US2179079A - Conversion of hydrocarbon oils - Google Patents

Description

Patented Nov. 7, 1939 UNITED STATES 2,119,019 i coNvEnsloN or nrnaocannoN oms Joseph G. Alther, Chicago, lll., assignot to Universal Oil Products Company, Chicago, lll., a' corporation of Delaware Application May 12, 1938, Serial No. 207,432

' 3Claims.

This is a continuation in part of my co-pending application, Serial No. 71,897, led March 31, 1936 now abandoned. It is also related tomy application, Serial No. 745,257, filed September 24, 1934 now abandoned, upon which application, Serial No. 71,897 is based, in part.

The invention relates to an improved process and apparatus for the pyrolytic conversion of hydrocarbon oils accompanied by the continuous l0 reduction of their high boiling components to coke.

As a special feature of the invention, the total heat required for cracking and ccking is imparted to the oil undergoing treatment prior to its introduction into the coklng zone, the latterbeing unheated except for the heat carried by the oil undergoing treatment. This is accompanied by employing a furnace of the type invented by the present applicant and now known in the art as an "equiiiux heater and also by separately heat- `ing the heavy oil charging stock for the system and intermediate liquid conversion products of the process in separate zones or cells of4 said equifiux heater. With a heater of this type I am able to obtain high rates of heat input and thereby heat the oil to the high temperature required for its reduction to coke without allowing it suiilcient cracking time in the heating coil to cause substantial coke formation and deposition in the zone. By employing this form of heater and by separately heating the charging stock and intermediate liquid conversion products, I am able to continuously reduce the heavy liquid conversion -products to coke in an unheated coking zone.

The coking zone is preferably of the continuous conveyor type which, in conventional practice, is iired to a high temperature. By eliminating the necessity of ring the coking zone I avoid contamination of the vaporous conversion products with combustion gases. This method of operation is distinctly advantageous since it is extremely difficult to separate desirable light vaporous and gaseous hydrocarbons evolving in the cracking and coking operation from combustion gases with which, according to conventional practice, they are mixed in any of the usual types of continuous colclng systems.

I am fully aware-of the fact that it is now common practice to crack relatively light and relatively heavy oils in independently controlled heating coils and that this type of operation has been employed in cracking systems wherein the heavy liquid conversion products are reduced to` coke. 'I'his type of operation has the advantage oi permitting more severe cracking of the rela- (Cl. 19E-48) tively light oil than that to 'which the heavy oil can be safely subjected Without encountering coking difiiculties ln the heating coil. Advantages are taken of this fact in the process of this invention to obtain the heat required, for coking the 5 heavy oil, in excess ofthat supplied by the heavy oil heating coil. 'I'he novelty of the, invention does not reside in lany single feature but rather in the advantageous and novel combination of the method of heating l0 employed, the two coil operation, and continuous coking attained Without ring the coking zone.

The accompanying diagrammatic drawing illustrates one specific form of apparatus embodying the features oi the invention and in which the l5 process of the invention may be conducted.V

Referring to the drawing, charging stock for the process, preferably comprising an oil of relai tively high-boiling characteristics, such as heavy crude petroleum, topped crude or other straight- 20 run or cracked residual oil, is supplied through line I and valve Z'to pump 3 by means of which it is directed through line 4 and valve 5 to heating coil 6, wherein it may be preheated to any desired temperature below that at which any ap- 25 preciable conversion thereof will occur, and the preheated oil is thence directed through line 1 to coil 8 wherein it is quickly heated, in the manner to be later morefully described, to a high cracking temperature, at the pressure, without 3Q allowing it to remain in the heating coil Yfor a sufiicient lengthv of time to permit any substantial formation and deposition of coke in this zone.- The temperature to which the charging stock is heated in coil 8 is, however, rsumcient to effect 35 reduction of the non-vaporous components of thel resulting conversion products to a heavy pitch-like'residue and the heated products are discharged from heating coil 8 through line 9V and valve I0 into coking zone I.

