US2037537A - Process for cracking oils - Google Patents

Description

April 14, 1936,

A. V. RITCHIE PROCESS FOR CRACKING OILS Filed Feb 4, 1930 A 7' TOR/VE Y I. Il @l Ill||||| Patented Apr. 14, 1936 2,037,537

UNITED STATES PATENT OFFICE PROCESS FOR CRACKING OILS Allan V. Ritchie, Elizabeth, N. J., ass'ignor to The Texas Company, New York, N. Y., a corporation of Delaware Application February 4, 1930, Serial No. 425,745

6 claims. (o1. 19th-481) The present invention relates in general to a for those in the neighborhood of the unit is inprocess for the conversion of higher boiling hyvolved. drocarbon oils into lower boiling oils, and more By the improvements contemplated by the presparticularly, to improvements in the manner of ent invention, the period of continuousl operation handling the charge introduced into a continuof ay cracking system may be prolonged to a con- 5 ously operating system. siderable extent beyond that ordinarily possible It has been the common practice for some time with previously known methods. This will enable to operate cracking units of various types in Athe use of the equipment during the greater persuch a way as to permit a more or less contincentage of the available time and will reduce the l0 uous flow of a charge of oil through heating losses, due to-shut-down for cleaning: and repair 10 chambers under pressure, with the result that purposes, toaminimurn. Furthermore, by virtueA the conversion of higher boiling oils may take of thev present improvements, the failure of tubes place uninterruptedly for a considerable period. or vesselsv carrying the oil undergoing conversion,

It has also been a recognized practice to mix will be materially reduced if not altogether elimiwith the charge of fresh oil, which is being nated. It is'a'n object of the invention in addition 15 constantly fed into the system, the condensate to providing the foregoing benefits to so modify from the air condensers or bubble towers, or the' present practice as to bring' aboutr a higher similar cooling devices through which the vapors percentage in the yield of gasoline from a given resulting from the cracking process are led. quantity of charge entering the system and to im- Under 4the usual methods of this type now being prove generally the ellciency of cracking units. 20 employed, the reiluxed or backtrappedV condensate Toward the end of bringing about the above is introduced into the charge of fresh oil before mentioned advantages, the present invention conthe latter enters or as it passes through the main templates the passage of only reluxed condensate heating unit such as a preheating coil. through those portions of thel tubing or vessels,

In connection with continuous cracking proccarrying the oil undergoing conversion, which are 2 5 esses of the type mentioned, it has been recognized subjected tothe most intenseA heat. At least three as highly advantageous to pass only comparaimportant advantages among those already specitively clean stock, composed of the fresh charge fied are derived from this method of handling and the reiluxed condensate, through the' heatthec'harge entering the system. In the rst place ing elements, such as coils, which are subjected the excessive formation of carbon' on the hottest 30 to the greater portion of the applied heat. The Surfaees 0f the System i'Sv largely eliminated bereason for this, as is well known, is to reduce as Cause little or no' free Carbon is carried in susfar as possible the excessive formation of carbon pension in the refluxed condensate. In the secdeposits on the walls of the tubes or vessels in ond place this COrlderlSate WhCh represents the as which the 0111s being heated. In spite of au eare most diicultly convertible portion 0f the total 35 which may be exercised in the operation of crack- Charge handled by the System is passed through ing units of various types now employed, it is the hottest portion of thesystem and is therefore found necessary to shut down each unit at perigiven the greatest Opportunity fOr breaking 11p odio intervals for the purpose of cleaning out the irlt lOWer bOlirlg OilS. A third advantage iS that 4 0 heavy deposits of sludge and carbon which graduovercracking of certain constituentsv of the origi- 40 ally accumulate in certain parts of the system nal charge, which'frequently takes place under the This applies to all forms of presently known COIIlmOn pract'ee, iS prevented by diverting the cracking installations, and while the period of more easily Cracked Components 0f the fresh continuous operation may Vary with a number of Charge from the, hottest portion? of the System' Another feature of the invention is in the 45 factors, a fair percentage ofA total available time .h

