OF STEAM Deg. C 211.2 213.9 239.6 247.911 FW I/L ENTHALPY Kcal/kg 194.23 195.51 218.36 220.0312 FW O/L ENTHALPY Kcal/kg 218.36 220.03 248.53 256.9513 EXT ENTHALPY Kcal/kg 813.40 814.15 731.72 743.7114 DRIP O/L ENTHALPY Kcal/kg 197.61 199.28 222.47 220.9315 DRIP I/L ENTHALPY Kcal/kg 222.47 220.93 - -16 DRIP I/L FLOW T/hr 39.41 - -17 TTD (10-4) Deg. C -1.00 -0.02 -0.50 0.1518 DRAIN APPROACH (7-3) Deg. C 5.0 5.2 5.0 1.910 NET HEAT LOAD 10̂ 6 KCAL 14.09 13.68 17.62 20.6111 SUB COOLING (10-7) Deg. C 16.9 17.98 22.3 32.0512 EXtn STEAM FLOW T/hr 22.89 22.25 34.60 39.4113 FW `DT' (4-3) Deg. C 22.9 23.2 27.9 33.8

OBSERVATIONS AND RECOMMENDATIONS:1. HPH-5 & 6 performance is satisfactory.

ENERGY AND EFFICIENCY MANAGEMENT GROUPHP HEATERS PERFORMANCE TEST

HPH 5 HPH 6

Structure

• Physical arrangements

• Construction

• Thermodynamics and other theories

• Performance

Physical Arrangements

General James M. Gavin Plant's units 1 and 2 are 1300 MW capacity each. (1974). With a total generating capacity of 2,600 MW, Gavin Plant ranks as the largest generating station in the state of Ohio. It is located along the Ohio River at Cheshire, Ohio, and has an average daily coal consumption of 25,000 tons at full capacity

UNIT SIZE (MW) Number of Heaters

0 – 50 3 – 550-100 5 or 6100-200 5 - 7Over 200 6 - 8

Typical number of feed water Heaters

No of extraction

Steam extraction stages

Connection to

Extraction steam pr, kg/cm2

Extraction steam temp, 0C

Steam flow T/hr

Ist -HPT 9 HPH-7 30 337 88

2nd -CRH 12 / CRH HPH-6 / Deaerator

26.2 314 77

3rd -IPT 15 HPH-5 / Deaerator

11.96 433 16.2

4th - IPT 18 LPH-4 6.47 368 26

5th – IPT 21 LPH-3 2.78 252 23

6th - IPH 23 LPH-2 1.28 172 28

7th - LPT 25 LPH-1 0.28 40-50 12.6

200 MW LMZ Unit [NTPC- Vindhyachal]

HP Turbine: 12 stages, IP Turbine: 11 stagesLP Turbine: 2 * 3 stages

200 MW LMZ Unit [NTPC- Vindhyachal]

0.91 bar , 45 0C

21 bar Main

Ejector

47.5 0C GSC-I

690CLPH-I GSC--2

1020CLPH-2

1260CLPH-3 LPH-4

FRS HPH 7 HPH-6 HPH-51830C2470C

ECO

2760C

Boiler drum

No of extraction

Steam extraction stages

Connection to

Extraction steam pr, kg/cm2

Extraction steam temp, 0C

Steam flow T/hr

Ist -CRH CRH HPH-6 40 340

2nd -IPH 5 HPH-5 28 390

3rd -IPT 13 Deaerator / TDBFP

22 385

4th – LPT 1 LPH-3 4-5 270

5th - LPH 3 LPH-2 1.3 180

6th - LPT 4 LPH-1 0.2- 0.3 < 120

500 MW LMZ Unit [NTPC- TALCHER-K]

HP Turbine: 12 stages, IP Turbine: 2*16 stagesLP Turbine: 2 * 5 stages

500 MW KWU Unit [NTPC- Talcher-K]

0.91 bar , 45 0C

35 bar GSC

46 0CDC

670CLPH-I

870CLPH-2

1200CLPH-3 LPH-4

FRS HPH-6 HPH-5

210 bar, 2560C

ECO-2

, 206 bar, 3070C

Boiler drum

47 0C

220 bar, 1800C

ECO-1

2950C

Closed feed water heaters with backward cascading

Heater drain cycle with drain injected down stream of heater (forward cascading)

Steam power plant with one open and three closed feedwater heaters

•Which type of arrangements are (a) and (b)?

