US2149828A - Process and apparatus for cracking oil - Google Patents

Description

March 7, 1939.` c. E.- BEATIE yPROCESS AND APPARATUS FOR CRCKING OIL Original Filed July 3l. 1920 l l i l I I I y INVENTOR l CECIL E. BEATIE B n ATTORNEY mwumgzou 5 ozwa nauw u@ Patented Mar. 7, 1.939

' PROCESS AND APPARTUS FOR CRACKING Cecil E. Beatie, Los Angeles, Calif., assignor, by

mesne assignments, to Power Patents Company, Jersey City, N. J., a corporation of Maine Original application July 31, 1920, Serial No. 400,531. Divided and this application October 7, 1936, Serial No. 104,411

8 Claims.

` This invention relates to a process and apparatus for cracking oil and .more particularly to a continuous process of cracking oil in stages.

' This application is a division of application Serial No. 400,531, i'lled July 31st, 1920, forfProcess of cracking oil.

Since the decomposing or cracking temperatures of mineral oils or Various distillates thereof are usually higher than their boiling temperatures, it is the common practice in cracking oils to place them under sucient pressure so that they may be raised to the decomposing temperature before they are vaporized. .When cracking oil under pressure, three factors, namely, pressure, temperature and time must be accurately controlled in order to secure the best results. If a high temperature is used for cracking, the oil must be subjected to such a temperature for only a short time. Conversely, if a low temperature is used for cracking, the oil must be held at such temperature :for a long time. Either pressuretemperature combination will produce substantially the same results but the higher temperatures are usually preferred because with them oil may be cracked more rapidly. When cracking oil on a commercial scale, there is a critical temperature for each different oil above which it is not practicable to go regardless of the time factor, because at these higher temperatures carbon is deposited so rapidly that the apparatus soon becomes clogged. y

For every cracking temperature, each oil appears to have a critical length of time, to which it may be subjected to such temperature before it will be broken down almost instantaneously into carbon and gases. With some oils, the point of fatigue or the point where the oil seems to suddenly decompose may occur While the oil has a comparatively high gravity. If, however, the temperature and pressure to which the oil is being subjected are changed or if carbon is removed from the oil, the oil may be reduced to a comparatively low gravity without danger of reaching the fatigue point. l

The heavier hydrocarbons decompose more easily, that is, at Alower temperatures and pressures, than the lighter hydrocarbons, and therefore it is desirable that oils of different gravities be decomposed separately. When a hydrocarbon is cracked, a plurality of different hydrocarbons are formed whose specific. gravities vary in series from the low specic gravity up to the high specic gravity. The hydrocarbons having a specific gravity higher .than that of gasoline or the desired hydrocarbons are usually separated from the desired hydrocarbons by condensation and returned to the still for retreatment. Those condensates having a specific gravity higher than gasoline preferably should not be mixed with the Another object of the invention is to provide Y a process of `cracking oil in stages in which the residuum oil from one stage advances to a succeeding stage for treatment at a lower temperature and heavier condensates of vapors formed in one stage advance to a preceding stage or in a direction countercurrent to the advance of the residuum.

Another object of the invention is to provide a continuous process of cracking oil by which the various gravities of oil formed successively in the course of the heat decomposition process may be cracked separately under different conditions of pressure and temperature.

Another object of the invention is to provide a process of cracking oil in stages by which the lighter or lower specic gravity constituents are cracked in the 'stages maintaining the highest temperature and the carbon and heavy residue are removed from the stag-e maintaining the lowest temperature. Y

Another object of the invention is to provide a process of cracking oil in stages by which the carbon which is formed in each of the stages is continuously and progressively carried forward through the stages to the point of discharge by a stream of fresh incoming oil advancing successively through the stages.

Another object of the invention is to provide a process of cracking oil in stages by which the heavier condensates are separated from the finished distilled residue and carbon formed in each stage and these condensates are progressively circulated through the various stages for retreatment therein under the proper conditions of pressure and temperature.

Another object of the invention is to provide a process of cracking oil by which the pressure and temperature of the oil and the time the oil is under predetermined pressures and temperatures may be accurately controlled.

A further object of the invention is to provide a process of cracking oil by Which the deposition of carbon in the treating apparatus may be effectively controlled.

