US2055015A - Conversion of hydrocarbon oil - Google Patents

Description

Sept 22; 1936 J. c. MORRELL CONVERSION 0F HYDROCARBON OIL original' Filed April 23, 1932 |NvENToR JACQUE C. MORRELL BY ATTORN Patented Sept. 22, 1936 PATENT OFFICE ooNvnnsioN or nrnaooimoN on.

Jacque C. Morrell, Chicago, Ill., assignor to I' Universal Oil Products Company, Chicago, Ill., a corporation of Delaware Application Apru z3, i932, serial No. 607,020

Renewed May 15, 1935 4 claims. l (el. 19e-48) -1 I.

This invention relates more particularly to the pyrolytic conversion of the heavier and less valuable portions oi crude petroleum such as the heavy distillates and residua produced therefrom in the primary distilling steps though the process is also applicable to heavy hydrocarbon oil mixtures produced from other sources.

In a more specific sense the invention comprises a process which permits the simultaneous l production of high yields of motor fuel fractions of improved anti-knock value along with the production of coke of low volatile content.

In the cracking processes at present used in oil refineries numerous diiculties are encountered when attempts are made to increase the yield of motor fuel from any given stock beyond a certain point. With the application of cracking conditions of increasing severity higher anti-knock motor fuel is produced, but the lyield diminishes on account of excessive gas formatIon, and carbon troubles, particularly in the tubes of lheating elements, limit the safe operating periods between cleanouts on account of the development o-f hot spots and the possibility of serious iires due to tube ruptures.

'I'he production of coke of low volatile content requires relatively high temperatures and low pressures, and if such conditions obtain in tubular heating elements there is an increased tendency toward deposition of hard carbon with resultant local overheating while if they obtain in both the tubes and the reaction zone high gas losses occur with a corresponding decrease in the overall yield in gasoline. The present process $5 comprises an improvement in operating steps a1- lowing the production oi' low volatile cokel along with a high yield of good anti-knock value gasoline as will be hereinafter fully described.

' In one speciiie embodiment the invention comprises cracking hydrocarbon oils at elevated temperatures and pressures during passage through a heating element and an enlarged reaction chamber, passing the cracked products to a reduced pressure coking chamber wherein fur- 5 ther conversion is eiected by the introduction of flue gases and reheated gaseous and liquid produ'cts from the process, separating coke from vaporous and gaseous products, fractionating the vapors and gases to produce a mixture of fixed gases and vapors of gasoline boiling range, inter-l mediate refluxes and heavier reuxes Suitable for further conversion, condensing said gasoline vapors and separating the flexed gases 'therefrom, separately heating said fixed gases and/or gasoline vapors and returning them to the coking chamber, separately heating said intermediate reiiuxes and returning them to the coking chamber and returning said heavier refluxes to the primary cracking zone for further conversion.

The nature of the process may be conveniently described in connection with the attached drawing, which shows diagrammatically in side elevation by the use of conventional gures a plant layout in' which characteristic operations may be conducted. i

, Referring to the drawing, raw charging oil may be introducedl to the plant from line I, containing control valve 2, and discharged through pump 3 and line II, containing a control valve 5, to mingle with heavy refiuxes from the line 9, these l5 refluxes coming from the plant fractionator 22 by way of line 6, valve L'pump 8, line 9 and valve I0. A portion of the raw charging oil may be introduced into the fractionator if desired, though' means forv this are not shown in the 20 drawing.

The combined feed of raw oil and fractionator reuxes passes through a heating elementv III disposed to receive heat from a furnace I I and during its passage through the element receives heat 25 sufficient to initiate a limited amount oi' cracking, a pressure being maintained at the same time by the use of succeeding valves in the lines following the reaction. chamber. 'I'he severity of cracking conditions imposed upon the com- 3g bined feed oils during theirpassage through the heating zone is preferably held within the range of operating conditions corresponding to a minimum of coke formation in the tubes, the temperature range corresponding to such conditions being approximately 850 to 950 F. and the pressure from 100 to 400 pounds per square inch, depending upon the character of the combined feed undergoing treatment and othercircumstances.

The heated products from element I0 pass to 40 enlarged chamber I4 either by way of line I2, conf taining control valve I3, or line I2', containing control valve I3', receiving reheated side cuts from the fractionator from line 44 as will be later described. Two alternate ows may be employed in 45 reaction chamber I4, depending upon the chari acter of the stocks treated. In one case corresponding to oils of relatively low carbon-forming tendencies the heated products may be passed downwardly through the reaction chamber and all products, both vaporous and non-vaporous, may pass through line I5 and control valve III to the low pressure coking chamber I'I.

