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CHAPTER 1
GENERAL
1.1 INTRODUCTION
The Crude Distialltion Unit of Bongaigaon Refinery and Petrochemicals Ltd is designed to
process 1.35 million tonnes per year of crude oil mi comprising !ahar"atiya#La"$a#
Rudrasagar in %&'1('13 ratio )y $eight. The Unit ia also capa)le of handling any of the
follo$ing feeds'
i*La"$a and Rudrasagar crudes in %+',+ ratio )y $eight.
ii*!ahar"atiya crude alone.
-u)se uent necessary modifications in the units ha/e )een done for processing of lo$
sulphur imported light Crude. Because of this0 the units are capa)le of processing lo$
sulphur Ra//a Crude as $ell.
The unit consists of the follo$ing sections'
Topping0-ta)ili ation and !aptha -plitters. The product of the unit are 2uel as0 -R !aptha0
LP 0 Reformer feed !aptha0 4ero component0 "ero# 0 4ero# 0 as 6il and Reduced Crude
oil. 2uel as is used as a fuel in the process heaters. 6ther unit products are either further
processed or )lended to produce finished products.
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1.2 STREAM FACTOR:
The on#stream hours for the operation of the Crude Distillation Unit is &+++ hours per
year.
1.3 DESIGN DATA:
The Crude Distillation Unit has )een designed to process 1.35 77TP8 of 8ssam crude. The
unit is also capa)le of handling lo$ sulphur crude li"e Ra//a crude0 Bonny light crude0La)uan crude etc.
Table 1.1 Typical Fee C!a"ac#e"i$#ic$
-l. !o Characteristics Units 8ssamcrude
Ra//a crude
1 Density 915 oC gm:cc +.&;
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Table 1.1 %c&'# .(
13 Charc. 2actor 4U6P 11.3; 11.(
1, ield Pattern Typical*C1 # C,C5 # 11+6C11+ # 1,56C1,5 # 1&+6C1&+ #
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PROCESS DESCRIPTION
2.1 GENERAL
Crude distillation unit is designed to process 1.3577TP8 of 8ssam Crude 6il produced
)y 6il ndia Limited 6! C.
Design TEput ,+5+ 7T:day
7inimum TEput
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4ero# CR is used as heating medium for sta)iliser re)oiler.The purpose of sta)ili er is to
sta)ili e naptha and to produce li uefied petroleum gas LP *.
LP $ithdra$n from -ta)iliser reflu drum is first $ashed $ith caustic and then $ashed
$ith $ater and then sent to Forton sphere for storage.
The sta)ili ed naptha is further split into light naptha 5+#11+*deg.C and hea/y naptha 11+#
1&+* deg.C in -plitter# . Feating medium for splitter# is 4ero# CR.
-plitter# )ottom is further split into reformer feed naptha 11+#1,;* deg.C and 4ero
component.Re)oiler heating medium for splitter# is Reduced Crude 6il from main
fractionator column.
8 uous ammonia is inGected in o/erhead /apour in main fractionator to com)at corrosion due
to hydrochloric acid /apour.
-ide strippers are used for "ero# 0"ero# and gas oil for stripping lighter ends. -tripping
steam superheated to a)out ,++deg. C is used as stripping media in all three strippers.
2.2 FEED SUPPL)
Crude oil is recei/ed )y pipeline and stored in four floating roof storage tan"s T4#18:B:C:D
each ha/ing a nominal capacity of
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rude oil to the Unit. !ormally only one feed pump $ill run. 2ailure of the feed pump $ill
cause a drop in discharge line pressures $hich $ill )e indicated in the control room audio#
/isually0 hence the spare feed pump $ill start automatically. There is a pro/ision also for
stopping any of these feed pumps through a push )utton and selector s$itch.
Temperature ndicator0 2lo$ Recorder and a 2lo$ ntegrator are pro/ided on the feed line
$ithin the )attery limit ahead of the crude preheat e changer train.
2.3 FEED PREHEATING
Crude oil is first preheated in a series of ele/en Feat e changers /i H#310H#330H#,0H#
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2., DESALTER
The Crude Desalter is a process /essel that remo/es $ater and there)y salt from the
crude. The $ash $ater is mi ed $ith crude $itd into the Crude Desalter. Demulsifying
chemicals are also added at this stage to pre/ent formation of ne$ emulsion and to assist in
)rea"ing do$n any emulsions that e ist $ith the crude. Thus0 Desalter /essel0 in addition to
allo$ing a certain residence time for the crude oil that allo$s separation of the $ater $ith the
help of gra/ity0 also pro/ides an electrostatic field to assist the )alance of $ater particles to
coalesce under the electrical charge and thus separates from the crude oil. The effluent $ater is $ithdra$n from the /essel under interface Le/el Control and the desalted and dehydrated
crude is $ithdra$n from the /essel under )ac"pressure.