With these and other objects in View, the invenseries of separate cracking coils arranged in stages. The residuum of oil from one stagepasses in succession to the succeeding stages. Immediately after the oil is cracked in the coils, the vapor is separated from the oil residuum, the pressure of the vapors reduced, Vand the vapors arecondensed to separate the heavy condensates from the final distillate. The residuum of each stage passes to a succeeding stage of lower temperature for its next treatment. The residuum which is separated from the vapors in each stage has its pressure reduced and passes to a surge tank where it is mixed with a heavy condensate from a preceding or a succeeding stage in accordance with the specic gravity of such condensate. This mixture is then pumped under pressure through the cracking coil of the next succeeding stage. The temperature and pressure of the oil as it passes through each of the cracking coils :is controlled to produce the maximum amount of gasoline, butthis temperature varies in the stage in accordance with the gravity of the oil being treated. For the vlighter oils, higher temperatures and pressures are used, and for the heavier oils, lower temperatures and pressures are used. In each of the cracking coils, the maximum temperatures and shortest time intervals are used Which will give the highest yields With practicable operating conditions.

In the accompanying drawing:

Fig. 1 is a diagrammatic flow sheet of a process embodying the preferred form of the invention.

Fig. 2 is a horizontal sectional view taken on the line 2-2 of Fig. 1 and comprises a conventional showing of the oat valve control mechanism in the bottom of the separato-rs.

A process of cracking an oil such vas crude oil, kerosene, gas oil or fuel oil to produce gasoline may be carried out inthe apparatus illustrated in the drawing as follows.: Crude or gasoil from storage I8 flo-ws through a line I2 to-a heat interchanger I4 and passes through a line I6 to a surge tank I8. From the surge tank I8 the doil is circulated for treatment in the apparatus of a first stage converter. The oil leaving the surge tank I8 is placed under pressure by means of a pump 20 and forced through a vcracking or -heating coil 22 positioned ina furnace 24. The heated and vaporized oil leaves the coil v22 through a line 2.6 and passes into a separator 28. Vapors separated from the oil in the separator 28 ovv through an otake 38 through a pressure-reducing valve 32 thence into the bottom of a spray condenser 34. In the condenser 34 the `vapo-rs are subjected to a spray of vheavy condensate which Vis* taken from an overow tank 36 by means of a pump 38 and passed through a cooling coil 48 to a spray nozzle 42 in the upper portion of the condenser. The heavy condensate removes,

\ all of the heavier portions of the oil and the A1inoil from 'the surge tank 56 is forced under pressure by means of a pump 58 through a line 68 to a cracking coil .62 mounted in a furnace 64. The oil cracked in the coil 62 passes through a line 66 to a second stage vapor separator 68. The vapors from the separator 68 pass into an oitake .18 and flow through a pressure-reducing valve 'I2 into a spray condenser 14. In the condenser 'I4 the vapors are condensed by means of a heavy condensate Which is taken from an overflow tank 'I6 by .means of a pump T8 and forced through a cooling coil 88 to a spray nozzle 82 mounted in the upper portion of the condenser I4. The finished distillate vapors pass through a line 84`to a condenser 86 and the distillate passes through a line 88 to a line 98 which connects with the nished distillate line 48.

The oil residuum from the second stage separator 68 flows out through a iioat-controlled valve 92 through a line 94 to a surge or storage tank 96. The surge tank 96 serves as the storage vfor oil to be treated in the apparatus of a third stage converter. The oil from the storage tank 96'is forced Vunder pressure by means of a pump 98 through a line |88 into a cracking coil '|82 mounted in a furnace |84. The oil cracked in the coil |82 passes through a line |86 to a separator |88 which has substantially the same construction as the separators 68 and 28. VThe vapors from the separator |88 pass through an oftake I I8 thro-ugh a pressure-reducing valve |I2 into a spray condenser ||4. The vapors in the condenser II4 are condensed by means of a heavy condensate which is taken from an overflow tank I I6 and circulated by means of a pump II8 through a cooling coil |28 to a spray nozzle |22 mounted in the upper portion of the condenser I|4. The finished distilled vapors from the condenser I I4 pass through a line |24 to a condenser |26 and the distillate passes through Aa line |28 which is connected with the nished distillate line 98.

