US1918670A - Apparatus for treating hydrocarbon vapors - Google Patents

Description

w. F. SIMS ET AL 1,918,670

APPARATUS vFOR TREATING HYDROCAREON VAPORS Filed Nov. 23, 1929 2 sheets-sheet 1 July 18, 1933.

2 Sheets-Sheet 2 06000 OOOO C0000 .COOOO W. F. SIMS ET AL Filed Nov. 23, 1929 ooood oooooo ooooo WBC @wm wb APPARATUS FOR TREATING HYDROCARBON- VAPORS July 18, 1933.

7AM W. 6240' c'lccoww Patented July 18, 1933i UNITED y STATES PATENT OFFICE WILLIS r. sins AND VENUS U. cLonn, or WICHITA rALLsQTEXAs, AssIGNoRs To rANHANnLn REFINING COMPANY, or wrcHrrA FALLS, sEXAs, A CORPORATION or L have method of cracking under vacuum and a 'rnXAs APPARATUS non TREATING HYnnoeARBoN vArons Application filed November 23V, 1929. .Serial No. 409,407.

. fuel from petroleum by the process conimonly known cracking. The present a pplication is a continuation iu part of our prior cmjiendiug application filed February 16, 1928, Serial No.72541,753, in which we described and claimed an improi'fed complete, plant for inacticing the ne. In the present case we shall describe tue same general system., together with improved pri ,y mary and cracking stills combined in one structural unit, as wel] as ('-erlain specilic features and methods of operation of thek plant as a while.

Very briefly stated, the invention we pre- Q sent has for its basis the discoveryou our part that by cracking, fractionating, and

cooling under a vacuum, in whole or in part, we can increase the yield of a product containing unsaturated connpounds and aromatics which eminently suitable for motor fuel; and that by suitably regulating the temperature-s 'and pressures (sub-atmospheric) in different parts of the system, we can not only yatly ecouomize heat and thereby econonnze fuel, but we can also pro duce a product containing practically 100% of the desired unsaturated and aromatic compounds. y

(')ur amiaratus. as it will be described, coinprises a inieheating still for the charging stock, a cracking still, preferably preceded by a flashpot into which the oil from the preeae is e: ai er 'i o iz. ai a r h t r \pi id l irt i ipois, rind f1 su( cession of iinerrelated fractionating towers or dephlegniators with one or more vacuum pumps, heat exch anger, cooler and separator, and an absorption tower, all arranged as will be described in detail hereinafter. In addition to the regulation of pressures in each element of the systfiim, from the preheater to the separator and absorber, we have found it possible to arrange a graduated heat transfer by means of which make-up oil, or re-V` 'hixed fractions to be crackeiil, take up practically all the heat energy in the cracked vapors. in a counter cin'rentY progressioii through the fractionators. The makesup oil and refluxed fractions instead of going direct lo the cracking still. have their tempera ture i f ed so that they can be converted into vapors 1n the flashpot, from which the vapors pass, together with those from the primary heater, to the cracking still. y

By maintaining a vacuum or a sub-atmospheric pressure in the cracking zone (and preferably in the flashpot and frac-tionators), cracking commences at a lower temperature, while the raising of the absolute temperature, together with the turbulent and rapid motion ofthe vapors through the cracking tubes due to the pull of the vacuum, causes a considerable increase in the amount of heat energy taken up per square foot of surface, with a co'rrespomling increase in the amount of cracked products.` Vithout limiting ourselvesV to one specific sot of pressures, we have found in actual practice that suitable pressu res for our system and our method are from l5 to GO pounds on the primary heating still', from 12 to la pounds absolute pressure on the flashpot, and from 6 to 14 pounds abso lute (or a higher vacuum) on our cracking zone, fractionating towers, cooler and sepa rater. It is 'to be understood that the word vacuum as used in this specification means therefore any pressure below that Iof the` atmosphere7 but the actual pressures employed will be stated in pounds absolute.

