US1755601A - Art of cracking hydrocarbons - Google Patents

Description

April 22, 1930.

E C. HERTHEL ART OF CRACKIN C[ HYDBOCARBONS Filed July 27, 1927 b 6 Va /pars to Condenser Z I 8 Fcflum'ng Mcdz'um Vapors from fiessure Still Refill x Condensate f0 fi'essl/m Still fig lNVENTR Fuyene (I fiert/zel ATTORNEYS V ietented Apr. 22, 1930 nrra snares PAEN? .EUGENE C. HEBTHEL, OF CHICAGO, ILLINDIS, .ZLSSIGNOR T SINCLAIR REFINING v COMPANY, OF NEW YORK, N. Y., A COBPDRATIQN OF MAINE ART OF CRACKING HYDROCARBONS Application filed July 27, 1927. Serial No. 208,741.

This invention relates to improvements in the operation of reflux condensers employed in connection with pressure stills for cracking heavier and higher boiling hydrocarbon oils, such as gas oil, for the production of lighter and lower boiling hydrocarbon oils, such as gasoline and gasoline-containing pressure distillates.

In cracking hydrocarbon oils by distillation under pressure, the components vaporized in the still proper usually comprise, in addition to the lighter constituents which go to make up the desired product, heavier tonstituents unsuitable as components of the de- 5 sired product and which by further treatment in the pressure still will yield additional quantities of constituents suitable as components of the desired product. Accordingly, it is common practice in the operation of pressure cracking stills to subject the vapors from the still to some refluxing operation to condense from the vaporsfor return to the still such heavier constituents. In one type of refluxing operation commonly employed for this purpose, some light oil Which largely or completely vaporizes at the temperature and under the pressure prevailing in the refluxing operation, such as a portion of the condensed pressure distillate "from the operation, 0 is introduced into direct contact with the vapors from the pressure still in a reflux condenser, the vapors being cooled and the heavier constituents condensed by the consequent vaporization. This type of refluxing 5 operation has several advantages but likewise several disadvantages. For example, as

commonly practiced in many instances, thecondensation of heavier constituents 1s eflect-- ed under conditions such that a substantial proportion of the light constituents suitable as components of the desired product which are present is entrained in the condensate, dissolved or entrapped, Without opportunity to escape before the condensed heavier constituents with entrained lighter constituents are again compelled to pass through the heating zone in the pressure still. This involves a tendency toward overcracking of such lighter constituents which are in this manner again subjected to the cracking conditions maintained in the pressure still, particularly if these cracking conditions are severe. Usually this results not only in a loss of such constituents, valuable as components of the desired product, but also in an excessive formation of carbon.

The present invention relates particularly to improvements in the operation of reflux condensers employed in connection with pressure stills for cracking hydrocarbon oils in which some such light oil, vaporizing substantially completely in the refluxing operation, is used as a refluxing medium. Que of the important advantages of the invention is reduction or elimination of the tendency, in such refluxing operations, of the condensed heavier constituents forming'the reflux condensate to carry back to the pressure still with them lighter constituents suitab e as components of the desired product. i According to the present invention, the light oil employed as a refluxing medium, instead of being introduced within a closely localized region within the reflux condenser, is introduced at a number of points through a more extended region within the reflux condenser and the proportion of the light oil introduced at each of these points is regulated to distribute and to make more uniform the cooling and condensation eflected in the re-' flux condenser and to distribute and to make more uniform the heat transfer between heavier components of the vapors and lighter components of the liquid in the reflux condenser. In carrying out this invention, extreme concentration within the reflux condenser ot the cooling consequent to vaporization of the light oil introduced is avoided.

This invention will be further described in connection with the accompanying drawings which illustrate, diagrammatically and conventionally, a reflux condenser shown in traentary elevation and partly in section, adapted, in connection with a pressure crackin still, for carrying out the invention.

eferring to the drawings, the reflux tower l is connected to a pressure cracking still by &

the vapor line 2 and the reflux return line 3.

The tower is provided iuteriorlwith bees 4. Vapors from the still enter t e lower part 5 of the tower through the line 2 and pass upwardly through the tower back and forth between the several baflies. Vapors remaining uncondensed escape from the upper end .of the tower through connection 5, and

through it are conducted to a condenser where the distillate product is condensed and collected. Pressure in the still system may be maintained through the reflux tower and regulated, for example, by means of valve 6 in the vapor connection between the reflux tower and the final condenser. For the production of gasoline from gas oil, for example, the pressure in the system may amount to as much as 100 pounds per square inch, 150 pounds, 300 pounds or more; Arranged in the upper part of the reflux tower, at points spaced a substantial distance along the path of vapor travel defined by the baffles, are three spray heads for the introduction of the refluxing medium, designated 7, 8 and 9.

