US2205766A - Apparatus for cracking oil - Google Patents

Description

P. E. KUHL. w v

APPARATUS FOR CRACKING OIL Filed March 10, 1937 4 Sheets-Shet 1 72A CTIOMA- /NG 7 7'0 wfi Ace (/MULA TOR VENT LINE .SEPAEATIVGV P. E. KUHL. 2 26536 APPARATUS FOR CRACKING OIL Filed March 10, 1937 4 Sheets-Sheet 2 n In h In IHIHIUH HIHIIII .l I

QE@ 2,, l" P 5 KUHL,

APPARATUS FOR CRACKING OIL Filed March 10, 1937 4 Shets-Sheet 3 INTER (ZED NDE AhSER In $1M To WEIR P. E. KUHL, 22%,?

APPARATUS FOR CRACKING OIL Fil ed March 10, 1937 4 Sheets-Sheet 4 S PARA T032 .35 PA P A TOR Patented June 25, 1940 PATENT OFFI f? j",

APPARATUS FOR CRACKING OIL Paul E. Kuhl, Cranford, N. .L, assignor to Standard Oil Development Company, a corporation of Delaware Application March 10,

3 Claims.

This invention relates to an apparatus for use in cracking hydrocarbon oil and pertains more particularly to an apparatus for controlling the cleanliness of the cycle stock obtained during ,5 the cracking. treatment, and which is normally subjected to further cracking treatment in the same or different cracking unit.

In conventional cracking processes, it is a practice to separate the cracked products into vapors and residue and to fractionate the vapors so separated to condense insufliciently cracked constituents as reflux condensate. This reflux condensate is then subjected to further cracking treatment in the same or different cracking unit. In order to insure a maximum amount of cracking of this reflux condensate during its passage through the cracking unit, it is essential that it be relatively free of residual and coke-forming constituents, for it is generally known that the amount of conversion which may be effected during the passage of the oil through the cracking vapor separating zone has. been obtained from a number of sources. One practice has been to pass the vapors from the vapor separating zone through intercondensers positioned in the vapor line leading from the vapor separator to the fractionating equipment wherein the vapors are caused to undergo partial condensation and sufficient condensate so formed is returned to the vapor separating zone to obtain the desired refluxing. According to this practice the separa tion of the dirty residual coke-forming constituents from the vapors is eifected partly in the top of the vaporizing zone and partly in the intercondensers. In order to provide the required amount of reflux medium under all conditions of operation and in addition, to provide means for accurately controlling the cleanliness of the reflux condensate and to recover the maximum amount of heat by exchange with feed the intercondensers are designed to produce more condensate than that necessary for refluxing the 1937, Serial No. 130,081

top of the vapor separator under any one given set of conditions.

While the amount of condensate formed in the intercondensers may be regulated by controlling the amount of cooling in the intercondensers, this method is too indirect to effect rapid and accurate control of the amount of refluxing so as to accurately regulate the cleanliness and color of. the condensate in the fractionating equipment and limits the amount of heat recovered.

A common practice in this type of cracking equipment is to combine the excess condensate over and above that required to effect the desired refluxing in the vapor separating zone with the cycle condensate formed in the fractionating equipment and to subject it to further cracking treatment therewith. Since, as already pointed out, separation of heavy residual and coke-forming constituents from the vapors is partly efiected in the intercondensers, it will be apparent that if aliquot portions of the total condensate from the intercondensers are returned to the vapor separator and the remaining condensate combined with the cycle condensate from the fractionating equipment, the condensate Will be contaminated with dirty constituents which degrade the cycle stock,

To avoid this, insofar as possible, it has been proposed to separately withdraw condensate formed in the separate passes of the intercondensers and return the dirtier condensate from the first passes to the vapor separator and the relatively cleaner condensate from the final passes of the intercondensers to the fractionating equipment to be combined with the cycle stock formed therein.

