US1930372A - Apparatus for treating hydrocarbon vapors - Google Patents

Description

Oct. 10, 1933. w F. $|M$ r AL 1,930,372

APPARATUS FOR TREATING HYDROCARBON VAPORS Original Filed Nov. 23, 1929 2 Sheets-Sheet l III 05/? Re nva J70 CK 573 Oct. 10, 1933. w 5 M$ r AL 1,930,372

firPARATUS FOR TREATING HYDROCARBON VAPOHS Original Filed Nov. 23; 1929 2 Sheets-Sheet 2 Patented Oct. 10, 1933 APPARATUS ,FOR. TREATING HYDROCAR- BON VAPORS Willis F. Sims and Venus U. Cloer, Wichita Falls,

Tex., assignors to Panhandle Refining Company, Wichita Falls, Tex., a corporation of Texas Application November 23, 1929 Serial No. 409,406

1 Claim.

Our invention relates to the treatment of hydrocarbon oils and especially to such treatment for the purpose of producing motor fuel from petroleum by the process commonly known as 5 cracking. The present application is a continuation in part of our prior copending application filed February 16, 1928, Serial No. 254,753, in which we have described and claimed an improved method of cracking under vacuum and a complete plant for practicing thesame. In

the present case we shall describe the same general system, together with improved primary and cracking'stills combined in one structural unit, and shall claim said unit construction, as

well as certain specific features and methods of operation of the plant as a whole.

Very briefly stated, the invention we present has for its basis the discovery on our part that by cracking, fractionating, and cooling under a vacuum, in whole or in part, we can increase compounds and aromatics which is eminently suitable for motor fuel; and that by suitably regulating the temperature and pressures (subatmospheric) in different parts of the system, we can not only greatly economize heat and thereby economize fuel, but we can also produce a product containing practically 100% of the desired unsaturated and aromatic compounds.

Our apparatus, as it will be described, comprises a preheating still for the charging stock, a cracking still, preferably preceded by a flashpot into which the oil from the preheater is expanded into vapors, and a succession of interrelated fractionating towers or dephlegmators with one or more vacuum pumps, heat exchanger, and cooler and separator, an absorption tower, all arranged as will be described in detail 40 hereinafter.

A particular feature which we shall claim herein both broadly and specifically, is the arrangement of theunit structure containing the preheating still and the cracking tubes. We

preferably arrange this with twin furnaces connected by an arched overhead opening, with burners iii both furnaces. The heat passing upward in the cracking furnace then follows a down draft through the preheating furnace,

which has upper and lower flue passages into the stack, containing dampers by means of which the heat supplied to the preheater tubes may be regulated.

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

22 of Fig. 3.

Fig. 3 is a horizontal longitudinal section of the same, taken on the line 33- of Fig. 2.

Referring first to Fig. 1, 1 designates a flashpot receiving the heated oil through valve, 23.

and pipe 52 from the pipe still in the furnace 2a. Charging stock is forced into said .pipestill through the pipe 53 by pump 54. The-oil may enter the flashpot as vapors already form'ed,'or it may be superheated oil transformed to vapor in this pot by release from pressure. The vapors from this flashpot passing through pipe55 to the cracking tubes 56 in the furnace 2, will be 7 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 on our flashpot. This is a vapor terns 9 perature and not an'oil temperature. The oil before entering the flashpot 1 must be at a temperature somewhat above this vapor temperature in. order to contain enough heat to take care of the latent heat of vaporization on enter- S5 ing the flashpot.

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. .1, the pipe still 57 is located in the furnace chaniber 20. supplied with top and bottom flue openings 5859 into the stack 60, each opening provided with a damper as shown, so that the draft through the pipe 57 may be regulated. The furnace chamber 2a is provided with burners'fil, presently to be described and the entire structure is connected to. the structure of the furnace .2 containing the cracking tubes 56, and main burners 62. The 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 60through either the lower or upper opening. 59 or 58, according to the adjustment of the dampers. ;W itli-the-upper draft of 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 crack ing tubes 56.-

The burners 61 placed under the primary heating tubes are usedin bringing the plant on stream at the beginning of a run. By using these burners 61 we do not have to fire the cracking tubes 56 (by means of burners 62) so heavily as would otherwise bethe 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 flashpot 1. After the plant is once on stream and the maximum fire is placed under the cracking tubes 56 by burners 62, the burners 6i may be turned down very low or completely out out and the temperature of the oil flowing in the primaryheater may thereafter be regulated by the proper useof 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 2.2. 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 enclosedwith thin metal plates 65-66-6768; The furnace 2 is lengthened out at both ends as shown in 2x and 23!, these two ends being arched as indicated in dotted lines 2w in Fig. 2, and constituting Dutch ovens projecting into which are the burners 62. Burners 61 project into the furnace 2a beneath 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 2x and 2g, and conveyed through the-arches 2w into the central chamber 2, passing upwardly therein through and around the cracking tubes 56 and thence being deflected by the arch 22 through the passageway 63a into the chamber 2a. If the burners 61 are in operation at the same time, for

purposes of bringing the plant on strearn, 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 asalready stated, and the maximum fire is placed under the cracking tubes 56, then burners 61 may be turned down very low or completely out out, and by regulating the dampers in flue 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 60 through the lower flue passage 58. a

The vapors from flashpot 1 are drawn through the cracking tubes 56 preferably at a temperature from 1000 F. to 1200 F., and a pressure of 6 to 14 pounds absolute is maintained on the of the vapors in the tubes causing'a greater heat transfer per square foot of heating surface. The vacuum pump 14 is locatedin such a position, with suitable connections through lines 30,

and separation tower 6, or the vacuum may be applied on the separator drum 10 and the vapors removed therefrom discharged into adsorm tiontower l1.

