US2121026A - Process for refining and converting oils - Google Patents

Description

June 2l, 1938. c. B. FORWARD PROCESS FOR REFININGHAND CONVERTING OILS Filed May 5, 1932 un-DWAIII' MmZOn :05...

Patented June 21, 1938 UNITED STATES PATENT OFFICE Chauncey B. Forward, Urbana, Ohio, assignor, by mesne assignments, to Forward Process Company, Dover, Del., a corporation of Dela- Application May 5, 1932, Serial No. 609,405

Claims.

'I'he present invention relates to the cracking of hydrocarbon oils in the vapor phase. More particularly the invention relates to an improved process for converting crude petroleum or highboiling point distillates thereof into synthetic gasoline or other low-boiling point distillates. The present process is a continuation in part of the inventions disclosed in my copending applications for patent, Serial No. 682,477, led December 24, 1923, and. Serial No. 330,490, led October 13, 1919, now Patent No. 1,903,810 granted April 18th, 1933.

Prior application Serial No. 330,490 filed in 1919 discloses a process for cracking petroleum oils containing heavy residues in which the oil was passed through coil sections mounted in preheaters and heated to a temperature suflicient to vaporize a substantial proportion of the oil. The resulting vapors and unvaporized oil constituents Were then discharged into a vapor liquid separator in which the heavy residual constituents were separated from vapors. The vapors were then passed at high pressure through a plurality of coil sections and heated to a high cracking temperature to convert the oil constituents into a very high percentage of gasoline or motor fuel content and a relatively small proportion 01E free carbon. The stream of vapors from the cracking coils was passed at high velocity into an enlarged chamber in which the free carbon was separated from the vapors. The vapors from the carbon separating chamber Wereconducted to a condensing system in which the desired gasoline product was recovered.

Prior application Serial No. 682,477 discloses a process for cracking hydrocarbon oils, particularly distillates, which are completely Vaporizable, by passing the distillate through a vapor heat exchanger in heat exchange with high temperature vapors produced in the cracking operation. The preheated oil was then conducted through a plurality of heating coils and brought to a temperature of approximately 850 F. after which it was passed through a further series of coils Where cracking was effected at temperatures of approximately 975 F. The oil vapors passing through the cracking coils were converted into a substantial proportion of gasoline and a relatively small proportion of free carbon. The resulting mixture was conducted from the cracking coil into an enlarged carbon settling column Where a temperature of from 850 to 900 F. was maintained solely by the heat of the vapors introduced into the column in which some further cracking occurs. The free carbon was settled out in the carbon settling column and the remaining vapors conducted to the heat exchanger for preheating the oil stock to be cracked. The vapors were fractionated to recover a gasoline produced in the cracking operation. A pressure of from 200 to 500 poundsvper square inch was maintained in the enlarged carbon settling column.

'I'he primary object of the present invention is to provide a method of converting high boiling oil to lower boiling products in a manner yielding a high percentage of high quality product Without production of substantial amounts of low grade liquid and solid residue.

To accomplish this object, the principal feature of the invention contemplates the treatment of the crude petroleum or other high-boiling oil and vapors thereof, in a continuously and rapidly flowing stream of relatively small cross section, to the successive steps of:r preheating; vaporization under pressure; separation of any unvaporized liquid; exposure of the iiowing vapor stream under high pressure to cracking temperatures for a period lof time suiiicient to effect substantial cracking while passing the vapor stream through the cracking zone at a velocity at which formation and deposition of coke or sludge in the cracking zone is prevented. Any

' free carbon formed is deposited at the discharge end of the cracking zone in a dry, flulfy form; separation of such carbon from the cracked gasoline vapors being accomplished by simple gravity settling in a carbon collecting chamber through whichl the cracked vapors pass at retarded velocity before entering the first element of the cooling and condensing train. Other objects and features of the invention will be apparent from the following description.

In the accompanying drawing I have shown in diagram apparatus adapted for the practice of the process of the present invention.

