DELAYED COKER UNIT (DCU)

 Page 1


DELAYED COKER UNIT 
(DCU) 
 
 
INTRODUCTION 
 
Delayed Coker unit is largestest of its type among all IOCL plants in 
India. This unit uses vacuum residue obtained from fractionation as the 
feed the main objective of this unit is to separate out middle distillates, 
and give products such as LPG and Naphtha. Coke obtained from this 
unit generates maximum amount of profit for this unit. 
 
MAIN PRODUCTS 
 
? Light Coker Gas Oil (LCGO) 
? Heavy Coker Gas Oil (HCGO) 
? Coker Fuel Oil (CFO) 
? Light Naphtha 
? Heavy Naphtha 
? Fuel Oil (FO) 
? Coke 
 
FEED CHARACTERISTICS  
 
The feed, which comes mainly, comes from fractionating column of units 
like AVU, DHDT; RFCCU is stored in DCU storage tank this is classified 
in two types: 
Hot Feed: which is at the temp. Of 240 C 
 
Cold feed: which is at temp. of 140 C 
 
There are four feed tanks in this unit. The final feed obtained before 
loading is the mixture. 
Its contains are: 
1. A mixture of hot and cold RCO (Reduced Crude Oil)  
2. The filterate obtained from 25-micron filter. 
3.  Heavy Cycle Oil from FCCU 
4. Refinery Slop 
 
Earlier this feed is used for producing TAR but since advent of DCU we 
have started using this unit to generate coke. 
 
PROCESS DESCRIPTION  
 
The delayed coking process is essentially a thermal cracking process to 
minimize refinery yields of residual fuel oil by conversion of the gas, 
Page 2


DELAYED COKER UNIT 
(DCU) 
 
 
INTRODUCTION 
 
Delayed Coker unit is largestest of its type among all IOCL plants in 
India. This unit uses vacuum residue obtained from fractionation as the 
feed the main objective of this unit is to separate out middle distillates, 
and give products such as LPG and Naphtha. Coke obtained from this 
unit generates maximum amount of profit for this unit. 
 
MAIN PRODUCTS 
 
? Light Coker Gas Oil (LCGO) 
? Heavy Coker Gas Oil (HCGO) 
? Coker Fuel Oil (CFO) 
? Light Naphtha 
? Heavy Naphtha 
? Fuel Oil (FO) 
? Coke 
 
FEED CHARACTERISTICS  
 
The feed, which comes mainly, comes from fractionating column of units 
like AVU, DHDT; RFCCU is stored in DCU storage tank this is classified 
in two types: 
Hot Feed: which is at the temp. Of 240 C 
 
Cold feed: which is at temp. of 140 C 
 
There are four feed tanks in this unit. The final feed obtained before 
loading is the mixture. 
Its contains are: 
1. A mixture of hot and cold RCO (Reduced Crude Oil)  
2. The filterate obtained from 25-micron filter. 
3.  Heavy Cycle Oil from FCCU 
4. Refinery Slop 
 
Earlier this feed is used for producing TAR but since advent of DCU we 
have started using this unit to generate coke. 
 
