US 3133014 A
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Description (OCR text may contain errors)
May 12, 1964 w. J. cRoss, JR
QUENCH SYSTEM FOR SYNTHETIC cRuDE Filed Deo. 30, 1960 United States Patent Oli ice lgli Patented May l2, 1954 3,133,014 QUENCH SYSTEM FR SYNTHETIC CRUDE Willis 3. Cross, Jr., Media, Pa., assignor to Air Products and Chemicals, Inc., a corporation of Delaware Filed Dec. 30, 1960, Ser. No. 79,793 9 Claims. (Cl. 2128-348) The present invention relates to hydrocarbon conversion systems and is particularly concerned with improvements in fractionation of the viapor eliluent from a hydrocarbon conversion reactor, wherein said vapor effluent includes small amounts of high-boiling hydrocarbons. The invention finds particular application in products separation and recovery uni-ts used in connection with hydrocarbon conversion systems wherein a hydrocarbon charge is converted to products including lower boiling materialls by thermal or catalytic cracking, hydrocracking, coking, vis-breaking, or the like.
In a typical system, as exemplified by catalytic cracking of a gas oil charge, the reaction products discharged as vapor eiiiuent from `the cracking reactor are cooled by heat exchange and sent to a so-called synthe-tic crude fractionating tower in which these product-s :are separated into desired fractions. in conventional installations there are withdrawn from the synthetic crude tower (l) an overhead fraction composed of gasoline and lighter products including fixed gas, (2) a middle distillate cut above the igasoline boiling range, generally designated as light fuel distillate, a portion of which in some instances may be recycled to the cracking reactor; and (3) a bottoms fraction, generally comprising materials having a midboiling point a'bove 600 F. It has ibeen the practice in a number of installations to recycle a portion of the cooled bottoms fraction to the synthetic crude :tower as a quench liquid and it has been found convenient to introduce such quench liquid directly into the vapor transfer conduit bringing the reaction vapors from the cracking reactor to the synthetic crude fractionating tower. In doing so, high boiling liquid is frequently deposited along the wall of the vapor transfer conduit and eventually becomes transformed to solid carbonaceous deposit, which deposit in time builds up to proportions on the wall of the conduit causing restriction to vapor flow, Vwith adverse elfects on designed operating pressure of the system. In sorne instances premature shut-down of the installation has been found necessary Ito remove coke or replace as section of the vapor transfer conduit because of excessive coke accumulation therein.
In accordance with the present -invention there is provided `an improved arrangement for introduction o-f quench liquid into a vapor transfer conduit, whereby excessive coke build up in the line is avoided. The improved arrangement involves locating the point of introduction of the liquid hydrocarbon quench in the vapor transfer conduit at a predetermined distance from the terminal outlet of the vapor conduit (i.e., :from the junction of the vapor conduit with Ithe wall of the synthetic crude tower) such that the periphery of the cone of liquid ejected from the quench line does not Contact the inner wall ofthe vapor transfer conduit along -a substantial portion of the path of flow; yet a suiiicient long path of concurrent flow of the liquid and vapors is had to provide the desired direct heat exchange contact of the vapors with the cool quench liquid.
The detailed operation of the invention will be understood and the advantages of the novel arrangement appreciated from the description which follows read in connection with lthe accompanying drawings illustrating practical embodiments thereof.
ln the accompanying drawings:
FIGURE l is a schematic diagram showing a typical piping arrangement for introduction of fluid charge into the lower sect-ion of a synthetic crude tower;
FIGURE 2 is a fragmentary view in longitudinal section, partly schematic, of the lower section of the synthetic crude tower and vapor inlet thereto, illustrating the novel liquid introduction arrangement in accordance with one embodiment of the invention; and
FIGURE 3 is a airagmentary view of a modified embodiment.
Referring now to FIGURE l, there is shown a vapor transfer conduit 10 through which the vapor hydrocarbon product from a reactor is passed -to the inlet of the synthetic crude tower 11. These reaction products may be vapor reactor effluent Ifrom cnacking or other conversion ope-ration .and include normally liquid hydrocarbons boiling above 600 F. The synthetic crude tower may have any conventional arrangement of tnactionating trays 12 known to the art and includes the usual provisions for Withdrawing one or more intermediate distillate cuts, diagrammatically indicated at I, as well as provisions lfor removal of -a lower boiling fraction indicated at O. Undistilled liquid is collected at the bottom of tower 11 provid-ing a reservoir of liquid 14. Between the liquid level and the lovvermost tray in the tower there is provided a vapor space l5;r the outlet of vapor conduit 1G discharges into such vapor space.
