US1758818A - Art of cracking hydrocarbon oils - Google Patents

Description

J. E. BELL ET AL ART OF CRACKING HYDROCARBON OILS My S, '1.930.

3 Sheets-Sheet l Filed Jan. 22, 1925 Jrj Il rf..

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' ART OF CRACKING HYDROCARBON OILS um l?,

Patented May 13, 1930 UNfiTEAD: 'STATE-s' .PA'rlalwY OFFICE- ;'rOHN E. BELL, DEOEAsED, LATE OE `BROOKLYN, NEW YORK-,1'i BY LOLA E.. BELL, EKECU- rmx, OE BROOKLYN, NEW YORK, AND EDWARD W. Isola, OE Locus'r VALLEY, NEW YORK, AssIeNOEs To sINOLAIE REEINING COMPANY, OE NEW YORK, N. Y., Acon- PQRATION 0E MAINE Am: 0E CEAOKINGKYDROGAEDON- OILs Applieation mea January 22, 1925. serial No. 8,984.

I This invention relates to improvements in cracking heavier hydrocarbon oils, such as gas oil, for the production of lighter hydrocarbon oils, such as gasoline or pressure distillate, by distillation under, pressure.

In cracking hydrocarbon oils by distillation under pressure, the oil is heated to a cracking temperature under pressure and the heavier oil, or a portion thereof, is broken down or cracked with the formation of lighter oils which are vaporized and driven off. The cracking operation takes place gradually andprogressively, part of the cracked constituents escaping as pressure distillate and part of the heaviercracked constituents remaining and mixing with the charge of oil in the pressure still. A small amount of asphaltic, or pitch-like' constituents, or

heavy tar is also formed by the cracking op Veration. This tar remains in the charge and gradually-accumulates due to the vapor-ization ofcracked constituents and to the pro-,k

"gressive formation of tar constituents.` This tar accumulating in the oil in the still tends p to deposit on thefheating surfaces of the still and in Contact therewith tends to form acarbonaceous deposit thereon closely adhering .A thereto. Such carbonaceous materials and the heavy tar accumulating in the still charge are poor conductors of heat 'and When'deposited on the heating surfaces of the still which are externally exposed to heating gases interfere with heat transfer and insulate the Wall from the protection afforded by the oil so that the Walls of the still are apt to become overheated, the temperature of the metal of the heat transferring Wall increasing over `that ofthe oil to an extent dependent upon Vthe thickness of the deposit and the amount of heat externally delivered to the Wall from the heatingfgases. As a consequence thepressure still must frequently be shut down for cleaning or the temperature of the heating gases' must be reduced below that whichv is most efficient. 'There v is also considerable danger involved due topossible bursting of the heat transferring Walls at overheated points. .The heating surfaces -over which heating gases are firstv circulated are exposed to the highest temperature of the heating gases and absorb the greatest amount of heat, and these Surfaces are most apt to suffer Heating surfaces immediately adjacent the furnace employed to heat the pressure still may also absorb a large amount of heat by i direct radiation from the furnace. y According to the present invention'the heating surfaces of the pressure still are p'ro` l tected byrapidly circulating the still charge thereover by mechanical forcing means, such as a pump, and reiluX or fresh oilor admixed reflux and fresh oil is employed in a particuy larvly advantageous wa'y to re late the composition' ofthe circulating 011, particularly with reference to its content of crackable constituents and Vcarbon and heavy tarry matter, as it is circulated over. the heating surfaces of the still. By employing mechanical forcing means for circulating the oil the ra `pidity ofthe circulation is promoted. With more rapid circulation the rate of heat transfer from the heating surfaces to the oil is increased and the capacity of 'the still is in creased. Rapid absorption of heat from the heated Walls of the still is thus effected,re ducing any tendency of the surfaces to become overheated by carrying the heat off in the oil and by maintaining the heating surfaces at a temperature more nearly approximating that of the circulating oil, While at the same time the rapid mechanical circulation of the oil assists in preventing or mate- Y rially reducing the formation of carbonaceous deposits on the heating surfaces and assists in carrying carbon and tar constituents With the circulating oil.

