US1900862A - Process for refining oils - Google Patents

Description

March 7, 1933. G` LAlRD PROCESS FOR REFINING OILSv Filed Aug. 6, 1927 www WILBUR G. LAIRD, or NEW YORK, N.

Patented Mar. 7, 1933 UNITED STATES PATENT OFFICE `NEW YORK, N. Y., A

Y., ASSIGNOR T0 HEAT TREATIN G COMP-ANY, OF

CORPORATION 0F DELAWARE PROCESS FOR REFINING oILs Application led August 6, 19,27. Serial No. 211,036.

This invention relates to an improved process and apparatus, for cracking mineral or hydrocarbon oils under superatmospheric pressure.

In the commercial cracking processes now in operation in which fuel oil, gas oil and similar stocks are cracked for the production of gasoline, it is found that the cracking system accumulates a large amount of oil of substantially the-kerosene range which .does not crack under the conditions used for cracking these ordinary cracking stocks. This relatively stable fraction (or fractions) usually accumulates in the fractionatlng tower of the cracking unit where it becomesa nuisance by placing the cracking operation out of an economical balance. This invention particuflarly relates to overcoming this difiiculty.

In cracking operations it is common practice to pass condensate from an ordmary dephlegmator or simple reflux condenser with the charging stock into the cracking zone. It has also been proposed to take the reflux :from the dephlegmator of a pressure still for a separatetreatment. In this case the reflux as separately cracked includes all 'fractions from the low boiing to the high boiling products and the high boiling products crack much more readily than the low boiling intermediates such for example, as kerosene. Furthermore, in systems of the type referred to in which a simple dephlegmator or radiator is used the distillates referred to as accumulating in the system areusually driven over into the final product; in the subsequent distillation of which .they form the residue. In

either case the refiner has this relatively stable i By the process of the present invention these various defects are overcome bypassing the cracked oil ing and classifying tower, where the specifically troublesome fractions are fractionally separated, withdrawn and crackedfi-n a supvapors into a combined condensplemental cracking zone under pressure and temperature conditions adapted to crack such oil fractions;`

Therefore the important objects of the invent-ion are:

To provide a process for the cracking of ydro'carbon oils in which substantially the whole of the-oil is converted into the desired final product;

To provide a process in which the light intermediate products are effectively cracked without subjecting the higher boiling cracking stock to excessive pressures and temperatures;

To provide a process in which crude petroleum may be treated for the effective cracking of all fractions other than the desired final product;

To provide a process in which vapors from the cracking process are partially cooled by low temperature light vapors;

To provide a process in which the vapors from the cracking process are fractionally condensed and certain of said condensates are selected and cracked in a separate zone;

tus for effecting the cracking bon oils, of-the type referred to, out the novel process.

Other and further objects will be apparent from the following -detailed description of the invention taken in connection with the accompanying drawing in which:

of hydrocarand to carry he figure is a diagrammatic elevational i view of the apparatus, parts being broken away to show the internal structure or certain elements.

y he original oil to be treated, which may be crude petroleum, fuel oil, gas oil or other raw fraction of petroleum heavier than kerosene, is introduced into the system by suita le pressure means (not shown) through a pipe 2, by which the oil is introduced into thefirst ofa series of condenser-heat exchangers 4 on a tower' 6. Fromthe vfirst unit 4 the oil .passes in series through the succeeding units as indicated by a heavy dotted line 8, leaving the lowermost unit 4 by a pipe 10 from which the now preheatedoil is introduced into a topping still-heat exchanger 12.

ioo

lflow pipes.

In this still the charging stock passes in heat exchange with hot residuum as explained later. The oil is now passed from the still 12 by valved pipe 14 then through a heater 16 and by a pipe 18 into a reaction or cracking chamber 20. Since considerable pressure may be lost in resistance in passing the oil through the exchangers 4 and the various other connections a pump 22 is placed in a bypass around the valve in pipe 14 in order to increase the pressure on the oil, if desired, before passing it through the heater 16. The vapors produced in the cracking of the oil in chamber 20 are discharged by a valved pipe 24 into the lower portion of the tower 6 in which they are subjected to condensation and rectification.

