US2036965A - Cracking system - Google Patents

Description

mi 7, 1936. I G. c. HA'mRovE 2,036,965

CRACKING SYSTEM Filed March 4, 1951 2 Sheets-Sheet 1 VINVENTYOR 5' 650/565 C/lea/earz Aprifi 7, 1936. c HARGRQVE 2,036,965

CRACKING SYSTEM Filed March 4, 1931 2 Sheets-Sheet 2- INVENTOR f zaez (7742690 1 BY w TTONEY Patented Apr. 7, 1936 PATENT OFFICE CRACKING SYSTEM George 0. Hargrove, Westfield, N. J., assignor, by

mesne assignments, to Gasoline ProductsCompany, 1110., Newark, Delaware Application March 4,

2 Claims.

My invention relates to pyrolytic processes and more particularly to a process for increasing by cracking relatively heavy hydrocarbons, the yield of light products within a gasoline range.

It has been found in cracking processes of the so called tube and tank type, which make use of a heating coil and reaction chamber, that in order to obtain the greatest yield from the stock charged without excessive coke formation, a considerable percentage of hydrocarbon must be recycled through the system. It has previously been undesirable to increase the reaction period to permit a greater conversion per cycle because of the considerable formation of carbon and coke in the system.

My process consists primarily in permitting an increase in the conversion and reaction period while maintaining a relatively low recycle ratio, by removing and fractionating the first vapors formed in a reaction chamber, allowing further conversion if desired of the remaining liquid, vaporizing this latter portion at reduced pressure and fractionating the vapor fraction formed.

One of the primary objects of my invention is to obtain a greater once through yield of hydrocarbons within the gasoline range and reduce the recycled stock ratio.

A further object is to obtain a cracking process in which the character and amount of the residuum products may be closely controlled.

Another object of my invention is to obtain a dry coke containing a low percentage of volatile matter.

I have shown in the drawings Figures 1, 2, 3, and 4 diagrammatic representations of various modifications of an apparatus suitable for carrying out my process. Referring to the drawings] in which like reference characters denote like parts, reference character I of Figure l designates a heating coil of conventional type which discharges the heated hydrocarbons to an auxiliary soaking drum; 2. The vapor products from this soaking drum are discharged through the line 3 controlled by the valve 3', to the fractionating tower 4. The liquid from the drum 2 is discharged through the line 5 controlled by the valve 5 to the soaking drum 6. This drum may be of the conventional vertical type used in the tube and tank process. The liquid and vapor products in the soaking drum 6 are withdrawn through .the line 1 controlled by the valve 1 and discharged into an evaporator 8 which is at lower pressure than the soaking drum. The vapors are withdrawn from the evaporator through the line 9 controlled by ,the valve 9 N. J., a corporation of 1931, Serial No. 519,927

and discharged to the fractionating tower 4. The liquid products in the evaporator may be removed through the line Ill controlled by the valve It and passed through a cooler to storage. The vapors from the top of the fractionating 5 tower are withdrawn through the line H, condensed in the condenser I2 and passed through the line 13 to storage or to other equipment where further processing may take place. Recycle stock may be removed from the bottom of the fractionating tower through line l4 controlled by the valve M to the accumulator l5. Fresh feed maybe admitted to the accumulator through the line I6. Charging stock for the heating coil is withdrawn from the accumulator 15 through the line ll by the pump I8.

The equipment shown in Figure 2 is similar to that in Figure 1 except that the vapor line 3 from the auxiliary soaking drum 2 is combined with the vapor line 9 from the evaporator to form the line 9 discharging into the fractionating tower 4. The combination is made in such a manner that the high velocities of the vapors from line 3 give an injector action in line 9" and thus cause a siphon effect in line 9.