In some instances, for example, a flxed amount of condensate from the initial passes of the intercondensers, sufficient to meet the minimum reflux requirements for the vapor separator, is returned thereto and any additional condensate necessary to efiect the desired cooling is obtained by returning aliquot portions of the condensate from the final passes of the intercondensers. While this mode of operation oifers some advantages over returning aliquot portions of the total condensate, it is open to the objection that the aliquot portion of the condensate returned to the vapor separating zone as a reflux medium is of the same composition as that combined with the reflux condensate from the fractionating equipment, whereas under the most ideal conditions the fraction combined with the reflux condensate should always be relatively cleaner than the condensate returned to the vapor separator.

It has also been proposed to provide sufficient valves and manifolding so that any one or more of the several condensates withdrawn from the separate passes of the intercondenser can be selectively passed either to the vapor separating zone or combined with the reflux condensate from the fractionating equipment. While this makes it possible to combine the cleanest condensate with the reflux condensate formed in the fractionating equipment and return the dirtiest fraction to the vapor separating zone, it'is' open to the objection that it increases the burden on the operator to properly regulate the numerous manifold valves required, and it also materially increases the cost of equipment due to the relatively high cost of the regulating valves so required.

In many cracking processes, particularly multicoil processes, it is frequently desirable to withdraw a heavy gas oil stream from the cracking unit for other process operations. For example, in two-circuit cracking processes, wherein one circuit operates on a heavy dirty stock under relatively mild cracking conditions and the other circuit processes a relatively cleaner stock under more drastic cracking conditions, in order to properly balance the unit so that both circuits operate at capacity, it is sometimes necessary to supply make-up oil to one or the other circuit. While such make-up oil can be obtained from an extraneous source, it often happens that such source is not available. In other cracking processes it is often desirable to inject a heavy oil into the furnace outlet or in the final passes of the heating coil in order to reduce the transfer line temperature and attain additional cracking of the heavy oil by the heat of the cracked products at the furnace outlet. My invention is particularly directed to such cracking processes.

One of the objects of my invention is to overcome the objections of the apparatus heretofore employed and provide a more simple and improved apparatus which will separately collect and selectively distribute condensate fractions removed from the separate passes of the intercondenser so that under all conditions of operation there will be produced a clean condensate fraction suitable for high temperature cracking, a heavy condensate containing some coke-forming constituents but suitable for mild cracking treatment and a dirty condensate containing the bulk of the coke-forming constituents which may be returned to the vapor separator as refluxing medium.

Another object of my invention is to provide an improved multi-coil cracking process and apparatus, wherein the charge of the separate coils may be properly proportioned under variable operating conditions to produce a maximum yield of gasoline.

Other and more specific objects of my invention will be apparent from the more detailed description hereinafter, in which reference will be made to the accompanying drawings.

In the drawings:

Fig. l is a diagrammatic flow diagram of a two coil oil cracking unit having my invention connected therewith;

Fig. 2 is an enlarged detailed sectional view showing the construction of the intercondensers;

Fig. 3 is an enlarged detailed view of the intercondensers and runback system.

Fig. 4 is a View of a second modification; and Fig. 5 is a view of a third modification.

Referring to Fig. 1, the line it designates a charging line through which the oil to be cracked is introduced to the system. The charging oil is preferably a relatively heavy oil such as crude, reduced crude or heavy gas oil containing residual constituents. The line It is provided with a pump H which forces the oil to the second of two condensers I2 and I3, located in the vapor line It, connecting the vapor separating zone E5 with the fractionating tower l6.

As shown in Fig. 2, the fresh charging oil passes into a lower header 1'! separated from the main body of the intercondenser [3 by means of a partition 8. The lower header ll communicates with an upper header 59 by means of tubes 26. The lower header ii is divided into a plurality of vertical compartments by means of partition walls 2| and 22, and the upper header is divided into a plurality of compartments by means of partition wall so that the fresh charging oil is caused to pass alternately upwardly and downwardly through the intercondenser in indirect 'countercurrent heat exchange relation with the cracked vapors passing therethrough as hereinafter described.

