US1629908A - Process for cracking hydrocarbon oils - Google Patents

Description

May 24, 1927 w. F. FARAGHER ET AL. 1629'908 PROCESS FOR CRACKING HYDROCARBON OILS Filed Jan. l5. 1921 MW MN kuma,

Patented May V24, .1927.'j

UNITED 4STATES PATENT OFFICE.

'WARREN F. FARAGHEB, AND WILLIAM ARTHUR GRUSE, 0F PITTSBURGH, v'PIlITll-SYL- i vaina,

vaina, A CORPORATION or muxas.

ASSIGNORS T GULF BEFINING `CQMIPANYy OF PITTSBURGH, PENNSYL- PROCESS FOR CRACKING HYDROCARBON OILS.

conduction of heat into the oil, and results in increased cost of gasoline-production,

.towing 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 toI the rapid burning out ot' the iron in contact with carbon These diihculties are encountered in externally heated stills of various kinds, including stills of the water-tube boiler type, where the oil is heated in its passage through a series'of tubes. v

Attempts have been made to overcome the difficulties mentioned by providing stirrers. in the still for agitation of the oil, and', in

stills of the water-tube boiler type, it has been'proposeol in oil cracking operations to provide mechanical stirrers or propellers for increasing the circulation through the heated tubes (a practice well known in steam boiler operations) but such mechanical stirrers and propellers are open to theiobjectionithat 1 they require stuffing boxes which must operate against highly heated oil and heated oil vapors athigh pressures.

proved method for cracking oils in which -the cracking. operation' is carrie out in a still of the water-tube boiler type,and in which a positive and efficient circulation of.

Vwithout mechanical agitators or propeller-s, and with avoidance or substantial avoidance vof .objectionabledeposition of carbon in .oil through the tubes isefected, according to the `present invention, by the introduction of a jet or a series of jets of gas, or by the internal generation of gas, acting on the air-lift principle, to bring about a rapid The present invention relates to-an imthe oil through the heatedtubes is effectedv the heated tubes. This circulation o f the and effective circulation of the oil through the hea-ted tubes..

The gases used fory effecting the circulation of the oil, according to the present invention, may with advantage be the fixed gases formed during the cracking operation, or the mixed gases and vapors taken from the vapor line of the still and recirculated; but other appropriate gases can be used, such as natural gas or casing-head gas, or other gaseous materials, such as steam, which have no objectionable effect upon the cracking operation. The introduction or reintroduction of these gases into the stillhas the further advantage of promoting the'regular removal of the lower boiling constituents resulting from the cracking operation as they are formed, thus preventing their remaining in the' still to lundergo further objectionable cracking or decomposition. When a portion of the gases or vapors produced by the cracking operation is recirculated through the' still, these gases maybe freed from a part or the whole of the readily condensible constituents before recirculation, oor the ho-t gases and vapors from the still can be recirculated with the removal therefrom of only thehigher boiling constituents.

The invention will be further illustrated and described in connection with the accompanying drawings, which show, in a somewhat conventional and diagrammatic manner, different forms of apparatus adapted' for the practice of the process of the invention.

In the accompanying drawings,

Fig. 1 shows one form of apparatus em-- bodying the invention invertical longitudinal section and with parts in elevation; and

' Fig. 2 is an end view of the apparatus of Fig. l, with the' furnace structure' removed. In the apparatus illustrated, the still is of 'the `water-tube vboiler type and is made up of the upper longitudinal drum 1,- the two lower transverse drums 2 and 4 with vertical connecting legs or tubes'3 :md5- respectively, and with 'a series of -tubes 6 connecting the two lower transverse drums and suitably arranged to be heated in a furnace cham- .ber 7.

The u per longitudinal drum 1'has a suitable ephlegmator 8 and a vapor pipe 9 leading therefrom is supplied to the-upper drum from an oil- Athe condenser 17.- O11 'the suppl -vapor plpe 13 connects the vapor space of the oil supply tank 10 with the vapor pipe 9 so that the same pressure will be maintained in the oil supply tank as in the still and so that oil will automatically flow from tank to the still to maintain a constant evel therein. An outlet for the residue is indicatedv at the bottom of the still at 15.

In the shorter depending legs 5 there are provided foot-pieces 14 through which gas is introduced from pipes 16. The gas is blown in through thefoot-pieces 14 so as to cause a rapid and positive flow of oil up through these legs. This, in turn, causes a rapid and effective circulation of oil through the heated tubes 6, the oil circulating downwardly through the leg .3 to the transverse drum 2, thence through the heated tubes to the drum 4 and upwardly through the legs 5, and being repeatedly recirculated in -this way. In this way the oil is kept `rapidly circulating-through thetubes 6 and deposition 0f carbon in these tubes, which is the chief source of trouble in stills of this type, is avoided or minimized. The tar and heavier sediment collect at the bottomof the transverse drum 2 and are discharged through the outlet 15.

