US2334341A - Process for recovery of tar oils - Google Patents

Description

Nov. 16, 1943. P. E, MALsoN I PROCESS FOR RECOVERY 0F TAR OILS Filed Sept. 22, 1942 /Nma Inl/enfer.' Par/rer 7W/'f7 Ma/son.

5g bis Hfromeyf L Patented Nov. 16, 1943 l V27,334,341 l PROCESS FOR RECOVERY Oli'` TAR ons! 1 AParker Erwin Maison,` East Altoil, Ill..` assigner to y Shell "Development Q'Co'inpany,` San Francisco,- Calif., acorporationY of Delaware f Application septmb'ersz, 1942, serial No. 459,343 v @15 claims."V 91;126975) Y This invention relates to anew andimproved prooessfor depressuring, steaming, and cooling a petroleum oil co-king chamber immediately after discontinuance of the coking-operation'of said chamber `and prior "tothe removal ofthe coke therein. More particularly, it dealswith the economical recovery of the residual oils which are present in the chamber after, the coking operation and which are removed as vapors during the depressuring and steaming (commonly referred to asV blowdown) of said coking chamber. Further, this invention deals more particularly with an economical process for the gradual cooling of the coke in thechamber, after said blow-down with steam, by the recirculation of a large volume of waterl at decreasing Vtem-- peratures through said coke in said chamber.

Previously, it'has been impractical to completely recover the residual oils removed during blow-down of a cracking coking chamber because of the large quantity of vapors which would have to be condensed to obtain such a complete recovery. Since thetemperature of the coke in such a chamber 'isV .loweredfrom about 800-1000 F. to about 1D0-200 F. in .as shortV a time as possibleby water, it isobvious that an enormous quantity of Water is necessary and that enormous amounts of oil andfwater vapors are produced, Usually the vapors from ,such blow-down are vented in a blow-olf pit in a field at a distance far enough away from the coking chamber that these vapors will not aiect'or hinder the eiiicient operation of the units of the refinery. Such procedureis obviously purely a waste of these oil vapors, yheat and water, al1

. of which represent a total loss so far as the operation of the cracking unit is concerned; Further, since a large portion Vof the residual oils removed from the coking'lchamber are fsub-f stantially as dense asorvdenser than water, they are not readilyV removed from refinery eiiiuents, and accordingly the drain from Vsaid blow-oii pits constitutes a bad contaminant for such eluents. Y

Also, previously there was little or no effort made to conserve the water used in Ycooling such chambers from about 310 l. to a temperature sufficiently low to permit opening of the chamber for removal of the coke therein. Here again,vthe water is usually run intoxthe reiineryeiiluent system or sewerwithout recirculationthrough the chamber or without any regard to controlling its temperature.4 Althouglfi water may be cheap, the Vamounts needed in such blow-down.andcool-v ing processes are very large over short periods ofn time and may,` not Ybeavailable in suicent quantities' atthe moment needed. Also, since thewater is used during a comparatively short period of timejandL throughv a restricted path,

, it may be necessary .to pump at a relatively high pressure from the water source. Accordingly,thev conservation of water is not an immaterial factor inl the'cost of'operation of such a ycoking unit.

It is the purpose of this invention to substantially completely, efficiently, and economically recover the residual -oils present in the vapors produced by the depressuring and steamingof a petroleumv oil .co-king chamber.' Another .purpose is to reduce the'oil contamination of the oil `refinery Water eiluentby the `removal of` said residual 'oils-andfthereb'y simplify the oil recovery from` said .eluent `Another purpose isito" reduce the `oil lfognuisancezatthe.bloWl-o pits. Still. another purpose is .to conserve` and; thereby reduce.v thev consumption of I the: water` for cooling such .coking chambers. L' z, ,1;

- The process.4 of this inventionis anmprovement in. one portion Vof thecycle of operation of. a cracking' cokingV chamber-more 4particularly, thatfportionoi the cycle between the'time theycoking chamber yis full Vimmediately after .shutting off thahot', oil feed,l and; the. opening of .the chamberior removing-the coke ptherein. In otherwords, it deals with the` depressuring,` steaming and cooling of the-coke in the chamber so it can .be'openedto the airand theV coke removed thereirom. z Generally, the yprocess or this 'invention consists of five main steps; namely, V(1),.depressuring; (2), steaming;l (3) hot watercooling; (4). cold water coolng,and (5) oil dehydration.;`

