US1724476A

US1724476A - Pyrogenetic cracking process

Info

Publication number: US1724476A
Application number: US226306A
Authority: US
Inventors: Richard W Hanna
Original assignee: Standard Oil Co
Current assignee: Standard Oil Co
Priority date: 1927-10-15
Filing date: 1927-10-15
Publication date: 1929-08-13
Anticipated expiration: 1946-08-13

Description

Aug 13, 1929.. R. w. HANNA PYROGENETIC CRACKING PROCESS Filed Oct. 15. 1927 Timmy;

womikv Patented Au 13, 1929.

UNITED STATES PATENT OFFICE.

RICHARD W. HANNA, OF IPIEDMONT, CALIFORNIA, ASSIGNOR TO STANDARD OIL COM- A IPANY, OF CALIFORNIA, OF SAN FRANCISCO, CALIFORNIA, A CORPORATION OF DEL AWARE.

rYnoGEnETIo-caAcKrne rnoonss;

Application filed October 15, 1927. Serial No. 226,306.

This invention relates to the art of c0nverting relatively high boiling point hydrocarbon oils such as mineral or petroleum oils into oils of relatively lower boiling point constituents by the use of high temperatures and pressures above atmospheric, a process of the type generally known as pyrogenetic cracking.

. When certain oils, such as those derived from California, or asphaltic base crude oils, are-subjected to pyrogenetic cracking, it is found difiicult to obtain a high yield of low boiling point constituents or naphtha without at the same time forming a heavyresiduum which will not meet the requirements of a commercial fuel, chiefly because the process results in the heavy residuum having a high sediment content. It is also difficult with such oils to obtain reasonably high yields of naphtha; or gasoline like constituents, without forming excessive quantities of coke within the system.

As ordinarily practiced, the mineral oil undergoing cracking treatment is passed through a furnace or heating zone into an enlarged reaction chamber from which vaporization may or may not take place and from which the liquid residuum is withdrawn.

The A. P. I. gravity of the liquid within thereaction zone of such processes is ordinarily much lower than that of. the feed oil, and an attempt is usually made to retain the oil in this vaporizing and reaction chamber for a long period of time. I

It has been discovered that theformation of carbon deposits and excessive quantities of coke in the cracking process, and also the formation of a residuum containing a high sediment content is dependent upon the length of time that the oil undergoing cracking is maintained in the reaction zone. Apparently the cracking reaction proceeds first with the formation of low boiling point constituents or naphtha and a heavy residuum, and if such heavy residuum is maintained at the cracking temperature for: a long period of time it undergoes further reaction,- princicracking temperature in a heating zone in whlch the oil passesth rough tubes or pipe coils located in afu'rnace. This results in the disadvantage of exposing a very large surface to extremely hot gases and thereby favoring the formation of coke in the tubes or pipe coils with the'result that the coke clogs the same, and arts thereof are overheated and decomposed It is an object of the present invention to provide a process for the pyrogenetic crack ing of mineral oils in which the difficulties and various disadvantages before mentioned can be overcome. More specifically, it is an object of the present invention to provide a pyrogenetic'cracking process in which a high yield of desirable gasoline like naphtha or.

low boiling point constituents may be obtalncd without the formation in the process of material quantities of coke and with the formation of aliquid residuum of suitable sedi ment content for use as commercial fuel.

In the process of the present invention, the formation of coke and sediment in the residuum to be withdrawn from the process is maintained at a minimum by holding the oil undergoin the cracking reaction in the reac-' tion zone or a comparatively short period of time, and thereby discharging from the reaction zone the heavy residuum more rapidly after its formation, I In order to obtain in the reaction zone a proper amountof cracking of the oils, provision is made in the process for bringing the temperature of the oil undergoing treatment in the reaction zone to a high reaction temperature, so that the comparatively short reaction period may still result in substantially thesame extent of cracking as obtained in the usual processes. ,The process of the present invention provides a means for raising the oil to be treated-to the high reaction temperature without the disadvantage of a high rate of heat supply in the furnace of the cracking process, and with a low rate of formation of coke i'n-the tubes orjpoils within such furnace This is accomplished, in the recess of the present invention, by first pally with the formation of carbon or cokp eatin the oil in such furnace at a comparaand an increase in its sediment content, and

this reaction takes place without any sub-' stantial increase in the amount of desirable low boiling point constituents to be produced in the process.

