US2046385A - Process of treating hydrocarbon oil - Google Patents

Description

July 7, 1936. c. KEITH, JR

PROCESS OF TREATING HYDROCARBON OIL Filed Feb. 10; 1934 H INVENTOR ATTORNEY wwmixh atente July 7, i936 PROCESS OF TREATING EARBON OH.

Percival 0. Keith, in, Peapack, N. 3., assignor to Gasoline Products Company, Inc.,

Newark,

N. 3., a. corporation of Delaware Application February 10, 193%, Serial No. 710,617

2 Claims.

This invention relates to processes for the treatment of hydrocarbon oils and pertains more particularly to processes for simultaneously producing lighter oils such as gasoline from the heavier higher boiling oils and at the same time forming high anti-knock gasoline from the heavy naphtha or other charging stock of a gasoline nature.

It is an object of my invention to provide a process for converting a relatively heavy charging stock, such for example, as crude residuum or the like, into lighter lower boiling point oil such as gasoline, while at the same time in an interrelated series of process steps converting relatively heavy naphtha or other gasoline-like oil of relatively low anti-knock value, into high anti-knock gasoline.

In accordance with my invention fresh rela- I tively heavy charging stock, such for example as crude residuum, heavy gas oil or the like, is passed in heat exchange with products of cracking produced in the process, so that the fresh charge is raised in temperature, and is then introduced into a flashing zone wherein it is further raised in temperature by contact with hot vapors; a relatively heavy condensate and unvaporized portions of the relatively heavy charging stock are withdrawn from the flashing zone and, after further heat exchange with hotter products of cracking, are introduced into an evaporating zone wherein partial vaporization thereof occurs by contact of the introduced oils with hot vapors rising through the evaporating zone; a mixture comprising unvaporized portions of the introduced oil and condensed portions of the rising vapors is withdrawn from the evaporating zone and passed through a viscosity breaking furnace wherein the mixture is subjected to a mild cracking operation of a viscosity breaking nature, and the resulting cracked products are reintroduced into the evaporating zone; vapors are 'passed from the evaporating zone to a separate fractionating zone wherein they are subjected to fractional condensation, the fractionated vapors 45 being removed and condensed as a desired disintroduced into the evaporating zone already mentioned. The final distillate mentioned y also be subjected to a stabilizing process if de= sired by being passed through a. separate stabilizing zone wherein the heat necessary to carrying out the stabilizing operation is derived from hot products of the cracking operation mentioned.

The above mentioned and furtherobjects and advantages of my invention and the manner of obtaining them will be 'made clear in the following description taken in conjunction with the accompanying drawing. The single figure of the drawing represents diagrammatically a cracking apparatus adapted to carry out my invention.

Referring more particularly to the reference numeral i indicates a charging line through which fresh relatively heavy charging stock, such for example as crude residuum, heavy gas oil or the like, is forced by pump 2, subsequently passing through indirect heat exchanger 3 into fuel oil flash tower 4, wherein it contacts with vapors rising from hot cracked products introduced at a lower point, the point of introduction of the fresh charging stock preferably being intermediate a plurality of bubble trays or other fractionating devices 5. By contact with the hot rising vapors a portion of the charging stock may be vaporized, the unvaporized portion, in mixture with any condensed portion of the rising vapors, being collected on trap-out tray 6, which is provided with a tall stand pipe 1 which forms, at an intermediate point in the-flash tower d, an accumulator tank or reservoir from which the mixed liquid may be withdra as, necessary. The liquid is withdrawn through pipe 8 and forced by pump 9 through indirect heat exchanger in intothe evaporator ll, either through refluxing line l2 or through line it, both of which are provided with control valves as shown. A similar control valve may -be placed around the indirect heat exchanger it in order to control the heat exchange operation taking place therein. The amount of oil introduced through line l2 into the evaporator it is preferably only that necessary in order to properly refrom which the mixed oil, comprising unvapors iz ed portions of the oil introduced through pipes l2 and I3 and condensed portions of the rising vapors, may be withdrawn for further treatment.

