US2023063A - Process of cracking petroleum hydrocarbons - Google Patents

Description

Dec. 3, 1935. c. B. .BUERGER PROCESS' OF CRACKING PETROLEM HYDROCARBONS Filed oct. 19, 1929 4 Sheets-Sheet l \W MW NJN. a TN Dec. 3, 1935. c. B. BUERGER 2,023,063v

PROCESS OF CRACKING PETROLEUM HYDROCARBONS Filed-Oct. 19, 1929 4 Sheets-'Sheet '2 65 62 67 FH?. JJ/"LL con ooo aan o l 0 0 00g V63 5I o j!" g:h u

J 3mm Dec. 3, 1935. Q B. BUERGER 2,023,063

PROCESS OF CRACKING PETROLEUM HYDROCARBONS Filed Oct. 19, 1929 4 Shee'hS-SheeI 5 Dec. 3, 1935. c. B. BUERGER PROCESS OF CRAOKING PETROLEUM HYDROCARBONS Filed Oct. l9, 1929 4 Sheets-Sheet 4 dual/wu,

Patented Dec. 3, 1935 UNITED STATES POCESS F CRACKING PETROLEUM HYDROCARBONS Charles B. Buerger, Pittsburgh, Pa., assignor to Gulf Rening Company, Pittsburgh, Pa., a

corporation or' Texas Application October 19, 1929, Serial No. 400,893 In Canada April 14, 1925 9 Claims.

This invention relates to processes of cracking petroleum, and it comprises a process of passing oil in a continuous stream through a sectional heater, heating the oil in one section to a cracking temperature and then passing it through a subsequent sectio-n wherein it is subjected to continued heating to continue the cracking reaction and to vaporize the more volatile products of said reaction, and then discharging the so-heated 10 stream from the heater for separation of the products resulting from the heating.

In the cracking distillation of petroleum it is desirable to bring the oil to, and then maintain it within, a certain elevated temperature range,

While supplying additional heat. This additional heat, if supplied at the p-roper stage of the cracking process will continue the cracking to a much more advanced stage, and Will do this without undue production of carbon and undesirable Q0 liquid and gaseous products. The elevated temperature range ordinarily most effective extends from about 800 F. to 1000 F., a substantially lower temperature being insuicient to elect the requisite rearrangement of the molecular structure of the oil undergoing treatment, while a very much higher temperature so affects that rearrangement as to produce undue quantities of undesirable products.

In accordance with the present invention the heating is so arranged and the conditions of operation are so maintained that the major portion of the cracking and vaporization, or all of it if desired, may be accomplished in the heating and cracking Zones of the heater. When so desired the cracking reaction may be checked as the oil emerges from the heater and one convenient way of precluding further cracking is to introduce a stream of cold oil into the stream of hot oil emerging from the heater. Or the stream may pass from the heater to a separating chamber where the vaporized and unvaporized constituents oi the stream are separated and immediately removed out oi the presence of one another. One other manner of handling the stream from the heater is to send it to a reaction chamber for extreme decomposition of the residuum.

I have found that in the cracking distillation of petroleum oils this cracking can be continued to an unusually advanced stage by passing the incoming oil, with or Without preheating, through one zone of a heater where the oil will be heated to a cracking temperature and then passing this oil from that zone to a subsequent zone in which the oil is subjected to further heating unaccom- .panied by substantial rise of temperature.

Briefly, my process constitutes heating the oil up to a cracking temperature and then passing the oil through a section of tubular heater at substantial velocity, having this tubular heater of such length that passage of oil therethrough will 5 consume a substantial period of time, and supplying heat to the oil in its passage through this section of the heater in proportion to the demands of the chemical and physical changes taking place in the oil during its passage there- 10 through. By having successive portions of the heater positioned in selected relation to one another in the furnace the process can be controlled to a nicety and can be performed without the production of large quantities of undesirably 15 light or undesirably heavy products.