PROCESS DESCRIPTION  
 
The delayed coking process is essentially a thermal cracking process to 
minimize refinery yields of residual fuel oil by conversion of the gas, 
naphtha, Gas Oil and Coke. The coker feed is vacuum residue from Arab 
mix crude’s or mixed supply (middle east crude). The feed stream is pre-
heated by HCGO product and pumparound exchangers and charged to 
the bottom section of the coker fractionator where it mixes with Heavy 
recycle liquid from the bottom tray. The combined coker feed and heavy 
recycle liq. is pumped to the coker heater where it is rapidly heated to 
the temp. Above the coking point. Significant coke formation in the 
heaters is therefore is avoided. 
             The heater effluents are charges to coke drum where further 
cracking reactions and subsequent polymerization takes place to form 
coke. The vapour products leave the top of the coke drum where they are 
immediately quenched with a slip stream of HCGO pumparound. The 
quenching stops the cracking and polymerization reactions. 
             Quenched coke drum effluents are charged to the coker 
fractionator where light gas, naphtha, LCGO, HCGO, CFO and heavy 
recycled liquids are separated. LCGO, HCGO and CFO are steam 
stripped to meet product specifications before cooling and final routing to 
battery limits. 
              The vapour from the coker fractionator is partially condensed 
and collected in the coker fractionator overhead receiver, which separates 
vapours, hydrocarbon liq. and sour water. Vapours are routed to the 
vapour recovery section. A portion of the hydrocarbon liq. is pumped to 
the coker fractionater top tray as reflux, and remaining portion is 
pumped to the vapour recovery section the part of the sour water goes to 
the recontact product coolers as awash, and the net production goes to 
OSBL for treatment. 
 The vapour recovery section separates the light products to 
debutanised naphtha C3/C4 LPG and Fuel gas. 
 The Wet Gas from coker fractionator overhead receiver is 
compressed into two stage wet gas compressor vapour discharge is 
partially condensed and separated in the recontact drum. The vapour 
effluents are stripped of the bulk of its H2S using lean amine in 
deethaniser feed gas scrubber. The H2S free vapour is then charged to 
the absorber section of the deethaniser primary absorber or stripper. The 
hydrocarbon liq. from the recontact drum is pumped to the stripper 
section. Mean while the sour water interstage drum and the recontact 
drum recycles to the coker fractionator over head receiver. 
 The Deethaniser separates the C2 and the lighter from the 
fractionator from the LPG and the naphtha. Absorption oil, a 
combination of coker fractionator overhead receiver hydrocarbon liquid 
and debutanised naphtha liq. recycle feeds the top tray. The deethaniser 
overhead vapour is contacted with LCGO in the Sponge Absorber to 
further reduce the loss of Naphtha. The resultant sour fuel gas is 
scrubbed free of H2S using lean amine in the fuel gas scrubber before 
routing to the sweet fuel gas to OSBL. 
             The deethanizer bottoms are routed to the debutanizer to 
Page 3


DELAYED COKER UNIT 
(DCU) 
 
 
INTRODUCTION 
 
Delayed Coker unit is largestest of its type among all IOCL plants in 
India. This unit uses vacuum residue obtained from fractionation as the 
feed the main objective of this unit is to separate out middle distillates, 
and give products such as LPG and Naphtha. Coke obtained from this 
unit generates maximum amount of profit for this unit. 
 
MAIN PRODUCTS 
 
? Light Coker Gas Oil (LCGO) 
? Heavy Coker Gas Oil (HCGO) 
? Coker Fuel Oil (CFO) 
? Light Naphtha 
? Heavy Naphtha 
? Fuel Oil (FO) 
? Coke 
 
FEED CHARACTERISTICS  
 
The feed, which comes mainly, comes from fractionating column of units 
like AVU, DHDT; RFCCU is stored in DCU storage tank this is classified 
in two types: 
Hot Feed: which is at the temp. Of 240 C 
 
Cold feed: which is at temp. of 140 C 
 
There are four feed tanks in this unit. The final feed obtained before 
loading is the mixture. 
Its contains are: 
1. A mixture of hot and cold RCO (Reduced Crude Oil)  
2. The filterate obtained from 25-micron filter. 
3.  Heavy Cycle Oil from FCCU 
4. Refinery Slop 
 
Earlier this feed is used for producing TAR but since advent of DCU we 
have started using this unit to generate coke. 
 