As illustrated in the accompanying drawing, the crude petroleum or high boiling oil distillate to be treated is forced under high pressure by'a pump I0 through preheating coils I2 within a hot vapor heat exchanger I4. After passing through the heat exchanger land therein becoming preheated to a temperature of about 300- 400" F., the oil passes underpressure through a pipe I6 into the iirst of a connected series of coils I8 of pipe of small diameter and great length. The first pipe coil I8 is mounted in the first member 20 of a connected series of heating, vaporizing and cracking chambers 20, 22, 24, 26, 28, 30, 32, 34, 36 and V38. After flowing through coils I8 in chamber 20 the oil continues its flow successively and uninterruptedly through similar coils I8 mounted in each of the chambers 22, 24, 26, 28 and 30. In passing successively through the coils of heat exchanger I4 and the rst few heating chambers 20 to 30, the oil is gradually heated to a temperature of about 850 F., so that all of the gasoline and higher boiling point components of the oil are vaporized, leaving only a small amount of the heaviest ends of the oil in an unvaporized liquid state. After passing through the coils I8 of chambers 20 to 30, the mixture of oil and vapors is discharged, still under high pressure and temperature, into a separatoi` 40. Due to the decrease in velocity of flow of the oil and vapor mixture through the enlargedv cross section of the separator 40, gravity separation of the unvaporized liquid residue from the major vaporized fraction of the oil takes place therein prior to the subjection of the vapors to substantial cracking.

Anyliquid residue collected at the bottom of separator 40 is continuously discharged through valved pipe 42 and conducted to a cooler 44, and thence to a storage tank 46. The oil vapors are conducted from the top of separator 40 by a continuation of coiled tubing I8 in a rapidly flowing stream successively through the coils of the vapor phase cracking zone of the apparatus in heating chambers 32, 34, 3S and 38. In this cracking zone the vapors are further heated under high pressure, (i. e., 200 to 500 pounds per square inch or more) to temperatures of 950 to 1000 F. Y

The cracked vapors issuing from the last chamber 38 of the cracking zone are conducted by a continuation of tubing I8, still under high pressure and temperature, through a valved inlet 48 into a carbon settling chamber 50. In chamber 50 the velocity of flow of the cracked oil vapors is reduced to a point where gravity separation takes place of the cracked vapors and any carbon formed in the cracking Zone. The drop in velocity flow of the vapor stream results from the relatively large cross section of the chamber 50 as compared to the small cross section of the coils I8 of the vaporizing and cracking elements. The relatively small amount of carbon formed as a decomposition product of the cracking operations in accordance with the present process is notable for having uniformly dry and finely powdered iuiy characteristics, resembling carbon black.

The process contemplates high Velocity of flow of the oil vapors through the cracking tubes of the apparatus,-i. ethrough the coils I8 of chambers 32 to 38 inclusive, and a prolonged time of exposure of the vapors to cracking temperatures in the chambers 32 to 38 and in the settling chamber 50, so that no deposition of coke or sludge takes place at any point in the' cracking tubes. The above-noted characteristics of the carbon residue of the cracking operation of the present process result apparently :from the controlled differential conditions of rapid turbulent flow of vapors and prolonged time of exposure of vapors to cracking temperatures and pressures in apparatus of the type, and with the small dimensioned cracking tubes of great length, illustrated in the accompanying drawing.

From the carbon precipitator 50 the cracked vapors pass out at a temperature of about 850 F. to 900 F. through valved pipe 5,2 into the Vapor heat exchanger I4, where they are cooled by direct heat exchange with the crude forced through the coils thereof by pump I0. High boiling point oils are separated from the cracked vapors by condensing in exchanger I4, and the lower boiling point cracked gasoline vapors pass out of the exchanger through a valved pipe 54 and are conducted through the coils of a condenser 56 and thence through a train of condensing and reiining apparatus (not shown).

The oil vapors in separator 40 are maintained under high pressure and at a temperature up to 800 F. to 850 F. The cracked oil vapors entering the carbon settling column 50 are maintained preferably under pressures of 400 to 500 pounds or higher and temperatures of 960 F. to 980 F. The temperature of the vapors drops during their sojourn in chamber 50 to about 850 F. to 900 F.