My process carries the cracking reaction to an advanced stage inthe tubular system and does not necessarily require the use of a reaction or capacity chamber. formed is much less in proportion to the amount of cracking accomplished than in prior known processes and that small amount of carbon which is formed does not tend to agglomerate and burn on the heating surfaces or block the passages 25 through which the material is directed after leaving the heater.

The accompanying drawings are illustrativeof various forms of apparatus useful in performing the process of my invention. 30

Figure 1 is a diagrammatic view of one form of tubular heater in a system which embodies a capacity chamber;

Figure 2 is a diagrammatic View of another formof heater in a system, wherein a capacity or 35 reaction chamber is omitted;

Figure 3 is a partly diagrammatic View, in vertical section, of the heater shown in Figure 1;

Figure 4 is a Vertical sectional View of another form of heater; 40

Figure 5 is a longitudinal sectional view of yet another form of heater;

Figure 6 is a plan View of the heater shown Figure 5, with the enclosing Wall removed from one corner of the upper portion, as indicated by 45 the line A-A of Figure 5.

Referring more particularly to the drawings and, rst, to the apparatus shown in Figures 1 and 3:

Two banks of tubes I0 are located in the 50 heater I I and operate in parallel, being fed with oil from a pump I 2, through pipe I3 which terminates in the branches I4 and I5 of the heating tubes. The oil iiows lirst through the bottom tube tier of each set, which is located in the zone 55 The amount of carbon 20 of greatest heat and where it absorbs the radiant heat of the re and partially cools the ascending combustion gases, thence to the next upper tier and so on up to the fth tier, and thence out through lines I6. As many of these heating tube tiers may be employed as may be necessary to bring the oil to a cracking temperature. The stream of oil need not be divided in its passage through the heater, but in this particular apparatus I nd it advantageous to send the oil, in two parallel streams, rst through ve tiers, or thereabouts, in a general upward direction, that is, in the direction of flow` of the combustion gases, and then deliver the oil to the top tier of a similar assemblage of tiers I1, and thence downwardly through this second series of tiers. As shown, the pipe I6, instead of leading directly outwardly and away from the heater, serves as a reentry and directs the oil, which by this time has been brought to cracking temperature, to the top tier located in a zone of less heat, and thence downwardly through these tiers. The heating in this zone is sufficient to Very substantially increase the amount of cracking. In the embodiment shown in the drawings there are eleven tiers of the upper tube series I'I, arranged for downward flow. The oil takes roughly twice as long to pass through the upper tube series as it does to pass through the lower bank of five tiers. From the last tier in the series the oil goes to exit tln'ough pipes I8 and I9 which terminate in a common collecting main 20.

As is shown in Figure 1 of the drawings, the heater may be advantageously used in a system y 4 employing a heat-insulated capacity chamber 2I.

In such case the line 20 extends into the heat insulated chamber and may deliver thereinto through a quieting pipe 22 which is open at both ends and terminates at its lower end at a point some distance above the bottom of the chamber and below the normal level of the oil therein, and terminates at its upper end some distance above the normal level of the oil in the chamber.

A safety valve 23 is provided to relieve abnormal pressures in the chamber 2|, the discharge pipe 24 leading to a place of disposition of oil vapors (not shown).

Vapors are conducted from chamber 2| through pipe 25 to a heat interchanger 26Y where they are scrubbed by incoming fresh oil from a pump or pumps 2'I. The hot vapors, as they come from the capacity chamber, are thereby cooled while the incoming oil absorbs this heat and enters the heater at a somewhat elevated tempertaure. Such cooling of the vapors causes condensation of their heavier portion, While lighter vapors pass through pipe 23 to a reflux condenser 29. Reflux condensate flows downwardly through pipe 30 into the upper part of the heat interchanger 26 where it encounters the rising warm vapors and undergoes a heat exchange therewith, similar to the action of the incoming oil. A pressure reducing valve 3| is located in the line 32 immediately beyond condenser 29, and the vapor after passing this valve enters the bottom of dephlegmator 33 where it is washed by downflowing condensate from reflux condenser 34. The combined condensate from 33 and 34 is Withdrawn through pipe 35 and cooled in coils 36. The vapors persisting beyond this point pass upwardly from the dephlegmator, through pipe 3'I to condenser 34, Where they are further fractionated, the liquid condensate previously mentioned passing back to the dephlegmator through linek 38. Uncondensed vapors are Withdrawn through pipe 39 and are condensed in coils 40.