•What are the merits and limitations of each?

Open type

Feed-water

heaters

Open type Feedwater heaters

Open type Feedwater heaters

Drain System

Normal drain system Emergency drain system

LPH 4 LPH 3 LPH 2

Drip Pump

CEP

DRIP SYSTEM

HPH 5 HPH 6 HPH 7

ECO

HPH > 4 Mpa > LPH

Heater Drains

Construction of Feedwater Heaters

Single tube feedwater heater with floating reverse channel

Low-Pressure, Single-Zone Horizontal Feedwater Heater

Typical straight condensing U tube feedwater heater

Typical two zone [ Condensing, Drain cooler] feed water heater

Typical two zone [ Condensing, Drain cooler] feed water heater

Details of Drain Cooler design

Typical three zone feed water heater

Drain inletExtraction steam inlet

FW outlet

FW inletDrain outlet

H P Heater

Low pressure feedwater heater© Alstom

Typical arrangements of

HP Heater

Desuperheating zone

Condensing zone

Drain cooling zone

HP Feedwater Heater with Tubular Header[660 MW, CEGB]

Desuperheating zone

Condensing zone

Drain cooling zone

Feed water inlet

Feed water outlet

STEAM

Desuperheating zone

Condensing zone

Drain cooling zone

In Plan View of Spirals of Tubes

HP Heater in Vindhyachal 200

MW LMZ Unit

Overall Size Tube Sheet OD 1560 mm , Total Length = 3350 mm

Tube Size 16 Dia. mm x 1.0 mm Thk x 2850 mm Leg Length

Nos. of Tubes 1150 Nos.Weight 5.0 M.Ton (Approx.)

Tube Ad. Brass to BS -2871 Pt.-3 CZ-111

Tubes Sheets SA-516 Gr. 70

HP, LP Feed water Heater

working on the main piping connection welds, trim piping and level control instrumentation on the feed-water heaters.

Level Control Instrumentation

Trim Piping and Insulation

North-dakota – Fixing the Feed water heater

A large tubesheet after drilling and overlay being moved to assembly area

A large tubesheet after drilling and overlay being moved to assembly area

LP Fedwater-1 heater in the condenser Neck

Overall Size Tube Sheet OD 1560 mm , Total Length = 3350 mm

Tube Size 16 Dia. mm x 1.0 mm Thk x 2850 mm Leg Length

Nos. of Tubes 1150 Nos.Weight 5.0 M.Ton (Approx.)

Tube Ad. Brass to BS -2871 Pt.-3 CZ-111

Tubes Sheets SA-516 Gr. 70

For 210 MW, low pressure heater, at Satpura T.P.S. Sarni Project,. 

Other Merits of Feedwater Heating?

• A smaller condenser and boiler

• Less steam to pass in the last stages of the turbine, eliminating the difficulties caused by passing large amount of steam

• Better turbine drainage

• Shorter blades at the low pressure part of the turbine?

Thermodynamic Analysis

Effect of no. of feed-water heaters on thermal efficiency of the cycle

Example 4 - SuperheatAn internally reversible Rankine cycle is determined by specifyingAn internally reversible Rankine cycle is determined by specifyinga maximum temperature of 427a maximum temperature of 427o o C, a quality at the turbineC, a quality at the turbinedischarge of 0.9, and a minimum condensing temperature of 21.1discharge of 0.9, and a minimum condensing temperature of 21.1ooC.C.Compare the Compare the thermal efficiencythermal efficiency with that of a with that of a Carnot cycleCarnot cycleoperating between the same temperature limits.operating between the same temperature limits.

