US2162300A - Process for treatment of hydrocarbons - Google Patents

Description

June 13, 1939.

J. FARRELL ET AL PROCESS FOR TREATMENT. OF HYDROCARBONS Filed May 17, 1935 .ruxui O2 3000 INVENTOR. JAMES L. FARRELL BY GERALD A. IBACH ATTORNEYS.

(ZEDu Patented June 13, 1939 PATENT OFFICE PROCESS FOR TREATMENT OF HYDRO- CARBQNS James L. Farrell and Gerald anew, whims burg, Tex., assignors to Phillips ll etrnlemn Company, Bartles'viile, @kla, a corporation of Delaware Application May 17, 1935, Serial No. 22,078

2 Claims.

This invention relates to the treatment of hydrocarbons and relates particularly to an improved process for the thermal conversion of petroleum hydrocarbons, and is particularly applicable to that type of conversion process utilizing tube coils in which the petroleum hydrocarbons are heated under pressure to conversion temperature and then are discharged through a pressure release valve into a separating chamber.

A principal object of this invention is to prevent the formation and deposit of carbon in the transfer line from the tube coils to the separating chamber of a hydrocarbon conversion still and in the pressure release valve.

Another object is to cool the highly heated fluid passingthrough the transfer line of a hydrocarbon conversion still in such a manner as to prevent the formation and deposit of carbonaceous matter inthe transfer line while at the same time avoiding a substantial drop intemperature of the fluid. v

A principal object of this invention is to cool substantially only a thin film of the heated hydrocarbon fluid passing through the transfer line,

- 5 withouts'ubstantially cooling the main mass of In petroleum conversionprocesses, such as the cracking of heavy oils to gasoline and the reforming of lighter oils, it is conventional practice to use tubular heating coils mounted in-a suitable furnace in which the petroleum stocks are heated to suitable conversion temperatures under pressure for a sufllcient period of time to effect the desired degree of conversion. The converted fluid is then passed through a pipe to a separating chamber where the fluid is separated into liquid and vapor fractions. This pipe is conventionally referred to as the transfer line. in the transfer line, usually in the immediate w vicinity of the separating chamber, is located a pressure relief valve for the purpose of controlling the pressure maintained on the fluid passing through the heating coil.

One of the chief difliculties encountered in the 4 operation of a processsuch as is described above 50 difficulty have been advanced.

Among the principal methods at present employed in an attempt to overcome this difliculty are those which involve rapid cooling of the fluid in the transfer line below an active reaction tem- -perature by indirect means such as heat ex- At some point changers and by direct introduction of relatively cool oil into the fluid. In the latter case the 0001 oil may be introduced before pressure release or after pressure release and frequently into the passages of the release valve itself in an effort 5 to prevent carbon deposits from clogging the valve. Both of these methods, while to some extent succcssful, are subject to certain disadvantages.

Heat exchangers of the high temperature, high 10 pressure type necessarily required for such service are relatively expensive and relatively complicated in design and are generally not preferred for such service.

Introduction of relatively cool oil is chiefly dis l5 advantageous in thatwhen the mixture of cool oil and converted fluid are introduced into the separating chamber, the liquid separated therein from vapors will contain a relatively large quantity of lighter constituents condensed as a result the direct introduction of cooling oil into the 30 converted fluid passing through the transfer line. Our invention contemplates the cooling of a small portion of the transfer line in such a man- .ner as to cool by indirect heat exchange a relatively thin annular'film of the heated fluid pass- 3 ing through the transfer line without substantially cooling the entire mass of fluid passing through the transfer line.

Our inventionis based upon the following theory:

When the products of a conversion reaction are 40 emitted from the conversion coil, tar is present, evidently in the form of a finely divided fog. This tar and lighter oils condense and forma film of relatively high viscosity on the inner wall of the transfer line and due to its viscosity and the friction set up by the wall of the transfer line, this film apparently moves at arelatively slower speed than the rest of the fluid through the transfer line. to the high temperature, for a relatively long time, of the fluid being transferred, which temperature is always far above the coking temperature of the tarfilm. Upon pressure release the oils or liquids lower in boiling point than the u Therefore the film is subjected tar are vaporized, subsequently leaving the tar deposited in the film on the inner wall of the transfer line. This condition results in coking of the transfer line film or of the same film within the passages of the control valve.

Since, in practice, this tar film cannot be prevented from forming, we have experienced that by cooling the outside of the transfer line at the point of tar film formation, and at the point of coke formation, the tar film temperature can be reduced to a point where coking of the tar will not occur.

We do not attempt to lower the temperature of the entire volume of converted products in the transfer line but merely attempt to control the film temperature within the transfer line or pressure control valve. This is accomplished, in a simple manner by placing an annular jacket about a short section of the transfer line and about'the passageways through the pressure release valve and circulating cooling fluid through the jacket in quantity sufllcient only to'cool the tar film below an active coking temperature without substantially lowering the temperature of the entire mass of converted products passing through the transfer line.

By our method of operation the temperature of the mass of converted products will generally not be lowered more than 10 F. and frequently less than 10 F., though this lowering can be increased to some extent without effecting another material advantage arising from our procass. This advantage lies in the fact that the converted products after passing from the transfer line through the release valve into a separating chamber will be at very nearly the same high temperature to which the hydrocarbons were heated in the conversion coil. i As a result the liquid tar contained in the products will be separated from vaporous materials at such high temperature and will be substantially free of lighter constituents and there is then no problem of a further separation step to remove lighter constituents from the tar. After the tar has been separated from the vapors in the separating chamber its temperature may be lowered 'below a coking temperature by any conventional manner such as cooling by steam.

