US2047779A - Conversion of hydrocarbon oils - Google Patents

Description

Patented July 14, 1936 CONVERSION OF HYDROCARBON OILS Jacob Benjamin Held, Chicago, Ill., assignor to Universal Oil Products Company,

Chicago, 111.,

- a corporation of Delaware Application March 29, 1934, Serial No. 717,922

7 Claims.

This invention particularly refers to improvements in the type of cracking process and apparatus wherein vaporous and liquid conversion products of the process are continuously separated during treatment in a heated reaction zone, both liquid and vaporous materials being continuously circulated to and from said reaction zone, each through a separate, independently fired heating coil wherein they are subjected to continued conversion, residual liquid being continuously withdrawn from the liquid cracking cycle and vapors being continuously withdrawn from the vapor cracking cycle and subjected to fractionation for their separation into reflux condensate and lower boiling fractionated vapors, which latter are condensed and recovered, the reflux condensate being subjected to further conversion in the same system.

In my United States Patent No. 1,936,874, I have disclosed a process of the character above outlined wherein the entire still comprising the reaction drum, the tubes and communicating headers comprising the liquid heating cycle and the tubes and communicating headers comprising the vapor heating cycle is located within a single furnace structure, the tubes of the liquid heating cycle being located beneath the reaction drum and the tubes of the vapor heating cycle being located above the reaction drum. Provision is made for supplying combustible fuel to a combustion space beneath the tubes of the liquid heating cycle while additional combustible fuel may be supplied to a combustion space between the reaction drum and the tubes of the vapor heating cycle in order to independently control the heating conditions in each cycle, more severe heating conditions being employed in the vapor heating cycle than in the liquid heating cycle. In the patent referred to raw oil charging stock for the process may be supplied either'to a fractionator of the system or direct to the liquid heating cycle'of the process and reflux condensate from said fractionator is returned to the liquid heating cycle.

The present invention embodies improvements to the process and apparatus of the above patent whereby hydrocarbon oil charging stock for the process is preheated and subjected to vaporization, by passing the same for example through serially connected tubes located adjacent the roof of the furnace, and is then introduced into either the vapor or liquid heating cycle, while reflux condensate from the fractionator of the system is passed through serially connected tubes located adjacent the floor of the furnace, wherein it is subjected to heating and vaporization, and is then introduced into the vapor heating cycle of the process.

By this method of operation both the charging stock and the reflux condensate are supplied to the cracking stage of the process in substantially vaporized state, thereby removing a considerable load from the liquid heating cycle of the process which, by the previous method of operation, was required to heat and vaporize a considerable quantity of both the charging stock and the reflux condensate. In this manner I not only reduce the quantity of liquid circulated through the liquid heating cycle of the process but also considerably lower its gravity since it is substantially devoid of low-boiling components vaporized in the charging stock and reflux condensate heating tubes.

One of the chief advantages of the improved process of the present invention resides in the reduced amount of vaporization occurring in the liquid heating cycle of the process. I have found that this materially reduced coke formation and deposition in the tubes of the liquid heating cycle, thereby appreciably increasing the yield of desirable light liquid products, decreasing the yield of gas and greatly prolonging the duration of the operating cycle of the process. The reasons for attributing the improved results of the present process at least in part to the reduced amount of vaporization in the liquid heating cycle, is based upon experiments wherein the addition of lowboiling oil to relatively heavy oil materially increased the coke formation and deposition in a tubular heating element under substantially the same cracking conditions of outlet temperature from is ordinarily obviated. Furthermore, im- 4 proved heat economy is effected in the furnace, due to the improved arrangement of the heating coils (addition of the floor and roof tubes) and the entire operation in general is materially facilitated.

The accompanying diagrammatic drawing illustrates one specific form of apparatus in which the process may be carried out.

Referring to the drawing, a furnace l comprising end walls 2 and 2', a roof 3, a floor 4 and side walls, not shown in the particular cross-sectional view here illustrated, contains a horizontally disposed drum or reaction chamber 5. Tubes 6 of a suitable heating coil "I are manifolded at their opposite ends into suitable drum headers 8 and 9 Which communicate with the lower portion of drum 5 through the respective risers I and II, the entire assembly comprising heating coil or tube bank I, headers 8 and 9 and risers I0 and II being located within the furnace beneath reaction drum and comprising, in conjunction with the lower portion of the reaction drum, the liquid heating cycle of the process.