The tower 6 as here shown diagrammatically is substantially the same as that shown in detail in applicants prior application Ser. No. 125,893, filed July 30, 1926. It will be .sufficient for the present description to point outthat the vapors entering the base of the tower pass alternately through liquid maintained on bubble plates and in heat exchange 'with charging stock in the exchangers 4. The

exchangers 4 are of the ordinary surface condenser type and the condensate produced from the vapors passed therethrough flows back onto the next lower bubble plate where it is subjected to the rectifying action of hot vapors. Unless otherwise treated as explained later the condensates pass from bubble plate to bubble plate by the usual overleaving the uppermost units 4 pass by a valved vapor line 26 through a condenser 28, from which the condensate and uncondensed gases pass to a` receiver trap 30. Condensate is withdrawn from the receiver by a valved pipe 32 while the gases pass by valved pipes 34 and 36 to a scrubber and storage (not shown).

In order to secure an eflicient heat vexchange in the units 4 it has been found desirable when operating on such charging stocks as fuel oil and lgas oil to introduce with these oils a small amount of gas in order to secure vaporization of part of the oil in the units 4. This gas may be supplied from the pipe 34 to the pipe 2 by means of a` booster 38.

The vapors If crude petroleum is charged into the system no as will be necessary,because this oil contains a sufficient quantity of low 4boiling point constituents to give the desired vaporizing effect in the exchangers. Furthermore when crude is treated it is topped of its light volatiles in the still.12, the vapors passing by: a valved vapor line 40 into the line 24 where they serve to initially cool the vapors or oil from the cracking chamber 20. In casesy in which a mixture of gas and other charging stock is treated, the gas may be separated from the oil in the still 12 and only the oil passed through the heater.

In any cracking process gasoline is only one of a number of various products produced, but since gasoline is the more desired product the other higher boiling products must be subjected to further treatment before they are finally converted to gasoline. Products such as gas oil or fuel oil may berecracked along with the initial stock if they have about the same boiling range but the oils of substantially the boiling range of kerosene which are produced in cracking, or, are derived from crude being cracked do not readily crack on such retreatment. In the present process the products of substantially this character are condensed in the column and withdrawn therefrom by one or more valved pipes 42 which aresuitably placed to draw lquid from the trays in the intermediate part of the column. The liquid condensate thus withdrawn is passed by a pipe 44, pump 46 and pipe 48 through a heater 50 from which it is introduced by a pipe 52 into a large cracking oil maintained under high pressure and temperature in this chamber is withdrawn by a pipe 56 and introduced into the base of the tower 6. A pressure reducing valve 58 is mounted in the line 56 since the pressure in the heater 50 and chamber 54 is maintained much higher than in the remainder of the system.

In the cracking operation products are produced which are heavier than the charging stock and usually settle out'in the reaction chambers. The hea residuum may be withdrawn from the c amber 20 by a valved pipe 60 and from the chamber 54 by a valved pipe 62. These pipes discharge into a common main which connects with a coil 64 in the still 12 where a portion of the heat in the residuum is transferred to the charging oil. From the coil 64 the residuum is passed by a valved pipe 66 into the central portion of a vapor-tight pressure thickener 68 where the carbon and tarry matter are separated from the clarified oil, the former being discharged by a valved pipe 70 which passes through a cooler 72, while the clarified oil is withdrawn through a pipe 74 by a pump 76 and passed through a conduit 78 into the main charging line 8 at any desired point.

Sincethe pressure on vthe oil undergoing conversion in the cracking still 54 is much higher than in any7 other part of the system, the residuum passed therefrom through ythe valved pipe 62 and delivered to 68 will partially vaporize due to the reduction in the pressure thereon. The vapors thus produced are therefore passed from the thickener through a vapor line 69 and condensed in a condenser 71, the condensate being trapped in a receiver 73. By cooling the vapors only sufficiently to effect their condensation, the condensate thus obtained may be retained comparatively hot and therefore chamber 54. The cracked sof . the pipe 14 or pump 22 it r of approximating 500 passed by pipe 75, valved as shown, directly into the heater 16 by the pump 22, or it may be delivered into pipe 74.

The heavier oils in the tower 6 collect in a comparatively large chamber 79 in the base th This chamber may be separate and distinct from the rectifying part of the tower. yIn this chamber the oil and condensate may be stripped of absorbed light ends by intro.- ducing gas through a distributor 80 mounted in the lower part of this chamber.l These oils 4 may be as heavy or heavier than the original charging stock and are therefore withdrawn by a pipe 482 and passed by a pump 84 into conduit 78 from which they mix with the charging stock passing to the heater 16.