We have found that our film cooling method need be applied only to a relatively short section of the transfer line, generally in the immediate vicinity of the pressure release valve. A section of the transfer line from 3 to 10 feet in length usually provides suflicient heat transfer surface to accomplish the desired purpose. The entire transfer line may be jacketed and cooled in the described manner if desired but this is usually not necessary.

The cooling fluid used may bejrelatively heavy oil, water, gas under pressure, volatile liquid or some form of artificial refrigeration may be used if desired.'

Other objects and advantages of our new invention will be readily apparent from the following description read in conjunction with the attached drawing which diagrammatically illustrates one form of apparatus which may be used in practicing our invention.

Referring to the drawing, a pipe I in communication with a supply of hydrocarbon oil, not shown, leads to a pump 2 from the discharge side of which a pipe 3 leads to a tubular heating and conversion coil 4 mounted in a suitable furnace I. A transfer line G leads from the outlet of conversion coil 4 into a separating chamber 1. In

aiqaeoo the drawing separating chamber l is diagramrnatically illustrated as a fractionating .tower and a liquid discharge pipe 9 leads from the lower portion of chamber 1. A. pressure release valve lit is shown in this particular modification to be placed at the discharge end of'the transfer line 6 but may be located at any other point in the transfer line 8. An annular jacket ii surrounds transfer line 5 and a pipe l2 leads from one end of jacket H into cooler Hi from which a pipe it leads to a pump l5 from which a pipe it leads to the other end of jacket I i. A pipe ill in which is mounted a valve IS, in communication with a suitable'source of supply of cooling fluid leads into pipe M.

The above apparatus will be utilized in the following manner when effecting conversion of hydrocarbons, for example in the reforming of naphtha.

Naphtha to be reformed will be drawn through pipe I by pump 2 which will pump the naphtha through pipe 3, thence through conversion coil 4 and transfer line 5 into separating chamber 1. In passing through conversion coil 4 the naphtha will be heated by heat generated in furnace 5.to a temperature of about 940 F. and maintained substantially at that temperature 'in coil 4 until reforming of the naphtha is as complete as desired. By manipulating pressure release valve 10 in transfer line 6, any desired pressure, generally above 100 pounds per square inch, may be maintained on the naphtha during its passage through the coil land transfer line 6. When the products of the naphtha reforming are released into separating chamber 1, they will separate into vaporous and liquid fractions, the vapors leaving the separating chamber 1 through pipe 8 and the.

To 4 control the temperature of the tar film which liquid leaving chamber 7 through pipe 9.

6 and will then flow from the other end of cooling jacket ll through pipe l2 which leads through cooler I3 into pipe l4 and thence to pump i 5, and the heat picked up by the cooling fluid as a result of contact with the hot wall of transfer line 6 will be removed in passage through the cooler 13. When sufficient cooling fluid has been introduced through pipe II to supply the cooling system, valve ll in pipe l'l will be closed and the cooling fluid will be continuously circulated through jacket ll, pipe I2, cooler l3, pipe l4, pump 15 and pipe l6 backto cooling jacket ll. Cooling fluid will be circulated at such a rate that while the tar film on the inside of transfer line 6 will be cooled below a carbonizing temperature, the mass of reformed material passing through transfer line 6 will not be substantially cooled. In this particular case, where the temperature of the reformed material at the point where transfer line G'ente": cooling jacket II is about 940 F., the temperature of the reformed material at the point of vaporization in valve It! will be about 930 F. v 1

By thus maintaining thetemperature of the reformed products at about 930 F., the liquid separated in chamber I from vapors will be substantially free of lighter constituents and will consist almost entirely of very heavy asphaltic material, which can then be cooled by flowing steam therethrough or by indirect; heat exchange with other fluid, etc.

By preventing coking of the tarfiim in the transfer line in the above described manner 'we have been enabled to lengthenthe average operating cycle of reforming stills from ten days or less to thirty days or more. i

We claim:

1. In a process for the conversion of hydrocarbons which comprises heating hydrocarbons to a conversion temperature under pressure and discharging the heated hydrocarbons through an elongated confined passageway into a separating zone, the improvement which comprises cooling a portion of said passageway by indirect heat exchange suiiicient to cool the thin film of conversion products adjacent the surface of thepassage to a temperature sufliciently low to prevent carbonization of said film, but so controlled that the remaining products passing through said passage will remain at substantially the conversion temperature.

2. In a process of converting hydrocarbons wherein the same are subjected to conversion conditions of time, pressure and heat in a conversion zone and then passed by way of a transfer line and then with reduction of pressure therein into a separation zone, the improvement of inhibiting the formation of coke in said transfer line which comprises circulating a cooling medium within a jacket about said transfer line and in indirect heat exchange relation with the conversion products therein at a point exteriorly of and immediately adjacent said separation zone and at a point in said line before'said reduction of pressure on said conversion products, regulating the cooling effect of said medium in such a manner that only those products which constitute the outer annular film thereof and which make direct contact with said transfer line to a temperature below that of which carbonization of said products constituting said film takes place, but the total, conversion products entering said separation zone are cooled not to exceed 10 F.

JAMES L. FARRELL. GERALD A. IBACH.

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