Depressuring (1)V comprises release .of the col:-l

ing pressureinthe chamber and recovering the oil in the vapors removed thereby. The heavier oils in ,the released vaporsgarelrst condensed-by a water spray in a trap. Then the lighteroils are condensed byl bubbling the remaining uncondensedfvapors into an opensteaming pit. De.

pressuring-is followed by` passing live steam (2) through the hot coking chamber to strip the oils and tars 'still remaining in the coke. These oil vapors are condensed ,in the same' tWo stages as mentioned intheY depressuringstep. After the steam has stripped out the lbulkoi these oils fromthe coke and assured'suicient porosityin the coke for subsequentlbperations, hot water (3) is introducedI into the Y chamber.` from` a -hot Water surge tank. soon aslthe hotpwate'r conwas the when the. chamber it isiurnedw seam which Strips 9111i. more Qilaprodilsihgvapors which.

At this time cold Water (4) is introduced into the chamber from a cold water surge tank and the vapors and water coming from the chamber are passed into the hot water surge tank mentioned above yuntil they reach a temperaturel of about 130 F., at which time they are passed into the cold water surge tank. The introduction of cold water is continued until the temperature of the chamber has been lowered su'ciently to permit the safe opening of the chamber 'so that the coke therein may be easily removed. The oil con.- densed and recovered in the pit above mentioned may be dehydrated (5) in any suitable manner,

- preferably by phase separation, to produce a dry oil iinal product. Y

The accompanying drawing shows a dov/ diagram of the improved coking chamber blowdown .recovery and cooling system of this invention; Referring to the drawing, the following` is detailed description of this improved process.

(1) Depr'essurz'ng-After the coking cycle in the coking chamber I has .been cut oli there exists a pressure of about 1.754200 pounds p. s. i. and normally a temperatureof about 80G-'1000" F. in the chamber.- which conditions must be lowered so that' the chamber may be opened and the coke removed. lThe first step tward this end consists of slowly opening the valve in vapor line I I at the top of the chamber so that the pressure .and oil vapors in the chambermay be released. These releasedoil vapors pass through line II into the oil trap I2 wherein they are cooled by a spray of water introduced 'into the trap through valved line'l3; The heavier and relatively higher boiloils in theV vapor are therein'condensed and collected'in the bottom of the trap, from which they are withdrawn through the'valved line I4 into the oil pit I5 continuously or from time to time, as desired. The uncondensed vapors, comprising the lighter lower boiling oils and steam generated from the Waterv spray for condensing the heavier oils inthe trap, are then passed through line'f into the bottom of an open steaming pit IIf partially lled withwater. The vapors entering said vtrap vary in temperature during the process from about-:800 to 215 and the vapors Vleaving said trap vary in temperature during th'e process from about .320 to' 215 F. The direct contact of these latter vapors with the Water condenses the lighter 'oils which neat on the surface of the Water in the pit; Whatever steam is not condensed by the water will pass `into theatmosphere aboveV the pit substantially -free from oil. 'As theligh'ter oils have anv A: P. I. gravity ranging between about.12.0 and 35.0, they accumulate on the surface 'of the water in pit II and are skimmed 'off by the 'gooseneck I8 into oil Dit I5.

l'.'Uhe heavier oils, which comprise about 95%'1by volume 'of theroil recovered and whichV are'collected in trap t2, are denser than water"(1.0).

Since thetemperature in the trap `varies lfrom a.

maximum of about 700-8U0 F. to a minimum of about 21d-235 F., and the pressure varies from a maximum of 30=50 pounds p; to 'about 0-2 p; s; i. gauge, it een readily be 5seen that s'libstantialli 'al1 of .the water introduced into the trap will be vapiiied and 'a'a's's out as steam through line it land into the open steaming pit II. The vapors passing 'from trapl range in temperature from about 215 to 320 F. when they nti' steaxi'fiing pit i-I and are under va pressure varying from 0 to about 30 pounds p. s. i. gauge. It is to be expected that some of the water vapor will not condense in open pit I'I, but will boil up and out through the surface of the water and oil nlm in the pit. Accordingly, pit I'I should havei suiiiciently high Walls to prevent bubbling over of the oil on the surface of the pit. In congested areas a tall stackinot shown). of suitable dimensions may be mounted over the pit I' I to disperse the vapors at a high elevation. Since the amount of lighter oils carried over into the pit is only "about 5% of the total oil recovered, passage through thewaterin the pit is normally suiicient to condense most of the lighter oils as Well as to condense enough water vapor to keep the amount of water inthe pit approximately constant.