Another suitable heating coil or tube bank I2 of tubes 6 is located within the furnace above. reaction drum 5, the tubes of bank I2 being connected at their opposite ends to headers I3 and I4 which communicate respectively through risers I5 and I6 with the upper portion of reaction drum 5. This assembly, in conjunction with the upper portion of the reaction drum, comprises the vapor heating cycle of the process.

Suitable impellers I! are located within each of the risers II], II, I5 and I6 for the purpose of assisting circulation of the liquid and vapors through the respective heating cycles. The arrows in the drawing indicate the'preferred direction of travel of vapors and liquid in their respective cycles and it will be noted that they flow countercurrent to each other through reaction drum 5; a suitable liquid level being preferably maintained in this zone so that the vapors occupy the upper portion and the liquid occupies the lower portion of this zone. The impellers I1 may be motivated in any suitable well known manner such as, for example, by means of motors I8 and connecting shafts I9.

Combustible fuel of any desired form, such as oil, gas or pulverized solid fuel, may be supplied to the combustion space of the furnace beneath tube bank 6 by means of suitable burners such as indicated at 2|. The materials undergoing combustion in zone 20 impart heat primarily by radiation to the tubes 5 of fluid conduit 22 located adjacent floor 4 of the furnace. The hot combustion gases pass upward over tube bank I, drum 5 and tube bank I2 and are withdrawn from the upper portion of the furnace through flue 23 to a suitable stack, not shown. Preferably additional combustible fuel is supplied in regulated amounts to combustion zone 24 of the furnace located between reaction drum 5 and tube bank I2 by means of suitable burners 2|. In this manner additional heat is provided for the vapor heating cycle of the process independent of the residual heat in the combustion gases from combustion zone 20, which latter zone supplied substantially the total heat for the liquid heating cycle. In this manner independent control is obtained over the heating conditions in each cycle, higher temperatures being desirable in all cases for the vapor heating cycle than those employed for the liquid heating cycle.

Another fluid conduit comprising bank 25 of tubes 6 is located in the case here illustrated adjacent the roof 3 of the furnace and raw oil charging stock for the process, which may be supplied through line 26 and valve 21 to pump 28, is fed through line 29 and valve 30 and may pass in series through adjacent tubes of bank 25, receiving heat from the hot combustion gases, prior to their removal from the furnace, through flue 23,

and from the hot refractory walls of the furnace.

The charging stock thus preheated, preferably to a temperature suflicient to effect substantial vaporization thereof, is discharged from tube bank 25 through line 3I and may be supplied to the liquid heating cycle, for example, through line 32 and valve 33, preferably being supplied to the body of liquid in reaction drum 5 at a point near the introduction of the heated liquid to this zone from tube bank I, or entering the vapor space in reaction drum 5 through line 34 and valve 35, preferably at a point near the point of introduction of the heated vapors to this zone from heating coil I2.

Residual liquid is withdrawn in regulated quantitles from the liquid heating cycle of the process, being discharged from header 9, for example, through line 36 and valve 31 to cooling and storage or to any desired further treatment, not illustrated. Vapcrous products are continuously withdrawn in regulated quantities from the vapor heating cycle of the process, being discharged, for example, from header I3 through line 38 and valve 39 to fractionator 40. Preferably the quantity of raw oil charging stock supplied to the system is substantially equivalent to the quantity of vaporous and residual liquid products withdrawn respectively from the vapor and liquid heating cycles of the system minus the quantity of reflux condensate returned, as will be later more fully described, to the vapor heating cycle so, that the process may be continuously operated without depletion of the materials undergoing treatment in the two heating stages.

