US2093279A - Process for the treatment of hydrocarbon oil - Google Patents

Description

P. c'. KEITH, JR

PROCESS FOR THE TREATMENT OF HYDROCARBON OIL Sept. 14, 1937.

Filed Nov. 16, 1933 MGQTM ATTORNEY Patented Sept. 14, 1937 UNITED STATES kATENT OFFICE PROCESS FOR THE TREATMENT OF HYDROCARBON OIL Percival C. Keith, Jr., Peapack, N. J., assigner to Gasoline Products Company,

Inc., Newark,

4 Claims.

This invention relates to processes for the treatment of hydrocarbon oil, and pertains particularly to processes for producing gasoline and intermediate products by cracking crude petroleum, or other relatively heavy charging stock.

It is an object of my invention to provide a process for separating a charging oil such as crude petroleum, reduced crude, or even lighter oil, into lighter fractionsV and relatively heavy residue, separately cracking certain of the lighter fractions, and the residue, combining the cracked products, separating the combined cracked products into vapors and a residue, removing and condensing certain relatively light vapors as a desired product, condensing and recycling for further cracking certain intermediate vapor fractions and extracting from the residue and recycling for further cracking, certain of the lighter constituents thereof.

Another object is to provide an improved method and means for preheating at a constant rate, charging stock for a cracking process, by indirect heat exchange thereof with hot products from the process, which after being cooled by the heat exchange step, are used at a variable rate in other steps of the process.

The above mentioned and other objects and advantages of my invention, and the manner of attaining them, will be made clear in the following description and accompanying drawing.

The single ligure of the drawing represents diagrammatically an oil cracking system embodying my invention. Referring more particularly to the drawing, reference numeral I indicates a charging line through which fresh, relatively heavy hydrocarbon. oil is introduced, by means of pump 2. This oil, which may be crude petroleum, reduced crude or even lighter oil, either virgin or cracked, passes through heat exchangers 3 and 4 into evaporator or stripper 5, preferably through line 6 having valve l, or alternatively through line 8 having valve 9 or through both lines simultaneously. Through line 6 the fresh oil is discharged over balile plates, or similar contacting means, I0, while through line 8 the discharge is directed into the trap-out tray II. The flow may be divi-ded between pipes 6 and 8 to maintain the desired temperature condition in the evaporator. In this evaporator the fresh oil, which may enter at a temperature of about 625 F., is subjected to further heating by contact withrising hot vapors, and resulting vaporized portions of the oil rise through the towerv condensation. The uncondensed vapors pass olf through vapor line I3 into fractionator I4 and the condensate formed in evaporator 5 is collected on trap-out tray II along with unvaporized portions of the fresh charge.

The mixture of condensate and unvaporized charging stock, free from lighter fractions, is withdrawn from trap-out tray II through pipe I5, and is forced by pump I6 through heating coils Il of combination furnace I8. The heated :l0 oil emerges from the furnace at a temperature which may vary considerably but which is suflicient to insure moderate cracking of the oil passing through the heating coils, for example sufficient to form from 8 toI 12% of products in the l5 gasoline boiling range per pass, preferably about 10%, this cracking being of a viscosity breaking nature. The temperature may range, for example, from 800 to 975 F., but preferably is about 860 F. Even higher temperatures may be used with charging stocks which have little tendency to form coke. The pressure used is preferably of moderate value, e. g. 250 pounds per l square inch, but higher or lower pressures may be selected. The pressure mayv range from 50 25 pounds per square inch, to 850 pounds per square inch for example, or even higher, depending on the stock being cracked, but I prefer the lower pressures of the order of 200 or 300 pounds, in most cases. The resulting highly heated cracked 30 products are then introduced through pipe IS into the lower part of evaporator 5, which may be held at the same pressure as the outlet of the heater coil, or at a somewhat lower pressure of, for example, about 220 pounds per square inch. Valve 20 is furnished to provide any desired pressure drop. The point of introduction of the cracked products is preferably below the level of the liquid in the lower part of the evaporator, but in any event is below trap-out tray II. Bailie plates or similar devices 2| are provided to prevent entrainment of heavy liquids in the vapors passing upwardly through the tower to a point above the trap-out tray.

