design challenges in low flue gas...

DESIGN CHALLENGES IN LOW FLUE GAS TEMPERATURE

HEAT EXCHANGER

INTRODUCTION

Edward Green (1799-1865)

•Inventor of fuel economisers

•Founded in Wakefield, UK, 1833

•Patented fuel economiser in 1845

•More than 180 years heritage

DRAX POWER STATION, UK 6 X 660 MW (1970-74) BABCOCK BOILER

NANAO POWER STATION 1 X 700 MW SUPPLIED 1997 IHI BOILER, JAPAN

LONGANNET POWER STATION, SCOTLAND, 3 X 600 MW – 1973

BABCOCK BOILER

DATANG INTERNATIONAL POWER GENERATION COMPANY 4 X 600 MW

HARBIN BOILER

YAO MENG POWER PLANT 4 X 300 MW

SHANGHAI BOILER

WEIHE POWER STATION 2 X 300 MW

DONGFONG BOILER

DATTLEN POWER STATION GERMANY, 1 X 1100 MW HITACHI BOILER

1515

15

30 30

15 155 510

2020

30 30

10

20 20

35

20

30

30

20

35

35 35

35

3 0

20

20

30

35

G AS F LO W Research & Development Fins placed in areas of highest heat transfer. Fin weld on sides of tube where maximum heat transfer takes place. Fin material not placed where dust can accumulate above and below the tube. Fin sizes optimised for efficient use of material.

GREENS STEEL H DESIGN

Weld

Current

Forge

Pressure

• Fins are held in the correct position by Jaws. • Current and forge pressure is applied to weld fins to tube. • Tube is precisely indexed forward for next fin weld.

GREENS STEEL H PRODUCTION

STEEL H PRODUCTION

Weld

Current

Forge

Pressure

PURPOSE BUILT MACHINES

OBJECTIVES OF GHE

• To reduce the exhaust gas temperature from 160 ~ 170 Deg C to

about 110 ~ 120 Deg C.

• While a Desulphurisation / Denitrification equipment are considered,

the GHE shall assist to reduce the inlet gas temperature thereby

reducing the water consumption.

• Similarly to reduce the inlet gas temperature for the next generation

ESP’s.

OPTIONS AVILABLE

• Option – 1: GHE installed after the ID Fan

OPTIONS AVILABLE

• Option – 2: GHE installed before ESP

OPTIONS AVILABLE

• Option – 3: GHE used to control the flue gas temperature entering

stack.

APPLICATION

The GHE used for recovering waste heat and the useful

recovered heat can be used for following

1. To produce chilled water in vapour absorption machine to be

used in air conditioning

2. To produce flash steam for Desalination

3. Increase feed water temperature at economiser inlet

4. In parallel to LP heater

1. PRODUCE CHILLED WATER IN VAM

Project: NTPC Ramagundam (1 x 500 MW)

Project Details: Waste heat recovery system is designed to

recover 500 kW of thermal heat from flue gases to produce 100

tons of refrigeration.

150°C 110°C

FAN

STACK ID FAN

HEAT

EXCHANGER ESP, CCR

Flue Gas

Hot Water

Chilled Water

95°C

85°C 7°C

Hot Water Chilled

Water

Flue Gas

FLOW DIAGRAM

PERFORMANCE DATA UNIT PROPOSED GHE

FLUE GAS TEMPERATURE

HEAT EXCHANGER INLET °C 152 HEAT EXCHANGER OUTLET °C 110

FLUE GAS FLOW RATE KG/H 40,250 NM3/HR 30,746

APPROXIMATE RADIATION LOSS % 2.0 FLUE GAS COMPOSITION V / V CARBON DIOXIDE % 12.2 WATER VAPOUR % 8 TO 11 (9.5) NITROGEN % 71.2 OXYGEN % 7.0 SOX MG/NM3 1520 NOX MG/NM3 472 SPM MG/NM3 151 FLUE GAS VELOCITY HEAT EXCHANGER, AVG M/S 8.52

GAS DRAFT LOSS (OVER HEATING SURFACE ONLY)

MM WG 35

WATER FLOW RATE TONS/HR 42.5 HOT WATER PRESSURE LOSS (FRICTION ONLY)

KG/CM2 1.0

WATER TEMPERATURE HEAT EXCHANGER INLET °C 85

HEAT EXCHANGER OUTLET °C 95

SALIENT FEATURES

• Air Conditioning using Waste heat of flue gas instead of using

Electricity or Auxiliary steam.

