Petroleum Refining Process.doc

8/11/2019 Petroleum Refining Process.doc

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ollo*ing the Second 2orld 2ar, $arious reforming +rocesses *ere introduced *hich im+ro$edgasoline /ualit and ield, and +roduced higher-/ualit +roducts. Some of these in$ol$ed the useof catal sts and=or h drogen to change molecules and remo$e sul+hur. Im+ro$ed catal sts, and

+rocess methods such as h drocrac ing and reforming, *ere de$elo+ed throughout the (;5's toincrease gasoline ields and im+ro$e anti- noc characteristics. hese catal tic +rocesses also

+roduced molecules *ith a dou le ond 8al enes9, forming the asis of the modern +etrochemical industr .

he num ers and t +es of different +rocesses used in modern refineries de+end +rimaril on thenature of the crude feedstoc and finished +roduct re/uirements. )rocesses are also affected economic factors including crude costs, +roduct $alues, a$aila ilit of utilities andtrans+ortation. he chronolog of the introduction of $arious +rocesses is gi$en in ta le (.

a le (. Summar of the histor of refining +rocessing

Year Process name Process purpose Process by-products

(45& Atmos+heric distillation )roduce erosene >a+htha, tar, etc.(4?' @acuum distillation Lu ricants 8original9

Crac ing feedstoc s 8(;7's9As+halt, residualCo er feedstoc s

(;(7 hermal crac ing Increase gasoline Residual, un er fuel(;(5 S*eetening Reduce sul+hur and odour Sul+hur (;7' hermal reforming Im+ro$e octane num er Residual(;7& 6 drogenation Remo$e sul+hur Sul+hur (;7& Co ing )roduce gasoline ase stoc s Co e(;77 Sol$ent e1traction Im+ro$e lu ricant $iscosit

inde1Aromatics

(;7 Sol$ent de*a1ing Im+ro$e +our +oint 2a1es(;7 Catal tic +ol meri"ation Im+ro$e gasoline ield and

octane num er )etrochemicalfeedstoc s

(;7? Catal tic crac ing 6igher octane gasoline )etrochemicalfeedstoc s

(;7; @is rea ing Reduce $iscosit Increased distillate, tar (;


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(;?< Catal tic de*a1ing Im+ro$e +our +oint 2a1(;? Residual h drocrac ing Increase gasoline ield from

residual6ea$ residuals

Basic refining processes and operations

)etroleum refining +rocesses and o+erations can e classified into the follo*ing asic areas:se+aration, con$ersion, treatment, formulating and lending, au1iliar refining o+erations andrefining non-+rocess o+erations. See figure ( for a sim+lified flo* chart.

igure (. Refiner +rocess chart

Separation . Crude oil is +h sicall se+arated fractionation in atmos+heric and $acuumdistillation to*ers, into grou+s of h drocar on molecules *ith $arious oiling-+oint ranges,called fractionsD or cutsD.

Conversion . Con$ersion +rocesses used to change the si"e and=or structure of h drocar onmolecules include:

decom+osition 8di$iding9 h dro-, thermal and catal tic crac ing, co ing and$is rea ing

unification 8com ining9 through al lation and +ol meri"ation alteration 8rearranging9 *ith isomeri"ation and catal tic reforming

treatment.
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Since the eginning of refining, $arious treatment methods ha$e een used to remo$e non-h drocar ons, im+urities and other constituents that ad$ersel affect the +erformance +ro+ertiesof finished +roducts or reduce the efficienc of the con$ersion +rocesses. reatment in$ol$es

oth chemical reactions and +h sical se+aration, such as dissol$ing, a sor+tion or +reci+itation,using a $ariet and com ination of +rocesses. reatment methods include remo$ing or se+arating

aromatics and na+hthenes, as *ell as remo$ing im+urities and undesira le contaminants.S*eetening com+ounds and acids are used to desul+huri"e crude oil efore +rocessing, and totreat +roducts during and after +rocessing. !ther treatment methods include crude desalting,chemical s*eetening, acid treating, cla contacting, h drodesul+huri"ing, sol$ent refining,caustic *ashing, h drotreating, dr ing, sol$ent e1traction and sol$ent de*a1ing.

Formulating and lending is the +rocess of mi1ing and com ining h drocar on fractions,additi$es and other com+onents to +roduce finished +roducts *ith s+ecific desired +erformance

+ro+erties.

!u"iliary refining operations . !ther refiner o+erations *hich are re/uired to su++ort

h drocar on +rocessing include light ends reco$er 3 sour *ater stri++ing3 solid *aste, *aste*ater and +rocess *ater treatment and cooling3 h drogen +roduction3 sul+hur reco$er 3 and acidand tail gas treatment. !ther +rocess functions are +ro$iding catal sts, reagents, steam, air,nitrogen, o1 gen, h drogen and fuel gases.

#efinery non$process facilities . All refineries ha$e a multitude of facilities, functions, e/ui+mentand s stems *hich su++ort the h drocar on +rocess o+erations. +ical su++ort o+erations areheat and +o*er generation3 +roduct mo$ement3 tan storage3 shi++ing and handling3 flares andrelief s stems3 furnaces and heaters3 alarms and sensors3 and sam+ling, testing and ins+ecting.

>on-+rocess facilities and s stems include firefighting, *ater and +rotection s stems, noise and +ollution controls, la oratories, control rooms, *arehouses, maintenance and administrati$e

facilities.Major Products of Crude Oil Refining

)etroleum refining has e$ol$ed continuousl in res+onse to changing consumer demand for etter and different +roducts. he original +rocess re/uirement *as to +roduce erosene as achea+er and etter source of fuel for lighting than *hale oil. he de$elo+ment of the internalcom ustion engine led to the +roduction of en"ene, gasoline and diesel fuels. he e$olution ofthe air+lane created a need for high-octane a$iation gasoline and 0et fuel, *hich is a so+histicatedform of the original refiner +roduct, erosene. )resent-da refineries +roduce a $ariet of

+roducts, including man *hich are used as feedstoc s for crac ing +rocesses and lu ricantmanufacturing, and for the +etrochemical industr . hese +roducts can e roadl classified asfuels, +etrochemical feedstoc s, sol$ents, +rocess oils, lu ricants and s+ecial +roducts such as*a1, as+halt and co e. 8See ta le &.9

a le &. )rinci+al +roducts of crude oil refining

6 drocar on gases sesLi/uified gases Coo ing and industrial gas


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Motor fuel gasIlluminating gasAmmoniaS nthetic fertili"er Alcohols

Sol$ents and acetone)lastici"ersResins and fi res for +lastics and te1tiles)aints and $arnish

Chemical industr feedstoc Ru er +roductsCar on lac )rinting in s

Ru er industrLight distillatesLight na+hthas !lefins

Sol$ents and diluentsE1traction sol$ents

Chemical industr feedstoc sIntermediate na+hthas A$iation and motor gasoline

Br -cleaning sol$ents6ea$ na+hthas Militar 0et fuel

Jet fuel and eroseneractor fuel

#as oil Crac ing stoc 6eating oil and diesel fuelMetallurgical fuelA sor er oilF en"ene and gasoline reco$er

6ea$ distillatesechnical oils e1tile oils

Medicinal oils and cosmetics2hite oilFfood industr

Lu ricating oils ransformer and s+indle oilsMotor and engine oilsMachine and com+ressor oilsur ine and h draulic oilsransmission oilsE/ui+ment and ca le insulation oilsA1le, gear and steam engine oilsMetal treating, cutting and grinding oilsGuenching and rust inhi itor oils6eat transfer oilsLu ricating greases and com+ounds)rinting in oils

)araffin *a1 Ru er industr)harmaceuticals and cosmeticsood and +a+er industriesCandles and matches


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Residues)etrolatum )etroleum 0ell

CosmeticsRust inhi itors and lu ricantsCa le coating com+ounds

Residual fuel oil >o. 5 oiler and +rocess fuel oilAs+halts )a$ing as+halt

Roofing materialsAs+haltic lu ricantsInsulating and foundation +rotection2ater+roof +a+er +roducts

Refiner -+roductsCo e Electrodes and fuelSul+honates EmulsifiersSul+huric acid S nthetic fertili"er Sul+hur Chemicals6 drogen 6 drocar on reformation

A number of chemicals a re used in, or formed as a result of, hydrocarbon processing. Abrief description of those which are specic and pertinent to rening follows:

Sulphur Dioxide

lue gas from urning high-sul+hur-content fuels usuall contains high le$els of sul+hur dio1ide,

*hich usuall is remo$ed *ater scru ing.

Caustics

Caustics are added to desalting *ater to neutrali"e acids and reduce corrosion. Caustics are alsoadded to desalted crude in order to reduce the amount of corrosi$e chlorides in the to*ero$erheads. he are used in refiner treating +rocesses to remo$e contaminants fromh drocar on streams.

Nitrogen oxides and carbon monoxide

lue gas contains u+ to &'' ++m of nitric o1ide, *hich reacts slo*l *ith o1 gen to formnitrogen dio1ide. >itric o1ide is not remo$ed *ater scru ing, and nitrogen dio1ide candissol$e in *ater to form nitrous and nitric acid. lue gas normall contains onl a slight amountof car on mono1ide, unless com ustion is a normal.

Hydrogen sulphide


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6 drogen sul+hide is found naturall in most crude oils and is also formed during +rocessing the decom+osition of unsta le sul+hur com+ounds. 6 drogen sul+hide is an e1tremel to1ic,colourless, flamma le gas *hich is hea$ier than air and solu le in *ater. It has a rotten eggodour *hich is discerni le at concentrations *ell elo* its $er lo* e1+osure limit. his smellcannot e relied u+on to +ro$ide ade/uate *arning as the senses are almost immediatel

desensiti"ed u+on e1+osure. S+ecial detectors are re/uired to alert *or ers to the +resence ofh drogen sul+hide, and +ro+er res+irator +rotection should e used in the +resence of the gas.E1+osure to lo* le$els of h drogen sul+hide *ill cause irritation, di""iness and headaches, *hilee1+osure to le$els in e1cess of the +rescri ed limits *ill cause ner$ous s stem de+ression ande$entuall death.

Sour water

Sour *ater is +rocess *ater *hich contains h drogen sul+hide, ammonia, +henols, h drocar onsand lo*-molecular-*eight sul+hur com+ounds. Sour *ater is +roduced steam stri++ingh drocar on fractions during distillation, regenerating catal st, or steam stri++ing h drogen

sul+hide during h drotreating and h drofinishing. Sour *ater is also generated the addition of *ater to +rocesses to a sor h drogen sul+hide and ammonia.

Sulphuric acid and hydrofluoric acid

Sul+huric acid and h drofluoric acid are used as catal sts in al lation +rocesses. Sul+huric acidis also used in some of the treatment +rocesses.