PROCESS DESCRIPTION  
 
The delayed coking process is essentially a thermal cracking process to 
minimize refinery yields of residual fuel oil by conversion of the gas, 
naphtha, Gas Oil and Coke. The coker feed is vacuum residue from Arab 
mix crude’s or mixed supply (middle east crude). The feed stream is pre-
heated by HCGO product and pumparound exchangers and charged to 
the bottom section of the coker fractionator where it mixes with Heavy 
recycle liquid from the bottom tray. The combined coker feed and heavy 
recycle liq. is pumped to the coker heater where it is rapidly heated to 
the temp. Above the coking point. Significant coke formation in the 
heaters is therefore is avoided. 
             The heater effluents are charges to coke drum where further 
cracking reactions and subsequent polymerization takes place to form 
coke. The vapour products leave the top of the coke drum where they are 
immediately quenched with a slip stream of HCGO pumparound. The 
quenching stops the cracking and polymerization reactions. 
             Quenched coke drum effluents are charged to the coker 
fractionator where light gas, naphtha, LCGO, HCGO, CFO and heavy 
recycled liquids are separated. LCGO, HCGO and CFO are steam 
stripped to meet product specifications before cooling and final routing to 
battery limits. 
              The vapour from the coker fractionator is partially condensed 
and collected in the coker fractionator overhead receiver, which separates 
vapours, hydrocarbon liq. and sour water. Vapours are routed to the 
vapour recovery section. A portion of the hydrocarbon liq. is pumped to 
the coker fractionater top tray as reflux, and remaining portion is 
pumped to the vapour recovery section the part of the sour water goes to 
the recontact product coolers as awash, and the net production goes to 
OSBL for treatment. 
 The vapour recovery section separates the light products to 
debutanised naphtha C3/C4 LPG and Fuel gas. 
 The Wet Gas from coker fractionator overhead receiver is 
compressed into two stage wet gas compressor vapour discharge is 
partially condensed and separated in the recontact drum. The vapour 
effluents are stripped of the bulk of its H2S using lean amine in 
deethaniser feed gas scrubber. The H2S free vapour is then charged to 
the absorber section of the deethaniser primary absorber or stripper. The 
hydrocarbon liq. from the recontact drum is pumped to the stripper 
section. Mean while the sour water interstage drum and the recontact 
drum recycles to the coker fractionator over head receiver. 
 The Deethaniser separates the C2 and the lighter from the 
fractionator from the LPG and the naphtha. Absorption oil, a 
combination of coker fractionator overhead receiver hydrocarbon liquid 
and debutanised naphtha liq. recycle feeds the top tray. The deethaniser 
overhead vapour is contacted with LCGO in the Sponge Absorber to 
further reduce the loss of Naphtha. The resultant sour fuel gas is 
scrubbed free of H2S using lean amine in the fuel gas scrubber before 
routing to the sweet fuel gas to OSBL. 
             The deethanizer bottoms are routed to the debutanizer to 
separate LPG from naphtha. The product LPG is scrubbed free of H2S 
using lean amine in LPG amine scrubber before routing to the OSBL. 
 The product naphtha is cooled and routed to the naphtha splitter. 
The naphtha splitter separates the debutanised naphtha into light and 
heavy naphtha. Light naphtha product is routed to the light naphtha 
amine scrubber to remove H2S and then caustic and water wash prior to 
being routed to OSBL. 
  The heavy naphtha is caustic and water wash prior to being 
routed to OSBL. 
 
COKER FRACTIONATOR 
 
 The coker fractionator separates the coke drum effluents vapour into 
light gas, naphtha, LCGO, HCGO, CFO and a heavy recycle stream. The 
column is provided with 36 trays and, is divided into two main sections 
by the HCGO drawpan. The upper section consists of the 25 valve trays; 
lower section contains 6 bubble trays and 5 baffle trays. The quenched 
coke drum effluent vapours flows upward through the baffle trays and 
bubble trays with cooling is accomplished by the contact with the down 
flowing reflux liquid. Heavy recycle liq. is condensed and over flow 
bottom baffle trays mixed with the freshcoker feed in the tower bottom as 
described earlier.  
         Net products flows to the upper tower section to the vapour risers 
in the HCGO drawpan. This vapour consists of the products, reflux and 
steam. The heat removal and fractionation is accomplished in the upper 
section of the coker fractionator.  
 
 
WET GAS COMPRESSOR 
 
The Wet Gas Compressor (WGC) controls the System Pressure of DCU. 
The WGC compresses the wet gases from the Coker Fractionator 
Overhead Receiver in two stages. The first page of this steam turbine 
driven compressor discharges vapour at 4.5 kilogram per square 
centimeter per gram. The vapour is then cooled to 40 degree Celsius in 
the Compressor Interstage Coolers and enters the Compressor Interstage 
Drum. Hydrocarbon Vapour, Hydrocarbon Liquid and Condensed water 
are separated in the drum. The condensed sour water is recycled under 
pressure back to the inlet of the Coker Fractionator Overhead 
Condensers as wash water. The Compressor Interstage Liquid Pump 
pumps the hydrocarbon liquid back to the inlet of the Recontact Product 
Coolers where it joins the second stage discharge stream from the Wet 
Gas Compressor. 
 