• Reduction in Auxiliary power of 0.4 MU/yr for Ramagundam STPS.

• Green House Gas (CFC & HCFC) free thermally driven 100 TR VAM

based AC system.

• Reduction in CO2 emission is 320 T/yr for Ramagundam Super

Thermal Power Station

• Potential of scale up to meet entire Air-Conditioning requirement

using waste heat from flue gas at power plants

STEEL H VS PLAIN TUBE

Sr.

No.

Parameters NTPC Ramagundam

STEEL H PLAIN

1 Tubes wide 13 15

2 Tubes High 28 58

3 Space required LxWxH 3 X 1.5 X 3.7 3 X 1.4 X 7.4

4 Total Tube Used (m) 800 1914

5 Heat Transfer Area m2 467 229

6 Weight (Tons) 11.3 15.1

7 Air Blasters, Nos. 4 8

8 Draft loss mmwc 65 90


Sr.

No.

Parameters NTPC Talchar

STEEL H PLAIN

1 Tubes wide 25 30

2 Tubes High 24 60

3 Space required LxWxH 4.75 X 2.75 X 3.5

5 X 2.6 X 8.3

4 Total Tube Used (m) 2250 7200


6 Weight (Tons) 29.4 43



2. PRODUCE FLASH STEAM FOR DESALINATION

Project: NTPC Simhadri.

Project Details: Waste heat recovery system is designed to

recover 795 kW of thermal heat from flue gases to produce 5 TPH

of net distillate at less than 5 ppm from 45000 ppm cooling tower

blow down water (using 1 TPH, 0.34 bar (a) saturated steam) using

Multi-effect Distillation System.

Main Flue

Gas Duct

Flue Gas

Heat

Exchanger

Flash

Chamber

Multi-

effect

Distillatio

n System

Main

Flue gas duct of power

plant

Flue gas from power plant @

125 0C

Flue gas to chimney @ 125 0C

Flue gas

heat

exchanger Flash

chamb

er

Multi effect

desalination

Cooling tower

blow down water

45000 ppm –

60000 ppm

Distillate

at < 5

ppm

Brine

reject

EDI Boiler make

up water

at < 0.05

ppm

< 0.5 % of total flue gas

@ 125 0C

ID fan

Flue gas back to

main duct at 100 0C

PERFORMANCE DATA UNIT PROPOSED GHE

FLUE GAS TEMPERATURE

HEAT EXCHANGER INLET °C 125 HEAT EXCHANGER OUTLET °C 100

FLUE GAS FLOW RATE KG/H 113,000 NM3/HR 86,259

APPROXIMATE RADIATION LOSS % 2.0 FLUE GAS COMPOSITION V / V CARBON DIOXIDE % 12 – 13 WATER VAPOUR % 9.5 NITROGEN % 71.2 OXYGEN % 7.0 SOX MG/NM3 1300 - 1600 NOX MG/NM3 400 – 500 SPM MG/NM3 150 FLUE GAS VELOCITY HEAT EXCHANGER, AVG M/S 9.7

GAS DRAFT LOSS (OVER HEATING SURFACE ONLY)

MM WG 40

WATER FLOW RATE TONS/HR 39 HOT WATER PRESSURE LOSS (FRICTION ONLY)

KG/CM2 1

WATER TEMPERATURE HEAT EXCHANGER INLET °C 72

HEAT EXCHANGER OUTLET °C 90

SALIENT FEATURES

• Retrieval of unused thermal energy from flue gas

• No membrane replacement in the RO desalination plant

• High product water 11 quality of < 2 ppm from Multi-effect

Distillation

• Possible to use power plant cooling tower blow down as source

water for desalination

• No chemical handling

• Possibility of 100 % availability

• Reduction in DM plant operating cost

• Electrical energy consumption of 1.5 kWh /m3 for desalination plant


Sr.