Solid catalysts

A num er of different solid catal sts in man forms and sha+es, from +ellets to granular eads to

dusts, made of $arious materials and ha$ing $arious com+ositions, are used in refining +rocesses.E1truded +ellet catal sts are used in mo$ing and fi1ed ed units, *hile fluid ed +rocesses usefine, s+herical +articulate catal sts. Catal sts used in +rocesses *hich remo$e sul+hur areim+regnated *ith co alt, nic el or mol denum. Crac ing units use acid-function catal sts, suchas natural cla , silica alumina and s nthetic "eolites. Acid-function catal sts im+regnated *ith

+latinum or other no le metals are used in isomeri"ation and reforming. sed catal sts re/uires+ecial handling and +rotection from e1+osures, as the ma contain metals, aromatic oils,carcinogenic +ol c clic aromatic com+ounds or other ha"ardous materials, and ma also e

+ ro+horic.

Fuels

he +rinci+al fuel +roducts are li/uefied +etroleum gas, gasoline, erosene, 0et fuel, diesel fueland heating oil and residual fuel oils.

%i&uefied petroleum gas '%(G) , *hich consists of mi1tures of +araffinic and olefinich drocar ons such as +ro+ane and utane, is +roduced for use as a fuel, and is stored andhandled as li/uids under +ressure. L)# has oiling +oints ranging from a out H?< C to74+ C, is colourless, and the $a+ours are hea$ier than air and e1tremel flamma le. he


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im+ortant /ualities from an occu+ational health and safet +ers+ecti$e of L)#s are $a+our +ressure and control of contaminants.

Gasoline . he most im+ortant refiner +roduct is motor gasoline, a lend of relati$el lo*- oiling h drocar on fractions, including reformate, al late, ali+hatic na+htha 8light straight-run

na+htha9, aromatic na+htha 8thermal and catal tic crac ed na+htha9 and additi$es. #asoline lending stoc s ha$e oiling +oints *hich range from am ient tem+eratures to a out &'< C, anda flash+oint elo* H


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flamma le mi1tures *hich can e easil ignited. his is a recogni"ed ha"ard that re/uiress+ecific storage, containment and handling +recautions, and safet measures to assure thatreleases of $a+ours and sources of ignition are controlled so that fires do not occur. he less$olatile fuels, such as erosene and diesel fuel, should e handled carefull to +re$ent s+ills and

+ossi le ignition, as their $a+ours are also com usti le *hen mi1ed *ith air in the flamma le

range. 2hen *or ing in atmos+heres containing fuel $a+ours, concentrations of highl $olatile,flamma le +roduct $a+ours in air are often restricted to no more than (' of the lo*erflamma le limits 8L L9, and concentrations of less $olatile, com usti le +roduct $a+ours to nomore than &' L L, de+ending on a++lica le com+an and go$ernment regulations, in order toreduce the ris of ignition.

Although gasoline $a+our le$els in air mi1tures are t +icall maintained elo* (' of the L Lfor safet +ur+oses, this concentration is considera l a o$e the e1+osure limits to e o ser$edfor health reasons. 2hen inhaled, small amounts of gasoline $a+our in air, *ell elo* the lo*erflamma le limit, can cause irritation, headaches and di""iness, *hile inhalation of largerconcentrations can cause loss of consciousness and e$entuall death. Long-term health effects

ma also e +ossi le. #asoline contains en"ene, for e1am+le, a no*n carcinogen *ithallo*a le e1+osure limits of onl a fe* +arts +er million. herefore, e$en *or ing in gasoline$a+our atmos+heres at le$els elo* (' L L re/uires a++ro+riate industrial h giene

+recautions, such as res+irator +rotection or local e1haust $entilation.

In the +ast, man gasolines contained tetra-eth l or tetra meth l al lead anti- noc additi$es,*hich are to1ic and +resent serious lead a sor+tion ha"ards s in contact or inhalation. an sor $essels *hich contained leaded gasoline at an time during their use must e $ented,thoroughl cleaned, tested *ith a s+ecial lead-in-airD test de$ice and certified to e lead-free toassure that *or ers can enter *ithout using self-contained or su++lied reathing air e/ui+ment,e$en though o1 gen le$els are normal and the tan s no* contain unleaded gasoline or other

+roducts.#aseous +etroleum fractions and the more highl $olatile fuel +roducts ha$e a mild anaestheticeffect, generall in in$erse ratio to molecular *eight. Lo*er- oiling-+oint li/uid fuels, such asgasoline and erosene, +roduce a se$ere chemical +neumonitis if inhaled, and should not esi+honed mouth or accidentall ingested. #ases and $a+ours ma also e +resent insufficientl high concentrations to dis+lace o1 gen 8in the air9 elo* normal reathing le$els.Maintaining $a+our concentrations elo* the e1+osure limits and o1 gen le$els at normal

reathing ranges, is usuall accom+lished +urging or $entilation.

Crac ed distillates contain small amounts of carcinogenic +ol c clic aromatic h drocar ons8)A6s93 therefore, e1+osure should e limited. Bermatitis ma also de$elo+ from e1+osure togasoline, erosene and distillate fuels, as the ha$e a tendenc to defat the s in. )re$ention isaccom+lished use of +ersonal +rotecti$e e/ui+ment, arrier creams or reduced contact andgood h gienic +ractices, such as *ashing *ith *arm *ater and soa+ instead of cleaning hands*ith gasoline, erosene or sol$ents. Some +ersons ha$e s in sensiti$it to the d es used tocolour gasoline and other distillate +roducts.


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Residual fuel oils contain traces of metals and ma ha$e entrained h drogen sul+hide, *hich ise1tremel to1ic. Residual fuels *hich ha$e high crac ed stoc s oiling a o$e 7?' C containcarcinogenic )A6s. Re+eated e1+osure to residual fuels *ithout a++ro+riate +ersonal +rotection,should e a$oided, es+eciall *hen o+ening tan s and $essels, as h drogen sul+hide gas ma eemitted.

Petrochemical feedstocks

Man +roducts deri$ed from crude-oil refining, such as eth lene, +ro+ lene and utadiene, areolefinic h drocar ons deri$ed from refiner crac ing +rocesses, and are intended for use in the

+etrochemical industr as feedstoc s for the +roduction of +lastics, ammonia, s nthetic ru er,gl col and so on.

Petroleum sol ents

A $ariet of +ure com+ounds, including en"ene, toluene, 1 lene, he1ane and he+tane, *hose

oiling +oints and h drocar on com+osition are closel controlled, are +roduced for use assol$ents. Sol$ents ma e classified as aromatic or non-aromatic, de+ending on theircom+osition. heir use as +aint thinners, dr -cleaning fluids, degreasers, industrial and +esticidesol$ents and so on, is generall determined their flash+oints, *hich $ar from *ell elo* H(4C to a o$e 5' C.

he ha"ards associated *ith sol$ents are similar to those of fuels in that the lo*er flash+ointsol$ents are flamma le and their $a+ours, *hen mi1ed *ith air in the flamma le range, areignita le. Aromatic sol$ents *ill usuall ha$e more to1icit than non-aromatic sol$ents.

Process oils

)rocess oils include the high oiling range, straight run atmos+heric or $acuum distillate streamsand those *hich are +roduced catal tic or thermal crac ing. hese com+le1 mi1tures, *hichcontain large +araffinic, na+hthenic and aromatic h drocar on molecules *ith more than (car on atoms, are used as feedstoc s for crac ing or lu ricant manufacturing. )rocess oils ha$efairl high $iscosities, oiling +oints ranging from &5' C to 74 C, and flash+oints a o$e (&(C.

)rocess oils are irritating to the s in and contain high concentrations of )A6s as *ell as sul+hur,nitrogen and o1 gen com+ounds. Inhalation of $a+ours and mists should e a$oided, and s ine1+osure should e controlled the use of +ersonal +rotection and good h gienic +ractices.

!ubricants and greases

Lu ricating oil ase stoc s are +roduced s+ecial refining +rocesses to meet s+ecific consumerre/uirements. Lu ricating ase stoc s are light- to medium-coloured, lo*-$olatile, medium- tohigh-$iscous mi1tures of +araffinic, na+hthenic and aromatic oils, *ith oiling ranges from 7?(C to 74 C. Additi$es, such as demulsifiers, anti-o1idants and $iscosit im+ro$ers, are lendedinto the lu ricating oil ase stoc s to +ro$ide the characteristics re/uired for motor oils, tur ine


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and h draulic oils, industrial greases, lu ricants, gear oils and cutting oils. he most critical/ualit for lu ricating oil ase stoc is a high $iscosit inde1, +ro$iding for less change in$iscosit under $ar ing tem+eratures. his characteristic ma e +resent in the crude oil feedstoc or attained through the use of $iscosit inde1 im+ro$er additi$es. Betergents are added toee+ in sus+ension an sludge formed during the use of the oil.

#reases are mi1tures of lu ricating oils and metallic soa+s, *ith the addition of s+ecial-+ur+osematerials such as as estos, gra+hite, mol denum, silicones and talc to +ro$ide insulation orlu ricit . Cutting and metal-+rocess oils are lu ricating oils *ith s+ecial additi$es such aschlorine, sul+hur and fatt -acid additi$es *hich react under heat to +ro$ide lu rication and

+rotection to the cutting tools. Emulsifiers and acteria +re$ention agents are added to *ater-solu le cutting oils.

Although lu ricating oils themsel$es are non-irritating and ha$e little to1icit , ha"ards ma e +resented the additi$es. sers should consult su++lier material safet data information todetermine the ha"ards of s+ecific additi$es, lu ricants, cutting oils and greases. he +rimar

lu ricant ha"ard is dermatitis, *hich can usuall e controlled the use of +ersonal +rotecti$ee/ui+ment together *ith +ro+er h gienic +ractices. !ccasionall *or ers ma de$elo+ asensiti$it to cutting oils or lu ricants *hich *ill re/uire reassignment to a 0o *here contactcannot occur. here are some concerns a out carcinogenic e1+osure to mists from na+hthenic-

ased cutting and light s+indle oils, *hich can e controlled su stitution, engineering controlsor +ersonal +rotection. he ha"ards of e1+osure to grease are similar to those of lu ricating oil,*ith the addition of an ha"ards +resented the grease materials or additi$es. Most of theseha"ards are discussed else*here in this Encyclopaedia .

Special products

-a" is used for +rotecting food +roducts3 in coatings3 as an ingredient in other +roducts such ascosmetics and shoe +olish and for candles.

Sulphur is +roduced as a result of +etroleum refining. It is stored either as a heated, molten li/uidin closed tan s or as a solid in containers or outdoors.

Co+e is almost +ure car on, *ith a $ariet of uses from electrodes to charcoal ri/uettes,de+ending on its +h sical characteristics, *hich result from the co ing +rocess.

!sphalt , *hich is +rimaril used for +a$ing roads and roofing materials, should e inert to mostchemicals and *eather conditions.