The components .of the vaporous conversion products supplied, as described, to fractionator 40 boiling above the range of the desired final light distillate product of the process are condensed in this zone as reflux condensate. Fractionated vapors of the desired end-boiling point are withdrawn, together with uncondensable gas produced by the process, from the upper portion of fractionator through line M and valve 42 to be subjected to condensation and cooling in condenser 43. The resulting distillate and gas passes through line 44 and valve 45 to collection and separation in receiver 46. Uncondensable gas may be released from the receiver through line 41 and valve 48. Distillate may be withdrawn from receiver 46 through line 49 and valve 50 to storage or to any desired further treatment. When desired, a regulated portion of the distillate collected in receiver 46 may be recirculated by means of line 5I, valve 52, pump 53, line 54 and valve 55 to the upper portion of fractionator 40 to serve as a cooling and refluxing medium to assist fractionation of the vapors and to maintain the desired vapor outlet temperature from the fractionator.

The reflux condensate formed in fractionator 40 is allowed to accumulate within the lower portion of this zone to be withdrawn therefrom through line 56 and valve 51 to pump 58, by means of which it is fed through line 59 and valve 60 to fluid conduit 22, passing through the adjacent tubes of the fluid conduit in series and being heated therein, preferably to a temperature sufficient to effect substantial vaporization of the oil. The heated reflux condensate is discharged from tube bank 22 through line 6| and valve 62, preferably entering the vapor heating cycle at a. point near the point of introduction of She berated vapors from tube bank I2 to reaction It is also within the scope of the present invention, when desired, to introduce all or a regulated portion of the charging stock into fractionator 40 to commingle with and assist fractionation of the vaporous conversion products in this zone. This may be accomplished, either with or without preheating a portion or all of the charging stock in heating coil 25, by means of line 63, controlled by valve 64, and line 65, controlled by valve 66. This method of operation is particularly desirable in case the charging stock contains an appreciable quantity of desirable low boiling materials, such as motor fuel or motor fuel fractions of good antiknock value, which may thus be blended and recovered together with the light distillate product collected in receiver 46 without being subjected to any unnecessary conversion or reforming. In any case when this method of operation is employed the components of the charging stock boiling above the range of the desired final light distillate product of the process, or the total charging stock, in case it contains no components within the range of the light distillate product, commingles with the reflux condensate formed in fractionator 40 and is subjected therewith to further heating and vaporization in heating coil 22, in the manner previously described. It is within the scope of the present invention, when the total charging stock is supplied to the fractionator, to eliminate heating coil 25 adjacent the roof of the furnace or to pass all or a regulated portion of the charging stock through this zone, prior to its introduction into the fractionator, or to utilize heating coil 25 in conjunction with heating coil 22 as a means of further heating the com bined feed (reflux condensate and charging stock) and subjecting the same to vaporization, prior to its return to the vapor heating cycle of the system, although means for accomplishing the latter are not illustrated in the drawing.

In a process of the character illustrated and above described, the preferred operating conditions may be approximately as follows: The temperature employed in the liquid heating cycle may range, for example, from 800 to 950 F. with a temperature in the vapor heating cycle of from 900 to 1050 F., for example, and the two heating cycles may employ any desired pressure-ranging from substantially atmospheric to 500 pounds, or more, per square inch superatmos pheric pressure. With temperatures in the vapor and liquid heating cycles of the order mentioned the reflux condensate may be subjected, prior to its return to the vapor heating cycle, to a temperature of the order of 700 to 900 F., for example, while the charging stock may be preheated, prior to its introduction into the vapor or liquid heating cycle to a temperature of the order of 500 to 800 F., or thereabouts, and preferably substantial superatmospheric pressures independently controlled, of course, for each stream, are employed in the reflux condensate and raw oil heating stages and, in any case, the pressure employed in these zones is no .less than that employed in the vapor and liquid heating cycles. Substantially the same or somewhat reduced pressures relative to the pressure employed in the vapor and liquid heating cycles may be utilized in the succeeding fractionating, condensing and collecting portions of the cracking system.