This mixed oil is withdrawn through pipe l1 and forced by pump l8 through the coils of viscosity breaking furnace or heater l9, wherein the oil is raised to a cracking temperature of,

ture.

line 20 having reducing valve 2| into the lower 7 part of evaporator preferably below the level of the liquid therein. The pressure maintained in .the evaporator may be the same or a somewhat lower pressure than that maintained at the'outlet of the viscosity breaking furnace, any pressure differential being insured by action of control, valve 2 I. The pressure in the evaporator may be, for example, about 200 pounds per square inch.

In the evaporator the introduced cracked productsseparate into vapors and liquid residue, the

I former passing upwardly through the evaporator past baflle plates or other contacting elements 22, thence through stand pipe l5 and past the bubble plates or other fractionating elements H in the upper part of the evaporator, directly contacting the relatively heavy oil introduced through pipe l2, with resulting partial condensation of the rising vapors and partial evaporation of the introduced relatively heavy oil.

' The vapors remaining uncondensed at the top of the evaporator pass out through vapor line 23 into bubble tower 24, wherein they are subjected to fractionation in the well known manner. Fractionated vapors pass off from the top of the bubble tower through vapor line 25 and condenser 26, the resulting condensate being collected in the receiver 21, which is also preferably held under substantially the same pressure as that of the evaporator II and bubble tower 24. In this separator, or receiving drum, gas separates from the liquid distillate, the former passing out through vent line 28 while the latter may be withdrawn from the process through draw-off pipe 29, but is preferably instead passed to a stabilizing tower 30. r

Another stream of fresh charging stock, such as heavy naphtha, natural gasoline or other gaso-' line like material having a relatively low anti-' knock value, is forced through line 3|, by action of pump 32, into the coils of cracking or reforming furnace 33, after having passed in any desired .quantities through indirect heat exchangers 34 and 35 wherein the fresh charging stock is subjected to heating by indirect heat exchange with a side stream withdrawn from the bubble tower 24 and with liquid residue withdrawn from the evaporator l I. Control valves are provided around the heat exchangers 34 and 35,

as indicated,- so that the desired heat exchange action may be secured. The preheated heavy naphthaor the like is combined-with reflux condensate withdrawn from the baseof bubble tower 25 +hrough pipe 36, and subjected to pressure created by pump 31, the resulting oil mixture passing through common pipe 38 into the coils of cracking furnace or heater. 33, wherein the mixture is raised to-a cracking temperature of, for example, in the neighborhood of 960 F., under an outlet pressure of, for example, about 800 pounds per square inch, and therein subjected to cracking and reformation such that The resulting cracked and reformed products pass from the furnace 33 through line 39, having reducing valve 40, into the base of evaporator ll, preferably below the level of the liquid therein. In the evaporator the cracked and reformed products undergo separation into vapors and liquid residue, similarly to the cracked products from the viscosity breaking furnace l9, the vapors rising through the evaporator while the liquid residue is withdrawn therefrom through line 4|, having reducing valve 42, and is introduced into a low point in fuel oil flash tower 4, preferably intermediate a plurality of baille plates or similar contacting devices 43. In this fuel oil flash tower a considerably lower pressure is maintained, for example, a pressure in the neighborhood of IS pounds per square inch, and as aresult of this decreased pressure the introduced liquid residue undergoes partial vaporization through the agency of its contained heat,

" so that the desired cooling action of heat exchanger 3 may be obtained and pump 41 being furnished to supplyany necessary pressure in order to eject the oil, as well as to return a portion thereof through valved line 48 in any volume necessary to maintain the desired low temperature in the base of the-fuel oil fiash tower, to

prevent coking thereof.

The vapors pass upwardly through fuel oil flash tower around the batlle plates 43 and through the stand pipe 1, in the upper portion of the flash tower being contacted with the heavycharging stock introduced through charging line and being subjected to partial fractionation by contact with baille plates .or other similar fractionating elements 5. The uncondensed vapors pass off from the top of the flashtower 4 through vaper line 49, heat exchanger 50 and auxiliary cooler or condenser 5|, into a receiving drum 52, from which distillate may be withdrawn through line 53 and passed, by action of pump 54, into the fuel oil flash tower through branch lines 55 and 53, for refluxing purposes, another portion being passed through line 51 and heat exchanger 50 into an intermediate point in the bubble tower 24, as a refluxing medium The heat exchanger 50 may be by-passed ifdesired, as shown. A

This temperature preferably should not rise above about 825 F. in order to insure that coke formation therein will not be excessive.

