Refinery Operations.doc

8/11/2019 Refinery Operations.doc

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Refinery Operations

The previous section described the manner in which the crude oil is received, passedthrough the various units to produce finished products or finished components that areblended to make finished products. The purpose of this section is to describe in a little moredetail how each of these processing is accomplished and its overall work by practicalapplication of the many principles covered earlier. Refinery has 13 process units and each has a specific function to purify or to rearrange themolecular structure or crack the molecules to make more desirable products. In all the unitsgreat emphasis is placed on the conservation of heat by the use of heat exchangers.The steam used in the process units is served by three headers under different pressures.The high pressure !.".# steam header will have a pressure of 31$% kg. per s&. cm., themedium pressure '. ".# steam will be under pressure of 1()* kg. per s&. cm. and the lowpressure +. ".# steam will be under a pressure of 3$* kg. per s&. cm. The air re&uired forpneumatic instruments and control valves and the cooling water are supplied from a centralsource for all the plants. Crude distillation unit - Plant No. I.The crude unit is the starting point for all refinery operations. The separation of crude oilinto raw products is accomplished in the crude unit by fractional distillation in fractionatingcolumns, based on their distillation range. The process does not involve any chemicalchanges. The unit consists of an electrostatic desaker, an atmospheric distillation tower anda two stage vacuum distillation sections. The unit is designed to process arius crudehaving a specific gravity of ($-** at a rate of 3 -)/ m3 0hr.

schematic representation of the crude oil and product flow is attached. The two crude feedpumps, located near the crude storage tanks, supplies the feed to the unit. The feed to theunit is passed through a desalter where the chlorides of calcium, magnesium and sodiumare removed. These salts form corrosive acids during processing and therefore are

detrimental to process e&uipments. 2y in ecting water to the crude oil stream these saltsare dissolved in the water and the solution is separated from the crude by means of anelectrostatic separator in a large vessel. The electrically charged grids coalesces the waterand aids separation from the crude. fter desalting the crude is heated through a series ofheat exchangers and then by a furnace to a temperature of 34356 and admitted to the flash7one of the atmospheric distillation tower.

8our fractions are separated in the atmospheric tower. The overhead vapours are condensedin a two stage system. The condensed li&uid from the first stage is used as reflux to thetower. The second stage li&uid together with the compressed and condensed vapours fromthe second stage is collected in the stablili7er feed accumulator. The li&uid in the stabili7erfeed accumulator is the feed to the 9apour Recovery unit. The uncondensed vapours fromthe stabili7er feed accumulator is routed to fuel gas system after removal of ! % : in thesulphur plant. The other three products separated are heavy naphtha, kerosene and diesel.The heavy naphtha is drawn from tray %- and is steam stripped to improve flash. The
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ma ority of this product is line blended with diesel from !: desulphurisation unit "lant ;o.*# and raw diesel to make finished !igh :peed iesel oil. small amount of the heavynaphtha is sent to 'erox treater. This treater oxidises mercaptans to disulphi)des therebyeliminating the unpleasant odour. The treated stream is used for blending hen this unit is shut down, kerosene is cooled and sentto intermediate storage tank through the kerosene product cooler at "lant ;o. .

iesel oil is drawn from plate 1(. pproximately *(? of the diesel oil is routed to !. :. .!ydrodesulphuriser "lant *# after heat exchange with crude and the balance is cooled andblended with the desulphurised diesel oil to produce !: product. >hen "lant ;o. * is shutdown, the total stream is cooled in the product cooler at "lant * and sent to storage.The stripped overhead li&uid streams from kerosene hydrode)sulphuriser, !: desulphuriserand lube oil hydrofinisher are sent to the atmospheric distillation tower after separating thewater in a dewatering drum. The hot reduced crude from the bottom of atmospheric distillation tower is furtherfractionated in the two stage vacuum distillation section. The vacuum maintained in thesefractionators makes it possible to fractionate the reduced crude at much lowertemperatures. 2ut for this vacuum, the higher temperatures re&uired to fractionate reducedcrude will result in cracking of the products. The reduced crude from atmospheric towerbottoms is further heated in presence of steam in the first stage vacuum heater andintroduced into the first stage vacuum tower. Three side)stream products spindle oil, lightneutral and intermediate neutral and an overhead product@gas oil are separated in the firststage vacuum tower. :pindle oil, light neutral and intermediate neutral are sent to the +ubeAil Bxtraction plants as feed stock or to storage. The distillates in excess of the lube oilre&uirements is sent hot as charge stock to 9acuum istillate esulphuriser "lant 13# priorto thermal cracking of these intermediate products. The gas oil is routed to thermal crackerfeed tank or directly to "lant 13. The bottoms product from first stage vacuum tower is reheated along with steam andfractionated to yield heavy neutral stream. 8lash 7one vapours of the second stage vacuumtower pass through a demister pad to prevent entrainment of asphaltenes into the heavyneutral stream. The heavy neutral stream is cooled and sent to intermediate storage tank ascharge to 8urfural