Referring to Figure 3, reference character l8 denotes a heating coil or pipe still from which the heated products are discharged to a soaking drum l9. Vapors from the upper part of this soaking drum are discharged through the line 20 controlled by the valve 20" to the fractionating tower 2|. Liquid products are withdrawn from the bottom of this drum through line 22 and the reducing valve 22' to the evaporating chamber 23. Vapors formed in this chamber are discharged through the line to the fractionating tower 2|. The liquid products are withdrawn from the evaporator through the line 25 controlled by the-valve 25. They may be passed through a cooling coil or a heat exchanger to storage as desired. Vapors are taken ofi from the top of the fractionating tower through the line 26 and passed through the condenser 21 from which the condensed products and vapors may be passed through the line 28 to a separator and thence through other processing equipment or to storage. Liquid products may be withdrawn from the fractionating tower for recycling through the line 29 and discharged to the accumulator 30. Fresh feed may also be admitted to the accumulator through the line 3!. The charging stock for the heating coil I8 is withdrawn from the accumulator by means of a pump 32 and passed through the line 33 to the coil.

Figure 4 is similar to Figure 3 except that the lines 20 and 24 from the soaking drum and the evaporator respectively are combined to form the line 24" before entering the fractionating tower. Here again as already described in connection with Figure 2, the connection between the lines forms an injector causing a siphon effect in line 24. V V

The operation of my process as shown by the apparatus in Figure 1, is as follows: i

The feed is withdrawn from the accumulator l5 through the line H by means of the pump I8 and charged to the heating coil I. The oil is brought to cracking temperatures of between 700 degrees and 1,000 degrees Fahrenheit and discharged to the auxiliary soaking drum 2. This drum may of the common soaking drum type used with tube and tank equipment. I have shown it in a horizontal position in Figures 1 and 2. This is a preferred arrangement, but the drum may be put, of course, in a vertical position. Vapors formed in this chamber are withdrawn through the pressure reducing valve 3 and the line 3 and discharged into the fractionating tower 4. Liquid is withdrawn from this auxiliary soaking drum through the line 5, preferably without any substantial reduction of the pressure and discharged to the soaking drum 6. Products from the soaking drum 6 may be discharged through the line I and the pressure reducing valve 1 to the evaporator 8 where vaporization takes place, the vapors being discharged into the fractionating tower 4 and the tar residue withdrawn from the system through the line H].

The vapors are removed from the auxiliary soaking drum 2 to a section where conversion can no longer take place and thus the tendency is eliminated to form fixed gases and non-condensables by over cracking the desirable light components already formed in the soaker 2.

By withdrawing the vaporous products formed and present in the auxiliary soaking drum through the line 3, it is possible to allow a greater time for conversion of the remaining liquid than could be permitted in the usual tube and tank arrangement. Inasmuch as cracking is dependent for one thing upon time, by increasing the time element for reaction a greater percentage of conversion takes place and thus an increased yield is obtained.

It is to be noted that the drawoif from the auxiliary soaker 2 is from the bottom so that the liquid products therein are discharged to the vertical soaker 6. The greater percentage of carbon formed is deposited in the soaker B, the operation being arranged preferably so that no substantial amount of coke is formed in the auxiliary soaker. It is found that most desirable conversion conditions are obtained with this process and that very little carbon will be precipitated in the evaporator 8.

Under certain conditions in operating the apparatus outlined above, it may be found that the quality and quantity of fuel oil or tar bottoms withdrawn from the bottom of the evaporator cannot be controlled to the most advantageous degree desired. There may be, for example, considerable gas oil left in the tar bottoms due to the fact that there is not sufficient carrying effect of the lighter vapors in the evaporator to carry the gas oil into the fractionating tower. To overcome this difficulty, I have arranged my apparatus as outlined in Figure 2. I have obtained a siphoning effect upon the evaporator by uniting its discharge line 9 with the vapor discharge line 3 from the auxiliary soaking drum. The pressure through the line 3 can be made considerably greater than the pressure through the line 9 due to the fact that there is a much greater pressure in the auxiliary soaker 2 than in the evaporator tower 8. Therefore, by discharging the high pressure vapors from the line 3 into the line 9 in the manner of operation of an injector, a siphon effect can be produced and the evaporator 8 run at a comparatively low pressure if desired. By this means a close control may be maintained upon the fractions taken from the evaporator tower, and a dry coke removed from the evaporator 8.