2.,.1 C"- e De$al#i'
Crude oil )rings salts along $ith it. Particularly those of sodium0 7agnesium etc.0metals li"e
8rsenic0 =anadium etc and mud. 8lthough these are present only in small amounts0 their
presence can result in serious pro)lem in do$n stream e uipments /i . heat e changers0
heaters and columns. Fence the need of their remo/al is important )efore processing.
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8t high temperatures0 7agnesium chloride decomposes and forms Fydrochloric acid0 $hich
corrodes trays in the top section of column and tu)es of o/erhead Condensers etc. The
presence of calcium and -odium salts can cause plugging of heat e changers and heater
tu)esI there)y rapidly reducing heat transfer coefficients. The presence of 8rsenic acts as a
poison to Platinum catalysts that may )e used in do$n stream process units.
Presence of these salts also promotes co"e formation in heater tu)es $hich results in
increased pressure drop as $ell as less heat transfer rates. The e cessi/e co"e formation
result in escalation of hot spots on heater tu)es $hich can ha/e serious and disastrous
conse uences for heater tu)es. 8t high temperatures0 salts in crude oil sho$ a tendency to
deposit along heat e change surface of the e uipment.
Caustic inGection in crude is done to neutrali e acids present in crude and con/ert them into
salts. These salts are then remo/ed )y Desalter $ater in Desalter. Brine is also associated $ith
crude as emulsions. To )rea" these light emulsions0 Demulsifier is added. n fact )oth caustic
solution and Demulsifier is added into the crude )efore the preheat train.
Desalter utilises electronic elements at ,15 /olts to coalesce and separate $ater from oil for
reducing the salt content in crude oil so that it is $ithin accepta)le and specified limits in
desalted crude. ?hen oil $ater mi ture enters the high /oltage electric field0 it separates intot$o phases in Desalter. The oil phase floats on top and o/erflo$s. ?hile $ater $ith its
dissol/ed salts0 metals0 mud and ron o ides settles do$n at the )ottom. Thus oil from
Desalter flo$s to the rest of the preheat train.
0
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2.,.2 De$al#e" e$$el De$c"ip#i&'
This is a single stage Desalter unit.Performance of it is as follo$s'
Hlectrical po$er re uirement J ,15=:5+ hert : 3 phase
Po$er Demand J ;54/a ma *
6perating Temperature:Pressure J 1
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2.* FURNANCE
Crude 6il from preheating e changers is further heated and partially /apori ed in
furnace 2#10 the temperature rising from
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2eed coming from the furnace enters the column in the flash one under tray 5. The flash
one temperature is maintained at 35& deg .C .-tripping steam is introduced at the )ottom of
the column to remo/e lighter fractions from the )ottom product i.e reduced crude oil.
2ractionator flash one temperature and pressure is normally maintained at a)out 35+
deg. C and 1.3 4g : s cm respecti/ely .
n Crude distillation column C# * 0the crude oil fractionates into num)er of distillates and
)ottom product .
Table 2.1 CDU P"& -c# a' i#$ #&p$ i$#illa#i&' "a' e$ '
PRODUCT RANGES2uel gas +#5+ deg.C
LP %+#%5 deg.C-R! 55#1++ deg.CR2! 11+#1,5 deg.C
4ero comp 1,5#1&+ deg.C4ero# 1&+#
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column from tray K
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2.0 STA4ILI5ER
The Crude Column o/erhead product BP# 1&+deg.C cut* is sta)ili ed )y remo/ing the gas
fraction up to C, in the sta)ili er column C#5.The -ta)ili er column has 3+ )u))le caps
/al/e trays . The tray material is of car)on steel and /al/es are of Cr steel.
The feed to the sta)ili er is preheated in 4# heat e changer H#(8 and 4# heat e changer H#
1+ and H#
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2. .1 Fi"$# Nap#!a Spli##e"
The sta)ili ed naptha is split in the 1 st !aptha -plitter C#% into an o/erhead light naptha
and a )ottom product. The 1 st !aptha -plitter C#% has 3+ )u))le caps /al/e type trays.