The second stage of the WGC compresses the vapour from the 
Compressor Interstage Drum upto a pressure of 16.87 kg/cm*cmg where 
Page 4


DELAYED COKER UNIT 
(DCU) 
 
 
INTRODUCTION 
 
Delayed Coker unit is largestest of its type among all IOCL plants in 
India. This unit uses vacuum residue obtained from fractionation as the 
feed the main objective of this unit is to separate out middle distillates, 
and give products such as LPG and Naphtha. Coke obtained from this 
unit generates maximum amount of profit for this unit. 
 
MAIN PRODUCTS 
 
? Light Coker Gas Oil (LCGO) 
? Heavy Coker Gas Oil (HCGO) 
? Coker Fuel Oil (CFO) 
? Light Naphtha 
? Heavy Naphtha 
? Fuel Oil (FO) 
? Coke 
 
FEED CHARACTERISTICS  
 
The feed, which comes mainly, comes from fractionating column of units 
like AVU, DHDT; RFCCU is stored in DCU storage tank this is classified 
in two types: 
Hot Feed: which is at the temp. Of 240 C 
 
Cold feed: which is at temp. of 140 C 
 
There are four feed tanks in this unit. The final feed obtained before 
loading is the mixture. 
Its contains are: 
1. A mixture of hot and cold RCO (Reduced Crude Oil)  
2. The filterate obtained from 25-micron filter. 
3.  Heavy Cycle Oil from FCCU 
4. Refinery Slop 
 
Earlier this feed is used for producing TAR but since advent of DCU we 
have started using this unit to generate coke. 
 
PROCESS DESCRIPTION  
 
The delayed coking process is essentially a thermal cracking process to 
minimize refinery yields of residual fuel oil by conversion of the gas, 
naphtha, Gas Oil and Coke. The coker feed is vacuum residue from Arab 
mix crude’s or mixed supply (middle east crude). The feed stream is pre-
heated by HCGO product and pumparound exchangers and charged to 
the bottom section of the coker fractionator where it mixes with Heavy 
recycle liquid from the bottom tray. The combined coker feed and heavy 
recycle liq. is pumped to the coker heater where it is rapidly heated to 
the temp. Above the coking point. Significant coke formation in the 
heaters is therefore is avoided. 
             The heater effluents are charges to coke drum where further 
cracking reactions and subsequent polymerization takes place to form 
coke. The vapour products leave the top of the coke drum where they are 
immediately quenched with a slip stream of HCGO pumparound. The 
quenching stops the cracking and polymerization reactions. 
             Quenched coke drum effluents are charged to the coker 
fractionator where light gas, naphtha, LCGO, HCGO, CFO and heavy 
recycled liquids are separated. LCGO, HCGO and CFO are steam 
stripped to meet product specifications before cooling and final routing to 
battery limits. 
              The vapour from the coker fractionator is partially condensed 
and collected in the coker fractionator overhead receiver, which separates 
vapours, hydrocarbon liq. and sour water. Vapours are routed to the 
vapour recovery section. A portion of the hydrocarbon liq. is pumped to 
the coker fractionater top tray as reflux, and remaining portion is 
pumped to the vapour recovery section the part of the sour water goes to 
the recontact product coolers as awash, and the net production goes to 
OSBL for treatment. 
 The vapour recovery section separates the light products to 
debutanised naphtha C3/C4 LPG and Fuel gas. 
 The Wet Gas from coker fractionator overhead receiver is 
compressed into two stage wet gas compressor vapour discharge is 
partially condensed and separated in the recontact drum. The vapour 
effluents are stripped of the bulk of its H2S using lean amine in 
deethaniser feed gas scrubber. The H2S free vapour is then charged to 
the absorber section of the deethaniser primary absorber or stripper. The 
hydrocarbon liq. from the recontact drum is pumped to the stripper 
section. Mean while the sour water interstage drum and the recontact 
drum recycles to the coker fractionator over head receiver. 
 The Deethaniser separates the C2 and the lighter from the 
fractionator from the LPG and the naphtha. Absorption oil, a 
combination of coker fractionator overhead receiver hydrocarbon liquid 
and debutanised naphtha liq. recycle feeds the top tray. The deethaniser 
overhead vapour is contacted with LCGO in the Sponge Absorber to 
further reduce the loss of Naphtha. The resultant sour fuel gas is 
scrubbed free of H2S using lean amine in the fuel gas scrubber before 
routing to the sweet fuel gas to OSBL. 
             The deethanizer bottoms are routed to the debutanizer to 
separate LPG from naphtha. The product LPG is scrubbed free of H2S 
using lean amine in LPG amine scrubber before routing to the OSBL. 
 The product naphtha is cooled and routed to the naphtha splitter. 
The naphtha splitter separates the debutanised naphtha into light and 
heavy naphtha. Light naphtha product is routed to the light naphtha 
amine scrubber to remove H2S and then caustic and water wash prior to 
being routed to OSBL. 
  The heavy naphtha is caustic and water wash prior to being 
routed to OSBL. 
 