.Furthermore, in the ordinary crackin process the oil to be treated is raised. to the Y tively ow pressure and to such temperature final heating of the oil to a temperature suflicient to effect a rapid cracking reaction is accomplished by compress ng the material undergoing treatment, thereby adding to the temperature of the mass through the heat of compression of the vapors formed in the furnace of the process.

The invention will be fully understood, together with various additional objects and advantages thereof, from a description of a preferred form or example of a process of cracking oils embodying the present invention. For this purpose there is hereinafter set forth a preferred example of aform of cracking process embodying the invention, the cracking process being described in connection with the accompanying drawings, which illustrate one form of an apparatus on which the process of the present invention may be performed. In the drawings, diagrammatic elevation of the cracking process.

Referring to the drawings, 1 represents a pipe or line which communicates with a suitable tank, not shown, which constitutes the supply of oil which is to be treated by this process. For example, thejoil of the process may be a gas oil of a gravity of 27 to 30 degrees A. P. 1., derived from a California crude oil. This feed oil is drawn through line 1 by suitable means such as the pump'18', and forced through a :pipe coil or heating 1 tubes 4, which are placed in a suitable furnace 5. In its passage through the coil or tubes 4., the oil is heated to a temperature preferably such as is only sufiicient to effect an incipient or moderate cracking of the oil. The oil passes in a rapid relatively small stream through'the heating zone so that all portions of the oil are heated to, a .uniform temperature. For example, the oil is heated in its passage through the coil or tubes 4' to a temperature of heating zone the heated oil preferablypasses directly into a separation zone or surge chamber 6. The pressure on the system at this point imposed by the combined action of the pump 18 and the heating is comparatively low, and'such as to permit a material formation of vapors from the oil undergoing treatment.- For example, the pressure maintained 50 uponthe oil in the heating zone or coils a and the separation zone or surge chamber 6'is about 250 pounds per square inch gauge.

In the separation zone or surge chamber 6 the vapors formed are permitted to separate from the liquid. The vapor is withdrawn through line '2 by a compressor 9,

which thereupon compresses the vapors to a substantially higher pressure, or sufficiently compresses the vapors as to draw a material quantity of heat from the heat of compression of such vapors. For example, in the preferred form of the process the vapors are compressed from 250 pounds to 600 pounds per square inch. This results inthe condensation of a part at least of the vapors. The

the figure represents a about 800 degrees 'F. From theliquid from the separation zone 6 is likewise drawn through a line 8 by a pump 10, and is forced at a similar pressure through the line 8 into a reaction zone or chamber 11, Which is preferably larger than the separation chamher 6. The liquid here meets the compressed gases, which enter through line 7 and the commingled mass has been raised to a materially higher temperature than the oil in heating coils 4, such as to permit a rapid cracking reaction to take place. For example, the temperature of the oil is '50 degrees higher than that to which the oil is raised in the heatin", zone 4, or the temperature of the oils is about 850 degrees'F. The proc- 'ess of the present invention, therefore, results in the oil being passed to the reaction zone or chamber 11 at a temperature materially above that at which the oil left the heating zone or furnace 5 of the process and without the necessity of the extraneous application .of heat which would result in a rapid formation of coke.

.In the reaction zone or chamber. 11 the desired cracking is regulated by the time andother operating conditions maintained in the react on zone or chamber. Preferably, a

relatively small volume of liquid to vapors is maintained in the reaction zone 11. The relative quantities of vapor and liquid to be held therein are adjusted by the position of the exit line 13 and valve 12. The line 13 leads to a vapor fractionating or separating zone .or tower 14, preferably entering the same at a point somewhat above the bottom. The process is not dependent upon any specific form of tower, as any tower which willfractionation, clean separation of is void of parts"w hich clog'easily give good cuts, and with coke may be employed. For example,

a suitable form of tower is one having its lower portion equipped with several baflles x19to serve as mist extractors,'and having in int its upper portion a number of bubble-cap plates 22 from one of which a line 16 leads to the suction side of the pump 18. The line 16 serves as a means for recycling interme-' diate boiling point constituents separated in the fractionating zone for further cracking in the system. Preferably, at the top of the tower near the vapor exit there is provided a coil 20 orother means through which cooling fluid may be circulated in the desired amount so as to prevent loss of any hydrocarbons suchas could by recycling be further decomposed to give a larger yield of desirable low boiling point oils. employed may be water or may be a part of the feed stock which will thereby be pre heated,.and so economize on the heat necessary to be supplied in the furnace 5.