Cracked residue or tar is withdrawn from the chamber 5 through line 22 having reducing valve 23, into the lower portion of a flash drum 24. This drum is equipped with a trap-out tray 25, located above the point of entrance of the residue, and a series of bafe plates 2l and bubble trays or other fractionating elements 2B, which serve partially to fractionate the vapors rising in the ash drum. The pressure maintained in the drum 2li is preferably materially lower than that maintained in the evaporator 5, being for example,

about `5 pounds per square inch, although higher `or lower pressures may be used. As a result of the reduction in pressure the lighter constituents Y of the introduced residue are vaporized and pass upwardly through the drum past the trap-out tray 25, being subjected to partial condensation by contact with the baille plates and fractionating elements 21 and 28, which are supplied with re- .flux from an external source, through pipe 3|, in Vthe usual manner.

Light fractionated vapors pass oi from the top of the tower through vapor line 32, heat exchanger 33 and cooler 34, into Vflash 'Y distillate receiver 35. A portion of this flash distillate may be removed through pipe 36 and forced by pump 31 through line 38, both into the pipe 3I and through a branch line 39 into conduit 22 which conducts the unvaporized residue I lto the flash drum. The liquid so introduced into the line 22 serves to'cool the products entering thelower part of the flash drum, thereby diminishing any tendency toward cokeY formation, either in'the valves 23 and 30, orfin the drum itself, and the liquid introduced through the line 3I serves as the cooling or refluxing mediumfor the upper portion of the'tower 24. f VThe condensate collected on trap-out tray 25, being substantially free from extremely heavy products which ten'd'very'easilyto Vform cokeY deposits under heat treatment, is removed through line 40 and Vforced by Ypump 4I into charging line I in mixture with the fresh charge,

for further heat treatment in connection thereplates 42 and bubble trays or other fractionating elements 43, withY the resulting formation of av reflux condensate, a portion of which is collected o-n a trap-out tray Y44, and the remainder of whichY Vcollects in the bottom of the tower.

'I'he condensate collected in the trap-out tray 44 is withdrawn through pipe 45 and passed under pressure generated by pump 46, which ispreferably adapted to cause a substantially constant flow ofV oil, in a. divided path both through line 41 and heat exchanger 48, and line 49 and heat exchangers 4, the division of Yilow being con-` trolled by valves V5I and 52. The two lines mentioned join at point 53 and from that point condensate is passed through line 54, having branch line55 and 56, into the tower 5, Ypipe 55 Ventering ata point above the baille plates 2 I, and

,pipe 56 entering above the bubble Vtrays I2, these two lines providing reflux medium for the operation of the tower. Line 51 isprovided for-introducing'a portion ofthe condensate as a refluxing medium over the baffle plates 42 in the lower portion of tower I4. Valvesl 58, 59, and 60 provide the'necessary control. Y

It is desired that the quantity of reflux con-Y Y densate passing in heat'exchange relation with the fresh charge, by agency of heat exchangers 4 shall be substantially constant whereby substantially constant preheating of the fresh charge may be assured. In order to maintain this flow of condensate'substantially unvaried, arflow controller 6I is placed inthe line 49 between heat exchangers 4 and its junction with line 41 at point 53, and this Vflow controller is arranged to operate a valve 62 in a return line 63, which f valve 58 is opened from a given position, by-pass valve 62 is automatically closed somewhat to compensate. It is also desired that the temperature Y in the base of the stabilizer tower8l)V be maintained substantially constant, and to insure this result bey-pass line 50, having valve 50', is provided. The hot oil flowing through line 41 is diverted through by-pass 50 automatically by opening or closing of valve 50 under control of temperature responsive device 48 located in circulating line 84, or otherwise adapted to determine the temperature in the base of the stabilizer tower. Any change in the flow of oil through line 49, which might-tend to occur as a result of Ya change in the settingV of valve 5I or valve l50',

is also compensated for bythe automatic adjustment of by-pass valve 62. By this,V arrangement of controllers all or part of the reux condensateV withdrawn from tower I4through` pipe 45, may be passed through pipes 55, 56 and 51 as areiiuxing medium, without altering the rate of 4heat transfer in exchangers 4 and 48. i