A particular feature which we shall claim herein is the arrangement of' the absorption tower and its relationto the fractionators whereby the gasoline which is carried olf entrained with the fixed gases from the sepa# rator can be stripped olf, and returned to the last fractionator from which it will go over to the cooler and bereturned to the separator for storage. For this purpose the fixed gases are either pumped or conductedl under their own pressure to a point near the bottom of theabsorption tower, while light gas oil, from the bottom of the Vfractionator tower, wither without an intake of make-up Voil which is preferably also light gas oil, is introduced into the upper part of the absorp`V tion tower, which tower contains means for lili) in the fractionators to be flashed and recracked without going through the primary heater. In addition to this direct effect upon the gas oil, it is also used to cool thegvapors in the fractionator into which it is pumped. An important feature of this operation is the heat exchanger between the last fractionator and the absorption tower. The oil drawn from the bottom ofthe absorption tower, eX- cept for its use as stripper' as aforesaid, is to be directly refluxed as stated. The oil drawn from the absorption tower, which carries with it the gasoline strippedeff therein, is returned to the upper part of the fractionators after passing through the heat eX- changer and receiving therein heat from the oncoming oil from the fractionator. In these respects the system is cyclic in its operation, as will further appear from the detailed description hereinafter. It conserves both gasoline vapors and heat, and permits only Waste gases to be finally discarded.

The details of construction will sufliciently appear from the description hereinafter.

Our invention is illustrated in the accompanying drawings, in which Fig. 1 is a diagrammatic side elevation With parts in section showing the general arrangement of our apparatus.

Fig. 2 is a vertical transverse section of the preheater and cracking still taken on the line 2-2 of Fig. 3. y

Fig. 3 is a horizontal longitudinal section of the same, taken on the line 3 3 of Fig. 2.

Referring first to Fig. l, l designates a lashpot receiving the heated oil through valve 23 and pipe 52 from the pipe still in the furnace 2a. Charging stock is forced into said pipe still through the pipe 53 by pump 54. The oil may enter the fiashpot as vapors already formed, or it may be superheated oil transformed to vapor in this pot by release from pressure. The vapors from this flashpot passing through pipe 55 to the cracking tubes 56 in the furnace 2, will be at or above the equilibrium boiling point of the oils from which they are produced. This equilibrium boiling point is referred to the temperature of the vapors under such pressures as that carried onour flashpot. This is a vapor temperature and not an oil temperature. The oil before entering the Hashpot 1 must be at temperature some what above this vapor temperature in order to contain enough heat to take care of the latent heat of vaporization on entering the lashpot.

The preheating is accomplished in an improved still, one form of which is shown in Fig. 1 and another form in Figs. 2 and 3. In Fig. l, the pipe still 57 is located inthe furnace chamber 2a supplied with top and bottom flue openings 58-59 into the stack 60, each opening provided with a damper as shown, so that the draft through thev pipe 57 may be regulated. The furnace chamber 2a is provided with burners 6l, presently to be described, and the entire structure is connected to the structure of the furnace 2 contain-ing the cracking tubes 56, and main burner 62. rIhe. two chambers 2 and 2a are connected by means of openings 63 so that the heated gases of combustion from burners 62, after passing through and around the cracking tubes 56, will be drawn through the passages 63 and then enter the stack 60 through either the lower or upper opening 59 or58, according to the adjustment of the dampers. lVith the upper draft 58 open, all the waste heat from the cracking furnace 2 passes through and around the preheating tubes 57, and the oil therein is thus raised to a temperature suitable for flashing and introduction as vapors into the cracking tubes 56.

The burners 61 placed under the primary heating tubes are used in bringing the plant on stream at the beginning of a run. By using these burners 6l w'e do not have to fire the cracking tubes 56 (by means of burners 62) so heavily as would otherwise be the case and the temperature of the oil in the primary tubes is quickly raised to such a point that vapor is formed when released to the iiashpot l. After the plant is once on stream and the maximum fire is placed under the cracking tubes 56 by burners 62, the burners 6l may be turned down very low or completely cut out and the temperature of the oil iiowing in the primary heater may thereafter be regulated by the proper use of the dampers as already stated.

Referring to Figs. 2 and 3, the enclosure 2a is built on the side of the main furnace 2, and they are connected by an arched roof 2z. The cracking tubes 56 and the preheating tubes 57 are disposed horizontally and parallel to each. other in the two chambers 2 and 2a, with their bends lying outside the end fire walls of the respective chambers, and enclosed with thin metal plates 65-66-67- 68. The furnace 2 is lengthened out at both ends as shown in 2a' and 2y, these two ends being arched as indicated in dotted lines 21o in Fig. 2, and constituting Dutch ovens projectingl into which are the burners 62. Burners 6l project into the furnace 2a be` neath the preheating tubes 57 and all the burners are fitted with valves. The heated gases and products of combustion from the burners 62 are received in the Dutch ovens Qafand 2y, and conveyed through the arches 21o into the central chamber 2, passing upwardly therein through and around the cracking tubes 56 and thence being deected by the arch 2z through the passageway 68a into the chamber 2a. If the burners 6l. are in operation at the same time, for purposes of bringing the plant on stream, then the damper in the upper flue 59 should be open and that in the lower flue 58 should be closed. After the plant is on stream. as already stated, and the maximum fire is placed under the cracking tubes 56, then burners 61 may be turned down very low or completely cut out, and by regulating the dampers in fiue passages 58 59, more or less of the heated gases coming through the passageway 63a may be deflected downwardly through and around the preheating tubes 57, and into the stack through the lower flue passage 58.