Extraction unit (Plant 8). part of the second stage vacuum tower bottoms, vacuum residuum, is cooled and sent to

2itumen ir 2lowing Cnit "lant D#. nother part is charged to the 9isbreaker "lant /# andthe balance is routed to light fuel oil blending. Plant 2 - Vapour Reco ery !nit
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The vapour recovery unit consists of two sections a# vapour recovery section and b# meroxtreating section. The function of vapour recovery section is to separate gas, +"E, lightgasoline and light naphtha from the overhead naphtha of atmospheric tower in plant 1. Themerox treating section is for sweetening of +"E, a mixture of light gasoline and light crackedgasoline for gasoline blending, a mixture of light naphtha and heavy naphtha for


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are oxidised to disulphides. The regenerated 'erox solution is then pumped to the extractor.The extracted disulphides are pumped to the crude feed in "lant I. The light gasoline 'erox treater is designed for a feed rate of /)- mGhr. consisting of amixture of light gasoline from vapour recovery section and light cracked gasoline fromvisbreaker fractionacor in "lant /. The 'erox solution is regenerated in the common systemfor +"E and 'erox. The treated gasoline is sent to storage and is blended with Reformatefrom "lant 3 to make motor gasoline. The 'erox treatment of light naphtha is a sweetening process. The 'erox catalyst isimpregnated in a bed of activated charcoal using methanol and made alkaline by circulatingcaustic soda solution as a preparation to receive the feed stock. This treating unit isdesigned for a feed rate of $% mGrir. consisting of light naphtha from 9apour Recoverysection and heavy naphtha from "lant I. The treated naptha is sent to storage and laterblended with other components to make


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The platforming unit converts the low octane naphtha from Cnifiner to high octanereformate by convertion of straight chain compounds into cyclic compounds. The reaction isendothermic and therefore the feed stream is reheated after each reactor. The unit consistsof three reactors operating in series with heaters before each reactor, a product separator, adebutini7er and hydrogen recycle facilities. The feed from the Cnifmer is mixed with hydrogen, passed through three sets of heatersand reactors. The reactor effluent from the final reactor is cooled by heat exchange and issent to a separator drum. The reaction produces hydrogen which is separated from thehydrocarbons and is partly recycled to the feed stream and balance is routed to the Cnifiner.The separated effluent is then sent to a debutini7er. The overhead product of debutini7er issupplied as a part of feed gas to hydrogen plant and the bottom product, the reformate is

sent to storage tank.

Plant $ -%erosene &ydrodesulp'urisation !nit The purpose of the plant is to reduce sulphur content of the raw kerosene by treating withhydrogen. uring the treatment some of the aromatic hydrocarbons are converted tocycloparaffins which results in an increase in the smoke point. The plant is designed to