The dry, fluiy carbon which `collects in precipitator 50 gradually accumulates and may be periodically removed through a relatively large valved pipe 58 to a second sealing chamber 60. From chamber 60 the carbon may be removed while the plant is operating without danger of lire, through a manhole 62, during periods when communication between chamber 00 and precipitator 50 is cut off by closingr valved connection 58. All of the heating chambers, heat exchangers, separators, and pipes conveying and holding the steam, hot oil and vapors are thoroughly insulated against heat losses with asbestos or other suitable heat insulating material.

Heating of the crude oil and vapors passing successively through the tube coils I8 of chambers 20 to 38 may be effected by indirect heat exchange with superheated steam or hot furnace gases passed successively in reverse direction to the flow of crude and vapors, through chambers 38 to 20 inclusive. When superheated steam is used as a heating medium, it is preferably generated in coils 64 of a flash boiler 66 to which feed water is continuously fed by a high pressure feed pump 68. Superheated steam at a temperature of 1150 F. to 1200 F. or higher and under a pressure above 250 pounds, is conducted from the boiler directly to manifolds 70, thence through the chambers 32--38 forming the cracking zone of the apparatus. After passing through chambers 32-38 the steam is conducted successively through the chambers 30--20 forming the preheating and vaporizing zone, from the rst element 20 of which the steam nally exhausts at a pressure of -200 pounds per square inch into a drum 'I2 having a valved offtake 54. The temperature of the steam in chamber 30 is maintained at about 850 F. to 900 F., and the temperature of the steam in drum 'I2 is normally maintained at about 400 F., or in other words at a temperature at which it is still suitable for use in industrial heating and for power purposes.

Valves are mounted at suitable points in the pipe connections wherewith to regulate and maintain the proper Working pressures in the oil preheating, vaporizing and cracking Zones. Likewise valved pipe connections are provided between the boiler or equivalent source of heating fluid and the separators whereby to permit preliminary heating of these apparatus elements in starting operations. Valved pipe connection 'I6 between chamber 60 and condenser 56 serves to release the small amount of vapors accumulating under pressure in chamber 60 periodically as a result of blowing carbon thereinto from the the time.

. carbonsettiingxcolurnn; Manhoie 1'4la1iords'intheliquidlstatethrough an elongatedzone 0f re` take place `in the coil section I8 mounted in vaporizing chamber 30, but the major portion ofthe cracking takes place in the coils of the cracking. zone `(chambers 32-38 inclusive) and in' carbon settling column- 50".

The heavy oil taken off from the bottomy of heat exchanger I4 throughvalved offtake '18, as well as that taken oif from the bottom of separator 40, carries substantially no free carbon in solution and accordingly is in a condition where it can be put through the process again,

either by itself or blended with some of the cru-de or distillate originally run.

The lower 3 to 5 rows of pipe in the flash boiler may be made of specially treated tubing or calorized pipe which will withstand several hundred degrees higher vtemperature than ordinary steel tubing without oxidizing. Since no direct heating of the oil pipes by re or llame is used in this process there is no excess localized heating of the oil. By reason of that fact, and the speed of travel of oil and vapors through the relatively small pipes composing the cracking coils, no Ideposit of coke or carbon occurs in them and the pipes are never fouled on that account and are as clean at the close of a run of any lengthof time as they were at the start, thus permitting continuous operation with no loss of time or expense to clean out the coils.

The temperatures and pressure specified both may vary considerably according to the grade or kind of oil being run through the apparatus at Likewise the character of cracked products obtained may be affected considerably by variation of the rate of iiow of oil and vapors through the system, as well as by the temperatures and pressure obtaining in the cracking zone. The temperatures and pressures claimed are those which practice has found to be approximately average when treating Mid-Continent oils but it will be understood that the method could still be operated to advantage commercially at higher or lower temperatures and pressures than those specifically stated above.

The invention having been thus described, what is claimed as new is:

1. The process of refining and converting oil herein described, consisting in preheating a continuously flowing stream of oil gradually and under high pressure, in heating this preheated oil to a higher temperature while under high pressure and separating the vapors and residue while under high but decreased pressure and prior to substantial cracking, in further gradually heating a rapidly flowing stream of said vapors at a temperature in excess of 950 F. and under high pressure to crack them in the vapor phase by maintaining a forced circulation of a fluid heating medium in indirect heat exchanging relation therewith, and in subsequently precipitating substantially dry carbon from the vapors by decreasing the speed of the vapors while maintaining them at cracking pressures and temperatures.