The vapors from flashpot 1 are drawn through the cracking tubes 56 preferably at a temperature from 1000o F. to 1200o F., and as already stated a pressure of 6 to 14 pounds absolute is maintained on the cracking tubes by vacuum pump 14. Thislow pressure on the vapors causes the temperature atwhich the cracking reaction takes place to be lowered. It also causes the velocity of the vapors, considering a constant gallonage of raw oil charged, to be higher than in a system operated at or above atmospheric pressure, and this vapor velocity gives a. more turbulent flow of the vapors in the tubes causing a greater heat transfer per square foot of heating surface. The vacuum pump 14 is located in such a position, with suitable connections, througli lines 30, 39, 40 and 42, and valves 3, el, 5, 19, `416, 20, 21 and 25, that the vacuum may be appliedat the discharge from theV tubes in the heating zone 2 pumping the va-l pors from said tubes to cooling and separation tower 6 or the vacuum may be applied on the separator drum 10 and the vapors removed therefrom discharged into absorption tower 11.

The vapors entering the cooling and separation tower 6 may be at or `below atmospheric pressure, depending on the point at which the vacuum is applied to the system, and will be at an elevated temperature, preferably from 1.000O F. to 1200o F., depending on the temperature found most suitable to give the largest practical yield of gasoline or related light oils. Because of this elevated temperature of these vapors they contain considerable quantities of heat that must be removed before the products of the reaction producedfin the tubes can be condensed and made stable under atmospheric conditions. This heat is removed in two ways: (1) by causing the hot vapors to come in Contact with a downward iiow of liquid oil, drawn from the bottom of cooling and separation tower 7 by pump 13, and discharged through valve 18 to tower 6, preferably contacted with the hot vapors over a series of baile plates placed in this tower; and (2) by caus-.

ing the vapors to come in contact with cooling coils 26, 26', 26 and 26 placed in this tower, through which oil of relatively lower temperature than the vapors is caused to flow by pump 15. This causes the heat to be utilized (1) by vaporizing the incoming oil from tower 7, and (2) by the absorption of the heat by the cooler oil flowing in the cooling coils. This cooling effect will cause a heavy residue to collect in the bottom of the cooling and separation tower 6 which is re- Y I in this tower is carried to such a pointthat a large portion of the vapors entering it are caused to condense to liquid. This liquid is drawn from tower 7 by pump 13 which discli-.arges a part of it into tower 6 at 18 and a part through the coils 26, 26, 26 and 26". Valves 18 and 47 are so located on the discharge line from pump 13 that all or any part of the liquid from the bottom of the cooling and separating tower 7 may be caused to discharge into either the tower 6 or the ons 26, eef, 2e, 26.

The vapors from the tower 7 enter another tower8 at or below atmospheric pressure depending on the point at which the vacuum is applied to the system and in tower 8 they are further cooled and fractionated. This tower is preferably of the bubble type. Cooling is effected by causing the vapors to come in contact with the coil 28 through which oil at a lower temperature than the vapors Visv caused to fiow by pump 15. This cooling allows a considerable portion of the vapors to be condensed and the condensed fractions are removed from the bottom of the tower through the heat exchanger 17 by the pump 15. A part of the oil, after having been cooled by passing through the heat exchanger 17, is discharged by pump 15 through valve 31 into the absorption tower 11, and a part of the oil is discharged through coils 28 and 27, 27 through valve 32. Valves 31 and 82 may be so opened or closed as to cause any desired quantity of oil to flow in either direction.