It is possible, of, course, by means of my process to operate without the formation of a residuum, but rather to separate all of the volatile material in the soaking drum or evaporator so that only a coke will be left therein. This is particularly true in operating with the siphon effect which I have disclosed in Figure 2. By operating in this manner, the major portion of the coke, of course, will be left in the evaporator 8. In such a case the equipment would be designed to facilitate the removal of the coke. Inasmuch as the heavy ends would thus be taken over into the fractionating tower, their separation and removal could take place therein. A second fractionating tower could, of course, be added to the equipment shown in order to complete the fractionation of the over head products. Such an addition would not depart from the spirit of my invention.

In Figure 3, I have shown a diagrammatic outline of a modification of the apparatus shown in Figure 1 which is suitable for carrying out my process. Charging stock is forced through the heating coil I 8 by means of the pump 32 and the heated products discharged into the soaking drum [9 which may be of the conventional form used in the tube and tank process and which may be positioned either vertically or horizontally. From this soaking drum, I can discharge the vapors directly through the line 2B and the reducing valve 20' to the fractionating tower 2|. The liquid products I withdraw from the line 22 and the reducing valve 22 and discharge to the evaporator tower 23 where they are flashed. The vapors from the evaporator pass to the fractionating tower and the tar residue or fuel oil is drawn off through line 25. By withdrawing through the line 20 as vapor a portion of the volume of hydrocarbons which has been discharged into the soaking drum, it is possible to keep the remaining volume in the soaking drum at cracking conditions for a greater period of time than would normally be the case. Thus a greater amount of conversion is permitted. Furthermore, I prevent the formation of excessive amounts of fixed gases and non-condensables by withdrawing vapor of desired characteristics before conversion of them has proceeded to an undesirable extent.

In this type of operation there also may be some difliculty in obtaining a close control over the fractions formed in the evaporator. In order to obtain the closest control, I have arranged to obtain a siphon effect by means of the comparatively high pressure vapors discharged from the soaker through the line 20 and thereduction valve 20'. I have shown an arrangement in Figure 4 in which I have combined the vapor discharge lines to the fractionating tower forming a single line 24" in such a fashion that by an iniii) iii)

jector action of the vapors from line 20 a siphon effect is produced in line 24 and in the evaporator 23. I am thus able to operate the evaporator at comparatively low pressures and obtain a coke containing a low percentage of volatile matter, for example, less than volatile matter.

It should be appreciated also in connection with the equipment shown in Figures 3 and 4 as already pointed out in connection with the proc-v ess and apparatus outlined in connection with Figures 1 and 2, that a non-residuum operation can be carried on in which all volatile matter is carried over from the evaporator or vaporizer 23, only coke remaining therein. In such an operation the major portion of the coke formed in the system would be found in the evaporator 23 rather than the soaking drum I9 and of course, the design of the evaporator would have to be such as to permit the removal of the coke. Such a non-residuum operation is facilitated by means of the siphon eiIect disclosed in connection with the apparatus indicated in Figure 4.

It is seen, therefore, that I have obtained a process in which the conversion time may be considerably increased without the usual attendant disadvantages of unprofitable coke formation. This permits a greater percentage of desirable cuts to be formed and also permits a lower recycle ratio. Greater once through yields of the desired light products are obtained with this process because of the greater conversion and also because of the removal of the light products as soon as they are formed and their further conversion into undesirable products eliminated. By means of the unique siphoning arrangement which I have disclosed, I am able to obtain a very close control of the products from my evaporator and furthermore, I am enabled to operate the evaporator at lower pressures and yet obtain a greater percentage of hydrocarbons overhead.

