US2006571A - Process and apparatus for cracking hydrocarbons - Google Patents

Description

July 2, 1935. G. c. HARGROVE ET AL 2,006,571

PROCESS AND APPARATUS FOR CRACKING HYDROCARBONS Filed Feb. 20, 1928 2 Sheets-Sheet l a A Nm am Hm uw @Mmm mmv .Sw ww uN @E Nw. NW

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PROCESS AND APPARATUS FOR CRACKING HYDROCARBONS 2 Sheets-Sheet 2 Filed Feb. 20, 1928 is@ QM 5, om 'eofge @Hargrgten Wa//er E. Mon/gomery gn @l/tow? QN uw ww.

VPatented July 2, 1935 I UNITED STATES PROCESS AND APPARATUS FOR CRACKING HYDROCARBONS Delaware Application February 20, 1928, Serial No. 255,581

4 Claims.

This invention relates to improvements in apparatus for treating hydrocarbon oils, and more particularly to apparatus for cracking crude oil, reduced crude, fuel oil, petroleum residuums and other heavy petroleum oils.

In oil cracking systems in which the oil being treated is maintained under super-atmospheric pressure in the cracking zone, it is customary to lead the conversion products to an evaporating chamber in which the pressure is reduced and the vaporization of the lighter fractions of the conversion products is facilitated. The evaporating chamber usually includes, or has associated with it, means for separating the lighter fractions of the products of conversion from the heavier fractions. `Such means may, for example, comprise a dephlegmating column into which the hot vapors are introduced near the base and led upward incounter currentrelation to relatively cool condensed portions of the vapors. In order to promote the condensation of the heavier fractions of said vapors, it has also been proposed to introduce cold fresh stock into the column directly into contact with said vapors. However, Where the fresh stock has consisted of relatively heavy hydrocarbons such as crude oil, reduced crude or similar "dirty oils, there has been a tendency for the accumulation of gummy or other diflicultly removable residues in the column which tend to interfere with its effective working.

According to the present invention it is proposed to promote the condensation of the heavier fractions of the conversion products in the separating zone by bringing fresh stock from the stock line or other source of supply into heat-exchanging relation with the conversion products, but maintained out of direct contact therewith while such products are in a vaporous state. It is also proposed, when a fresh stock consisting of unskimmed crude or the like is being used, to carry the heat exchange to such a point that lighter fractions of such fresh stock will be vaporizecl. These lighter fractions are then separated from the unvaporized fractions and subjected to suitable refluxing or condensing action to eiect a separation from the lighter gasoline constituents of any heavier fractions carried with the gasoline vapors, which heavier fractions may either be introduced into the charging line or stored or used in any suitable manner.

The invention also includes means forv mixing 'the condensed portion of the conversion products with the unvaporized portion of the fresh stock andfor controlling the proportions of each of these materials introduced into the cracking zone.

The invention also includes means for maintaining the fresh crude orother stock material under pressure in the preheating coils and means for bringing the thus preheated stock into a zone Where the pressure is maintained. relatively low in order to facilitate the vaporization of its lighter fractions.

One of the objects of the invention is to provide means for better controlling the composition of the oil introduced into the cracking zone. Another object of the invention is to eiect more eiiicient utilization of the heat contained in the products of conversion coming from the cracking zone and the application of the heat thus extracted to Vaporize the lighter fractions of the fresh stock, thereby eliminating the necessity for subjecting such stock to an initial distillation by means of heat from an extraneous source. Another object of the invention is to promote condensation of the heavier fractions of the conversion products in the separating zone without introducing relatively heavy and dirty oil therein.

Other objects and advantages of the invention will appear from the following description taken in conjunction with the accompanying drawings:

In the drawings:

Fig. l is a diagrammatic side elevation, partially in section, of an apparatus embodying one form of the present invention.

Fig. 2 is a diagrammatic side elevation of an apparatus in general similar to that shown in Fig. l Withfthe furnace omitted and with the structure modified to include a flash tower and an auxiliary dephlegmator.