Tar and coke collect in the bottom of the capacity chamber 2| and are withdrawn continuously or from time to time, by a pump 4 I, through 5 line l2 to a tar cooler 43 or to some point of disposal. Ordinarily, I seek to adjust conditions so that any given portion of oil is exposed to a cracking temperature for about eight hours; and I iind it advantageous to make the amount of oil 10 circulated, that is going through the tubular heating system in a given time about twice the amount of oil entering the system as replenishing oil in the same space of time. In so doing, the amount of oils returning to the cracking system 15 from the heat exchanger and the reflux condenser as a result of scrubbingand heat interchange actions is usually about equal to the amount of replenishing oil introduced. In other words, the amount in circulation in the heating tubes at any 20 given time is about equal to the total of the replenishing oil and of the returned or reiluxed oils coming back to the cracking system at the same time; and I am able to secure a high velocity in the cracking tubes without increasing the amount 25 of reflux unreasonably, with acceleration of the cracking action in the major body of oil and easy maintenance of cracking temperatures in such body.

Oil may be withdrawn from the capacity cham- 30 ber through a pipe 44 which may connect to the fresh oil and reflux supply line. Thus a portion of the hot oil from the capacity chamber may be continuously recirculated for further cracking.

According to my invention in one of its modi- 35 ed forms, as shown in Figure 2 of the drawings, the heater may comprise a furnace structure I5 which includes a combustion chamber 46 and a heater chamber ill, separated by a bridge wall 48. Oil is forced by a pump 49 through pipe 59 40 to the lowermost tier of a tube series 5I, this tier being locate-d in the coolest Zone of the heat absorbing chamber. 'Ihe oil passes in a generally upward direction through the successive tiers counter to the flow of combustion gases t5 and is thereby preheated. It is then passed through pipe 52 to a coil 53 situated to receive the radiant heat of the furnace. Not only does the coil 53 receive radiant heat of the furnace, but in this particular arrangement it also receives 50 an appreciable amount of the convective heat. In this series of tubes the oil is brought to a cracking temperature but before the cracking has proceeded to any substantial degree the oil is conducted back to a zone in the flue where the 55 conditions of heating are less severe. This Zone is here shown as three tiers marked 13. The flow of oil in the apparatus shown in Fig. 2 is into the lowermost tier of the section I3 and then countercurrent to the furnace gases. This 60 counterflow in section I3 is not essential under all conditions. From section I3 the oil nally leaves the heater through pipe 5. and passes through a separating chamber 55. The separating chamber may be a part of the reux con- 65 denser 55, which reflux condenser is provided with baliles 5l. Condensate in the reflux condenser ilows downward over these bafles to the trap 53 and is subsequently returned to the heater in a manner hereinafter described. Further vaporiza- 70 tion and conversion is not desired in the separating chamber 55. Neither is it desired that there be any condensation therein and so chamber 55 is provided with insulation 59. In preferably open Communication with reflux condenser 56 is a 75 radiator 60 consisting of a number of air cooled passages through which the vapors travel to a common header 6|. Vapors from the header are delivered to the condenser 62 for final condensation. Pressure may be maintained in the system by means of the pressure regulating valve 63 between the reflux condenser and the final condenser, or by means of a similar valve 64 beyond the final condenser. Of course another valve is placed on the residuum outlet to assist valves 63 and 64 in maintaining the desired pressure.. The final condenser may be of the usual type consisting of a coil in a tank 65 through which water is circulated by means of an' inlet 60 and an outlet El. Reux condensate from the radiator 00 and condenser 55 flows over baiiies 51 to the trap 58 and from there is delivered through line 08, pump and lines '|2 and 50, back to the entrance of the heater. The liquid oil going to the separating chamber 55 .is immediately and continuously removed through line 69, valved at 10. It may be sent to any type of still or stripper for the separation of a distillate which can be returned as charge oil to the system. Chamber 55 is shown broken away to indicate that it is of sufficient depth to provide against any vapor escaping through drawoif line 60. Nevertheless it is ordinarily maintained substantially empty of liquid oil so that no substantial conversion or vaporization of oil occurs therein. The bulk of the carbon ows out in the form of small particles with the residuum from the separating zone 55. Vapors condensed in radiator B0 and baffles 5l are collected in trap 58 as heretofore described and from here the condensate is pumped by pump 1| through line l2, which communicates with the incoming fresh oil line 50. The incoming oil is thereby heated to some extent prior to entering the bank of tubes 5| in the heater.

