US1891218A - Cracking process for hydrocarbon oils - Google Patents

Description

Dec. 13, 1932. D. PYzEL CRACKING PROCESS FOR HYDROCABON OILS Filed July 24, '1:9212- q llwwm! SFS M701?.- aA//a Fria,

5MM Z@ TToRMSYJ Patented Dec. 13, 1932 UNITED sTATEs PATENT OFFICE DANIEL PYZEL, OF PIEDMONT, CALIFORNIA, ASSIGNOR, BY MESNE ASSIGNMENTS, TO UNIVERSAL OILv PRODUCTS COMPANY, A CORPORATION 0F SOUTH DAKOTAl CRACKING PROCESS FOR HYDROCARBON OILS Applicatidn filed July 24, 1922. Serial No. 576,926.

Myinvention relates to the art of cracking hydrocarbon oils. It is a well known fact that many of the natural petroleum oils and t-heir derivatives may have the molecular structure materially modified by subjecting them simultaneously to heat and pressure, this operation being commonly termed cracking. The cracking reaction changes the molecular structure of certain portions of the oil producing oils thatcontain a smaller number of carbon atoms per molecule than A the original oil. Such oils are lighter, more volatile, and commercially more valuable than the original product. A rearrrangement of the molecule may be accomplished by adding hydrogen but in the ordinary cracking process it is accomplished by converting the oil in'to a lighter portion having a smaller number of carbon atoms per molecule, and a heavier portion having a much larger number of carbon atoms per molecule than the original oil. free carbon or it may be a tar or other substance containing a considerable proportion of carbon. All such substances whether free carbon or semi-solid carbonaceous substances having a large proportion of carbon are hereinafter referred to as carbon.

y Many 'petroleum oils, (and by petroleum oils, as used herein, I mean natural petroleum oils' or their derivatives) when subjected to heat readily break up to set free carbon and produce an oil having a lower carbon content. The actual breaking up and rearrangement of the oil requires some time, however, so that it is not only necessary to raise the oil to a cracking temperature, but it is also necessary to maintain the oil at or near that temperature for a sufficient time to allow the cracking reaction to tak'e place. It is also necessary, in the case of many oils,- to maintain the oil under pressure during the entire time of the cracking reaction.

- The prior wrt processes have been devised for cracking oils.

These processes have .been carried on, for

The heavier portion may be example, in two general types of apparatus, namely:-

A (A) Stills of large volume in which the oil 1s heated under pressure. In devices of this character the still may be first charged with oil and as the reaction progresses fresh oil may be run into the still, the lighter cracked products being taken off as vapor until the amount of carbon in the oil becomes so high that the carbon commences to deposit on the walls and particularlyv on the heated surfaces of the still. This is often disastrous to the still as these deposits have a high heat insulating value and as soon as deposition v the pressure necessary for the reaction. It

is therefore necessary to use such processes largely on oils which do not produce large amounts of carbon upon being cracked and it is also necessary not to carry the concentration of carbon in the still too high.

(B) Apparatus in which a considerable portion or all the heating is done in tubes the oil passing through these tubes and being delivered into large reaction chambers in which the cracking reaction takes place and in which carbon is deposited. The capacity of the reaction chamber to receive the depositedcarbon limits the amount of oil that can be run through, it being common practice to run until the reaction chamber becomes so full of carbon that it is necessary to shut down and clean it out.

In both forms of apparatus, it is common practice to provideeither a large still,or a large react-ion chamber which is operated under pressure and in which the carbon accumulates as the cracked products are distilled oil' therefrom. In both types of apparatus the carbon increases until it is necessary to shut down and clean it out, the amount of the oil that it is possible to run at one batch being limited to the capacity of the still or reaction chamber to safely contain the carbon. Since the apparatus may be run at temperatures as high as 900 degrees Fahr. it is uneconomical to shut down and thoroughly cool it for cleaning and the cleaning operation is both expensive and troublesome. Moreover the manufacture of large stills or reaction chambers having a diameter of from six to ten feet capable of withstanding considerable pressures is both difficult and expensive and these big stills or reaction chambers containing oil under high temperatures and pressures form a very serious property and life hazard. Moreover the operation of both types of apparatus requires a very high degree of technical supervision since in the operation of both types there is a danger point in carbon concentration beyond which the operation cannot be safely carried.