process /%)* nG0hr. of raw kerosene from "lant I or from intermediate storage. Thehydrogen re&uirement is met by the hydrogen rich gas from !: A desulphuriser andbalance is made up from "lant II. The feed mixed with hydrogen is passed through thereactor after heating to the re&uired reaction temperature in the charge heater. fterseparation of the reaction gases and excess in a two stage separators, the effluent is sent tothe stripper. The stripper bottoms is the finished product which is sent to the productstorage after cooling. The hydrogen rich gas from the separator is sent as feed to hydrogenplant or to fuel gas after recovering the !i : by amine treating in sulphurplant. Plant - iesel Oil &ydrodesulp'urisation Plant The function of this plant is to desulphurise the part of the diesel approximately *(?#produced in "lant I by catalytic hydrogenation. The desulphurised diesel and the balance ofthe raw dieseland heavy paphtha are line blended in this unit to produce !: product. The plant isdesigned to process 31$* mGhr. of feed. The hydrogen gas is supplied from Cnifmer, +ube oil!ydrofinisher and9acuum istillate ! : units. The hydrogen re&uirement over and above that supplied bythese units is met from the hydrogen plant.The feed mixed with recycle gas and make up hydrogen is heated in a furnace and passedthrough the reactor. The effluent from the reactor is cooled and the excess hydrogen and


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other products of reaction are separated in a separator drum. The li&uid Is steam stripped ina stripper. The overhead system of this stripper is common to the stripper in "lant 13 also.The desulphurised diesel is yielded from the bottom of the stripper. The hydrogen richrecycle gas from the separatordrum is treated with 1*? 'B solution to remove !i : before recycling. portion of theseparator off)gas is sent to "lant * as treat gas. The li&uid from the overhead system of the

stripper is sent to I6)%% in "lant I and the vapours to the overhead system of atmospherictower.

Plant * - Vis+rea,er and 'er#al Crac,erThe function of the 9isbreaker and Thermal cracker units is to process high viscosity9acuum Residuum and desulphurised vacuum distillate from "lant 13 respectively into lowerviscosity products. This process therefore helps to upgrade the product directly by producinglow viscosity gas oils and naphthas. 9isbreaker is essentially a thermal cracking unitoperated under mild condition i.e., lower severity. In a thermal cracking unit a heavy oil isheated and maintained at a high temperature for a period of time. This breaks up the largermolecules into smaller molecules falling in the range of gas to gas oils. The maindisadvantage of the process is that the products obtained by thermal cracking tend tobecome unstable due to the olefihic compounds. The unit consists of a thermal cracker furnace, a visbreaker furnace, a visbreaker flashtower, a common fractionator and other facilities.The products obtained areF@+ight gasoline .... %)3 m30hr6racked naphtha .... 3)- m30hr.6racked gas oil .... 3*)% m30hr.Thermal tar ... 13D m30hr.9isbreaker tar ... 31) m30hr.

The design feed rate for the Thermal 6racker is D.( m30hr of a mixture of vacuumdistillates from "lant 13 and feed rate of the 9isbreaker *(./ m30hr. of 9acuum Residuumfrom "lant I. The Thermal cracker feed is heated to a temperature of 4356 under a backpressure of 1-./ kg0cm% and is admitted to the visbreaker fractionator. The furnace isdesigned to provide sufficient residence time for effecting the cracking of the molecules. Thevisbreaker feed is heated to atemperature of 4356 under a pressure of 1*.1 kg0cm%. The visbreaker tar is separatedfrom the furnace effluent in the visbreaker flash tower. The overhead vapour of the flashtower is routed to the visbreaker fractionator for fractionation. The visbreaker tar is routed

to !eavy 8uel after adding cracked gas oil as cutter stock to maintain the desired viscosity.The product yielded from the 8ractionator are thermal tar, cracked gas oil, cracked naphthaand cracked light gasoline. The thermal tar is cooled in a tempered water cooling system in"lant I and is routed to light fuel oil rundown. The gas oil draw off from the tower is used forthree different purposes.They area# to provide &uench for the furnace effluents of both furnaces, b# to provide lean oil toabsorber to recover the gasoline fractions in the gas and c# to provide tray wash for thevisbreaker fractionator. The heat available in these streams are utilised to produce steam or


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to heat up other streams. The net gas oil is steam stripped and routed to the light fuel oilrundown along with thermal tar. 6racked naphtha is drawn from tray ;o. 14 and is sent tothe Cnifiner as feed stock. The overhead vapours are condensed and collected in thefractionator overhead drum. The li&uid is pumped to a debutini7er tower and the gases arerouted through an absorber to recover the gasoline fractions. The lean oil for the absorberare gas oil and naphtha. The absorbed gases are routed to fuel gas system through "lant

1%. The debutini7er tower yields light cracked gasoline as bottom product and the overheadgases are sent along with the gases from the absorber to fuel gas system. The light crackedgasoline is sweetened in the 'erox treater in "lant % along with light gasoline and laterblended to gasoline.