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 anelevated temperature, preferably from 1000 F. to 1200 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 produced in 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 flow 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 baflle plates placed in this tower; and (2). by causing 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 causea heavy residue to collect in the bottom of the cooling and separation tower 6 which is removed from the system by pump 12.

The vapors from tower 6' enter the tower '7, at or below atmospheric pressure depending on the point at which vacuum is placed on the system and in tower '7 they are further cooled and fractionated. This tower is preferably of the bubble type. Thecooling is effected by causing the vapors to come into contact with cooling coils 27' and 27, through which oil of relatively lower temperature-than the vapors entering the tower is caused to flow by pump 15. The cooling in this tower is carried to such a point that a large portion of thevapors' entering it are caused to condense to liquid. This liquid is drawn from tower 7 by pump. 13 which discharges a part of 'it into tower 6,. at 18 and a part through the- coils 26, 26, 26"and 26. Valves l8 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 thetower 6 or the coils 26, 26, 26", 26".

.The vapors from the tower 7. enter another tower 8 at or below atmospheric pressure. depending on the point at which the vacuum is applied to the system, and in' tower 8 theyjare further cooled and fractionated. This tower is preferably of thebubble type Cooling is effected by causing the vapors to come in contact with the coil 28 through which 011 at alower temperature than the vapors is caused to flow by pump 15. This cooling allows a considerable portion of the vapors to be condensed and the condensedfractions are, removed from :the bottom of the tower through the heatexchanger 17 by the pump 15.; 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 A part of the oil,-,aft er V part of the oil is discharged through coils 28 and 27, 27' through valve 32. Valves 31 and 32 may be so opened or closed as to cause a desired quantity or all 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 then discharged into tower 8 through valve 33. The temperature of the liquid entering tower 8 may be controlled by passing by the heat exchanger with a portion of the cold liquid from absorber 11. This bypass may be of any suitable or desired construction, and is shown at a: in the drawings. The liquid from absorber 11 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 tower 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 or lower depending on the point at which the vacuum is applied to the system. This condensate, because of the cooling and separation it has previously had, is gasoline or related light oils and is collected in separator drum 10. This light liquid is removed from the separator drum 10 through valve 29 by a pump not shown in the drawings.

The vapors that collect in separating drum 10 are either drawn from it by vacuum pump 14 or are caused to pass into absorbing tower 11 by reason of their own pressure. This also depends on the point at which the vacuum is applied to the system. These vapors flow in 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 11 is preferably of the bubble type.

The fixed gases pass from the tower 11 through line 470 to the atmosphere, or to burners under the furnace, or to commercial gas lines.

The bottoms from tower 8, either with or without make-up oil delivered through line 34 and valve 35, not required as absorption oil in the tower 11, are returned to the system and used as cooling oil in coils 28, 2'7, 2'7, 26, 26", 26", which are placed in towers 8, '7 and 6. The line conducting this oil to cooling coils 28, 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. The heated liquid from coils 26, 26, 26" and 26" is conducted through line 22 and through valve 38 to flashpot 1 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 operated on vapors from petroleum gas oil of approximately 30 B. gravity with a vacuum capable of holding up a 5-inch column of mercury maintained on the system at the separation drum valve 29, gave a yield of 16 to 60 percent of light oils having a New Navy gasoline boiling range and 3 to 5 percent of absorbed light oils which when separated resembled natural gasoline in its boiling range. This gasoline is high in unsaturated and aromatics containing from 60 to percent unsaturated compounds and from 10 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 use 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 under treatment. The equipment shown is that used when operating on vapors produced from 28 to 36 B. 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 different products,'one being the finished gasoline or related light oilthe desired product for which the plant was designedanother 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 incoming vapors, and as an absorbing oil to remove the very light gasoline like material, that is entrained in the gas from the separator drum.

What we claim is:

A cracking still and a preheating still combined in one structural unit containing two chambers divided by a central fireproof partition with an opening above the same, burners for firing said cracking still, on one side of the partition, burners for firing the preheating still on the other side of the partition, means for regulating the admission of fuel to each of said burners, and a stack having a plurality of flue openings, located at different levels in the outer wall of the preheating still chamber, with means for opening and closing said flue openings, whereby the heated gases and products of combustion from the cracking still chamber may be directed through the preheating still chamber, or directly into the stack, at will.

WILLIS F. SIMS. VENUS U. CLOER.

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