is required for these shutdowns to clean out and manner of return??? t e reheatd. reuxed con' repair the units. The presence of carbon, furden-sate to th mamhpody of. 011'., m, the System' thermore, at points where theA most intense heat eemi; r Isle (grltgnoftshgg 1s applied, has given rlse frequently to the failure throughout its, Course in the System by introdu 50 of the tubes or vessels containing the oilv undering the remixed, materaLaer it has been inde going conversion. Failures of thischaracter not pendeni-,ly reheated, at a point inA the system Only entail eXpehSe h1 the repair 0f the SYStem where the heavier oils` are collected. As is well and iny the loss of oilv contained in the system at known in any cracking system, the process of the' time of the failure, but considerable danger conversion tends to producev a residual body of 55 oil which, as it passes through the system, becomes constantly heavier and more viscous. This is due largely to the fact that the lighter or lower boiling constituents are constantly being carried away. Therefore, the introduction of the relatively light reheated, reiiuxed condensate into the system at a point where the later stages of the conversion process are going on tends to balance off the natural increase in density encountered at this point. Furthermore, as a result of this introduction of the refluXed constituents, at a later stage in the process than heretofore, the load upon the hot oil or surge pumps which handle this refluXed material is reduced to a considerable extent. This is due to the fact that the pressure at the point of introduction is lower and the surge pumps will not have to overcome the pressure built up by the fresh charge pumps so that as a consequence the operating expense is appreciably reduced.

With the foregoing and other incidental objects in view, the invention will now be described in connection with the accompanying drawing in which Fig. l is a diagrammatic showing of certain apparatus and connections for carrying out the invention, and Fig. 2 diagrammatically illustrates a modification of a part of the system shown in Fig. l.

For the purpose of illustrating the invention, it has been disclosed with relation to a cracking unit of the type employing a preheating coil through which the charge of oil is rst passed before being passed into one or more vertical drums in which a cracking temperature and pressure is maintained. Thus there may be provided a furnace I carrying a plurality of tubes connected in series by suitable manifolds at the ends, thereby creating a long continuous coil such as indicated by the numeral 2 in the drawing. A fresh charge of oil may be introduced into this coil by means of a pump 3a. through an inlet pipe 3, and after passing through the series of tubes, may emerge and be conducted by means of a pipe 4 to one or more of the vertical drums or stills, such as designated 5 and 6. Preferably there will be a battery of these vertical stills, four being shown in the drawing, including two additional stills i and 8, and all being connected in series by means of pipes 9 just below the liquid level in the drums and by means of vapor lines IIJ above the liquid level. The battery of stills may either be merely heat insulated or may be supplied with heat from a suitable source to make up for the heat losses. Vapors of lower boiling oils which result from the conversion process are conducted by means of a pipe I I to a dephlegmator or condenser or a fractionating column, such as a bubble tower, or similar equipment, such as designated by the numeral I2. The necessary cooling of the tower to provide the proper temperature control may be effected in any suitable Way, as by passing the vapors from the top of the tower to a reflux condenser |20 where a portion will be condensed and may be returned as a reiluxing medium to the tower. That portion of the vapors which remains in the vapor state may then be led in any suitable way to final condensing apparatus I2I and an accumulator drum |22 for collection while. the higher boiling portions which condense or are separated out in the apparatus I2 will be backtrapped by means of pipe I3 to a hot oil surge pump I4. A pipe I5 leading from the output side of the pump may serve to introduce the refluXed condensate into a series nf tubes shown diagrammatically in the form of a coil I6 below the coil 2 in the furnace I. The other end of coil I5 is preferably connected by a pipe line II to one or both of the vertical stills 'I and 8. Suitable valves as shown will preferably be located in the lines 4 and II for controlling the distribution of the fresh charge as well as the reiluXed condensate. The valve designated I'II may be of ordinary construction or of the pressure reducing type if desired. If of the latter type a higher pressure may be maintained in the coil I 6 than is employed in the rest of the system.

Heat is `applied in the usual way to the furnace I below the coil I6 and it will be apparent that this coil, or the tubes which in effect go to make it up, are subjected to the most intense heat while slightly lower temperatures will prevail in the area surrounding the coil 2. It will be apparent, therefore, that the fresh charge which is somewhat easier to crack than the lower boils ing refluxed material, will be subjected to less intense heat than the reflux so that substantially the same rate of conversion may be maintained for both. This will be particularly true if a reducing valve is employed in the line Il so that higher pressures may be maintained in coil I6. Furthermore it will be noted that the lighter reiluxed material is mixed with the heavier residual oil which will have collected in the drums 'I and 8, and will therefore tend to make the contents of all of the drums more uniform in their composition. This, among other things, will tend to prolong the operating period for a single run by virtue of the fact that the carbon deposits will be more evenly distributed. In addition, as hereinabove pointed out, the introduction of the condensate into the later stages lof the process, as in the stills 'I and 8, places a less burden upon the surge pump I4 due to the pressure drop occasioned by the frictional resistance to the flow through the coil 2 and the stills 5 and 6. Little or no carbon will be formed in the coil I6 so that the tube failures now commonly encountered will be eliminated or materially reduced.