In a specific operation in the embodiment shown in Figures 1 and 2 the following pressures may be employed. The heating and cracking coil I may be maintained at its outlet under a pressure of about 750 lbs. and substantially the same pressure may be maintained in the reaction chambers 2 and 6, although if desired chamber 6 may be maintained under a somewhat lower pressure than that maintained in chamber 2 and, if desired, chamber 2 may be maintained under a somewhat lower pressure than that maintained in coil I. It is to be understood, however, that sufficiently high pressures are to be maintained in the coil l and chambers 2 and 6 to maintain a substantial portion of the oil in liquid phase. Similar pressures may be employed in the coil l8 and chamber iii in the modification illustrated in the other Figures (3 and i).

In connection with the pressures mentioned above, the fractionating tower (4 or 2|) in Figures 2 and 4 may be maintained under a materially lower pressure, say for example, pressures between about 100 and about 200 lbs. and the low pressure distilling chamber, or evaporator (8 or 23) may be maintained at a still lower pressure, say from 25 to 50 lbs., although atmospheric or subatmospheric pressures may be maintained in the distilling or evaporating chamber. When the latter mentioned pressures are maintained in the low pressure distilling or evaporating chamber it may be desirable to maintain lower pressures within the fractionating tower (4 or 2|), say pressures of from about 50 to 100 lbs.

In the apparatus shown in Figures 1 and 3 the fractionating tower (4 or 2|) is maintained under a pressure somewhat lower than the pressure maintained in the low pressure distilling or evaporating chamber (8 or 23).

It will be apparent to those skilled in the art that there are certain modifications which could be made and which would not depart from the spirit of my invention. 1, therefore, do not wish to be limited by the specification and drawings, but only by the appended claims.

What I claim is:

1. The method of cracking hydrocarbon oils for the production of relatively lower boiling oils therefrom which comprises subjecting such oil to cracking under a high superatmospheric pressure, separately withdrawing vaporous products from said cracking operation and passing them to a fractionating operation maintained under a materially lower superatmospheric pressure, separately withdrawing liquid residual products from said cracking operation and passing them to a second cracking zone wherein they are subjected to further cracking under superatmospheric pressure, discharging substantially all of the fluid products from said second zone into a distilling zone maintained under a pressure substantially below that maintained in said fractionating operation wherein vaporous and non-vaporous products are separated, withdrawing vapors from said low pressure distilling zone and forcing them into said fractionating operation by the energy of the vapors flowing under high pressure from said first-named cracking operation to said .fractionating operation.

2. The method of cracking hydrocarbon oils for the production of lower boiling oils therefrom which comprises flowing said oil through a heated zone in a confined stream and heating it during its flow therethrough to a cracking temperature while maintaining the said stream under a high superatmospheric pressure, discharging the stream of oil into an enlarged zone maintained under a high superatmospheric pressure wherein separating of cracked vaporous and liquid residual products results, separately withdrawing separated Vapors from said enlarged zone and passing them in a confined stream to 1 a fractionating zone maintained under a materially lower pressure, separately withdrawing liquid residual products from said enlarged zone and discharging them into a distilling zone maintained under a pressure materially below I the pressures maintained in said enlarged zone and said fractionating zone whereby vaporizable constituents of said residual products are separated in the form of vapors, separately withdrawing evolved vapors from said reduced pressure distilling zone and commingling them with the said stream of vapors under high pressure flowing to said fractionating zone from said enlarged zone, said commingling of the vapors being so effected that the stream of vapors under high pressure have an injector action on the vapors from the reduced pressure distilling zone, thereby ejecting the latter vapors from the distilling zone to maintain a reduced pressure therein and to cause the latter vapors to be forced into the said fractionating zone maintained under the said higher pressure.

GEORGE C. HARGROVE.

Images