US1996091A - Process for converting high boiling point oils - Google Patents

Description

April 2, 1935. R. E. WILSON 1,996,091

' PROCESS FOR CONVERTING HIGH BOILING POINT OILS Qriginal Filedno-j. 1, 1926 Patented Apr. 2 1935 Fl CE PROCESS FOR of Indiana CONVERTING HIGH BOILING POINT OILS Robert E. Wilson, Chicago, n1., assignor a Standard Oil Company, Whiting, Ind., a corporation Application November 1, 1926, Serial No. 145,515

Renewed January 8, 1932 10 Claims.

The present invention relates to improvements in processes for effecting the conversion of higher boiling point distillate oils, such as naphtha bottoms, gas oil and heavier distillates, if desired, into lower boiling point hydrocarbon ing points. following description, illustrated by the accompanying drawing, in which apparatus capable of carrying out the present invention is shown diagrammatically in section.

The drawing shows a sectional view through a furnace and illustrates diagrammatically the arrangement of the tubes through which the oil to be converted is forced in carrying out a process exemplifying the present invention. In the lower portion of the furnace'setting 5 there is provided one or more'combustion chambers 6, to which fuel is supplied by burners I and in which combustion takes place. The walls 8 of the combustion chamber are constructed of a suitable refractory material capable of withstanding the direct heat of the flame; for example, they may be constructed of carborundum or other similar material. Combustion takes place substantially completely within the combustion chambers 6 and the combustion gases pass therefrom into a large flue 9 in the rear of the furnace by which they are conducted to the upper portion of the furnace as hereinafter set forth. A vertical wall or partition Ill separates a compartment above the combustion chamber 6 from the flue 9 which receives the combustion gases, and this compartment, indicated by the numeral 1 I, is closed at its top by the partition l2 of fire brick or other suitable refractory material, such as a suitable chromium-iron alloy. The compartment II is exposed to the radiant surface of the walls 8 of the combustion chambers 6 and is heated substantially entirely by radiant heat therefrom, although if desired, it may be in part heated by combustion gases. The portion of the setting above the compartment ll may be divided into two passes, as by partial partition I; of suitable refractory material. Of these the lower pass is indicated by the numeral l4 and the upper pass by the numeral I5. The combustion gases from the combustion chamber 6, pass upwardly through the vertical flue 9 and then traverse successively the flues l4 and I5, finally reaching the stack l6.

The tubes which receive the oil to be cen verted are mounted within the furnace and are designated individually by the numeral l1. These tubes are connected in series in sections and the pass of the oil therethrough is as follows:

The oil enters the furnace through the inlet pipe l8 and first traverses the economizer section in the pass l5 nearest the stack travelling in countercurrent to the flow of combustion gases.

oils, for example, of the gasoline range of boi1- It will be fully understood from ,the'

This section extends from broken line A to broken line B in the form shown in the drawing. From this section the oil passes through line l9 (suitably a thermally insulated linepassing outside of the furnace) to the screen section of pipes in the pass I 4 first reached by the combustion gases. This pass extends from C to D and through this pass the oil flows concurrently with the flow of the combustion gases. From the last pipe of this section, at the point D, the oil'flows through the line 20 to the lower of the rows of pipes located in the compartment ll, heated by. radiant heat from the walls ofthe combustion chamber 6. The oil then travels in series through the pipes of this radiant'section, first traversing the row of pipes nearest the combustion chamber and then in succession the more remote rows of pipes in the compartment ll, finally making its exit from the last pipe of the" uppermost row ed to the heating action of radiant heat alone and finally again subjected to the heating action of the combustion gases. While the furnace is a preferred type of furnace for carrying out the present invention and the flow of the oil relative to the heating elements as hereinbefore set forth has likewise been found highly desirable, the invention is not limited either to the structure or the particular method of operation shown, as will be more fully hereinafter pointed out. The particular means herein set forth has the advantage that it is readily adaptable to the control of operation which constitutes the present invention.