In order to provide for an emergency, such as created by the failure of a tube, a by-pass in the form of pipe I8 may be provided between the line I5 and the charge line 3. Suitable valves I9 and 2i) may then be placed as indicated in the line I5 and pipe I8 respectively. Normally, the valve I9 will be open and the valve 2l! Will be closed, so that the refluxed material will follow the course above indicated, but in the event of a failure in one of the tubes forming the coil I6, the valve I9 may be closed and the valve 26 opened, so that the reflux will be mixed with the fresh charge and pass through the coil 2. The loss of a considerable quantity of oil will be eliminated in this way and a great deal of the danger connected with a tube failure will be avoided. It will be understood that the drums 5, S, 1 and 8 are provided with the usual means for drawing off the residual oils from time to time as well as for cleaning out the carbon at the end of a long run.

In cracking systems heretofore employed it has frequently been the practice to construct the preheating coils out of tubes having a diameter of about 3 inches and in instances where certain of the tubes have been arranged to form a section of coil separate from other tubes forming another section of coil the entire charging stock has been merged and passed through at least a acca-5s? portion of the tubing. According to the present invention, however, the stock is split, as between fresh charge and refluxed material, and passed in parallel relation through separate sections of the preheater. In adapting the present invention to a preheater of an existing cracking unit, therefore, it may be found advisable to change the tubes forming the coils 2 and I6' by reducing them in diameter to say 21/2 inches. This will have the effect of maintaining substantially the same speed of flow of the charge as before, and will tend to increase the efficiency of the unit by raising the ratio of heating surface to cross sectional area.

As a modification (shown in Fig. 2) of the method of operation already described in the earlier sections the condensate collected in the line I3 from the dephlegmator I2 may be sent directly to the stills 1 and 8, if desired, without being passed first through the preheating coil I6. For this purpose a perforated coil I5I may, for example, be placed in the bottom portions of each of the stills mentioned and the refluxed condensate may be forced through these coils by the pump I4 directly into the heavier oils to be found at these points in the system. The incoming lighter oil will, among other things, as inthe previously described method, lessen coke formation in these stills by the tendency to wash out some of the coke in the form of an emulsion along with the tar'that iswithdrawri from time to time.

While one admirable form of the invention has been described in the foregoing sections, and some variations have been suggested, it will be understood that the presentdisclosure is illustrative only and that many modifications are contemplated within the scope of the claims which follow.

What I claim is:

1. The method of converting hydrocarbon oils into lower boiling products which comprises flowing a confined stream of fresh oil charging stock through a heating coil in a furnace and heating it to cracking temperature during its flow therethrough, discharging the stream of highly heated oil into the first of a plurality of series connected enlarged closed-cracking zones through which the oil flows in progression and in which it is maintained at cracking temperature under superatmospheric pressure, withdrawing vapors generated in said enlarged cracking zones and passing them to a fractionating zone wherein undesired higher boiling constituents of said vapors are condensed and thereby separated as reflux condensate, withdrawing and collecting the fractionated vapors, passing reflux condensate in a confined stream directly through a second heating coil in said furnace and heating it during its flow therethrough to a cracking temperature while maintaining it under superatmospheric pressure, burning fuel in said furnace adjacent to said second coil and remote from said first coil whereby the desired degree of heat is imparted toeach of said streams, and discharging said independent stream of highly heated condensate into one of said enlarged cracking zones which is subsequent to the said cracking zone into which is discharged the said stream of fresh oil charging stock.

2. The method of converting hydrocarbon Oils into lower boiling products which comprises flowing a confined stream of fresh oil charging stock through a heating coil in a furnace and heating it to cracking temperature during its flow therethrough, discharging the stream. of highly heated oil into the rst of a plurality of series connected enlarged closed cracking zo-nes through which the oil flows in progression and in which it is maintained at cracking temperature under superatmospheric pressure;. maintaining substantially uniform pressure conditions in said cracking zones, withdrawing vapors generated in said enlarged cracking zones and passing them to a fractionating Zone wherein undesired` higher boiling constituents of said vapors are condensed and thereby separated as reflux condensate, withdrawing and collecting the fractionated vapors, passing reux condensate in a confined stream direct- Y ly through a second heating coil in said furnace and heating it during its flow therethrough to a higher cracking temperature while maintaining it under superatmospheric pressure, burning fuel in said furnace adjacent to said second coil and remote from said first coil whereby the desired degree of heat is imparted to each of said streams, and discharging the said independent stream of highly heated condensate into one of said enlarged cracking zones which is subsequent to the said cracking zone into which is discharged the said stream of fresh oil` charging stock.

