US1833162A - Cracking of oil - Google Patents

Description

Nov. 24, 1931. E* c. HERTHEL CRACKING OF OIL O riginal Filed July 14 Il l- @SNE wtl

S www INVENTOR I a W BY 2 i i '1.9

ATTORNEYS i' Patented Nov. 24, 193.1 l

4warren STATES" PATENT OFFICE EUGENE 0. HERTHIi, F CHICAGO, ILLINOIS, ASSIGNOR TO SINCLAIR REFINING v BANY, OF NEW'YORK, N. AY., A CORPORATION COM- cnacxme or on.

l" Appueatimmea my 1.4,

This invention relates to an improved method and apparatus for-cracking heavier hydrocarbon oils for the production of lighter hydrocarbon oils therefrom. This application is in part a continuation of a prior application' filed 'September 24, 1923, Serial o. 664,502. 1 f

In the cracking ofheavier hydrocarbon oils in externally lheated stills, the vheavier 1b' oil is heated to a high temperature under 'pressure and the heat necessary for raising the oil to thev cracking temperature' is applied directly to the Walls of thepressure still, in the case of a shell still. and to the heating tubes in the case of a tube still.

As .the cracking operation progresses, the

formation of carbon and tar lconstituents takes place and the extent to which the cracking operation can be carried in 'a single'run is limited by the accumulation :of such cons'tituents which tend to settle or separate out on the heating surfaces and to forma layer of so-called carbon thereon vyhich interferes with theheat transfer and, unless periodically removed' by cleanin ,causes overheatingof the `walls or tubes o the still. Toavoid or minimize the danger of such carbon separation on the heating surfaces, the run i'scommonly .stopped before the accumulation of heavy tar constituents becomes too great, or the 'tar is continuously Withdrawn and fresh feed supplied to maintain the charge in a sutciently duid condition topermit continued operation for a longer period ofv time. The danger of such carbon separation and resulting failure of the still walls .or tubes is greatest where the intense heat of the furnace gasesfirst comes in contact with the still Walls or tubes and Where the 40 greatest amount of heating-takes place.

According to the present invention, the

v V pressure still itself, Whether ofa shell or tube type, is protected from the intense furnace heat, and this heat is applied'in such a way.

as to increase the eiliciency and capacity of the still.

According to the present invention, I provide an auxiliary heating coil arranged between the lirebox and the main heating surfaces of the still and I recirculate part `'carried lout in the pressure still itself; but

main body of oil in the pressure still.

192s. serial l No. 43,467.

of the heating gases which havepassed overA the heating surfaces again over the heating y surfaces, including the auxilia y coil, together with fresh products of comb stion from the iirebox. The recirculation of part of the heating gases assists in protectingthe heating sure faces from the intense furnace heat and improvesthe heatingl operation, and by arrang' ing the auxiliary coil intermediate the fire- ,box and the heating surfaces of the still proper the temperature. of the heatingv gases is further reduced rby the heat absorbed in the auxiliary coil before rtheycome in con tact with the main heating, surfaces of the 'still while Athe heat absorbed iii the auxiliary a5 coil is also `usefully employed.

'I he auxiliary coil is used for carrying out A a separate cracking operation which may be independent of the cracldngl operation which is 'advantageously combined with the pressure still operation so'that the o il subjected to the cracking operation inthe preliminaryv cracking coil is` discharged into the Where the preliminarycracking coil vis combinedin its operation with the pressure still, the reflux from a reflux tower on the pressure still, or the 'reflux or heavier ends of the pressure distillate, may advantageously be utilized as charging stock for the auxiliary cracking coil, so that. this reflux will lbe returned through the auxiliary cracking coil to the main body of voil in the pressure still. This reflux oil returnedto vthe still itself may advantageously be admixed with fresh feed which may be utilized for assisting `the refluxing action* in the reiiux tower and, then supplied, freed from its lighter constituents and admixed with the redux, to the auxiliary/.cracking coil, and subjected to a partial cracking operation therein before it is introduced into the pressure still itself.-

By utilizing in the auxiliary cracking coil a fresh charging stock or a mixed reiiux and feed,rwhich is free from carbon and tar conthis cracking coil is subjected to heating gases 100 i eo' 'i at high temperature; while the auxiliary cracking coil is further protected by the recirculation of art of the heating gases and the walls or tu s of the pressure still proper are protected both .by the absorption of heat inthe auxiliary coil and by the recirculation of part of the heating gases. Overheating of the walls or tubes of the pressure still proper is thus avoided and a milder heating f these ture -will absorbed bythe oil in the auxiliary 'the tubes through walls or tubes is obtained such thatthe danger of objectionable carbon deposit is reduced and the cracking operation vcan be carried to `a furtherl ,extent than would otherwise be feasible.