2. Steming.-After the pressure in chamber I0 has .been released as described above, raw

steam-under pressure, say about 150 pounds p. sfi., is introduced into the bottom of thechamber '.throughthe valved line 20 to cool `the chamber'.l to remove any residual oils remaining` on the coke therein Whichwere not previouslyremoved by'depr'essuring and to assure' suiiicient porosity. of` the coke for: subsequent operations. The resulting steam and 'oil vaporszare'again passed 'through vapor line II into trap I2 and pit H,A as described above, until the temperature of the vapors coming .from chamber I0 has' been reduced from a maximum of about 800-1000 F. to a'minimum ofv about GOO-'700 F.; at which time the steam entering through'valved line 20 is cutoff.

vThis. .completes 'the steps of the process.

3. .Hoz water cooling-nner the tem'ygieraturey in coking chamber l0 has been reduced gradually as fara/s practical by steaming, hot water from surge tank 30 at an average temperature of' about'175 vF.' andnot lower than about 130".

cokeand are 'passed oi as 'describedV above' 'A through valve-d une H into traplz and pit-l1v as before. is present inthe vapor, it may pass directly into pit` Il through Valved -line 33, bypassing trap'IZLl When cooling has progressed to the point where the ,outlet vapors from the top of the chamber are :fat a temperature of about 310 F.i25 FL. the valved line II (or 33, whichever is open) 4is closed and valved line 3d isfopened so that -thevapors and hot water rising to the top ofchamber I0 are passed back into the hot water 'surge tank 30. By making thisA change at about 310 F. and at a pressure of abouty 50# per sq. in.l it caribe assured that very little, if

any, hotwater will enter the trap I2 and-emul-` sify the oil-therein. If this oil in the trap did emulsify it would pass on through line I6 and overflow pit I'I, thereby necessitating the pump'' ing of large volumes of water containing oil into thev water 'eluent system, and defeat one im' portant purpose of this .invention Simultaneously with the opening oifvalved` line 321, pump '3I isfstopped and v'alved line 32'v is closed 'to prevent lany further hot water fromy blow-down recovery- However, if substantially no heavyoil beingintroduced into chamber III.y -The water lost from the hot water surge vtank 30 as steam is made up from water from cold water surge tank 40 after passing it through the coke in the chamber I whereby itrisheated. Ordinarily, an excess of hot water is available `in the surge tank 30 and must be continuouslyor intermittently withdrawn through valvedline 3 5, in the bottom of tank 30 to the sewer, or it may be,

passed over a cooling water tower V(not shown) and returned to the cold water surge tank 40. This hot wateris substantially free ,ofV oil, i. e., less than .002% oil, and accordingly would not contaminate the sewer or cold water in surge tank 40. However, if sufficient hot wateris not available in the hot water vsurge tank 30 to prevent'iurther` steaming in chamber I0, cold water also may beV introduced into the bottom of the chamberv through valved line 42V and pump 4I from cold water surge tank 40. i

4. Cold water molina-When the vapors and steam stop coming from chamber I and valved lines I I (or 33) and 32 are closed as noted above, pump 4I is started and cold water from cold water surge tank 40 is introduced through valved line 42 into the bottom of chamber I0. When the water coming from the top of chamber I0 through valved line 34 has reached a temperature not higher than about 130` F., valved line 34 is closed and valved line 43 is opened. This cuts oil. hot waterreturn to the hot water'surge tank 30 and opens the return line to the. cold water surge tankV 40. When the water from the chamber I0 has been reduced to a temperature of about 10U-130 F. orsuiliciently low so that chamber I0 can be openedand coke therein removed, pump 4I is stopped and valved lines 42 and 43 are closed. The cold water passed from cold water surge tank 40 to the hot water surge tank I3 is made up continuously at a low rate through the cold water makeup valved line 44 into the cold water surge tank 40. The cold water in surge tank 40 normally has an average temperature of about 90 F., depending on atmospheric temperature, and a maximum temperature of not over about 130 F. In some cases recirculation of thecold water may not be necessary; however, the more the water is recirculated the smaller is the amount neededfor cooling. l t

A modication of this Aprocess not shown on the drawing comprises running water from cold water surge tank 40 into trap I2 through valved line I3; however, the water introduced into trap I2 through line I3 should be as cold as possible, and preferably as low as about 60 F.

