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DELAYED COKER UNIT DCU HEATER

DCU Heater

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Page 1: DCU Heater

DELAYED COKER UNIT

DCU HEATER

Page 2: DCU Heater

SPECIAL OPERATIONS OF DCU HEATERS

DELAYED COKER HEATER

• The most important piece of equipment in delayed coker is the fired heater.

• In this demanding service carefully controlled time/temperature profiles are critical for profitable production.

• Furnace residence time must be strictly controlled to avoid premature coke formation in the tubes resulting in premature shutdown.

Page 3: DCU Heater

SPECIAL OPERATIONS OF DCU HEATERS

HEATER AT DELAYED COKER -

PR

32501250

2664

3250

3250

3250

1250

2064

17000

8050

FOUR PASSES

COMMON CONVECTION SECTION

DIFFERENT RADIATION SECTION

Page 4: DCU Heater

TYPICAL PROBLEMS IN FIRED HEATERS

HIGH EXCESS AIR OPERATION

FOULED CONVECTION SECTIONS

HIGH STACK TEMPERATURES

OVER FIRING

UNEVEN FIRING

FLAME IMPRINGEMENT

Page 5: DCU Heater

COMPARISION OF HEATER EFFICIENCY AT VARIOUS EXCESS AIR AND STACK

TEMPERATURESEXCESS AIR

(%)O2 IN FLUE GAS

%

VARIOUS STACK TEMPERATURES (C)

150 175 200 225 250 280 315 375 425 480 540

15.00 3.00 91.76 90.44 89.11 87.77 86.42 85.06 83.60 80.59 78.11 75.25 72.35

20.00 3.82 91.52 90.15 88.77 87.39 85.98 84.57 83.15 80.28 77.36 74.40 71.39

25.00 4.56 91.29 89.87 88.44 87.01 85.55 84.09 82.62 79.64 76.61 73.55 70.43

30.00 5.24 91.05 89.58 88.10 86.61 85.11 83.62 82.07 78.99 75.87 72.69 69.47

40.00 6.46 90.58 89.01 87.43 85.84 84.24 82.60 81.00 77.71 74.37 70.99 67.55

50.00 7.49 90.10 88.43 86.76 85.06 83.36 81.64 79.92 76.43 72.28 69.28 65.63

Page 6: DCU Heater

HEATER INTERLOCKS

LOW LOW PASS FLOW78-FZT-1702/3/4/5 A/B < 17.1tph

HIGH HIGH FG KOD LEVEL78-LZT-1902 A/B/C > 90 %

HIGH HIGH FG PRESSURE 78-PZT-1906A/B/C/D > 2.5kg/cm2

HIGH HIGH PILOT PRESSURE 78-PZT-1904 > 3.1 kg/cm2

HIGH HIGH FO PRESSURE78-PZT-7740/7741/7742/7743 > 8

(dual mode)/ 7.5 (FO mode)

LOW LOW ATOMISING STEAM / FO DIFF. PRESSURE

78-PDZT-7713/7714/7715/7716 < 0.5 kg/cm2

HIGH HIGH HEATER OUTLET PRESSURE

78-PZT-1806 A/BC/D/E/F/G/H/I/J/K/L > 34

KG/CM2

HIGH HIGH COT78-TZI-1812 A/BC/D/E/F/G/H/I/J/K/L >

520 ©

LOW LOW FG PRESSURE 78-PZT-1906A/B/C/D <

2 kg/cm2

LOW LOW PILOT PRESSURE 78-PZT-1904 < 0.1 kg/cm2

LOW LOW FO PRESSURE78-PZT-7740/7741/7742/7743 < 7

kg/cm2

TRIP SWITCH A

TRIP SWITCH B

TRIP SWITCH D

TRIP SWITCH C

PROCESS TRIPS:

Page 7: DCU Heater

HEATER INTERLOCKS

TAKE OTHER FD TO 80% LOAD

ID TIRPsensed by 78-ST-2101 < 100rpm or 78-YL-

2153

FO/FG CUT OFF

HIGH HIGH ARCH PRESSURE 78-PT-2110A/B/C = 0mmWC

TRIP ID FANHIGH CAST APH TEMP 78-TT-2155A/B/C > 290 ©

OPEN MSD

BOTH FD TRIP sensed by 78ST2102/ST2103 < 100 rpm FD101AS1

(MCC) or 78YL2151A/YL2152B

TRIP SWITCH

HIGH HIGH ARCH PRESSURE 78-PT-2110A/B/C =2/3/4 mmWC

OPEN MSD then TRIP BOTH FD FANS

HEATER TRIP

AIR & APH INTERLOCKS:

