US1849479A - Process for converting hydrocarbon oils - Google Patents

Description

March l5, 1932. w. M. cRoss PROCESS FOR CONVERTING HYDROCARBON OILS Filed Oct. l2 1925 2 Sheets-Sheet w Q k.

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March 15, 1932. w. M. cRoss PROCESS FOR CONVERTING HYDROCARBON OILS Filed Oct. 12, 1925 2 Sheets-Sheet 2 Patented Mar. 15, 1932 UNITED STATES PATENT lOFFICE A WALTER M'. CROSS, 0F KANSAS CITY, MISSOURI, ASSIGNOB, BY' MIESN'E ASSIGNMENTS,

T GASOLINE PRODUCTS COMPANY, INC.,

'Honor DELAWARE or WI'LMINGToN, DELAWARE, A CORPORA- PBOCESS' FOR CONVERTING HYDROCARIBON OILS Application led October 12, 1925. Serial No. 62,012.-

This invention relates to improvements in a process for converting hydrocarbon oils,

and refers'more particularly to a process in which oil is first cracked and subsequently distilled at a pressure above atmospheric, the

temperature and pressure conditions in the distillation stage being controlled so that cracking is terminated at the discharge of the cracked products from the cracking stage.

This application is a continuation in part of a prior application Serial No. 128,839 filed November 1, 1916.

Among the salient objects of the invention are, to provide a. process in which oil is coursed through a circuitous passage in a heating tube where i* is raised to a cracking temperature and dischar ed thence into a reaction chamber wnere t e temperature and pressure conditions are regulated to prevent any substantial vaporization during the cracking reaction; to provide a process in which the oil is maintained in the reaction stage for a sulicient period of time for it to attain a substantial equilibrium, in which state it is discharged in a highly heated condition to a distillation stage wherein a reduced pressure is maintained; to provide a process in which, upon discharge from the reaction stage, the cracking reaction is terminated and distillation of those products having a boiling point below the temperature in the distillation zone is effected; to provide a process in which the vapors taken off are subjected to a refluxing and final condensing action and a portion of the reflux condensate recycled to-the heating stage for retreatment, and, in general, to provide a process and apparatus of the character hereinafter described in more detail.

Fig. 1 is a diagrammatic side elevational view of the apparatus with parts in section and parts broken away.

Fig. 2 is a collection of charts, designated as Chart 1, Chart 2, Chart 3 and Chart 4, of actual operating tests upon two oil samples of the same character treated according to the plot of conditions. One sample is designated by a full line in the respective charts,

while the second sample is designated by a dotted line.

Referring to the drawings, at 1 is shown a furnace in which are mounted the heatin tubes 2. The furnace is preferably heat by means of gas burners diagrammatically shown at 3. Four (4) is a reaction chamber; 5 is an evaporating tower; 6 is a bubble tower or reflux condensing apparatus; 7 comprises the final condensing stage and 8 is a receiving tank. At 9 is shown an accumulator tank in which reflux condensate is collected prior to its recirculation by means of the pump 10 to the heating coil for retreatment. Eleven (11) is a cooler by means of which the heavier residual products unvaporized in the evaporating stage are cooled prior to being directed to storage.

Referring now more particularly to the operation, a charging stock isintroduced to the system from an convenient source through the line 12 an is directed, by means of the pump 13 and aline 14, through a preheating coil 15 positioned in the top of the tower 6. This coil, in addition to preheating the incoming charging stock, serves as a dephlegmating apparatus for the vapors in the top of the tower. Passing from the coil 15, the oil is discharged through the line 16 into the heating coils 2 where it is raised to a conversion temperature. The temperature of the furnace is controlled together with the velocity of the oil so that the charging stock, in its passage through the furnace, is `raised to a conversion temperature without substanthe heating coil the oil is in a condition of incipient conversion.

The oil, on being discharged from the heating coil, is directed through the transfer line 17 into the reaction chamber 4 which is preferably forged from a steel billet. This chamber which is heavily insulated to prevent loss of heat through radiation, is of such size that the time vfor the oil to pass throughthe chamber is proper to substantially complete the conversion initiated in the heating coils. There is'no heat added to the reaction chamber, and therefore the oil must rely upon the tial decomposition, i. e., on its discharge from heat supplied in the heating coil to consummate the cracking reaction.

