US2170169A - Treating hydrocarbon oil - Google Patents

Description

Aug. 22,1939.

0. W. WATSON TREATING HYDROCARBON OIL Filed June 10, 1937 INVENTOR CLAUDE 14447 50 (LA 1%.W

ATTORNEY Patented Aug. 22, 1939 PATENT OFFICE TREATING HYDROCARBON OIL Claude W. Watson, Yonkers, N. Y., assignor to The Texas Company, New York, N. Y., a corporation of Delaware Application June 10, 1937, Serial No. 147,437

2 Claims.

This application is a continuation-in-partof a joint application of applicantsxand' Victor Stapleton, Serial No. 24,794, filed June'4, 1935; which joint application is a continuation of ap= plication Serial No. 475,168, filed August 14', 1930:

This invention relates to the conversion of higher boiling hydrocarbon oils into lower boil enable a higher rate of cracking per pass and to improve the anti-knock or non-detonating properties of the gasoline produced without thereby having a corresponding increase in gas' or coke production. There is a temperature limit to the heat that can be applied to the fresh charging stock without producing excessive deposition of coke; this limitation obtains in the case of the ordinary gas oil charging stocks that are employed in cracking and is true to an even 5 greater extent in cases where a petroleum reside uum is employed as the cracking stock. In accordance with my invention the fresh charging stock is heated, preferably to a cracking temperature, but not to such a high temperature "as to cause excessive deposition'of coke and condensate obtained in the process is subjected to more rigorous cracking conditions of 'a naturecalculated to increase the anti-knock properties of the gasoline product produced. Thus the condensate that is cycled through thecracking zone may be subjected to a cracking temperature for a longer periodof time than that of the fresh charging stock, or the condensate may be subjected to higher cracking temperature than that 'of the fresh charging stock or to both increased temperature and time of reaction, to thereby increase the 'rate of cracking per pass-and increase the anti-knock value of the gasoline product.

Other objects of the invention that may be mentioned are to enable an increase of the charging rate on a given equipment and to increase the thru-put and amount of cracking for a given unit of time.

In a preferred manner of carrying on. the invention the fresh charging stock is passed through a coil or tubular heater wherein theoil is subjected to progressively increasing temperatures so that the temperature of'the oil is increased intransit through the coil until the oil attains a maximum temperature whenit is discharged into the cracking still. If the stock is of a character to permit of a limited amount or cracking being carried on in the coil without danger of excessive coke deposition this cracking may be permitted, although as a rule we prefer to bring the oil to a cracking temperature and'remove it from the heating coil before any substantial cracking takes place. The oil in'the" cracking still is subjected to cracking and dis tillation and reflux condensate obtained from fractionating the evolved vapors is conducted to a cracking coil which is provided with a soaking section so that the oil, after having been brought to a desired cracking temperature, may be maintained at the cracking temperature for a period of time in transit through the coil so that the desired cracking may take place. The oil thus being cracked may then be discharged into the cracking still. In a preferred arrangement the stream of fresh charging stock from the heating coil and the stream of condensate from the cracking coil are merged to form a combined stream of oil at the temperature desired for cracking.

One method of heating the two coils employed in the process is to install theheating coil for the freshcharging stock in a furnace in such a way that the flow of oil through the coil is countercurrent to the flow of furnace gases so that the temperature of the flowing oil Will'thus be progressively increased in transit through the coil and will be discharged therefrom when the highest temperature is reached, while the coil for the condensate is so disposed in the furnace that the flow of oil will be in substantially the same direction of travel as that of the furnace gases, so that the oil at an intermediate point in the coil will reach a maximum cracking temperature beyond which there will be no further rise, the oil being maintained during its transit through the latter part of the coil at a desired cracking temperature.

In practicing the invention I withdraw the liquid from the cracking still at such a rate that there is no material body of liquid oil held in the still. When a liquid body is'held in the still at cracking temperatures coke formation occurs due to the breaking down of the polymers, or. certain high molecular hydrocarbon compounds that are readily reduced to coke or carbon, but by removing the'liquid from the still substantially as it is separated out therein from the vapors and by removing this liquid rapidly from the cracking zone it is possible to prevent the conversion of these polymer bodies into coke, while at the same time to maintain a large volume of vapor in the still held at cracking temperatures so: that conversion in the vapor phase may take place. In this way a gasoline product of high anti-knock value may be produced.

In order to more fully .describe the invention reference will now be had to the accompanying drawing which illustrates examples of the invention wherein:

Fig. l is a diagrammatic sectional elevation showing apparatus constructed in accordance with the invention constituting an embodiment thereof.