In the operation of this apparatus, it is not necessary to maintain, in addition to the stream of oil subjected to cracking temperature, a second body of oil subjected to conversion conditions, since all the desired c onversion may be accomplished in thetubes of the heater.

Another form of heater useful in performing the process of my invention is shown in Figure 4, wherein oil is delivered through tubes located in a relatively cool portion of the heat absorbing chamber of a furnace and is there preheated. It is then heated to a cracking temperature by passing it through a portion of the heater exposed to the radiant heat of combustion in the furnace, and is subsequently passed through two series of tube tiers, the second of which is subjected to gases direct from the combustion chamber andthe first of which is subjected to gases which have given up part of their heat to the last mentioned tube bank and which have been reheated by the regulated addition of further gases direct from the furnace. Referring to the drawings the heater 84 comprises a combustion chamber 85 and a tube bank chamber or heat absorbing chamber 85, connected by upper and lower flues or passages 8l and 88 which permit directed passage of hot combustion gases from the combustion chamber 85 to the tube bank chamber 00. Dampers 89 and 90 are located in these passages for regulating the ow of gases therethrough. The stack is indicated at 9|. A firing opening 92 is provided in the front of the furnace and into this opening an oil, gas or other suitable burner 93 is introduced. In operating according to my invention oil to be treated is drawn from a source of supply through suction line 94 by the pump 95, which discharges it under high pressure through the line 9B to the upper series of tubes 9i. After passing through the tube bank 9`| the oil passes through a connecting 5 line 98 to the tubes 99 positioned in the top of combustion chamber 85. Leaving tubes Q9 through connection |60 the oil enters tube bank ll and then passes through connection |02 to tube bank |03, after which it leaves the heater 10 through line |04 and may then be delivered to any suitable apparatus for separation of the desired products. Several suitable forms of separating and recovering apparatus have already been described. The inlet line 96 and the disl5 charge line I4 are provided with valves |05 and |06 respectively, to permit any desired control ofthe stream. Incoming relatively cool oil is rst subjected in the tube bank 91 tothe heat of the gases immediately before they escape 20 to the stack 9|, and removes the last available heat therefrom. The oil, not yet up to what might be called the critical range, in which its heating must be very delicately controlled, is next exposed in coil 99 to the radiant heat of 25 combustion, the apparatus being so proportioned and the firing so controlled as to here permit the greatest heat absorption consistent with safety. The oil then passes to the series of tubes ii where it absorbs heat from a mixture of those 30 gases which have already given up most of their available heat to tube series |03 and hot combusticn gases entering direct from the furnace through passage 3l. Further heating of the oil takes place in the series of tubes |03, where it 35 is exposed only to hot gases entering the tube chamber through passage 88. For the purposes of this invention the two banks I0! and |03 may be considered as a single bank, which has been specially arranged in this form for convenient 40 means of maintaining an uncommonly small temperature drop of the heating gases over a large portion of the heater.

The apparatus embodiment illustrated in Figures 5 and 6 comprises a vertical cylindrical fur- 45 nace le, enclosed by a wall '|5, and heated by a burner 16. Disposed vertically around the Walls are tubes which are seriately arranged and through which is passed the material to be heated. Four separate rows of such tubes, 11,50 78, 19, and 80 are illustrated, the rows being disposed in concentric c'ncular form near to the outside wall '|5.

