DCU Trainingfor New Engineers

• Introduction to Refinery operation• Overview Of Crude Distillation• Delayed Coking• History OF Delayed Coking• Overview of DCU• Process description• Operating modes• Chemistry of Delayed coking• Process variables

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Following Units Come Under Refinery Operation:

Unit: Date Commissioned

CDU-I 6th Feb 1979

DCU-I 21st Sept 1981

CCU 29th Dec 1981

CDU-II May 1995

DCU-II May 1996

Delayed Coking

• It is a Thermal conversion process where Heavy residue from CDU or/else VDU bottoms are upgraded to more usable hydrocarbon products, such as Gas, LPG, Kerosene, Gas oil and Coke.

• Pet coke first made in 1860s in Pennsylvania.• Only one still was used.• Lighter components evaporated• Coke was scrapped out.• Cokers with horizontal stills and distillation column and tube furnace

developed after 1920’s• Decoking was still the crude manual process• First vertical delayed coker was built in 1929 by Standard Oil

Company.• The concept of recycle was developed subsequently• Hydraulic cutting system was first patented by Shell oil in 1930.

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• Cokers became popular after 2nd world war.

>> use in Diesel engine locomotives

>> Use of gasoline in planes

>> development in automobile industry.

• Catalytic processes developed during this period had problem of catalyst poisoning.

• Cokers helped removal of asphaltic content along with metals.

• From 1950 to 1970 coking capacity increased 5 folds

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Worldwide crudes are becoming heavier, containing more bottom residues, high CCR, metals, etc.

Increasing thrust on residue upgradation - Zero residue refinery

Higher operating/capital cost of other residue upgradation technologies

Ability of Delayed Cokers to convert even heaviest residues to lighter distillates - Permits refiners to process wide variety of crudes, dispose low value byproducts

Improved profitability through integration with other secondary conversion units

Process Description

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Continuous operation

Feed circuit till the feed furnace

Fractionator along with product strippers & associated equipment

Batch operationCoke drumCycle time

Coke drum feeding time durationTypical cycle time 24 hrs.

Process Description

Diagram

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Coker Cycle• Chamber Changeover : 0 hrs• Depressurisation : 0.25hrs• Steam Cooling : 2hrs• Low rage water : 3hrs• Deluge cooling : 2hrs• Draining : 1.5 hrs• Deheading : 2 hrs• Drilling / Decoking : 6 hrs• Heading : 2 hrs• Pressure testing :1 hr• Vapor heating/ changeover : 5 hrs• Idle time : 8hrs

Process Description

Diagram

• Decoking Operation

- Carried by high pressure water jet- J et pump with a Discharge pressure of 164kg/cm sq.- Coke handling equipment : Galick Crane- W ater reuse/ recirculation system

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Process Description

Diagram

Operating modes

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Operating Characteristics

• Two Modes– Needle coke mode– Pet coke mode

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Process Description

• Feed:Assam Crude Atm Residue (data IIP and R&D Faridabad)– W t % on crude : 40%– Sp Gravity : 0.9802– CCR : 5.99 - 6.8 wt%– Asphaltene : 1.81- 2.1 wt%– Aromatics : 51.6 wt%– Saturates : 48.4 wt %– W ax 43.4 : 43.4(24.5) wt%– Pour point : +48 OC– Sulphur : 0.49 wt %– Metals• V : 0.24 Ni : 1.78 Fe: 14.4• Cu : 0.13 Zn : 0.94BGR - IOCL

• Feed:Ravva Crude Atm Residue( Data Cairn Energy and R& D Faridabad)– W t % on crude : 33%– CCR : 3.1 wt%– Asphaltene : 0.8wt%– Aromatics : 25.5wt%– Saturates : 74.5 wt%– W ax Content : 47 %– Sulphur : 0.08 wt %– Metals :