COKER FRACTIONATOR 
 
 The coker fractionator separates the coke drum effluents vapour into 
light gas, naphtha, LCGO, HCGO, CFO and a heavy recycle stream. The 
column is provided with 36 trays and, is divided into two main sections 
by the HCGO drawpan. The upper section consists of the 25 valve trays; 
lower section contains 6 bubble trays and 5 baffle trays. The quenched 
coke drum effluent vapours flows upward through the baffle trays and 
bubble trays with cooling is accomplished by the contact with the down 
flowing reflux liquid. Heavy recycle liq. is condensed and over flow 
bottom baffle trays mixed with the freshcoker feed in the tower bottom as 
described earlier.  
         Net products flows to the upper tower section to the vapour risers 
in the HCGO drawpan. This vapour consists of the products, reflux and 
steam. The heat removal and fractionation is accomplished in the upper 
section of the coker fractionator.  
 
 
WET GAS COMPRESSOR 
 
The Wet Gas Compressor (WGC) controls the System Pressure of DCU. 
The WGC compresses the wet gases from the Coker Fractionator 
Overhead Receiver in two stages. The first page of this steam turbine 
driven compressor discharges vapour at 4.5 kilogram per square 
centimeter per gram. The vapour is then cooled to 40 degree Celsius in 
the Compressor Interstage Coolers and enters the Compressor Interstage 
Drum. Hydrocarbon Vapour, Hydrocarbon Liquid and Condensed water 
are separated in the drum. The condensed sour water is recycled under 
pressure back to the inlet of the Coker Fractionator Overhead 
Condensers as wash water. The Compressor Interstage Liquid Pump 
pumps the hydrocarbon liquid back to the inlet of the Recontact Product 
Coolers where it joins the second stage discharge stream from the Wet 
Gas Compressor. 
 
The second stage of the WGC compresses the vapour from the 
Compressor Interstage Drum upto a pressure of 16.87 kg/cm*cmg where 
the vapour combines with the Interstage Drum Hydrocarbon liquid and 
the Recycled sour water from the Coker Fractionator Overhead Receiver. 
The combined stream is cooled and condensed in the Recontact Product 
Coolers and enters the Recontact Drum. Vapour from the drum flows to 
the bottom of the Deethanizer Feed Gas Scrubber. 
 
The Deethanizer Feed Gas Scrubber is a packed Column where counter 
current contact with Lean Amine removes about 90% of the H2S from the 
Vapour Stream. The Lean Amine Pumps increase the pressure of the 
Lean amine from OSBL for all of the users in the Delayed Coker Unit. 
Lean Amine from these pumps flows under flow control to the top of the 
Deethanizer Feed Gas Scrubber. The sweetened vapour steam from the 
Deethanizer Feed Gas Scrubber flows to the Feed Gas Scrubber to 
remove any entrained amine prior to entering the Deethanizer. 
 
Hydrocarbon liquids from the Recontact Drum are pumped on flow 
control with level reset to the Deethanizer Feed Coalescer to remove any 
free water prior to entering the Deethanizer. The water recycles to the 
Coker Fractionator Overhead Receiver Sour water from the Recontact 
Drum is withdrawn under level control and routed to the inlet of the 
Compressor Interstage Coolers. 
DEETHANIZER 
 
The deethanizer (Primary Absorber/Stripper) is a column with 60 total 
trays that is divided by an internal head into 2 sections of 30 trays each 
that are essentially separate columns. This design utilizes a Recontact 
drum for additional cooling on the Absorber liquid and Stripper vapour. 
The feeds, the columns themselves, and the flows to and from the 
Recontact drum are discussed first; then he flows forward to other items 
of equipment are discussed. 
 