The fresh charging oil after passing through the secondof the two intercondensers it emerges therefrom and is forced through the first of the two intercondensers, wherein it passes in fur ther. heat exchange relation with the vapors from. the vapor separating zone l5. This inter- .condenser i2 is of the same construction as the interconclenser l3.

The fresh oil after passing through the first of the two intercondensers emerges therefrom through line M which connects with a heating coil 25. A by-pass line 26 around theintercondensers i2 and I3 is provided so that any desired amount of fresh oil may icy-pass the intercondensers and thus control the amount of cooling of the vapor therein.

The oil during .its passage through the heating coil 25 is heated to a cracking temperature maintained at cracking temperature for a period sufiicient to effect the desired cracking thereof. This crackingmay be in. the nature of a viscosity breaking treatment, the objective of which is to produce a relatively high yield of clean. condensate amenable to high temperature cracking treatment which will result in a maximum yield of high anti-knock gasoline.

The cracked. products then pass through transfer line 27 having a pressure control valve 2'1" to the-vapor separating zone 55, wherein vapors separate from residue. Residue separated in the vapor separating zone i5 is withdrawn therefrom through line 23 and passed to storage receptacles (not shown) or subjected to further flash distilling-treatment to vaporize additional constituents.

While I have shown a simple coil cracking unit, it will be understood that in lieu of carrying the desired amount of cracking to completion within the heating coil 25, the products from-the heating coil may pass to a conventional soaking drum or reaction chamber wherein further cracking is attained.

The upper end of the vapor separating chamber 55 may be provided with suitable baffles, such as disc and doughnut baffles to aid in knocking back residual constituents entrained in the vapors. Vaporsseparated in'the vapor separating chamber i5 pass overhead through line I4 to the main body ofintercondenser I2.

As shown in Fig. 2, the main body of the intercondenser is provided with vertical baflles 29, separating .the intercondenser into .a plurality of cooling zones through. which thevapors pass alternately upward .and downward in indirect countercurrent heat exchange contact with the fresh oil in the tubes 20. l

, The vaporsduring their passage through the intercondenser are subjected to progressive cooling by the fresh oil an'dlhigher boiling constituents thereof are condensed. I

The condensate formed in the separate passes of the intercondenser is separately withdrawn through outlet ports'3l, 32-, 33 and 34, connecting with downwardly extending pipes 35--38, respectively, whichconnect with a common manifold line 39. It will be understood that the first condensate formed in the initial pass of the intercondenser will be the heaviest dirtiest condensate and the condensate formed in the succeeding passes will become progressively lighter and cleaner.

The vapors after passing through the first intercondenser I2 and undergoing partial condensation therein continue through vapor line I4 to intercondenser I3, wherein they are subjectedto further partial condensation. As already described, the second intercondenser I3 is of the same construction as intercondenser I2. The condensates formed in the separate passes of the second intercondenser I3 are withdrawn through lines 42, 43 and 44, which connect with the main manifold line 39.

The vapors after passing through the second intercondenser continue through line I4 to the fractionating tower I6 wherein they are subjected to fractionation to condense insufficiently cracked constituents as reflux condensate. Vapors remaininguncondensed in the fractionating tower I6 pass overhead through line 45toa condenser 46 wherein the desired distillate is condensed. Products from the condenser 46 then pass to a distillate receiver ll, wherein fixed gases separate from the distillate. The desired distillate is withdrawn fromthe receiver 4'! through line 48 and thefixed gases pass overhead through line 49 provided with a-valve 59 which may be used for maintaining the desired pressure on the separating and fractionatingequipment. A part of the distillate may be recycled to the top of. the fractionating tower through line 5i as a reflux medium. l

Coming now'to the intercondenser runback apparatus, as shown in Figs. 1 and 2, one end of the manifold line 39 receiving the condensate withdrawn from theseveralpasses of the intercondensers, connects with line 52 having throttle valve 53.