Plant - /itu#en 0ir /lo1in !nitThe 2itumen ir 2lowing plant is designed to process 4) T0hr. of vacuum residuum fromthe crude unit to produce %( metric tons per stream day of -(01(( penetration asphalt and% .% T0: of 3(0 ( penetration asphalt. The feed stock is expected to have a penetration of 1/( mm.The vacuum residuum feed is split into two streams a# converter feed and b# blendingstock. In the converter the aromatics in the feed are oxidised to asphaltenes by air and theproduct from the converter will have a penetration between 3() ( mm. The feed to theconverter enters in the top section and meets a counter)current air stream supplied by acompressor. The stock yielded from the converter meets the specification of 3(0 (penetration grade. portion of this is sent to the 3(0 ( asphalt storage tank and thebalance is blended with the blending stock to produce -(01(( penetration asphalt.The off)gases from the converter are cooled by direct contact with water to remove oil andthen burnt in the heater I 8)3.

Plant 8-3urfural Extraction !nit The 8urfural Bxtraction Cnit processes portions of all vacuum distillates in blocked outoperations as the first step in converting these distillates into lubrication oil blendingcomponents. The extraction process removes aromatic and oxygenated compounds whichhave low viscosity index and tend to become unstable. The viscosity index of a componentis based on a comparison of viscosity of the component with that of two reference oils which

have the same viscosity at %1(58 as that of the component. 9iscosity index gives anindication of the reduction in viscosity of the component at higher temperatures incomparison with that of the reference oil.The components in the feedstock that have low viscosity index form the smaller percentageof the feed. 8urfural has an affinity for the aromatic and oxygenated compounds and,therefore, it is used for extracting them from the feed. The extracted aromatics are calledextract and the refined stream is termed as raffmate.


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The plant is designed to process four feed stocks@spindle oil, light neutral, intermediateneutral and heavy neutral, into two grades each of high viscosity index !9I# and mediumviscosity index '9I# products. These feed stocks are run on a blocked out operation. Thefeed rates for the different stocks are tabulated below.:tock. Rate for !9I operation. Rate for '9I operation 1. :pindle Ail 3D mGhr. 33 mGhr.%. +ight neutral 3%)/ nG0hr. 33 m30hr.3. Intermediate neutral %D mGhr. 3/ mi0hr.

. !eavy neutral %3 mGhr. 33 ms0hr. The raffinates from this unit are sent as the feed stock to the 'B= dewaxing unit throughintermediate storage tanks.8or the purpose of discussion the unit may be divided into foursections. They areH a# 8eed Bxtraction system, b# Raffinate system, c# Bxtract system, d#8urfural recovery and drying system.

The air in the feedstock is removed by passing the feed through a deaerator. The deaeration

of the feed stock is necessary to prevent oxidation of the furfural which will result in furfurallosses and cause fouling and corrosion of the e&uipments. The deaerated feed is thenheated to the re&uired temperature and introduced in the extraction column. Thetemperature of the feed is maintained low enough to minimise the solubility of the paraffiniccomponents in furfural solvent. The extraction is effected in the extraction column known asrotating disc contactor in which the furfural and feed are mixed thoroughly. 8urfural isintroduced at the top section of the extraction column and the feed at or near the bottomsection. The extract mix is drawn from the bottom of the column and is routed to the extractrecovery section and raffinate mix is routed to the raffinate recovery section to recoverfurfural from the respective streams. The ma or portion of furfural from the raffinate mix is recovered by heating the mixture in aheater and separating the furfural in the Raffinate vacuum flash tower. The bottom streamof the raffinate flash tower is then steam stripped to recover the residual solvent in raffinatestripper. The solvent free raffinate is then routed to storage. The furfural from the extractmix is recovered in a three stage system operating under different pressures. The solventrecovered from both of the systems are segregated into two streams called dry solvent,which does not come in contact with steam and wet solvent which comes in contact withsteam.The solvent recovery system consists of two fractionators and 2 and the 62' surge drum.The water and furfural mixture from the overhead of the raffinate and extract strippers areseparatedin the 62' surge drum. The separated furfural is dried in the fractionator and the furfuralfrom water is recovered in fractionator 2. The dry furfural collected in the bottom of the fractionator is pumped back to the extraction column.