In a typical `arrangement for handling the vapor effluent from a catalytic crashing reactor, the eiuent vapo-rs -from the reactor may be withdrawn generally at a temperature in the range of about 840 to 925 F. and are reduced in temperature, enroute to the synthetic crude tower, by about 200 to 350 F. For example, the temperature of the liquid reservoir le in the bottom of the synthetic crude tower may be in the order of 600e650 F., while the vapor temperature measured thereabove in space 15 may be up to about 50 lhotter :or cooler, for example in the range ofl about S50-700 F.
The highest boiling fraction B is withdrawn Ifrom the bottom of tower 11 by line 16. In some instances, provision may be made (not shown) for removal of fine catalyst powder (that may be present in the bottoms product. In systems employing liuidized cracking catalyst, the product B may be in 'the form of a sludge that is recycled, with included catalyst powder, to the catalytic reactor. From an intermediate level in liquid reservoir i4, another portion of the liquid is withdnaum by means of a line 17 and recycled to the vapor feed conduit iti, being cooled `enroute b-y suitable heat exchangers 18. The liquid circulated by line 17 serves, among other things, to maintain an adequate liquid reservoir i4 in the bottom of colurnn 11 and is particularly needed for that pur-pose when the content of high boiling materials in the charge is rather low. The cooled liquid introduced into conduit 1li also serves as a direct quench to cool the vapor in that line.
The point of introduction of the quench liquid into conduit l0 has heretofore often been selected primarily on the basis of pipe layout convenience, and diers among individual installations. In order to assure adequate mixing between the vapors and the liquid for heat exchange it has been the usual practice to select one or more points of introduction of the liquid into conduit 10 which are at a comparatively long distance up-stream of the discharge outlet of that conduit into vessel l1. No fixed rule has been followed with respect to the manner of intersection between line 17 and conduit l0. For example, the liquid quench line 17 has been connected into a long horizontal run of conduit 10, through a T coupling (i.e., normal to the conduit) or through a Y coupling providing an acute angle pointing downstream of the conduit. In other instances the smaller line 17 has been passed through the intersected wall into conduit and oriented in a direction to discharge the liquid concurrently along the axis of the stream of vapors. In other installations, line 17 is brought in at a convenient elbow in conduit 10 and arranged therein so that the direction of discharge is concurrent with the stream of vapors. As has already been indicated, the location of the juncture between line 17 and conduit 10 merely on the basis of piping convenience frequently results in detrimental coke deposit in the vapor conduit.
In practice of the present invention the location of the discharge outlet of the quench liquid from line 17 into the vapor conduit 10 is xed within predetermined limits and the liquid is discharged in a manner to assure good mixing with the vapors as these enter the column 11. One embodiment of the invention is illustrated in FIG- URE 2. This embodiment may be used in those installations in which conduit 10 has a comparatively long horizontal run up-stream of its discharge outlet. Line 17 is provided with a discharge nozzle 20 within conduit 1@ directed axially downstream at approximately the center of conduit 10. This conduit 10 is shown as connected to vessel 11 through a short flanged neck piece 19, so that the neck 19 constitutes a continuous extension of conduit tl. The discharge outlet 21 of the nozzle may be located at such distance from the terminus 2.2 of extended conduit 10 that the periphery of the cone of liquid 23 discharged from nozzle 20 does not intersect the wall of conduit 10 at any point 11p-stream of the flanged connection with neck 19. The periphery of the cone need not necessarily clear the circumference of the extended conduit at point 22, as illustrated. The periphery of the cone of liquid may contact the wall of conduit 10 within a short distance up-stream of neck 19, provided that the force of the liquid stream constantly directed against the internal wall of the conduit remains sucient to sweep along the wall and thereby prevent build up of coke thereon.
In the preferred embodiment of the invention, nozzle 20 is provided with a vaned portion 25 which serves to impart a whirling motion to the stream of liquid passing through the nozzle. This type of nozzle is described in detail in U.S. Patent No. 2,906,705 issued to the present inventor. It comprises a member having a plurality of internal inclined vanes or baies arranged to impart an axial rotation of the uid stream within the nozzle at a location terminating approximately l to 11/2 nozzle diameters from the discharge outlet of the nozzle. The vanes are fixed in the nozzle and are inclined at an angle of 20 to 70 to the central axis, preferably at about 45, and are uniformly spaced about the axis of the nozzle. This form of nozzle discharges the liquid in the form of a rotating peripheral layer having a hollow core. Other known types of liquid discharge nozzles may be ernployed.