In the application of the invention in connection with a pressure still of the shell type, the auxiliary coil may be arranged in the heating liuc or in .the path of the hottest gases at an intermediate point between the lirebox and the still proper, so that the' furnace gases which come in ontact with the heating surfaces of the still will have been cooled considerably below their initial temperature, while the intense heat'of the'high temperaroducts of combustion from the `firebox cracking coil. Where such a shell still is provided with a reflux tower, or where the distillate therefrom is subjected to -reiiuxing and separation of .the heavier constituents therefrom at a lowerpressure than that of the still itself., the reiux, either with or without additional feed, can be used as the charging Yto be obtained.` With' such a tubular still,

i A the` auxiliary crackin coil may likewise be 'combined to receive t e reiiux 'from the still itself or theheavier part of the distillate therefrom and may similarly discharge the partially cracked oil back into the main body still. f t

With either t pe of still, means are provided for` with rawing part ofthe heating of -oil undergoing cracking in the tubular gases which have passed over the heating surfaceslof the still and which have thereby been artially'cooled and for returning suc with vrawn gases at'about the temperature at which they would otherwise escape and` admixin them with freshvhot roducts of combustion from the lirebox be ore the resulting mixture passes over the heating surfaces of the still whereby the fresh heating 1n thy would otherwise escape, the tempering is eii'ected without decrease in .eiiciency may be accompanied by an increase 1n Aeiliciency. v

The invention is ofspecialvalue and application in conjunction with pressure stills provided with reflux towers into which the fresh feed is introduced and from which the reflux and a'dmixed feed can be circulated es are tempered.l By employing the heat. gas gases at about the temperature at which throughv the auxiliary cracking -coil before their introduction into the still proper.l The reflux towers may be operated at the same pressure maintained in the pressure still and the refluxed oil, or reiuxed oil with admixed,

feed, circulated 4through the auxiliary crackin coil, either by gravity. or convection cir-4 cu ation or by means of a pump; or the vapors from the pressure still maybe reduced to a lower pressure and subjected to a refluxing operation and the heavier reiuxed distillate, with or without admixed feed, pumped y through they ordinary cracking coil and thence back to the rmain body of oil inthe pressure still.` f

Where the reflux toweris operated'at. still pressure, the tower and auxiliary coil may be so arranged relativeto veach other`,.and

the coil may be'so constructed that iowvof the oil through the coil and into, the still will be obtained by gravity and convection;

although this circulation may be effected or Y increased by means of a circulating pump or other means for increasing the circulation."`

The invention will be further described in connection with the accompanying drawings illustratin"I apparatus embodying the invention and adapted for the practice of the procl ess of theinvention, but it will be understood that the invention is illustrated thereby butv not limited thereto.

In the accompanying drawings, h Fig. '1 shows a tubular pressure still embodying the invention, the showing bein largely conventional and dia rammatic, an partly in section `and partly 1n elevation;

Fig. 2 is a sectional view-ofone end of the auxiliary cracking coil taken on the line 2 -2 of Fig. 3; y

Fig. 3 is a top view of the auxiliary cracking coil taken on the linc83 of Fig. 2;

1While the invention is applicable in connection with cracking stills of different types, yet it is of particular advantage in connection with a tubular cracking still of the character illustrated. This cracking still is ofthe gens` eral .construction illustrated in U. S.. Letters- Patent No. 1,285,200, -grantedto the ySinclair- Refining Company, November 19, 1918, on

the application of Edward W. Isom.