No.

Parameters

NTPC SIMHADRI

STEEL H PLAIN

1 Tubes wide 22 24

2 Tubes High 18 54

3 Space required LxWxH 3.5 X 2.5 X 2.7 3.5 X 2.1 X 6.9

4 Total Tube Used 1089 3564


6 Weight (Tons) Ton 15.5 24.3



3. FEED WATER HEATING

Project: Reduction in backend temperature by recovering heat

before ESP at Hindalco Renukoot. (70 MW COEGN PLANT).

Project Details: It is economiser retrofit project for improving heat

recovery in existing plant. Heat duty of economiser increased from

2MW to 4.7MW. Feed water temperature in economiser increased

from 117°C to 135°C. Flue gas temperature at economiser outlet

decreased from 174°C to 140°C.

4. IN PARALLEL TO LP HEATER

The GHE is used to heat the condensate return and act in parallel to

LP Heaters, thereby reducing the steam consumption. The steam

thus saved is used to generate additional incremental power.

FREQUENTLY ASKED QUESTIONS

1. What is the lowest temperature possible at the outlet

with carbon steel?

The outlet gas temperature is determined by sulphur

content in coal, acid dew point etc.

Generally the target outlet temperature is 110 - 120

DegC. The operation temperature of heating tubes shall

be taken care with respect to acid dew point. In some

cases heating tubes shall use Corten Steel either fully or

partly.

2. Is the system installed in main duct or slip

stream?

What is the largest size in service for this

application?

Usually the system installed in main duct. Depending

upon the layout it can be installed on a bypass also. At

present the largest, LT Econmiser is in operation on a

600 MW unit, in China in main duct.

3. What is the effect on ID fan loading due to

GHE’s placed in the flue gas path?

• If LT Economiser is installed before ID fan, the flue gas

impact on ID fan is:

Flue gas temperature--------lower

Flue gas volume----------less

Draft loss of flue gas----------larger

The new operation point shall be checked on ID fan

performance curve.

• If LT Economiser is installed after ID fan, flue gas

volume will not change and draft loss will become larger.

Use of ID fan’s existing head margin to kill the additional

draft loss caused by LT Economiser is recommended.

4. For the improvements done in GHE to increase the heat

duty, how much is increase in ID fan loading / system

resistance in the flue gas path?

The increase of ID fan loading will vary on case to case

basis. It is determined by GHE parameters and ID fan

parameters. The below table provides a reference

Item Description Unit 600 MW 450 MW 300 MW

GHE Thermal Duty KW 22205 17622 9824

Increase in power for ID KW 393 156 65

Decrease in power for FGD KW 80 52 24

5. What is Heat Transfer Area / Pressure Drop (in

GHE / associated duct), space requirement,

overall size of installations?

Heat transfer area is determined by project requirement.

If the project wants to generate large quantity water and

recover more flue gas waste heat, a large heating area is

needed. Space and draft loss impact each other. If there

is a large space left to install GHE, the gas velocity

through economiser can be low, and the draft loss can

be low. On the other hand, if the space is very little, the

unit is designed very compact, and draft loss will be high.

If the space is a constraint, the allowable draft loss will

be very low and use of elliptical tube is recommended.

