US2030365A - Treatment of hydrocarbon oil - Google Patents

Description

Feb. M, i936.

CRACK/IV 21 v FUR/V1755 CRACK/1V6 FUR/VAC:

W. W. GARY TREATMENT OF HYDROCARBON OIL Filed Feb. 1, 1953 INVENTOR- WRIGHT w. GARY,

BYAOY M ATTORNEY- Patented Feb. 11, 1936 UNITED STATES PATENT OFFIC TREATMENT OF HYDROCARBON OIL Application February 1, 1933, Serial No. 654,569

4 Claims.

This invention relates tothe pyrolytic decomposition of hydrocarbon oil, more particularly petroleum and petroleum oils, for the recovery of valuable products, such as gasoline or naphtha,

5 therefrom.

I have observed that residual oils or tars resulting from the pyrolytic decomposition of virgin stocks, such as crude petroleum or virgin gas oil, contain constituents which, while of high specific gravity, are not necessarily the lowest boiling constituents of such residues or tars, and are capable of being subjected to further cracking without excessive coke formation.

My invention therefore has for an object the provision of an improved process of and apparatus for effecting pyrolytic decomposition of petroleum oils, in which a separation of constituents is effected in such manner as to permit further cracking, while avoiding excessive coke formation, and has for further objects such additional improvements in operative advantages and results as may be found to obtain in the process and apparatus hereinafter set forth and claimed.

According to my invention, I eifect the pyrolytic decomposition of a virgin stock in a plurality of mild cracking stages, the residue or tar from each stage, after evaporation of a portion of the lower boiling constituents thereof, being delivered to a subsequent stage and there mildly 3 cracked, the products being evaporated and the unvaporized residue being further cracked, until a residue of a predetermined specific gravity, for example, a specific gravity of 0 A. P. I., is obtained.

35 Preferably, the treated products from the several stages are delivered to a common evaporator, the resultant vapors being combined and delivered to a common fractionating tower to produce a. composite stock suitable for further cracking 40 under relatively drastic conditions, while the several residual oils or tars are segregated and separately subjected to further cracking, as has been indicated hereinabove.

Preferably, the temperature conditions main- 45 tained in the several cracking operations are moderate in character, such as will produce a mild cracking or viscosity breaking effect rather than a drastic cracking of the oil being treated. Each one of the series of cracking operations may be carried out at a temperature somewhat higher than that of the preceding operation.

For example, a series of three cracking operations may be carried out at temperatures approximating 860 F., 870 F. and 880 F., respectively, at a pressure of, say, 250 pounds per square inch in each instance.

On the other hand, it may be preferable in many instances to carry out the several cracking operations at approximately the same tempera- 5-- ture, the times of contact in the several operations being successively increased, if desired.

My invention also contemplates flashing the ultimate tar or residual oil from the evaporator under a reduced pressure, the pressure in the 10 evaporator being preferably relatively close to the pressure or pressures maintained in the several mild cracking operations, and fractionation of the vapors liberated in the evaporation and flashing stages in the usual manner. 5 Such fractionation may be so carried out as to produce a composite stock suitable as a charging stock for a relatively drastic cracking operation, such for example. as a vapor-phase cracking operation carried out at a temperature of, for ex- 20' plates the provision of an evaporator comprising a plurality of sections adapted toreceive products from a plurality of cracking coils, and having trap-out trays or other suitable means for segregating and drawing off residual oil or tar from each'of said sections and conveying it to the heating coil discharging into the following section.

In order that my invention may be clearly set forth and understood, I now describe, with reference to the drawing accompanying and form- 40 ing a part of this specification, a preferred form and manner in which my invention may be practiced and embodied. In this drawing, the single figure is a more or less diagrammatic view of apparatus for effecting. pyrolytic decomposition of hydrocarbon oil in accordance with my present invention.

Referring to the drawing, a hydrocarbon oil, such for example as a crude petroleum or a virgin gas oil, is drawn from a suitable source, (not shown), through a conduit I and delivered by means of a pump 2 and a conduit 3 to a heat exchange coil 4 located in the upper part of a fractio-natlng tower 5. In the coil 4, the oil is preheated by heat exchange with vapors in the tower 5, and the preheated oil then passes through a conduit 6 and a branch conduit I having a valve 8 to an evaporator 9.