According to the .present invention, -reflux, or fresh oil, or admixed reliux and fresh oil, is first circulated in heat exchanging'relation With the heating gases atr their highest temperature before they are circulated over other heating surfaces' of the pressure still, and, as the light cracked constituents are vaporized and the oil loses its content of crackable hydrocarbons and as the concentration ofcarbon' and tar constituents in- 1creases, the oil is circulated in heat exchanging relation with heating gases which have been tempered and reduced in temperature by heat exchange with the reflux or fresh oil the vaporized constituents are subjected toy av reiiuxing operation'the reiuX is substan- I tially free from carb-on and tar constituents.'

Fresh oil, likewise, is free fromtar and carbon formed by the cracking reaction, and it usually containsr a larger amount of .morev easily cracked constituents. When 'reu-x, or fresh oil, or admired reflux and fresh'oil are admixed with a part of the still charge, they assist in .reducing the concentration of carbon' and tar constituents and in maintaining the concentration of tar constituents be#v low saturation in that part of the charge. Thetheating gases while at highest temperature are thus passed over .heating surfaces which are in contact with circulating oil relatively free of tar constituents, or in which the A concentrationI of tar is least, and as the tar concentration increases the oil is circulated over heating'surfaces in contact with progressively tempered and cooler heating gases. The lighter crackable constituents of the reflux or fresh oil are also subjected to advantageous cracking conditions by heat eX- chaige with the hottest heating gases. The heating surfaces of the pressure still most apt to suffer are thus protected by rapid absorption of the heat transferred therethrough in heating and cracking the oil constituents of the reflux or fresh oil circulated thereover and this heat available at high temperature is advantageouslyemployed in a useful cracking operation rather than in the further cracking of tar constituents while a reduced concentrationof tar constituents is maintained in the oil circulating over these initial heating surfaces preventing or materially reducing the formation of carbonaceous deposits thereon. Tlie heat available in the heating gases, the temperature of which has been lowered by the heat absorbed in heating and cracking the reflux, or fresh oil, or admixed redux and fresh oil, is then further employed to advantage in cracking the circulating oil as tar constituents accumulate therein.A I

In one particularly advantageous way of carrying out the present invention, the vapors from the cracking operation. are subjected to a refiuXing operation in direct contact with fresh oil and the reflux and admixed fresh oil are employed to protect the heating surfaces of the pressure still while 'at the same time the reflux and .admixed fresh oil are subjected to advantageous cracking conditions. rfhe reiiux and adniixed fresh oil are thus first circulated in heat exchanging relation with the heating gases at their highest 'temperature before they are passed over other heating surfaces vifa/saaie of the pressure still, and, as the light cracked' the concentration of tar constituents increases, the oil is circulated. in heat exchanging relation with heating gases which have been teinepered and reduced in temperature by heat exchange with the reflux and admixed fresh oil by passing the oil of increased tar contentover more remote heating surfaces of lthe lpressure still. The' heating gases while at highest temperature are thus passed over heating surfaces which are in contact' with oil relatively free of tar constituents, or in which the concentration of tar is least, land 'as the tar concentration increases `the oil is passed over heating surfaces in4 contact with progressively tempered and cooler heating gases. The'lighter crackable constituents of the refluxand adiniXed fresh oil arelalso subjected to advantageous cracking conditions by heat exchange with the-hottest heating gases. The heating surfaces of the pressure still most apt to suffer are'thus protected by absorption of the heat transferred therethrough in heating and cracking the oil constituents ofthe refluxy Aand admixe'd fresh oil and this heat available at high temperature is advantageously employed in a useful cracking operation rather than in the further cracking of tar constituents while a reduced concentration of-tar4 constituents is maintained in the oil in contact with these initial heating surfaces preventing or materiallyreducing the formation of carbonaceous deposits thereon.

The heat available in the heating gases, the

temperature of which has been lowered by the heat'absorbed in heating' and cracking the reflux and adiniXed fresh oil, is then further employed to advantage in cracking the oil as tar constituents accumulate therein.