The tray material is of car)on steel . -ta)ili ed naptha from the )ottom of the -ta)ili er is fed
to C#% at tray 15.
The o/erhead /apors at a temperature of (,#(& deg.C are condensed in H#1%. The condenser
li uid is ta"en from the reflu drum and a part is sent to the top of the column as reflu and
)alance is routed through cooler H#
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preheating the crude and cooled in H#1( and routed as 4ero component to storage C#;
)ottom.
2. LPG CAUSTIC 6ASH
Caustic is inGected into crude to con/ert all the chlorides eg. 7gCl
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CHAPTER 3
OPERATION OF CDU
3.1 INTRODUCTION
There is a large amount of preparatory $or" performed )y the operating cre$ to operate the
plant efficiently. 8 planned chec" of all units not only ensures smooth start up )ut also
ac uaintance $ith the operations of /arious sections comprising of /aried /ariety e uipments
to run them. -tart up is critical and includes operation of each e uipment .6peration includes
proper inspection of /essels 0columns 0piping and instruments.
3.2 FUNCTIONAL TESTS
8ll motors and pumps including dosing pumps $ill undergo functional test to chec" their
performance.
3.2.1 M&"$
Hach motor should )e chec"ed and started to ensure that it has the correct direction of
rotation .The motor speed should )e chec"ed to ensure that rpm is correct. 8fter a short run
each )earing should )e felt to ensure that it is free and not o/erheated.
3.2.2 P-7p$
enerally the pump is opened and chec"ed to ensure that it contains no foreign material.
Cleanliness of suction line and installation of fine strainer should )e ensured.
1+
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3.3.3 I'$#"-7e'#$
% i ( C&'#"&l al8e$ '
?e should ma"e certain that the de)ris are not lodged in the control
/al/e.Hach control /al/e installation should )e chec"ed for full tra/el of the
/al/e. t should also )e ensured that each control /al/e is at proper position
close or open* at right air pressure.
% ii( Di99e"e'#ial p"e$$-"e #"a'$7i##e"$ a' "ecei8e"$:
6rdinarily these should )e cali)rated locally against a $ater column and the
cali)ration chec"ed at the recei/er 0$hich may )e recorder or indicator.
% iii( Ti !#'e$$ #e$#:
The purpose of this test is to chec" the tightness of flanges0 Goints0 manholes
etc. This test $ill )e done $ith steam. Before conducting this test0 all the
safety /al/es should )e placed in position and properly lined up only after
testing.
3., OPERATING PROCEDURE
The Crude Distillation Unit is steam purged in sections to free all /essel and piping of air.
8fter displacing air from the system0 the hydrocar)on feed $ill )e ta"en in the unit.
1/
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Unit charge pump located in offsites ta"es suction from crude oil tan"s and deli/ers into the
crude distillation column. 8fter )uilding up ade uate le/el in the column0 circulation is
esta)lished.
Feater is fired and transfer temperature gradually raised to normal /alue of 355 deg.C.
=arious product streams are $ithdra$n and circulating reflu is adGusted according to the
temperature in the column.
6/erhead naptha product is routed to sta)ili er $here lighter ends up to )utane are
remo/ed. The sta)ili ed naptha is routed to 1 st splitter.C5#11+deg.C cut is o)tained as
o/erhead and sent to naptha storage. The )ottom product is routed to < nd splitter $hich also
$or"s in a similar manner. Feating medium of re)oiler $ill )e reduced crude.11+#1,5 deg.C
cut is o)tained as o/erhead product of < nd splitter and pumped to storage as Reformer feed.0
the )ottom product is 1,5#1&+deg.C cut $hich is routed to 4ero# storage tan". 8fter
sta)ilising the unit 0the inGection of chemicals is started.
3.* E UIPMENT OPERATING PROCEDURE
Fi . 3.1 Ce'#"i9- al P-7p
1( CENTRIFUGAL PUMPS:
8 centrifugal pump is a rotodynamic pump that uses a rotating impeller toincrease the /elocity of a fluid. Centrifugal pumps are commonly used to mo/e
10
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li uids through a piping system. The fluid enters the pump impeller along or near to
the rotating a is and is accelerated )y the impeller0 flo$ing radially out$ard into a
diffuser cham)er0 from $here it e its into the do$nstream piping system.