The upper (Absorber) section receives the vapour from the Feed Gas 
Scrubber KOD at the bottom. It receive on the top tray, Tray 60, the 
Fractionator overhead liquid from the Recontact Naphtha Pumps and the 
recycled, cooled Debutanizer bottoms (Lean Naphtha) from Debutanizer 
Bottoms Pumps. 
 
These liquid streams absorb LPG from the gas feed. The liquid from the 
Tray 54 is pumped through the Deethanizer Intercooler into the 
Deethanizer water separator. The Hydrocarbon liquid flows from the top 
of the separator back to the column and enter on tray 53. The water from 
the bottom of the separator flows under interface level control on its own 
pressure back to the Coker Fractionator Overhead receiver. The bottoms 
stream from the column section flows to the Recontact Drums via the 
Compressor Interstage Coolers. 
                  
Page 5


DELAYED COKER UNIT 
(DCU) 
 
 
INTRODUCTION 
 
Delayed Coker unit is largestest of its type among all IOCL plants in 
India. This unit uses vacuum residue obtained from fractionation as the 
feed the main objective of this unit is to separate out middle distillates, 
and give products such as LPG and Naphtha. Coke obtained from this 
unit generates maximum amount of profit for this unit. 
 
MAIN PRODUCTS 
 
? Light Coker Gas Oil (LCGO) 
? Heavy Coker Gas Oil (HCGO) 
? Coker Fuel Oil (CFO) 
? Light Naphtha 
? Heavy Naphtha 
? Fuel Oil (FO) 
? Coke 
 
FEED CHARACTERISTICS  
 
The feed, which comes mainly, comes from fractionating column of units 
like AVU, DHDT; RFCCU is stored in DCU storage tank this is classified 
in two types: 
Hot Feed: which is at the temp. Of 240 C 
 
Cold feed: which is at temp. of 140 C 
 
There are four feed tanks in this unit. The final feed obtained before 
loading is the mixture. 
Its contains are: 
1. A mixture of hot and cold RCO (Reduced Crude Oil)  
2. The filterate obtained from 25-micron filter. 
3.  Heavy Cycle Oil from FCCU 
4. Refinery Slop 
 
Earlier this feed is used for producing TAR but since advent of DCU we 
have started using this unit to generate coke. 
 
PROCESS DESCRIPTION  
 
The delayed coking process is essentially a thermal cracking process to 
minimize refinery yields of residual fuel oil by conversion of the gas, 
naphtha, Gas Oil and Coke. The coker feed is vacuum residue from Arab 
mix crude’s or mixed supply (middle east crude). The feed stream is pre-
heated by HCGO product and pumparound exchangers and charged to 
the bottom section of the coker fractionator where it mixes with Heavy 
recycle liquid from the bottom tray. The combined coker feed and heavy 
recycle liq. is pumped to the coker heater where it is rapidly heated to 
the temp. Above the coking point. Significant coke formation in the 
heaters is therefore is avoided. 
             The heater effluents are charges to coke drum where further 
cracking reactions and subsequent polymerization takes place to form 
coke. The vapour products leave the top of the coke drum where they are 
immediately quenched with a slip stream of HCGO pumparound. The 
quenching stops the cracking and polymerization reactions. 
             Quenched coke drum effluents are charged to the coker 
fractionator where light gas, naphtha, LCGO, HCGO, CFO and heavy 
recycled liquids are separated. LCGO, HCGO and CFO are steam 
stripped to meet product specifications before cooling and final routing to 
battery limits. 
              The vapour from the coker fractionator is partially condensed 
and collected in the coker fractionator overhead receiver, which separates 
vapours, hydrocarbon liq. and sour water. Vapours are routed to the 
vapour recovery section. A portion of the hydrocarbon liq. is pumped to 
the coker fractionater top tray as reflux, and remaining portion is 
pumped to the vapour recovery section the part of the sour water goes to 
the recontact product coolers as awash, and the net production goes to 
OSBL for treatment. 
 The vapour recovery section separates the light products to 
debutanised naphtha C3/C4 LPG and Fuel gas. 
 The Wet Gas from coker fractionator overhead receiver is 
compressed into two stage wet gas compressor vapour discharge is 
partially condensed and separated in the recontact drum. The vapour 
effluents are stripped of the bulk of its H2S using lean amine in 
deethaniser feed gas scrubber. The H2S free vapour is then charged to 
the absorber section of the deethaniser primary absorber or stripper. The 
hydrocarbon liq. from the recontact drum is pumped to the stripper 
section. Mean while the sour water interstage drum and the recontact 
drum recycles to the coker fractionator over head receiver. 
 The Deethaniser separates the C2 and the lighter from the 
fractionator from the LPG and the naphtha. Absorption oil, a 
combination of coker fractionator overhead receiver hydrocarbon liquid 
and debutanised naphtha liq. recycle feeds the top tray. The deethaniser 
overhead vapour is contacted with LCGO in the Sponge Absorber to 
further reduce the loss of Naphtha. The resultant sour fuel gas is 
scrubbed free of H2S using lean amine in the fuel gas scrubber before 
routing to the sweet fuel gas to OSBL. 
             The deethanizer bottoms are routed to the debutanizer to 
separate LPG from naphtha. The product LPG is scrubbed free of H2S 
using lean amine in LPG amine scrubber before routing to the OSBL. 
 The product naphtha is cooled and routed to the naphtha splitter. 
The naphtha splitter separates the debutanised naphtha into light and 
heavy naphtha. Light naphtha product is routed to the light naphtha 
amine scrubber to remove H2S and then caustic and water wash prior to 
being routed to OSBL. 
  The heavy naphtha is caustic and water wash prior to being 
routed to OSBL. 
 