• V : 1ppm Na : 16ppm Ni : 1ppm Fe: 1ppm Cu :<1ppm

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• Additional feedtypes

– Slop from unit– RFO and CFO recycle

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• Furnace- COT : 496-499 oC- BFW : 0.4 m3 /hr/pass for secondary flow of 40m3

/hr/pass or 1vol%- Recycle ratio : 0.8-0.9

• Coke Chamber- After quench Temperature 438 – 440 oC- Bottom Temperature 490-495 OC- Top Pressure 2.1-2.3 kg/cm2g- Bottom Pressure 4.5 – 5 kg/cm2g

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• Quench Column

- Top Temperature 430-435 oC

• Fractionator

- Top Pressure 1.50 – 1.55 kg/cm2g

- Top Temperature 102-105OC

- Bottom Temperature 360-370 OC

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NB : Design fig is as per Assam crude RCO & Actual yield is as per mixed (Assam + Ravva) crude RCO.

Coke + Loss

CFO + RFO

Coker Kero + CGO

Coker Naphtha

Gas + LPG

PRODU CT S

13.513.0

29.024.2

43.143.0

6.8 7.5

7.612.3

ACT U AL ( W T % )

DE S IG N( W T % )

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Coker Naphtha MS Pool Coker Kero HSD

LGO

HGO LDO

CFO

RFO LSHS

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• Used in the manufacture of Graphite electrode.

• Must have low Low Coefficient of thermal expansion (CTE) i.e expansion between 0 oC and 50 oC

• Must be able to withstand a temperature of 2800 oC.

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•Feed Characteristics•Should have low Asphaltene content (below 1wt%)•Should be aromatic•Should have low sulphur content

Feeds used in DCU- RFO (DCU Product)

- CFO (DCU Product) - CLO ( Bottom product of FCCU) FBP 550 oC

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•Furnace•COT : 502-504 oC•BF W : 0.3m3 /Pass •Recycle ratio : 1.2-1.3

●Chamber - After quench Temperature 442 oC - Bottom Temperature 495 - 498 OC- Top Pressure 2.7-3 kg/cm2g- Bottom Pressure 5 - 5.5 kg/cm2g

Needle Coke Mode

Operating parameters

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• Quench Column- Top Temperature 435-438 oC

• Fractionator- Top Pressure 2.1 – 2.3 kg/cm2g- Top Temperature 110-112OC- Bottom Temperature 370 - 372 OC

● Cycle time : 30-36 hrs

Needle Coke Mode

Operating parameters

BGR - IOCL 100%100%100%100%Total20%--- CLO70%80%85%85% RFO10%10%15%15% CFO

-10%-- RCO    Feedstock comp      

3631605658368167Feed Processed4000810084008200NCFS Prepared1.221.2  M/S GIL1.081.23, 1.221.411.41MS HEG

1.0351.1--IOC (R & D)      CTE Value * 10‾6

551.55605414887Total CNC

149---Double Calcined402.55605414887Single Calcined

    Calcined Needle Coke665.737349811290.4Green Needle Coke

    Production of Needle Coke

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BGR - IOCL100%100%100%100%100%Total

-2%3%5%- CLO100%82%83%83%81% RFO

-16%14%13%14% CFO----5% RCO     Feedstock comp       

96001271612680116117331Feed Processed103001356212933119948631NCFS Prepared1.3231.31- 1.33M/S GIL1.421.301.34 1.26MS HEG

1.25/ 1.391.251.311.1941.22IOC (R & D)     CTE Value * 10‾6

1962.0914131655.61222.501175.7Total CNC-----Double Calcined

1962.0914131655.61222.501175.7Single Calcined(322.59+1639.5)    Calcined Needle Coke

201819662153.12059.81291Green Needle Coke   sold to M/S GIL Production of Needle Coke