The evaporator 9 is provided with a plurality of trap-out trays II, I2 and I3, which divide the tower into a plurality of sections I4, I5, I6 and I1. Each of said sections may be provided, as shown, with baille plates I8, located in the upper part thereof.

Fresh oil is discharged into the upper section I4 through the conduit 1, and is then stripped of its volatile constituents, leaving a residue comprising a reduced crude or a tar, which is drawn from the trap-out tray II through a conduit 2I and forced by means or a pump 22 through a cracking furnace 23, where it passes through tubes or other heating units (not shown) in which it is subjected to a cracking temperature, preferably under an elevated pressure.

The treated products from the cracking furnace 23 are discharged through a conduit 24 having a valve 25 into the section I5 of the evaporator 9 underlying the trap-out tray II, preferably at a point just below the bafiie plate I8. Here evaporation of the lighter constituents occurs, the evaporated materials passing off in vapor form, leaving a residue or tar which collects upon and is withdrawn from the trap-out tray I2 by means of a conduit 25.

The residual is delivered through the conduit 26 by means of a pump 21 to a second cracking furnace 28, where it is subjected to cracking conditions, and the cracked products pass through a conduit 29 having a valve 30 to the next section I6 of the evaporator 9. Here evaporation and separation of lighter constituents take place, and the residue or tar is withdrawn from the trap-out tray I3 through a conduit 32 and delivered by means of a pump 33 to a third cracking furnace 34.

In the furnace 34, the residue or tar from the trap-out tray I3 is subjected to cracking conditions, and the cracked products pass through a line 35 having a valve 36 to the bottom section ll of the evaporator 9.

The combined vapors from the several sections I4, I5, I6 and I1 of the evaporator 9 pass through a vapor line 40 to the lower part of the fractionating tower 5, the interior of which is provided with plates or trays H of conventional type. Under the influence of reflux condensate obtained by heat exchange with the oil passing through the coil 4, fractionation of the vapors.

takes place, heavier constituents of the vapors being condensed and collected in the bottom of the tower 5, from which they may be removedthrough a drawoff line 42 having a valve 43.

Uncondensed vapors reaching the top of the tower 5 pass through a vapor line 45 to a condenser 46, and the cooled products pass through a conduit 5I to a separator 52. The condensate,

comprising light distillate is withdrawn from the separator 52 through a condensate line 53 having a valve 54, while uncondensed gas passes off through a gas line 55 having a valve 56.

The composite stock withdrawn from the bottom of the tower 5 is preferably delivered through the conduit 42 by means of a pump 6| and a conduit 62 having a valve 63 to a cracking furnace 64, wherein it is subjected to cracking conditions, preferably of a more drastic character than those maintained in the furnaces 23, 28 and 34. The cracked products pass through a transfer line 05 having a valve 66 to the bottom section II of the evaporator 9. Vapors from the oil or tar from the trap-out tray cracked products from the furnace 64 pass upward through the evaporator 5, while the residual oil collects in the bottom of the evaporator 5 with the residue from the products from the furnace 34.

A portion of the charging stock withdrawn from the tower 5 may be withdrawn through a branch conduit 'II and delivered through valved inlets 12, I3, 14 and I5 to the baffle plates I8 located in the various sections of the evaporator 5. The number of sections thus supplied with reflux oil may be varied as desired. Fresh oil may be supplied as reflux to the baffle plates I8 in the sections I5 and I6 of the evaporator 5 through valved branch lines I6 and I1 communicating with the conduit 6.

Where, as in the preferred instance, the evaporator 5 is maintained under an elevated pressure of from 50 to 250 pounds per square inch, for example, 200 pounds per square inch, the tar collecting in the bottom of the evaporator 5 may be flashed under a lighter constituents. Thus, the tar from the bottom of the evaporator 5 may pass through a conduit 8| having a pressure-reducing valve 82 to a flash tower 83, maintained under a relatively low pressure of for example from atmospheric pressure to a pressure of 50 pounds per square inch.