The pressure still illustrated1 in Fig. 1 is away from the heating rnace, the vertical lheating tubes 2 arranged in the heating iiue madeup ofthe bulk supply-tank 1 locatedl i of the furnace, and circulating pipes 3, 4.and 5 connecting the lower and upper ends of the vertical tubes, respectively, with lthe bulk supplytank and a circulating` pump 6 for circulating the oil from the-bulk supply tank through the vertical tubes and back to the bulk supply tank. Arranged above the bulk supply tank is the reflux tower 7 having a series of baffles therein and connected with the vapor dome of the bulk suppl tank through the vapor line 8. An over owA reflux line 9 leads back from the reflux tower to the bulk supply tank. lThe vapors from the top of the reflux tower escape through the vapor line 10 to the condenser 12 where the vapors are condensed and received in the l receiver 13 from which the uncondensed vapors and gasvare drawn off through the pipe 14 and the. liquid condensate through the pipe 15. The pressure-may be regulated and reduced by means of a regulating valve 1l between the reflux tower and condenser or by the valve 14 located beyond the receiver.

The furnace construction for heating the tubes of the still comprises a firebox 16 suitably heated as by gas or oil burners 17, a vertical Hue 18 leading upwardly from the firebox to the upper end of the heating flue containing the vertical tubes, a heating flue having baffles 2O and 21 therein for causing the gases to pass over the vertical tubes in three successive passes and an outlet flue 22 leading to the stack. From a point adjacent the outlet flue 22 to a point near the lower end of the flue 18, a return connection 41 is arranged for recirculation of part of the heating gases. As illustrated, the connection includes a steam jet blower, although a f an or other suitable forcing means may be used.

Located above the bridgewall 19 and between the vertical flue 18 and the flue containing the vertical tubes 2 is the auxiliary cracking coil 23 having an inlet connecting pip`e 24 and outlet pipe 25 leading to the manifold at the upper ends of the vertical tubes.' A pipe 26 having a .valve'27 thereln connects the inlet of the' coil tothe discharge side of the circulating pump 6. This pipe may be used in starting thestill in opera-tion.

An auxiliary tank or reservoir 28 is arranged to receive the reflux and admixed feedv from the reflux tower 7 through connection 29. This tank or reservoir has ai vent v pipe 30 leadingback to thereflu'x tower.

The tank or reservoir 28 lis also connected through the pipes 31 and 32 to the feed line 24 of the. auxiliary coil. pump 33 is Varranged to, pump the oil through the auxiliary coil, while the yconnecting dpi e 34 permits circulation by gravity an iiy convection when the pump 33 is not used. A branch pipe 36 leads from connection 32 to the bottom of thebulk supply tank. The pipes 31 and 36 have control valves therein by which one or the other or both of these pipes can be shut olf when desired. A feed line 35 enters the inlet pipe 24 of the auxiliary coil and permits the direct introduction of fresh feed as it is desired. A tar draw-ofi' connection for use during the operation of the still is shown at 37 and a tar draw-olf for discharging the still is shown at 38.

The auxiliary reservoir or tank 28 -is shown as located within the bulk supply tank 1, although it is not in ope'n communication therewith except through the pipe connections. This location of the auxiliary reservoir is not essential but is convenient and enables a tank construction to beused which does not needto withstand high pressure as the pressure inside and out is approximately the same. Where the auxiliary tank or reservoir is located within the bulk supply tank it will be evident that valves such as those inl the pipes 31 and 36 should have operating handles which extend out through suitable stuffing boxes in the walls of the bulk supply tank. Test cocks (not shown) may be provided for ascertainingthe level of the o1l in this auxiliary tank or reservoir.

A feed line 39 is provided for feeding fresh oil to the top of the reflux tower 7. An additional Vfeed line 40 is provided for feeding oil to the bearings of the pump 6. Additional feed can also be introduced through the auxiliary coil through the feed line 35 as above noted.

The auxiliary coil 23 is made up of a series of pipes connected at their ends as indicated in F1gs. 2 and 3 and arranged so that the oil flows therethrough in `a single pass in a generally upward direction, the flow' being thus assisted by convection.

' When the still is initially charged, oil y may be circulated from the main charge of oil through the auxiliary crackin coil, for example, y closing the valve in tle pipe 31 Vand opening' the valve in the pipe 36 when the circulating pump l33 will draw oil from the bulk supply tank 1 and circulate it throu h the auxiliary coil; or the valve 27 may e opened and oil from the discharge side of the pump 6 may be circulated through the auxlliary coil; or fresh feed may be introduced through the feed line 35.