2a1es and as+halts are solid at am ient tem+eratures, and higher tem+eratures are needed forstorage, handling and trans+ortation, *ith the resulting ha"ard of urns. )etroleum *a1 is sohighl refined that it usuall does not +resent an ha"ards. S in contact *ith *a1 can lead to

+lugging of +ores, *hich can e controlled +ro+er h gienic +ractices. E1+osure to h drogensul+hide *hen as+halt and molten sul+hur tan s are o+ened can e controlled the use ofa++ro+riate engineering controls or res+irator +rotection. Sul+hur is also readil ignita le atele$ated tem+eratures. As+halt is discussed else*here in the Encyclopaedia .


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Petroleum Refining Processes

6 drocar on refining is the use of chemicals, catal sts, heat and +ressure to se+arate andcom ine the asic t +es of h drocar on molecules naturall found in crude oil into grou+s ofsimilar molecules. he refining +rocess also rearranges the structures and onding +atterns of the

asic molecules into different, more desira le h drocar on molecules and com+ounds. he t +eof h drocar on 8+araffinic, na+hthenic or aromatic9 rather than the s+ecific chemical com+ounds +resent, is the most significant factor in the refining +rocess.

hroughout the refiner , o+erations +rocedures, safe *or +ractices and the use of a++ro+riate +ersonal +rotecti$e clothing and e/ui+ment, including a++ro$ed res+irator +rotection, is neededfor fire, chemical, +articulate, heat and noise e1+osures and during +rocess o+erations, sam+ling,ins+ection, turnaround and maintenance acti$ities. As most refiner +rocesses are continuous andthe +rocess streams are contained in enclosed $essels and +i+ing, there is limited +otential fore1+osure. 6o*e$er, the +otential for fire e1ists ecause e$en though refiner o+erations areclosed +rocesses, if a lea or release of h drocar on li/uid, $a+our or gas occurs, the heaters,

furnaces and heat e1changers throughout the +rocess units are sources of ignition.

Crude oil pretreatment

,esalting

Crude oil often contains *ater, inorganic salts, sus+ended solids and *ater-solu le trace metals.he first ste+ in the refining +rocess is to remo$e these contaminants desalting 8deh dration9in order to reduce corrosion, +lugging and fouling of e/ui+ment, and to +re$ent +oisoning thecatal sts in +rocessing units. Chemical desalting, electrostatic se+aration and filtering are threet +ical methods of crude-oil desalting. In chemical desalting, *ater and chemical surfactants

8demulsifiers9 are added to the crude oil, heated so that salts and other im+urities dissol$e intothe *ater or attach to the *ater, and are then held in a tan *here the settle out. Electricaldesalting a++lies high-$oltage electrostatic charges in order to concentrate sus+ended *aterglo ules in the ottom +ortion of the settling tan . Surfactants are added onl *hen the crude oilhas a large amount of sus+ended solids. A third, less common +rocess in$ol$es filtering heatedcrude oil using diatomaceous earth as a filtration medium.

In chemical and electrostatic desalting, the crude feedstoc is heated to et*een 55 C and (??C, to reduce $iscosit and surface tension for easier mi1ing and se+aration of the *ater. hetem+erature is limited the $a+our +ressure of the crude-oil feedstoc . oth methods ofdesalting are continuous. Caustic or acid ma e added to ad0ust the +6 of the *ater *ash, and

ammonia added to reduce corrosion. 2aste *ater, together *ith contaminants, is discharged fromthe ottom of the settling tan to the *aste *ater treatment facilit . he desalted crude oil iscontinuousl dra*n from the to+ of the settling tan s and sent to an atmos+heric crudedistillation 8fractionating9 to*er. 8See figure &.9

igure &. Besalting 8+re-treatment9 +rocess


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tem+eratures. he lighter 8lo*er oiling +oint9 fractions diffuse into the u++er +art of the to*er,and are continuousl dra*n off and directed to other units for further +rocessing, treating,

lending and distri ution.

ractions *ith the lo*est oiling +oints, such as fuel gas and light na+htha, are remo$ed from the

to+ of the to*er an o$erhead line as $a+ours. >a+htha, or straight-run gasoline, is ta en fromthe u++er section of the to*er as an o$erhead stream. hese +roducts are used as +etrochemicaland reformer feedstoc s, gasoline lending stoc s, sol$ents and L)#s.

Intermediate oiling range fractions, including gas oil, hea$ na+htha and distillates, areremo$ed from the middle section of the to*er as side streams. hese are sent to finishingo+erations for use as erosene, diesel fuel, fuel oil, 0et fuel, catal tic crac er feedstoc and

lending stoc s. Some of these li/uid fractions are stri++ed of their lighter ends, *hich arereturned to the to*er as do*nflo*ing reflu1 streams.

he hea$ier, higher- oiling-+oint fractions 8called residuum, ottoms or to++ed crude9 *hich

condense or remain at the ottom of the to*er, are used for fuel oil, itumen manufacturing orcrac ing feedstoc , or are directed to a heater and into the $acuum distillation to*er for furtherfractionation. 8See figure 7 and figure


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acuum distillation

@acuum distillation to*ers +ro$ide the reduced +ressure re/uired to +re$ent thermal crac ing*hen distilling the residuum, or to++ed crude, from the atmos+heric to*er at highertem+eratures. he internal designs of some $acuum to*ers are different from atmos+heric to*ers

in that random +ac ing and demister +ads are used instead of tra s. Larger diameter to*ers maalso e used to ee+ $elocities lo*er. A t +ical first-+hase $acuum to*er ma +roduce gas oils,lu ricating oil ase stoc s and hea$ residual for +ro+ane deas+halting. A second-+hase to*er,o+erating at a lo*er $acuum, distills sur+lus residuum from the atmos+heric to*er *hich is notused for lu e stoc +rocessing, and sur+lus residuum from the first $acuum to*er not used fordeas+halting.

@acuum to*ers are t +icall used to se+arate catal tic crac er feedstoc s from sur+lus residuum.@acuum to*er ottoms ma also e sent to a co er, used as lu ricant or as+halt stoc ordesul+huri"ed and lended into lo*-sul+hur fuel oil. 8See figure and figure 5.9

igure . @acuum distillation +rocess

igure 5. Schematic of $acuum distillation +rocess


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,istillation columns

2ithin refineries there are numerous other smaller distillation to*ers, called columns, designedto se+arate s+ecific and uni/ue +roducts, *hich all *or on the same +rinci+les as atmos+hericto*ers. or e1am+le, a de+ro+ani"er is a small column designed to se+arate +ro+ane fromiso utane and hea$ier com+onents. Another larger column is used to se+arate eth l en"ene and1 lene. Small u lerD to*ers, called stri++ers, use steam to remo$e trace amounts of light

+roducts 8gasoline9 from hea$ier +roduct streams.

Control tem+eratures, +ressures and reflu1 must e maintained *ithin o+erating +arameters to +re$ent thermal crac ing from ta ing +lace *ithin distillation to*ers. Relief s stems are +ro$ided ecause e1cursions in +ressure, tem+erature or li/uid le$els ma occur if automaticcontrol de$ices fail. !+erations are monitored in order to +re$ent crude from entering thereformer charge. Crude feedstoc s ma contain a++recia le amounts of *ater in sus+ension*hich se+arate during start-u+ and, along *ith *ater remaining in the to*er from steam +urging,settle in the ottom of the to*er. his *ater ma heat to the oiling +oint and create aninstantaneous $a+ori"ation e1+losion u+on contact *ith the oil in the unit.

he +reheat e1changer, +reheat furnace and ottoms e1changer, atmos+heric to*er and $acuumfurnace, $acuum to*er and o$erhead are susce+ti le to corrosion from h drochloric acid 86Cl9,h drogen sul+hide 86 &S9, *ater, sul+hur com+ounds and organic acids. 2hen +rocessing sourcrudes, se$ere corrosion can occur in oth atmos+heric and $acuum to*ers *here metaltem+eratures e1ceed &7& C, and in furnace tu ing. 2et 6 &S *ill also cause crac s in steel.


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2hen +rocessing high-nitrogen crudes, nitrogen o1ides, *hich are corrosi$e to steel *hen cooledto lo* tem+eratures in the +resence of *ater, form in the flue gases of furnaces.

Chemicals are used to control corrosion h drochloric acid +roduced in distillation units.Ammonia ma e in0ected into the o$erhead stream +rior to initial condensation, and=or an

al aline solution ma e carefull in0ected into the hot crude oil feed. If sufficient *ash *ater isnot in0ected, de+osits of ammonium chloride can form, causing serious corrosion.

Atmos+heric and $acuum distillation are closed +rocesses, and e1+osures are minimal. 2hensour 8high sul+hur9 crudes are +rocessed, there ma e +otential e1+osure to h drogen sul+hidein the +reheat e1changer and furnace, to*er flash "one and o$erhead s stem, $acuum furnaceand to*er, and ottoms e1changer. Crude oils and distillation +roducts all contain high- oilingaromatic com+ounds, including carcinogenic )A6s. Short-term e1+osure to high concentrationsof na+htha $a+our can result in headaches, nausea and di""iness, and long-term e1+osure canresult in loss of consciousness. en"ene is +resent in aromatic na+hthas, and e1+osure must elimited. he dehe1ani"er o$erhead ma contain large amounts of normal he1ane, *hich can

affect the ner$ous s stem. 6 drogen chloride ma e +resent in the +reheat e1changer, to*er to+"ones and o$erheads. 2aste *ater ma contain *ater-solu le sul+hides in high concentrationsand other *ater-solu le com+ounds, such as ammonia, chlorides, +henol and merca+tan,de+ending u+on the crude feedstoc and the treatment chemicals.