In order to accomplish heating of thel charging stock under the desired conditions, which involve the use of relatively high rates of heat input and a relatively short time for the oil at cracking temperature in the heating coil, a fur- 45 nace of the general type illustrated at 44 is preferably utilized. The main structure of the specific form of the furnace here illustrated comprises side walls 45 and 46, a roof 41, a, floor 48 and end walls which are not shown in the 50 p particular view of the drawing here illustrated. The` interior of the furnace -is divided by means of `a suitable wall 49, into two independently red heating zones or cells 50 and 5i. A uid conduit 8 comprising, in the case here illus- 55 l tally disposed tubes 53 is located within cell 5| midway between walls 46 and 49. Adjacent tubes throughout iiuid conduit 8 are connected at their ends in series by means of suitable return bends indicated in the drawing by the single lines 54 connecting the near end of adjacent tubes. Adjacent tubes in the two opposite rows of fluid conduit 3| are arranged in staggered formation and are connected at their ends in series by means of other suitable headers indicated by the lines 55. Separate combustion and heating zones 58 and 51 are located on opposite sides of fluid conduit 8 and controlled amounts of combustible fuel and air are supplied to each of these zones by means of suitable burners indicated at 58. Similar burners 58 also supply combustible fuel and air in regulated amounts to combustion and heating zones 59 and 60 located on opposite sides of fluid conduit 3|. A plurality of burners 58, supplying fuel to each of the combustion zones 58, 51, 59 and 68, are preferably arranged in a row extending from one end to the other of eacho1' the combustion zones so that a substantially continuous sheet of flame travels downward from near the tip of the burners to the lower portion of each of the combustion zones and preferably each of the burners is tilted slightly toward the adjacent wall of the furnace, as indicated in the drawing, so that the ames impinge upon each of the walls opposite the two iiuid conduits, heating the same to a highly radiant condition. In this manner radiant heat is transmitted from the materials undergoing combustion and from the hot refractory furnace walls to opposite sides at each of the tubular elements of fluid conduits 8 and 3| whereby a high rate of heating is obtained in each of the uid conduits.

In the particular case here illustrated, the combustion gases from both combustion and heating zones '58 and 5| commingle in the lower portion 0f the furnace beneath wall 49 and the commingled gases are directedthrough fluid heating zone |'l5 to a suitable stack, not illustrated. Two separate iiuid conduits 6 and 29 are located within fluid heating zone 6|. Each of the uid conduits 6 and 29 comprise a plurality of rows -of horizontally disposed tubes to which fluid heat is transmitted from the hot combustion 'gases passin'g thereover. A suitable checker wall or the like, such as indicated at IIB, may be provided, when desired, in the path of flow of the combustion gases ahead of fluid heating zone 8| in order to secure better distribution of the gases in this zone.

The function of the several heating coils is to supply to the relatively light and relatively heavy oils undergoing treatment substantially all of the heat required for cracking and for reducing the heavy liquid yconversion products to coke. It should be understood that the invention is not limited to the specific ow of oils through the .furnace here indicated so long as the streams of light and heavy oils supplied thereto are subjected to independently controlled heating conditions, both streams heated to a. high cracking temperature and at least the heavy oil stream subjected to high rates of heat input and permitted only a short time in the heating coil after it has reached an active cracking temperature. There are also other speclc forms of heaters which employ high rates of heat input to the oil, by utilizing direct and reflected radiant heat, which may be successfully utilized. However, the equinux type of heater has .been found most advantageous for this type of service and is the preferred form.

Coking zone in the particulary case here illustrated, comprises a continuous belt type conveyer |2, motivated by any suitable means, not illustrated inthe drawing, and disposed within a suitable insulated housing I3. The belt of the conveyer is preferably constructed of suitable metal or metallic alloy and in the casehere illustrated has upturned edges |4 for retaining the heavy non-vaporous conversion products which are discharged onto the belt at the inlet end of the coking zone through line 9 and which are reduced to coke during their passage through this zone. A layer of coke'is thereby accumulated on the belt and is continuously removed at the discharge end of the coking zone by means of a suitable scraper I8. Provision is also made for directing a spray of cooling material, such as water, for example, onto the surface of the coke layer at the discharge end of the conveyer, which serves to cool the carbonaceous material and shrink the same away from the metallic conveyer belt, thereby assisting its removal. Introduction of the cooling material may be accomplished by means of line I5, valve IS'and one or a plurality of suitable nozzles indicated at The coke removed from the conveyer, by means of scraper I8 or by cooling, or both, is discharged from the coking zone through a suitable outlet I9, communicating with a conveyor 20, by means of which the coke is discharged from the system. Preferably a portion of the outlet |9 and conveyor is immersed in a suitable quenching medium, not shown, whereby the coke is cooled to a sufllciently low temperature to prevent combustion thereof upon being discharged to the atmosphere.