Within. the separation zone 14 the hydrocarbon oil is separated into three compo nents; one, the desired low boiling point constituentswhich pass off as vapors; second, the

The cooling fluid to be cal intermediate boiling point constituents which are recycled in the process and, third, the heavy residuum which is reduced to suitable properties as to oil. ing point constituents leave the separation zone 14 as vapors and pass through line 15 that within the reaction zone 11, for example,

the pressure in the separation zone 14 is above 200 pounds per square inch. In the preferred form" of theprocess the valve 12 in line 13 thereof operates as a pressure releasing valve, releasing the pressure from about 600 pounds to 200 pounds per square inch, and is the dividing point between the high and low pressure zones. At the bottom of the separation zone or tower 14 is a line 17 by means of which the heavy liquid collected in the space ,below the plate21 is withdrawn from the system. This heavy residuum is usually about 9 to 12 degrees A. P. I. in gravity, and suitable for use as a commercial fuel.

Formed as in the process of the present invention, it is found exceptionally free from sediment, and because of its prompt and complete removal from the system tends to prevent excessive coke formation in the process.

All lines and chamber shown are preferably heavily lagged or insulated to prevent, as far as possible, heat losses by radiation. Exception to this may be made in the separation zone or tower 14, as it may be desirable to leave parts of the same bare to take advantage of air cooling. The process of the present invention is preferably a continuous process. I

A material advantage of the present process resides in the fact that the cracking reaction may be carried on under high pressures which are maintained, however, only on the reaction zone and not upon the heating zones or vapor separating systems. Another advantage of the present invention resides in the fact that an exceptionally. high reaction temperature is maintained in the reaction zone and a higher degree of cracking attained without the application of'high temperatures in the heating zone. In this way surface cracking is minimized and the process produces less carbon and gas.

While the process of the p'resent invention is well adapted to carry out the objects of the present invention, it isunderstood that various modifications and changes in the de:

tails of the process may be made without departing from the-present invention, and the present invention includes all such modifica- The desired low boiltions and changes as come within thescope of the following appended claims.

I claim:

1. A process of cracking mineral oils which.

comprises heating the oil under pressure to a temperature sufiicient to form vapors from such oil, then separating the oil into vapors and liquid, separately raising the pressure I on said vapors and liquid and recombining the same whereby the oil is materially raised in temperature by the heat'of the compression of the vapors and brought to a pyrogenetic decomposition temperature, and passing the oils into a reaction zone.

2. A process of cracking mineral oils which comprises heating the oil under pressure to a temperature sufficient to form vapors from such oil, then separating the oil into vapors and liquid, separately raising the pressure on said vapors and liquid and recombining the same whereby the oil is materially raised in temperature by the heat of the compression of the vapors and brought to a pyrogenetic decomposition temperature, passing the oils into a reaction zone, and therein maintaining a comparatively small volume of liquid to vapor.

3. A process of cracking mineral oils which comprises heating the oil under pressure to a temperature suflicient toformvapors from such oil, then separating the oil into vapors and liquid, separately raising the pressure on- 1 said vapors and liquid and recombining the same whereby the oil is materially raised in temperature by the heat of the compression of the vapors and brought to a pyrogenetic decomposition temperature, passing the oils into a reaction zone and therein maintaining a comparatively small volume of liquid to vapor, withdrawing the oil from said reaction zone, and separating and recycling an intermediate fraction thereof.

4. A process of decomposing or cracking mineral oils which comprises continuously passing oil into a heating zone under pressure to thereby raise the oil to a temperature of incipient or moderate cracking and vaporize a part of said oil, continuously separating the oil into vapor and liquid, continuously and separately raising the pressure on said vapor and liquid and continuously recombining the same, whereby the heat of the compression of said vapors materially raises the temperature of the oil and the oil is brought to a high reacting temperature, and continuously passing the oil into a reaction zone.

5. A process of decomposing or cracking mineral oils which comprises continuously passing oil into a heating zone under pressure to thereby raise the oil to a temperature of incipient or moderate cracking and vaporize a part of said oil, continuously separating the:

g por and liquid and continuously 'recombinrating the oil into desired low boiling point ing the same, whereby the heating of the comconstituents, intermediate constituents and 10 pression of said vapors materially raises the heavy residuum, and continuously recircutemperature of the oil and the oil is brought lating the intermediate point constituents to a high reacting temperature, continuously through the heating zone to said reaction zone. passing the oil into a reaction zone, continu- Signed at San Francisco this 1st day of ously removing and releasing part only of the October, 1927. i pressure on said oil and continuously sepa- RICHARD W. HANNA.