Crude oil con ersion processes

Con$ersion +rocesses, such as crac ing, com ining and rearranging, change the si"e andstructure of h drocar on molecules in order to con$ert fractions into more desira le +roducts.8See ta le 7.9

a le 7. !$er$ie* of +etroleum refining +rocesses

Process name Action Method Purpose Feedstoc s ProductsFractionation processesAtmos+hericdistillation

Se+aration hermal Se+aratefractions

Besalted crudeoil

#as, gas oil,distillate, residual

@acuumdistillation

Se+aration hermal Se+arate*ithoutcrac ing

Atmos+hericto*er residual

#as oil, lu e stoc ,residual

Con!ersion processes"#ecompositionCatal tic

crac ing

Alteration Catal tic +grade

gasoline

#as oil, co e

distillate

#asoline,

+etrochemicalfeedstoc

Co ing )ol meri"ation

hermal Con$ert$acuumresiduals

Residual, hea$oil, tar

>a+htha, gas oil,co e

6 drocrac ing 6 drogenation

Catal tic Con$ert tolighterh drocar o

#as oil, crac edoil, residuals

Lighter, higher/ualit +roducts


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ns6 drogen steamreforming

Becom+osition

hermal=catal tic

)roduceh drogen

Besul+huri"edgas, ! & ,steam

6 drogen, C!,C! &

Steam crac ing Becom+osition

hermal Crac largemolecules

Atmos+hericto*er hea$

fuel=distillate

Crac ed na+htha,co e, residuals

@is rea ing Becom+osition

hermal Reduce$iscosit

Atmos+hericto*er residual

Bistillate, car

Con!ersion processes"$nificationAl lation Com ining Catal tic nite

olefins andiso+araffins

o*eriso utane=crac er olefin

Iso-octane 8al late9

#reasecom+ounding

Com ining hermal Com inesoa+s andoils

Lu e oil, cattacid, al metal

Lu ricating grease

)ol meri"ation )ol meri"ation

Catal tic nite t*oor moreolefins

Crac er olefins 6igh octane na+htha, +etrochemical stoc s

Con!ersion processes"Alteration%rearrangementCatal ticreforming

Alteration=deh drogenation

Catal tic +gradelo*-octanena+htha

Co er=h drocrac er na+htha

6igh-octanereformate=aromatic

Isomeri"ation Rearrangement

Catal tic Con$ertstraightchain to

ranch

utane, centane,ce1ane

Iso utane=+entane=he1ane

&reatment processesAmine treating reatment A sor+tion Remo$e

acidiccontaminants

Sour gas,c drocar ons*ith C! & and6 &S

Acid-free gases andli/uid h drocar ons

Besalting 8+re-treatment9

Beh dration A sor+tion Remo$econtaminants

Crude oil Besalted crude oil

Br ing ands*eetening

reatment A sor+tion=ther mal

Remo$e6 &! andsul+hur

com+ounds

Li/uidh drocar on,L)#, al lated

feedstoc

S*eet and drh drocar ons

urfurale1traction

Sol$ente1traction

A sor+tion +grademiddistillate and lu es

C cle oils andlu e feedstoc s

6igh-/ualit dieseland lu e oil

6 drodesul+hur i"ation

reatment Catal tic Remo$esul+hur,contaminants

6igh-sul+hurresidual=gas oil

Besul+huri"edolefins


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6 drotreating 6 drogenation

Catal tic Remo$eim+urities=saturateh drocar ons

Residuals,crac edh drocar ons

Crac er feed,cistillate, lu e

)henole1traction Sol$ente1traction A sor+tion=ther mal Im+ro$elu e$iscositinde1,colour

Lu e oil asestoc s 6igh-/ualit lu eoils

Sol$entdeas+halting

reatment A sor+tion Remo$eas+halt

@acuum to*erresidual,cro+ane

6ea$ lu e oil,cs+halt

Sol$entde*a1ing

reatment Cool=filter Remo$e*a1 fromlu e stoc s

@acuum to*erlu e oils

Be*a1ed lu e asestoc

Sol$ente1traction

Sol$ente1traction

A sor+tion= +reci+itation

Se+arateunsaturatedaromatics

#as oil,ceformate,cistillate

6igh-octane gasoline

S*eetening reatment Catal tic Remo$e6 &S,con$ertmerca+tan

ntreateddistillate=gasoline

6igh-/ualitdistillate=gasoline

A num er of h drocar on molecules not normall found in crude oil ut im+ortant to therefining +rocess are created as a result of con$ersion. !lefins 8al enes, di-olefins and al nes9are unsaturated chain- or ring-t +e h drocar on molecules *ith at least one dou le ond. heare usuall formed thermal and catal tic crac ing and rarel occur naturall in un+rocessedcrude oil.

!l+enes are straight-chain molecules *ith the formula C n6 n containing at least one dou le ond8unsaturated9 lin age in the chain. he sim+lest al ene molecule is the mono-olefin eth lene,*ith t*o car on atoms, 0oined a dou le ond, and four h drogen atoms. Bi-olefins8containing t*o dou le onds9, such as (,&- utadiene and (,7- utadiene, and al nes 8containinga tri+le ond9, such as acet lene, occur in C and lighter fractions from crac ing. !lefins aremore reacti$e than +araffins or na+hthenes, and readil com ine *ith other elements such ash drogen, chlorine and romine.

Cracking processes

ollo*ing distillation, su se/uent refiner +rocesses are used to alter the molecular structures ofthe fractions to create more desira le +roducts. !ne of these +rocesses, crac ing, rea s 8orcrac s9 hea$ier, higher- oiling-+oint +etroleum fractions into more $alua le +roducts such asgaseous h drocar ons, gasoline lending stoc s, gas oil and fuel oil. Buring the +rocess, some of


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the molecules com ine 8+ol meri"e9 to form larger molecules. he asic t +es of crac ing arethermal crac ing, catal tic crac ing and h dro-crac ing.

"hermal cracking processes

hermal crac ing +rocesses, de$elo+ed in (;(7, heat distillate fuels and hea$ oils under +ressure in large drums until the crac 8di$ide9 into smaller molecules *ith etter anti- noccharacteristics. his earl method, *hich +roduced large amounts of solid, un*anted co e, hase$ol$ed into modern thermal crac ing +rocesses including $is rea ing, steam crac ing andco ing.

is rea+ing

@is rea ing is a mild form of thermal crac ing *hich reduces the +our +oint of *a1 residuesand significantl lo*ers the $iscosit of feedstoc *ithout affecting its oiling-+oint range.Residual from the atmos+heric distillation to*er is mildl crac ed in a heater at atmos+heric

+ressure. It is then /uenched *ith cool gas oil to control o$ercrac ing, and flashed in adistillation to*er. he thermall crac ed residue tar, *hich accumulates in the ottom of thefractionation to*er, is $acuum flashed in a stri++er and the distillate is rec cled. 8See figure ?.9

igure ?. @is rea ing +rocess

Steam crac+ing

Steam crac ing +roduces olefins thermall crac ing large h drocar on molecule feedstoc s at +ressures slightl a o$e atmos+heric and at $er high tem+eratures. Residual from steamcrac ing is lended into hea$ fuels. >a+htha +roduced from steam crac ing usuall contains

en"ene, *hich is e1tracted +rior to h drotreating.

Co+ing

Co ing is a se$ere form of thermal crac ing used to o tain straight-run gasoline 8co er na+htha9and $arious middle distillate fractions used as catal tic crac ing feedstoc s. his +rocess socom+letel reduces h drogen from the h drocar on molecule, that the residue is a form ofalmost +ure car on called co+e. he t*o most common co ing +rocesses are dela ed co ing andcontinuous 8contact or fluid9 co ing, *hich, de+ending u+on the reaction mechanism, time,tem+erature and the crude feedstoc , +roduce three t +es of co eFs+onge, hone com andneedle co e. 8See figure 4.9

igure 4. Co ing +rocess


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,elayed co+ing. In dela ed co ing, the feedstoc is first charged to a fractionator tose+arate lighter h drocar ons, and then com ined *ith hea$ rec cle oil. he hea$feedstoc is fed to the co er furnace and heated to high tem+eratures at lo* +ressures to

+re$ent +remature co ing in the heater tu es, +roducing +artial $a+ori"ation and mildcrac ing. he li/uid=$a+our mi1ture is +um+ed from the heater to one or more co erdrums, *here the hot material is held a++ro1imatel &< hours 8dela ed9 at lo* +ressuresuntil it crac s into lighter +roducts. After the co e reaches a +redetermined le$el in onedrum, the flo* is di$erted to another drum to maintain continuous o+eration. @a+ourfrom the drums is returned to the fractionator to se+arate out gas, na+htha and gas oils,and to rec cle hea$ier h drocar ons through the furnace. he full drum is steamed tostri+ out uncrac ed h drocar ons, cooled *ater in0ection and deco ed mechanicall

an auger rising from the ottom of the drum, or h draulicall fracturing the co e ed *ith high-+ressure *ater e0ected from a rotating cutter.

Continuous co+ing. Continuous 8contact or fluid9 co ing is a mo$ing ed +rocess *hicho+erates at lo*er +ressures and higher tem+eratures than dela ed co ing. In continuousco ing, thermal crac ing occurs using heat transferred from hot rec cled co e

+articles to feedstoc in a radial mi1er, called a reactor . #ases and $a+ours are ta enfrom the reactor, /uenched to sto+ further reaction and fractionated. he reacted co eenters a surge drum and is lifted to a feeder and classifier *here the larger co e +articlesare remo$ed. he remaining co e is dro++ed into the reactor +reheater for rec cling *ithfeedstoc . he +rocess is automatic in that there is a continuous flo* of co e andfeedstoc , and co ing occurs oth in the reactor and in the surge drum.

Health and safety considerations

In co ing, tem+erature control should e held *ithin a close range, as high tem+eratures *ill +roduce co e *hich is too hard to cut out of the drum. Con$ersel , tem+eratures *hich are toolo* *ill result in a high as+haltic content slurr . Should co ing tem+eratures get out of control,an e1othermic reaction could occur.

In thermal crac ing *hen sour crudes are +rocessed, corrosion can occur *here metaltem+eratures are et*een &7& C and


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hot co e. In emergencies, alternate means of egress from the *or ing +latform on to+ of co edrums is needed.

urns ma occur *hen handling hot co e, from steam in the e$ent of a steam line lea , or fromhot *ater, hot co e or hot slurr *hich ma e e1+elled *hen o+ening co ers. he +otential

e1ists for e1+osure to aromatic na+hthas containing en"ene, h drogen sul+hide and car onmono1ide gases, and to trace amounts of carcinogenic )A6s associated *ith co ing o+erations.2aste sour *ater ma e highl al aline, and contain oil, sul+hides, ammonia and +henol. 2henco e is mo$ed as a slurr , o1 gen de+letion ma occur *ithin confined s+aces such as storagesilos, ecause *et car on adsor s o1 gen.

Catalytic cracking processes

Catal tic crac ing rea s u+ com+le1 h drocar ons into sim+ler molecules in order to increasethe /ualit and /uantit of lighter, more desira le +roducts and decrease the amount of residuals.6ea$ h drocar ons are e1+osed at high tem+erature and lo* +ressure to catal sts *hich

+romote chemical reactions. his +rocess rearranges the molecular structure, con$erting hea$h drocar on feedstoc s into lighter fractions such as erosene, gasoline, L)#, heating oil and +etrochemical feedstoc s 8see figure ; and figure ('9. Selection of a catal st de+ends u+on acom ination of the greatest +ossi le reacti$it and the est resistance to attrition. he catal stsused in refiner crac ing units are t +icall solid materials 8"eolite, aluminium h drosilicate,treated entonite cla , uller s earth, au1ite and silica-alumina9 *hich are in the form of

+o*ders, eads, +ellets or sha+ed materials called e1trudites.

igure ;. Catal tic crac ing +rocess

igure ('. Schematic of catal tic crac ing +rocess
http://www.ilo.org/oshenc/images/stories/enlarged/Part12/OIL_imgs/OIL10F27.jpghttp://www.ilo.org/oshenc/images/stories/enlarged/Part12/OIL_imgs/OIL010F8.jpg


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here are three asic functions in all catal tic crac ing +rocesses:

ReactionFfeedstoc reacts *ith catal st and crac s into different h drocar ons. RegenerationFcatal st is reacti$ated urning off co e.

ractionationFcrac ed h drocar on stream is se+arated into $arious +roducts.