Condensate from manifold 39 withdrawn through line 52 may pass through line 54 to fractionating tower H3 or be passed through line 55 to an accumulating tank 56 where'it combines with clean condensate stock formed in the fractionating tower It or with other clean stock'from an extraneous source introduced into the accumulator through line 5% The opposite end of the-manifold line 39 communicates through line 58 with the vapor separator I5. Line 58 is provided with a branch 59 to permit thewithcl'rawal of any desired part or all of condensate passing through line 58. A third line 63 having a control valve BI connects with the mid-section of the manifold 39.

As already pointed out, in the objects of my invention I provide a simple runback system for the condensate formed in the intercondensers,

which makes possible the separation of the total condensate collected in manifold line 39 into a clean fraction suitable for high temperature cracking, which is withdrawn through line 52, a relatively heavier and dirtier intermediate fraction suitable for more mild cracking which is withdrawn through line 60 and a heavy dirty the manifold 39 and may be further treated as hereinafter described.

Referring particularly to the modification shown in Figs. 1 and 2, the pipe line 58 connecting'the end of the manifold 39 with the vapor separator I5 is provided with an upwardly extending inverted U-bend, having the apex communicating with a vent line 62. Vent line I32 connects with the vapor line I4 beyond the second intercondenser I3.

Another vent line 63 connects the opposite end of the manifold 39 with the vapor line I l beyond the second intercondenser I3 and preferably at substantially the same point as vent line 62 so that the top ofthe inverted U-bend and the opposite end of the manifold are maintained under substantially the same back pressure. The height of the top of the inverted U-bend above the manifolddetermines the level of liquid in the manifold-and intercondenser legs. This height should be such that the hydrostatic pressure of the condensate in the leg of the U-bend connected to the manifold is sufficient to maintain a level of condensate in each of the legs leading from the intercondensers to the manifold and thus prevent Vapors from the intercondensers from entering the manifold and agitating the condensate col- -lected therein.

The level of liquid condensate in the individual "45 legs 35, 36, 31 and 38 for the first intercondenser, and ll, 42, 43 and 44 for the second intercondenser; will vary with the vapor pressure above the liquid, so that the level of liquid in the individual legs will be progressively higher from left to right as shown in Figs. 2 and 3, due to the drop in pressure of the vapors during their passage through the intercondensers. The height of the inverted U-bend above the manifold should be sufiicient therefore to provide a liquid seal be tween the first leg 35 and the manifold.

Since the top of the U-bend is under substantially the same pressure as the vapors issuing from the intercondensers, condensate in the final leg 44 of the intercondenser I3 will be at substantially the same level as the top of the inverted U-bend. The top of the inverted U should therefore be below the vapor outlet line I4 of the second intercondenser in order to prevent con- I densate from overflowing into the vapor line and preferably below the condensate outlet ports of the intercondensers to prevent the condensate from rising into the body of the intercondensers.

It will be understood that in order to function as above described, the back pressure on the liquid condensate discharging over the inverted 3 U -bend in line 58 should not exceed the exit pressure of vapors passing through the line Id at the point of merger of vent line 62 therewith. When discharging this condensate into the vapor separator I5 as shown, without employing a pump separator i5.

in the line, the distance from the point of entry of condensate to the top of the inverted U-bend should be suiiicient to provide a hydrostatic pressure in the column of liquid in the leg of the inverted U-bend adjacent the separator at least equal to the .drop in pressure between the separator at the point of. entry of the condensate therein, and the vapor line H! at the point of merger of vent line 62. The manifold should therefore be positioned above the point of entry of the condensate into the separator at a height suflicient to overcome the pressure drop between the separator at the point of entry of the condensate, and the pressure of the vapors in the initial pass of the first intercondenser !2.

In lieu of employing hydrostatic pressure of condensate in the vertical leg of the inverted U- bend to force the condensate into the vaporizer a pump maybe used in line 58. However, it is preferred to use hydrostatic pressure wherever possible to reduce pumping costs.