The Raffinate from this unit is the feed stock for the 'B= dewaxing unit. The extract ismixed with vacuum distillates and supplied to Thermal 6racker as feed stock.


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Plant 4 - e1axin !nit The function of this unit is to improve the pour point of the feed stock by removing waxfrom the feed stock. The unit is designed to process - grades of furfural raffinates andunextracted light netural, intermediate neutral and heavy neutral vacuum distillates. Thedewaxing is carried out on a blocked out operation. The dewaxing operation removesenough of heavy paraffins from the feed stock to lower the pour point of the product tomeet the specification. The table given below indicates the design feed rates for thedifferent feed stocks. :tock. !9I stock '9I stock +9I stock feed rate. feed rate. unextracted# feed rate.1. :pindle oil 1)% m:0hr. %)/ rnGhr. @%. +ight neutral 3 .3 mGhr. 3/.3 mGhr. 3/./ mGhr.3. Intermediate 3/.4 m:0hr. 34./ m$0hr. 3-. m30hr.

. !eavy ;eutral %4. mGhr. %4.3 mGhr. %D.* mGhr. The dewaxing is accomplished by mixing the waxy charge with a solvent oil consisting ofe&ual proportions of 'ethyl Bthyl =etone 'B=# and Toluene, chilling the mixture toprecipitate the wax and then filtering the resultant slurry to separate the wax.The feed stock is line mixed with the solvent and is chilled in a series of exchangers using

vapourising ammonia as a cooling agent. The chillers are specially designed to scrape outthe wax deposits on the heat transfer surface so as to have efficient heat transfer. fterpassing through the chillers the temperature of the solvent and feed mixture is lowered to@1- to@%156 at which all the wax components crystallise.The scream is passed through the 9acuum Rotary filters. The filter consists of a shell and acylindrical drum with the filter cloth. 2y means of a vacuum maintained inside the filterdrum through a system of internal pipes, the solvent and oil are drawn through the filtercloth leaving a layer of wax on the cloth. The filter drum is continuously rotated by anelectric motor and a rotary valve at the end of the filter drum sub ects the filter cloth tovacuum or pressure. The wax layeris removed. The wax mix and the dewaxed oil are pumped to their respective section wherethe solvent is recovered and re)used.

The facilities for solvent recovery from the wax mix and dewaxed oil are identical. Thecharge is heated using steam and is admitted to a flash tower where most of the solvent isrecovered. Theflash tower bottoms is then admitted to a stripper where it is steam stripped to remove thebalance of the solvent. The solvents separated from the stripper and flash tower aresegregated.


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The stripped wax is routed to a storage tank and is blended with other components toproduce fuel oil. The dewaxed oil is sent to the +ube Ail !ydrofmisher "lant 1(# as feedstock. The wet solvent from the overhead of the stripper is collected in the solvent decanterwhere the water and solvent are separated. To minimise solvent losses the water from thedecanter is passed through a 'B= fractionator where the dissolved solvent is steam strippedand separated.

Plant 56 - 7u+e Oil &ydro finis'in !nitThe lube oil hydrofinisher employs a hydrogenation process to improve colour stability andlengthens the oxidation period of the finished lube stocks. The hydrogenation reducessulphur, oxygen, nitrogen and undesirable carbon forming compounds without damaging theother properties of the lube oils. The plant is designed to process all the eleven lube oil stocks from 'B= unit on a blocked)out operation. The feed rate for the spindle oil !9I and '91 will be 3(./ m3 0hr. and for allother stocks will be %D.- mGhr. The products from this unit are the finished lube oil blendingcomponents and are delivered to off)plot storage tanks.The process flow through this unit is similar to the other hydrogen treaters. The feed ismixed with hydrogen, heated in heater and passed through a three bed reactor. Recycle gasis added to thesecond and third bed to control the temperature. The effluent is cooled and separated fromthe excess hydrogen and the other gases formed by reaction. The off)gas from theseparator is 'B treated to remove !7 : and is recycled to the reactor and the feed stream,and part of it sent to "lant * as make)up gas. The make)up hydrogen for this plant issupplied from !ydrogen plant "lant ;o. II#. The li&uid from the separator is steam strippedin a vacuum stripper and then dried