The vaporous conversion products supplied to the coking zone and the vapors evolved in this zone during the coking operation may he withdrawn therefrom through line 2| and directed through valve 22 to fractionation in fractionator 23, wherein their components boiling above the range of the desired nal light distillate product of the cracln'ng and coking operations are condensed, as reflux condensate. 'I'he reflux condensate may be withdrawn from the lower portion of fractionator 23 and, directed through line 24 and valve 25 to pump 26 by means of which it is fed through line 21 and valve 28 to heating coil 29 and thence through line 38 into cracking coil 3|, wherein it is heated at a -product discharged from coil 3|, coking of the heavy liquid residue is accomplished on the continuous conveyer without supplying additional heat to the coking zone. lThe advantages of this `practice have been previously outlined.

The vaporous products from coking chamber II will, in many cases, contain relatively small" amounts of entrained or dissolved heavy liquids,

such as tars, pitches and the like, of a high coke- .boiling' materials from the lower boiling vaporous products may be accomplished, in which case the high-boiling liquids removed from the vapors in the tar'separating zone may be either removed from the system or returned, all or in part, to the heavy oil heating coil or direct to thecoking zone, as desired'. This particular feature has been previously disclosed by the present inventor in connection with another type of coking operation and, for the sake of simplicity, it is omitted from the present drawing.

Fractionated vapors of the desired end-boiling g point, preferably comprising materials within the boiling range of motor fuel, of good antiknock value, and uncondensable gas, are removed from the upper portion of fractionator 23 and directed through line 34 and valve35 to condensation and cooling in condenser 36. The resulting distillate and uncondensed gases pass through line 31 and valve 38 to collection and separation in receiver 39. Distillate may be withdrawn from receiver 39 through line 42 and valve 43 to storage or toany desired furtherv treatment. Regulated portions of the distillate collected invrcceiver 39 may, when desired, be recirculated by vwell known means, not shown in the drawing, to the upper portion of fractionator 23 to serve as a cooling and reuxing medium in this zone for assisting fractionation of the vapors and Ato maintain the desired vapor outlet temperatures from the fractionator. Y

Gaseous products of the operation which remain uncondensed and undiss'olved in the distillate are removed from receiver 39 through line 40 and valve 4I. Since this operation ordinarily produces a large amount of heavy olenic gases, such as propene and butene, the gases recovered from receiver 39 are ordinarily suitable as charging stock for a catalytic polymerization process and are preferably, although not necessarily, used as such.

The preferred range of operating conditions which may be employed in an apparatus such as illustrated and above described may be approximately as follows: The heavy charging stock. may be subjected in the relatively short-time heating coil to which it is supplied to a temperature, measured at the outlet therefrom, of from 900 ,to 975 F.,` or more, preferably at a pressure which may range from substantially atmospheric upto a superatmospheric pressure of 150 pounds, 'or thereabouts, per sq. in. Preferably, to obtain vshort time and high temperature, rates of heating of the order of 15,000 to`20,000 B.t. u./ *hour/sq. ft. of external heating surface are employed in coil 8. The heating coil to which the reux condensate is supplied and wherein it is preferably subjected to more severe cracking than the charging stock may employ an outlet onversion temperature ranging, for example, 'from 900 to 1000 F., preferably at a superatmospheric pressure measured at the outlet of the 75 iheating coil, of from 150 to 800 pounds, or more,

per sq. in. The rates of heating employed in coil 3| may be and are preferablyless than that in coil 8 but are ordinarily not less than approximately 10,000 B. t. u./sq. ft./hour. Preferably longer cracking time is provided for the light oil stream in coil 3| than that afforded the heavy oil stream in coil 8. The coking zone maybe operated at a slight superatmospheric pressure sucient to overcome thepressure drop through the succeeding fractionating, condensing, and' co1- lecting equipment, although higher pressures may be employed in this zone, when desired, and,

when it is constructed to withstandA higher pressures, the fractionating, condensing, and collecting portions of the system may employ pressures substantially the same or somewhat lower than that utilized in the coking zone. Preferably, however, a slight subatmospheric or substantially atmospheric pressure is employed in the coking zone. This may be accomplished,`for example, by exhausting the gaseous productsv from the receiverof the system through a blower or steamjet exhauster, not illustrated.

