US1946938A - Conversion of hydrocarbon oils - Google Patents

Description

Feb. 13, 1934. L. c HUFF CONVERSION OF HYDROCARBON OILS Filed May 27, 1932 FIG. 2

RECEIVER \NVENTOR LYMAN C. HUFF ATTORNEY FRACTIONATOR COOLER FURNACE FURNACE l Patented Feb. 13, 1934 UNITED STATES CONVERSION OF HYDROCARBON OILS Lyman 0. Hull, Chicago, Ill., assignor to Universal Oil Products Company, Chicago, 111., a corporation of Delaware Application May 27, 1932. Serial No. 613,876

6 Claims. (Cl. l96-58) This invention relates to the conversion of hydrocarbon oils for the production of substantial yields of desirable light products and refers more particularly to an improved method and means of preventing the accumulation of coke in the reaction chamber of a cracking system.

A type of cracking system which has recently come into commercial prominence utilizes a reaction chamber maintained at superatmospheric pressure and a reduced pressure vaporizing chamber in series. It is common practice in this type of cracking system to spray the heated oil from the heating element of the system into the upper portion of the reaction chamber against the reaction chamber walls. This permits quick separation of liquid and vaporous products, allowing the residual liquid to flow downward over the inner surface of the chamber walls while the vaporous products pass downward through the vapor space comprising substantially the entire cross sectional area of the chamber. Both vaporous and'residual liquid products are withdrawn from the lower portion of the chamber and both or, when desired, only the residual liquid, are directed to the reduced pressure vaporizing chamber where further vaporization of the residual oil is accomplished without substantial further conversion.

When the charging stock and conversion conditions employed are such that a sufiicient quantity of residual oil is formed to maintain a rapidly moving film of oil on the walls of the reaction chamber the residual oil passes rapidly through the chamber without being subjected to prolonged conversion time in the reaction zone and without excessive coke formation in this zone. However, when such conditions do not exist and particularly when relatively low boiling charging stocks are employed and the quantity of residual oil is not sufiicient to maintain a positive and rapid flow of liquid down the walls of the chamber, the increased time to which this liquid is subjected to the conversion conditions obtaining in the reaction chamber may result in the formation of substantial quantities of coke or carbonaceous material which may adhere to the walls of the chamber and/ormay be washed out with the liquid, tending to block or obstruct the passage of conversion products from the reaction chamber to the vaporizing chamber.

It is the primary purpose of the present invention to avoid coking in the high pressure reaction zone and/or in the'line leading from the high pressure reaction zone to the reduced pressure vaporizing zone of a cracking system of the type described. This is accomplished by supplying an additional quantity of liquid oil to the reaction chamber, introducing it into this zone in such a manner thatv it Will spread and flow downward over the inner surface of the walls of the chamber for the purpose of maintaining a rapidly to moving film or body of oil on the reaction chamber walls, thus increasing the rate of flow of the total oil body, including the residual oil resulting from cracking, and materially decreasing the time to which the residual oil is exposed to es heavy condensate separated from the vapors withdrawn from the reduced pressure vaporizing zone prior to their fractionation, residual oil withdrawn from the vaporizing chamber and oil from an external source such as heavy gas oil. The

most suitable type of oil for this purpose is one 30 which will not readily decompose or crack to form coke under the conditions to which it is subjected while in the reaction chamber but which preferably contains a substantial propor tion of material which will remain unvaporized as in the reaction zone.

By passing the washing oil over the walls of the chamber, instead of spraying it through the vapor space of the chamber or commingling it with the stream of heated oil entering the chamber, excessivecooling of the vaporous products in the reaction chamber is avoided so that conversion of' the vaporous products may continue during their passage through this zone.

'When cooling of the residual oil is required, as

well as'dilution and hastening of its flow through the reaction zone, the washing oil may be cooled to the desired temperature prior to its introduction into the reaction chamber. Preferably, however, in order to insure minimum cooling of the 10 vapors, the washing oil is heated, prior to its introduction into the reaction chamber. This practice permits the use of a larger quantity of oil without obtaining any more cooling than would be obtained by a much smaller quantity of cooler oil, thus giving more dilution of the residual oil and hastening its flow. The washing oil may be introduced into the reaction chamber at a temperature, for example, of the order of 400 to 750 Obviously the desired tempera- Specific examples of types of to lid til

true will vary with difierent types of washing oil as well as with different operating conditions in the reaction chamber and the range of temperatures mentioned is only arbitrary. However, the temperature to which the washing oil is heated is in all cases below the temperature which will cause cracln'ng of the particular oil used to form any appreciable amount of coke under the conditions to which it is subsequently exposed in the reaction chamber.

