US1601727A - Process and apparatus for cracking hydrocarbon oils - Google Patents

Description

Oct. 5 1926.

w. F. FARAGHER ET AL PROCESS AND APPARATUS FOR CRACKING HYDRQCARBON OILS Filed Jan. 15, 192] 2 Sheets-Sheet 1 Oct 5 1926.

W. F. FARAGHER ET AL PROCESS AND APPARATUS FOR CRACKING HYDROCARBON OILS Filed Jan 15, 1921 2 Sheets-Sheet 2 Patented Oct. 5, 1926.

. UNITED STATES PATENT OFFICE.

WARREN F. FARAGHER, WILLIAM ARTHUR GRUSE AND FREDERIC HORACE GARNER, OF PITTSBURGH, PENNSYLVANIA, ASSIGNORS TO GULF REFINING COMPANY, OF PITTSBURGH, PENNSYLVANIA, A CORPORATION OF TEXAS.

I PROCESS AND APPARATUS FOR CRACKING HYDROCARBON' OILS.

Application filed. January 15, 1921. Serial No.'437,48l.

This invention relates to an improved method and apparatus for making motor fuel. or gasoline bycracking hydrocarbonoils, such as the higher boiling fractions and residualoils of petroleum or shale oil dis tillation. More particularly, the invention relates to improvements inthe cracking of oil in a horizontal cylindrical boiler type of still of the general type referred to in our copending applications Serial Nos. 437,482 and 628,501, which is heated externally to the cracking temperature.

When such oils are subjected to cracking in an externally heated still, seriousdifiiculties are encountered in large-scale operations, due to the depositions of a carbonaceous solid, commonly referred to as carbon, on the heated walls of the still. Such a deposition of carbon interferes with the conduction of heat into the oil, and results in increased cost of gasoline-production owing to the necessity of cleaning the carbon from the still walls and the loss of operating time during such cleaning operations; while the life of the still wall is comparatively short due to the rapid burning out of'the iron in contact with carbon. Attempts have been made to overcome the difiiculties mentioned by providing stirrers in the still for agitating the oil, but such stirrers are open to the objection that they require stufling boxes which must operate against highly heated oillor hot oil vapors at high pressures.

According to the present invention, the cracking operation is carried out in a horizontally arranged cylindrical still, such as is, commonly used in cracking oils, but the cracking operation is carried out without objectionable carbon deposition and accumulation on the heated bottom of the still,-

and with avoidance or substantial avoidance of the objections above referred to.

In carrying out the improved crack ng operation of the present invention, we provide a plurality of directing bafiles, longi-.

tudinally arranged in the still and spaced apart to permit circulation of oil therebe tween, and between the bafiles and the still walls, and we maintain an effective circulation of .the oil'in the still around the baflies and between the .baflles and the heated still walls by the introduction of currents of gas between the battles or between the bailies and the still walls so that the entire body of oil 'in the still is kept in continuous and effective circulation and heated to a substantially uniform temperature throughout, and so that objectionable carbon deposit on the heated bottom of the still will be prevented orremoved by the circulating oil. The number of longitudinal baflles provided may vary in shape and arrangement, as well as in number, provided they permit efiective circulation of the entire body of oil in the manner above described; This circulation takes place along both sides of the heated bottom of the still,

in opposite directions, either toward or away the still walls, in opposite directions to the center of the still at the bottom, and thence ret'urnedlupwardly through the central portion of the still for recirculation. Where more than two longitudinal bafiles are provided, a. series of currents or cycles of the oil will be formed.and the gas jets, in this case, will usually be arranged in the alternate spaces between the directing battles. so that the 'oil will have an upward flow through the alternate spaces and a downward flow through the-intermediate spaces; while the flow between the outer baffles and the still Walls will be either upward 'or downward, depending upon whether the gaseous current is introduced into these spaces or not. The longitudinal spaces through which the oil flowsunwardly may be divided by transverse partitions into a series of passages, in each of which a gas jet or gas jets are arranged, thus giving a series of air-lift spaces; while the intermediate spaces between the bafiies, through which the oil has a downward flow, are left open and unobstructed throughout their lenjgth. I

he invention will be further illustrated and described in connection with the accom pany1ng drawings, whlch show, in a somealong the line 33 of Fig. 4 and the line 44 of Fig. 3, respectively, show an apparatus with a somewhat modified form and arrangement of directing battles.

Fig. 5 shows a further modified form and arrangement of directing bafies. y

In the apparatus of Figs. 1 and 2, the still 1 is a horizontally arranged cylindrical boil er type of still such as is commonly used in the cracking of oil. It is arranged in a suitable furnace setting so that it is heated either by direct heat or by products of combustion in the furnace chamber 2. The still is provided with a suitable oil supply pipe 3 through which a regulated supply of oil can be introduced either in the form of successive charges or in a more or less continuous manner. The oil supply can be automaticallyregulated in any suitable manner (not shown), to maintain a constant level in the still. The residue outlet from the still is indicated at 5. The still has a dephlegmating column 26 leading to the vapor pipe and condenser (not shown).