Case

Stu

dy 1

GREENS STEEL H CASE STUDY

CASE SUMMARY

IHI in Japan had an existing coal fired boiler that was under performing. IHI failed to meet customer guarantees. It was decided that if it was possible to

improve the economiser performance the overall boiler efficiency would be increased

The problem was there was no additional space to add extra heating surface in the chamber so Greens

supplied a Steel H Retrofit Economiser


Section of Plain Tube Economiser

Section of Steel H Economiser

Case

Stu

dy 1


DETAILS PLAIN TUBE STEEL H

Chamber Size 22413 wide x 5555 long x 1600 high

No. of Tubes 3232 2288

Rows 202 rows (22110mm) 202 rows (22205mm)

High 16 rows (1483mm) 11.3 rows (1100mm)

Gas Temp In oC 488.33

Gas Temp Out oC

423.23 402

Water Temp In oC

278

Water Temp Out oC

308.34 321.1

Duty KW 26672 38674

Case

Stu

dy 1


CONCLUSION

The Steel H Unit provided a 45% increase in duty and at the

same time an effective heating surface for use in boilers with high

dust laden fuels.

RESULT

IHI placed the order for a Steel H unit with Greens

Case

Stu

dy 1

PEAT FUEL BFB BOILER WITH GREENS STEEL H ECONOMISER

GREENS STEEL H CASE STUDY Case

Stu

dy 2

Economiser

Case

Stu

dy 2


CASE SUMMARY

ESB Ireland wanted to know how a plain steel economiser

would compare commercially and technically to a Steel H

Economiser.

The following is an extract from the presentation made by

Greens.

REQUIRED PERFORMANCE DETAILS

• 274MW Peat Fired BFB Boiler.

• Maximum gas velocity 15 m/s.

• Economiser thermal duty 30.5MW

• Chamber Size 6100mm wide x 10700mm long.

• 643 tonnes/hr gas in at 422°C out 283 °C.

• 336 tonnes/hr water in at 258°C and 174.5 bar.

Case

Stu

dy 2


P l a i n T u b e S t e e l ‘ H ’

Tube OD, mm Tube Effective Length, mm Tube pitch, h x v, mm Rows wide Rows High Total economiser height, m

42.4

9,000

90 x 90

56

124

16.600

38.1

9,400

79 x 79

70

36

4.685

ARRANGEMENT

STEEL ‘H’

v PLAIN TUBE


Stu

dy 2


Fin Pitch, mm Total tube used, m Total Heating Surface, m2

Number of Banks Weight Tonnes

N/A

66,525

8,324

6

446

23.5

25,508

12,042

2

240

ARRANGEMENT

STEEL ‘H’

v PLAIN TUBE


Stu

dy 2


Economiser Cost (Assembled Banks) Tube cleaning System Cost

Rs 6,97,00,000

(241%)

Rs 28,50,000

18 off

Rs 2,89,00,000

(100%)

Rs 13,50,000

11 off

CAPITAL COSTS ESTIMATE

STEEL ‘H’

v PLAIN TUBE


Stu

dy 2


Flue Gas Velocity, max m/s Pressure loss, gas side mm WG Feed water velocity avg, m/s Pressure loss, water side, bar

15.1

160

1.35

2.6

15.0

65

1.35

0.9

OPERATION

STEEL ‘H’

v PLAIN TUBE


Stu

dy 2


Theoretical power required, kW (friction loss + static head) Associated fan absorbed power, assuming 80% efficiency, kW Cost of Operation

482.3

602.9

Rs 23,33,00,000

199.7

249.6

Rs 9,66,00,000

FANS OPERATIONAL COSTS

STEEL ‘H’

v

PLAIN TUBE

Cost of operation assuming 15 years

at 8600 hours and Rs 3.0 kWh


Stu

dy 2


Theoretical power required, kW (friction loss + static head) Associated feed pump absorbed power, assuming 70% efficiency, kW Cost of Operation

47.5

67.8

Rs 2,62,00,000

15.5

22.1

Rs 85,52,000

PUMPS OPERATIONAL COSTS

STEEL ‘H’

v

PLAIN TUBE




Stu

dy 2


FANS PUMPS TUBE CLEANING (STEAM) TOTAL OPERATIONAL COSTS

23,33,00,000

2,62,00,000 ?