The heaters 16 and 50 are preferably of the pipe still furnace type in which the oil passes through, a continuous coil mounted in the furnace. Whilethe react-ion or soaking chambers 20 and 54 maybe of any type, they are here shown as being of the ball mill construction describedin detail in application Ser. No. 180,728 filed April 4, 1927. The same mode of operating these chambers may be employed as'described in `the said application. f

en it is desired to crack gas oil, for example, the process ,may be carried out as ollows: gas oil is passed through the exchangers 4 and still 12 from the line 2, under a pressure of fromlOO to 300 pounds per square inch. By the time the oil reaches has a temperature F. so that a relatively small amount of heat need be added in the heater 16, therefore the oil may be passed therethrough at yacomparatively high velocity in order to avoid coking in the coils. n the soaking drum 20 and tower 6 a pressure of from 75 to 300 pounds per square inch is maintained, the actual pressure used depending on the peculiar characteristics of the charging stock and capacity of drum 20.- Tlie larger the drum; the longer any given quantity of oil can be maintained under the cracking conditions of pressure and teniperature. The vapors entering the tower 6 from the drum 20 include all fractions even to unconverted gas oil and polymerized heavier products vaporizing under the conditions. These vapors are subjected to frac-v tional condensation and rectification in the column so that they form a series of condensates of decreasing average boiling point.

' The cut temperature on the tower is preferably maintained so that vapors comprising gasoline of the proper end point-will be -passed for condensation in the -condenser 28. The condensates produced in the upper condensers 4 may berefluxed back onto theupper bubble tray where they are rectied :and keep back higher boiling materials.

The condensates comprising substantially the kerosene fraction are taken from any I plate or plates in the column on which they accumulate and passed by one or more of the pipes 42, pipe 44, pump 46 and pipe 48 through the heater 50 and into vcracking chamber 54. This'kerosene fraction is maintained under high pressures in the heater and soaking drum in order to effect its cracking. Pressures of from 200 to 700 pounds per square inch maybe used depending on the nature of the stock being cracked and the cracking time allowed by the size of the chamber 54. For strai sures above 500 pounds have been found desirable because at lower possible to maintain the oil in liquid phase .at temperatures of from 750 to 900 F. which are necessary to eii'ect cracking. The oil in this part of the system is in liquid phase, the hot oil being tlashed'to vapor upon its entry into the chamber 79 through the pressure reducing valve 58. The valve ght kerosene prespressures it is imof pipe 56 if desired.

By the above described process of classi fying the various grades of oil produced in the cracking operation and selectively cracking them under proper conditions suitable to the particular product selected, the loss due to repassage of certain light oils through the cracking unit with heavier oils may be decreased to avoid the coking of hieavy oils cracked und their lighter content and to increase the yield of gasoline. Since every product is cracked under its peculiar conditions there is a minimum of heat or other energy applied to the oil to effect its complete conversion.

In the cracking of gas oil and higher boil- .ing cracking stocks as described for example in connection with the operation of heater er conditions necessary to crack the percentage conrange in accordance with the operation of the law of massaction. As indicated above the subjection of any nparticular cracking stock such as gas oil to cracking conditions of temperature and pressure produces, beside gasoline, other hydrocarbons both of higher and lower boiling point range than the charging stock. Cracking also produces hydrocarbon (gases) boiling below the gasoline range. In order to derive the greatest possible advantage from the mass action effect, a part of the gases produced in the process is mixed with the charging stock by means of the booster 38. The intermediate material may be introduced through pipe 2 or at any convenient point in the charging line leading to the heater 16. If fuel oil is being treated in the chamber 20, the oil in chamber 79 which is passed into the feed line 8 will usually contain sufiicient intermediate material to hold back the formation of such material and shift the equilibrium to increased gasoline production. In any case the proportion of intermediate material and gas to charging stock, passed with the charging `stock through the heater 16 should be equal to the proportion of such materials which would be formed when the particular charging stock is cracked alone. Since the temperatures and pressures in chamber 20 are adjusted at any particular time for the particular charging stock being treated, the intermediates will not be cracked to apreciable extent, but as pointed out above, the cracking of these materials accumulating in the system, in the chamber 54 is one of the primary objects of the invention.

Gas from the booster 38 may be passed with the oil introduced into the heater and cracked in chamber 54. Under the pressures used in this part of the apparatus the gas would be practically forced into solution in the oil and through such intimate contact shift the equilibrium from the production of substantial amounts of gas and carbon or coke. The formation of uncondensable gases in cracking operations appears to be intimately associated with carbon or coke i formation and therefore, if the formation of gases is restrained, carbon or coke formation will also be decreased.