Referring more particularly to Fig. 1 of the drawing, I indicates generally the furnace which contains a plurality of heating coils Il connected by a transfer line I2 to a forged steel reaction chamber I4, in which the cracking continues and carbon is permitted to deposit. The reaction chamber I4 is heavily insulated to prevent loss of heat therefrom, and is provided with manhole covers I5 at each end thereof, which may be taken olf during shutdowns to permit the removal of carbon from the chamber. The products of conversion other than carbon are discharged from the conversion or reaction chamber I4 through the discharge line I6 controlled by a pressure reducing valve Il. The discharge line I6 discharges into an evaporator I8, the overhead products from which pass through a line I9 into a imgTi-:Nr OFFICE dephlegmator or bubble tower 20 in which the vapors are reiiuxed. The bottoms from the evaporator are drawn oi through a pipe 2I controlled by a valve 22, and pass first through a fuel oil cooler 23 and thence to storage through the pipe 24. While not an essential element of the present invention, a level regulator 25, which may be of any well known type, is shown for controlling the liquid level in the evaporator I8. The regulator 25. controls the admission of steam to the steam line 26 to open the power operated valve 22 when the level in the evaporator rises too high, and shuts olf the supply of steam and permits the valve 22 to close when the level drops below the desired position. In practice there will be a nearl'lsteady drawoif of the fuel oil through the p1pe The overhead products from the dephlegmator 2Ilv pass through a vapor line 2'I to a condenser 28. Beyond the condenser 28 is arranged the usual valve controlled gasoline distillate receiver 29 having the customary valved outlet for permanent gases which controls the pressure in the condenser and fractionating apparatus. The reflux condensate collecting in the bottom of the dephlegmator is drawn oi through the line 30 controlled by a power operated valve 3l and conducted to a mixing or accumulator tank 32. The liquid level regulator 33, which is similar to the regulator 25 on the evaporator I8, controls the admission of steam to the steam line 34 and thereby controls the valve 3|. The discharge line I6 and the line 30 are shown as connected to an emergency cooler 35 by means of valved pipes 36 and 31 respectively, the valves in these pipes being ordinarily closed, and opened only in the event that it is necessary to withdraw the material under treatment from the system under unusual conditions.

The stock to be treated is picked up from a stock tank 38 by the low pressure pump 39 and forced through line 40 to the pipe coils 4I and 42 located in the tops of the bubble tower 20 and the evaporator I8, respectively. The coils 4I and 42 are provided with valve controlled by- passes 43 and 44, respectively. The heavy oil passing through the coils 4I and 42 is preheated therein and serves to cool the vapors in the two towers, the amount of stock passing through the coils being regulated in accordance with the temperature conditions which it is desired to maintain in the towers. It will be understood that automatic temperature controlled valves may be utilized if desired in connection with the coils 4I and 42 and their by-passes to correctly proportion the amount of oil passing through the coils. The outlet of coil 42 is connected to a. line 45 which discharges into the mixing tank 32, a power operated valve 46 in this line being controlled by the level regulator 41 -which governs the upper level in the mixing tank 32. vThe line is also connected to a pipe 48 controlled by a power operated valve 49 and discharging into a return stock cooler 50. The level regulator 41 controls both the valve 46 and the valve 49, the connections being such that one valve is opened as the other is closed. The amount of fresh stock necessary to maintain the proper temperature in the bubble tower 20 and the evaporator I8 is usually more than sufficient to maintain the proper level in the mixing tank 32, and therefore the excess oil is by-passed through the pipe 48 into the return stock cooler 5U and from there returned through the line 5I to the stock'tank 38. By means of this arrangement the relative amounts of fresh feed and reflux condensate from the bubble tower fed into the mixing tank to make up the charging stock'may be controlled, at the same time permitting the regulation of the temperatures of the evaporator and the bubble tower by circulating the necessary amount vof fresh stock through the coils 4I and 42 as a cooling medium independently of the make-up require.- ments, since the excess `stock is returned to the stock tank.

Where the mixing tank is operated under pressure, the control valve 46 may be replaced by a check valve preventing back flow from the mixing tank. In this case, when the level regulator 41 opens the valve 49 in the line 48 leading to the return stock cooler, the fact that the pressure in the cooler is less than that in the mixing tank will cause the excess oil to flow through the cooler.

An annular `pan 52 is placed beneath the coil 42 to collect the hydrocarbons condensed in the upper part of the evaporator I8, and a run back 53 conducts this condensate to the bubble tower 20.