A light condensate may be removed throughy pipe 66, from trap-out tray 65, located near the top of the fractionator, and be forced by pump 61 through heatY exchangers 3 and adjustable auxiliary cooler 69 back into the top of the fracgthe distillate .formed being that desired for the final product. y

These vapors pass off from the top of the fractionator through vapor line 10 and condenser 1I through line ,12, havingrreducing valve 13, into the primary gas separator 14. The fractionator I4 may be held under substantially the same pressure as that of the evaporator 5, or a slightly lower pressure, e. g. 220 pounds per square inch, and the primary gas separator 14 may likewise be held under substantiallythe same pressure as that of the Vfractionator I4, or a somewhat lower pressure. In the primary gas separator fixed gases and very light vapors, mainly those lyingV outside of the desired gasoline boiling range, are separated and pass off through partial condenser or fractionator 15, and vapor line'16, while the Vliquid condensate collecting in separator 14 is removed through draw-off line 11, and forced by pump 18 through heat exchanger 19 vand auxiliary heater 19' into an intermediate point in the stabilizer tower.V 80, which is preferably held ata higher pressure than thatV of the fractionator I4, for example, about 400 pounds per square inch, although higher or lowerrpressure Vmay be used. The reference numeral 8|' indicates a reiluxing line through which a cool refluxing medium maybe introduced into the top of the stabilizing coiumn in the usual manner. The stabilized gasoline is withdrawn from the bottom of the stabilizer 8U through line 8|, and passed through heat exchanger 'I9 and cooler 82, into receiver 83. A quantity of the stabilized gasoline is preferably removed from the bottom of the stabilizer through line 84, circulated by pump through heat exchanger 48, and returned to the stabilizer at a higher temperature to supply added heat for aiding the stabilization process.

By means of the heat exchanger I9 the gasoline to be stabilized in the stabilizer 80 is first preheated by indirect heat exchange with the nished stabilized gasoline withdrawn from the bottom of the tower. The heat exchanger 48 on the other hand, provides means whereby additional heat necessary for reboiling may be supplied to the base of the stabilizer, this heat being derived from reflux condensate withdrawn from fractionator I4. 'I'his reflux is at the same time cooled, so that it will have the desired temperature for introduction as reflux into the evaporator 5 and fractionator I4.

Reflux condensate collecting in the base of fractionator I4 is withdrawn through line 86 and forced by pump 81 through vapor phase heating coils 88 of furnace I 8. The highly heated cracked products pass from the furnace through line 89 at a relatively high cracking temperature into the lower part of evaporator 5, preferably below the liquid level therein. The temperature of the cracked products leaving heating coil 88 may vary considerably depending on such factors as the character of the charging stock and character of the desired products, as well as the applied pressure and time of heating contact. It may, for example, vary over a range of from 875 to 1200 F. but suitably is from 900 to 1000 F., preferably about 950 F. The pressure of the products leaving the vapor phase heating coil 8B may be from a few pounds to several hundred pounds higher in value than the pressure maintained in evaporators 5, preferably, however, the pressure is about '750 pounds per square inch, gauge. The necessary reduction in pressure of the vapor phase cracked products prior to their entrance into evaporator 5, is effected by a pressure reducing valve 90, located in the line 89. The time of passage of the clean condensate through the heating coil 88 is preferably so selected that a relatively large amount of cracking of the products in the gasoline 'boiling range, per pass, is effected. The cracking per pass may be, for example, from 15 to 25%, preferably about 20%, although the percentage permissible will necessarily vary with different charging stocks, the cleaner the stock the higher the cracking percentage possible.