The cracking product, or what is termed as synthetic crude or crude equivalent, is discharged from the reaction chalnber through a pipe 18 controlled by a valve 19. Through this pipe the highly heated products are introduced to a heat exchanger or reboiling element 20 which consists of two headers connected by tubes positioned near the bottom of the bubble tower 6. A liquid level of reflux condensate is maintained somewhat above the top of the reboiler so that the oil, at a high temperature discharged from the reaction chamber, gives up a portion of its heat to the oil body in which the reboiler is immersed, thereby serving to reboil or vaporize olf some of the lighter fractions from the oil body and at the same time cool the oil discharged from the reaction chamber.

From the reboiler the oil is passed through a line 21 to the evaporating tower 5. Instead of directing the oil from the reaction chamber through the reboiler, it may, if desired, be by-passed through the line 22 by closing the valve 19 and opening` the valve 23. In case the oil is by-passed around the reboiler, or in any event if it is desirable to cool the f oil passingI through the line 21, a cooler hdrocarbon may be introduced through the pipe 24 controlled by a valve 25. If so desired, steam may be injected in the bottom of the evaporator 5 through the pipe 44', and introduction of the same controlled by a valve 45 interposed in the line. The valves 19 and 23 serve to maintain a differential pressure in the reaction chamber and the evaporator 5. In this latter stage, which is herein termed as the distillation stage, a pressure is maintained above atmospheric but below that maintained in the reaction stage. The amount of reduction of temperature and pressure between the reaction stage and the evaporator stage is controlled to terminate the cracking of the oil on its discharge from the reaction stage and produce only distillation of the lighter fractions of the synthetic crude in the evaporating tower. This pressure differential and reduction in temperature necessarily will vary according to the character of the oil used, as when certain stocks are being treated the optimum operating conditions must be ascertained by actual operation. Besides the loss in heat due to circulation throu h the reboiler 20, there will be considera le heat loss through evaporation in the evaporating tower.

The vapors evolved in the evaporating tower 5 pass off through the line 26 and are directed into the bottom of the bubble tower where they are subjected to a refluxing action. Temperature conditions are controlled in this tower to permit vapors which will produce a distillate having an end boiling point of substantially that of end boiling point gasoline to pass overhead through the pipe 27. This relief line 32 regulated by a valve 33. This receiver also serves as a gas separator, the gas taken off through the line 32 may be returned and burned in the furnace 3 or subsequently stripped for further low boiling point fractions.

The liquid level is maintained in the bottom of the evaporator 5 by means of an automatic liquid level regulating device 34 controlling the valve 35 in the draw off line 36. This draw off line directs the unvaporized material, which consists substantially of the heavier oils having the characteristics of fuel oil, to the cooler 11 from which the cooled products are discharged through the line 37 to storage. The reflux condensate knocked back into the tower 6v gravitates against the upward flow of the vapors and is collected in the bottom of the tower where the level is maintained by means of the liquid level regulating device 38, which automatically controls the level of the pool in the bottom of the tower above the reboiler by manipulation of the valve 39 in the line 40, in which is also interposed a valve 41. The refiux condensate drawn olf through the line 40 passes to the accumulator tank 9 from which it is withdrawn through the line 42, controlled by a valve 43, by the pump 10 and discharged through a line 44 into the charging oil lino 16 wherein it is combined with the charging stozk and recirculated through the heating co1 s.