COKER FRACTIONATOR 
 
 The coker fractionator separates the coke drum effluents vapour into 
light gas, naphtha, LCGO, HCGO, CFO and a heavy recycle stream. The 
column is provided with 36 trays and, is divided into two main sections 
by the HCGO drawpan. The upper section consists of the 25 valve trays; 
lower section contains 6 bubble trays and 5 baffle trays. The quenched 
coke drum effluent vapours flows upward through the baffle trays and 
bubble trays with cooling is accomplished by the contact with the down 
flowing reflux liquid. Heavy recycle liq. is condensed and over flow 
bottom baffle trays mixed with the freshcoker feed in the tower bottom as 
described earlier.  
         Net products flows to the upper tower section to the vapour risers 
in the HCGO drawpan. This vapour consists of the products, reflux and 
steam. The heat removal and fractionation is accomplished in the upper 
section of the coker fractionator.  
 
 
WET GAS COMPRESSOR 
 
The Wet Gas Compressor (WGC) controls the System Pressure of DCU. 
The WGC compresses the wet gases from the Coker Fractionator 
Overhead Receiver in two stages. The first page of this steam turbine 
driven compressor discharges vapour at 4.5 kilogram per square 
centimeter per gram. The vapour is then cooled to 40 degree Celsius in 
the Compressor Interstage Coolers and enters the Compressor Interstage 
Drum. Hydrocarbon Vapour, Hydrocarbon Liquid and Condensed water 
are separated in the drum. The condensed sour water is recycled under 
pressure back to the inlet of the Coker Fractionator Overhead 
Condensers as wash water. The Compressor Interstage Liquid Pump 
pumps the hydrocarbon liquid back to the inlet of the Recontact Product 
Coolers where it joins the second stage discharge stream from the Wet 
Gas Compressor. 
 
The second stage of the WGC compresses the vapour from the 
Compressor Interstage Drum upto a pressure of 16.87 kg/cm*cmg where 
the vapour combines with the Interstage Drum Hydrocarbon liquid and 
the Recycled sour water from the Coker Fractionator Overhead Receiver. 
The combined stream is cooled and condensed in the Recontact Product 
Coolers and enters the Recontact Drum. Vapour from the drum flows to 
the bottom of the Deethanizer Feed Gas Scrubber. 
 
The Deethanizer Feed Gas Scrubber is a packed Column where counter 
current contact with Lean Amine removes about 90% of the H2S from the 
Vapour Stream. The Lean Amine Pumps increase the pressure of the 
Lean amine from OSBL for all of the users in the Delayed Coker Unit. 
Lean Amine from these pumps flows under flow control to the top of the 
Deethanizer Feed Gas Scrubber. The sweetened vapour steam from the 
Deethanizer Feed Gas Scrubber flows to the Feed Gas Scrubber to 
remove any entrained amine prior to entering the Deethanizer. 
 