The vent lines 62 and 63 in addition to equalizing pressure at opposite ends of the manifold,

permit vapors formed in the manifold, by commingling relatively colder condensate formed in the latter passes of intercondensers with the relatively hotter condensate formed in the earlier passes of the intercondensers, to rapidly separate from the condensate. It has been found, for example, that unless vent lines of this character are provided having sufficient capacity to rapidly separate the vapors formed in the manifold 39, there is a constant surging of condensate back and forth longitudinally of the manifold 39, which prevents effective separation of the light, intermediate and heavy condensate within the manifold.

The line 53 connecting the manifold 39 with the vapor separator 15 has a downwardly extending U-shaped section forming a liquid seal between the vapor separator and vent line 62.

. The construction above described permits control, by means of control valve 53, of the amount andcharacter of condensate collected in manifold line 39 which passes'through line 52 to be combined with clean condensate stock for further cracking treatment, the control by means of valve 85 of the amount and character of intermediate condensate'withdrawn through line 60, and the automatic diversion of the remaining heaviest and dirtiest condensate through line 58 to the the In many cases it is desirable to control amount ofreflux returned to the vapor separator i5 and to divert the rest either through line 60 or e2. This may be accomplished by the modification shown in Figure 4.

. Referring to Figure 4, the line 52 is provided with an inverted U-bend and a control valve 58' is positioned in the line 58 leading to the separator it. By properly regulating the valve 58' and valve ti any desired amount of the heaviest and intermediate fractions of the condensate from. manifold 39 may be withdrawn through lines 53 and 69 respectively, and the remaining lightest and cleanest fraction is automatically diverted through line 52 to the fractionating tower it or accumulator 5%.

In other cases, it is sometimes desirable to control the amonut of condensate from the manifold passing to the separator l5 and also control the amount and character of condensate passing through line 52. This may beaccomplished according to the modification shown inFigure 5. In this modification the line 60 connected with the mid-section .of the manifold 39 is provided with an inverted'U-Lbend and lines 52 and 58 are provided with control valves .53 and 58' whereby regulatable quantities of the dirtiest and the cleanest fractions may be withdrawn from opposite ends of the manifold and remaining intermediate condensate automatically withdrawn through line 60.

In this case, in addition to the two vent lines 62 and 63 leading from opposite ends of the manifold to the vapor line [4, a third vent line :69 from the top of the inverted 'U-bend in line 60 is provided. Additional vent lines may also be provided in the other modification if desired.

Referring again to Figure 1, reflux condensate condensed in fractionating tower l 6 is withdrawn through line 64 and passed to the accumulator tank 56, Liquid collected in accumulator 56 is withdrawn therefrom through line 65 and forced by pump 68 through a second heating coil 87 located in furnace 68. This condensate charge during its passage through the heating coil is heated to a relatively high cracking temperature and maintained at such temperature, either in the coil or in an associated reaction chamber (not shown) for a period sufiicient to effect maximum conversion into high anti-knock gasoline while avoiding troublesome coke deposits in the cracking zone.

The cracked products after undergoing the desired conversion pass through transfer line 69 to the vapor separator I5 where they combine with products from the heating coil 25 and are subjected to separation and fractionation therewith as hereinbefore described.

Referring again to Fig. 1 the intermediate condensate withdrawn from. manifold 39 through line fill discharges into an accumulator tank 10 from which it may be withdrawn for purposes hereinafter described.

This condensate, while unsuitable for cracking under the high temperature conditions maintained in coil 61 may be subjected to cracking under lower temperature conditions. This cracking may be accomplished by passing this fraction to the low temperature cracking coil 25 through lines H, 12, 13, pump '14, lines 15 and 76, or it may be introduced through line 17 to the transfer line 21 wherein it is subjected to additional cracking with the cracked products from the coil. As a further alternative, a part or all of this fraction may be introduced through line 18 into the transfer line 69 conveying cracked products from the high temperature cracking coil 61 to the vapor separator I5.

If desired, a part of this condensate may be introduced through line 19 and pump to the bottom of theseparator Hi to quench the products therein to a temperature below active cracking so as to avoid troublesome coke deposits in the tar outlet 28 and to control viscosity of the tar so removed.