Catal tic crac ing +rocesses are $er fle1i le and o+erating +arameters can e ad0usted to meetchanging +roduct demand. he three asic t +es of catal tic crac ing +rocesses are:

fluid catal tic crac ing 8 CC9 mo$ing ed catal tic crac ing

thermofor catal tic crac ing 8 CC9.

Fluid catalytic crac+ing

luid- ed catal tic crac ers ha$e a catal st section 8riser, reactor and regenerator9 and afractionating section, oth o+erating together as an integrated +rocessing unit. he CC usesfinel +o*dered catal st, sus+ended in oil $a+our or gas, *hich acts as a fluid. Crac ing ta es

+lace in the feed +i+e 8riser9 in *hich the mi1ture of catal st and h drocar ons flo* through thereactor.

he CC +rocess mi1es a +reheated h drocar on charge *ith hot, regenerated catal st as itenters the riser leading to the reactor. he charge com ines *ith rec cle oil *ithin the riser, is$a+ori"ed and is raised to reactor tem+erature the hot catal st. As the mi1ture tra$els u+ thereactor, the charge is crac ed at lo* +ressure. his crac ing continues until the oil $a+ours arese+arated from the catal st in the reactor c clones. he resultant +roduct stream enters a column*here it is se+arated into fractions, *ith some of the hea$ oil directed ac into the riser asrec cle oil.

S+ent catal st is regenerated to remo$e co e *hich collects on the catal st during the +rocess.S+ent catal st flo*s through the catal st stri++er to the regenerator *here it mi1es *ith

+reheated air, urning off most of the co e de+osits. resh catal st is added and *orn-outcatal st remo$ed to o+timi"e the crac ing +rocess.

/oving ed catalytic crac+ing

Mo$ing- ed catal tic crac ing is similar to fluid catal tic crac ing3 ho*e$er, the catal st is inthe form of +ellets instead of fine +o*der. he +ellets mo$e continuousl con$e or or

+neumatic lift tu es to a storage ho++er at the to+ of the unit, and then flo* do*n*ard gra$itthrough the reactor to a regenerator. he regenerator and ho++er are isolated from the reactor


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steam seals. he crac ed +roduct is se+arated into rec cle gas, oil, clarified oil, distillate, na+hthaand *et gas.

0hermofor catalytic crac+ing

In thermofor catal tic crac ing, the +reheated feedstoc flo*s gra$it through the catal ticreactor ed. @a+ours are se+arated from the catal st and sent to a fractionating to*er. he s+entcatal st is regenerated, cooled and rec cled, and the flue gas from regeneration is sent to acar on mono1ide oiler for heat reco$er .


Regular sam+ling and testing of feedstoc , +roduct and rec cle streams should e +erformed toassure that the crac ing +rocess is *or ing as intended and that no contaminants ha$e enteredthe +rocess stream. Corrosi$es or de+osits in feedstoc can foul gas com+ressors. 2hen

+rocessing sour crude, corrosion ma e e1+ected *here tem+eratures are elo*


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Catal st regeneration in$ol$es steam stri++ing and deco ing, *hich results in +otential e1+osureto fluid *aste streams *hich ma contain $ar ing amounts of sour *ater, h drocar on, +henol,ammonia, h drogen sul+hide, merca+tan and other materials, de+ending u+on the feedstoc s,crudes and +rocesses. Safe *or +ractices and the use of a++ro+riate +ersonal +rotecti$ee/ui+ment 8))E9 are needed *hen handling s+ent catal st, recharging catal st, or if lea s or

releases occur.

Hydrocracking process

6 drocrac ing is a t*o-stage +rocess com ining catal tic crac ing and h drogenation, *hereindistillate fractions are crac ed in the +resence of h drogen and s+ecial catal sts to +roduce moredesira le +roducts. 6 drocrac ing has an ad$antage o$er catal tic crac ing in that high-sul+hurfeedstoc s can e +rocessed *ithout +re$ious desul+huri"ation. In the +rocess, hea$ aromaticfeedstoc is con$erted into lighter +roducts under $er high +ressures and fairl hightem+eratures. 2hen the feedstoc has a high +araffinic content, the h drogen +re$ents theformation of )A6s, reduces tar formation and +re$ents uild-u+ of co e on the catal st.

6 drocrac ing +roduces relati$el large amounts of iso utane for al lation feedstoc s and alsocauses isomeri"ation for +our +oint control and smo e +oint control, oth of *hich are im+ortantin high-/ualit 0et fuel.

In the first stage, feedstoc is mi1ed *ith rec cled h drogen, heated and sent to the +rimarreactor, *here a large amount of the feedstoc is con$erted to middle distillates. Sul+hur andnitrogen com+ounds are con$erted a catal st in the +rimar stage reactor to h drogensul+hide and ammonia. he residual is heated and sent to a high-+ressure se+arator, *hereh drogen-rich gases are remo$ed and rec cled. he remaining h drocar ons are stri++ed or

+urified to remo$e the h drogen sul+hide, ammonia and light gases, *hich are collected in anaccumulator, *here gasoline is se+arated from sour gas.

he stri++ed li/uid h drocar ons from the +rimar reactor are mi1ed *ith h drogen and sent tothe second-stage reactor, *here the are crac ed into high-/ualit gasoline, 0et fuel and distillate

lending stoc s. hese +roducts go through a series of high- and lo*-+ressure se+arators toremo$e gases, *hich are rec cled. he li/uid h drocar ons are sta ili"ed, s+lit and stri++ed, *iththe light na+htha +roducts from the h drocrac er used to lend gasoline *hile the hea$ierna+hthas are rec cled or sent to a catal tic reformer unit. 8See figure ((.9

igure ((. 6 drocrac ing +rocess


Ins+ection and testing of safet relief de$ices are im+ortant due to the $er high +ressures in this +rocess. )ro+er +rocess control is needed to +rotect against +lugging reactor eds. ecause of the


26/57

o+erating tem+eratures and +resence of h drogen, the h drogen sul+hide content of the feedstoc must e strictl e+t to a minimum in order to reduce the +ossi ilit of se$ere corrosion.Corrosion *et car on dio1ide in areas of condensation must also e considered. 2hen

+rocessing high-nitrogen feedstoc s, the ammonia and h drogen sul+hide form ammoniumh drosul+hide, *hich causes serious corrosion at tem+eratures elo* the *ater de* +oint.

Ammonium h drosul+hide is also +resent in sour *ater stri++ing. ecause the h drocrac ero+erates at $er high +ressures and tem+eratures, control of oth h drocar on lea s andh drogen releases is im+ortant to +re$ent fires.

ecause this is a closed +rocess, e1+osures are minimal under normal o+erating conditions.here is a +otential for e1+osure to ali+hatic na+htha containing en"ene, carcinogenic )A6s,h drocar on gas and $a+our emissions, h drogen-rich gas and h drogen sul+hide gas as a resultof high-+ressure lea s. Large /uantities of car on mono1ide ma e released during catal stregeneration and changeo$er. Catal st steam stri++ing and regeneration creates *aste streamscontaining sour *ater and ammonia. Safe *or +ractices and a++ro+riate +ersonal +rotecti$ee/ui+ment are needed *hen handling s+ent catal st. In some +rocesses, care is needed to assure

that e1+losi$e concentrations of catal tic dust do not form during recharging. nloading co edcatal st re/uires s+ecial +recautions to +re$ent iron sul+hideinduced fires. he co ed catal stshould either e cooled to elo*


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Se$ere corrosion, leading to e/ui+ment failure, *ill occur should *ater contact the +hos+horicacid, such as during *ater *ashing at shutdo*ns. Corrosion ma also occur in +i+ing manifolds,re oilers, e1changers and other locations *here acid ma settle out. here is a +otential fore1+osure to caustic *ash 8sodium h dro1ide9, to +hos+horic acid used in the +rocess or *ashedout during turnarounds, and to catal st dust. he +otential for an uncontrolled e1othermicreaction e1ists should loss of cooling *ater occur.

!l+ylation

Al lation com ines the molecules of olefins +roduced from catal tic crac ing *ith those ofiso+araffins in order to increase the $olume and octane of gasoline lends. !lefins *ill react *ithiso+araffins in the +resence of a highl acti$e catal st, usuall sul+huric acid or h drofluoric acid8or aluminium chloride9 to create a long- ranched-chain +araffinic molecule, called al+ylate 8iso-octane9, *ith e1ce+tional anti- noc /ualit . he al late is then se+arated and fractionated. herelati$el lo* reaction tem+eratures of (' C to (5 C for sul+huric acid, &? C to ' C forh drofluoric acid 86 9 and ' C for aluminium chloride, are controlled and maintained refrigeration. 8See figure (7.9

igure (7. Al lation +rocess

Sulphuric acid al+ylation. In cascade-t +e sul+huric acid al lation units, feedstoc s, including +ro+ lene, ut lene, am lene and fresh iso utane, enter the reactor, *here the contact thesul+huric acid catal st. he reactor is di$ided into "ones, *ith olefins fed through distri utors toeach "one, and the sul+huric acid and iso utanes flo*ing o$er affles from "one to "one.Reaction heat is remo$ed e$a+oration of iso utane. he iso utane gas is remo$ed from theto+ of the reactor, cooled and rec cled, *ith a +ortion directed to the de+ro+ani"er to*er.Residual from the reactor is settled, and the sul+huric acid is remo$ed from the ottom of the

$essel and recirculated. Caustic and=or *ater scru ers are used to remo$e small amounts of acidfrom the +rocess stream, *hich then goes to a de-iso utani"er to*er. he de utani"er iso utaneo$erhead is rec cled, and the remaining h drocar ons are se+arated in a rerun to*er and=or sentto lending.

Hydrofluoric acid al+ylation. here are t*o t +es of h drofluoric acid al lation +rocesses:)hilli+s and !). In the )hilli+s +rocess, olefin and iso utane feedstoc is dried and fed to acom ination reactor=settler unit. he h drocar on from the settling "one is charged to the main


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fractionator. he main fractionator o$erhead goes to a de+ro+ani"er. )ro+ane, *ith trace amountsof h drofluoric acid 86 9, goes to an 6 stri++er, and is then catal ticall defluorinated, treatedand sent to storage. Iso utane is *ithdra*n from the main fractionator and rec cled to thereactor=settler, and al late from the ottom of the main fractionator is sent to a s+litter.

he !) +rocess uses t*o reactors *ith se+arate settlers. 6alf of the dried feedstoc is chargedto the first reactor, along *ith rec cle and ma e-u+ iso utane, and then to its settler, *here theacid is rec cled and the h drocar on charged to the second reactor. he other half of thefeedstoc goes to the second reactor, *ith the settler acid eing rec cled and the h drocar onscharged to the main fractionator. Su se/uent +rocessing is similar to )hilli+s in that the o$erheadfrom the main fractionator goes to a de+ro+ani"er, iso utane is rec cled and al late is sent to as+litter.