Ihe highly heated cracked products entering the base of evaporator 5 through line 89 aid in separating into vapors and liquid residue, the cracked heavy oil introduced through line I9, the highly heated vapors passing upwardly through the evaporator and aiding in heating the fresh charge and reflux condensate from tower 24 introduced through line 6, and stripping the lighter fractions therefrom.

The heavy flashed residue or tar remaining in liquid form in the base of flash drum 24 is withdrawn through draw-off pipe 9| and is forced by pump 92 through cooling coil 93 into receiver 94. A portion of the cooled tar is diverted through by-pass pipe 95 having control valve 96, into the pipe 9I, just at the point where it leaves the flash drum 24. This recirculated cooled tar serves to prevent the deposition of carbonaceous materials or other heavy products in the pipe 9I, both by cooling the tar immediately upon its removal from the flash drum, and by increasing the velocity thereof through the pipe 9| above that which would obtain if this material were not recirculated.

While I have shown the two heating coils I1 and I8 as located in a single furnace having independent combustion chambers for portions o f the two coils, and a common convection section for other portions of the two coils, a separate furnace may be used for each of the heating coils, such an arrangement lending slightly greater flexibility to the system.

In operation fresh charging stock of a relatively heavy nature, such for example, as a Mexican crude oil, reduced crude, or the like, is introduced into the unit through pipe I, and passes through the heat exchangers 3 and 4, wherein the temperature thereof is raised by indirect heat exchange with condensate withdrawn from the fractionator I4, the temperature attained by the charging oil being, for example, about 625 F. more or less, and the heated oil is introduced into the evaporator 5, either at a point above the baille plates I0, or at a point adjacent the trap-out tray I I, or both. The introduced oil is heated in the evaporator to a somewhat higher temperature by the hot vapors rising from the bottom of the evaporator, and as a result lighter portions of the fresh charging stock separate as vapors from the heavier portions which remain in liquid form and are collected on the trap-out tray II. 'Ihe vapors are subjected to partial condensation in the upper portion of the evaporator 5, and those remaining uncondensed pass off from the top thereof through vapor line I3, into the fractionator I4, the boiling characteristics of these vapors being regulated by the cooled refluxing liquid introduced through pipe 56. The unvaporized portions of the fresh charge, commingled with condensed portions of the vapors rising through the evaporator 5, are removed through line I5 and raised to a cracking temperature in the heated coil I'I, this temperature being preferably about 860 F., more or less, although higher or lower temperature may be used, for example from 800 to 975 F., depending upon the character of the charging stock. This temperature and the cracking time should be great enough, however, to produce a moderate amount of cracking of the stock passing through the heater, the amount of cracked products in the gasoline boiling range formed per pass being as great as possible without deleterious deposition of coke in the heating coils and associated apparatus. The amount of conversion may be, for example, 8 to 12% per pass, preferably about 10%, this cracking step being in the nature of a viscosity breaking operation. The pressure at which the cracked products emerge from the heating coil II is preferably about 250 pounds per square inch, although higher or lower pressures may be used, ranging, for example, from 50 pounds per square inch upwards. The highly heated cracked products are then introduced into the base of evaporator 5 wherein they undergo separation into vapors and a liquid residue, the vapors rising through the tower vagainst a downwardly owing stream of reflux from pipe 55, and those remaining uncondensed serving to raise the temperature of the fresh charge introduced through line SJTheliquidresidue remaining in the base of the evaporator is preferably vn'thdrawn through line 22 and passed through reducing valve 23, into thebase of ash drum 24, preferably maintained under a very low pressure, such Vas 5 pounds per square inch, wherein light products separatel as vapors from a heavy liquid residue or tar. If desired part or all of this residue may be diverted from the process through line |0| and cooler |92, into receiver |03. The vapors released in flash drum 24 pass upwardly therethrough and are subjected to partial condensation by the action of contacting elements 21 and 28, which may be baille plates and bubble trays respectively, and the downwardly Yflowing reflux liquid introduced through line 3|. Condensate formed iscollected on the trap-out tray 25 and this may have a temperature of, for example, about 630 F., althoughlhigher or lower temperature may be used. Y This condensate is passed Vthrough the line 40'into the charging line where it mingles with the fresh stock and is recycled through the system. Any portion ofthe condensate from the line 40 which is not vaporized in the evaporator 5 is caught on trap-out tray and recycled through the viscosity breaking. heating coil |1. VThose vapors which remain uncondensed at the top ofthe flash drum 24 pass off through line 32, heat exchanger 33, and cooler 34 into the flash distillate receiver 35. A 'portion'of Vthe flashrdistillate collected therein may be forced through pipes 36 and 38 into the top of the flash drum Y24 as reflux, and another portion may be divertedV through line 39 into thek line 22 to commingle with the hot residue therein and prevent coking of the valves 23 and 30, and associated apparatus. In order that the level of the liquid in receiver-35 `shall not rise Vabove a predetermined value, Va Vportion of the Vnism 98 which is connected with Valve 99 Vand serves to open that valve'upon a predetermined rise of liquid in the flash drum 35, thereby diverting an additional amount thereof through line `91. TheV tar accumulating in the baseof flash drum V24 may be withdrawn through drawoff line 9| and cooler 93 into receiver 94.V During the drawing off of the tar a quantity'of the cooled tar may be recirculated through line 95 and the pipe 9| just at the point Where it leaves the drum 24, this circulating liquid serving to increase the fluid velocity through the pipe 9|, while at Vthe same time cooling the tar therein and in this manner preventing the deposition of, heavy materials in that line. Reference numeral |04 indicates a relief valve set to openV whenexcessive pressure is exerted in drum 24.