Figs. 2 and 3 are partial sectional elevations illustrating modifications of the invention Wherein furnaces with radiant heat sections are employed.

Referring now to the drawing and more particularly to Fig. 1, it will be seen that the apparatus illustrated includes a heating coil A, cracking. coil B, cracking stills C, fractionating tower .D. condenser coil E and distillate receiver F.

The coils A and B are mounted in a furnace I provided with heating means at H and with a flue [2 so that the passage of furnace gases is upwardly through the furnace with the coil B in the hotter section of the furnace. The furnace may advantageously be provided with baffles (not shown) to prevent the channeling of the gases directly to the flue and so as to insure an even distribution of heat in accordance with modern furnace practice. Fresh charging'sto'ck is drawn from a suitable source by a pump 13 which forces D is withdrawn through a line IE to a hot oil pump ll by which the condensate is conducted through a line 88 to the lower end of the coil B. The oil passes upwardly through the coil B and is discharged at the upper end thereof into the .outlet l 9.

It will be noted that the flow of oil through the-coil B follows substantially the flow of furnace gasesso that the oil, after traversing the lower tubes of the coils to which the highest temperature is applied, continues into zones of lower furnace temperatures with the result that in a certain intermediate point in the coil the oil reaches'a maximum temperature beyondwhich point the temperature of the oil does not rise. Thus the latter portion of the coil B affords a soakingsection in which a desired cracking temperature may be maintained for a desired length of time. The flow of oil through the coil A is substantially counter-current to the flow of furnace gases so that the oil in transit is continuously flowing into zones of increased furnace temperature with the result that the oil attains its maximum temperature substantially in a the lowest row of tubes to thereby deliver oil at approximate- .ly the maximum temperature to the transfer line 55,- -There is'thus no appreciable soaking section in the coil Aywhen once the oil has attained its maximum temperature it is rapidly discharged.

The outlet lines l5 and i9 which extend from coils A and B,-respectively, are shown connected toa common transfer line 20 so that the two ployed. The transfer line 20 is shown as eX tending to the upper part of the still 2|. A line 23 interconnects the lower portions of the stills 2| and 22. When connected in this manner the stills are adapted for an operation in which liquid is prevented from accumulating in the stills. Tar or residue lines 24 and 25 extending to a common tar header 26 are shown for withdrawing liquid from the stills. By withdrawing liquid substantially as it separates out in the stills little or no liquid may be maintained in the stills; thus the liquid level may be held below the level of the line 23 by withdrawing tar from both lines 24 and 25, or with both liquid and vapors flowing through the line 23 the tar may be withdrawn through the line 25. In the event the stills are heated the heat may be applied to the stills intermediate their ends and as the liquid that settles out in the bottom of stills outside of the heating zone is rapidly withdrawn the conversion of the polymer products or high carbon-forming oils to coke may be practically eliminated. Instead of heating the stills they may be suitably insulated but. in any event by having practically no body of liquid in the stills, at most only small amounts in the bottoms. the conversion of heavy liquid bodies into coke is practically done away with, while large volumes of vapor are maintained in the stills at cracking temperatures.

A vapor line 2! is shown extending from the still 22 to the fractionating tower D. The fractionating tower may be of any suitable construction, such as a bubble tower, and may be provided with cooling means to control the end point of the overhead vapor fraction and to supply the reflux necessary for fractionation. This cooling may be supplied by providing a cooling coil in the upper part of the tower D, by pumping back to the upper part of the tower a portion of the distillate from the receiver F, by providing the tower with a reflux condenser, or by any other suitable means. A vapor line 28 conducts vapors to the condenser coil E and the condensate is collected in the receiver F having a gas outlet line 29 and a distillate outlet line 30.

In Fig. 2 is shown an apparatus which includes a furnace l0 and coil A, similar to the furnace H1 and coil A shown in Fig. 1. The coil B, hOW- ever, isformed with a radiant heat section 33. Thus hot condensate withdrawn from the fractionating tower D by the hot oil pump ll may be directed through the line I8 to a row or section 34 of the coil B which is subjected to the highest temperature convection gases. The oil passes thence through radiant heating tubes 33 and then flows through the other rows 35 of the coil B. Thus the condensate by being first passed through the row or section of tubes 34 is subjected to the most highly heated convection gases. The oil then passes through the high temperature radiant heat tubes 33 and finally through the remaining section 35 of the convection'tubes B wherein the furnace gases will be at a lower temperature than that applied to the convection tubes 34 or radiant tubes 33, so that the latter} portion of the coil B constitutes a soaking sectior in which the desired cracking temperature may be maintained. The oil in transit through thecoil B may be subjected to a rapid rise in temperature in the section 34 and to a less rapid increase in temperaturein the radiant heatsection .33, withno rise, or onlya comparatively'slight rise, in the section 35,- the oil reaching a point either in the radiant section 33 or at an intermediate point in the final section 35 beyond which the temperature does not rise.