In the flash tower 83, the tar from the evaporator 5 is flashed under a reduced pressure, as aforesaid, and the final residue or tar is removed through a draw-off line 84 having a valve 85. The liberated vapors, which leave the top of the flash tower 83 through a vapor line 86, may pass through a line 81 having a valve 68 to a condenser 89. The cooled products then pass through a conduit 9| to a separator 92, from which condensate may be withdrawn through a conduit 93 having a valve 94 and pumped to the tower 5, by a pump 96 having a valve 91.

As an alternative mode of procedure, the vapors from the flash tower 03 may pass through conduits 86 and I0 I, the latter having a valve I02, to a bubble tower I03, where they are fractionated. Uncondensed vapors then pass through a vapor line I04 to a condenser I05, and the cooled products are delivered through a pipe I06 to a separator I01 having a valved gas ofitake I08. Condensate leaves the separator I01 through a conduit I09 having a branch III provided with a valve H2 and a pump II3 for delivering a part of the condensate to while the remainder of the condensate is withdrawn through a branch conduit II4 having a valve I I5 for storage or further treatment, as desired.

Relatively heavy oil collecting in the bottom of the bubble tower I03 is withdrawn therefrom through a draw-off line I2I having a branch line I22 provided with a valve I23 and leading to stor age and a branch line I24 having a valve I25 leading to the conduit 42 on the intake side of the pump 6I. Thus, all or a portion of this oil may be delivered to the cracking furnace 64 or as reflux to the evaporator 9, together with oil from the tower 5.

While the temperatures and pressures employ-ed throughout the system will vary with the nature of the particular charging stock and the nature of the results desired, I ordinarily prefer to so regulate the conditions of temperature and pressure within the furnaces 23, 28 and 34 that cracking takes place to substantially the same lower pressure to removethe tower I03 as reflux,

ao'awscs extent. in each furnace; Thus, the. temperatures to which the oils are subje'ctedin the=furnaces:.23 2B and 34 may besuccessivelyincreased.. On v the other. hand, the .temperaturesimaintained in .these furnaces may be.substantially'identical, in which case-I prefer to employ relatively and successively increasing. times of. contact, and inany event, I prefer to maintainsuch conditions in these furnaces that only a mild cracking effect-is produced in each, preferably from 62 to 8. percent and not over l2percentin any: case crack per pass (i. e. percent of gasoline produced perpass).

Thus, in a particular instance in which the material supplied through the conduit l comprises a virgin gas. oil having a specific gravity of 34 A. P. I., the oil passing throughthe cracking furnace 23 may be brought to a temperature ofiabout 860 F., while the oil passing through the cracking furnace 28 may be brought to a somewhat higher temperature of for example about 870 F., and the oil passing through the crack-- ing furnace 34 may be brought to a still higher temperature of for example about 880 F. Or the temperatures maintained in the furnaces 23, 28 and 34 may be similar, for example about 860 F., the times of contact being preferably increased and in any event so regulated that a mild cracking effect is produced in each furnace.

In general, due to the fact that the material charged into each of the furnaces 23, 28 and 34 comprises principally a residual material, the cracking conditions which are maintained in the furnaces 23, 28 and 34 are of a mild nature, for example, within the range commonly employed for viscosity-breaking operations and effective to produce a limited amount of cracking without causing an undesirable coke formation.

On the other hand, the temperatures maintained in the furnace 64 are preferably considerably more drastic and may for example be of the order of from 950 to 1000 F., the operation thus taking place in the vapor phase and the cracking effect being considerably greater than that which takes place in the furnaces 23, 28 and 34.

In the instance cited, the pressures maintained in the various cracking furnaces are suitably elevated and may be of the order of 250 pounds per square inch, while the evaporator 9 is maintained under a slightly lower pressure of, for example, 200 pounds per square inch, as aforesaid.

While I have shown three mild cracking operations carried out in the furnaces 23, 28 and 34 respectively, I do not limit myself to any particular number of individual cracking operations, the actual number being governed by the nature of the material charged and the nature of the cracked products. In the specific instance mentioned hereinabove, however, the residual materials withdrawn from the trap-out trays l I, I2 and I3 may have specific gravities of 26, 20 and 12 respectively, while the tar withdrawn through the conduit 8| from the bottom section I! of the evaporator 9 may have a specific gravity of approximately 0 A. P. I.