Sul+huric acid and h drofluoric acid are dangerous chemicals, and care during deli$er and

unloading of acid is essential. here is a need to maintain sul+huric acid concentrations of 4 to; for good o+eration and to minimi"e corrosion. o +re$ent corrosion from h drofluoric acid,acid concentrations inside the +rocess unit must e maintained a o$e 5 and moisture elo*< . Some corrosion and fouling in sul+huric acid units occurs from the rea do*n of sul+huricacid esters, or *here caustic is added for neutrali"ation. hese esters can e remo$ed fresh-acid treating and hot-*ater *ashing.

+sets can e caused loss of the coolant *ater needed to maintain +rocess tem+eratures.)ressure on the cooling *ater and steam side of e1changers should e e+t elo* the minimum

+ressure on the acid ser$ice side to +re$ent *ater contamination. @ents can e routed to soda ashscru ers to neutrali"e h drogen fluoride gas or h drofluoric acid $a+ours efore release. Cur s,

drainage and isolation ma e +ro$ided for +rocess unit containment so that effluent can eneutrali"ed efore release to the se*er s stem.

6 drofluoric acid units should e thoroughl drained and chemicall cleaned +rior toturnarounds and entr , to remo$e all traces of iron fluoride and h drofluoric acid. ollo*ingshutdo*n, *here *ater has een used, the unit should e thoroughl dried efore h drofluoricacid is introduced. Lea s, s+ills or releases in$ol$ing h drofluoric acid, or h drocar onscontaining h drofluoric acid, are e1tremel ha"ardous. )recautions are necessar to assure thate/ui+ment and materials *hich ha$e een in contact *ith acid are handled carefull and arethoroughl cleaned efore the lea$e the +rocess area or refiner . Immersion *ash $ats are often

+ro$ided for neutrali"ation of e/ui+ment *hich has come into contact *ith h drofluoric acid.

here is a +otential for serious ha"ardous and to1ic e1+osures should lea s, s+ills or releasesoccur. Birect contact *ith sul+huric or h drofluoric acid *ill cause se$ere s in and e e damage,and inhalation of acid mists or h drocar on $a+ours containing acid *ill cause se$ere irritationand damage to the res+irator s stem. S+ecial +recautionar emergenc +re+aredness measuresshould e used, and +rotection should e +ro$ided that is a++ro+riate to the +otential ha"ard andareas +ossi l affected. Safe *or +ractices and a++ro+riate s in and res+irator +ersonal

+rotecti$e e/ui+ment are needed *here +otential e1+osures to h drofluoric and sul+huric acids


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during normal o+erations e1ist, such as reading gauges, ins+ecting and +rocess sam+ling, as *ellas during emergenc res+onse, maintenance and turnaround acti$ities. )rocedures should e in

+lace to assure that +rotecti$e e/ui+ment and clothing *orn in sul+huric or h drofluoric acidacti$ities, including chemical +rotecti$e suits, head and shoe co$erings, glo$es, face and e e

+rotection and res+irator +rotecti$e e/ui+ment, are thoroughl cleaned and decontaminated

efore reissue.

#earranging processes

Catalytic reforming and isomeri1ation are +rocesses *hich rearrange h drocar on molecules to +roduce +roducts *ith different characteristics. After crac ing, some gasoline streams, althoughof the correct molecular si"e, re/uire further +rocessing to im+ro$e their +erformance, ecausethe are deficient in some /ualities, such as octane num er or sul+hur content. 6 drogen 8steam9reforming +roduces additional h drogen for use in h drogenation +rocessing.

Catalytic reforming

Catal tic reforming +rocesses con$ert lo*-octane hea$ na+hthas into aromatic h drocar ons for +etrochemical feedstoc s and high-octane gasoline com+onents, called reformates2 molecularrearrangement or deh drogenation. Be+ending on the feedstoc and catal sts, reformates can e

+roduced *ith $er high concentrations of toluene, en"ene, 1 lene and other aromatics useful ingasoline lending and +etrochemical +rocessing. 6 drogen, a significant -+roduct, is se+aratedfrom the reformate for rec cling and use in other +rocesses. he resultant +roduct de+ends onreactor tem+erature and +ressure, the catal st used and the h drogen rec cle rate. Some catal ticreformers o+erate at lo* +ressure and others at high +ressure. Some catal tic reforming s stemscontinuousl regenerate the catal st, some facilities regenerate all of the reactors duringturnarounds, and others ta e one reactor at a time off stream for catal st regeneration.

In catal tic reforming, na+htha feedstoc is +retreated *ith h drogen to remo$e contaminantssuch as chlorine, sul+hur and nitrogen com+ounds, *hich could +oison the catal st. he +roductis flashed and fractionated in to*ers *here the remaining contaminants and gases are remo$ed.he desul+huri"ed na+htha feedstoc is sent to the catal tic reformer, *here it is heated to a$a+our and +assed through a reactor *ith a stationar ed of i-metallic or metallic catal stcontaining a small amount of +latinum, mol denum, rhenium or other no le metals. he t*o

+rimar reactions *hich occur are +roduction of high-octane aromatics remo$ing h drogenfrom the feedstoc molecules, and the con$ersion of normal +araffins to ranched-chain oriso+araffins.

In +latforming, another catal tic reforming +rocess, feedstoc *hich has not eenh drodesul+huri"ed is com ined *ith rec cle gas and first +assed o$er a less e1+ensi$e catal st.An remaining im+urities are con$erted to h drogen sul+hide and ammonia, and remo$ed eforethe stream +asses o$er the +latinum catal st. 6 drogen-rich $a+our is recirculated to inhi itreactions *hich ma +oison the catal st. he reactor out+ut is se+arated into li/uid reformate,*hich is sent to a stri++ing to*er, and gas, *hich is com+ressed and rec cled. 8See figure (


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!+erating +rocedures are needed to control hot s+ots during start-u+. Care must e ta en not to rea or crush the catal st *hen loading the eds, as small fines *ill +lug u+ the reformerscreens. )recautions against dust *hen regenerating or re+lacing catal st are needed. Smallemissions of car on mono1ide and h drogen sul+hide ma occur during regeneration of catal st.

2ater *ash should e considered *here sta ili"er fouling has occurred in reformers due to theformation of ammonium chloride and iron salts. Ammonium chloride ma form in +retreatere1changers and cause corrosion and fouling. 6 drogen chloride, from the h drogenation ofchlorine com+ounds, ma form acids or ammonium chloride salt. he +otential e1ists fore1+osure to ali+hatic and aromatic na+hthas, h drogen-rich +rocess gas, h drogen sul+hide and

en"ene should a lea or release occur.

3someri1ation

Isomeri"ation con$erts n- utane, n-+entane and n-he1ane into their res+ecti$e iso-+araffins.Some of the normal straight-chain +araffin com+onents of light straight-run na+htha are lo* inoctane. hese can e con$erted to high-octane, ranched-chain isomers rearranging the onds

et*een atoms, *ithout changing the num er or inds of atoms. Isomeri"ation is similar tocatal tic reforming in that the h drocar on molecules are rearranged, ut unli e catal ticreforming, isomeri"ation 0ust con$erts normal +araffins to iso-+araffins. Isomeri"ation uses adifferent catal st than catal tic reforming.

he t*o distinct isomeri"ation +rocesses are utane 8C


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)entane=he1ane isomeri"ation is used to increase the octane num er con$erting n-+entane andn-he1ane. In a t +ical +entane=he1ane isomeri"ation +rocess, dried and desul+huri"ed feedstocis mi1ed *ith a small amount of organic chloride and rec cled h drogen, and heated to reactortem+erature. It is then +assed o$er su++orted-metal catal st in the first reactor, *here en"eneand olefins are h drogenated. he feed ne1t goes to the isomeri"ation reactor, *here the

+araffins are catal ticall isomeri"ed to iso+araffins, cooled and +assed to a se+arator. Se+aratorgas and h drogen, *ith ma e-u+ h drogen, is rec cled. he li/uid is neutrali"ed *ith al aline


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materials and sent to a stri++er column, *here h drogen chloride is reco$ered and rec cled. 8Seefigure (5.9

igure (5. Isomeri"ation +rocess

If the feedstoc is not com+letel dried and desul+huri"ed, the +otential e1ists for acid formation,leading to catal st +oisoning and metal corrosion. 2ater or steam must not e allo*ed to enterareas *here h drogen chloride is +resent. )recautions are needed to +re$ent 6Cl from enteringse*ers and drains. here is a +otential for e1+osure to iso+entane and ali+hatic na+htha $a+oursand li/uid, as *ell as to h drogen-rich +rocess gas, h drochloric acid and h drogen chloride, andto dust *hen solid catal st is used.

Hydrogen production $steam reforming%

6igh-+urit h drogen 8; to ;; 9 is needed for h drodesul+huri"ation, h drogenation,h drocrac ing and +etrochemical +rocesses. If not enough h drogen is +roduced as -+roductsof refiner +rocesses to meet the total refiner demand, the manufacture of additional h drogenis re/uired.

In h drogen steam reforming, desul+huri"ed gases are mi1ed *ith su+erheated steam andreformed in tu es containing a nic el ase catal st. he reformed gas, *hich consists of steam,h drogen, car on mono1ide and car on dio1ide, is cooled and +assed through con$erters *herethe car on mono1ide reacts *ith steam to form h drogen and car on dio1ide. he car ondio1ide is scru ed *ith amine solutions and $ented to the atmos+here *hen the solutions arereacti$ated heating. An car on mono1ide remaining in the +roduct stream is con$erted tomethane. 8See figure (?.9

igure (?. Steam reforming +rocess

Ins+ections and testing must e conducted *here the +ossi ilit e1ists for $al$e failure due tocontaminants in the h drogen. Carr o$er from caustic scru ers to +re$ent corrosion in

+reheaters must e controlled and chlorides from the feedstoc or steam s stem +re$ented fromentering reformer tu es and contaminating the catal st. E1+osures can result from contaminationof condensate +rocess materials such as caustics and amine com+ounds, and from e1cess


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h drogen, car on mono1ide and car on dio1ide. he +otential e1ists for urns from hot gasesand su+erheated steam should a release occur.