The vapors in the tower 8 are also cooled by the liquid from the bottom of the absorption tower 11 which is pumped from tower 11 by pump 16 through heat exchanger 17 where the temperature of this liquid is raised by liquid flowing in a counter current from the bottom of tower 8, and it is Vthen discharged into tower 8 through valve 83. The temperature of the liquid entering tower 8 may be controlled by passing by the heat exchanger with a portion of the relatively cool liquid from absorber 11. This by-pass may be of any suitable or desired construction, and is shown at in the drawings. The liquid from absorber 1l contains the very light fractions not condensed by water cooling coil 9. These absorbed light fractions are removed from this liquid on its entrance into rtower 8 due to the heat it gains in heat exchanger 17 and the hot vapors entering tower 8.

The vapors from the tower 8 are caused to pass. through water cooling coils 9 where 'they are condensed at atmospheric pressure l() are either drawn Jirom it by vacuum pump lsor are caused to pass into absorbing tower ll by reason of their own pressure. When thus passing into the absorbing tower by their own pressure,A their path is through pipe 250, through valve 25 (both valves 20 and 2l beine` closed and so to the tower ll throuO-h,

the pipe 30a. This also depends on the point which the vacuum is applied to the system. These vapors V[low vin a counter-current to the cooled liquid from the bottom of the tower 8 and the lighter gasoline or related lighter oils are absorbed in this liquid. The tower ll is preferably of the bubble type.

The lixed gases pass from the tower 1l through line l70 to the atmosphere, or to burners under the furnace, or to commercial gas lines.

The bottoms from tower S, either .with or without make-up oil, delivered through line El and valve 35, not required as absorption oil in the tower ll, are returned to the sys tem and used vas cooling oil in coils 28, 27, 27, 26, 26, 26, wnich are placed in towers 8, 7 and 6. The line conducting this oil to heat exchanging coils 2S, 27 and 27 has valves 36 and 37 so situated that all or any part of this liquid can be caused to flow through them. he heated liquid from coils 26, 26", 26 and 26' is conducted through line22 and through valve 38 to llashpot l where all or a considerable portion of this oil is vaporized. The vapor so produced is retreated in the :furnace 2 by being drawn through the tubes placed in this furnace.

The apparatus described above when op.- erated on vapors 'from petroleum gas oil of approximately 300 B. gravity with a vacuum capable of holding up a -inchcolumn ot mercury maintained ou the system at the separation drum valve 29, gave a yield ot 16 to 60 percent of light oils having a New Navy Gasoline boiling range and 3 to 5 percent ot absorbed light oils which when separated resembled natural. gasoline `in its boiling range. This gasoline is high in uny washed v tree oli the heavy saturateds and aromatics containing from 60 to 8() percent unsaturated compounds and from l0 to 25 percent of aromatic compounds, and is a very desirable motor fuel.

By varying the combinations of valves, pumps, direct and reflux feed, it is possible to the same apparatus in various ways and for different operations, with different classes of oils. The type of equipment will, of course, also vary with the kind of vapors Linder treatment. The equipment shown is that used when operating on vapors produced from 28 to 256 gravity gas oil derived from petroleum. In this case the heat is removed in four successive stages, in such a manner as to cause the vapors to condense into four dillerent products, one being the linished gasoline or related light oil-the desired product for whichthe plant was designed-another product being a heavy residuum, and the two other products being a heavy and a light gas oil respectively, which are used in the system to maintain the desired temperature on the incolning vapors, and as an absorbing oil to remove the very light gasoline like material, that is entrained in the gas from the separator drum.

Tn operation, the l'irst tower 6 is used largely as a heat exchanger. The surface otithe' coils 26, 26, 26, 26 should be such as to transfer enough of the heat contained in the vapors to the charging oil so that the vapors leaving this tower will be at from 7200 to 6500 F. At this temperature there will be a very heavy asphaltic material re moved from these vapors which if allowed to remain in the tower 6 would eventually harden and plug the tower, hence we provide valve 18 through which a quantity of the heavy gas oil froml the bottom of #7 tower may be introduced into tower 6. This heavy gas oil dissolves the asphaltic material removed from the vapors in tower 6 and carries it to the bottom of the tower where it is drawn ol by pump 12 as iiuel oil. The heavy gas oil introduced into this tower also serves as an added cooling medium for the incoming vapors and gives us a more flexible control over the temperature of the gases leaving the tower. This tower 6 contains at its top the heat exchanger 26, 26, 26 and 26 and in the bottom baille pans over which the heavy gas oil is made to flow to keep it asphalt-like material.