Line 621s furnished. so that a portion of the. reflux condensate formed in bubble tower. 24

aoeaass may be diverted from the process, if necessary, in order to establish balanced operating conditions. Cooling is supplied to the top of the bubble tower by withdrawing a stream of reflux condensate from a trap-out tray through pipe 63, passing the liquid so withdrawn through indirect heat exchanger 34, wherein it is cooled by indirect contact with relatively cool light gasolinelike charging stock, and is then returned to the top of the bubble tower in necessary quantities by action of pump 66, the quantity so returned being controlled, for example by a temperature responsive automatic valve 65.' Reference numeral 66 is applied to a liquid level indicator attached to the base of the bubble tower.

It may be preferable to subject the distillate collected in the receiver 2! to stabilization, and to this end the distillate may be passed through pipe 61 and be forced by'action of pump 68, through indirect heat exchanger 69, into an intermediate point in the lower portion of the stabilizer tower 38, to any one of a plurality of different inlets, as shown. In the stabilizer tower undesirably light gases are separated from liquid which it is desired to include in the final distillate, the gases passing off from the top of the stabilizer tower through line 10 and partial condenser it into reflux drum 12, the amount of cooling supplied by the condenser H being regulated by the level of the liquid in the reflux drum, as indicated diagrammatically by the apparatus interconnected by a dotted line I3. Refluxing liquid is returned from the reflux drum to the top of the stabilizer tower through line M by action of pump l5. In order to maintain the desired temperature in the base of the stabilizer tower a quantity of liquid is collected on trap-out tray i6, withdrawn therefrom through pipe i7, and forced by pump 78 through indirect heat exchanger l9, thence back into the base of the stabilizer tower. Reflux condensate is withdrawn from trap-out tray 80 located in the base of bubble tower 2% and passed through the other side of the indirect heat exchanger l9 inregulated quantities automatically controlled by temperature responsive valve mechanism Bl. After passing through the indirect heat exchanger it a portion of the reflux condensate is returned under pressure generated by pump 82, through line 83 to the bubble tower 26, at an intermediate point therein, for refluxing purposes, branch line 86 being furnished for this purpose. Another portion of the cooled reflux condensate is passed through line 35 into the top of evaporator it as a cooling medium, the quantity being regulated as desired by control valve 85. Reference numeral 81 indicates a liquid levelindicator for the base of the stabilizer tower.

Operation In operation fresh relatively heavy charging stock, such, for example, as California reduced crude of about 16 A. P. I. gravity, is passed through the charging line i and heat exchanger 3 into the fuel oil flash tower l, wherein the descending stream of fresh charging stock contacts the rising stream of hot vapors and is heated, a portion thereof perhaps being vaporized while heavier fractions of the rising vapors are condensed by the cooling action. Unvaporized portions of the fresh'charging stock and condensed fractions of the rising vapors collect on the trap-out tray 6 and are withdrawn through line 8, passed through heat exchanger it wherein they are further heated, and are introduced into at evaporator ii, a portion thereof being utilized as the reflux and being introduced about bubble plates or other fractionating elements in the evaporator, the remainder thereof being injected directly on to the trap-out tray B6 on which collect unva-porized portions of the introduced liquid oil and condensed fractions of the hot vapors rising through the evaporator. This mixture of introduced liquid oil and condensate forms a composite charging stock for viscosity breaking furnace or heater l9, through which it is passed by way of conduit H. In passing through the coils of the viscosity breaking furnace the heavy oil is raised to a cracking temperature of a moderate value, for example in the range of 840 to 880 F., preferably about 860 F. and is subjected to a moderate amount of cracking therein of a viscosity breaking nature, the percentage of conversion to products in the gasoline boiling range, per pass, being, for example, from 8% to 12%, preferably about 10%. The pressure at the outlet of the viscosity breaking furnace may be, for example, from 200 to 400 pounds per square inch, more or less, but is preferably in the neighborhood of 200 pounds per square inch. The resulting viscosity broken products pass through the line it into the base of the evaporator H, preferably below the level of the liquid in the base thereof so that an agitating action is obtained.