'I'he residuum from the separator |88 flows through a iloat-controlled valve |38 to a line |32 and thence into the heat interchanger I4 from which it passes through a line I 34 to a residuum storage tank |36. The mechanism used for controlling valves 92 and |38 for discharge of residuum from separators 68- and |88 may be the same as that shown in Fig. 2 for separator 28.

The heavy condensate condensed in the condenser 34 of the rst stage converter overows from the tank 36 and passes through a line |38 to the surge tank 96 for the third stage converter. A line |48 may also be connected 'between the line |38 and the surge tank I8 by which the heavy condensate may pass to the surge tank I8 for retreatment in the first stage converter. The heavy condensate recovered in the condenser 'I4 of the second stage converter overows from the tank 'I6 and passes through a line |42 to the surge tank I8 for the first stage converter. A line |44 may also be connected between the line |42 and the surge tank 56 by which the heavy condensate from the second stage converter may pass to the surge tank 56 for retreatment. The heavy condensate from the condenser H4 of the third stage converter overflows from the tank I I6 and passes through a line M6 to the surge tank 56 for the second stage converter. A line |48 may also be connected between the line |46 and the surge tank by which the heavy condensate from the third stage condenser may pass directly to the surge tank 96 for retreatment.

With the apparatus outlined above, the heavy condensates formed in the different stages of the cracking may be passed to a surge tank in a preceding or the same stage to be mixed with a residuum oil in accordance with the specic gravity of the oil to be treated and in accordance with the specific gravity of the heavy condensate. In the preferred form of the invention, the main body of the oil or the residuum remain-v ing in the separators of the ldierent stages advances from the first to the third stage converters to be subjected to progressively lower temperatures. The heavy condensates formed in the various stages, however, advance from the third to the first stage converters or in a countercurrent direction to the advance of the oil. All of the free carbon formed in the cracking operation is carried forward continuously with the main body of the oil and is ldischarged with the residuum from ythe separator of the third stage converter, which converter is maintained at the lowest temperature. By this means the carbon or residue is separated from the oil in the lower temperature stage of the apparatus where the carbon is least liable to cause trouble in the operation.

The cracking of oil in separate stages permits the various decomposition products of the oil to be grouped separately and treated separately under the most favorable conditions of temperature and p-ressure. The oil may be handled in each stage by a pump to accurately control the time period and therefore the higher temperatures may be used by circulating the oil at high velocities. The high velocity circulation of the oil further assists in carrying residuum and carbon through the apparatus so that it will not become clogged and also serves to carry the vapors out of the heated Zone as soon as they are formed so that the vapors will not be supercracked. A sample of the oil being treated in each of the converters may be removed to determine the amount of free carbon in the oil and accordingly the three factors, time, pressure and temperature used in the cracking coil of each stage converter may be accurately regulated to obtain the desired finished distillate and the maximum evaporation or cracking.

In' the first stage converter-the fresh incoming fuel or gas oil is circulated so rapidly through the cracking coil that the oil is not cracked to any appreciable extent but is merely topped or vaporized so that the vapors'may be fractionally condensed. The heavy condensate which is mixed with the fresh incoming oil, however, has resulted from two previous heat treatments of oil and condensates in the third and second stage converters, and receives another cracking treatment in the coil cf the rst stage converter. This mixture of crude oil and condensate has the lowest speciiic gravity ofl any of the oil mixtures which are to be treated, and is subjected to the highest temperatures. Y

The oil treated in the second stage converter consists of the residuum of the rst stage converter and the heavy condensate from the third stage converter. The residuum is subjected to a lower temperature and pressure in the second stage converter and is therefore further vaporized. The heavy condensate which has previously had a cracking treatment in the third stage converter is given its second cracking treatment.

The oil treated in the third stage converter consists of a mixture of the residuum from the second stage converter and the heavy condensate formed in the rst stage converter. The residuum being treated under a lower temperature and pressure than that maintained in the second stage converter is further vaporized. Any of the oil passing through the coil of the third stage converter which has not been vaporized by the heat treatment in the third stage converter passes` out of the apparatus as a residuum which is controlled to be suitable for fuel oil purposes. 'Ihe heavy condensate of the mixture treated in the third stage converter is given its rst cracking treatment in the second stage converter.