2. In a process of converting oil, comprising heating a rapidly flowing stream of oil of re-;

, stricted cross section to a temperature in excess of 750 F. and separating the vapors generated thereby from unvaporized oil without substantial cracking, passing the separated vapors substantially free from hydrocarbon constituents in stricted. cross sectionfat high velocity whereby all components are maintained in intimate admixture and gradually superheating the vapors thereinto a temperature in excess of 950 degrees F., discharging the superheated vapors into an enlarged zone' wherein the velocity of said vapors is reduced, maintaining the temperature of the vapors in said enlarged zone above the cracking temperature and controlling the time of exposure ofv said vapors t'ol'the cracking treatment.` inthe last mentioned elongated heating zone and in said enlarged zone so as to permit the precipitation of only substantially dry carbon in said enlarged zone.

3. 'I'he process of cracking mineral oils which comprises passing the oil constituents to be cracked while substantially all in vapor state and at an initial temperature of about 800 to 850 F. in a confined stream and at high velocity through a heating and cracking zone, heating the oil vapors of said stream to a cracking temperature of approximately 1000 F. and effecting substantial conversion of said vapors in said zone, passing the resulting highly heated vapors into an enlarged externally unheated digesting zone in which the vapors are maintained at a cracking temperature solely by the heat from the vapors passed into said enlarged zone, maintaining a pressure of from 200 to 500 lbs. per square inch in said zones, maintaining the heating and cracking conditions in said Zones such that a substantial portion of said vapors areconverted to constituents suitable as motor fuel, precipitating substantially dry carbon from the vapors in said enlarged zone by decreasing the velocity of the vapors introduced thereinto from said heating and cracking Zone, passing the resulting cracked vapors from said enlarged zone, and recovering a condensate suitable as a motor fuel from the vapors passed from said enlarged zone.

4. The process of cracking mineral oils which comprises passing the oil constituents to be cracked While substantially all in vapor phase in a confined stream and at high velocity through a heating and cracking zone, heating the oil vapors of said stream to a cracking temperature of from 950 to 1000 F. and effecting substantial conversion of said vapor stream to lower boiling constituents in said zone, passing the resulting highly heated vapors into an enlarged digesting zone, passing the introduced vapors through said enlarged Zone at a relatively reduced velocity in substantially unobstructed flow and precipitating therein only substantially dry carbon present or formed in the vapors introduced into said enlarged digesting Zone, maintaining a superatmospheric pressure in said zones of two hundred pounds per square inch i and maintaining the vapors in said zones a sufflcient length of time to convert a substantial portion thereof to constituents suitable as motor fuel, passing the resulting cracked vapors from said enlarged zone, and recovering a condensate suitable as a motor fuel from the vapors passed from said enlarged Zone.

5. The process of converting mineral oil into lower-boiling products, which comprises subjecting mineral oil traveling in a stream of relatively small thickness to heat at temperatures below that at which substantial cracking takes place but sufciently high to vaporize a desired portion of said oil while leaving heavy constituents of the oil as liquid commingled with the vapors, separating such liquid from the vapors,

passing said'vapors at high velocity through a heated coi1 and heating the vapors therein until a substantial proportion thereof has been converted into lower boilingl point constituents, maintaining the conditions of velocity and temperature in said heated coil such that no substantial deposition of carbon occurs from the heating of the vapors therein, discharging the vapors into an enlarged chamber wherein the temperature is below that maintained in said coil but is maintained sufciently high to effect additional cracking substantially only by the superheat of said vapors passing said vapors through said chamber slowly enough to permit separation of any carbon formed by the cracking to occur and precipitating only substantially dry carbon from the vapors introduced into said enlarged chamber by the decrease in velocity of the vapors passed therethrough, and recovering a relatively loW boiling condensate from the cracked vapors.

CHAUNCEY B. FORWARD.

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