&iscellaneous refinery processes

%u ricant ase stoc+ and 4a" processes

Lu ricating oils and *a1es are refined from $arious fractions of atmos+heric and $acuumdistillation. 2ith the in$ention of $acuum distillation, it *as disco$ered that the *a1 residuummade a etter lu ricant than an of the animal fats that *ere then in use, *hich *as the

eginning of modern h drocar on lu ricant refining technolog , *hose +rimar o 0ecti$e is toremo$e undesira le +roducts, such as as+halts, sul+honated aromatics and +araffinic and iso-

+araffinic *a1es from the residual fractions in order to +roduce high-/ualit lu ricants. his isdone a series of +rocesses including de-as+halting, sol$ent e1traction and se+aration andtreatment +rocesses such as de*a1ing and h drofinishing. 8See figure (49

igure (4. Lu ricating oil *a1 manufacturing +rocess

In e1traction +rocessing, reduced crude from the $acuum unit is +ro+ane de-as+halted andcom ined *ith straight-run lu ricating-oil feedstoc , +reheated and sol$ent e1tracted to +roducea feedstoc called raffinate. In a t +ical e1traction +rocess *hich uses +henol as the sol$ent, thefeedstoc is mi1ed *ith +henol in the treating section at tem+eratures elo* &'< C. )henol isthen se+arated from the raffinate and rec cled. he raffinate ma then e su 0ected to anothere1traction +rocess *hich uses furfural to se+arate aromatic com+ounds from non-aromatich drocar ons, +roducing a lighter-coloured raffinate *ith im+ro$ed $iscosit inde1 ando1idation and thermal sta ilit .

Be*a1ed raffinate ma also e su 0ect to further +rocessing to im+ro$e the /ualities of the asestoc . Cla adsor ents are used to remo$e dar -coloured, unsta le molecules from lu ricating-oil ase stoc s. An alternate +rocess, lu e h drofinishing, +asses hot de*a1ed raffinate andh drogen through a catal st that slightl changes the molecular structure, resulting in a lighter-coloured oil *ith im+ro$ed characteristics. he treated lu e oil ase stoc s are then mi1ed and=or com+ounded *ith additi$es to meet the re/uired +h sical and chemical characteristics of motoroils, industrial lu ricants and metal-*or ing oils.

he t*o distinct t +es of *a1 deri$ed from crude oil are +araffin *a1, +roduced from distillatestoc s, and microcr stalline *a1, manufactured from residual stoc s. Raffinate from thee1traction unit contains a considera le amount of *a1, *hich can e remo$ed sol$ente1traction and cr stalli"ation. he raffinate is mi1ed *ith a sol$ent, such as +ro+ane, meth leth l etone 8MEK9 and toluene mi1ture or meth l iso ut l etone 8MI K9, and +recooled inheat e1changers. he cr stalli"ation tem+erature is attained the e$a+oration of the +ro+ane in


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the chiller and filter feed tan s. he *a1 is continuousl remo$ed filters and cold sol$ent*ashed to reco$er retained oil. he sol$ent is reco$ered from the de*a1ed raffinate flashingand steam stri++ing, and rec cled.

he *a1 is heated *ith hot sol$ent, chilled, filtered and gi$en a final *ash to remo$e all traces of

oil. efore the *a1 is used, it ma e h dro-finished to im+ro$e its odour and eliminate all tracesof aromatics so the *a1 can e used in food +rocessing. he de*a1ed raffinate, *hich containssmall amounts of +araffins, na+hthenes and some aromatics, ma e further +rocessed for use aslu ricating-oil ase stoc s.

Control of treater tem+erature is im+ortant to +re$ent corrosion from +henol. 2a1 can clog se*er or oil drainage s stems and interfere *ith *aste *ater treatment. he +otential e1ists fore1+osure to +rocess sol$ents such as +henol, +ro+ane, a meth l eth l etone and toluene mi1tureor meth l iso ut l etone. Inhalation of h drocar on gases and $a+ours, aromatic na+hthacontaining en"ene, h drogen sul+hide and h drogen-rich +rocess gas is a ha"ard.

!sphalt processing

After +rimar distillation o+erations, as+halt is a +ortion of residual matter *hich re/uires further +rocessing to im+art characteristics re/uired its final use. As+halt for roofing materials is +roduced air lo*ing. Residual is heated in a +i+e still almost u+ to its flash+oint and chargedto a lo*ing to*er *here hot air is in0ected for a +redetermined +eriod of time. he deh drogenation of the as+halt forms h drogen sul+hide, and the o1idation creates sul+hur dio1ide. Steam isused to lan et the to+ of the to*er to entrain the contaminants, and is +assed through a scru er to condense the h drocar ons.

@acuum distillation is generall used to +roduce road tar as+halt. he residual is heated and

charged to a column *here $acuum is a++lied to +re$ent crac ing.

Condensed steam from the $arious as+halt +rocesses *ill contain trace amounts of h drocar ons.An disru+tion of the $acuum can result in the entr of atmos+heric air and su se/uent fire. Inas+halt +roduction, raising the tem+erature of the $acuum to*er ottom to im+ro$e efficienccan generate methane thermal crac ing. his creates $a+ours in as+halt storage tan s *hichare in the flamma le range, ut not detecta le flash testing. Air lo*ing can create some

+ol nuclear aromatics 8i.e., )A6s9. Condensed steam from the air lo*ing as+halt +rocess maalso contain $arious contaminants.

Hydrocarbon sweetening and treating processes

Man +roducts, such as thermal na+hthas from $is rea ing, co ing or thermal crac ing, andhigh-sul+hur na+hthas and distillates from crude-oil distillation, re/uire treating in order to eused in gasoline and fuel oil lends. Bistillation +roducts, including erosene and otherdistillates, ma contain trace amounts of aromatics, and na+hthenes and lu ricating-oil asestoc s ma contain *a1. hese undesira les are remo$ed either at intermediate refining stages or

0ust +rior to sending +roducts to lending and storage, refining +rocesses such as sol$ent


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e1traction and sol$ent de*a1ing. A $ariet of intermediate and finished +roducts, includingmiddle distillates, gasoline, erosene, 0et fuel and sour gases need to e dried and s*eetened.

reating is +erformed either at an intermediate stage in the refining +rocess or 0ust eforesending finished +roducts to lending and storage. reating remo$es contaminants from oil, such

as organic com+ounds containing sul+hur, nitrogen and o1 gen, dissol$ed metals, inorganic saltsand solu le salts dissol$ed in emulsified *ater. reating materials include acids, sol$ents, al alisand o1idi"ing and adsor+tion agents. Acid treatments are used to im+ro$e the odour, colour andother +ro+erties of lu e ase stoc s, to +re$ent corrosion and catal st contamination, and toim+ro$e +roduct sta ilit . 6 drogen sul+hide *hich is remo$ed from dr D sour gas ana sor ing agent 8diethanolamine9 is flared, used as a fuel or con$erted to sul+hur. he t +e oftreatment and agents de+ends on the crude feedstoc , intermediate +rocesses and end-+roducts+ecifications.

Sol ent treatment processes

Solvent e"traction se+arates aromatics, na+hthenes and im+urities from +roduct streams dissol$ing or +reci+itation. Sol$ent e1traction +re$ents corrosion, +rotects catal st in su se/uent +rocesses and im+ro$es finished +roducts remo$ing unsaturated, aromatic h drocar ons fromlu ricant and grease ase stoc s.

he feedstoc is dried and su 0ected to continuous countercurrent sol$ent treatment. In one +rocess, feedstoc is *ashed *ith a li/uid in *hich the su stances to e remo$ed are moresolu le than in the desired resultant +roduct. In another +rocess, selected sol$ents are added,causing im+urities to +reci+itate out of the +roduct. he sol$ent is se+arated from the +roductstream heating, e$a+oration or fractionation, *ith residual trace amounts su se/uentlremo$ed from the raffinate steam stri++ing or $acuum flashing. Electric +reci+itation ma e

used for se+aration of inorganic com+ounds. he sol$ent is then regenerated to e used again inthe +rocess.

+ical chemicals used in the e1traction +rocess include a *ide $ariet of acids, al alis andsol$ents, including +henol and furfural, as *ell as o1idi"ing agents and adsor+tion agents. In theadsor+tion +rocess, highl +orous solid materials collect li/uid molecules on their surfaces. heselection of s+ecific +rocesses and chemical agents de+ends on the nature of the feedstoc eingtreated, the contaminants +resent and the finished +roduct re/uirements. 8See figure (;.9

igure (;. Sol$ent e1traction +rocess

Solvent de4a"ing remo$es *a1 from either distillate or residual ase stoc s, and ma e a++liedat an stage in the refining +rocess. In sol$ent de*a1ing, *a1 feedstoc s are chilled heate1changer and refrigeration, and sol$ent is added to hel+ de$elo+ cr stals that are remo$ed


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$acuum filtration. he de*a1ed oil and sol$ent are flashed and stri++ed, and the *a1 +assesthrough a *ater settler, sol$ent fractionator and flash to*er. 8See figure &'.9

igure &'. Sol$ent de*a1ing +rocess

Solvent de$asphalting se+arates hea$ oil fractions to +roduce hea$ lu ricating oil, catal ticcrac ing feedstoc and as+halt. eedstoc and li/uid +ro+ane 8or he1ane9 are +um+ed to ane1traction to*er at +recisel controlled mi1tures, tem+eratures and +ressures. Se+aration occursin a rotating-disc contactor, ased on differences in solu ilit . he +roducts are then e$a+oratedand steam stri++ed to reco$er +ro+ane for rec cle. Sol$ent de-as+halting also remo$es sul+hurand nitrogen com+ounds, metals, car on residues and +araffins from feedstoc . 8See figure &(.9

igure &(. Sol$ent de-as+halting +rocess

Health and safety considerations.

In sol$ent de*a1ing, disru+tion of the $acuum *ill create a +otential fire ha"ard allo*ing airto enter the unit. he +otential e1ists for e1+osure to de*a1ing sol$ent $a+ours, a mi1ture ofMEK and toluene. Although sol$ent e1traction is a closed +rocess, there is +otential e1+osure tocarcinogenic )A6s in the +rocess oils and to e1traction sol$ents such as +henol, furfural, gl col,MEK, amines and other +rocess chemicals during handling and o+erations.

Be-as+halting re/uires e1act tem+erature and +ressure control to a$oid u+set. In addition,moisture, e1cess sol$ent or a dro+ in o+erating tem+erature ma cause foaming *hich affects the

+roduct tem+erature control and ma create an u+set. Contact *ith hot oil streams *ill cause s in urns. he +otential e1ists for e1+osure to hot oil streams containing carcinogenic +ol c clicaromatic com+ounds, li/uefied +ro+ane and +ro+ane $a+ours, h drogen sul+hide and sul+hur

dio1ide. Hydrotreating processes

6 drotreating is used to remo$e a out ;' of contaminants, including nitrogen, sul+hur, metalsand unsaturated h drocar ons 8olefins9, from li/uid +etroleum fractions such as straight-rungasoline. 6 drotreating is similar to h drocrac ing in that oth the h drogen and the catal st areused to enrich the h drogen content of the olefin feedstoc . 6o*e$er, the degree of saturation is


37/57


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ammonia should a sour *ater lea or s+ill occur. )henol ma also e +resent if high- oiling- +oint feedstoc s are +rocessed.