A line 54 is connected to the bottom of the mixing tank 32 and to the suction side of a booster pump 55. The outlet from the booster pump 55 connects tothe suction side of a high pressure hot oil pump 56, the discharge side of which, in turn is connected by a line 5l to the inlet of the heating coils II. A vent line 58 is connected to the top of the mixing tank 32 and discharges into the bubble tower 20 above the liquid level therein, for example, between the fifth and sixth plates, to permit vapors which may be generated in the tank 32 to be fractionated in the bubble tower 20.

The discharge side of the low pressure pump 39 is also connected to the tank 32 by a pipe 59 controlled by a power operated valve 60 governed by a regulator 6 I The regulator 6I establishes a minimum level for the mixing tank 32, and in the event of the level dropping down asfar as the range of the regulator 6I, the valve 60 is opened and stock passed directly into the mixing tank 32 to obtain the necessary minimum level therein. In practice this situation will never arise and this is merely a safeguard to prevent the suction line 54 connected to the charging pumps 55 and 56 from becoming uncovered. It is very undesirable to permit the cold stock to enter the tank 32 for the reason that this would throw oil' the temperature balance existing throughout the system, and it is therefore desirable for the operator to watch either the oat arm on the regulator 6I or the liquid level in an ordinary gauge glass adjacent thereto, so that the pump 39 may be speeded up, or the charging pumps and 56 slowed down to permit the level in the mixing tank to build up rather than to maintain this level by the addition of fresh, cold stock directly to the tank.

When the apparatus is being operated on crude oil, the crude is withdrawn from the tank 38 by the pump 39, preheated in the coils 4I and 42 and discharged into the tank 32, where it is stripped of its natural gasoline content and the skimmed crude mixed with the clean overhead recycle stock, discharging from the bottom of the bubble tower 20. This mixture is drawn olf through the line 54 by the pumps 55 and 56 and charged into the heating coils II of the furnace I0 where it is raised to a cracking temperature. From there the material being treated is discharged into the reaction chamber I4, and is then vaporized by its contained heat under reduced pressure in the evaporator I8, the heavy residual oil being drawn oif from the evaporator I8 through the line 2| and sent to storage. The residual material drawn off from the evaporator I8 is marketable fuel oil, and is relatively free from bottom settlings as compared with the fuel oil bottoms produced by the cracking of a similar stock in a pressure distillation process. The vapors from the evaporator I8 pass into the bubble tower 20 through the line I9, the condensate collecting in the bubble tower being directed to the mixing tank 32 as described, and the gasoline distillate from the dephlegmator being condensed under pressure if desired in the condenser 28. The natural gasoline contained in the preheated crude will be largely stripped therefrom in the mixing tank 32 and will pass into the bubble tower 20 through the line 58, being mixed with the cracked gasoline in the 'final gasoline distillate. To promote easy stripping of the crude, it is desirable to introduce the preheated crude into the mixing tank near the top thereof and above the inlet for the recycle stock, as shown in the drawing. Although the bubble tower 20 and the mixing tank 32' are under substantially the same pressure by reason of being in free and open communication through the vent line 58, the positive discharge of recycle stock from the bubble tower to the mixing tank is assured by mounting the mixing tank at a lower level, thus giving a hydrostatic head.

If desired, as for example when a crude oil having a relatively high gasoline content is being treated, the line 45 may be connected with a supplementary evaporator or flash tower 62 as shown in Fig. 2. In this case a pressure regulating valve 63 may be provided in the line 45, so that the crude in the coils 4I and 42 may be maintained under a substantially higher pressure than is maintained in the iiash tower 62 in order to secure the maximum stripping action. The flash tower 62 is shown as connected by aline I9a with a separate fractionating system, such as the dephlegmator or bubble tower B4, thus permitting the natural gasoline from the crude to be collected separately from the cracked gasoline. The condensate collecting in the dephlegmator 64, which will consist substantiallyof kerosene and fractions of similar gravity, may be led to the mixing tank 32 through the line 65 or to storage through a line 56, by suitably manipulating the valves 6l and 68. The stripped crude which collects in the bottom of the flash tower 62 may be led continuously or intermittently to the mixing tank 32 through the line 69 controlled by valve 10. The emergency cooler 35 and the return stock cooler 50 are omittedfrom the showing in Fig. 2. However, it will be` understood that either or both of these features may be included.