9th8th7th6th5thPARTICULARS

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Parameters Unit

1st Run

2nd Run

3rd Run

4th Run

5th Run

6th Run

7th Run

8th run Export

                   Requireme

nt

Bulk density - 4/6 gm/100cc - -82.00

079.00

0 82 82 77 79 -

Real density gm/cc 2.130 2.130 2.160 2.160 2.15 2.12 2.15 2.14

2.14 - 2.15 ( - 0.075 mm)

Sulphur %wt 0.540 0.540 0.350 0.500 0.48 0.45 0.41 0.39 0.38 - 0.46

VMC % wt 0.160 0.160 0.060 0.310 0.29 0.18 0.15 0.15 -

Ash % wt 0.100 0.100 0.300 0.200 0.28 0.3 0.15 0.14 0.03-0.10

VBD ( - 8/14) gm/cc 0.970 0.970 - - 0.78 - - -

0.97 - 0.82 (-6.7+ 3.35)

PD gm/cc - - - - - - - - -

CTE (0 TO 50 0C)mm/mm/

0C*10-7 *** - - - - - - - 1.0-1.5

CTE (25 TO 600 0C)mm/mm/

0C*10-6 1.410 1.410 1.100 1.035 1.22 1.194 1.31 1.25 -

Sizing + 6 mesh % - - - - - - - - -

Moisture % - - - - - - - - 0.02 - 0.10

Mercurial Density gm/cc - - - - - - - - -

HGI   48 48 39 43 39 41 37 35

40-50 (3.35mm), 28-35 (-1mm)

Coking Chemistry

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Courtesy : The Chemistry and Technology of petroleum 2nd Ed

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Paraffins

Benzene ring Compounds

Polycondensed Aromatic Rings

• Feedstock can be divided into asphaltenes and maltenes.

• Alphaltenes are n-heptane insolubles and maltenes are n-heptane solubles.

• Maltenes include resins, aromatics and saturates.• Asphaltenes are high molecular weight polynuclear

aromatics having low H-C ratio• Resins are low molecular wt asphaltenes• Saturates include Naphthenes, Paraffins.• Higher the asphaltenes higher is the coke make.

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Coking Chemistry

o Free radical Chain reaction

o Thermal decomposition of hydrocarbon molecules to two free radical fragments.

RCH2CH2CH2R’ -> RCH2ċH2 + R’ċH2

o Free radicals are reactive species which takes the reactions forward in a reaction mass.

o The reactions that follow are :-

Combination reactions

Disintegration reactions

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• n-paraffins combine to form larger molecules before decomposition

• i-paraffins normally produce more olefins

• Dealkylation of alkylated aromatics or alkylated naphthenes takes place between 350 to 500 OC.

• Aromatic ring destruction takes place above 500oC

• Condensed ring aromatics decompose at around 450OC.

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Coking Chemistry

• Coke is formed by formation of Thermally stable Pol y nuclear Aromatics(P N A).

• P N A form by p recipitation by v irt u e of its insol u bilit y in the mother solv ent.

• The relative aromaticit y or p araffinicit y of the feed effects the sol u bilit y w hich effects the rate of p reci p itation.

• The q u alit y of the feedstock decides the final sha p e and com p osition of the final coke.

• H ence, for formation of hi g h q u alit y needle coke feedstock q u alit y is ver y important factor.

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Coking Chemistry

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Coking Chemistry

Process Variables

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0

20

40

60

80

100

0 10 20 30FEED CCR, Wt%

PR

OD

UC

T Y

IEL

D,

Wt%

COKE GAS GASOLINE GAS OIL C5 +

Process Variables

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Temperature Gas Distillate Coke

Drum pressure Coke

Gas

Distillate

Process Variables

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Recycle Coke ( w t % ) N a p htha H ea v y Gas oil

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• Coke drums have restrictions in max size• Coke drum size bottleneck in increasing plant

t’put.• Multiple (<2) coker drums provides higher t’put

but more slop and loss• Shorter cycle time allows higher t’put to be

processed

Process Variables

Thank Y ou

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