Objects of invention The object of my invention is to provide an apparatus for, and process of, cracking petroleum oils which may be operated continuously over long periods under high temperatures and pressures and in treating .oils

which produce a large proportion of carbon.

A further obj ect of the invention is to provide a means for preventing depositions of carbon in those portions of the apparatus subj ected to heat and pressure.

Further objects and advantages will be made evident hereinafter.

Desmiptz'on and method of operation Referring to the drawing which is diagrammatic I employ a feed tank 1 from which the oil to be treated is taken by a feed pum 2 and delivered into a heating coil 3. his coil consists of a plurality of tubes contained in a heating furnace 4 which is heated by any suitable means such as an oil or gas burner 5. The oil in passing through the coil 3 is heated by the products of combustion in furnace 4 about the coil 3 to cracking temperature or to a temperature 'quite close to such a cracking temperature. The oil passes through the coil 3 at such a velocity that there is very little tendency to deposit carbon therein.

The oil at or near the cracking temperature is passed from the coil 3 into and through a series of reaction coils 10. These coils consist of tubes carried in reaction furnaces 14 which are heated by any'suitable means such as an oil or gas burner 16. The oil in the reaction coils 10 is held at or near the cracking temperature during its passage therethrough by means of the products of combustion inside the furnaces 14. The cubical contents of the reaction coils and the rate of iow of the oil therethrough are made such that the oil is held at a cracking temperature for a sufficiently long period to effect an economical cracking thereof. At the same time the pressure established by the pump 2 is maintained in the heating coil 3 and the reaction coils 10, this pressure being sufficient to prevent complete vaporization of the oil in the heating and reaction coils, thus keeping the reaction within the limits of the two phase (liquid and vapor) reaction7 The oil is delivered from the reaction coils 10 through a valve 20. After passing through the valve 20 the heated oil is delivered through a central jet into an injector 21, the space around this central jet in the injector being supplied with cold oil through a pipe 23. The pressure is reduced by the valve 20 and the injector 21 to at or near atmospheric' pressure. The cold oil mixing immediately with the heated products delivered from the valve 20 forms a mixture which is at a very much lower temperature than the cracking temperature in the heating and reaction coils and this temperature is further reduced by passing the mixture through a condenser 25. The condenser reduces the mixture to temperatures not much in excess of atmospheric.

The cooled mixture is then passed through a gas trap or separator 28 and into the first of a series of settling tanks 30, passing sucoessively through these tanks and into a receiving tank 31. The cooling oil' delivered to the pipe 23 is taken from one of the settling tanks 30 and delivered under some pressure to. the injector 21 by means of a pump 29. The gas from the gas trap 28 may be used for fuel in the heating and reaction furnaces.

In the settling tanks 30 the carbon largely settles out of the oil and the oil ,may be finally taken from the receiving tank 31 and fractionated in any of the various and well known manners. This oil consists of a mixture which is materially lower in carbon and commercially much more valuable than the oil originally delivered to the feed tank 1.

In starting up the apparatus to prevent carbon deposition, it is desirable to .circulate the oil through a circulation line 40 from the receiving tank to the feed tank which may be accomplished by a transfer pump 41. Each of the settling tanks 30 is provided with a'by-pass pipe 50 so that it may be cut out of service for the purpose of olea-ning out the carbon that accumulates therein. Since these tanks are under atmospheric pressure and substantially under atmospheric temperatures, they may be of very cheap construction and of large capacity. A drain pipe 60 allows any tank 30 to be drained at will.