If desired, the flash tower 62 may be omitted, in which event the line 45 will lead directly t0 the mixing tank 32 and a line leading to the supplemental dephlegmator 64 instead of to the dephlegmator 20 may be provided, thus insuring the collection of the natural gasoline and the cracked gasoline separately. In this case the mixing tank may be advantageously operated at a lower pressure than that existing in the dephlegmator 20, for example, at atmospheric pressure, in order to secure the maximum stripping action.

Another possible modification of the apparatus is to eliminate the mixing tank and use the bottom of the dephlegmator 20 as a reservoir to perform the functions of the tank 32. In such case,

the line 54 connected to the suction side of the chargingpumps 55 and 56 would be connected directly to the bottom of the dephlegmator 2l), and the preheated crude line 45 would discharge into the dephlegmator 20 at or about the same level as the vapor inlet line I9 from the evaporator I8. The pipe 48 and the power-operated valves 45 and 49 would be used as shown, but would be controlled simultaneously by a level regulator on the dephlegmator 20 similar in construction to the regulator 41. However, we prefer to employ the mixing tank 32 because of the flexibility of control thereby provided, particularly with respect to the disposition of the natural gasoline stripped from the crude, operating the mixing tank at a different pressure than that existing Lin the dephlegmator, and maintenance of the desired ratio of fresh stock to recycle stock Vin the charging, mixture, all as above described.

An additional operating advantage of the mixing tank is that it is easier to clean the tank of any fouling which may occur from using a dirty residual oil as the fresh feed than it would be to clean the dephlegmatorif a similar charging stock were discharged directly thereinto.

Other changes and modifications will suggest themselves to those skilled in the art, and we therefore do not desire to be limited except by the scope of the appended claims.

What we claim is:

1. In an oil cracking system, a cracking unit including a reaction chamber, an evaporator connected directly with the reaction chamber and to which products of conversion are transferred from the reaction chamber, a dephlegmator, means for passing vapors from the evaporator directly to the dephlegmator, a coil in said evaporator in the path of vapors passing therefrom, a coil in the dephlegmator in the path of vapors passing therefrom, a mixing tank, means for passing a charging stock serially through said coils and into the mixing tank, means for passing reflux condensate separated in the dephlegmator to said mixing tank, and means for transferring the mixture collected in the mixing tank to the cracking unit.

2. In an oil cracking system, a cracking unit including a reaction chamber, an evaporator connected directly with the reaction chamber and to which products of conversion are transferred from the reaction chamber, a dephlegmator, means for passing vapors from the evaporator directly to the dephlegmator, a coil in said evaporator in the path of vapors passing therefrom, a coil in the dephlegmator in the path of vapors passing therefrom, a mixing tank, meansfor passing a charging stock serially through said coils and into the mixing tank, means for passing reflux condensate separated in the dephlegmator to said mixing tank, means for passing vapors separated in the mixing chamber to said dephlegmator, and means for transferring the mixture collected in the mixing tank to the cracking unit.

3. An oil cracking apparatus comprising in combination a heating coil, a vapor separating chamber dephlegmator and a final condenser serially connected in the order named; a crude oil stripping tank; a coil within said dephlegmator and another coil within the vapor space of said chamber; means for withdrawing oil from said chamber; means for passing crudeoil serially through the coils within said dephlegmator and chamber and thence into said stripping tank; means for passing reiiux condensate from said dephlegmator into said tank, and means for supplying liquid under'pressure from said tank to said heating coil, and a vapor connection between said tank and dephlegmator.

4. The process of treating hydrocarbon oil which comprises passing oil through a cracking zone wherein it is raised to a cracking temperature and subjected to conversion, introducing the resulting cracked products into a separating zone wherein vapors separate from liquid residue, -withdrawing said liquid residue from said separating zone, passing vapors from said separating zone into a fractionating zone wherein fractional condensation thereof occurs, removing fractionated vapors from said fractionating zone and condensing them as a desired product, removing reiiux condensate from said fractionating zone and introducing it into an accumulating zone, passing fresh charging Vstock in indirect heat exchange relation with vapors resulting from the separating operation taking place in said separating zone, introducing the resulting preheated fresh charging stock into said accumulating zone, removing light fractions from said accumulating zone, as vapors, condensing a portion of the rst mentioned vapors in said separating zone and collecting the resulting condensate free from portions of said liquid residue, passing condensate so collected into said fractionating zone, and removing liquid oil from said accumulating zone and passing it to said cracking zone for conversion therein.

GEORGE C. HARGROVE. WALTER B. MONTGOMERY.

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