In carrying out the invention, the heating surfaces of the pressure still may be further protected and the heating of the pressure still charge equalized by providing progressively increased areas of heat transfer between the oil and the heating gases as the tar con-v tentof the circulating oil increases and as the temperature of the heating' gases decreases. The heating effect is thus equali'zed by increasing the area of heat transfer as the temperature of the heating gases decreases ywhile an increased area of'heating surface is provided in Contact with the circulating oil the heating gases are first brought in heat exchangingrelation, further promoting rapid absorption of heat from the hot still walls in contact With the hottest heating gases. The

mechanical forcing means-may also'be aroil increases.

sure still charge may also becontrolled and ranged and operated to maintain most rapid circulation overthe initial heating surfaces whether or notthe area of heat transfer is increased as the tar content of the. circulating The tar content of the presing tar content, and circulating reflux, or

fresh oil, or admiXed reflux and fresh oil,

through the stage or cycle in which` the oil is subjected to heat exchange with the heati ing gases off-highest temperature, In one aspect, the process of the present invention may be considered a process in which the reflux, or fresh oil, or admired reux and fresh oil, are first lsubjectedto a more or less intense cracking treatment and then, as tar and carbon accumulatein the oil, to a digestion treatment in which the cracking temperature may advantageously be maintained by mechanically circulating loil from a body of the oil in heat exchanging relation with the heating gases from'the initial cracking treatment and back to the body.

'While the invention is of particular `advantage where the same stream of heating gases 1s employed for heating the oil in the successive stages of the process as the tempera-ture of the heating gases is progressively reduced, certain advantages o f the invention may be obtained by employing heating gases of separately regulated temperature in the successive stages, employing, .hotter heating gases for initially heating and cracking the refiuX, or freshr oi-l, or admixed reflux and fresh oil, and progressively cooler heating gasesfor heating the circulating oil of progressively. increasing tar contentin the successive stages:

The -invention will be further'described in connection with the accompanying drawings which illustrate in a diagrammatic way one form of apparatus adapted for carrying out the process of the invention. The apparatus illustrated is described and claimed in an lapplication filed -April 8, 1921, Serial o. 459,555, which has imatured into Patent 1,547 ,994, and the process of the present invention is of special value and application in connection with pressure stills of this general character. The process `of the invention ment D being arranged in the last may, however, be carried out in other andi diferent apparatus.

In the accompanying drawings.: Fig. 1 represents a pressure still, in elevation and section with parts broken away and with va condenser diagramatically shown,

'- adapted for carrying out the process of the invention, l

Fig. `2 is a fragmentary section on an en larged scale 'on line 2 2 of Fig. 1, and

' Fig. 3 is'a fragmentary section on Aan en-.

larged scale online 3-'-3 of Fig. 1.

Thelpressure still illustrated comprises 41 drum 4 and a series of tubular heating elements communicating therewith arranged in the heating flueofa' furnace 5. The heating .flue comprises a series ofconnected vertical lues .6, 7, 8 and 9,' the flue 6 also connecting with thefurnace 5 and the flue 9 with a stack .flue l0. The flues are arranged so that the heating gasesv from the furnace are passed successively therethrough to the stack.

A draft tube 11 is arranged kfor withdrawingA waste heating gases from a point adjacent the exit of the heating flue 9 and returning them to the fluef6" for tempering.the heating gases fresh from thefurnace 5 in the flue 6. l 'Y The draft tube may be operatedby a steam jet or other suitable forcing means.` By returning waste heating gasesin thisrway, the heating gases are tempered in the iirstheating flue, the volume-and rate of vcirculation of the. heatinggases through the heating iues isV increased, and the available heat in the 'recycled gases may be further utilized. By- passes 12 and 13 provided with regulat- Vingdampers 14' and 15 are provided for further controlling the distribution ofA heat in the several lines.

The still. drum 4 is provided internally.