In operating conversion processes under pressure, it has hitherto been found that the extent of conversion taking place in the coils must be carefully limited to 5, 10 or at most 12 to 13% as a maximum in order to prevent rapid choking of the coils by coking and consequent shut-down therein at least under critical temperatures, will permit the formation of vapor but will maintain the mixture of vapor and unvaporized liquid in the form of a foam in which the vaporized portion is maintained as discontinuous bubbles and 'yet not permit vaporization to the extent that the unvaporized stock carried along as'drops or a film in a vapor medium. For example, with a charging stock passing through the coil of the nature of gas oil, and with a maximum tempera ture attained of about 915 F., a minimum pressure of 1100 lbs. per square inch must be maintained. With variations in the maximum temperature attained, there may be corresponding variations in the pressure required; thus, as an approximate rule, it may be stated that a variation of 15 F. 'in temperature attained in either direction requires a corresponding variation in the minimum pressure required of about 100 lbs. on the oil. Similarly, variations in the charging stock necessitate variations in the corresponding temperature and pressure conditions. Thus, with a charging stock of the nature of naphtha bottoms, a minimum pressure of 1100 lbs. per square inch is required where the maximum temperature attained by the oil'is about 880 F. With this as a guide the required temperature pressure correlation may readily be determined for each charging stock by a short period of observation.

JIn conjunction with the required pressure and temperature conditions as hereinbefore set forth,

"in accordance with my invention there should be a minimum velocity of the oil flowing through the tubes of at least 60 lbs., and preferably of about 80 to 90 lbs. of oil per square inch of tube cross section per minute; and withthis, the heat must be so applied that the metal wall of the tubes (while clean) through which the oil flows is at no point more than 20 F., and preferably not more than F. above the maximum temperature to which the stream of oil is heated. By operating in this manner, the most rapid application of heat occurs while the oil is at a temperature below about 750 F., and the'rate of applicationjof heat decreases as the temperature of the oil increases. Thus, in

the type of furnace shown, after the oil leaves the preheating section extending from A to B, it enters the highly heated section in pass I 4 extending from C to D. The oil is still relatively cool at this time, being substantially below 750 F. and heat is therefore imparted to it at a veryrapid rate while the relatively cool oil prevents excessive to B in pass I5, through which it flows concurrently with the combustion gases, so that the temperatures of the oil and the combustion gases heating it gradually converge and the rate of application of heat to the oil therefore gradually dc- 1,99e,oo1

creases. By operatingin this manner, the conditions required by this invention, that the metal walls of the tubes (while clean) through which the oil flows be at no point more than 20 F. above the maximum temperature to which the stream of oil is heated, may be maintained. This speciflvention are preferably conducted upon oils which .1

may be designated as clean cracking stocks; that is distillate oils the maximum boiling point of which in an Engler distillation at atmospheric pressure is not above 750 F. As set forth, above, ,the particular correlation of temperature and pressure is determined by the precise nature of the oil undergoing treatment. By operating upon such an oil in the manner above set forth,

12 to 20% gasoline or even higher may be pro-- duced from the oil in a single pass without refluxing and without extensive coke formation, the oil preferably being initially preheated to say 400 to 500 F. by vapor heat exchange or by other suitablemeans. The other oils not regarded as-clean cracking stocks may be operated on advantageously in accordance with the present invention, as the extent of conversion and/or length of run may be. greatly increased by its use.

If desired, the products of conversion leaving the coil after being treated in accordance with the invention, may be retained at cracking temperature and pressure in an enlarged chamber for further conversion.

I claim: 1

1. The method of pipe still conversion of hydrocarbon oils under pressure which comprises flowing a distillate oil heavier than gasoline through a. metallicly confined passage heated to cracking temperatures exceeding 850 F., re-

so'that the maximum temperature attained by the metallic walls of the confined passage is not more than 20 F. higher than the maximum temperature attained by the oil.

2. The method of pipe still conversion of hydrocarbon oils under pressure which comprises flowing a distillate oil heavier than gasoline through a metallicly confined passage heated to cracking temperature, maintaining a velocity of flow of the oil through the passage of at least 60 lbs. per square inch of tube cross section per minute, maintaining a pressure upon the oil in the passage such that, at its maximum temperature, it provides a continuous flowing liquid stream in which vapor is present? as discontinuous bubbles, and applying heat to the metallic walls of the passage at a maximum temperature not more than 20 F. above the maximum temperature of the oil.

3. The method of pipe still conversion of hydrocarbon oils under pressure which comprises flowing a distillate gas oil through a metallicly confined passage under pressure, the temperature attained by the oil and the minimum pres- 'attained by the oil.