ss

bb

aa

ccdd

pd

paTT

Example 4 - Given and computed data

Process HBTU/lbm

WBTU/lbm

QBTU/lbm

a-b 1391 0 1391b-c -441.5 441.5 0c-d -950 0 -950d-a 0.5 -0.5 0Net 0 441

Example 4 - Thermal efficiency

Rankine Thermal efficiencyRankine Thermal efficiency

The Carnot efficiency

316.01391

441

579.081.699

26.29411

H

CC T

T

Key Performance Indicator

• TTD• DCA• TR• PRESSURE DROP

Terminal Temperature Difference

• TTD = TS - FW OUTLET TEMP

TS saturation temperature corresponding to shell pressure

Sensible heat transfer

Latent

heat transfer

Sensible heat transfer

Drain Cooling Zone

Condensing

Zone

Desuper heating Zone

TTD

DC A

Ts

Extn

FW

FW

Drain

Thermal profile in different zones of H P HEATER

High TTD Causes Effects

• Tube fouling/Plugging• Non condensable gases

(Air) blanketing• Flooding

– Tube leakage– Level control

• Low shell pressure• Excessive venting

• Bled steam flow• Heater concerned• Subsequent heater• Turbine steam flow

TTD and Feed Water temp

Feedwater outlet temperature [0C]

Terminal difference [0C]

30-110 2.8110 -148.9 5.6148.9 – 204.4 8.3204.4 – 273.9 11.1

Drain Cooling Approach

• DCA = Drain out let temp - FW inlet temp

Sensible heat transfer

Latent

heat transfer

Sensible heat transfer

Drain Cooling Zone

Condensing

Zone

Desuper heating Zone

TTD

DC A

Ts

Extn

FW

FW

Drain

Thermal profile in different zones of H P HEATER

High DCA Causes Effects

• Tube fouling/Plugging• Low water level

– LCV malfunction

• Drain cooler inlet not submerged

• Bled steam flow• Heater concerned• Subsequent heater• Turbine steam flow

NTHR : Net Turbine Heat Rate

Temperature Rise

• TR= FW outlet temp - FW inlet temp

Low TR Causes Effects

• TTD high • DCA high

• Bled steam flow• Heater concerned• Subsequent heater• Turbine steam flow

Sample Calculation for Feedwater Heater

Plot the points and calculate TTD DCA, TR, Extraction flow

Terminal Temperature (TTD)TTD = t sat – t fw out = 252.8- 251.1 =1.7 0C.

Drain Cooler Apporach Temperature (DCA)DCA = t drains - t fw in = 202.8- 194.3 = 8.5 0C..

Temperature Rise (TR)TR = t fw out – t fw in = 251.1-194.3 = 56.8 0C

Extraction Steam Flow = (Qe) = [Qf (hfw out – hfw in) + Qdrain in (hdrains out- hdrains in)] / (hext – hdrains out )Where:Qf = Feed Flow; Qdrain in = Drain Inlet flow; h fw out = Feed Water Enthalpy at HPH Out.; hfw in = Feed Water Enthalpy at HPH in hdrains out = Enthalpy of Drain Out; hdrains in = Enthalpy of Drain Inhext = Enthalpy of Extraction Steam

751.2* (259.7 – 196.8)+0Qe = ------------------------------------- = 90.2 t/hr (729.4 – 205.95)

Why Performance Testing?

• Prior to outage - Plan maintenance• Post outage - Evaluate effect of work

done• Normal operation

– Trending– HR deviation accounting– Optimize operation

• FW temp 1ºC results in 2.2 kcal/kwhr ( 200 MW) > 3336 Rs/day

1.34 kcal/kwhr (500 MW) > 4299 Rs/day

How Performance Deviates?

• Input parameters / process variables– FW inlet temp/ Extrn Steam inlet Pre & temp

• Deterioration of equipment or system itself– Tube failure, exfoliation, blocking of tubes

• Generic problems– Malfunction of one of its components like DCV

• Design problems– System resistance, size or capacity

HEATER PERFORMANCE DETERIORATION

• Air accumulation• Steam side fouling• Water side fouling• Drainage defects• Parting plane leakage

Air accumulation

• Increased TTD• Possible elevation of steam-to-heater

temperature• Reduced temperature rise of feed water or

condensate.• 0.5 % steam is venting inevitable for good

venting

Steam side fouling

• Progressive increase of TTD• Drain temperature unaffected• Reduced feed water temperature rise• Eventual tube failure due to mechanical

weakening• Accumulation of debris in the heater shell.