ONE FD TRIP78-ST-2102/78-ST-2103

< 100rpm

Page 8: DCU Heater

TRIP SWITCH A

FORCE CLOSE FG SDV

FORCE CLOSE FO RETURN SDV

DECREASE HIGH HIGH TRIP PRESSURE OF FO TO ALL PASSES

FORCE CLOSE ATOMIZING STEAM CONTROL VALVE OF ALL PASSES

FORCE ZERO OUT ALL PASS FO CONTROL VALVE

FORCE CLOSE FO SUPPLY SDV

DECREASE HIGH HIGH TRIP PRESSURE OF FG TO ALL PASSES

FORCE ZERO OUT ALL PASS FG CONTROL VALVE

HEATER INTERLOCKS

Page 9: DCU Heater

TRIP SWITCH B

FORCE CLOSE FG SDV

FORCE CLOSE FO RETURN SDV

DECREASE HIGH HIGH TRIP PRESSURE OF FO TO ALL PASSES

FORCE CLOSE ATOMIZING STEAM CONTROL VALVE OF ALL PASSES

FORCE ZERO OUT ALL PASS FO CONTROL VALVE

FORCE CLOSE FO SUPPLY SDV

DECREASE HIGH HIGH TRIP PRESSURE OF FG TO ALL PASSES

FORCE ZERO OUT ALL PASS FG CONTROL VALVE

OPEN MAIN STACK DAMPER

HEATER INTERLOCKS

Page 10: DCU Heater

DECREASE HIGH HIGH TRIP PRESSURE OF FG TO ALL

PASSES

FORCE ZERO OUT OF ALL PASS FG CONTROL VALVE

FORCE CLOSE FG SDV

HEATER INTERLOCKS

TRIP SWITCH C

Page 11: DCU Heater

TRIP SWITCH D

FORCE CLOSE FO RETURN SDV

DECREASE HIGH HIGH TRIP PRESSURE OF FO TO ALL

PASSES

FORCE CLOSE ATOMIZING STEAM CONTROL VALVE OF

ALL PASSES

FORCE ZERO OUT ALL PASS FO CONTROL VALVE

FORCE CLOSE FO SDV

HEATER INTERLOCKS

Page 12: DCU Heater

HEATER COKING REASONS HEATER CHARGE PROPERTIES

Sodium content – causes rapid fouling Asphaltene content – increases fouling rate Calcium content Crude properties API & viscosity – higher, higher the rate of fouling

OPERATING PARAMETERS Higher heater outlet temperatures Process velocity

• Low mass flow velocity increases film temperature• Loss of turbulizing medium• Low flow (6ft/sec) exponentially increases the fouling rate

Uneven heat distribution “hotspots or cold spots in heater box” Residence time above cracking threshold Low flow (Turndown) or poor flow distribution Feed interruptions

OTHER ISSUES Burner tip plugging Uneven firing in heater

Page 13: DCU Heater

DECOKING OPTIONS

OPERATING PROCEDURES

• STEAM AIR DECOKING Performed when heater is offline. Heater is completely out of service.

• MECHANICAL PIGGING Performed when heater is offline. Mechanical pigs are sent into the tubes with a hydraulic medium.

• ONLINE SPALLING Performed when heater is in service. One pass is taken off service and rest of the passes are inline.

Page 14: DCU Heater

SPECIAL OPERATIONS OF DCU HEATERS

STEAM AIR DECOKING

• PRINCIPAL MECHANISMS: Spalling Coke burning

SPALLING:The relatively cooler steam 'cools' shocks the hot tube surfaces causing cracking of coke and breaking away of the coke from tube surface. The broken particles are picked up by the high velocity steam and scour the remaining surface.

COKE BURNING:The BURNING period consist of injection of Steam & air simultaneously while the furnace is being fired at a higher rate. The Air ignites and consumes any coke remaining on the tube after spalling. The burning effectively removes all hard coke deposits on the tubes.

