Benefits of an air preheater replacement unit in a … · Benefits of an air preheater replacement...

Benefits of an air preheater replacement

Benefits of an air preheater

replacement unit in a large CDU

furnace


Content 1) Existing situation

2) Design criteria

3) Replacement

4) Results



2) Design criteria

3) Replacement

4) Results


Stack

234.000 kg/h

225°C

Actual process flow

Furnace

250.000 kg/h

445°C

275°C

B-Damper

APH-A APH-B

Duty 13,9 MW

3 heaters


Furnace of 170 MW, 2 DEKA APH’s with both 14 MW duty



2) Design criteria

3) Replacement

4) Results


Check of design data according to operation

FGI: 445°C

FGO: 300 °C

DT-Air: 190°C

O2 out of furnace:

3%, wet


Check of design data according to operation

170 MW


New flue gas exit temperature target for the new APH

Lowering the stack temperature by 140 °C would save about 7% fuel.

0

5

10

15

20

25

0 100 200 300 400 500

10

0%

- F

urn

ace

eff

icie

ncy

in %

Stack temp. in °C

Furnace efficiency


3 other heaters:

17 kg/s @ 300 °C

1% H2S max.

Check stack conditions, worst case

110m

Draft: 6 mbar

CDU4 heater

50 kg/s, 300 °C

100 ppm H2S

Acid DP: 135 °C

67 kg/s, 283°C

CDU4 heater

50 kg/s, 154 °C

100 ppm H2S

67 kg/s, 173 °C

BEFORE

3 other heaters:

17 kg/s @ 300 °C

1% H2S max.

110m

Draft: 5 mbar Acid DP: 135 °C

AFTER

300°C 189°C


Check ID-fan conditions

With lower flue gas flow rate passing through ID-Fan, higher pressure increase can be

used without reducing safety margin.


Stack

Combustion

Air

364 °C

234.000 kg/h

16 °C 16 °C

154 °C

Design parameters of new APH

Furnace

250.000 kg/h

445°C

5 mbar

7 mbar


Stack

252.000 kg/h

19°C -10 °C

144 °C

Hot Air Recirculation for air preconditioning

Furnace

250.000 kg/h

445°C

353°C

8 % HAR


Stack

234.000 kg/h

16°C

183 °C

Cold Air Bypass for performance adjustment

Furnace

250.000 kg/h

475 °C

389°C

10% CAB

352°C


Advantage of HAR vs. CAB

For equal metal skin temperature, HAR offer 34°C hotter air, equivalent to 2,2

MW duty (difference between +25 and -10°C).


Advantage of HAR vs. CAB

Air inlet temperature is not depending of outside conditions, less fouling and less

condensation in the air preheater.

0

5

10

15

20

25

30

35

05/11/2011 00:0007/11/2011 00:0009/11/2011 00:0011/11/2011 00:0013/11/2011 00:0015/11/2011 00:0017/11/2011 00:0019/11/2011 00:0021/11/2011 00:00

Air

te

mp

era

ture

, °

C

Date

HAR AMB


Air Preheater selection

Counter flow plates

Fully welded

High efficient

Compact and light


Material selection

Cold end temperature approx. 83°C

Because of acid dew point being higher than

the cold end metal temperature of the heat

exchanger, a plate made from SS304 has

been chosen:

Cr-content: 17,0-18,5 %

Ni-content: 8,5-10,5 %


Material selection – dew point consideration

Depending on H2S in the fuel (from few ppm to 100 ppm) the dew point can vary

from 73 to 107 °C (VDI 4760)

0

20

40

60

80

100

120

140

160

180

200

1 10 100 1,000 10,000

Aci

d D

ew p

oin

t °

C

SO2 content, ppm ADP-10 Vol % H2O ADP-20 Vol % H2O



2) Design criteria

3) Replacement

4) Results


Pre-assembly in largest possible components, with insulation


Transport by ship


Dismantling of old units within 3 days


Removal of the old DEKA-type APH: weight approx. 65 to.


Dismantling of old installation

The old APH unit has been completely removed


Placing the new air plenum on the prepared structure requires a high degree of

accuracy.


Installing the new APH: weight of only 42 tons with higher performance than the

original.


Ready for start-upon the 1st of November 2011


New APH Layout



2) Design criteria

3) Replacement

4) Results


Flue gas outlet temperature

Flue gas outlet temperature decreased from 310°C to 166°C

0

50

100

150

200

250

300

350

24/10/2011 00:00 13/11/2011 00:00 03/12/2011 00:00 23/12/2011 00:00 12/01/2012 00:00 01/02/2012 00:00 21/02/2012 00:00

Flu

e g

as o

utl

et t

em

pe

ratu

re (

°C)

Date

2011 2008


Hot air outlet temperature

Hot air outlet temperature average of 356 °C after start-up.

0

50

100

150

200

250

300

350

400

450

24/10/2011 00:00 13/11/2011 00:00 03/12/2011 00:00 23/12/2011 00:00 12/01/2012 00:00 01/02/2012 00:00 21/02/2012 00:00

Air

ou

tlet

te

mp

era

ture

of

AP

H, °

C

Date

2011

Average Temp before replacement


Heater efficiency

Heater efficiency increase from 81,2% to 90,1%

0

10

20

30

40

50

60

70

80

90

100

03/11/2011 00:0008/11/2011 00:0013/11/2011 00:0018/11/2011 00:0023/11/2011 00:0028/11/2011 00:0003/12/2011 00:0008/12/2011 00:0013/12/2011 00:00

He

at e

ffic

ien

cy o

in %

Date

2011 2008


Duty / Throughput ratio

Duty / throughput ratio reduction from 0,126 MW/m3/hr by 22% to 0,098 MW/m3hr.

(average throughput of 1110 m3/h)

0

0.05

0.1

0.15

0.2

0.25

24/10/2011 00:00 13/11/2011 00:00 03/12/2011 00:00 23/12/2011 00:00 12/01/2012 00:00 01/02/2012 00:00 21/02/2012 00:00

Du

ty /

Th

rou

ghp

ut

, M

W /

m3

/hr

Date

2011 2008


NOx increase

NOx increase prediction to 215-290 mg/Nm3 in line with API 535, fig. 9.

Then back to range of 150-200 mg/N3 after burner adjustment.

0

50

100

150

200

250

300

350

400

24/10/2011 00:00 13/11/2011 00:00 03/12/2011 00:00 23/12/2011 00:00 12/01/2012 00:00 01/02/2012 00:00 21/02/2012 00:00

NO

X, c

orr

ect

ed

, mg/

Nm

3

Date

2011

Nox range in 2008

Limit


Summary Reduction of the flue gas outlet temperature by 144°C.

Increased of Air temperature to burners by 151°C.

Increase of heater efficiency by 8,9% point.

Reduction of duty/Throughput ratio by 22% (0,028 MW/m3/hr)

Saving of approx. 10,1 MW at current average heater duty of

114 MW.

CO2 saving of 18.271 to/year

Fuel saving of 855 Nm3/h.

Payback less than 2 years based on fuel saving based on current average firing duty.


Questions?


Thank you for your Attention

BD-Heat Recovery Inc.

Dr. Olivier Brasseur

Email: [email protected]

Date post:	07-Sep-2018
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