In Fig. 3 a further modification is illustrated in which the radiant heat section of the coil B is composed of an inner row 36 and an outerrow 31. The condensate from the line 18 passes through a convection section 38 which is subjected to the highest temperature convection gases. The oil then flows through the inner section 30 of the radiant tubes and finally through the outer section 31. The radiant heat applied to the section 31 will be of a somewhat lower temperature than that applied to the inner section 36 so that the outer section 3'! of radiant tubes may constitutein effect a soaking section. Thus in the case of the furnace arrangements shown in both Figs. 2 and 3 the oil during the latter portion of its travel through the cracking coil B, after having reached a maximum ternperature, may be maintained at a desired cracking temperature. In this way a sufficient time element is provided for cracking in the coil without, however, allowing an uninterrupted rise in temperature which might cause excessive deposition of coke.

In starting a run it is advantageous to pass the fresh charging stock through both coils A and B until operating conditions have been established and when sufficient condensate is being formed in the fractionating tower D the introduction of fresh charge to the coil B may be discontinued and only the liquid withdrawn from the tower D directed into the coil B. To provide for this starting up operation a valved connection (not shown) may extend from the outlet of the coil A to the inlet of the coil B.

In practicing the invention the liquid separated out in the stills is withdrawn substantially as it is formed to .thereby avoid keeping any material volumeof liquid oil at cracking temperatures in the stills. The outlet l5 of the coil A may be held at temperatures around 850 F. and the outlet IQ of the coil B may be held at temperatures of about 950 F.-9'75 F. With these outlet temperatures for the coils A and B the mass of vapors in the stills C may well be held at temperatures not lower than about 850 F. and preferably at temperatures around 875 F.-900 F. By operating at temperatures of 950 F.-975 F. in the coil B with temperatures of about 850? F.-925 F. in the stills C, it is possible to avoid the excessive gas loss which occurs in the high temperature vapor phase cracking processes and to produce a gasoline product of high anti-knock value which does not have the inferior qualities characteristic of the high temperature vapor phase cracked product and which may be as satisfactorily treated, as by means of sulphuric acid or other treating means, as a strictly liquid phase cracked product. Furthermore, by maintaining the temperature in the cracking stills C at about 850 F.-925 F. while preventing the accumulation of liquid therein, not only is the production of gasoline of high anti-knock value eiT-ected but at such temperatures under the conditions of rapid removal of liquid from the cracking zone a condition of liquidity with respect to unvaporized constituents may be established and maintained which makes possible the continued rapid removal of liquid from the cracking zone and the prevention of the accumulation of liquid therein.

The temperatures stated herein are based on the use of the common charging stocks employed in cracking operations, such as gas oil and crude residuum, and are basedon the use of pressures of several hundred pounds, such as for example 400 pounds, which I have found to be a very satisfactory pressure for the common charging stocks. However, the pressure used may vary from say 100 pounds up to 1000 pounds or even higher. Vapor phase cracking processes have usually been carried on under comparatively low pressures but in the practice of my invention, when carrying on an operation in which practically no liquid is held in the stills C and in which a mas-s of vapors is held therein at cracking temperatures, I prefer to use higher pressures than have been employed in the past and prefer to use pressures in excess of 200 lbs. It may be that the use of this high pressure aids in the production of a gasoline product which, although possessing a high anti-knock value, does not have the inferior qualities characteristic of the usual vapor phase product. As a rule I prefer to use pressure-s of the order of 400 lbs., since maximum yields can generally be obtained at this pressure with the minimum production of gas and coke.

The introduction of stocks of the nature of crude residuum into the cracking stills wherein liquid is prevented from accumulating serves to establish and maintain a condition of liquidity therein with respect to unvaporized constituents which enables the rapid removal of liquid from the cracking zone and the avoidance of coking. When a material body of liquid is maintained under cracking conditions in the cracking zone the introduction of such heavy stocks as crude residuum only serves to aggravate the tendency toward coking therein but when liquid is prevented from accumulating in the cracking zone the introduction of the heavy stock containing constituents which remain unvaporized under the conditions therein actually serves to prevent coking by pro-, ducing. a. sort of flushing action and establishing and maintaining a condition of liquidity adjacent the outlet from the cracking zone enabling the continued removal of liquid therefrom to thus prevent the accumulation of liquid therein. Thus with temperatures in the cracking stills of about 850 F.-925 F. the addition of the heavy stock containing unvaporized constituents to the highly heated stream of cycle condensate from the coil B actually facilitates the continued rapid removal of liquid from the cracking stills to thus prevent the accumulation of liquid therein.