in a vacuum drier to remove traces of water. The product from the vacuum drier is cooledand then sent to storage. The overhead li&uid from the stripper is pumped to I6)%% in "lantI.

Plant 55 - &ydro en PlantThe function of "lant II is to produce enough hydrogen for the use in the hydrofinishers. Theplant converts the light hydrocarbon gas feed into hydrogen by reaction with steam inpresence of catalyst at a temperature of -1*56. The reaction proceeds as followsF6! J !% ( @) 6A J 3!%6A J !% ( @@ 6A% J !%!eavier hydrocarbons and steam react to form 6! , 6A and 6A% , and then 6! reactswith steam as shown above. The hydrogen plant is designed for a feed rate of 1/-( m3 0hr. of hydrocarbon gas notheavier than butane to produce 11,1/( m30hr. of hydrogen. The normal feed to the plantconsists of all the platformer stabili7er off)gas plus a mixture of off)gas from "lant ,
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stabili7er off)gas from "lant %. uring "latformer shutdown, all the feed gas will be suppliedby "lant %. The feed gas from "lant and plant % are combined and 'B treated in "lant 1%to remove 1)h : before it Is sent to the hydrogen plant.The process can be divided into three sections a# reforming b# shift conversion and c#methanation. The feed gas is desulphurised by passing through two 7inc oxide beds. Thedesulphurised feed is then mixed with sufficient steam to complete the reaction through the

shiftconversion and passed through the reforming furnace. The radiant tubes in the furnace arefilled with reforming catalyst. The temperature is maintained at -1*56. Reaction I# iscompleted when it leaves the reforming furnace and reaction %# is partially attained.Therefore, the reforming is followed by a catalytic conversion at lower temperature, which isknown as shift conversion. In the shift converter the steam and 6A react to form 6A7 and!i.The gas leaving 6(% absorber contains small amount of carbon monoxide and carbondioxide which are detrimental to the catalyst in hydrodesulphurisers as they form corrosiveacids during the processing. Therefore 6A and 6(% are reconverted to methane by acatalytic reaction with hydrogen which is called methanation. The reaction proceeds asfollows F6A% J !% @@) 6! J%!%(6A J 3!%@))6! J !%(The reaction takes place over a nickel catalyst at a temperature of 31*56. The methanatoreffluent gas is hydrogen of 4*? purity and sent to the two stage compression system.!ydrogen re&uirements of "lants and * are met after the first stage compression and thatof "lant 13 and 1( after second stage compression.

The heat in the reformer effluent is used to produce steam in a waste)heat boiler and thissteam is used for the process. :upplementary re&uirement is obtained from !.". steam andexcess, if any, isrouted to the '" steam header.

Pant 52- ulp'ur Reco ery Plant The hydrogen treating of kerosene, diesel, vacuum distillates nd lube oil componentproduces hydrogen sulphide. !ydrogen s ulphide is also present in crude which is evolvedwith gases from"lant I and "lant %. In the sulphur plant, the hydrogen sulphide is recovered by absorptionby a 1*? solution of 'B .

The absorbed !%: is then recovered from 'B solution and is converted into sulphur. Theconversion of !7 : to elemental sulphuris accomplished in two stages)first in the thermal reaction boiler andsecondly by in the catalytic converter. The reaction proceeds as followsF%!% : J 3!% (@) % :(% J %!% ( I#:(% J %!% : @@ 3: J %!% ( %#Reaction ;o. %# is partially completed In the reaction boiler and is completed in theconverters.