Any oil which has not been vaporized in any of the various stages never goes through the same cracking or heating elements twice and therefore the length of the time in which any particular portion of the oil remains under treatment may be accurately controlled to prevent the oil from reaching the fatigue stage or a point where it will be broken down with an excess formation of carbon. The treatment of oil in each stage consists of a finishing cracking operation to form a iinished distillate, an intermediate cracking operation to form a heavy condensate, a cleaning or topping operation to form vapors for the finished distillate and the heavy condensate, and the removal of carbon from the finished distillate and heavy condensate. In each stage the vapors formed are fractionally condensed to separately collect the finished distillate and the heavy condensate. The carbon separated is deposited in the residue to be advanced to a following stage and the heavy condensate free from carbon advances to a preceding stage. Although the heavy condensate may be mixed with a residue containing carbon, it has a lower specic gravity than the oil mixture of the stage in which it was formed and is mixed with an oil which is subjected to a different temperature and pressure than the temperature and pressure of the stage in which it was formed so that the operation does not tend to bring the oil toward a ffatigue point. On the other hand, the residue containing the carbon advances to a succeeding stage where it is mixed with a lighter condensate and the mixture is subjected to a lower temperature and pressure than the pressure and temperature maintained in the stage where the carbon was formed. The heavy condensates which are added to the residuum to make up a mixture for circulation through a heating element serve to decrease the viscosity of the oil mixture, and since this condensate has all been vaporized in a prior heat treatment, it will be practically al1 cracked in its second heat treatment.

Although the process of 'treating oil has bee illustrated and described as being carried out in three stages, it is to be understood that the invention is not limited to a three-stage process. Some oils may be properly treated in less than three stages and other oils may require more than a three-stage treatment. Thenumber of stages to be used and the specific temperatures and pressures in each stage depend entirely upon the character of the oil being treated and the kind of finished product to be obtained.

The method of separating the finished distillates from the vapors removed from the separators in the various converters is particularly advantageous in that a clean separation may be accurately made. 'I'he vapors are scrubbed with condensates of vapors of the same general type and any desired amount of condensate may be used for the scrubbing operation. The temperature of the condensate used for scrubbing may be accurately controlled by cooling the coils through which they are circulated and in this way a large body of ccndensates of any desired temperature may be circulated through the condenser. This scrubbing operation will prevent any of the higher fractions of oil going over into the nished distillate and will thus do away with the necessity of rerunning the finished distillate to obtain a nished product.

The preferred form of the invention having been thus described, what is claimed as new is:

l. A continuous process for converting higher boiling point hydrocarbon oils into oils of lower boiling point of the type of gasoline, which comprises passing the highV boiling point oil to be cracked through a high pressure heating and cracking zone in a stream of restricted cross section to effect cracking and vaporization of the oil, introducing the highly heated stream of cracked oil products from Vsaid cracking zone into the upper portion of an enlarged Vertical separating chamber wherein vapors are separated from unvaporized oil constituents, withdrawing the separated vapors from said enlarged chamber substantially below the top` thereof and fractionating them to produce a reflux condensate and an overhead vapor containing gasoline constituents, discharging the separated unvaporized oil constituents from the bottom of said enlarged chamber through a oat valve controlled line and without returning the same to said high pressure zone passing them into a second cracking Zone of lower pressure in which the unvaporized oil constituents are heated and subjected to cracking conditions, separating vapors from unvaporized residue resulting from the cracking in said second zone and fractionating the resulting vapors to produce a reflux condensate and an overhead vapor containing gasoline constituents, and passing said reflux condensates into said high pressure cracking zone to supply at least in part the high boiling oil to be cracked therein.

2. The process of cracking oil, which comprises passing the oil to be cracked through a long heating coil wherein it is subjected to cracking conditions while owing in a stream, discharging the stream of highly heated cracked oil products from said coil into the upper portion of an enlarged vertical vapor separating chamber in which the oil constituents introduced from said coil pass downwardly therein, discharging the separated unvaporized oil from the bottom of said chamber through a valvedline, the valve of which is operated from a oat control in the bottom of said chamber, conducting the unvaporized oil from said line through a second heating zone of lower temperature and then into a seco-nd Vapor separating chamber, cooling and condensing portions of the vapors from said vapor separating chambers in separate reiluxing zones, conducting uncondensed vapors from said reuxing zones for final condensation and collection, and passing rellux condensate from said refluxing zones into said heating coil for retreatment. Y