Water side fouling

• Gradual increase of TTD.• Oil

– LPT bearing oil through seals– Deposition occurs in HP heaters, worst hit at

highest pressure heater.

Drainage defects

• Damaged flsahbox internals• Reduced orifice opening• Enlarged orifice opening• Heater drain CV/ bypass valve malfunction.

Parting plane leakage

• Short circuiting of FW• TTD high• DCA high• TR less

Feedwater Heater Impact on Thermal Performance

UNIT : I 6th July 05

S.No DESCRIPTION UNITS DESIGN TEST DESIGN TEST READINGS:

1 UNIT LOAD MW 200 203 200 2032 FW PRESSURE KSC 190 177.3 190 177.33 FW INLET TEMPERATURE Deg. C 189.33 190.7 212.23 213.94 FW OUTLET TEMPERATURE Deg. C 212.23 213.9 240.08 247.75 SHELL PRESSURE KSC 19.94 20.00 33.88 38.106 EXT STEAM TEMPERATURE Deg. C 473.3 355.87 DRAIN OUTLET TEMP. Deg. C 194.33 195.9 217.23 215.88 DRIP LEVEL mm 218 2669 FW FLOW T/Hr 584 558 584 558

CALCULATIONS:10 SATN. TEMP.OF STEAM Deg. C 211.2 213.9 239.6 247.911 FW I/L ENTHALPY Kcal/kg 194.23 195.51 218.36 220.0312 FW O/L ENTHALPY Kcal/kg 218.36 220.03 248.53 256.9513 EXT ENTHALPY Kcal/kg 813.40 814.15 731.72 743.7114 DRIP O/L ENTHALPY Kcal/kg 197.61 199.28 222.47 220.9315 DRIP I/L ENTHALPY Kcal/kg 222.47 220.93 - -16 DRIP I/L FLOW T/hr 39.41 - -17 TTD (10-4) Deg. C -1.00 -0.02 -0.50 0.1518 DRAIN APPROACH (7-3) Deg. C 5.0 5.2 5.0 1.910 NET HEAT LOAD 10̂ 6 KCAL 14.09 13.68 17.62 20.6111 SUB COOLING (10-7) Deg. C 16.9 17.98 22.3 32.0512 EXtn STEAM FLOW T/hr 22.89 22.25 34.60 39.4113 FW `DT' (4-3) Deg. C 22.9 23.2 27.9 33.8

OBSERVATIONS AND RECOMMENDATIONS:1. HPH-5 & 6 performance is satisfactory.

ENERGY AND EFFICIENCY MANAGEMENT GROUPHP HEATERS PERFORMANCE TEST

HPH 5 HPH 6

EEMG HPH PERFORMANCE TEST REPORT RAMAGUNDAMUNIT IV DATE: 9-Jul-05S.No DESCRIPTION UNITS DESIGN HPH 5 HPH 5A HPH 5B DESIGN HPH 6 HPH 6A HPH 6B

1 UNIT LOAD MW 500 5002 FW PRESSURE KSC 218 203.4 203.4 218.0 202.8 202.83 FW INLET TEMPERATURE Deg. C 166.7 173.5 173.6 208.1 216.2 212.74 FW OUTLET TEMPERATURE Deg. C 208.1 216.2 212.7 253.7 257.1 256.95 DRIP O/L FLOW (INDICATION) T/Hr 122.35 148 135 45.27 134.9 126.06 EXT STEAM PRESSURE KSC 18.63 21.00 19.89 43.00 45.1 45.07 EXT STEAM TEMPERATURE Deg. C 429 411.5 411.5 342.6 350.6 350.68 DRAIN OUTLET TEMP. Deg. C 171.5 183.4 181.4 212.9 219.8 219.59 DRIP LEVEL mm -10 -6 -1 510 FW FLOW T/Hr 770 771.0 771.0 770.0 771.0 771.0