This completes the water cooling steps. Y

5. Oil dehydration- The oils recovered from the above process and accumulated in the oil pit I5 still contain from about 5 to 35% by volume of water, which should be removed if the oil is to be put to an efficient use., This may be done in a dehydrator 50 or by other conventional dehydrating means not shown. Thus the wet' recovered oil may be withdrawn from pit I5 through valved line 5I as a nal wet oil product, or it may be passed into dehydrator 5I)` through valved line52 for the separation of some of the water in the oil. Recovered oil having the same or. greater density than water is introduced into dehydrator 50 through gooseneck 53 between the lower oil phase and the upper water phase so as to aid in its separation. Often an intermediate oil-water emulsion phase forms at .the end of Vat `a pressure of about pounds p. s. i.

gooseneck 53 in the dehydrator. The upper or water phase is withdrawn `from dehydrator 50 through the gooseneck 54 and valved line 55, andrdiscarded to the sewer. The lower oil phase is withdrawn from the bottom of the dehydrator through valved line 56 and may be further dehydrated or used as it is, whichever is desired.

It is important to maintain the contents of dehydrator 50 at a temperature not in excess of 160 F. because the gravity of water changes with changes in temperature at a different ratefrom the gravity of the oil recovered, both gravities being normally about the same at about 160 F;

If the temperature'in dehydrator 50 is maintained between about 140'and 150 F. the water phase Withdrawn from dehydrator 50 through lines 54 and 55 is clear and the oil phase contains only from about 1 to 5% water.

If the oil-water emulsion layer in the dehydrator 50 becomes too large and substantially no separation is obtained, it maybe withdrawn from dehydrator 50 through valved line 51 and pumped by pump 58 through valved lines 59 and 32 into coking chamber I0 right after the depressuring step (1) when the coke and chamber are hot enough to vaporize the oil in the emulsion and thereby break it, producing oil vapors which may again be condensed as described above in trap I2 and pit I'I.

The heavy oil recovered by the process of this invention is highly aromatic in nature and has an A. P. AI. gravity ranging from about 0.0 to 8.0. Normally it has a pour point ranging from about 5 to 75 F., a Saybolt Universal Viscosity at 100 F. of between 120 and 400 seconds, and a Saybolt Universal viscosity at 210 F. of between 30 and 500 seconds. Suchan oil has vmany uses; for example, it is a good blending stock for fuel oils, as well as prolic source of oy-products of polycyclic type.

C The several pieces of apparatus employed in carrying out the process of this invention may be of any convenient or conventional design provided it will withstand the conditions involved in carrying out the process.

The following specific example of actual plant operation will clearly illustrate the many advantages and economy `of the above process.

Emamfple.-A 500 barrel capacity Dubbs coking chamber, at a temperature'of 900 F., was depressured and steamed for 45 minutes with approximately 40,000 pounds `of steam introduced At the end of this time the steam was cut oi'f and the temperature of the vapors from the chamberwas found to be'about'lOO F. Hot water atatemperature of about 175 F. was pumped under a pressure of 300 pounds p. s. i. into the bottom of the chamber, slowly at rst and then more rapidly, as the chamber cooled, up to a rate of about600 gallons per minute, at whichtime the outlet vapors had decreased to a temperature of about 310 F. and were free of oil. The vapors were then switched to the hot water surge tank, and the hot water was turned off and cold water turned on under a pressure of about 200 pounds p.`s. i. and a rate of about Z50-1400 gallons per minute. Water was continuously withdrawn from the hot water surge tank at a rate of about 100V gallons per minute to the sewer to prevent its overflow. `As the water came out of the top ofthe chamber it was reduced in pressure to about 85 pounds-p. s. i.V due' to the resistance of the' coke in the chamber. of hot water used varied between about 40,000