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The !i : stream from the 'B regenerator is mixed with proper proportion of air and isreacted in the reaction boiler. The reaction is exothermic. The heat evolved is utilised toproduce '" steam. The gases are then passed through the two converters. The gas fromthe convertor is passed through a coalescer which removes entrained sulphur from thegases. +i&uid sulphur is withdrawn from reaction boiler, converters and the coalescer into apit. The sulphur is shipped in a li&uid state from the pit or is sent to the refrigeration systemfor solid ification. The tail gas from the coalescer is burnt in the stack of the heater in "lant- or alternatively in the flare stack. :ulphur plant has the facilities to process all the sour water collected from various plants. Inthis section the water is stripped off all hydrogen sulphide in the sour water stripper and thestrippedwater is drained to sewer.

Plant 5" - Vacuu# istillate &ydrodesulp'urisation !nit The 9acuum istillate ! : unit processes the vacuum distillates in excess of that needed tomeet the lube oil product re&uirements. The desulphurised product is the feed to theThermal 6racker in "lant /. The plant Is designed to process 3./ m3 0hr. of feed which is amixture of the following components.

a# 8irst stage vacuum tower gas oil from "lant I .3 m30hr.b# :pindle oil distillate from "lant I 1(.- m3hr.c# +ight neutral distillate from "lant I -.- m30hr.d# Intermediate ;eutral distillate from "lant I 1*.4* m30hr.

e# 8urfural unit extracts 3.D* m30hr. Total 3./ m30hr. The process flow through the ! : unit is similar to that in the other ! : units. The reactorhas three beds of catalyst proportioned to give approximately e&ual rise in temperature.Recycle gas isadmitted in between the beds to limit the temperature rise across the bed. The recyclegases are amine treated to remove !%:. The reactor effluent is steam stripped to removelight hydrocarbons.

The stripper overhead vapours are condensed in the common overhead condenser of the!: A stripper in "lant *. The desulphurised vacuum distillate is fed directly to "lant / as

feed or cooled and sent to the visbreaker feed storage tank.

!tilities yste#


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Ctilities are the common re&uirements that are necessary for the refining of crude oil. Thesecommon items, that are necessary for the proper operation of the refinery, are re&uired insuch &uantities that it is economical to supply them from a central source rather thanprovide separate facilities for individual plant. The items that come under utilities are steam,electricity, cooling water, boiler feed water, fuels and compressed air facilities.>ater supply to the refinery comes from the wells located 1 to %( kilometers away from

the refinery. These wells are operated by the :tate >ater :upply department. de&uatefacilities to ensure uninterrupted water supply are provided at the site. /oiler 3eed 9ater reatin and tea# :eneration

schematic representation of the treated water system and steam is shown in theaccompanying figure. To prevent scale formation in the tubes of the steam generatinge&uipment the feed water must be treated. :alts of silica, magnesium, calcium and iron inthe water form scales. Axygen, carbon dioxide, hydrogen sulphide are corrosive gases. Theraw water from the fresh water pond containing hardness of about %1( ppm is first softenedin a cold lime softener to about 11* ppm. >ater is then passed through a set of cat)ionicsofteners.

The ion)exchange softeners are filled with resins. The cat)ionic softener removes thecalcium magnesium and sodium ions by exchanging place with hydrogen ion. The bed isregenerated periodically by dilute hydrochloric acid. The anionic softener removes thesulphate, chlorate and silica ions by replacing the hydroxyl ions in the anionic resin. The bedis regenerated with a weak solution of sodium hydroxide. The demineralised water is used as feed water to the main boilers and waste heat boilers inthe units. The steam to the units is supplied by means of common headers running throughthe plants and to the tank farm. There are three systems of steam supply a# the highpressure steam under a pressure of 31)* kg. per s&. cm. b# the medium pressure steam ata pressure of 1()* kg. per s&. cm. c# the low pressure steam of 3.* kg. per s&. cm.pressure. There are three boilers to supply the steam re&uirements of the units and for powergeneration. In addition to these boilers steam is also produced in "lants /, D, II and 1%. Themain boilers are operated at a pressure of *( kgs per s&. cm. This very high pressure steamis used for a# driving two turbo)generators to produce electricity b# to drive the turbines of two of the cooling water pumps c# to supply !. ". steam and d# to make)up there&uirements of '" steam and +" steam. The !" steam obtained by desuperheating thesteam from the boilers is used for turbine drives in the boiler and water treatment sections.The '" steam is supplied from turbines of the generator and from the boilers in the unit.The balance is made up by desuperheating steam from the main boiler. The low pressuresteam is derived from the generator turbine exhaust steam from the cooling water pumpturbines, exhaust of the turbine drives in the boiler plant and from the boilers in "lant 1%.The low pressure steam is used for deaeration of the boiler feed water, for heating