In the evaporator ii the vapors passing upwardly around baffle plates or other contacting devices 22, through the stand pipe 85 and then through bubble plates, or other devices of a similar nature, it, at the same time being subjected to cooling action by contact with the liquid oil being introduced through pipe 82, and by contact with refluxing liquid introduced at the top of the evaporator through pipe 85. The vapors remaining uncondensed at the top of the evaporator pass through vapor line 23 into a lower level of the fractionator 26, wherein these vapors are subjected to fractionation in the usual well known manner. The fractionated vapors are removed from the top of the fractionator through pipe 25 and condenser 26, the resulting condensate being collected in the receiver 27. Reflux condensate formed in the fractionator is withdrawn through pipe 36 and passed to the coils of cracking furnace or heater 33 in mixture with fresh heavy naphtha or similar gasoline-like charging oil, which haspreferably been pre viously preheated by passing through heat exchangers 36 and 35, respectively.

In the furnace 333 the mixture of reflux condensate and heavy naphtha is raised to a cracking temperature of a relatively high value, e. g. in the range of 900 to 1000 F. thereabouts, preferably in the neighborhood of 960 F., and is therein subjected to cracking of the heavier products and reformation oi those in the gasoline boiling range. The quantity of gasoline-like products in the output from the cracking furnace 33 will be relatively high, particularly on account of the presence of the heavy naphtha or the like in the charge for the cracking furnace. The percentage of gasoline-like constituents in the cracked and reformed products emerging from the furnace will be strongly dependent upon the amount of naphtha or the like introduced through the charging line 3i, with respect to the amount of reflux condensate with which it is combined. For example where the amount of naphtha and the amount of residuum charged to the process are approximately equal the percentage of gasoline in the output of the 5 The operation in cracking furnace 33' is preferably so conducted that the outlet pressure of the furnace is relatively high,e. g. about 800 pounds per square inch, although pressures even lower or higher may be used. For example the pressure may range from 200 pounds per square inch to 1000 pounds per square inch, more or less. The cracked and reformed products from the cracking furnace 33, after reduction in the pressure thereof by action of reducing valve 40, pass into the evaporator I l and therein undergo separation into vapors and liquid residue similar-.

1y to the products in the viscosity breaking furnace l9.

Liquid residue collecting in the base of the evaporator l l is withdrawn through pipe 4 I, pressure reducing valve 42 and is introduced into fuel oil flash tower 4, which is maintained under a pressure considerably lower than that in the evaporator, the pressure in the flash tower being, for example, in the neighborhood of 15 pounds per square inch. As a result of the reduction in pressure the introduced liquid residue undergoes separation into vapors and liquids in the fuel oil flash tower, the vapors rising upwardly past the baflie plates 43 or the like, through stand pipe 1 and past the bubble trays or similar fractionating elements 5, the resulting fractionatlng vapors being removed *from the top of the tower through vapor line 49 and heat exchanger 50 and cooler 5|, respectively, the resulting condensate being collected in the accumulator 52. Condensate so collected is pumped back in desired quantities as reflux for the baille plates 43 and bubble trays 5, while any remainder is di- The distillate collected in the receiver 21 may be subjected to conventional.stabilization in the tower 30, the heat necessary for effective stabilizing operation being obtained from the reflux condensate passing downward through the bubble tower or fractionator 24. To this end reflux condensate is collected on trap-out tray 8|] and passed through the heat exchanger I9 and then returned in desired quantities as a refluxing medium to an intermediate point in the fractionator 24 and to an upper point in the evap- 60 oratorv II. The gasoline distillate enteringthe stabilizing tower 30 from the receiver -2'lis preheated by passing all or a part thereof through heat exchanger 59, and refluxing is accomplished by returning to the top of the stabilizer tower a quantity of condensed lighter products which has been collected in the receiver 12; The level of condensate'in the receiver 12 is maintained constant-by an automatic valve mechanism I3 which regulates the cooling action of adjustable cooler 70 ll automaticallyso as to form the necessary amount of condensate.