Page 15: DCU Heater

STEAM AIR DECOKING

OPERATING PROCEDURES

FURNACE

CONVECTION INLET

RADIATION OUTLET

STEAM INLET FOR SPALLING

TO DECOKING POT

Heater is taken out of service Steam line / decoking pot connections are made Steam is charged Heater firing is gradually increased Water coming out of decoking pot is observed

COIL

STEAM FLOW

SPALLING OF TUBES

Page 16: DCU Heater

STEAM AIR DECOKING

OPERATING PROCEDURES

FURNACE FURNACE

FLOW DIRECTION - NORMAL FLOW DIRECTION - REVERSAL

REVERSAL OF FLOW DURING SPALLING

CONVECTION INLETCONVECTION INLET

RADIATION OUTLETRADIATION OUTLET

TO DECOKING POT

TO DECOKING POTSTEAM INLET

STEAM INLET

Page 17: DCU Heater

STEAM AIR DECOKING

OPERATING PROCEDURES

FURNACE

CONVECTION INLET

RADIATION OUTLET

STEAM INLET

TO DECOKING POT

AIR INLET

SAMPLING

COKE BURNING

Page 18: DCU Heater

MECHANICAL DECOKING - PIGGING

Coke is removed from the heater tube by pumping a metal studded foam or plastic pig with water. The metal studded pig rotates such that it scrapes the coke off the inside of the heater tube.

Different size abrasiveness pigs are used in the decoking process. “Pigs” are slightly smaller than the inside diameter of the heater tube

Usually pigs are pumped through heater several times forward and backward until overall differential pressure across the heater tube (inlet to outlet) is restored to the original SOR condition.

Typical decoking time varies from 18 to 24 hours per pass depending on the set-up type.

Page 19: DCU Heater

ONLINE SPALLING

OPERATING PROCEDURES

TYPICALFOR

OTHER PASSES

TYPICALFOR

OTHER PASSES

HP BFW

HP STEAM

CONVECTIONZONE

RADIATIONZONE

CONVECTION INLET

RADIATION OUTLET

CONVECTION OUTLET

HEATER CHARGE

Page 20: DCU Heater

ONLINE SPALLING

Coke is removed from the heater tube by varying the steam and condensate flowrate in the fouled tube such that a thermal shock is created that breaks off coke from the tube.

The spalling medium will transfer the coke particles into the heater effluent (as other passes are in line) and into the coke drum.

One pass is spalled while the other coils of the heater remain in normal hydrocarbon mode.

Typical spalling time is around 16-24hrs per pass.

Page 21: DCU Heater

GAIN IN SKIN TEMPERATURE AFTER ONLINE SPALLING

OPERATING PROCEDURES

OVERALL GAIN OF SKIN TEMPERATURES AFTER APRIL'10 ONLINE SPALLINGH101

DESCRIPTION PASS A PASS B PASS C PASS D BEFORE AFTER GAIN BEFORE AFTER GAIN BEFORE AFTER GAIN BEFORE AFTER GAIN10th tube East 537.51 523.09 14.43 536.39 525.88 10.51 524.50 515.34 9.16 545.00 521.85 23.1510th tube West 533.86 506.34 27.52 580.75 575.15 5.59 577.11 544.70 32.41 OUT OUT OUT8th tube East 557.02 526.83 30.19 570.87 553.05 17.82 538.51 528.36 10.15 532.24 507.27 24.978th tube West 557.01 536.15 20.86 601.43 590.29 11.13 591.04 547.35 43.70 542.83 521.58 21.256th tube East 566.33 538.06 28.27 584.52 532.81 51.71 547.99 528.68 19.32 569.66 531.58 38.086th tube West 562.12 524.79 37.33 610.54 558.79 51.75 OUT OUT OUT 555.62 526.83 28.784th tube East 569.05 531.19 37.86 616.79 551.65 65.14 564.33 540.23 24.10 573.80 529.50 44.304th tube West 571.94 534.36 37.58 617.33 544.13 73.19 603.74 558.93 44.81 574.81 534.55 40.262nd tube West 588.09 547.84 40.25 602.17 531.75 70.42 573.92 552.45 21.47 583.01 533.99 49.032nd tube West 610.18 580.03 30.15 616.27 545.87 70.40 607.55 559.21 48.33 585.19 541.86 43.33Middle Skin 609.68 588.78 20.90 615.02 600.58 14.44 614.63 564.90 49.73 OUT OUT OUT