As a specific example of the operation of the process of the present invention as it may be practiced in an apparatus such as illustrated and above described; the charging stock is a Mid- Continent crude of about 38 A. P. I. gravity containing approximately 5 percent of materials boiling at 180 F., and about 3% percent at 437 F. The charging stock is preheated in a bank of tubes located adjacent the roof of the furnace to a temperature of approximately 550 F. at a superatmospheric pressure of about 300 pounds per square inch and is introduced into the vapor space of the reaction drum. The temperature of the oil in the liquid cycle of the ysl0 tem as it enters the reaction drum is maintained at approximately 875 F. The temperature of the vapors in the vapor heating cycle, measured at their point of entrance to the reaction drum, is maintained at approximately 950 F. A su- 5 peratmospheric pressure of approximately pounds per square inch is maintained in the reaction drum and is reduced in the fractionator and succeeding equipment to substantially atmospheric pressure. Reflux condensate from 20 the fractionator is reheated in a bank of tubes located adjacent the floor of the furnace to a temperature of approximately 800 F. and is introduced into the vapor heating cycle of the system. 35

This operation may produce, per barrel of charging stock, approximately 60% of 400 endpoint motor fuel of good anti-knock value and about 28% of good quality residual liquid suitable as fuel, the remaining 12%, or thereabouts, 30 being chargeable principally-to uncondensable I claim as my invention:

1. A process for converting hydrocarbons which comprises cyclically circulating a closed 35 ring of liquid hydrocarbon oil and a closed ring of hydrocarbon vapor, maintaining said rings separate from each other during part of their travel and while separated heating the liquid ring to a distillation temperature and the vapor ring to a cracking temperature, passing vapors evolved from the liquid ring into the vapor ring, removing vapors from the vapor ring and subjecting the same to fractionation to condense heavier fractions thereof, vaporizing resultant reflux condensate externally of said rings and introducing vapors thus formed directly into the vapor ring, and finally condensing the fractionated vapors.

2. A process for converting hydrocarbons which comprises cyclically circulating a closed ring of liquid hydrocarbon oil and a closed ring of hydrocarbon vapor, maintaining said rings separate from each other during part of their travel and while separated heating the liquid ring to a distillation temperature and the vapor ring to a cracking temperature, passing said rings through a common zone during another portion of their travel whereby vapors evolved from the liquid ring are transferred to the vapor 6 ring, heating charging oil for the process externally of said rings sufiiciently to vaporize a. substantial portion thereof and then introducing the same to said common zone.

3. A process for converting hydrocarbons 6 which comprises cyclically circulating a closed ring of liquid hydrocarbon oil and a closed ring of hydrocarbon vapor, maintaining said rings separate from each other during part of their ring, heating charging oil for the process externally of said rings sufiiciently to vaporize a substantial portion thereof and then introducing the same to said common zone, removing vapors from the vapor ring and fractionating the same to condense heavier fractions thereof, vaporizing resultant reflux condensate externally of said rings and independently of said charging oil, introducing vapors thus formed directly into the vapor ring, and finally condensing the fractionated vapors.

4. A conversion apparatus comprising a furnace, a drum in the furnace, a heater above and a heater below the drum and positioned in the furnace, means for cyclically circulating vapors through the drum and upper heater, means for cyclically circulating liquid oil through the drum and lower heater, a heating coil in the furnace, and means for passing oil through said coil and then into the drum.

5. A conversion apparatus comprising afurnace,'a drum in the furnace, a heater above and a heater below the drum and positioned in the furnace, means for cyclically circulating vapors through the drum and upper heater, means forcyclically circulating liquid oil through the drum and lower heater, a heating coil in the furnace, and means for passing oil through said coil and then into the cyclically circulating vapors.

6. A conversion apparatus comprising a furnace, a drum in the furnace, a heater above and a heater below the drum and positioned in the furnace, means for cyclically circulating vapors through the drum and upper heater, means for cyclically circulating liquid oil through the drum and lower heater, a heating coil in the furnace, a fractionator and means for supplying a portion of the vapors thereto, and means for passing reflux condensate from the fraetionator through said coil and then into the cyclically circulating vapors.

7. A conversion apparatus comprising a furnace, a drum in the furnace, a heater above and a heater below the drum and positioned in the furnace, means for cyclically circulating vapors through the drum and upper heater, means for cyclically circulating liquid oil through the drum and lower heater, a heating coil in the upper portion of the furnace, a second heating coil in the lower portion of the furnace, a fractionator and means for supplying a portion of the vapors thereto, means for passing charging oil through one of said coils and then into the drum, and means for passing reflux condensate from the fractionator through the other of said coils and then into the cyclically circulating vapors.

JACOB BENJAMIN HEI'D.

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