The temperature in-the base of the evaporator I l is maintained at such a low value as to prevent coking by withdrawing a portion of the liquid res-.

idue therein, passing it in indirect heat exrected through heat exchanger 50 into an inter-' mediate point in the fractionator 24. The liquid change with cooler liquid in heat exchangers l0 and 35 and returning the cooled liquid to the base of the evaporator. The temperature in the base of the evaporator is preferably kept below a value of about 825 F. in order to insure a reasonable length oi run without coking difliculties. j A similar withdrawing and returning arrangement is provided for the base of the fuel oil flash tower 4 in order to maintain the necessary low temperature. The liquid oil withdrawn from the base of the flash tower through pipe 44 is cooled by passage through indirect heat exchangerl, at the same time preheating the fresh heavy charging stock which also passes through the heat exchanger, and the cooled oil is then returned to the base of the flash tower through pipe 43. The character of the liquid drawn 011' from the base of the fuel oil flash tower may be regulated by proper adjustment of the pressure in the flash tower, this adjustment being accomplished by means of pressure reducing valve 42. The higher the pressure in the flash tower the lighter will be the heavy naphtha charging stock may be of any desired value but preferably the quantities of residuum charging stock and heavy naphtha charging stock are approximately equal. While it is ordinarily desirable to treat virgin residuum and a virgin heavy naphtha according to the present process, it is also possible successfully to operate on a charging stock which has previously been subjected to some degree of cracking. In place of a residuum the heavy charge may be, for example, a heavy cracked gas oil, and the heavy naphtha may be a cracked product. If desired a product falling entirely in the gasoline boiling range may be introduced into the system for reformation by passage through the cracking furnace or reforming furnace 33 but ordinarily it is more desirable to take a heavy naphtha which falls partly within the gasoline boiling range and partly within a slightly higher boiling range. A suitable heavy naphtha charging stock is, for. example, one having an initial boiling point of about 300 F. and an end point of about 420 to 425 F.

While I have described a particular embodiment of my invention for the purposes of illustration it should be understood that various modiflcatlons and adaptations thereof may be made within the spirit of the invention the appended claims.

' I claim:

1. The process of treating hydrocarbonv oil which comprises passing fresh heavy charging stock in indirect heat exchange with liquid residue withdrawn from a flashing zone, then introducing the preheated charging stock into direct contact as set forth in with hot vapors rising through said flashing zone,

collecting unvaporlzed portions of the fresh charging stock and'condensed portions of the'rlsing vapors at an intermediate point in said flashing zone, withdrawing the resulting mixture and introducing it, after indirect heat exchange, with liquid residue withdrawn from the base ofan evaporating zone, into. an upper level insaid evap-.

orating zone in direct contact with hot rising vapors, collecting unvaporized of the.

introduced mixture and condensed portions of the rising vapors at an intermediate point in said evaporating zone as a composite charging stock, removing composite charging stock so formed from said evaporating zone and passing it through a first cracking zone wherein it is raised to a cracking temperature and subjected to conversion, introducing the resulting cracked products into a lower point in said evaporating zone wherein separation thereof into vapors and liquid residue occurs, said vapors passing upwardly through said evaporating tower in contact with said mixture introduced thereinto, removing uncondensed vapors from the top of said evaporating zone and fractionating them to form a final desired distillate and reflux condensate, mixing with reflux condensate so formed gasoline-like hydrocarbons of relatively low anti-knock value and passing the mixture through a second cracking zone wherein it is raised to a relatively high cracking temperature and subjected to cracking and refonnation, introducing the resulting cracked and reformed products into a low point in said evaporating zone, and passing liquid residue from said evaporating zone into a low point in said flashing zone with an accompanying reduction in pressure whereby said liquid residue undergoes partial vaporization and vapors pass upwardly through said flashing zone in contact with said fresh heavy charging stock.

2. A process in accordance with claim 1 wherein fresh heavy naphtha changing stock from an external source'is passed in indirect heat exchange relation with said liquid residue subsequently to the indirect heat exchange contact of said residue with the mixture of fresh charge and condensate withdrawn from said flashing zone and introduction into said evaporating zone, and heavy naphtha so heated is used as a source of said gasoline-like hydrocarbons of relatively low anti-knock value which are combined with said reflux condensate for cracking.

PERCIVAL C. KEITH, JR.

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