H102DESCRIPTION PASS A PASS B PASS C PASS D

BEFORE AFTER GAIN BEFORE AFTER GAIN BEFORE AFTER GAIN BEFORE AFTER GAIN10th tube East 555.36 525.49 29.87 572.84 545.67 27.17 OUT OUT OUT 560.76 536.17 24.5810th tube West 590.18 557.85 32.33 557.42 535.05 22.37 528.75 517.12 11.63 560.25 529.26 30.998th tube East 598.48 556.46 42.02 588.52 554.58 33.94 554.08 528.43 25.65 583.50 535.32 48.188th tube West 576.00 553.42 22.58 576.98 539.28 37.70 562.04 548.73 13.31 603.75 553.32 50.436th tube East 615.59 560.93 54.66 577.52 536.14 41.39 576.68 543.90 32.78 611.27 546.18 65.096th tube West 594.10 543.10 51.00 570.52 526.59 43.93 541.55 518.92 22.63 596.41 535.63 60.794th tube East 605.34 536.60 68.74 605.48 552.67 52.81 590.54 550.53 40.01 OUT OUT OUT4th tube West 576.59 529.07 47.52 613.64 561.18 52.46 545.41 519.48 25.93 610.91 540.04 70.872nd tube West 605.11 539.15 65.96 589.12 530.93 58.20 588.08 541.53 46.55 607.93 538.67 69.262nd tube West 583.99 537.03 46.96 OUT OUT OUT 564.74 533.83 30.91 606.22 535.36 70.87Middle Skin 655.57 603.48 52.10 602.33 563.74 38.59 616.56 571.10 45.46 OUT OUT OUT

Page 22: DCU Heater

H101 BEFORE Vs AFTER SKIN COMPARISION

Page 23: DCU Heater

H102 BEFORE Vs AFTER SKIN COMPARISION

Page 24: DCU Heater

STEAM AIR DECOKING PROS & CONS

ADVANTAGES

Fool proof method. Best method for complete removal of coke and restore SOR condition

DISADVANTAGES

Time & Cost (Maintenance and unit production loss) Potential tube erosion and tube thinning Testing is a little difficult, GC of the sample is to be done for satisfied results. Entire heater need to be taken out of service, hydro-test of coil need to be done after decoking.

Page 25: DCU Heater

PIGGING PROS & CONS ADVANTAGES

Usually performed faster than SADC Heater box can be opened during pigging and other maintenance jobs can be done Post pigging checks are easy open the header plug and check for coke and repeat pigging if not satisfactory Lesser metal loss and erosion than SADC Dedicated operational manpower not required as it is done by external agency. No sudden expansions or contraction i.e. no thermal shock so potential tube damage is minimal

DISADVANTAGES Pigging quality entirely depends on the external agency. Huge risk, if pigging is not successful the time lost and money lost would be huge. Could cause scratches on the inside of the tube which could become potential coking sites. Not a fool proof method, as internal inspection of the tubes is not possible. Entire heater need to be taken out of service and hydro-test of coil is necessary.

Page 26: DCU Heater

ONLINE SPALLING PROS & CONS

ADVANTAGES Heater need not be taken out of service as one pass would be in spall mode and the other passes would have hydrocarbon Immediate feed back on the effectiveness once pass is back in service, as running conditions in the pass are immediately restored Extends heater length without a shutdown Takes less time 16-24 hrs per pass hence can be done every quarter as per convenience for extended heater lengths.

DISADVANTAGES May not remove the coke completely and eventually decoking would be necessary Highly risky operation as feed out and feed in are done with VR and not by conventional method of FLO and then VR Potential tube damage due to sudden expansion and contraction Potential permanent coking of the tube if temperatures are not controlled properly Can be performed on a 3 or 4 pass heater(supplying one reactor) without any problem, if it is a 2 pass heater supplying one reactor this is not recommended Huge shot coke formation might be there because of high vapor velocities