These three spray heads are connected to a common supplylinelO through which the refluxing medium is supplied by means of the pump 11. A light oil which vaporizes substantially completely under the conditions prevailing in the tower, for example a portion of the pressure distillate from the operation or an oil of corresponding character, is introduced into the tower indirect contact with the vapors flowing upwardly through the tower through these spray heads. As this light oil is vaporized, the vapors flowing through the tower are cooled and the heavier constituents of these vapors are condensed. The condensate flows downwardly through the tower over the bafiles and, from the lower end of the tower, back to the pressure still through line 3. The return connections to the pressure still may include a pump or other forcing means for returning this condensate. As the condensate flows downwardly through the tower in contact with the rising vapors, lighter constituents of the condensate are driven out of it by heat absorbed in condensing heavier constituents of the vapors.

In carrying out the present invention, the light oil refluxing medium supplied through the spray heads may be distributed, for example, 50% through head 9, 35% through head 8 and 15% through head 7. The consequentcooling is thus distributed over a greater proportion of'the path of vapor travel through the tower than is the case Where all of the refluxing medium employed is introduced at a single oint in the path of vapor travel. Likewise, y rogressivelv diminishing the proportion o? the refluxing medium introduced from the point nearest the vapor outlet toward the oint nearest the vapor inlet, the cooling e ect may be distributed to establish a temperature gradient promoting uniformity of condensation as the'proportion of heavier and more easily condensable constituents in the vapors increases toward the vapor inlet. Sometimes it is advantageous, while maintaining this general distribution of the refluxing medium, to supply a more limited proportion of the refluxing medium through the spray head nearest the vapor outlet as where any entrainment of serious consequence is encountered. For example, the light oil refluxing medium supplied through the spray heads may be distributed, 10% through head 9, 60% through head 8 and 30% through head 7. It will be understood that the foregoing proportions are given to illustrate, not to limit, the invention.

Where the cooling is concentrated in a closely localized region in the reflux condenser, as is quite common in ordinary practice, there is a corresponding tendency toward condensation in that region of both lighter and heavier constituents of the vapors while both lighter and heavier constituents remain unconden'sed. By distributing the cooling effect, in accordance with this invention, condensation of heavier constituents without condensation of lighter constituents is promoted. At the same time, better opportunity is aflorded for revaporization from the condensate of any condensed or entrained lighter constituents, while more complete condensation from the Va )OIS of heavier constituents is also promoted. The invention may be utilized, in the case of any particular refluxing operation or practiced in any reflux condenser to improve either capacity, efiiciency or both.

I claim:

1. In refluxing operations employed in conjunction with the cracking of hydrocarbon oils by distillation under pressure, the improvement which comprises passing the vapors from the pressure distillation through a reflux condenser, introducing into the reflux condenser in direct contact with the vapors passing therethrough at a plurality of points spaced a substantial distance along the path of vapor travel a light oil which is vaporized substantially completely under the conditions prevailing in the reflux condenser, and returning condensate from the reflux condenser to the pressure distillation, whereby entrainment in the reflux condensate of light constituents suitable as components of the desired distillate is reduced.

2. In refluxing operations employed in conjunction with the cracking of hydrocarbon oils'bydistillation under pressure, the improvement which comprises passing the vapors from the pressure distillation through a reflux condenser, introducing into the reflux condenser in direct. contact with the vapors passing therethrough at a plurality of points spaced a substantial distance along the path of vapor travel a light oil which is vaporized substantially completely under the conditions prevailing in the reflux condenser, the light oil supplied being distributed so that the proportion supplied at the point nearest the vapor inlet to the reflux condenser is less than the proportion supplied at a further point in the path of vapor travel, and returning condensate from the reflux condenser to the pressure distillation, whereby entrainment in the reflux condensate of light constituents suitable as components of the desired distillate is reduced.

3. In refluxin operations employed in conjunction with t e cracking of hydrocarbon oils by distillation under pressure, the improvement which comprises passing the vapors from the pressure distillation through a reflux condenser, introducing into the reflux condenser in direct contact with the vapors passing therethrough at a plurality of points spaced a substanial distance along the path of vaport-ra 'el a 1i ht oil which is vaporized substantially comp etely under the conditions prevailing in the reflux condenser, the light oil supplied being distributed so that the proportion supplied at the point nearest the vapor inlet-to the'reflux condenser is less than the proportion supplied .at a further point in the path of vapor travel and so that the proportion supplied at the point nearest the vapor outlet from the reflux condenseu is less than the proportion supplied at an intermediate point nearer the vapor inlet to the reflux condenser, and returning condensate from the reflux condenser to the pressure distillation, whereby entrainment in the reflux condensate of light constituents suitable as components of the desired distillate is reduced.

In testimony whereof, I have subscribed my name.

EUGENE C. HERTHEL.

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