Since the apex angle of the cone of liquid discharged from nozzle 20 will vary with the type of nozzle and to some extent with the linear discharge velocity, the variation in angle and magnitude of velocity must be taken into consideration in determining the location of the nozzle. In the usual systems in commercial use the linear discharge velocity of the liquid from the nozzle lies in the range of about l0 to 40 feet per second. For nozzles of the type illustrated, at this velocity range the included angle at the apex of the cone is about 54 i 1. At a 54 included angle the axial distance D' from the terminus 21 of the nozzle to the base of the cone at point 22 will be approximately twice the radius of the base of the cone at that location (cot 27=l.96l). As an example of a typical arrangement wherein conduit 10 has an internal diameter of 30 inches and the nozzle 20 has an internal diameter at its discharge outlet of 1/10 to the diameter of conduit 10, say 4 to 6 inches, the periphery of the cone of liquid will just about clear the wall of conduit 10 when the discharge outlet 21 is located generally at a distance D from the outlet 22 of conduit 10 which is approximately equal to the internal diameter (D) of conduit 1G. In practical operation, this exact location of the nozzle outlet may be varied within definite limits lying generally between about 2.5 to 0.8 times the internal diameter of conduit 10; so that in the illustrated case D may be 24 to 75 inches. At such indicated location of the discharge outlet 21 of the nozzle within conduit 10, substantial freedom from excessive coke build up is assured, while good mixing of the liquid quench with the vapor stream in conduit 10 is obtained. It should be noted that owing to the progressive constriction by the layer of vapors surrounding the cone of liquid, the periphery of the cone will be contracted inwardly toward its axis, distorting the conical pattern (See FIG- URE 3). For that reason the external periphery of the expanding stream of discharged liquid will usually clear the circumferential wall of neck portion 19 even in ceratin instances when the circumference at the base of the theoretical cone exceeds that of the neck portion. How ever, as already indicated a short parth of concurrent liquid ow along the wall is not detrimental.
In FIGURE 3 there is shown a slightly modilied nozzle arrangement that is preferred for installations in which conduit 10 has an elbow within a convenient horizontal distance from the wall of vessel 11.
Obviously many modilications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.
What is claimed is:
l. In the fractionation of a synthetic crude eiiiuent obtained from a hydrocarbon conversion reaction, wherein said eliiuent is fractionated by introducing the same at least partially in vapor state into a tractionating tower for separation into several cuts including (a) a gasoline-containing cut and (b) a bottoms product having a mid-boiling point above 600 F., and wherein a portion of said bottoms product is cooled and admixed in liquid state for direct heat exchange with the hot vapor eliluent directed to the iractionating tower; the improvement which comprises introducing said portion of cooled liquid bottoms axially into the vapor conduit carrying the flowing stream of said vapor eflluent at a location up-stream ot said fractionating tower, said liquid being introduced by discharging a circumferentially expanding cone of said liquid concurrently into said owing vapor stream, and said location being `so selected that the expanding cone of liquid does not Contact the inner wall of said conduit along a substantial portion of the path of ilow of said liquid toward said tower.
2. The method as defined in claim l wherein said liquid is discharged into said vapor transfer conduit at a linear velocity of l0 to 40 feet per second and said location is at a distance from the outlet of the vapor conduit approximately equal to the internal diameter of said conduit.
3. The method as defined in claim l wherein said location is at a distance from the outlet of the vapor conduit which is 0.8 to 2.5 times the internal diameter of said conduit.
4. The method as defined in claim l wherein said liquid is initially discharged in the form of a substantially conical stream expanding to the full diameter of said conduit at said outlet, and said location of the discharge is at a distance upstream from said outlet equal to twice the radius of base of the cone at said outlet.
5. The method according to claim 4 wherein said conical stream is in the form having a peripheral rotating liquid layer and a hollow core.
6. In combination with a fractionating column having a laterally extending uid inlet conduit: a liquid feed nozzle (A) within said conduit having a discharge outlet spaced from the intersection of the column with the conduit and arranged to discharge a circumferentially expanding cone of liquid in an axially downstream direction Within said conduit, means (B) for withdrawing liquid products from a reservoir thereof in the bottom of said column, additional and separate means (C) for withdrawing liquid product from said reservoir for recycling to said column, said latter means (C) supplying the liquid to said nozzle (A); heat exchange means for cooling the recycled liquid prior to its admission into said nozzle (A); the outlet of said nozzle being at a location Within said conduit approximately equal to 0.8-2.5 times the internal 1() 8. The combination as deiined in claim 6 wherein said nozzle is provided with a plurality of inclined Vanes arranged to impart axial rotation to the iluid stream passing through said nozzle.
9. The combination as defined in claim 6 wherein said nozzle, at its outlet, has an internal diameter of 1/5 to 1A@ the internal diameter of the surrounding conduit.
References Cited in the lile of this patent UNITED STATES PATENTS 1,853,552 Darlington Apr. 12, 1932 2,366,521 Guichet Jan. 29, 1945 2,906,765 Cross Sept. 29, 1959