Advantages of process It will be seen that the oil is rst quickly heated to a cracking temperature in the heating coil 3 and then maintained at or near that temperature in the reaction coils 10. The necessary heat to maintain this temperature and supply heat for the cracking reaction and the vaporization of light products is supplied through the walls of the reaction coils 10, from the burners 16. The proportion of the coils 10 is such that the oil moves therethrough with sufiicient rapidity to prevent deposition of carbon therein but sufficient time is allowed to allow the cracking reaction to take place. Since the coils 10 are of small diameter their effective heating surface is large. For example, if the reaction coils are three inches in diameter their eective surface will be twenty four times as great as the effective surface of a cylindrical still six feet ,in diameter and of the same cubical contents as the reaction coils 10. This allows the same amount of heat transfer as in the case of the large still with one twenty-fourth the dierence in temperature between the gases of combustion outside the tubes and the oil inside the tubes and this low temperature of the hot gases inside the reaction furnaces 14 prevents overheating of -the tubes and consequent deposition and baking of carbon thereon. Also the movement of the oil in the tubes is sulficiently rapid to further greatly increase the eiiciency of heat transfer and considerably increase this ratio of twenty-four to one. Moreover the first cost and cost of maintenance and repair of small tubes is greatly less than that of large stills, and the factors of safety of the tubes can be economically made much higher than is possible in large stills or reaction chambers.

It will be further seen' that the cracking pressure is maintained throughout the heating and cracking coils and that it is released 'in the valve 2O and the injector 21. A release in pressure would naturally result in an immediate vaporization ofthe lighter and more volatile portions of the oil. If this vaporization were allowed to take place freely, the

cracked fractions' would immediately be set free -as vapor and there would immediately be a. strong tendency of the carbon Ato deposit on any surface to which it would cling. This would be due in part tothe fact that the carbon 'and particularly the heavy tarry hydrocarbons are held more or less in solution in the more volatile portions of the mixture and the vaporization of these volatiles would be accompanied by a corresponding depositionw lof the dissolved heavy tars and carbons.l This deposition is prevented by the immediate injection and mixing of cold oil with the mixture of hot products leaving the reaction coil. This injection not only cools the mixture and thus prevents vaporization of the more Volatile oils contained therein but it also supplies additional volatiles from the settling tanks which volatiles have been in a measure freed from their solids and semi-solids by settling.

It will further be seen that although my process does not and cannot prevent the for-v 30 which are not under pressure and which can therefore be readily cleaned beingbypassed so that the process need not be inter-4 rupted during the cleaning operation.

I claim as my invention:

1. A' process for the conversion of hydrocarbon oils consisting in heating a stream of oil to a cracking temperature, in passing such heated oil through a reacting zone where the oil is maintained under a superatmospheric pressureand' where a substantial portion of the oil remains in liquid phase, in continuously introducing said oil to a zone of lower pressure in such a manner as would permit vaporization of said oil, and in checking such .vaporization by introducing regulated quantities of acooling medium to said zone of reduced pressure.

2. An oil conversion process consisting in heating a stream of hydrocarbon oil in a coil to a cracking temperature above the boiling point of the constituents thereof, in passing such oil through a reacting zone where cracking occurs, in maintainlng a superatmospheric pressure on the oil in said heating coil and said reacting zone to prevent vaporization of a substantial portion of said oil, in continuously introducing said heated oil to a zone of reduced pressure, and in substantially checking the vaporization of said heated oil by the regulated introduction of a cooler mass of hydrocarbon oil to said zone of reduced pressure.

3. A continuous process for the conversion of hydrocarbon oil, consisting in advancing a stream of oil through a heating zone to be heated to a cracking temperature, in passing said heated oil through a reaction zone where conversion occurs, in maintaining a superatmospheric pressure on the oil stream and on the oil in such reaction zone to prevent vaporization of a substantial quantity of said oil, in introducing said heated oil to a zone of lower pressure in such a manner as would permit vaporization of the chemical constituents thereof, and 'in substantially checking such vaporization of the heated oil by the introduction of a regulated quantity of cooler oil to said zone of reduced pressure.

In testimon whereof, I have hereunto set my hand at an Francisco, California, this 14th day of July, 1922.

DANIEL PYZEL.

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