DCU FURNACE

TROUBLESHOOTING: “HIGH TUBE

METAL TEMPERATURE”

C K SINHASenior Manager Technical Services,

sinhack@indianoil.in

1

TO COKE DRUM

1

2

7

25

28

1

2

7

25

28

� 2 - Pass Bottom FiredNatural draft Furnace

� Design Fired duty- 8.16Gcal/hr

� Low Nox flat flameburner

� Total 36 no of tubes inradiation section

� Tube metal T t’coupleon tube no 1,2,7,25,28 &shock zone (SZ) tube

HC

BFW BFW

HC

S Z

2

FURNACE

OVERVIEW

3

� Rise in tube metal temperature(TMT) in short time

� No on-line spalling facility

� Frequent SAD

� Frequent DCU outage

� Reduction in Refinery Profit

PROBLEM

4

Problem Analysis

5

FIELD CHECKS

� CROSS CHECKING OF TMT BY THERMOGRAPHY

� FEED PROPERTY , FG PROPERTY

� CONTAMINATION OF FEED WITH RESIDUE

� FURNACE FEED PUMP SUCTION STRAINER

� START-UP CIRCULATION PUMP SUCTION STRAINER

� TRAMP AIR

� FIRED DUTY

520

540

560

580

600

620

640 1-N

1-M

1-S

2-N

2-M

2-S

7-N

7-M

7-S

25-N

25-M

25-S

28-M

SZ-1

SZ-2

TMT TREND OF PAST RUN-1

25TH TUBE

7TH TUBE & BELOW

SHOCK ZONE

6

TMT TREND OF PAST RUN-2

520

540

560

580

600

620

640 1-N

1-M

1-S

2-N

2-M

2-S

7-N

7-M

7-S

25-N

25-M

25-S

28-M

SZ-N

SZ-S

SHOCK ZONE

25TH TUBE

7TH TUBE & BELOW

7

520

540

560

580

600

620

640

660

1-N

1-M

1-S

2-N

2-M

2-S

7-N

7-M

7-S

25-N

25-M

25-S

28-M

SZ-N

SZ-S

TMT TREND OF PAST RUN-3

SHOCK ZONE25TH & 28TH

TUBE

7TH TUBE & BELOW*One additional t’couple installed on 25th in Middle position and on

28th in Middle position 8

9

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

Series1

Series2

-1.00

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

Series1

Series2

0.00

2.00

4.00

6.00

8.00

10.00

12.00

ConvDelP-1

ConvDelP-2

CONVECTION COIL PRESSURE DROP

� HC flow 29 m3/hr� BFW to convection coil flow rate 0.32 m3/hr� CIT- 325⁰C , COT- 492.5⁰C� Furnace draft- 7 mmWC� O2 analyzer reading- 8 vol%� Convection O/L T- 433⁰C� Stack T- 230⁰C� Flue gas T at arch- 740⁰C� Flue gas T at floor-620⁰C� Fuel Gas flow- 560 kg/hr

10

OPERATING CONDITIONS

110

1

2

3

4

5

6

7

8

9

10

300

350

400

450

500

550

600

650

700

CrOvT-1

COT-1

CrOvPr-1

O/L Pr-1

PROCESS TEMPERATURE DURING SAD WITH SAME DRAFT AND O2 IN FLUE GAS

12

� HIGH DRAFT, HIGH EXCESS AIR, HIGH TMT IN SHOCK ZONE &

RADIANT TOP ZONE

� HIGH HEAT TRANSFER IN CONVECTION TUBES

� HIGH RADIATION INLET TEMP

� CONVECTION COIL FOULING

� HIGH AMOUNT OF HEAT AVAILABLE IN RADIATION TOP ZONE

� COKE FORMATION IN RADIATION TOP ZONE AT FAST RATE

� COKE LAYER IN 25TH & 28TH TUBE

� TUBE 1 & 2 VERY CLEAN

OBSERVATIONS

13

• Reduce the draft inthe furnace box toshift the heat transferto radiation bottom

• Increase the HCvelocity at theradiation inlet toslow down coke layerformation in radiationtop tubes

14

NEW OPERATING CONDITION

� HC flow 29 m3/hr/pass� BFW to convection coil flow rate 0.32 m3/hr/pass� BFW to radiation I/L coil flow rate 0.2 m3/hr/pass� CIT- 325⁰C , COT- 495⁰C� Convection O/L T- 420⁰C� Furnace draft- 2.3 mmWC� O2 analyzer reading- 3.2 vol%� Stack T- 210⁰C � Flue gas T at arch- 730⁰C� Flue gas T at floor-620⁰C� Fuel Gas flow- 530 kg/hr

15

RESULTS

16

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

Series1

Series2

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

Series1

Series2

CONVECTION COIL PRESSURE DROP

500

520

540

560

580

600

620

1-N

1-M

1-S

2-N

2-M

2-S

7-N

7-M

7-S

25-N

25-M

25-S

28-M

SZ-N

SZ-S

NEW TMT TREND RUN-1

SHOCK ZONE

25TH & 28TH TUBE

7TH TUBE & BELOW

17

18

500

520

540

560

580

600 1-N

1-M

1-S

2-N

2-M

2-S

7-N

7-M

7-S

25-N

25-M

25-S

28-M

SZ-N

SZ-S

25TH & 28TH TUBE7TH TUBE & BELOW

SHOCK ZONE

NEW TMT TREND RUN-2

19

BEFORE

AFTER

20