Surmounting the vertical cylindrical section and in open communication with the furnace is 55 a ,rectangular bank of seriately connected heating tubes 8|, enclosed on the sides, ends, and top by the wall 82, and this bank of tubes is in turn surmounted by a stack 83 through which the furnace gases, after having given up their heat, 60 escape to the atmosphere.

in the performance of my process the oil to be cracked is forced by the pump |01 through line i0!! into the top tube tier of the tube bank 8l which surmounts the cylindrical furnace. The 65 oil passes back and forth across the top tube tier and then passes downward to and across succeeding tube tiers to the lowermost tube tier |09. Leaving the lowermost tube tier |00 of the tube bank 8i, the oil passes through connection 70 to the entrance of the innermost tube circle 80 of the vertical cylindrical heating section. From this point the oil passes successively through. alternate tubes of rows 80 and 'I9 until it has passed completely around the cylindrical furheat from the furnace as well as convective heat. .After passing through tube bank 8| ythe oil is -heated in the radiant section comprising the two innermost rows, I9 and 80, of the vertical cylindrical heating section and in its passage through this section of the heater the oil is brought to a cracking temperature. In the best practice of my invention the heating sections, the flowof oil, and the fire maintained in the furnace will be so proportioned with relation to one another'that the oil will be brought to a cracking temperature in the heating sections just described, but Vwill `not undergo substantial cracking therein. After being brought to cracking temperature in its passage through tube rows 19 and 80, the soheated oil is passed to and through the tube rows .11 and 'I8 in the manner already described and it is subjected to further heating in its passage through these rows. The oil is passed through rows 'H and I8 for the purpose of maintaining it at cracking temperature and furnishing the heat necessary to maintain the cracking reaction and to provide latent heat of vaporization for the products of the cracking reaction which can exist at a cracking temperature only in vapor form. It will be seen that this designof apparatus, in the form of rows 'l1 and T8, provides a very ample soaking zone in which the oil can be maintained at cracking temperature and the cracking reaction continued to the desired extent.

In pumping the oil to be cracked through my tubular heater I always maintain a velocity of flow sulhcient to prevent stratification in the tubes of liquid and vaporA components.

It will be seen that my invention resides largely in the provision of and use of a soaking coil for the continued treatment of the oil after it has been brought to a cracking temperature. This soaking coil is advantageously located slightly away from the Zone oi most severe heating conditions.

The substance of this application except as to those portions relating exclusively to the specific embodiments shown in Figures 2, 4, 5, and 6, will be found in my application Serial Number 620,797, filed February 23, 1923, which application maturedinto Patent 1,796,138 on March 10, 1931. The substance of those portions of this applica- 'tion relating exclusively tothe specific embodiment shown in Figure 4 will be found in my application Serial Number 202,048, led June 28, 1927, which application matured into Patent Number 1,838,211 on December 29, 1931.

What I claim is:

1. In the cracking distillation of petroleum, a process of heating the oil to be cracked which comprises passing the oil through a seriately arranged tubular heater, heating the oil to cracking temperatures in one zone of the heater by subjecting it to the hottest gases of a furnace, further heating the oil in a second zone of the said heater by subjecting it to furnace gases which have already surrendered part Yof their heat in the first mentioned zone, passing the oil through the second zone in a course countercurrent to that of the furnace gases, and deliver- `ing the so-heated stream for subsequent steps of the cracking process.

2. In the cracking distillation of petroleum a 'tube bank chamber adjacent to a furnace, heatingv the oil to a cracking temperature in one zone ofthe heater by subjecting it to the hottest gases of the furnace, further heating the oil in a subsequent zone of the said heater by subjecting it to furnace gases which have already surrendered part of their heat in the first mentioned Zone, passing the oil through said subsequent zone downwardly in a course counter to that of the furnace gases, and discharging the so-heated material from the furnace.