The other alternative flow which may be used in the case of oils of relatively high coke-forming tendencies consists in adding the products from the heating element to the lower portion of the reaction chamber through a line I2', containing control valve I3. In this method of operation the heavier residual liquids are quickly separated.

from the vapors in the bottom of the reaction chamber so that they receive less cracking time than the vapors which must traverse theentire length of the chamber before being released through line I5' and control valve I6. Thus, the vapors are more extensively cracked in the reaction chamber than the non-vaporous products, and coke formation is minimized.

'Ihe pressure employed in coking chamber I1 is preferably lower than that employed in the previous cracking zone and the temperatures are preferably higher. To insure these conditions which are necessary for production of a high grade low volatile coke, combustion gases may be introduced through a line 66, containing a control valve 61, from any source such as, for example, the various furnaces of the process, suitable blowers or pumps having been used to step up the pressure to the necessary point. In addition, reheated side cuts and/or intermediate hydrocarbon fractions from sources outside the process may be introduced into the coking chamber from line 46 and reheated end product gases and liquids from the process may be introduced from line 64, containing control valve 65, the previous heat treatment of these heat-carrying media being described in order in following paragraphs. The coking chamber is shown having a line I8, containing control valve I9, to permit the withdrawal of any liquid accumulations at any period in the operations of the plant in which they may accumulate.

It will be seen from a recounting of the `various provisions made for furnishing additional heat to the low pressure coking chamber through the media of ue gases and highly heated products of the process that conditions may be modified to take care of any particular situation, by controlling the relative proportions of flue gas and other heated materials added. Thus, ue gases at temperatures of from 1100 to 1700 F., or thereabouts, may be admitted unless it is found that relatively high temperatures are necessary to produce coke of low volatile content and coking may also be induced by the use of process liquids superheated to temperatures in excess of 1,000 F., these products being concurrentlycracked to increase their anti-knock value.

'I'he vaporous products from the coking chamber may pass through aline 20, containing control valve 2|, and enter a fractionator 22 which is preferably of a design and capacity suiicient for separating vapors of gasoline boiling range as an overhead fraction, leaving insuiciently converted refluxes to be returned to the cracking and/or coking zones of the process. The overhead fractions may pass through line 23, containing control valve 24, and through condenser 25 in which the cooled fixed gases and gasoline boiling range liquids may be conducted to a receiver 28 by way of a line 26 and a control valve 21, this receiver having a gas release line 29, containing control valve 30, and a liquid draw line 3| containing control valve 32.

Side cuts which may be advantageously employed as heat carriers for the coking step may be withdrawn through such lines as line 33, containing control valve 34, and line 35, containing control valve 36, these lines leading to a pump 31. If desired, outside stocks of the general character of such side cuts may be introduced to line 33 from a line I', containing a valve 2. Pump 31 discharges through line 38 and control valve 39 into and through a heating element 40 disposed to receive heat from a furnace 4I and the side cuts are preferably heated to produce a controlled degree of cracking and bring them to a temperature suitable for best operating conditions in the succeeding reaction and/ or coking chamber to which they may be subsequently introduced. The generally light character of these side cuts will normally require relatively high temperatures and pressures for their decomposition, characteristic temperatures being included between 950 and 1l00 F., more or less, and pressures of several hundred pounds.

The heated and cracked side cut fractions may pass through a line 42, containing controlvalve 43, and having branch line 44, containing control valve 45, and leading to line I2 and branch line 46, containing control valve 41, and leading to coking chamber I1. The relative amounts diverted to the transfer line from the primary heating element and to the coking chamber will be adjusted to produce optimum treating effects.

The invention further contemplates the use of both the gases and the overhead distillates from the process as heat-carrying media when benefits are obtained by their use or when in the case of the liquid condensates they are improved in antiknock quality by further heat treatment. Thus, a portion of the fixed gases from the process may be diverted to a pump 50 through a branch line 48, containing a control valve 49, and discharged therefrom through a line 5I, containing a control valve 52, and leading to line 38 or a portion thereof may be diverted from line 5I to line 60 to be presently described through line 53, containing control valve 54.

A portion of the end point distillates may be separately heated in heating element 62 disposed to receive heat from a furnace 63, passing throughline 51, containing control valve58, to pump 59 which discharges through line 60, containing control valve 6I. Line v(il) is shown in operating conjunction with line 38 through branch line 55, containing control valve 56.

From the description of the various recirculating lines just given it will be evident that any of the products of the process may be heated singly or in combination with other products in either of the auxiliary heatingelements 40 and 62 so that the process is seen to possess complete flexibility in the matter of re-forming the primary products or utilizing them as heat carrying media for the coking operation.

As an example of the improvedresults obtainable in" the production of high yields of good antiknock gasoline along with the production of low volatile coke, an example may be cited involving the cracking of a Mid-Continent topped crude, first by ordinary cracking processes in which conditions are chosen to permit coking under pressure in the reaction chamber and, second, by operations characteristic of the process of the present invention involving the use of a low pressure, high temperature coking chamber following the high pressure reaction chamber, re-formation of side cuts from the fractionator and their introduction into the coking chamber and the use of hot flue gases in the coking chamber.