A pressure differential may be maintained between the coils A and B, the coil B being preferably held at the higher pressure, and ifdesired the pressure in the stills C may be maintained lower than that in either or both of coils A and B. A valve is indicated in the transfer line 20 which maybe used for dropping the pressure in' the stills C. A valve is also indicated in the vapor line 21 so that the desired fractionation carried on in the tower D may, if desired, be conducted at a lower pressure than that obtaining in the stills C.

In one method of operation contemplated by the invention the temperatures of the outlets of coils A and B may be substantially the same but by reason of the prolonged time during which the oil in the coil B is subject tothis temperature, or to temperatures inexcess thereof, considerable cracking may take place in the coil B, while in the coil A, on account of the limitation on the time element, there may be little or no cracking. As a rule, however, I prefer to operate with a higher outlet temperature in the coil B.

The invention has in View one method of operation in which the cycle condensate exceeds "in volume that of the fresh charging stock that is passed through the coil A. Thus, for example, the oil passed through the coil B in a given unit of time may be several times the volume of the oil passed through the coil A in a given unit of time. By applying a relatively high temperature to the large Volume of oil passing through the coil B it is thus possible to use a considerably lower temperature in the coil A and yet have the mixture of oil passing through the transfer line 20 at a sufficiently high temperature to accomplish the character of cracking desired. Thus in some cases the temperature to which the oil is brought in the coil A may be even below a temperature adequate for a commercial rate of cracking (for example 600 F.), but by applying a sufiiciently high temperature to the larger volume of oil in the coil B, the temperature of the composite hydrocarbon mixture in the stills C may be maintained sufiiciently high for the purposes desired.

Instead of heating the coils A and B in a single furnace, such as the furnace it, separately fired furnaces may advantageously be used for heating the coils. This arrangement facilitates a greater flexibility in operation over an arrangement in which both coils are heated in the same furnace. In one method of operation contemplated by the invention, the coil B may be heated in a fired furnace and the coil A heated entirely by heat exchange with hot products obtained in the operation. Thus for example, the fractionat' ing tower D may be equipped with interiorly disposed coils through which fresh charging stock may be passed, and in a preferred embodiment one coil may be provided in the upper section of the tower D and another coil may be provided in the lower part of the tower, so that the charging stock may be first brought in heat exchange with the vapors in the upper end of the tower to thus preheat the charge to a certain degree and provide the desired cooling at the upper end of the tower and the preheated charge may then be passed into the coil in the lower part of the tower to be thereby brought into heat exchange with the hot vapors entering from the vapor line 2?, so as to thus absorb excess heat in the vapors and bring the charging stock to a desired temperature for commingling with the highly heated condensate from the coil B and for entry into the cracking still C.

The invention in one of its aspects contemplates the production of a distillate having a maximum anti-knock value with a minimum production of coke and gas. Charging stocks employed in cracking operations vary considerably with respect to the anti-knock characteristics of the gasoline product formed, and in order to show the advantage of the invention in increasing the anti-knock value of the distillate obtained, reference may be had to the treatment of a gas oil charging stock obtained from so-called paraffin base crude petroleum, such as ordinary Mid- Continent crude. Such a charging stock, when subjected to the ordinary cracking conditions employed in the so-called bulk pressure distillation method, in which a large body of liquid oil is held at cracking temperatures, may yield a pressure distillate having, for example, 'an octane number of about 14, (measured as the number of parts of iso-octane added to ten parts of normal heptane) or of about 58 (measured as a percentage of iso-octane in normal heptane).

In the practice of my invention fresh charging stock may be brought to a cracking temperature of, say 850 F. in the coil A, in which there is no soaking section, and from which the heated oil is passed directly into the cracking stills C, and the cycle condensate may be subjected to cracking temperatures in the coil B of about 950 F.-975 F., the cracking temperature being maintained so that extensive cracking may take place in the coil B, after which the heated products are passed directly into the stills C. By rapidly withdrawing liquid separated out in the stills C and maintaining no appreciable volume of liquid therein the stills contain a mass of vapor which may be held at cracking temperatures of, for example, 850 15 1-925 F. under pressures of upwards of 200 pounds, preferably around 400 pounds.