The vapors removed from the top of evaporator 5, which for example, may have Va temperature of about 750 F. and a pressure of 220 pounds per square inch, are introduced into the fractionator I4'Y through line |3 having a valve I3' therein. The pressurev in the fractionator Yis preferably approximately the same as thatin the., evaporator 5,;or slightly lower, for example 220 Ypounds per square inch, anynecessary adjustment thereof being made by means of valve I3'. In the fractionator |4 the introduced vapers undergo fractionation in the usual manner,

' trap-out tray with the resulting formation of reflux conden-y sate, a portion of which collects on trap-out tray Y44, and another portion of which collects in the base of the fractionator I4. The condensate collected on tray 44 is removed through pipe 45 and forced through lines 41 and 49 which joinV at point 53. The line 41 has heat exchanger 48 therein, by means of which the reflux condensate is broughtinto indirect heat exchange relation with gasoline removed from and returned to stabilizer column 80, thereby serving to heat the gasoline and maintain the desired temperature in the stabilizer tower. Line 49, on the other hand, is provided with heat exchangers 4, by means of vwhich heat is extracted fromr the reflux condensate and transferred to the fresh l charge passing through line VThe commingled` streams of condensate from lines 41 and 49, including any flash distillate from line 91 pass from point 53 through lines 55 and 56 to a point charge, is insuredby means of the flow controller 6|, which adjusts by-pass or control valve 62 in such manner as to maintain constant the flow of reflux condensate through the heat exchangers 4, any excess of reflux condensate over.

thatv necessary for refluxing in fractionator I4 and evapcratorS being returnedY through line 63 to the fractionator I4. Condensate collecting in the base of fractionator |4y is withdrawn through line 86 Yand passed through vapor phase heating coils 88, wherein it is raised to a cracking temperature of, for example, about 950 F. and is held at a cracking temperature for avsuficiently long time to insure a kmoderate amount of cracking. VWhile the temperature to which the oil is raised may vary considerably, for example, from 875 to 1200 F., the Ytemperature is most desirably kept within the range of 900 to 1000o F., preferably about 950 F., and the time of contact is adjusted to produce a crackheated cracked products are, then reduced in:

pressure by action of reducing valve and introduced into the base of the'evaporatorfS, preferably below the level of the liquid residue therein, and aid in reboiling that residue, resulting vapors rising through the column and contacting with the fresh charge at a point above the The reflux liquid introduced through lineY 55, and the baffle plates or other contacting means 2| serve to prevent entrained particles of heavy residue from rising with these vapors to a point above the trap-out tray.