25,95,00,000

TOTAL OPERATIONAL COSTS

STEEL ‘H’

v

PLAIN TUBE



TOTAL OPERATIONAL SAVING WITH STEEL H 15,43,48,000

ANNUAL OPERATIONAL SAVING WITH STEEL H 1,02,89,000

9,66,00,000

85,52,000 ?

10,51,52,000


Stu

dy 2

CASE STUDY 3

• 1,000MW Coal Fired Boiler.

• 286 Coils at 110mm Horizontal pitch to match wall tubes.

• Chamber 4950mm wide with coils supported from wall.

• Maximum gas velocity 15 m/s.

• 1,960 T/h gas at 533°C in / 370 °C out.

• 2,715 T/h water in at 296 °C and 300 bar.

CASE STUDY 3

Horizontal pitch (mm) 110 110 110

Vertical pitch (mm) 115.65 79 79

Tube o/d (mm) 50.8 34 31.8

Rows wide 286 286 286

Effective length (m) 4,810 4,050 4,050

Fin pitch (mm) Bare 12.7 25

Plain Tube Spiral Fin Steel ‘H’

CASE STUDY 3

Velocity (m/s) 14.9 14.4 14.7

Rows high 69 37 37

Total tube used (m) 94,275 42,247 42,399

Heating Surface (m²) 15,046 18,323 24,580

Total Height (m) 10.4 3.7 3.7

Number of banks 4 2 2

Weight (tonnes) 1,100 400 500

Press Loss (mm WG) 72 64 43

Economiser Cost (%) 100 65 63

Supportable at ends Yes No Yes

Plain Tube Spiral Fin Steel ‘H’

Wea

r R

ate

mg

kg

-1

30° 60

°

90

°

0°

In line tube arrangements

offer lowest impact angles

and minimum erosion.

From the centre line of the

tube the erosion rate increases

to a maximum at about 30º.

Then decreases rapidly as

angle approaches 0º.

Staggered In-line

Tube protected while fins can collect heat. Minimum loss of heating surface. Stainless Steel notched and formed to suit the tube. Held in place by wrap around the tube.

Ero

sio

n P

rote

ctio

n

GREENS DESIGN EXPERTISE

Boiler electrical output 350MW

Fuel: Coal

Commissioned May1997

Inspection

carried out in

April 1998.

Photograph

taken looking

down

Through tube

in direction

of gas flow.

6 Boilers each 660MWe.

Owned by National Power Plc, UK

Fired by coal with 17.5% ash.

First Unit on line 1973.

ECONOMISER Underside of

Economiser during

Installation.

Unit #3 Boiler commissioned in 1974

Inspected 31st May 1994.

No cleaning before inspection.

All gas passages clear of fouling.

No ash accumulations.

Recorded on the 25th July

1999.

Unit #1 158,206 hours.






500MW Boiler after firing With Orimulsion.

• Coal • Lignite • Heavy Oil • Orimulsion • Garbage or Refuse (EFW) • Bio Fuels (Rice husks/ Bagasse/Wood Straw) • Waste Heat Recovery (Cement, Coke) • Pulverised Fuels • Bubbling Fluidised Bed • Circulating Fluidised Bed • Incineration

Fu

el &

Co

mb

ustio

n

GREENS APPLICATIONS FOR STEEL H

GREENS ECONOMISERS

Recovery of Waste Heat from boiler & process flue gas streams in the Power Generation, Refining, Chemical, Process and general industries.

Individually designed to client's requirements

Industrial Economisers Greens Industrial Economisers are designed to operate with both shell package type and water tube boilers. The economic range starts at 5 Tonne/Hour.

Wide Variety of Fuels/Combustion

Power Station Economisers Greens Economisers operate with large utility super critical power boilers, ranging from 100 MW 1100 MW.

Thank You

Contact us: [email protected]

design challenges in low flue gas...

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