products in storage tanks and in some strippers in the unit. 3uel yste# The fuel supply for the heaters in the process plants and boilers comes from the fuel gassystem and the fuel oil system. 8uel gas is primarily produced from the vapour Recoveryunit and thedesulphurisers. The fuel oil is supplied from a tank of D4( cubic meters capacity by meansof a pump. The pump discharges into a header that runs to all the heaters and boilers. To


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products like gasoline naphtha which have vapour pressure not high enough for pressuretanks, but high enough to have losses due to evaporation are stored in floating roof tanks tominimise the lossof product due to evaporation. The relative advantages and needs for the type of storagewill be discussed in B&uipment 8undamentals. The crude oil is brought from "ersian Eulf by tankers and is pumped from the harbour by a3(L crude oil line to the crude tanks. The crude is then pumped to "lant ;o. I after settlingand water draw off. The oil is processed into different fractions in the various units.The +"E, naphtha, kerosene and T8)*( are received from the units directly in the producttanks. The raw diesel, desulphurised diesel and heavy naphtha are line blended in "lant *and is received in the diesel storage tank. The kerosene and diesel are provided with acommon intermediate tank for storing the raw products during the shut down of "lants and *.The reformate from "lant ;o. 3 and treated gasoline light gasoline# are also provided witha surge tank as a cushion for the gasoline blending re&uirements. Product /lendin

The products that are made by blending are a# gasoline, b#


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basin, by means of a common underground sewer system.In the sewer basin oil and water are separated. The separated oil is pumped to the wet sloptanks -(1, -(3 and -( . The water from the sewer basin is pumped by two electric pumpsto the separator box for the recovery of oil. The oil separates from the water while flowingthrough the "I separator and is skimmed off by an ad ustable skimmer.The collected oil is pumped to the wet slop tanks. The skimmed water then flows to the

oxidation basin which also serves as water reservoir for fire fighting purposes. The oxidationpond provides enough residence time for oxidation of any traces of oil that elude separationat the "I :eparator by microbiological organisms. The water overflowing from the oxidationpond is routed to the 2uckingham canal. "rovision is made to collect any oil thataccumulates in the oxidation pond at the outlet of the pond.

Ane must not get an impression that all the oil that is drained in the sewer is recovered.:ome of the oil drained is lost to atmosphere by vapourisation, some by adhering to thesludge and someby oxidation in the pond. 9ery small &uantity of oil is also lost via the effluent going to thecanal from the oxidation pond. These losses may even be as high as 1.*? to % ?.Therefore, it is very important that operators take special care not to drain oil to the sewerexcept when it is unavoidable and absolutely necessary. raining of sample point beforesampling should be limited to the extent necessary to obtain a representative sample. ripsand leaks from the oints in thepipelines and e&uipments should be repaired promptly. Remember that part of the oildrained is always lost to the atmosphere by evaporation, through the sludge and byoxidation in the pond and this oil could have been a valuable product. Remember thatconsiderable sum of money can be lost by these types of non ) recoverable oil loss.

Corrosion In'i+itors 0nd 0dditi es !sed In Process !nits In the various phases of operation suitable inhibitors and chemicals for corrosion protection,fouling prevention and foam prevention are added depending on the nature of the stream.These chemicals are added in very small &uantities and are usually expensive. The purposeof the addition of the inhibitors and chemicals is to achieve longer lengths of operation andlonger life of the e&uipment. The addition of these chemicals and inhibitors are thereforevery important and should be done within specified limits and conditions. The variouschemicals and inhibitors are used.

Refinery Operations.doc

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