By operating in this way, it is possible to apply to the hydrocarbons temperatures even exceeding 900 F. without obtaining excessive coke production, and under the temperatures employed a high rate of cracking per pass may be obtained resulting in the production of a distillate, as collected in the receiver F, having a high antiknock quality, such for example as having an octane number of around 22-26 (measured as the number of parts of iso-octane added to ten parts of normal heptane) or of about 68-72 (measured as a percentage of iso-octane in normal heptane) or even higher. The cracking in the vapor phase, which takes place in the still C, appears to aid in the production of the high anti-knock product, and by using the moderate temperatures employed, as compared to the high temperatures usually employed in vapor phase cracking processes, the excessive production of gas and coke is avoided. Furthermore by carrying on the operation under higher pressures than have been employed in vapor phase cracking methods, not only is the production of gas reduced but the production of a distillate of high anti-knock value is promoted. It may also be noted that While the hydrocarbons are subjected to temperatures sufficiently high to produce the desired high antiknock product that nevertheless no liquid oil containing high carbon-forming polymer products is unduly subjected to cracking temperatures. Thus, in the coil A the fresh liquid charge is brought to a cracking temperature but is not subjected therein toany soaking time. The reflux condensate, which is passed through the coil B, may be subjected tomorerigorous cracking conditions than the fresh charging stock without forming excessive quantities of coke, so that cracking of combined liquid and vapor constituents may take place in the coil B. The products from both coils A and B are, however, passed into the stills C from which the liquid constituents are immediately withdrawn so that cracking with respect to the liquid constituents is limited while the cracking of the vapor constituents is prolonged in the stills C especially in the second still 22. Thus a gasoline product may be produced having a maximum anti-knock value, but with a minimum production of coke and gas.

Obviously many modifications 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.

I claim:

' 1. In the conversion of higher boiling hydrocarbon oils into lower boiling ones, the process that comprises introducing a stream of oil comprising liquid and vaporous constituents at cracking temperature into the upper part of an enlarged cracking chamber, maintained at a cracking temperature under superatmospheric pressure, wherein liquid is prevented from accumulating, passing a condensate stock through a heating coil wherein the condensate is heated to a cracking temperature and utilizing the resultant heated products to constitute at least a portion of said stream of oil introduced into the upper part of said enlarged cracking chamber so that conversion of the hydrocarbons occurs by means of the heat supplied by said heated products, causing vapors and non-vaporized oil to flow downwardly in an unobstructed path through said cracking chamber, removing resultant products comprising vaporous and liquid constituents from the lower part of said cracking chamber and introducing them into the lower part of a subsequent cracking, chamber wherein conversion is continued and wherein vaporous products rise in an unobstructed path, maintaining said subsequent cracking chamber at a cracking temperature under superatmospheric pressure, removing liquid residue from the lower part of said subsequent cracking chamber at a rate adequate to prevent the accumulation of liquid therein, removing separated vapors from the upper part of said secondary cracking chamber and passing said vapors to a fractionating zone wherein they are fractionated to separate out a condensate and subjecting said condensate to cracking.

2. In the conversion of higher boiling hydrocarbon oils into lower boiling ones, the process that comprises introducing a stream of oil comprising liquid and vaporous constituents at cracking temperature into the upper part of an enlarged cracking chamber, maintained under superatmospheric pressure, wherein liquid is prevented from accumulating, passing cycle condensate through a heating coil wherein the condensate is heated to a cracking temperature and utilizing the resultant heated products toc'onstitute at least a portion of said stream of oil introduced into the upper part of said enlarged cracking chamber so that conversion of the oil constituents occurs by means of the heat supplied by said heated products, causing vapors and non-vaporized oil to flow downwardly in an unobstructed path through said cracking chamber, removing resultant products comprising vaporous and liquid constituents from the lower part of said cracking chamber and introducing them into the lower part of a subsequent cracking chamber wherein conversion is continued and wherein vaporous products rise in an unobstructed path, maintaining said subsequent cracking chamber under superatmospheric pressure and effecting a separation of vapors from liquid residue therein, maintaining a temperature in both of saidcracking chambers of upwards of 850 F., removing liquid residue from the lower part of said subsequent cracking chamber at a rate adequate to prevent the accumulation of liquid therein, removing separated vapors from the upper part of said secondary cracking chamber and passing said vapors to a fractionating zone wherein they are fractionated to separate out a condensate and directing said condensate to said heating coil.

CLAUDE W. WATSON.

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