As an example of one specific operation of the process as it may `be conducted in an apparatus such as illustrated and above described, the charging stock is a residual oil produced by cracking and iiash distillation. It has a gravity of approximately A. P. I. and is supplied to the heavy oil coil from the asn chamber at a temperature of approximately 750 F. It is quickly heated in the heavy oil coil to an outlet temperature of`approximately 970 F. at a superatmospheric pressure of'about 50 pounds per sq. in. at the inlet of the coil and substantially ,atmospheric pressure at the coil outlet. The light oil stream from fractionator 23 is heated in the light oil cracking coil to an outlet temperature of approximately 1050" F. at a superatmospheric pressure of about 350 pounds per sq. in.' and the two heated streams are commingled and introduced into the surfaceof the continuous con,

'veyer in the coking zone after the pressure'on the light oil stream is released. The deposited coke is removed from the opposite end of the conveyer, quenched and discharged from the system. The coking zone-is operated at substantially atmospheric pressure. The vaporous products evolved in and supplied to the coking zone are cooled by indirect heat exchange with the light oil stream being Supplied to the light oil cracking coil, whereby heavy liquid particles, such as tars and the like, are removed from the vapors prior to their fractionation by the formation of the reflux condensate whichr comprises the light oil cracking stock.v The fractionation is controlled to give a distillate product of approximately 400 F. end boiling point. The reflux condensate supplied bythe light oil cracking coil has 'a gravity of approximately 18 to 20 A. P. I.

The above described operation will produce per barrel of charging stock approximately 47% of 400 F. end-point gasoline of good antiknock value and about 65 pounds of petroleum coke suitable as domestic or industrial fuel'. The remainder is chargeable principally to gas and loss.

I claim: 1. A process of cracking and continuous coking which comprises, quickly heating a residual oil to a temperature of the order of 900 to 975 F. f

by passing the same through a heating coil subjected to high rates of heating by direct radiation from flames and hot refractory surfaces in a furnace ,without allowing the oil suiilcient time in the heating coil to cause substantial coke formation and deposition therein, simultaneously and separately heating a lower boiling oil to a cracking temperature of the order of 950 to 1050* discharging resultant highly yheated products of both heating steps onto the moving surface of a conveyer disposed within a coking zone and thereon effecting reduction of the high-boiling components of theheated products to coke without additional heating, removing said coke from the coking zone, separately removing vaporous hydrocarbons supplied to and evolved within the coking zone therefrom, 4fractionating the vapors to form a relatively clean condensate of lower boiling characteristics than the first mentioned oil,- supplying said condensate as said lower boiling oil to the second mentioned heating step, subjecting resultant fractionated vapors of the desired end-boiling point to condensation and recoveringA and separating the resulting distillate and uncondensed gases.

2. A process of cracking and continuous coking which comprises, subjecting a residual oil in a heating coil to rates of heating of the order of 15,000 to 20,00 B. t. u.s per hour per square foot of external surface of said coil and thereby quickly heating the same to a temperature of the order of 900 to 970 F., simultaneously andseparately heating a lighter hydrocarbon oil to a higher cracking temperature at substantial superatmospheric pressure under conditions of more prolonged cracking time in another heating coil employing lower rat'es of heating than the rstnamed coil but of the order of at least 10,000 B. t. u.s per hour per square foot of external surface of said coil, discharging resultant highly heated products from both heating coils at substantially atmospheric pressure onto the moving surface of a conveyer disposed within a coking zone and thereon reducing their high-boiling components to coke solely by the heat contained in the products supplied thereto, continuously removing the accumulated coke from said conveyer and discharging the same from the coking zone, separately removing from the coking zone vaporous components of the heated prod ucts supplied theerto, fractionating the vapors to form a relatively clean condensate of lower boiling characteristics thanthe flrst mentioned oil, supplying said condensate .as said lower bollu ing oil to the second mentioned heating coil, subiecting resultant fractionated vapors of the de sired end-boiling point to condensation and re covering and separating the resulting distillate and uncondensed Bases.

3. A cracking an'd coking apparatus which comprises, in combination, a heating coil dini posed within afurnace to receive on both sides thereof radiant heat from flames and hot refractory surfa'ces of said furnace over which said iiames are passed, a heating coil of materially greater length than that ilrst mentioned and dis-l posed within a furnace to receive on both sides thereof radiant heat from flames and hot refractory surfaces over which said llames are passed, means for passing a continuous Stream of oil through the first mentioned heating coil, means .for passing .another stream of different hydrocarbon oil continuously through the second men- .tioned heating coil. means forl separately controlling the rates of'heating to which said separate streams are subjected'and means for independ# ently controlling the final temperature to which said separate streams are heated, a coking zone comprising a continuous conveyer disposed within an insulated housing, means for lsupplying highly heated products from each of said heating coils onto the surface of said conveyer. means for removing accumulated coke from said conveyer and discharging the same from the coking zone, means for separately removing vapors from the coking zone, a fractionator to which vaporous products from the coking zone are supplied, means for returning reflux condensate formed in said fractionator to the second men- 4 v tioned heating coil and means for condensing and recovering the fractionated vapors.

`JOSEPH G. ALTHER.

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