After the pressure still has been raised to cracking conditions of temperature and pressure, the cracked vapors from the stillwill rise in the reflux tower 7 and will come in contact with the fresh feed introduced through the line 39 to the top of the tower. By providing a sullicient number of baliles practically all of the feed for the still can be introduced .in this way and a pressure distillate approximating a gasoline distillate directly obtained with return of the heavier constituents in the liquid state to the bottom of the reflux tower. This reflux and admixed feed collects in the reservoir or tank `cracking coil 23. where it is subjected to the hottest gases from the furnace. The cracked oil is discharged into 'the top circulating line of the still rand is returned to the bulk supply'tank. The unvaporized portion of the o ilso returned forms apart of the still Vcharge and isf-circulated therewith through.

It: will be evident that the rate of circulation ofthe oil should be regulated so that a constant supply is provided and so as to maintain a level of oil in the reservoir 28. By introducing all or practically all of the fresh feed into the top of the rel'lux'tower and bringing it-into intimate contact withthe yvapors therein, a constant supply .of reliux and admixed feed is provided. Should the` reservoir 28 become full the additional reflux and feed will collect in the bottom of the reflux tower and will overflow through the'pipe 9 to the bulk supply tank l. i

After the high temperature furnace gases initially tempered by admixture with recirculated cooler heating gases have been ref duced in temperature by passage through the auxiliary coil, they then pass over the vertical't-ubes of the pressurestill at a lower temperature and serve to heat these tubes with out danger of objectionable overheating.` A milder heating and cracking' action is thus obtained 'so 'thaty the still charge can be crackedto a further extent Without danger the vertical tubes.

of objectionable ,carbon deposit on the tubes and with the obtainin,0r of heavierjesiduum F so that objectionable overcracking will be avoided While effective cracking will nevertheless be obtained, and the resulting cracked oil will then be introduced into the pressure..

still to admix withfthe oil and vapors therein.

The operation olf-the pressure still in this way, with circulation of the feedand reflux through the auxiliary coil and with recirculation of part of the heating gases, and with circulation vof the main charge ofthe still through tubes heated vfollower temperatures, f gives an increasedfurnace eliiciencyy with longer runnin'gtime before itis necessary to shut down Afor cleaningyand with increased capacity of operation oftheA pressure still, while also permitting a reductionof ypressuretar while underpressure to ahigher 'specific grav-ity without detriment toltheop-J eration.

the cracking therein of kerosene fractions and lighter oils which are more diliicult to crack in ordinary pressure stills. Such kerosene fractions may be those produced by the pressure still itself or supplied from another source.

The addition of an auxiliary cracking coil in conjunction with the operation of the pressure still also permits the introduction of an increased amount 0f feed through the top of the reflux tower and a fractionation of the vapors from the still to much nearer a linished gasoline than is commonly obtained, and this without any diiiiculty in regular operation.

The entire pressure still system is protected from the intense furnace heat by recirculating a part of the heating gases which have passed overthe heating surfaces of the still and, admixing this recirculated cooler gas with the yfresh heating gases from the furnace before they are passed over the heating surfaces of the still, sothat the heating gases usedfor heating the main charge of oil in the still itself are tempered by the combined effect of the recirculated gases and the action ofthe auxiliary cracking coil in absorbing the initial intense heat of the heating gases. The recirculation of waste heating gases in this way increases the velocity of flow of the heatingv gases improving heat transfer and since the waste heating gases are returned at substantially the temperature at which they would otherwise be discharged, both 'the efficiency and capacity of the pressure still may be further increased. It will thus be seen that the present invention provides animproved construction and method of operation of pressure stills whereby the intense furnace heat of the heating furnace is utilized in an auxiliary cracking operation where such intense heat is advantageous, and that the cracking operation of the main pressure still is carried out with the. furnace gases which have been cooled by their utilization in the preliminary cracking operation.