In the high pressure coking operation in a plant of the ordinary coil and chamber type the temperature maintained at tle exit of the heating pounds per square inch, for example, 500 to 600 element may be 930 to 935 F. and the pressure approximately 250 pounds per square inch. In the improved process of the present invention using a setup generally similar to that shown in the drawing, the temperature and pressure may be approximately the same with introduction of the heated products from the primary heating element into the bottom of the reaction chamber and the separation at that point of the heavier coke-forming products as described in connection with the drawing. The pressure in the coking chamber may be approximately 30 to 50 pounds per square inch and the temperature from 1100 to 1200o F. Approximately 40% of the flue gas product from the primary cracking furnace may be introduced from the coking chamber and a side cut representing that portion of the gasoline product boiling between 325 to 400 F. may be re-formed in the secondary heating element at a temperature of 1000 F. and a pressure of 500 pounds per square inch and introduced into the coking chamber.

The yields and quality of products which may be obtained from the older and more generally used type of operation are indicated in Table I, while those which may be produced bythe use of the present process are given in Table II.

Table I Gasoline, 54.5 gr., 400 E. P.,

75 O. N.* 58% by volume Gas oil, 29.0 gr 5% by volume Coke, 14% volatile content 100# per bbl. raw oil Fixed gas.v 600 cu. ft./bbl.raw oil Table II Gasoline, 53.5 gr., 405 E. P.,

82 O. N.* 60% by volume 6% by volume 884i-L per bbl. raw oil Gas oil, 28.0 gr Coke, 4% volatile content-- Fixed gas 590 cu. ft./bbl. raw oil *Octane number.

and communicating reaction chamber, the vapors and non-vaporized-residue from. which are discharged into a coking drum, the vapors leaving the coking drum being subjected to fractionation to produce an overhead product, which is recovered, and an intermediate reux condensate and a heavy reflux condensate which is returned, together with the charging stock, tothe heating coil for further conversion, the improvement which 'comprises subjecting the intermediate reflux condensate to cracking conditions of temperature and superatrnospheric pressure in an independent heating coil and then' introducing at least .a portion thereof to said reaction chamm ber, simultaneously subjecting a portion of the overheadproduct to elevated tempera-tine in a third independent heating coil and introducing the same into the coking chamber to devolatilize and coke the non-Vaporized contents therein.

2. A conversion process which comprises heating hydrocarbon oil to cracking temperature under pressure in a primary heating zone, discharging the heated oil into an enlarged reaction zone maintained under cracking conditions of temperature and pressure, removing vapors and unvaporized oil from the reaction zone and distilling the latter in a separating -zone maintained under lowerpressure than the reaction zone, fractionating the vapors and separating therefrom relatively heavy and light reiiux condensates and a fraction containing hydrocarbons boiling within the gasoline range, returning such heavy reflux condensate to said primary heat,-

ving zone, heating the light reflux condensate in a secondary heating zone to higher cracking` to the reaction zone, heating a portion of said fraction in a third heating zone suiiiciently to enhance the anti-knock value thereof and introducing the same to the separating zone to assist the distillation of the unvaporized oil therein.

3. A conversion process which comprises heating hydrocarbon oil to cracking temperature under pressure in a primary heating Zone, discharging the heated oil into an enlarged reaction zone maintained underv cracking conditions of temperature and pressure, removing vapors and unvaporized oil from the reaction zone and distilling the latter in a separating zone maintained under lower pressure than the reaction zone, fractionating the vapors and separating therefrom redux condensate heavier than gasoline and a lighter `fraction containing hydrocarbons boiling within the gasoline range, heating such reflux condensate in a secondary heating zone to higher cracking temperature than the oil. in said primary zone and then introducing at least a portion thereof to the reaction zone, heating a portion of said fraction in a third heating zone suiiiciently .to enhance the anti-knock value thereof and introducing the same to the separating zone to assist the distillation of the un'- vaporized oil therein.

4. In a process wherein hydrocarbon oil is subjected to cracking conditions of temperature and? pressure in a heating coil and communicating vreaction chamber, the vapors and non-vaporized residue discharged into a coking drum, the vapors leaving the coking drum being subjected to fractionation to produce an overhead product, which is recovered, an intermediate reflux condensate containing heavy gasoline ends and a heavy reflux condensate which is returned, together with charging stock, tothe heating coil for further conversion, the improvement Which comprises subjecting the intermediate reiiux condensate containing said heavy gasoline ends to cracking troducing the same into the coking drum whereby to devolatilize and coke the non-vaporized` contents therein, and introducing hot flue gases into the coking drum to further assist in devolatilizing and coking the non-vaporized residue therein.

JACQUE C. MGRRELL.

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