While I have shown two separate interconcondensers l2 and I3, it will be understood that my invention is not limited thereto. A single intercondenser of desired capacity or three or more intercondensers may be substituted therefor.

Other cooling agents may be used instead of using charging oil as a cooling medium for the intercondensers l2 and I3.

Having described the preferred embodiment, it is understood that my invention is not limited thereto but includes such other variations and modifications as come within the spirit and scope thereof,

I claim:

1. In an oil cracking apparatus, a vapor separator for separating cracked products into vapors and residue, a fractionating tower for condensing insufficiently cracked constituents of the vapors, a vapor conduit connecting said vapor separator with said fractionating tower, intercondensers for fractionally separating the highest boiling constituents of the vapors passing through said vapor conduit into a plurality of fractions of different boiling points, a manifold conduit, means for in troducing said higher boiling fractions into said manifold at spaced points longitudinally thereof in the order of their boiling ranges, whereby the lightest fraction of said higher boiling condensates is introduced into said manifold adjacent one end thereof and the heaviest fraction is in troduced adjacent the opposite end thereof, a pipe connecting the end of said manifold receiving the lightest fraction of said condensates with the fractionating tower, a second pipe connecting at the opposite end of said manifold with said vapor separator, a throttle valve positioned in the first named pipe connections for regulating the amount of condensate passed therethrough, vent pipes communicating with the ends of the manifold and with the vapor conduit for maintaining a substantially uniform back pressure on the condensates within said manifold and a third pipe connection communicating with said manifold conduit at a medial point for withdrawing an intermediate condensate fraction therefrom. 2. In an oil cracking apparatus a vapor separator for separating cracked products into vapors and residue, a fractionating tower adapted to fractionally condense insufiiciently cracked constituents of the vapors as reflux condensate,

a vapor conduit connecting said vapor separator with said fractionating tower, means for fractionally separating the highest boiling constituents of vapors from said vapor separator into a plurality of separate condensate fractions of different boilingranges, a manifold conduit for receiving said condensate fractions, means for introducing the separate condensate fractions into said common manifold at spaced points longitudinally thereof in the order of their boiling ranges, pipes connected to each end of said manifold for withdrawing condensate therefrom, a

throttle valve in one of said pipes for regulating the amount of condensate passing therethrough, vent pipes communicating with the ends of the manifold and with that portion of the vapor conduit connecting the intercondensers and the fractionating tower for maintaining a substantially uniform back pressure on the condensate within said manifold and athird pipe connected with said manifold at a medial point therein to remove an intermediate condensate therefrom;

'8. In an oil cracking apparatus, a vapor separator for separating cracked products into vapors and residue, a fractionating tower for fractionally condensing insufficiently cracked constituents of said vapors as reflux condensate, a vapor conduit connecting said vapor separator with said fractionating tower, an intercondenser positioned in said vapor conduit adapted to fractionally condensing a high boiling fraction of said vapors, means separating said intercondenser into a plurality of cooling zones of progressively lower temperatures, means for separately removing condensate formed in each of said cooling zones, a horizontal manifold conduit adapted to receive the separate condensates withdrawn from said cooling zones at spaced points longitudinally thereof in the order of the relative boiling ranges of said condensate, pipe line connecting the end of said-manifold receiving the lightest condensate with said fractionating tower, a second pipe line connecting the other end of said manifold with said vapor separator, a throttle valve positioned in said first mentioned pipe line for controlling the amount of condensate passing to said fractionating tower, an inverted U-shaped section formed in said second-named pipe line adapted to form a liquid seal so as to maintain said manifold completely filled with condensate, a vent pipe connecting the U-shaped section with that portion of the Vapor conduit connecting the intercondensers and the fractionating tower and a second vent pipe connecting the end of the mani-.

fold receiving the lowest boiling condensate with said section of the vapor conduit connecting the intercondensers and the fractionating tower to prevent turbulence of condensate contained therein and means for removing condensate from an intermediate point in said manifold.

PAUL E. KUHL.

Images