It will further be seen that the preliminary cracking operation which utilizes the intense .heat of the highest temperatures of the furnace may advantageously be combined with the operation of the pressure still utilizing ,the furnace gases'subsequentlyat a lower temperature such that a milder cracking action is obtained and that, Where these operations are combined, the feed for the auxiliary cracking coilmay advantageously be supplied in thev forni of reflux, or of reflux and admixed feed from the' reflux tower of the pressure still` j.

f The temperature and pressure employed in tha-carrying out of'the' process 'and in the in Operationof the apparat-tiscali be varied'with .'ljhe yhigher temperature to whichthe-aux iliary cracking l coilfis subjected `also-,-Ipermits different, characters of charging* stock. Where o rdzm'aryv gasl oil is employed in the 1. The improvement `in the operation vof externally heated pressure stills, which com-- prises heating a body of oil to a cracking temperature by positively clrculating the oil over externally heated surfaces in the pres` surelstill and circulating heating gases from a. lirebox externallyover the' heating surfaces of the pressure still, forcing -tar-free oil once only througha separate cracking coil interposed between the heating surfaces of the pressure still and the lireboxand thence, directly into the pressure still, and recirculat-v ing heating gases which have passed over the separate cracking coil or the heating surfaces of the pressure still and admixing them with the heating gases from'thelirebox before the freshheating gases pass over the heating surfaces ofthe pressure still.

2. The improvement inthe operation of externallyjheated pressure stills, which -colnprises'heating a' body of oil to a cracking temperatureby.positively circulating the oil yover externally heated surfaces in the pres sure still and circr lating heating gases from a irebox external y over the heating surfaces of the pressure still. subjecting the vapors from the pressurestill to a refluxing operation and forcing the reflux therefrom once `only through a separate cracking coil interposed between he heating surfaces of the pressure still and he {irebox and re-circulating heating gases Awhich have passed over the heating' surfaces ofthe pressure still and* admixing them with the heating gasesfrom the firebox before thefresh heating gases pass over the separate cracking coil or the heating surfaces of lthe pressure still.

3. The improvement in the operation of ,externally heated pressure. stills, which comprises heating a body of oil to a cracking temperature by positively circulating the oil over externallyheated surfacesin the pressure still andcirculating heating gases from a frebox externally over the heating surfaces of the pressure still, subjecting vapors from the pressure still to a reiluxing operation and'l forcing the reiiux'therefrom in 'admixture with fresh oil once only through a separate cracking coil interposed between the'heating surfaces of the pressure stillv and the lirebox and thence directly into the pressure still,

4and re-c'ir'culating vheating gases which `have passed over the heatingl surfaces lof the ressure still and admixing them with the eating gases from the furnace before the fresh heating gases pass over the separate cracking coil or the heating surfaces of the pressure still.

. 4. Inv the operation of externally heated pressure still systems in which a 'charge of oil v is heated to the cracking temperature by circulating the oil from Va bulk supply tank through a heater and back to the bulk sup- \ply tank by circulating heating gases from a lirebox in indirect heat exchanging relat1on with the oil in the heater-,the improvement which comprises passing tar-free oil once only through a separate heating coil interposed between the heater and the firebox and into the-'pressure still system, and re-circulating heating gases which .have passed in heat exchanging relation with the oil in the heaterand admixing them with the heating gasesfrom the lirebox before the fresh heating gases pass in heat exchanging relation with the oil inthe separateheating coil or in said heater. 5. An apparatus'for cracking heavier hylroc'arbon oils for the' production of lighter hydrocarbon oils therefrom, comprising a V.

circulatory cracking still and means for positively circulating oil over the heating surfaces thereof, a furnace for heating the same, a slngle pass auxiliary cracking coll interposed between the tire box of the furnace and the heating surfaces of the pressure still ar- ^ranged to discharge into the still, means for independently circulating tar-freeoil once only through said auxiliary cracking coil and thence directly to the still, and means for recirculating heating gases which have passed over the heating surfaces of the still and adfire box in the furnace.

In testimony. whereof I aiix my signature. Y EUGENE C. HERTIIEL. t

mixing them with heating gases leaving the1L CERTIFICATE 0F CORRECTION.

PatenRm 1,833,162. 'l y 'l Granted Norember 2.4, 1931 to EUGENE C. HERTHEL.

. It kis'here'by certified that error appears in the printed specification of the abovenumbered patent Vrequiring correction as follows:l vPage 2 ,A line 89, for "ordinary" read auxiliary; pag'e; lines 26 and 27, claim l, strike outthe words "the separate cracking coi) or" and insert the samejafter "over" in line 30, of same claim; and that the said Letters Patent shouldcbe read with these'F corrections therein that the same may conform to the record of the case in the ,"PatentzOffice'. l'

signed ma sealed this 9:1; any of irritate-ny,v Ayn. 1932.."

M. J. Moore,"

t (Seal.) -Y Actingommissioner of Patents. 7

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