4. The method of pipe still conversion of hydrocarbon oils under pressure which comprises flowing a distillate gas oil through a metallicly confined passage under pressure, the temperature attained by the oil and the minimum pressure thereupon being so correlated that with a maximum temperature of about 915 F. the pressure is at least 1100 lbs. per square inch and with every 15 deviation from said temperature, a corresponding deviation of lbs. in minimum pressure is permitted, maintaining a veloc-' 'ity of flow of the oil through the passage of at least 60 lbs. per minute per square inch of cross sectional area, retaining the oil within the heated passage until a conversion into gasoline boiling point fractions exceeding 12% of the oil introduced has been effected, and controlling the application of heat so that the maximum wall temperature attained by said passage is not over 20 F. above the maximum temperature attained by the oil.

5. The method of pipe still conversion of hydrocarbon oils under pressure wherein an oil heavier than gasoline is forced to flow through a confined passage in a furnace, applying heat to said confined passage to bring the oil to a temperature in excess of 850 F. in successive stages while maintaining the walls of the passageway at a temperature above the temperature of the contacting oil and not more than 20 F. above the maximum temperature attained by the oil, said-confined passageway and flowing 011 being heated by convection from hot combTi'stion gases in an early stage of the flow, by radiant heat from the combustion chamber of the furnace in an intermediate stage of the flow, and in a later stage of the flow by convection from combustion gases cooled and previously used in heating the confined passageway in said early stage, and maintaining superatmospheric pressure upon the oil within the passageway.

6. The method of pipe still conversion of hydrocarbon oils under pressure inwhich an oil heavier than gasoline is caused to flow through a confined passage and heat is applied to said confined passage to bring the oil to a temperature in excess of 850 F. while maintaining the walls of the passageway at a temperature above the temperature of the contacting oil and not more than 20 F. above the maximum temperature attained by the oil while the oil is flowing in said confined passage through a furnace in successive stages, the confined passage with the flowing oil therein being heated by convection from hot combustion gases in said furnace in an early stage of its flow, and subsequently, in a later stage of its flow, by convection with said combustion gases traveling concurrently with the flow of oil through the passageway, after said gases have" been used and cooled in said early stage of flow, and maintaining a superatmospheric pressure upon the oil within the passageway.

7. The method of converting hydrocarbon oils which comprises introducing oil heavier than gasoline at a temperature below 750 F. into a continuous confined passageway, applying heat to said confined passageway to bring the oil passing therethrough to a, temperature in excess of 850 F. while maintaining the walls of the confined passageway at a temperature above the temperature of the contacting oil and at no point more than 20 F. above the maximum temperature attained by the oil passing through the passageway and retaining the oil in the confined passageway until a conversion into lower boiling oils exceeding 12% of the oil introduced has been effected.

8. In the cracking of hydrocarbon oils, the method of heating which comprises passing a restricted stream of the oil at a high rate of velocity through a radiant heat zone of a furnace and heating the same therein to the desired maximum cracking temperature substantially entirely by radiant heat, thence passing the oil stream through a convection zone of the furnace, passing combustion gases from the radiant heat zone into the convection zone as a source of heat for the latter, and altering the heating characteristics of the combustion gases in transit from the radiant heat zone to the convection 'zone and prior to their use in the heating of oil in the convection zone to maintain the oil at said desired maximum temperature in the convection zone while avoiding any substantial increase in such maximum temperature.

9. In the crackingv of hydrocarbon oils, the method of heating which comprises passing a restricted stream of the oil at a high rate of velocity through a radiant heat zone of a furnace substantially without the main streamof combustion gases and heating the same therein to the desired maximum cracking temperature preponderantly by radiant heat, thence passing the oil stream through a convection zone of the furnace, passing combustion gases from the radiant heat zone into the convection zone'as a source of heat for the latter, and altering the heating characteristics of the combustion gases in transit from the radiant heat zone to the convection zone and prior to their use in the heating of oil in the convection zone to maintain the oil at cracking temperature to thereby effect soaking thereof.

10. In the crackingof hydrocarbon oils, the method of heating which comprises passing a restricted stream of the oil at a high rate of velocity through a radiant heat zone of a furnace substantially without the main stream of gases and heating the same therein to the desired maximum cracking temperature preponderantly by radiant heat, thence passing the oil stream through a convection zone of the furnace, passing combustion gases from the radiant heat zone into the convection zone as a source of heat for

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