E1cessi$e contact time and=or tem+erature *ill create co ing in the unit. )recautions need to eta en *hen unloading co ed catal st from the unit to +re$ent iron sul+hide fires. he co ed

catal st should e cooled to elo*


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S*eetening 8merca+tan remo$al9 treats sul+hur com+ounds 8h drogen sul+hide, thio+hene andmerca+tan9 to im+ro$e colour, odour and o1idation sta ilit , and reduces concentrations ofcar on dio1ide in gasoline. Some merca+tans are remo$ed ha$ing the +roduct ma e contact*ith *ater-solu le chemicals 8e.g., sul+huric acid9 that react *ith the merca+tans. Caustic li/uid8sodium h dro1ide9, amine com+ounds 8diethanolamine9 or fi1ed- ed catal st s*eetening ma

e used to con$ert merca+tans to less o 0ectiona le disul+hides.

)roduct dr ing 8*ater remo$al9 is accom+lished *ater a sor+tion, *ith or *ithout adsor+tionagents. Some +rocesses simultaneousl dr and s*eeten adsor+tion on molecular sie$es.

Sulphur recovery

Sul+hur reco$er remo$es h drogen sul+hide from sour gases and h drocar on streams. heClause +rocess con$erts h drogen sul+hide to elemental sul+hur through the use of thermal andcatal tic reactions. After urning h drogen sul+hide under controlled conditions, noc out +otsremo$e *ater and h drocar ons from feed-gas streams, *hich are then e1+osed to a catal st to

reco$er additional sul+hur. he sul+hur $a+our from urning and con$ersion is condensed andreco$ered.

0ail gas treatment

oth o1idation and reduction are used to treat tail gas from sul+hur reco$er units, de+ending onthe com+osition of the gas and on refiner economics. !1idation +rocesses urn tail gas tocon$ert all sul+hur com+ounds to sul+hur dio1ide, and reduction +rocesses con$ert sul+hurcom+ounds to h drogen sul+hide.

Hydrogen sulphide scru ing

6 drogen sul+hide scru ing is a +rimar h drocar on feedstoc treating +rocess used to +re$ent catal st +oisoning. Be+ending on the feedstoc and the nature of the contaminants,desul+huri"ation methods *ill $ar from am ient-tem+erature-acti$ated charcoal a sor+tion tohigh-tem+erature catal tic h drogenation follo*ed "inc o1ide treating.

Sat and unsat gas plants

eedstoc s from $arious refiner units are sent to gas treating +lants, *here utanes and utenesare remo$ed for use as al lation feedstoc , hea$ier com+onents are sent to gasoline lending,

+ro+ane is reco$ered for L)# and +ro+ lene is remo$ed for use in +etrochemicals.

Sat gas plants se+arate com+onents from refiner gases, including utanes for al lation, +entanes for gasoline lending, L)#s for fuel and ethane for +etrochemicals. here are t*odifferent sat gas +rocesses: a sor+tion-fractionation or straight fractionation. In a sor+tion-fractionation, gases and li/uids from $arious units are fed to an a sor er=de-ethani"er *here C & and lighter fractions are se+arated lean-oil a sor+tion and remo$ed for use as fuel gas or

+etrochemical feed. he remaining hea$ier fractions are stri++ed and sent to a de utani"er, andthe lean oil is rec cled ac to the a sor er=de-ethani"er. C 7=C< is se+arated from +entanes in the


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Lu ricating oils are lends of refined ase stoc s

As+halt is lended from $arious residual stoc s de+ending on its intended use.

Additi$es are often mi1ed into gasoline and motor fuels during or after lending to +ro$ides+ecific +ro+erties not inherent in +etroleum h drocar ons. hese additi$es include octaneenhancers, anti- noc agents, anti-o1idants, gum inhi itors, foam inhi itors, rust inhi itors,car urettor 8car on9 cleaners, detergents for in0ector cleaning, diesel odouri"ers, colour d es,distillate anti-static, gasoline o1idi"ers such as methanol, ethanol and meth l tertiar ut l ether,metal deacti$ators and others.

atch and in-line lending o+erations re/uire strict controls to maintain desired +roduct /ualit .S+ills should e cleaned and lea s re+aired to a$oid sli+s and falls. Additi$es in drums and agsneed to e handled +ro+erl to a$oid strain and e1+osure. he +otential for contacting ha"ardousadditi$es, chemicals, en"ene and other materials e1ists during lending, and a++ro+riateengineering controls, +ersonal +rotecti$e e/ui+ment and +ro+er h giene are needed to minimi"ee1+osures.

Au'iliary Refinery Operations

Au1iliar o+erations su++orting refiner +rocesses include those *hich +ro$ide +rocess heat andcooling3 +ro$ide +ressure relief3 control air emissions3 collect and treat *aste *ater3 +ro$ideutilities such as +o*er, steam, air and +lant gases3 and +um+, store, treat and cool +rocess *ater.

*aste water treatment

Refiner *aste *ater includes condensed steam, stri++ing *ater, s+ent caustic solutions, coolingto*er and oiler lo*do*n, *ash *ater, al aline and acid *aste neutrali"ation *ater and other

+rocess-associated *ater. 2aste *ater t +icall contains h drocar ons, dissol$ed materials,sus+ended solids, +henols, ammonia, sul+hides and other com+ounds. 2aste *ater treatment isused for +rocess *ater, runoff *ater and se*erage *ater +rior to their discharge. hesetreatments ma re/uire +ermits, or there must e rec cling.

he +otential e1ists for fire should $a+ours from *aste *ater containing h drocar ons reach asource of ignition during the treatment +rocess. he +otential e1ists for e1+osure to the $ariouschemicals and *aste +roducts during +rocess sam+ling, ins+ection, maintenance andturnarounds.

(retreatment

)retreatment is the initial se+aration of h drocar ons and solids from *aste *ater. A)Ise+arators, interce+tor +lates and settling +onds are used to remo$e sus+ended h drocar ons, oilsludge and solids gra$it se+aration, s imming and filtration. Acidic *aste *ater isneutrali"ed *ith ammonia, lime or soda ash. Al aline *aste *ater is treated *ith sul+huric acid,h drochloric acid, car on dio1ide-rich flue gas or sul+hur. Some oil-in-*ater emulsions are first


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heated to hel+ se+arate the oil and the *ater. #ra$it se+aration de+ends on the different s+ecificgra$ities of *ater and immisci le oil glo ules, *hich allo*s free oil to e s immed off thesurface of the *aste *ater.

Sour 4ater stripping

2ater containing sul+hides, called sour *ater, is +roduced in catal tic crac ing and h dro-treating +rocesses, and *hene$er steam is condensed in the +resence of gases containingh drogen sul+hide.

Stri++ing is used on *aste *ater containing sul+hides and=or ammonia, and sol$ent e1traction isused to remo$e +henols from *aste *ater. 2aste *ater *hich is to e rec cled ma re/uirecooling to remo$e heat and=or o1idation s+ra ing or air stri++ing to remo$e an remaining

+henols, nitrates and ammonia.

Secondary treatment

ollo*ing +retreatment, sus+ended solids are remo$ed sedimentation or air flotation. 2aste*ater *ith lo* le$els of solids is screened or filtered, and flocculation agents ma e added tohel+ se+aration. Materials *ith high adsor+tion characteristics are used in fi1ed- ed filters oradded to the *aste *ater to form a slurr *hich is remo$ed sedimentation or filtration.Secondar treatment +rocesses iologicall degrade and o1idi"e solu le organic matter theuse of acti$ated sludge, unaerated or aerated lagoons, tric ling filter methods or anaero ictreatments. Additional treatment methods are used to remo$e oils and chemicals from *aste*ater.

0ertiary treatment

ertiar treatments remo$e s+ecific +ollutants in order to meet regulator dischargere/uirements. hese treatments include chlorination, o"onation, ion e1change, re$erse osmosis,acti$ated car on adsor+tion, and others. Com+ressed o1 gen ma e diffused into *aste *aterstreams to o1idi"e certain chemicals or to satisf regulator o1 gen content re/uirements.

Cooling towers

Cooling to*ers remo$e heat from +rocess *ater e$a+oration and latent heat transfer et*eenhot *ater and air. he t*o t +es of to*ers are counterflo* and crossflo*.

In counterflo* cooling, hot +rocess *ater is +um+ed to the u++ermost +lenum andallo*ed to fall through the to*er. >umerous slats, or s+ra no""les, are locatedthroughout the length of the to*er to dis+erse the *ater flo* and hel+ in cooling.Simultaneousl , air enters at the to*er ottom, creating a concurrent flo* of air againstthe *ater. Induced draft to*ers ha$e the fans at the air outlet. orced draft to*ers ha$ethe fans or lo*ers at the air inlet.

Crossflo* to*ers introduce airflo* at right angles to the *ater flo* throughout thestructure.


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Recirculated cooling *ater must e treated to remo$e im+urities and an dissol$edh drocar ons. Im+urities in cooling *ater can corrode and foul +i+ing and heat e1changers, scalefrom dissol$ed salts can de+osit on +i+es, and *ooden cooling to*ers can e damaged micro-

organisms.

Cooling to*er *ater can e contaminated +rocess materials and -+roducts, includingsul+hur dio1ide, h drogen sul+hide and car on dio1ide, *ith resultant e1+osures. here is

+otential for e1+osure to *ater treatment chemicals or to h drogen sul+hide *hen *aste *ater istreated in con0unction *ith cooling to*ers. ecause the *ater is saturated *ith o1 gen from

eing cooled *ith air, the chances for corrosion are intensified. !ne means of corrosion +re$ention is the addition of a material to the cooling *ater *hich forms a +rotecti$e film on +i+es and other metal surfaces.

2hen cooling *ater is contaminated h drocar ons, flamma le $a+ours can e$a+orate into the

discharge air. If a source of ignition or lightning is +resent, fires ma start. ire ha"ards e1ist*hen there are relati$el dr areas in induced-draft cooling to*ers of com usti le construction.Loss of +o*er to cooling to*er fans or *ater +um+s can create serious conse/uences in +rocesso+erations.

Steam generation

Steam is +roduced through heater and oiler o+erations in central steam generation +lants and at$arious +rocess units, using heat from flue gas or other sources. Steam generation s stemsinclude:

heaters 8furnaces9, *ith their urners and a com ustion air s stem draft or +ressure s stems to remo$e flue gas from the furnace, soot lo*ers, andcom+ressed air s stems *hich seal o+enings to +re$ent flue gas from esca+ing

oilers, consisting of a num er of tu es *hich carr the *ater=steam mi1ture through thefurnace +ro$iding for ma1imum heat transfer 8these tu es run et*een steam distri utiondrums at the to+ of the oiler, and *ater collecting drums

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