Awith a series of partitions 16, 17 and 18 di# riding the drum into a series of compartments A, B, C and D and acorresponding series of heating elements separately communicating with each of these compartments are arranged in the heating ues. The heating element connected to compartment A is arranged in iue 6, that is theiiue through which the heating gases` are first pased, the heating element of the next compartment B in theV next flueA 7 and so on, the heating element-connected to the last com arteating Hue 9 through which the .coolest heating gases are circulated. The partitions in the drum do not completely shut o the compartments from each other butextend a short distance above the normal liquid level therein -leaving a common vapor space in the upper part ofthe drum. Overow pipesl9, 20 and 21 are 'arranged .for progressively transfer- `ring oil to successive compartments in-the Each of of upwardly inclined tubes 23 arranged through the heating flue for heat exchange with!y the heating gases therein, connecting headers 24, another series of upwardly inclined tubes 25 arranged through the heating iiue, and a header 26., I n order tofacilitate cleaning and repair the headers are arrangedi outside of the heating lines and are formed with plugged hand holes in alignment with nthe heating tubes. In order to equalize the` heating etl'ect in the several heaters, to promote relatively more rapid circulation in the .first heaters, and to provide 1an increased areaj of heat transfer as the tar content of the oil increases, as will presently appear in more detail, the heattransferring area of the several heaters is progressively increased as the temperature o the `heating gases declines. In the apparatus illustrated, the heater connected to theflrst compartment A has four tubes in each group,that connected to cornpartment B eight tubes, that connected to compartment nected tothe last compartment D sixteen tubes.-

Y Arranged above the drum 4 is a reflux tower 27 adapted to receive vapors from the va or space of the drum 4 and to discharge re ux into the first compartment A connected to the heating element arranged in heat exchangin relation with the hottest heating gases. connection28 is provided for introducing fresh oil into the upper part of the reflux tower over the bailles therein and 'in direct contact with the vapors therein.

Another connection 29 discharging into the first compartment A is also provided for the introduction of fresh oil directly thereto. The vapors escape from the reflux tower through vapor line 30 to a condenser diagrammatically illustrated at 31. The pressure in the still may be reduced and controlled by a regulating valve 32 arranged between the reliux tower and the condenser or by a valve 33 arranged beyond the condenser. Where fresh oil is introduced through the reflux tower, thereiux tower may be covered or protected with suitable heat insulation, such as an asbestos or mineral wool jacket. Or the reflux tower maybe arranged to operate by external cooling,`such as air cooling.

The still drum is advantageously insulated against heat loss.

The headers 22 in each group are connected to a common horizontal header 34 which is in turn connected through pipe 35 to the discharge side ot a circulating pump. |llhe headers 26 in each group are arranged to discharge into the corresponding compartment in the drum t. A connection 86 is also provided between each compartment in the drum twelve tubes and that conployed.

mesme and the ,inlet side of the circulating pump dischargingA through the heater connected to thatcompartment. IIn Figs. l and 3 of the drawings the connections between the-comlmunicating compartments, pumps and heating elements are designated by the reference characters 35 and 36 with the letter corresponding to the compartment with which they communicate. appended. A separate pump may be employed for each of the com partments. It is advantageous, however, to arrange the pumps in a common casing and to'use a common -driving means as shown in the drawings. The pumps shown in the drawings are ofthe rotary piston type, sometimes known as Connersville pumps, and are particularly adapted for use' in carrying out,

the process of the invention but it will be apparent that pumps of other suitable construction adapted to handle hot oil at the cracking temperature may be employed. Thelpumps t shown are independent and the oil is' separately circulated through each of them, partitions 37 being arranged between the several pump chambers'to confine the oil in each circulating stream to that stream. A valved outlet 38 is providedin the connection 35D for dischargin tar from the pressure still during the crac ing operation.

In carrying out the process of the invention in the apparatus illustrated, the still is initially charged with oil through connection 29 while the pumps are in operation, the oil successively overiiowing into the adjacent compartments as thev preceding compartments and circulating connections are iilled, and brought to the cracking temperature and pressure 1n the usual way. ".The oil in the rst compartment A and the connected heatingelement `first reaches the cracking temperature and the oil in the successive compartments and heaters reaches the cracking temperature in order. The pumps are continuously operated during the operation to maintain a forced and rapid circulation of the oil from each of the several compartments through the connected heating element and back to the same compartment. Each of the several pumps withdraws oil from the compartment to which it is connected through connection 36 and forcesit upwardly through the corresponding heating element back to the compartment. "lhe pressure employed mayd'er with diiierent' charging stocks and for the production of different pressure distillates. With gas oil character charging stocks for the production. of gasoline character distillates, pressures up to 90 to 125 pounds per square inch or more may be employed. In cracking a kerosene character charging stock to produce a. gasoline character distillate, considerably higher pressures may be used, for example, pressures up to 300 pounds per square inch or more may be em- After the still charge is brought to the partments and pass upwardly through the reflux tower 27, and the introduction of fresh oil is begun. Fresh oil may be-introduced either through connection 28 or throughcon-- Vvnection 29 or lthrough both connections. In