A specific embodiment of the invention may comprise subjecting a hydrocarbon oil to conversion conditions in a heating coil, introducing the heated materials into the upper portion oi an enlarged reaction zone wherein their liquid components flow downward over the walls of the vessel and wherefrom liquid and vaporous products are withdrawn to a reduced pressure vaporizing and separating zone, subjectlug vapors tl. from to fractionation, returning refhnr cor nsate resulting from said fractionation to the heating coil for further conversion, subjecting vapors from said fractionation to condensation, and collecting the resulting products, subjecting raw oil charging stool: for the system to indirect contact and heat exchange with vapors passing irom said vaporizing zone to said iractionating zone and returning condensate resulting from said heat exchange to the upper portion of said reaction zone to increase the quantity or liquid passing downward over the walls of said reaction vessel.

Fig. i or the attached diagrammatic drawing illustrates one specific form of apparatus incorporating the features of the present invention. Raw oil charging stock for the system may be supplied through line 1 and valve 2 to pump 3 from which it may be fed through line l, valve 5, heat exchanger 6, line 7, line 8and valve 9 to heating element 10. It will be understood that, when desired, all or any portion or the raw oil may be supplied directly to heating element 10 or may be preheated by other well known means, for example by introducing it into tractionating column 2, although suchother means are not illustrated in the drawing.

Heating coil to is located in a furnace ll of any suitable form and the oil supplied thereto is heated to the desired conversion temperature preferably at a substantial super-atmospheric pressure. The heated oil is discharged through line 12 and valve 13 into reaction chamber 14,

which is also preferably maintained at a substantial super-atmospheric pressure. Non-vaporous residual oil may flow downward over the walls of chamber is and is withdrawn from the lower portion thereof, together with. vaporcus products, through line 16 and valve it to vaporizing charm ber 18, which is preferably maintained at substantially reduced pressure relative to that em ployed in chamber l i and wherein vaporous and non-vaporous products are separated.

' Vapors from chamber 18 may pass through line 19 and valve 20 into heat exchanger fiwherein they are indirectly contacted with raw oil supplied thereto, as already described, and wherein their heaviest components are condensed. Materials irom chamber 18, remaining vaporized in heat exchanger 6, pass through line 21 into fractionator 22 wherein their insufficiently converted components are condensed, collecting as reflux condensate in the lower portion of this zone to be withdrawntherefrom through line 23 and valve 24 to pump 25 and supplied therefrom through i e B a d valve 27 to beat g coil to incense for further conversion. When desired, apart-ion or all of the reflux; condensate may be directed from line 26 through line 28, valve 29, line i and valve 5 to heat exchanger 6 together with any raw oil fed therethrough, as already described.

Vapors from fractionator 22 pass through. line 30 and valve ill to be subjected to condensation and cooling in condenser 32, distillate and uncondensable gas rrom. which. passes through line 33 and valve 3a to be collected in receiver 35. Uncondensablc gas may be released from the receiver through line 36 and valve 3?. Distillate may be withdrawn from this zone to storage or elsewhere, as desired, through line 38 and valve 39. A portion of the distillate from receiver may, when desired, be recirculated by well known means, not shown in the drawing, to the upper portion of tractionator 22 to assist fractionation of the vapors.

Residual oil may be withdrawn irom chamber 13 through line so and may withdrawn, allor in part, from the system to storage or to any desired further treatment through line and valve 42. v A portion or residual oil may, when desired, be passed through valve do, in line so, to pumpit to be fed therefrom through line we valve 46 into line 5'! and thence to r action charm her it, as will be later more fully described.

The heavy components or the vapors from chamber 18 which are condensed in heat ex= changer 6 are withdrawn from this aonethrough line 47 and may be passed, all or in part,'through line aii and valve la baclr into vaporizing chamber 18 or, all or in part, through line so and valve v 51 into fractionator 22. A portion or all. of this condensate may be passed through valve 53, in line d7, to pump 5% to be fed therefrom through line 55 and valve 56 into line 5*! and t ience to reaction chamber is, as will be later described.

In a similar manner a portion or the raw oil charging stock for the system may be diverted from line 4i and supplied through line 58, valve 59, into line 5'? and thence to chamber 1+1, as will be later described. Reflux condensate from tractionator' 22 may be diverted from line 26 and sup plied through line so, valve 61, into line 57 and. thence to chamber is in a manner to be later described.

Preheated raw oil'or preheated combined reed (raw oil and reflux condensate) as the case may be, from heat exchanger 6 may be directed through valve 52, in line '3, into line 5'? and thence to reaction chamber is, as will be later described more fully.

It is also within the scope of the invention to introduce any suitable oil such as gas oil, topped crude, etc., from an external source or any suit-= able relatively heavy liquid product from the same or another cracking system through line so, valve and line 5'? for transmission to chamber la, as will be presently described.