Hydrocarbon liquids from the Recontact Drum are pumped on flow 
control with level reset to the Deethanizer Feed Coalescer to remove any 
free water prior to entering the Deethanizer. The water recycles to the 
Coker Fractionator Overhead Receiver Sour water from the Recontact 
Drum is withdrawn under level control and routed to the inlet of the 
Compressor Interstage Coolers. 
DEETHANIZER 
 
The deethanizer (Primary Absorber/Stripper) is a column with 60 total 
trays that is divided by an internal head into 2 sections of 30 trays each 
that are essentially separate columns. This design utilizes a Recontact 
drum for additional cooling on the Absorber liquid and Stripper vapour. 
The feeds, the columns themselves, and the flows to and from the 
Recontact drum are discussed first; then he flows forward to other items 
of equipment are discussed. 
 
The upper (Absorber) section receives the vapour from the Feed Gas 
Scrubber KOD at the bottom. It receive on the top tray, Tray 60, the 
Fractionator overhead liquid from the Recontact Naphtha Pumps and the 
recycled, cooled Debutanizer bottoms (Lean Naphtha) from Debutanizer 
Bottoms Pumps. 
 
These liquid streams absorb LPG from the gas feed. The liquid from the 
Tray 54 is pumped through the Deethanizer Intercooler into the 
Deethanizer water separator. The Hydrocarbon liquid flows from the top 
of the separator back to the column and enter on tray 53. The water from 
the bottom of the separator flows under interface level control on its own 
pressure back to the Coker Fractionator Overhead receiver. The bottoms 
stream from the column section flows to the Recontact Drums via the 
Compressor Interstage Coolers. 
                  
 The lower (Stripping) section of the Deethanizer strips ethane and lighter 
components from the LPG and Naphtha. It receives the liquid from the 
Recontact Drum on its top tray, tray 30. 
             
The Stipping section is configured with 3 Reboilers. At the bottom of the 
column, the liquid from the tray 1 flows preferentially to the shell side of 
the Deethanizer Bottoms reboiler by thermosiphon action. This Reboiler 
uses LCGO Pumparound as heating medium, and is designed for 90% of 
the bottoms reboil duty. Liquid from the bottom sump of the column 
flows to the shell side of the Deethanizer Bottoms Steam Reboiler by 
thermosiphon action. This Reboiler uses MP steam as the heat source, 
and is designed for 50% of the required bottom reboil duty although it is 
expected to do only 10%. The additional capacity provides flexibility to 
handle start-up and upset conditions. There is a partial draw from Tray 5 
liquid to the Deethanizer Side Reboiler under flow control by 
thermosiphon action again. The hot Debutanizer Bottoms Stream is the 
heating medium. The vapour from the top section Flows to the Recontact 
Drum via the Compressor Interstage coolers. 
 
SPONGE ABSORBER 
 
Deethanizer Overhead Vapour flows from the top of the absorber section 
to the bottom of the Sponge Absorber a simple absorber with 21 trays. 
Cooled lean sponge-oil (LCGO) from the LCGO stripper is fed to the top of 
the Sponge Absorber primarily to reduce the loss of Naphtha in the 
Deethanizer Overhead Vapour Stream, but also to absorb a little more 
LPG. The flow of the lean sponge oil was discussed previously with the 
flow of LCGO Product. The Sponge Absorber Overhead Vapour (Sour Fuel 
Gas) is routed to the fuel gas Scrubber for H2S removal. Rich Sponge oil 
from the Sponge absorber bottoms is used to cool the lean sponge oil 
(Light Coker Gas Oil) in the LCGO Lean/Rich Sponge Oil Exchangers and 
is returned to the Coker Fractionator. 
 
Deethanizer Bottoms liquid flows by its own pressure to the Debutanizer 
under flow control reset by level control in the bottom of Stripper section 
of the Deethanizer. 
 
DEBUTANIZER 
 
The debutanizer column is provided with 36 trays and separates its feed 
into an overhead product of C3/C4 LPG and bottom product of 
Debutanized Naphtha. Overhead vapour is totally condensed against 
cooling water in the Debutanizer Overhead Condensers and is routed to 
the Debutanizer Overhead receiver.