. area of heat transfer and consequent reducany case, thenreflux and fresh oil Iare introducedv into {compartment-A. As the'v refluxf and freshfoil arefintroduced into compartment A, oil from this first compartmentwhich has been deprived of a part of 'its crackable constituents and -contains some'tar constituents overiowsinto the second compartment B- where it is further cracked and a further part of its components are vaporized. In the same way oil is transferred from compartment B to compartment C and from com partment C to compartment D as the cracked .constituents are vaporized and as the tar accumulates, the 011 1n the successive com partments containing `less and vless of the original oil constituents and more andmore heavy tarry constituents. Tar may be with` drawn from the last compartment D during the progress of the cracking operation continuously or. from time to time throughreonnection 35D. The introduction of fresh oil divided and introduced partly into .the re-` iux tower andpartly into compartment A directly or may all be introduced directly into compartment A.

The heating gases from the furnace 5.are

passed successively over the heating elements connected to compartments A, B, C and D in order, so that the oil in the first compartment A, including the reiux and fresh oil,

is-mechanically circulated in heat exchanging relation with the vheating gases of highest temperature, that in the second compartment B- is mechanically circulated in heat exchanging relation with heating gasesof a somewhat lower` temperature, and so on. The

- heat absorbed by the oil circulating from and to the lfirst compartment Alis employed to crack the oil constituents of the. reflux andL fresh oil and thisl oil is rapidly circulated? over the initial heating suiraces protecting. themagainst the highest te peratureofthe' heating gases, and as the tar content of the 'oil increases it is transferred to. successive compartments where it is circulated in-heat exchange with heating gases of progressive- 1y lower temperature. At the same timethe heating effect in the successive compartments is equalized by the progressively increased areav of heat transfer provided, and thedif- {iculties and dangers lncident to the formation of carbonaceous deposits arematerially reduced due both to thedecreased temperature of the heating gases and the increased tion in the rate of heat transfer per unit of area. In all of the heating elements the ab,

sorptionof heat by the rapidly circulating oil protects the heating surfaces, particularly in the first where the heating element isexposed to the hottestheating gases and `where the circulating oil contains the reflux land fresh :oil and the least content of` tar, and the most rapid circulation is maintained.

It will thus be seen that the present invention provides an improved method of crackf ing hydrocarbon oils by distillation under lated over the heating surfaces in contact with the hottest heating gases consists of fresh oil and reflux while the heating gases cooled and tempered in this initial heating operation are employed to further heat and crack tlie oil as carbon and tar constituents accumulate in it. rlhe oil circulating through 'the still thus initially consists offresh oil and reiiux andis first circulated in heat exchanging relation with the hottest heating gases, and, as the fresh oil and reiiux constiti uentsare cracked and vaporized and as the circulating oil becomes heavier and carbon and tar constituents accumulate therein, the oil is mechanically circulated in he'at exvention provides an improved -method of cracking hydrocarbon oils lby distillation under pressure in externally heated pressure stills in which fresh oil is supplied to the cracking operation and in which the fresh oil `is first employed lto promote and control a refiuxing operation to .which the vapors from the pressure still are subjected and then, in admixture with the'reflux, is mechanicah.