The amountv and 60,000 gallons, wi th;a loss to sewer;` and-ftheformation y ol steam vof between about 5.000. andn 20,000 gallons.- --The amount of, cold water consumed was between about 151,000 and 30,000' gallons, most of which went -to replacethe hot water lost from the 'hot water surge tank. The cold water makeup was introduced into the cold twater` surgetank during Coldwater circulationgat aY rate of from 150 to 350 gallons per minute. As many as 5 chamberaeachof 500 barrels-capacity, may be handled ,within a periodV of 24 hours-,fand 2 or 3 rnay 7be cooled simultaneously with the'indiicated'amount of cold waterymakeup. vg

Oil was recoveredrrom the-vaporsy in the trap and steaming pitfduring the operation yofthe process with the aidof a cold water sprayhaying a-temperature of about F., which wasinjected into the trap to hold a constant outlet temperature toaboutg350 F. The rate of water sprayed varied from about 30 gallons to about 5 gallons per minute', decreasing gradually as lthe vapors entering the trap decreased in temperature. The pressure; in the trap varied from about 30 to 3 pounds p. s. i. during'thisutime. rhe heavy oil collected yper cyclel amounted to about barrels and had a water content 'of about Y20% by volume.- Thisoil after dehydration in adehydrator of the type disclosed herein had an A. P. I. gravity of below8.0 and gave a yield 'of about65 barrels of heavy oil.-

Iclaim as my invention?. l. In-acontinuousprocess for recoveringjresidual tars and oils removed Vfrom a vpetroleum oil coking chamber during'blowdown ofsaid cham berpthesteps comprising depressuring said chamber substantially a-t the temperature of said coking to produce oil vapors, passing steamfthrough said chamber until its temperature has been lowered from said coking temperature to between about 600 F. and '700 F. to strip the oils therefrom and produce mixed steam and oil vapors, introducing hot water into said chamber to coolthejvapors to a temperature of between about 285 F. and335 F. and to produce more vsteam yand oil vapors, contacting said steam 'and oilA vapors thus produced in a trap to-a temperature above about;2l5 F. with a'spray of Acoldfwater to condense relatively high boiling oils heavier than water in said vapors, passing the uncondensed lower boiling oil vapors intof'an open' steaming pit to condense/atleast a major partr of the remaining oils in said vrvapors, collecting the condensed oils.. and introducing cold water into saidchamber to cool said chamber-"to below about-130 F. f 2. The process of claim'lswherein the hot'water introduced into said chamber is at a temperature above about 130 F. I 3. `The process of claim 1 wherein the hot'water introduced into said chamber has an average temperature of about 175 Ffand is 'introduced under a pressure of about 300pounds per square inch. 'x f I 4.- The process of claim 1 wherein vthe vaporsv entering said trap have a temperature ranging between about 215F. and 800 F. 5.` The process of claim.1 wherein the vapor leavingsaid trap have ajtemperature'rangingv betweenl 215 F. and 320 and 'a pressure of less than 50 pounds Del' Square inch..'

6.l '1"he` process-Jefl claim 1 wherein the coldi; water introduced in saidchamber has anaaveragef; temperature jor about and is introduced:-

under a,-

rh pressure ofi-about 200poundsper`=squaref 111C v`;

IOS

7.. lnfa process for recovering residualtars andV oils removed from apetroleum oill coking charm.

ber at the end-ofthecoking cycle, the ysteps comprising Vvdepressulrigsaid. chamber 'substantially atthe temperature of said cokingto produce oil vaporspassingsteam through said chamber until its temperature is lowerdrom said coking temperature Yto between about 600 F. and 700`F..to strip oils .therefrom and `toproduce mixed steam and oil vapors, introducing h ot water into said chamber to cool the, vapors to a temperature of between about 285vF. and 335 andto produce more steam `and oil vapors, contactingsaid steamA and oil vapors ina trap, maintained 'at a teinperature between about'215 F. and 800 F. with a spray of cold water tocondense relatively high boilingoils heavier than .water in said, vapors,

passing the uncondensed lowerboilingoil vapors into an open steaming pit .to'condens'eat least a major portion of the remaining lighter oils in said vapors, skimming 'thelghter oils from said pit, ,combining the oils thus condensedin said trap and pit in a separate receiver and then dehydrating v them in a dehydrator maintained at a temperature below about 160 F. to produce an oilphase, and awater phase, separating said phases, and finally introducing cold water into said chamber when the temperatures of said vapors have reached about 310 F. to produce hot water and water vapors and to c ool said chamberto below about F.