It will be obvious to those skilled in the art that While I have described my invention hereinabove with reference to one or more specific illustrative examples and embodiments my invention is not limited to the specific details of such illustrative examples, but may variously be practiced and embodied within the scope of the claims hereinafter made.

I claim:

1. Apparatus for the treatment of hydrocarbon oil,=comprisin'gi a vertical evaporator tower having'ia. plurality of vertically displaced trap-out trays therein, means for introducing charging oil into anupper. level in said tower above a first one of said trap-out trays, means for removing liquid from said trap-out tray, raising it to a cracking temperature and introducing it into said tower below said first trap-out tray and above a second trap-out tray, means for removing liquid oil from said second trap-out tray, raising it to a. cracking, temperature and returningit to said tower. ata point below said second trap-out tray, and means for removing vapors from said tower at a point above said first trap-out tray.

2; The improvement in the process of pyrolytically decomposing hydrocarbon oil which comprises delivering heated oil to an evaporation zone in which vapors are free to pass upwardly while separate pools of oil are collected at vertically-spaced intervals in said zone out of the path of travel of said vapors, withdrawing oil collected from one of said pools, directly from said evaporating zone and passing it in a stream of restricted cross-sectional area through a first heating zone wherein it is raised to a cracking temperature and subjected to conversion, discharging the resultant stream of cracked products into said evaporation zone at a point below said one of said pools, whereby cracked residual liquids from said first heating zone are prevented from returning to said first heating zone, withdrawing oil from a. still lower one of said pools, passing it in a stream of restricted cross-sectional area through a second heating zone wherein it is raised to a cracking temperature and subjected to conversion, and discharging the resultant stream of cracked products into said evaporation zone below said lower one of said pools, whereby cracked residual liquids from said second heating zone are prevented from returning to said second heating zone.

3. The process of treating hydrocarbon oil which comprises discharging preheated relatively heavy oil into a first separating zone wherein vapors separate from liquid residue, removing said vapors and forming a desired distillate therefrom, removing liquid residue from said first separating zone at such a rate as to prevent the accumulation of a large body of liquid therein and passing liquid so removed directly through a cracking zone, in a stream of restricted cross-sectional area, wherein it is raised to a cracking temperature and subjected to conversion, introducing resulting hot products of conversion into a second separating zone wherein vapors separate from liquid residue, passing vapors from said second separating zone into said first separating zone, while excluding said vapors from said cracking zone, removing liquid residue from said second separating zone at such a rate as to prevent the accumulation of a large body of liquid therein, passing liquid sowithdrawn directly through a second cracking zone in a stream of restricted crosssectional area wherein it is raised to a cracking temperature and subjected to conversion, introducing resulting hot products of conversion into a third separating zone wherein vapors separate from liquid residue, passing vapors from said third separating zone into said second separating zone while excluding said vapors from said second cracking zone and removing liquid residue from said third separating zone.

4. The process of treating hydrocarbon oil which comprises discharging preheated relatively heavy oil into a first separating zone wherein vapors separate from liquid residue, removing said vapors and forming a desired distillate therefrom, removing liquid residue from said first separating zone and passing it through a cracking zone wherein it is raised to a cracking temperature and subjected to conversion, introducing resulting hot products of conversion into a second separating zone wherein vapors separate from liquid residue, passing vapors from said second separating zone into said first separating zone, while excluding said vapors from said cracking zone, removing liquid residue from said second separating zone, passing it through a second cracking zone, in a stream of restricted crosssectional area, wherein it is raised to a cracking temperature and subjected to conversion, introducing hot products of conversion into a third separating zone wherein vapors separate from liquid residue, passing vapors from said third separating zone into said second separating zone, while excluding said vapors from said second cracking zone, removing liquid residue from said third separating zone and introducing it into a flashing zone under reduced pressure to cause additional vaporization thereof, fractionating resulting vapors to form a clean condensate charging stock, passing said clean condensate charging stock through a third cracking zone wherein it is raised to a vapor phase cracking temperature and subjected to conversion, separating resulting hot products into vapors and a liquid residue in a fourth separating zone and passing vapors from said fourth separating zone into said third separating zone.

WRIGHT W. GARY.

Images