The temperature ot the vapors entering tower 7 should be approximately at the equilibrium boiling point of these vapors under the conditions maintained in that tower. At this temperature the quantity of heat to be removed from these vapors is only that heat due to the condensation of the heavy gas oil we desire to remove in tower V7 and the heat we must extract from the vapors themselves in order to cool the vapors to such a temperature that the heavy gas oil will liquify and drop out of the vapors; thereforethe heat exchanger at the top of this toweris smaller than the heat exchanger in tower 6. In cooling the vapors in this exchanger there is a certain quantity of lighter oils which will be absorbed from the vapors by the condensing heavy gas oil. In order to thoroughly strip this heavy gas oil of these light oils we cause these condensed heavy gas oils to flow downward through the tower over a series of bubble pans or the equivalent thereof in contact with the vapors entering this tower.

Tower 8 operates on the same general principles as tower 7, except that it is used to remove the light gasoline absorbed from the vapors entering tower ll, In this tower enough heat is taken from the vapors enter ing it to cause the condensation oi a light oil and to cool the vapors until they are made up of only lixed gases and the desired gasoline like vapors. .As the quantity of heat removed in this tower is less than the heat to be removed in the preceding towers, we have shown the heat exchanger at the top of this tower with only one coil, 2S; Below this coil we have bubble pans 5l which serve to strip the condensed light gas oil ot its absorbed gasoline and also to strip the absorbA ing oil from tower ll of :its light gasoline by contacting them preferably in counter-eurrent with the incoming vapors.

The vapors from tower 8 pass to water cooler 9 where they are brought to atmospheric temperature under which condition the gasoline like material all condensed except t'or that entrained in the fixed gases. This condensed liquid and the fixed gases are separated in drinn l0, the gasolinelike niaterial going to storage or any other place desired and the fixed passing to tower ll where they are stripped of their entrained light gasoline by flowing counter current to a down flow of light gas oil removed from the bottom of tower 8 or. otherlightgas oil introduced from an outside source through valve 35.

The light gas oil from the bottom o'l" tower 8 is drawn through heat exchanger 17 by pump 15 where it loses its heat to cold oil drawn from the bottom of tower ll. This exchange of heat here cools the light gas oil from tower 8 to such an extent that it ncan be used in tower 11 and when it 1s introduced again into tower 8 very little added heat from vapors entering tower 8 is necessary for the complete removal of the light gasoline this oil has absorbed while passing through v tower 11. By this system of stripping the absorbing oil of its light gasoline content in the presence of the heavier gasoline vapors, we `get a productA more stable under atmospheric conditions than is gasoline produced in the ordinary way and having the light strippings from the absorbing oil added to it afterwards. In other words, the absorbing tower 41l operating in connection with the tower 8, constitutes a stabilizing system which also takes advantage of the heat a wailable in bottoms from tower 8, and uses the same to strip the absorbing oil of its light gasoline content. y

That we claim is:

l. In a plant or' the class described a plurality ol serially connected ifractionating units containing serially connected heat exchangers, a plurality of means connected each to `one of said fractionators adapted to withdraw condensateI therefrom, an outlet connection from each oi said means to a eorrespending heat exchanger or preheating coil, in a preceding fractionator, and means to force condensate through said heat exchangers, whereby heavier and lighter condensate in succession may be drawn oil and relluxed for retreatment the surfaces of said heat exchanging units increasing in size in proportion to the specii'ic gravities of the several grades of condensate supplied thereto` and therefore proportionately to the temperatures required to vaporize the same.

2. In a plant of the class described, la plu rality of serially connected fraetionating units containing serially connected heat exchangers, means connected to a plurality oli said iractionators as individual units adapted to draw off and force condensate therefrom through said heat exchangers, means for supplying cracked vapors to the iirst one of said fractionating units, means for partially condensing the vapors in each unit and for passing unconde'nsed vapors to thenext unit, means for condensing an d separating the vapors from the last unit, an absorption unit connected to said separatinov means and adapted to receive fixed gases and entrained light gasoline therefrom, means for exposing the same in said absorption unit to contact with an absorbing oil, whereby said oil may strip oft the entrained light gasoline, means to return said oii to the last unit of the fractionating system for recovery of said light gasoline, and means for drawingoi'i1 condensate from the last unit of the fractionating system and forcing the saine in part through said heat exchangers in the fractionators for reliux cracking, and in partinto the upper portion of the absorption unit to act therein as absorbing oil.

WILLIS F. SIMS.-V VENUS U. OLDER.

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