It is recognized as common practice to heat an oil in a coil and discharge it at a cracking temperature into a reaction chamber. It is known to be old in the art to maintain the pressure and temperature conditions such as phase. In the operation of the Cross proc` ess there has been described a method of treatment whereby an oil which out of equilibrium, or a fraction of a crude oil, such as gas oil, fuel oil, kerosene or other types of cracking stock, is treated in this manner and for a sufiicient length of time in the reaction chamber to bring the oil back into equilibriuln, which means that there is produced within the oil an increased percentage of low boiling point fractions. It is recognized that a crude oil as found in nature 1s substantially at an equilibrium or in a stable stato at the temperature and ressure conditions to which it is subjecte in the earth. On being pumped or discharged from the earth, if temperature and pressure conditions are relatively different from those to which it has been accustomed, its character will change and it will gradually assume an equilibrium or stable state at the new temperture and pressure conditions to which it is subjected. Charging stock, which is out of equilibrium, introduced into a cracking system is converted to a synthetic crude or crude equivalent which is substantially in equilibrium at the high temperatures and pressures maintained in the reaction stage. The reaction toward this equilibrium is tremendously accelerated by the same heat and Aressure. When substantial e uilibrium has een established this oil is disc arged into a subsequent distillation stage maintained at a substantial pressure but at a pressure below the pressure in the reaction stage; also, the temperature conditions are controlled to the extent that there is effected distillation'under pressure within the evaporator due to the contained heat of the oil and the reduction of pressure, without cracking. It is this distillation under pressure without cracking that distinguishes and differentiatesl this stage of distillation from the usual liquidvapor crackin methods at the present time prevalent in t e cracking art. To further distinguish and bring out the differences between those methods and the practice described, it is iirst important to point out that in a process in which pressure distillation is accompanied by cracking, there is present in a vaporizing stage an oil which is attempting to attain an equilibrium due to the temperature and pressure conditions imposed. Inasmuch as there is continuously being taken of by vaporization certain of the lighter fractions, this equilibrium is constantly being upset and there is an ever changing molecular rearrangement of the liquid oil body in addition to the change in character occasioned by the extracting of the lighter fractions in the form of vapors. To these processes there is charged a cracking stock which is out of equilibrium, similar in its character to the cracking stock introduced to the heating tubes of the present-system. The evaporating stage of the system herein disclosed, however, has introduced thereto an oil which is substantially in equilibrium and from which is distilled oil' the lighter fractions without any molecular rearrangement of the liquid body itself. The heavierl unvaporized products which are withdrawn and directed to storage' in the form of fuel oil, are substantially the same in character as the heavy bottoms in the synthetic crude discharged from the reaction chamber, while the lighter fractions pass overhead and are iinally recovered as gasoline distillate or recycled in the form of reiiux condensate. Actual tests were made on a charging stock, the`characteristics of which are shown in Chart 1. The operating conditions under which this charging stock was treated are shown in Charts 2 and 3. It will be noted that the temperature according to Chart 2 was raised to substantially 450 C. In both tests it was held at said temperature for about forty minutes, after which the temperature was reduced. In one case, designated by the dotted line, the synthetic crude wasrapidl cooled. In the test shown b the full line, t e synthetic crude or cracke oil, after being raised to 450C7 C. was cooled to approximately 350 C. and was held at this temperature for about three hours, during which time there was absolutely no evidence of cracking. The line is practically horizontal with no upward deviations showing the generation of ygases produced during the reaction.

In chart 3 the pressures are shown on the two tests and are plotted against the time. In both tests the pressure was raised by generation of the autogeneous gases to 1,000 pounds and in one case with the reduction of temperature as shown in Chart 2 by the dotted line the pressure was also reduced and atmospheric distillation made of the resulting crude. In the other ca-se, as described above, the temperature was reduced to substantially l350" C. and the pressure to 700 pounds Where it was held for practically three hours at which time the synthetic crude was cooled, the pressure reduced, and a distillation curve plotted according to Chart 4 made from the resulting oil. In Chart 4 the two curves shown in dotted and full lines correspond to the dotted and full line curves of Charts 2 and 3. This curve conclusively shows that there was no diiit'erence in the two synthetic crudes run in this manner. The variations in the two curves shown in Chart 4 are such as would naturally occur in observing and recording on laboratory apparatus and are not such as would show any-characteristic difierences in the oils. l

I claim as my invention:

1. The process of oil conversion which comprises the steps of heating oil to a cracking temperature in a heating stageV and before any substantial decomposition takes place passing it to a digestion stage where the cracking initiated in the heating stage is substantially consummated, the oil remaining in the digestion stage for a sufficient period of time to attain substantially an equilibrium at the temperatures and pressure existing therein, cooling the cracked product and vaporizing a portion of a reflux condensate by passing the said cracked product into heat conductive contact with said reux condensate and discharging the cracked products into a stage maintained at temperature and pressure conditions reduced to the extent that further cracking of said oil is terminated wherein the lighter fractions are distilled olii, and subjecting the distilled products to a reflux action by passing the vapors through a body of refiux condensate.

2. A processof oil conversion which comprises the steps of preheating oil, passing the oil to a heating stage Where it is raised to a cracking temperature, and before any substantial decomposition takes place passing it to a digestion stage Where'the cracking 1nitiated in the heating stage is substantially consummated, the oil remaining in the digestion stage for a sufficient period of time to attain 'substantially an equilibrium at the temperatures and pressure existing therein, cooling the cracked product and vaporizing a portion of a reflux condensate by passing the said cracked product in heat conductive contact with said reflux condensate, discharging the cracked products into a stage maintained at temperature and pressure conditions reduced to the extent Where further cracking of said oil is terminated wherein the lighter fractions are distilled oli, subjecting the distilled vapors to cooling by passing them through a body of reflux condensate, then subjecting the vapors to a dephlegmation Whereby only the desired lighter fractions are allowed to pass to a condensing stage, cycling the refiux condensate to the heating stage.

WALTER M. CROSS.

and re-

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