3. The method of converting hydrocarbon oils into lower boiling products which comprises flowing a confined stream of fresh oil charging stock through a heating coil in a furnace and heating it to cracking temperature' during its flow therethrough, discharging the stream `of highly heated oil into the first of a plurality of series connected enlarged closed cracking zones through which the oil flows in progression and in which it is maintained at cracking temperature under superatmospheric pressure, withdrawing vapors generated in said enlarged cracking Zones and passing them to a fractionating zone wherein undesired higher boiling constituents of said vapors are condensed and thereby separated as reflux condensate, withdrawing and collecting the fractionated vapors, passing reflux condensate in a confined stream directly through a second heating co-il in said furnace and heating it during its flow therethrough to a cracking temperature while maintaining it under superatmospheric pressure, burning fuel in said furnace adjacent to said second coil and remote from said flrst coil whereby the desired degree of heat is imparted to each of said streams, discharging the said independent stream of highly heated condensate into one of said enlarged cracking Zones which is subsequent to the said cracking zone into which is discharged the said stream of fresh oil charging stock and separately withdrawing heavy liquid residual products from said enlarged cracking zones and discharging them from the system.

4. The method of converting higher boiling oils into lower boiling oils which comprises heating a confined flowing stream of fresh oil charging stock to cracking temperature under superatmospheric pressure by passing it through a first heating coil in a furnace, introducing the stream of highly heated oil into an enlarged reaction zone wherein further cracking of the highly heated oil occurs, passing resulting cracked products from said reaction zone into a separate enlarged zone, wherein vapors separate from residue, removing vapors from said zone last mentioned and subjecting them to fractional condensation to separate vapors of desired boiling range from heavier fractions as condensate, heating condensatey so formed to a cracking temperature under superatmospheric pressure by passing it through a second heating coil in said furnace, burning fuel in said furnace adjacent said second coil but remote from said first coil whereby the oil in said second coil is heated to a higher temperature than the oil in said rst coil, introducing resulting highly heated condensate into said enlarged Zone second mentioned at a point remote from that at which vapors are removed therefrom, and condensing the fractionated vapors to form a desired distillate.

5. The method of converting higher boiling oils into lower boiling oils which comprises heating fresh oil charging stock to cracking temperature under superatmospheric pressure by passing it through a first heating coil in a furnace, introducing the stream of highly heated oil into an enlarged reaction zone wherein further cracking of the highly heated oil occurs, passing the resulting cracked vapors and liquids from said reaction zone into a separate enlarged zone, wherein vapors separate from residue, removing vapors from a point near the top of said zone last mentioned and subjecting them to fractional condensation to separate vapors of desired boiling range from heavier fractions as condensate, heating condensate so formed to a cracking temperature under superatrnospheric pressure by passing it through a second heating coil in said furnace, burning fuel in said furnace adjacent said second coil but remote from said rst coil whereby the oil in said second coil is heated to a higher temperature than the o-il in said rst coil, introducing the highly heated condensate into said enlarged Zone second mentioned at a point near the base thereof, and condensing the fractionated vapors .to form a desired distillate.

6. The method of converting higher boiling oils into lower boiling oils which comprises heating fresh oil charging stock to cracking temperature under superatmospheric pressure by passing it through a first heating coil in a furnace, introducing the stream of highly heated oil into an enlarged zone wherein a cracking temperature is maintained and vapors separate from liquids, passing separated liquids from said reaction Zone into a separate enlarged zone, wherein vapors separate from residue, subjecting resulting cracked vapors to fractional condensation to separate vapors of desired boiling range from heavier fractions as condensate, heating condensate so formed to a cracking temperature under superatmospheric pressure by passing it through a second heating coil in said furnace, burning fuel in said furnace adjacent said second coil but remote from said first coil whereby the oil in said second coil is heated to a higher temperature than the oil in said first coil, introducing resulting highly heated condensate into said enlarged Zone second mentioned at a point remote from that at which vapo-rs are removed therefrom, and condensing the fractionated vapors to form a desired distillate.

ALLAN V. RITCHIE.

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