8 centrifugal pump $or"s )y the con/ersion of the rotational "inetic energy0typically from an electric motor or tur)ine0 to an increased static fluid pressure. This
action is descri)ed )y Bernoulli s principle. The rotation of the pump impeller
imparts "inetic energy to the fluid as it is dra$n in from the impeller eye centre* and
is forced out$ard through the impeller /anes to the periphery. 8s the fluid e its the
impeller0 the fluid "inetic energy /elocity* is then con/erted to static* pressure due
to the change in area the fluid e periences.Centrifugal pumps are used in the crude distillation unit e cept Crude oil charge
pump0 -ta)ili er feed pump and sta)ili er reflu pump. 8ll mechanical Go)s are
completed. Cooling $ater pro/ision and steam is opened for any dead cooling in the
pumps. Then oil le/el is chec"ed and flushing is done if oil is dirty or contains any
foreign material. The suction /al/e is opened and motor is energi ed .Pump is started
and stopped immediately. Discharge pressure is chec"ed and opened slo$ly.
2( HEAT E;CHANGERS
8 heat e changer is a de/ice )uilt for efficient heat transfer from onemedium to another. The follo$ing are the /arious type of heat e changers0 in
CDU.
1a* Feat H changers'
)* Re)oilers'c* Condensers'd* Coolers'
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Ope"a#i' $#ep$ '
Cooling medium /ent /al/e is opened. Drain /al/e and flushing oil /al/es areclosed. !o$ cooling medium /ent /al/e is opened0 li uid is allo$ed to come out thenagain closed. Then open the cooling medium outlet /al/e and fully open the inlet/al/e also. Feating side /ent /al/e is opened and all flashings are shut off. 2inally thenormal inlet and outlet temperatures are chec"ed
3.+ NORMAL OPERATING CONDITIONS
FURNANCE E UIPMENT NO: 11F< 1(
Table 3.1 Ope"a#i' 8a"iable Da#a$ &9 9-"'ace
SER ICE CRUDE OIL STEAM
Total duty0774Cal:Fr
1(.3 +. /( Te7pe"a#-"e p"&9ile:
Column top temperature 15, deg.CRe)oiler outlet temperature 1(% deg.C
2eed temperature 1;< deg.C
23
2ig 3.1 =arious 6perational e uipments
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Differential pressure transmitter Differential pressure recei/ers
Centrifugal pump Control /al/e
Feat e changer
2,
CHAPTER ,
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UALIT) CONTROL OF CDU PRODUCTS
-amples are ta"en at regular inter/als to see if the desired specifications are met or some
correcti/e solutions are necessary .-ometimes samples are ta"en to find out the effect of
certain changes )rought a)out in the operating conditions. The samples ha/e to undergo
chemical and physical tests.
,.1 TESTS ON LPG
2ollo$ing tests are carried out'
1. Density test
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2or copper strip corrosion0 LP samples are chec"ed )y la)oratory. To ensure cu strip
uality 0 LP samples are chec"ed $ith lead acetate solution in e/ery shift. n the LP $ash
section 0 replenishment of spent caustic $ith fresh caustic is done as per La).Report.
?hene/er LP fails in Cu strip0 different parameters are adGusted. 8lso0 the
recirculation caustic and $ater is replaced $ith fresh ma"e#up )ased on cu strip.
,.2 TESTS ON SRN
1. Density test
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C
Cu#corfrosion 9 3& deg. C for 1hr.0 deg. C
!ot $orse than 1
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Table *.2 Typical U#ili#ie$ C&'$-7p#i&' pe" 7&'#! :
-l. !o. UT L T H- C6!-U7PT 6!
1. 2uel 6il (&& 7T
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3. Caustic -trength 1+@? -
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Study of Process andOperations of Crude DistillationUnit of IOCL-BGR
Kirti Vard an
A4STRACT
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Crude distillation unit of BRPL has an annual crude processing capacity of 1.35 77TP8.
The main products of CDU are LP 0 -traight Run !aptha0 Reformer 2eed !aptha0 4ero# 0
4ero# 0 4ero component0 as oil and Reduced Crude
6il. t $as commissioned in 1(;(.
This report discusses the /arious aspects of an operating refinery /i ' process0 operations0
maintenance 0 uality control 0 of crude distillation unit CDU* of B.R.P.L I supported )y
/arious ta)les0 data and figures.
During the proGect $or"0 understood the $or"ing and operation of this unit. Plant
operations included operating procedures of distillation columns0 pumps0
2urnaces0 control /al/es and /arious instruments.
.