Arranged within the still is a series of six longitudinally arranged baflies, arranged in pairs. The inner pazr of baflles 6 and 7 are centrally and symmetrically arranged, while the two outer pairs of baflles 8 and 9 are arranged at equal distances from the center of the still. These baflies are supported in any suitable manner, as by securing them to the heads of the still, and they are spaced apart from thebottom of the-still to permit the circulation of oil therebetween. The battles extend from near the bottom of the still to a considerable height which, in the preferred practice, is such that the upper edges of the bafiles are submerged in the oil a sufficient distance to permit free circula tion of the oil over them.

Arranged between the baflles of each of the three pairs are perforated gas introduction pipes, the central pipe 10 being arranged between the central baflies 6 and 7, and the outer p es 11 being arranged between the bafiies 8 and 9. Gas is supplied to these pipes through suitable inlet pipes 12 and 13, I

of the oil inthe spaces between the'dilferent pairs of baflies and between the outer baflles 9 and the stillwalls. That is, the oil is caused to flow downwardly in the 'alternate spaces between the baffles and between the outer baffles and the still walls, and u wardly in the intermediate spaces, due to t e air-lift action of the gas jets introduced, so that .the oil flows under the lower edges of the battles, between these baflles and the still walls, and also over the upper edges of the battles. A series of circulation paths or cycles of oil is thus established and maintained so that the entire body of oil in the still is kept in vigorous and effective agitation and circulation,-and so that the oil is lgept in circulation over the heated bottom wall of the still and objectionable carbon deposition thereby substantially prevented or. removed. The lower edges of the baflies cause rapid eddy currents to be formed which have a scouring action upon the still wall, tending to keep it free from carbon deposit. The diflerent parts of the body of oil are thus caused to mingle and intermingle in the course of the circulation so that the entire body of oil is heated to approximately the same temperature, with resulting uniformityof the heating action and'avoidance of objectionable local overheating, as well as substantial avoidance of a dead layer of oil along the still bottom which has heretofore been the chief cause of carbon trouble and deposit.

In the apparatus of Figs. 3 and 4, the still is of the same general construction as that of Fi 1 and 2, and the same parts are indicated b; with the letter a appended thereto. The directing baflies, in Figs. 3 and 4, are somewhat curved,'and have a transverse section resembling that of a Venturi tube. So also, in the arrangement of Figs. 3 and 4, a series of transverse partitions 21 may be provided in the longitudinal space between the baflles llO the same reference characters,

to divide up this longitudinal s ace-into a tudinal bafiies, for the downflow of the oil therethrough, are left open and unobstructed.

In the apparatus of Fig. 5, the general construction and arrangement is similar to that of Fig. 1, and the corresponding parts are indicated by the same reference characters with the letter b appended thereto."

The directing baffles, however, are somewhat inclined so that they are, closer at the top-than at the bottom, in order to reduce the speed of gas separation and assist in maintaining the foam in the still.

The gas which is used for bringing about the circulation and stirring of the oil may with advantage be the fixed gas formed during the cracking operation, after, the condensible constituents have been removed therefrom in the condenser, but other appropriate gas can be used, such as natural gas or casing-head gas or other gaseous material. such as steam, which has no objectionable effect upon the cracking operation. This fixed gas may be drawn off at the still pressure, where the condenser is'maintained underthe same pressure as the still as in the preferred practice, or at a. lower pressure, where the condenser 1s maintained at a lower pressure; and it can then be passed through a compressor or gas booster (not shown) for increasing its pressure sufficiently to force it into' the still at the desired rate and under the appropriate pressure. Instead of using the fixed gases after condensible constituents have been separated therefrom, a part of themixed vapors and gases can be drawnoif from the vapor.

line at substantially the still temperature and pressure and recirculated, thustaking advantage of the temperature of these gases as well as their pressure.

The introduction of the gas currents not only serves to insure effective agitation and circulation of the oil, in the manner above described, but it promotes the regular removal of the lower boiling constituents resulting from the cracking operation as they are formed, and prevents their remaining in the still for long periods of timeto undergo objectionable decomposition. The exthe temperature of the oil will thus be raised into that range of temperatures most favorable to the cracking operation with the production of considerable naphtha and gasoline and relatively little gas and carbon, and without objectionable local overheating of the oil to the still higher'temperatures at which much gas and carbon are formed. This uniformity of temperature of the oil body as a whole is brought about by the continuous and effective circulation of the entire body of oil, with resulting increased uniformityof the cracking operation, while the oilthat is heated by its circulation between the baflles and the still walls is continuously removed so that the formation of a dead layer of oil is prevented, with resulting prevention of the heating of such a layer to objectionably high temperatures.

It is one advantage of the invention. that it brings about an effective circulation of the oil without the use of moving mechanism and therefore without the use of stufiing boxes, so that all connections of the still may be welded and made gas-tight.