3. The process of cracking oil, which comprises passing the oil to be cracked through a heating and cracking coil wherein it is subjected to cracking conditions and cracked While flowing at high velocity in a stream of restricted cross section, discharging the stream of highly heated cracked oil products from said coil into the upper portion oi an enlarged vertical reaction chamber wherein said products flow downwardly and the unvaporiyzed `oil constituents separate from vapors, separately removing the vapors from the chamber at a point substantially below the top thereof and passing them to fractionating equipment for condensing out the desired gasoline product, and withdrawing the unvaporized oil constituents from the lower portion of said chamber in such a way .as to prevent the rise of liquid therein above a predetermined level near the bottom of said chamber by withdrawing said unvaporized oil constituents through a valved line, the valve of which is operated by means of a float control in the lower` portion of said chamber whereby the carbon formed in the cracking operation is continuously carried forward out of the apparatus so that it will not become clogged.

4. The process of cracking residue containing mineral oil stock of relatively high specific gravity, which comprises mixing therewith a distillate stock of relatively lower specific gravity to form a cracking stock of lower specific gravity than said mineral oil stock, passing the resulting mixture at a high pressure in a confined stream of restricted cross section through a heating Zone in which the oil of said stream Yis subjected to cracking conditions of temperature and pressure and cracked, maintaining a suiciently high velocity in said stream to carry forward the residue and carbon formed in the cracking operation to prevent clogging of the apparatus, discharging the resulting highly heated and cracked oil constituents into the upper portion of an enlarged vertical separating chamber in which the oil constituents pass downwardly and the unvaporized portion thereof collects in the lower part of the chamber, withdrawing separated vapors from said chamber at a point substantially below the top thereof and fractionating them to produce a reux condensate and a gasoline fraction, withdrawing the separated unvaporized oil constituents containing the carbon formed in the cracking operation from the bottom of said chamber through a valved line, the valve of which is operated from a oat control in the lower portion of said chamber and preventing return of said withdrawn unvaporized oil to said cracking zone, and mixing said reflux condensate with said residue containing oil charging stock to supply at least in part the said distillate stock.

5. The process defined by claim 4 in which said residue containing stock is produced in a separate pressure cracking operation by subjecting a relatively heavy hydrocarbon oil to cracking in a confined stream of restricted cross section and in which the resulting highly heated products are separated into vapors and unvaporized oil containing residual constituents.

6. The process deiined by claim 4 in which a sample of the cracking stock passed to the heating zone is removed and its free carbon content determined, and controlling the cracking conditions in said heating zone in accordance with the carbon content of said stock.

7. The process of cracking mineral oils for the production of gasoline, which comprises passing the oil to be cracked in a stream at high velocity through a heating and cracking zone in which the oil is subjected to cracking conditions under pressure and cracked, conducting the stream ofhighly heated and cracked products into a large vertical externally unheated separating chamber in which vapors are permitted toseparate from unvaporized oil, discharging the separated unvaporized oil from the bottom of said chamber in such a way as to prevent the rise of liquid in said chamber above a predetermined level near the bottom of the chamber thereby providing for the free movement of vapors in said chamber above said predetermined level, separately discharging all of the vapors in a stream from said chamber at a point remote from the point of introduction of said stream of cracked products, fractionating said discharged vapors to produce a reflux condensate and a gasoline fraction, and avoidingthe return of said discharged unvaporized oil to said heating and cracking Zone.

8. An apparatus for the continuous cracking of high boiling point oils which comprises a pipe still furnace in Which a continuous cracking coil is mounted for heating and cracking the oil, an enlarged Vertical separating chamber, and means for conducting the highly heated cracked oil products from the coil of said furnace into the upper portion of said enlarged chamber, a Vapor line from said enlarged chamber adapted to remove vapors therefrom at a point remote from the point of introduction of the cracked oil products into said chamber, a residue Withdrawal line from the botom of said chamber having a control Valve, means for operating said control Valve from a float mounted in said chamber near the bottom thereof, fractionating means for producing a reux condensate from the vapors discharged through said vapor line. and means for conducting said reflux condensate to the inlet of said cracking coil in said furnace.

CECIL E. BEA'I'IE.

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