The gas oil or other material treated in heater 16 and cracking chamber 20 or other cracking elements not shown, may be cracked in liquid phase under conditions similar to the operation on the lower boiling stock cracked in the chamber 54. In such a case the tower 6. may be operated at substantially atmospheric pressure or at a maximum pressure of about 50 pounds per square inch, and the chamber 79 used as a vaporizing chamber. The valve in pipe 26 or the valves beyond the {inal condenser may be used vfor holding the desired pressure in the tower 6.

In passing bers 20 and 54 into the chamber 79 some small amount of carbon which does not settle out, of course passes to this chamber, but it has been found insuilicient to cause any trouble in the heater 16. The ends of the pipes 24 and 56 which extend into the cracking chambers are bent up so as to decant off the relatively clear oil. On the other hand the ends of the residuum pipes 60 and 62 extend down inthe chambers so as to remove the heavier sludges and carbon.

The cracking chambers 20 and 54 may Vbe conveniently operated in pairs, one of each Y pair being in use While the other is being rothe oil directly from the chamgr tated and cleaned. As, for example, the

-chamber cut out of service may be held under considerable pressure and rotated While th oil therein is hot. In this way the carbon and coke will all be ground olf the walls by the heavy metal balls and thoroughly mixed with the hot oil. After rotating the chamber a sufficient time the oil-carbon mixture may then be withdrawn into the thickener 68.

Where inconvenient to use more than one cracking chamber in each position it may be continuously or intermittently rotated at a slow rate to keep coke from depositing in the chamber. If a relatively heavy oil 1s being treated in chamber 20 more carbon and tarry matter will be formed therein and therefore rotation of this chamber should be more frequent, residue being withdrawn during rotation.

The thickener 68 is preferably operated under substantially the same pressure as chamber 20 so that a minimum amount of vaporization of the oil is permitted.

.The classifying tower 6 while shown as having the condensers 4 constructed integral therewith may be constructed with these placed on brackets on the sides of the tower proper. Likewise the number of bubble plates and condensers may be varied as also the number of bubble plates between the condensers. Furthermore it is understood that an ordinary bubble plate tower without condensers may be used. In actual practice a larger number of plates is used than the num'- ber shown and a separate tower may be used to treat the vapors from the oil cracked in chamber 54.

Where suliicient vapors are produced to accommodate separate fractionatingtowers for the different cracking chambers` the intermediate condensates from the different towers may be passed to the heater 50 while the heavy condensate and clear residuum from such towers or vaporizing chambers, such as 79, will be passed to the heater 16. Large towers however have been found to give better results than small ones and therefore a single large tower is preferably used when possible. It is understood that where a larger number of cracking chambers are used in a oup than shown and a separate tower is used for each, the selective action will be carried out in each tower and each class of cracking stock condensate obtained from the several towers will be delivered to a single cracking chamber.

While the applicants selective method of cracking has been described in respect to certain materials it is understood that the invention is not limited thereto since its application is equally applicable to other charging stocks. Furthermore the invention is not limited to selecting a single material from the classifying tower since a large number of different cuts may be made in the tower, all of which may be separately withdrawn and cracked under the conditions suitable for each particular oil. In a practical installation of the apparatus it is preferred to have small storage tanks in the lines 42 or 44 and 74 to allow for fluctuations in the production and use of the various materials passing therethrough. These features as well as the showy ing of insulation is omitted from the drawing for the sake of simplicity.

Insulated storage tanks used in the lines 42 make it possible to vary the stock crackednn chamber 54 at various intervals. That is, during one period of say 1 or"2 hourslight kerosene may be cracked at a very high pressure,.then heavy kerosene at a lower pressure, then light gas oil at a still lower pressure, and so on, with the cycle being repeated. In a similar manner clarified' heavy residuum which may be much easier cracked than the stock being crackedv in chamber 20 may be exclusively cracked at appro riate intervals in this chamber, under con itions particularly adapted for its cracking without excessive decomposition.

Having thus described my invention, what I claim as new is:

A process of converting relatively heavy hydrocarbons into lower boiling point iydrocarbons, comprising passing oil through a cracking coil and then into a large reaction zone, heating the oil to a cracking temperature in said coil, dischargin the vapors mto a vapor fractionating zone w ere partial condensati on occurs, withdrawing the heavy c011- densate from the base of the tower and passing it with said oil throu h said coil, withdrawing the relatively hghter but insuiiciently cracked condensate from an intermediate point in 'said fractionating zone then passing it through a separate crackin coil and into a large cracking zone maintained under relatively high pressure and cracking temperature and subjecting the va ors l evolved from said lighter cracked oil to actional condensation -in Ysaid frwctionating zone. In testimony whereof I aix my signature. v WILBUB G. LAIRD.

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