3. In the cracking distillation of petroleum a process of heating oil to be cracked which comprises continuously passing the oil through a seriately arranged tubular heater situated in a tube bank chamber adjacent to a furnace, preheating the oil in an early stage of its passage therethrough, heating the oil to a cracking temperature in a further zone of the said heater by subjecting it to the hottest gases of the furnace heating the oil in a subsequent Zone of the said heater by subjecting it to furnace gases which have already surrendered part of their heat to the preceding zone, passing the oil through said subsequent zone in a course counter to that of the furnace gases, and discharging the heated material from the heater; each of the zones of the said heater being heated by furnace gases derived from the same furnace.

4. Aprocess of heating petroleum oils in tubulai` coils situated in a furnace which comprises rst passing the oil through a section of coil located in the hottest zone of the furnace comprising a plurality of rows of tubes in which the flow of oil through the tubes of each row is substantially transverse to that of the flow of furnace gases and in which the passage of oil from row to row is in substantially the same direction as that Yof the flow of furnace gases and then passing the oil through a section of coil located in a less highly heated zone of the furnace comprising a plurality of rows of tubes in which the flow of oil through the tubes of each row is substantially transverse of the ilow of furnace gases and in which the passage of oil from row to row is substantially counter-current to that of the furnace gases.

5. A process of heating petroleum oils in tubular coils situated in a furnace which comprises first passing the oil through a section of coil located in the hottest zone of the furnace and arranged to absorb radiant heat comprising a plurality of rows of tubes in which the flow of oil from row to row is in substantially the same direction as that of the flow of furnace gases, and then passing the oil through a section of coil located in a less highly heated Zone of the furnace comprising a plurality o-f rows of tubes in which the ilow of oil through the tubes of each row is substantially transverse of the flow of furnace gases and in which the passage of oil from row to row is substantially countercurrent to that of the furnace gases.

6. In the cracking distillation of petroleum oil by heating in several stages, the steps which comprise establishing and maintaining a circulation of oil to be cracked through a plurality of constricted heating Zones and a flow of heated furnace gases, supplying heat to said heating zones by indirect contact therewith, passing the oilinitially through a constricted heating Zone in a direction concurrent to the ilow of the said furnace gases, then passing said oil to and through a second constricted heating zone wherein the oil is heated by the furnace gases which have been contacted with the initial constricted heating zone, passing the oil through said second constricted heating Zone in a direction countercurrent to the flow of said furnace gases, and then passing said oil into a capacity chamber maintained at cracking temperatures.

7. The process of claim 6 wherein the oil is passed upwardly through said initial heating zone and downwardly through said second heating stage.

8. A process of heating petroleum oils in tubular coils situated in a furnace which comprises rst passing the oil through a section of coil located in the hottest zone of the furnace comprising a plurality of rows of tubes in which the ow of oil through the tubes of each row is substantially transverse to that of the flow of furnace gases and in which the passage oi oil from row to row is in substantially the same drection as that of the flow of furnace gases, then passing the oil through a section of coil located in a less highly heated zone of the furnace comprising a plurality of rows of tubes in which the ow of oil through the tubes of each row is substantially transverse of the ow of furnace gases and in which the passage of oil from row to row is substantially countercurrent to that of the furnace gases, delivering the so-heated oil into the zone of a maintained body of oil to complete the reaction, and finally withdrawing the vapors and residuurn for condensation and recovery of the products of said heating.

9. A process of heating petroleum oils in tubular coils situated in a furnace which comprises rst passing the oil through a section of coil located in the hottest Zone of the furnace and arranged to absorb radiant heat comprising a plurality of rows of tubes in which the flow of oil from row to row is in substantially the same direction as that of the flow of furnace gases, then passing the oil through a section of coil located in a less highly heated zone of the furnace comprising a plurality of rows of tubes in which the ow of oil through the tubes of each row is substantially transverse of the flow of furnace gases and in which the passage of oil from row to row is substantially countercurrent to that of the furnace gases, delivering the soheated oil into a zone of accumulated oil to carry the reaction to completion, removing and condensing the generated vapors and separating and withdrawing a residuum.

CHARLES B. BUERGER.

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