K In fractionator |4 the rising vapors adjacent the top of `the column are refluxed by light condensate removed from trap-out tray 65, cooled in heat exchangers 3 by indirect contactwith fresh charge and, if desired, further cooled in auxiliary water cooler 69. The cooled condensate is then introduced in desired quantities into the top of the fractionator tower, the cool light condensate so returned serving to control the boiling characteristics of the vapors leaving the fractionator, to give the desired gasoline distillate. These vapors are condensed in condenser 'H and are then introduced into the gas separator 14, either with or without a reduction in pressure thereof. In the separator 1d the fixed gases and very light vapors which have not been condensed in passage through condenser ll, pass off as vapors through the partial fractionating column 'l5 and pipe l to an absorber column or any other desired destination. The incompletely stabilized distillate is removed from separator 'i4 and passed through line ll, at an increased pressure generated by pump "i8, through heat exchanger 'I9 into an intermediate point in stabilizer columnll, wherein it undergoes stabilization in the usual manner, the stabilized gasoline being removed through draw-off line 8l and heat exchanger 'i9 wherein it gives up contained heat to the distillate being introduced int-o the stabilizing column, and is collected in the receiver 83 after cooling in cooler 82. Any fixed gases and extremely light hydrocarbon vapors pass off from the top of the stabilizer column through line lfl in the usual manner. A portion of the distillate from separator 'i4 may be diverted through pipe l1 and cooler 'i8' into the top of the fractionator column I4 as a refluxing medium in the usual manner, control being effected by valve |19.

While I have described a particular embodiment of my invention for the purpose of illustration, it should be understood that various modifications and adaptations thereof, occurring to one skilled in the art, may be made within thespirit of the invention as set forth in the appended claims.

I claim:

1. The process of treating hydrocarbon oil which comprises heating fresh relatively heavy hydrocarbon oil to a cracking temperature under superatmospheric pressure, to cause cracking thereof, introducing the resulting cracked products into a vaporizing zone wherein vapors separate from a liquid residue, removing said vapors and introducing them into a fractionating zone wherein heavier fractions are separated as condensate from lighter fractions as vapors, removing hot condensate from said fractionating zone and passing the removed condensate, while still hot, in indirect heat exchange relation with said fresh oil, to preheat said fresh oil, dividing said removed condensate, after the heat exchange step, into two streams, introducing one stream into said vaporizing zone as av refluxing medium,

returning the other stream into said fractionat-I ing zone, varying the quantity of oil passing through said one stream to give the desired refluxing effect in the vaporizing zone, and varying said other stream to regulate the amount of preheating of said fresh oil.

2. A process according to claim l wherein upon variation of said one stream to produce a desired reiuxing effect, said other stream is correspondingly varied to maintain substantially constant the flow of condensate in indirect heat exchange with said fresh oil.

3. A process according to claim 1 wherein added oil is injected into said two streams at the point of junction thereof and wherein upon variation of said one stream to produce a desired refluxing effect, said other stream is correspondingly varied to maintain substantially constant the flow of condensate in indirect heat exchange with said fresh oil.

4. In the treatment of hydrocarbon oils in which the oil is subjected to cracking conditions, resultant products of cracking subjected to vaporization in a vaporizing zone and separated Vapors subjected to fractionation in a fractionating zone, the method of preheating charging stock to the system and controlling refluxing therein which comprises withdrawing hot condensate from the fractionating zone and cycling said condensate in a closed circuit by passing the withdrawn condensate in indirect heat exchange with fresh charging stock for the system to thereby preheat such charging stock, dividing theresultant cooled condensate after the heat exchange step into two streams, conducting one stream to said vaporizing zone as a reuxing medium, conducting the other stream to said fractionating zone as a reuxing medium, varying the quantity of oil passing through said one stream to give the desired refluxing effect in the vaporizing chamber and varying said other stream to regulate the amount of preheating of said fresh charging stock.

PERCIVAL C. KEITH, JR.

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