It will be understood that any one or any combination of the materials above mentioned, namely, residual oil from chamber 18, condensate from heat exchanger 6, row oil charging stool:

for the system, rellur; condensate from fractionator 22, preheated oil from heat exchanger 6 and oil from an external source, may be supplied to the reaction chamber as a washing medium.

The oil or comrningled oils chosen as the wash ing medium may be directed from line- 5? through line 66, valves 67, 68 and 69 into chamber it. Instead of feeding the washing oil into the upper portion or the reaction chamber, as de Mil l it

scribed, it is within the scope of the invention to introduce the oil and spray it against the walls of the chamber at any other point in the chamber. This will be more fully described and illustrated in connection with Fig. 4 and line 80 having valve 81 illustrates means for introducing the washing oil into the lower portion of the chamber. V

As already mentioned, the oil thus supplied to chamber 14 is preferably introduced into the reaction zone at a fairly high temperature in order to avoid excessive cooling of the vaporous products in thereaction chamber. A heating coil 71, located in a furnace 72, of any suitable form, is provided for the purpose of heating the oil from line 57 to the desired temperaturawhen such heating is required. The oil may be supplied, all or in any desired proportion, through valve '70, in line 57, to heating coil 71 and is discharged therefrom through line 73 and valve 74 into line 66 and thence to chamber 14.

It is possible that oils obtained from within the system to be used as washing oil in chamber 14 may be at too high a temperature for the purpose required. In this case and when otherwise desirable the washing oil may be cooled, prior to their introduction into the reaction chamber, in cooler 7'7, by means of diverting all or any portion of the oil from line 66 through line 75 and valve '76 into the coolerand thence through line '78 and valve 79 back into line 66 and to chamber 14.

Fig. 2, which is a fragmentary cross-sectional view of the upper portion of chamber 14, illus trates one manner in which the washing oil may be supplied to the upper portion of chamber 14, through line 66 to be there preferably sprayed against the walls of the vessel by means of a suitable spray device, forexample, such as indicated at 82 while the heated oil from heating coil 10 is introduced through line 12 and sprayed against the walls of chamber 14 by means of a spreader flange, as indicated at 15. In this manner an increased quantity of oil is made to flow downward over substantially the entire length of the inner surface of the walls of the chamber, thus decreasing the time which the residual conversion products remain in this zone, as already explained.

Another method and means for introducing the heated oil from heating coil 10 and the washing oil into the upper portion of the reaction chamber 14 is illustrated in Fig. 3, in'which the line from heating coil 10 is again indicated by the number 12, therecirculating line by 66 and the spray, which in this case takes the form of a spreader flange, similar to number 15 in Fig. 2, is indicated at 83.

It is also within the scope of the invention to introduce the washing oil at any desired point in the reaction chamber and to more clearly illustrate this feature Fig. 4 of the attached drawing illustrates a case in which the flushing and cooling oil is introduced into the lower portion of the reaction chamber near the outlet of vaporous and residual liquid products from this zone.

Referring to Fig. 4, reaction chamber 14 is shown in fragmentary cross-section. The line 12 supplying heated oil from the heating element enters the upper portion of chamber 14 and is pointed downward at the central portion of the chamber. The conversion products are removed from the bottom of chamber 14 through line 16 and the chamber may, as illustrated in this figure, be provided with a cone shaped outlet 86.

Line 80, as here illustrated, enters the lower portion of the chamber and terminates in a spray coil 84, of any suitable form, adjacent the lower head 85 of the chamber. By means of this arrangement the heavy liquid entering'chamber 14, through line 12, drops through the chamber at a rapid rate and is withdrawn through line 16, while the lighter vaporous products pass more slowly through the chamber and are withdrawn through the same ,line. When this method of introducing and withdrawing materials from the reaction chamber is employed, the residual liquid will splash against the walls of manway 8'7, outlet 86 and a portion of the lower head of the chamber 85 and this material tends to coke on the walls and obstruct the outlet. By providing a spray, as indicated, for the intro duction of washing oil, the walls of the chamber against which the residual oil splashes are continuously washed and the residual oil is rapidly removed from the reaction zone.

The oil thus supplied to chamber 14 may also serve as a protecting fluid or diluent for the residual oil to prevent its rapid conversion to coke or carbonaceous material, particularly when the oil thus employed is more refractory to cracking than the residual liquid conversion products. When cooling of the recirculated oil is employed it may also serve to decrease the temperature of the residual liquid conversion products in chamber 14 to prevent their conversion to coke. These latter features are, however, auxiliary to the main purpose which is to increase the quantity of oil flowing downward over the walls of the reaction chamber and thus decrease the time to which liquid residual products of the conversion are exposed to the conversion conditions in the reaction chamber. It is worthy of emphasis, however, that the method of passing the washing oil over the walls of the chamber, as provided by the present invention, permits cooling of the washing oil and substantial cooling of the residual oil without substantial cooling of the vapors in the reaction chamber.