1 SATN. TEMP.OF STEAM Deg. C 207.8 216.3 213.6 253.4 257.7 257.62 FW I/L ENTHALPY Kcal/kg 171.2 178.0 178.1 214.2 222.7 219.03 FW O/L ENTHALPY Kcal/kg 214.2 222.7 219.0 263.8 267.6 267.44 EXT ENTHALPY Kcal/kg 791.3 781.5 781.9 733.5 736.8 736.95 DRIP O/L ENTHALPY Kcal/kg 173.5 186.0 183.9 217.8 225.4 225.06 DRIP I/L ENTHALPY Kcal/kg 217.8 225.4 225.0 - - -7 DRIP I/L FLOW T/hr 67.7 72.9 - - -8 TTD Deg. C -0.3 0.1 0.9 -0.3 0.6 0.79 DRAIN APPROACH Deg. C 4.8 9.9 7.8 4.8 3.6 6.810 NET HEAT LOAD 10̂ 6 KCAL 33.146 34.49 31.53 38.17 34.61 37.3111 SUB COOLING Deg. C 32.9 32.2 37.91 38.0712 EXtn STEAM FLOW T/hr 48.3 57.91 52.72 74.05 67.66 72.8913 FW `DT' Deg. C 41.4 42.7 39.1 45.6 40.9 44.2

PREVIOUS TEST RESULTS 9/5/051 TTD Deg. C -0.3 0.2 1.2 -0.3 0.3 0.42 DRAIN APPROACH Deg. C 4.8 7.6 8.3 4.8 6.3 7.83 NET HEAT LOAD 10̂ 6 KCAL 33.1 31.8 31.2 38.2 36.3 37.44 SUB COOLING Deg. C 33.1 32.7 38.2 38.15 EXtn STEAM FLOW T/hr 48.3 52.8 52.1 74.1 71.9 74.06 FW `DT' Deg. C 41.4 40.5 39.8 45.6 44.2 45.5

OBSERVATIONS AND RECOMMENDATIONS:1. HPH-5B FW DT is less and DCA is more.Its performance is to be observed.

CALCULATIONS:

513513

Heat transferred

• Q= U* A* LMTD• LMTD = (ITD-TTD) / Loge (ITD/TTD)

• Heat Balance Extrn steam flow*( h ext – h drainout) = Qfw *( h fwout- h fwin) - Qdrainin *(h drainout- h drainin)

Determine the condition at Pt 6 and on T-S diagramme, show all the points? The pump has isentropic efficiency of 80%.

Why NRVs are provided in Steam extraction lines ?

• When the turbine trips, the reheat stop and intercept valves close rapidly. The closing of the turbine valves causes a momentary vacuum that moves through the turbine stages. This vacuum tends to pull the extraction steam back into the turbine and decrease the extraction stage pressure. As a result, the heater shell pressure drops, causing a rapid decrease in the saturation temperature in the heater shell. With a supply of hot water in the heater shell, the water flashes to steam and attempts to flow back to the turbine extraction. This influx of energy back into the turbine causes a rapid overspeed condition.

• As a result, a non-return valve is installed in each extraction line that automatically closes the line to prevent steam from re-entering the turbine. In some cases, two non-return valves are installed in series. The non-return valve is a check-type valve because a gate valve could not close fast enough.

• When heaters are installed in the upper part of the condenser, there is no room for a non-return valve. As a result, the quantity of water held in the shell is limited, and an anti-flash baffle may be installed above the water level to restrict the flow of any flashing steam.

Drain System- Alarm & Interlocks

• High heater water level - alarm

• High-high heater water level – •actuation of check valves, • closing of extraction line isolation valve,•actuation of bypass

• Automatic switch to emergency drain system when the heater that the condensate is flowing into, is shut off or is at too low a pressure at low load operation

• Automatic limitation of load when strings or feedwater heaters are shut off and the feedwater heater is not designed for the corresponding operation

Automatic Extraction

100 00C 75 00C 50 00C

TTD

Heat Capacity in %

15

5

100 %%200 %% 300 %%