8. The process of claim 'lwherein perature in the dehydrator is maintained between about F. and 150 F.

9. The process of claim bined'oils havevan A. PQI. fgravityof lless than about 8..

10; In va continuous process-for recovering re-A sidual tars and oils removed yfrom a petroleum oil Y cokingchamberat the end ofthe o o-king cycle,

the steps comprising 'depressuring said chamber substantially' at the temperature ci said coking to produce oil vapors, passing steam through said chamberuntil its temperature has been lowered from said coking temperature tobetween about 600 F. and 700F., to strip the oils therefrom and to produce mixed st'eainand .oil vapors, in-

troducing hot walter into .said chamber to cool,

oils heavier than water in said vapors, passing the uncondensed lower boiling oil'vapors into an open steaming pit to condense at leastl a major portionof the remaining' lighter loils in said vapors, skimming the'Y lighter oils from said pit,

combining the oils thus condensed andv dehydrat ,1 returning said emulsion'to said chamber'while'it is at a'tempera'ture above about 600 F. whereby the'emulsion is revaporized, and iinally introduc-g ing cold water into said chamber when the temperature of the vapors'therefrom has reached about''l" F. to produce hot water and water vaporslan'dtocool'said chamber to below about 13ioF; 1' I c 11. In `a .continuous 'process'for recoverin'g're-4 sidual tars and oilsrerhoved'from a 'petroleum oil cokingnchamber during `blowdown oisaid cham;v

the teml 'l wherein .the com? ber, the steps comprising depressuring said chamber substantially at the temperature ofA said coking to produce oil vapors, steaming said chamber until its temperature has been Alowered from said coking temperature to betweenabout 600 F.

and 700 F. to strip oils therefrom and to produce mixed steam and oil vapors, cooling said chamber with water from a hot water surge tank until the vapors have a temperature Vof between about 285F. and 335 F. and to produce more steam and oil vapors, condensing said steam and cil vapors thus produced, and collecting the condensed oil therefrom, further cooling said chamber with cold water from a cold water surge tank to produce hot water and water vapors which are substantially free from oilrand are collected in said hot water surge tank until said waterfrom said chamber has a temperature of not below about 130 F., at which temperature the water is returned again to Vsaid cold water surge tank, thereby cooling said chamber to atemperature about 130 F., andcontinually adding fresh water to said cold water surge tank.

12. The Aprocess of claim'll wherein the average temperature of the hot water in the hot waterV surge tank is about 175 F. and isl introduced into said chamber under a pressure of about 300 130 F. at which timethey are returned to said Y 15. In'a continuous process for recovering residual tars and oils removed from a petroleum oil j coking chamber at the end of the coking cycle,

the steps comprising depressuring said chamber substantially atrthe temperature of said coking to produce oil vapors, passing steam through said chamber until its temperature has been lowered from said coking temperature to between about 600 F. and r100 F. to strip the oils therefrom and to produce mixed steam and oil vapors, cool--V ing said chamber with hot water ata temperature above about F. from a hot water surge tank until the vapors have a temperature of between about 285 F. and 335 F. to produce more steam and oil vapors, contacting said steam and oil vapors thus producedin a trap at a temperaturefabove about 215 F.with a spray of cold water to condense relatively high boiling oils heavier than water in said vapors, passing the uncondensed lower boiling oil vapor into an open steaming pit to condense at least a portion of the yremaining lighter oils in said vapors, skimming the lighter oils from said pit, combining the oils thus condensed and dehydrating them, the combined oils having an A. P. VI. gravity of less than 8, and finally further cooling said chamber with cold water from a cold water surge tank, said cold water having an average temperature of below 130 F., to produce hot water and water vapors Y which are substantially free from oil and are collected in said hot water surge tank until Vthey K have cooled to a temperature of not below about cold water surge tank, said cold waterV cooling said chamber to a temperature below about 130 F.

PARKER ERWIN MALSON.

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