The features of the invention are applicable to any type of cracking system operated under any temperature and pressure conditions ranging, for example, from 800 to 1200 F, and from substantally atmospheric pressure to'super-atmospheric pressure as high as 2,000 pounds or more per square inch. In the type of system illustrated and above described, however, the preferred operating conditions are 900 to 1000 F. or thereabouts in the heating coil with pressures ranging from 100 to 800 pounds per square inch, more or less, at the outlet from the heating element and in the reaction chamber and with substantially reduced pressures ranging from substantially atmospheric to 100 pounds, or thereabouts, per square inch, in the vaporizing, fractionating, condensing and collecting portions of the system. It will be understood, however, that the principles of the present invention are not limited to use with any particular range of conversion conditions. It is one of the salient features of the present invention, however, that higher temperatures may be safely employed in the heated oil entering the reaction chamber than when no provision is made for diluting and rapidly removing the residual oil from this zone.

As a specfiic example of the advantages of the features of the present invention let us first consider a cracking operation in an apparatus similar to that illustrated in the drawing except that the principles of the present invention are not employed. The charging stock is a as" A. P. I. gravity Pennsylvania kerosene distillate which is subjected, in the heating element, to'a temperature of approximately 935 F. A pressure of approximately 400 pounds per square inch is employed in the reaction chamber and a reduced pressure of approximately 50 pounds per square inch is employed in the vaporizing chamber. This operation may yield approximately '73 percent of motor fuel of high antiknock value, about 7 percent of heavy residual oil, approximately 650 cubic feet of gas per barrel of charging stock and a total of approximately 20 percent, based on the charging stock, of coke, gas and. unaccountable loss.

By recirculating to the upper portion of the reaction chamber, in the manner described, condensate from the heat exchanger, in an amount equal to approximately 30 percent by volume of the charging stock, at a temperature of approximately 700 F. and without materially altering the other operating conditions, a yield of better quality residual oil amounting to approximately 10 percent of the charging stock may be produced with a corresponding decrease in the coke and gas formation. The yield and quality of the motor fuel remains substantially unchanged and the operating cycle may be increased by several days, due to the absence of excessive coke formation on the walls of the reaction chamber and/or in the line between the reaction chamber and vaporizing chamber.

It will be understood that the foregoing example is only illustrative and does not limit the invention to the conditions or advantages mentioned.

I claim as my invention:

1. In a cracking process of the character wherein hydrocarbon oil is heated to cracking temperature under pressure while flowing in a restricted stream through a heating zone, thence discharged into the upper portion of an enlarged vertical reaction zone maintained under cracking condi tions of temperature and pressure, both vapors and unvaporized oil passed downwardly through the reaction zone whereby conversion of the va pors occurs in the reaction zone, and the vapors and unvaporized oil are withdrawn from the lower portion of the reaction zone; the improvement which comprises passing a washing oil, other than said unvaporized oil. downwardly over neeaass the inner surfaces of the reaction zone, the washing oil being at an elevated temperature such as to prevent substantial cooling of the vapors whereby the conversion of the vapors in the reaction zone is not interfered with but said elevated temperature being insufilcient to cause substantial coking of the washing oil in the reaction zone.

2. In a cracking process of the character where-= in hydrocarbon oil is heated to cracking temperature under pressure while flowing in a restricted stream through a heating zone, thence discharged into the upper portion of an enlarged vertical reaction zone maintained under cracking condl= tions of temperature and pressure, both vapors and unvaporized oil passed downwardly through the reaction zone whereby conversion of the vapors occurs in the reaction zone, and the vapors andunvaporized oil are withdrawn from the low er portion of the reaction zone; the improvement which comprises passing a washing oil, other than said unvaporized oil, downwardly over the inner surfaces of the reaction zone, the washing oil being introduced to the reaction zone at a temperature of the order of 400 F. to 750 Tr. whereby substantial cooling of the vapors and substantial 1W coking of the washing oil in the reaction zone are prevented.

3. The process as definedin claim 1 further characterized'in that the unvaporized oil withdrawn from the reaction zone is flashed distilled by pressure reduction and resultant residual oil utilized as said washing oil.

4. The process as defined in claim 1 further characterized in that the vapors withdrawn from the reaction zone are cooled and resultant con llii densate utilized as said washing oil.

5. The process as defined in claim 1 further characterized in that the vapors withdrawn from the reaction zone are cooled and then fractionated, the heavier condensate formed by the initial lli cooling being utilized as said washing oil and the lighter condensate formed by the fractionation being supplied to the heating zone.

6. The process as defined in claim 1 further characterized in that said washing oil comprises at least a portion of the raw charging oil for the cracking process.

LYMAN c. HUFF.

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