, .90 heating surfaces and in which the oil-circuchanging relation with the cooler heating vgases from the preceding heating operation.` .It will further be seen that the presentV inly VcirculatedI over heating surfaces of the pressure still to heat exchange with the hot- I test heating gases while thelightercrackable constituents are subjected to particularly ad ing-operation to be carried out over a prolonged period without, however, decreasing Athe rate of cracking by reducing ,the temperaturevof the heating gases or otherwise. Another important advantage of the inven tion is that it enables an improved application of the heating gases to the cracking operation so that both the efficiency and the capacity of the pressure still may be increased.-

' sure by circulating heating gases in heat exchanging relation successively with the oil in the cycles in the order of increasing tar content, maintaining progressively increasing areas of heat transfer between the heating gases and the oil in the successive cycles in the same order, subjecting the vapors from the cracking operation to a refluxing operation, and returning the reflux to the first cycle in Which the tar concentration is least.

2. An improved method of cracking hydrocarbon oils, which comprises heating a body of oil -to a cracking temperature under pressure by circulating oil from the body in heat exchanging relation With heating gases and back to thebody, subjecting the vapors from the cracking operation to a refluxing operation, and circulating the reflux at a more rapid rate in heat exchanging relation with the heating gases before the heating gases are brought into heat exchanging relation with thefoil in the first said heating operation.

3. An improved method of cracking hydrocarbon oils, which comprises circulating the oil in each of a series of cycles and heating the oil to a cracking temperature under pressure in each cycle, transferring oil to successive cycles as the tar-content of the oil increases, subjecting the vapors formed to a refluxing o eration, returning the reiiux to the first o said cycles, circulating heating gases for supplying the heat absorbed in the cracking operation first in heat exchanging relation with the oil in the cycle to which the reflux and fresh oil are returned and thereafter over the successive cycles, and maintaining the most rapid circulation in the cycle to which the reflux and fresh oil are returned.

4. An improved method vof cracking hydrocarbon oils, which .comprises circulating theoil in each of a series of cycles and heating the oil to a cracking temperature under pressure ineach cycle, transferring oilv to` successive cycles "as thetar-content of the oil increases, subjecting the vapors formed to a refluxing operation inI direct contact Y'With fresh oil, returning the reflux and admixed' fresh oil to the first of said cycles, circulating heating gases for supplying the heat absorbed in the cracking operation first in heat exchanging relation with the oil in the cycle to which the reux and fresh oil are returned and thereafter over the successive cycles, and maintaining the most rapid circulation in the cycle to Which the reflux and fresh oil are returned.

5. An improved method of cracking hydrocarbon oils, which comprises heating a body of oil to a cracking temperature under pressure by circulating oil from the body in heat exchangingrelation with heating ases and back to the body, circulating frcs oil at a more rapid rate. in heat exchanging relation with the heating gases before the heatinggases are brought into heat exchanging relation with the oil in the first said heating operation, and circulating oil from the second mentioned heating operation to the first mentioned heating operation.

6. An improved method of cracking hydrocarbon oils, which comprises circulatin the oil in a series of cycles, transferrinor oi to successive c cles as the tar content of? the oil increases, eating the oil to a cracking temperature under pressure by circulating heating gases in heatexch'anging relation successively with the oil in the cycles in the order of increasing tar content, subjecting the vapors from the cracking operation to a refluxing operation, returning reflux to a cycle in which the concentration of tar is less than that in the cycle in which the tar con-- y tent is greatest, and 'maintaining more rapid circulation in a cycle in which the tar concentration is less than that in the cycle in which the tar concentration is greatest.

7. A process of cracking hydrocarbon oils consisting in passing the oil through a heating coil wherein it is subjected to a conversion temperature, in discharging the heated oil into an enlarged conversion chamber, in passing the vapors issuing from said conversion chamber to a dephlegmator in-returning reflux condensate from the dephlegmator to said heating coil, in condens- 111g the vapors issuing from the dephlegmator and in collecting the resulting distillate, in circulating unvaporized oil from said conversion chamber through an independent 'heating element wherein it is subjected to a lower temperature than the oil in said coil and back to the conversion chamber, in preventing the return of unvaporized oil which .i jecting them to a refluxing operation, passi ing the reflux at a more ra id rate than that employed in the first said eating operationin heat exchanging relation with the heating gases-before the heating gases are brought into heat exchanging relation with the oil in the first said heating operation.

In testimony whereof We affix our signatures.

LOLA R. BELL, Eeeum'm of the Last Will amd'Testament of .707m E. Bell, Deceased.

f EDWARD W. ISOM.

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