I Inasmuch as the accumulation of carbon on the still walls is prevented or minimized,

the cracking operation can be continued for.

relatively long periods of time, the oil being supplied continuously through the oil inlet pipe and the residue being removed continuously or periodically through the residue outlet ipe. When a considerable accumulation .o carbon in suspension in the oil has been brought about, the entire body of residue can be removed and a fresh charge introduced without the'necessity of opening the still to clean it of carbon deposit. F i

It will be understood that the stills are provided with suitable pressure, temperature and level indicating devices (not shown), as well as with means for producing'and maintaining within the still the necessary temperature and pressure conditions for the cracking operation. The cracking operation may thus be carried out under the regulated pressure, for example, of between 60 and 500 lbs. per square inch, and preferably in the neighborhood of 75 to .150 lbs. per square inch, depending upon the nature of the oil to be cracked and the roducts desired. The prevention of obectionable carbon deposit on the heated stillwalls prevents weakening of the walls by overheating, such as results when the bottom wall of the still becomes incrusted with a thick layer of carbon deposit or coke.

Owing to the continuous circulation and substantially uniform temperature of .the entire oil body, the cracking operation is improved, with high yields of gasoline and lower gas and eokeloss'es, and hence into a greater or less extent before it enters the still. A part of the necessary heat can be supplied by means of a heat interchanger through which the still bottoms are dis charged; while a part of the preheating can be effected by bringing the oil into heat tween longitudinally arrange interchanging relations with the hotvapors from the still, thereby making the heat of these vapors available in the preheating operation. The oil feed can, for example, be passed through the condenser for the vapors from the still, or through one or more of the series of such condensers, where such a series is used for cooling and condensing the-vapors. The preheating efiect thus secured, may be supplemented, if desired, by further preheating of the oil feed in any suitable manner, and the preheating of the oil can advantageously be carried to such a degree as to vaporize and remove any water present therein before the oil enters the still.

In illustrating the various forms'of apparatus in the accompanying drawings, we have omitted the heat insulation or lagging of the still, connecting pipes, etc., but it will be understood that, in practice, suitable heat insulation. will be provided to avoid objectional losses from all exposed parts of the still and of the system which become heated.

From the foregoing description it will be seen that the improved method and apparatus of the present invention, ,enable the cracking operation to be carried out in an improved and advantageous manner, with effective agitation and circulation of the entire body of oil in the still, and with resulting uniformity of temperature and of cracking, as well as with effective circulation of the oil over theheated bottom of the still and the prevention'of the formation of a dead layer of oil and objectionable carbon de osit on the heated still walls, this circulation of the oil bein effected bebafiles and between such bailles and the still walls,

in a cyclic manner, so that the oil is caused to flow upwardly or downwardly along the side walls of the still, in opposite directions, either toward or" away from the center of the'still at the bottom, while the entire body of oil is kept in circulation around the bafiles in sucha wa that all arts of the oil are effectively agitated an circulated.

In referring to the cracking of oil in the present specification and claims, we intend to include the treatment of various hydrocarbon oils, and more particularly the tillation, for the production of motor fuel or gasoline; but other oils, such as lignite or coaltaror tar-oils, etc., can be similarly treated; and we include all such materials within the term oil, as used in the accompanying claims.

It is to be understood that a plurality of stills of the designs disclosed in this specification may be arranged in series and the oil to be cracked passed through them consecutively. n

1. The vmethod of cracking oils which comprises heating a body of oil in a still to a cracking temperature by the external application of heat to thestill, sub-dividing the main body .of oil in the still into a plurality of vertically disposed smaller bodies freely communicating at their upper and lower ends respectively, and causing circulation of the-oil in the still in a plurality of paths or cycles by introducing upwardly flowing gaseous currents acting on the airlift principle into some but not all of the sub-divided smaller bodies near the lower.

end thereof.

2. The method of cracking oils which comprises heating a body of oilin a still -to a cracking-temperature by the external application of heat to. the still, sub-dividing the main body of oil in the still into a plu- Y rality of vertically disposed smaller bodies andfrom the still walls, and means for in troducing a plurality of gaseous currents,

acting on the air-lift principle, into alternate passages between said baffles for effecting circulation of the oil.

4. An apparatus for cracking oils, comprising a horizontally arranged still, means for heatin said still externally, a plurality of vertica ly arranged baflles in said still spaced apart from each other and from the still walls, and means for introducing upwardly flowing gaseous currents, acting on the air-lift principle into alternate passages between the bafiles for brin ing about the circulation of the oil in a pluralit of difli'erent paths between the bafiles an between the bafiles and the still walls.

5. An apparatus for cracking oils, comprising a horizontally arranged still and fected around the baflles and between the 1 means for heating said still externally, a. baflles and the still walls in a plurality of series of vertically arranged longitudinal different paths or circuits.

baflies in the still spaced apart from each In testimony whereof we aflix our signaother and from the still galls, said baflles tures.

being arranged below the normal liquid level in the still bottom, and means for in WARREN F. FARAGHER.

troducing gaseous currents between alternate WILLIAM ARTHUR GRUSE.

baffles, whereby circulation of the oil is ef- FREDERIC HORACE GARNER.

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