The construction and arrangement, as well as the number, of the tubes, and of the depending legs, joining the upper longitudinal drum with. the two lower transverse drums, can be varied. AThe construction and arrangement should preferably be such as to give a substantially uniform distribution and flow of the oil through the tubes.` This uniformity of distribution and of flow can be promoted, for example, by providing a plurality ofdepending legs, such?A as are shown at 5'. The provision of a plurality of such legs, each with a gas inlet pipe for securing an air-lift action therein, permits the regulation of the flow through the tubes, to a greater or less extent, by-varying the gas introduced into the different legs. For example, if an increased velocity of flow is produced in the outer legs 5, this will tend to increase thepfiow of oil through the outer pipes, thus preventing-or reducing the tendency for the oil to flow more slowly in the outer tubes than in the centrally arranged tubes. i

In the operation of the apparatus and the carrying out of the oil cracking process, the

oil isheated by its passage through the .tubes 6 and pressure is maintained in the still 4by placing a suitable regulating valve 18- in the vapor line, preferably beyond the condenser as shown, thereby confining the vapors and fixed gases developed by the process and maintaining the proper pressure for the cracking operation. The oil inflow is supplied from the oil reservoir 10 in which the oil level is maintained in any suitable manner, as by a pump controlled by an automatic fioat device (not shown). There are no stuffing boxes or moving parts of the still, but rapid and effective circulation of the oil through the heating tubes is nevertheless effected by the introduction of gas in the manner described.

The operation is continuous and can be continued for long periods of time, the residuum accumulating. and being removed through the outlet 15 and the oil being automatically supplied to maintain a constant level within the still. The rapid circula; tion of the oil within the still promotes uniformity of heating and of cracking, thusavoiding or minimizing local overheating. The continuous rapidcirculation of the oil through the heated tubes causes the oil in contact with the heated Walls of the device to" be continuously swept or scoured off so that the formation of a dead layer of oil is prevented, with resulting prevention or substantial prevention of the heating oflsuch a layer to objectionably high temperature.

It is one advantage of the invention that the use of moving mechanism is avoided, so that stuffing boxes are avoided, and so 'that all connections of the stilhmay be welded and made gas-tight.

The introduction of a current or currents of gas not only serves to insure effective agitation and circulation of the oil, 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 to undergo further decomposition. The excess gas, resulting from the cracking operation, can be discharged from the still in any ofl the usual ways, while the gas that is to be recirculated through the still can be freed from undesired high boiling constituents in a suitable dephlegmator, and from the desired condensible constitutents in a suitable condenser, and canv then be passed through a pump or gas-booster 19 and sufficiently increased in pressure to 'be used again.

By drawingy off the admixed fixed gases and vapors, from the vapor pipe 9 atstill pressure and at substantially still temperature -through connection 20, and by recirculating and reintroducing .these gases for bringing about the circulation of the oil, the amount of work required for compression of the gases is reduced and the sensible heat of the gases can be sufiiciently conserved s o that they exert no objectionable cooling effect when reintroduced.

In the apparatus illustrated the heated tubes are made slightly curved so as to avoid strains set up by expansion and contraction.

The oil supply to the still may be preheated to a greater or less extent, preferably to such a degree as to vaporize and remove any Water present therein before the oil is supplied to the still. By preheating the oil in this way',` the preheating effect required from the tubes will be correspondingly reduced. yA part of the heat necessary for the preheating can be supplied by nieans of a neat interclianger through which the still bottoms are discharged; while a part ot' the pieheating may be effected bybringing the oil into heat interclianging relation with the hot vaporsfrom the still, for example, by passing the oil through the condenser for the vapors of distillation and cracking, or through one or more of the series. of condensers where such a series is used. The preheating effect thus secured may be supplemented, if desired. by further preheating of the oil in any suitable manner. Owing to the rapid and continuous circulation of the oil through the heated tubes, uniformity of heating is promoted, and the resulting cracking operation is of a inoie uniform chai'acter and results in an increased yield of gasoline and lower gas and coke losses, and hence an increased capacity or increased yields for a given size still, as compared with a still which is not provided with means for effecting such circulation.

It will, of course, be understood that the manner of introducing the gases for bringing about and promoting the circulation can bevaried, for example, the gas iets can be varied in number and arrangement, as Well asin shape and location, provided only 'that they' serve as means for `eilecting the constant and substantially uniform circulation of the oil through the heated tubes'.

Iii illustrating the apparatus in the accompanying drawings, we have omitted the heat insulation or lagging of the still, con= nec-ting pipes, etc. but it will be understood that, in practice, suitable heat insulation will be provided 'to avoid objectionable losses I' from all exposed parts of the still and of the system which become heated.

It will be understood that the stills will,

l in practice, be provided with suitable "temperature, pressure and level indicating devices (not shown) as well as 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 outl vundera'regulated pressure, for example, of

between 60 and 500 pounds persquare inch,

land preferably inthe neighborhood of 7 5. to

1.50 pounds per square inch, depensding upon the nature'ofv the oil to be crack'ed and the products desired. v

In referring to the cracking of oil in the. present specification and claims, we in,-l tend to include the treatment of various'hy'-v drocarbon oils, and more particularly the;`

treatment of higher' boilingfractions and' residual oils of petroleum or shale oil distillation, for the vproduction of motor fuel or cation may be arranged in series and the oil to be cracked passed through them consecutively. v

We claim: l. The method- 0f cracking oils in a pressure still, which comprises maintainingA a pool of oil and circulating oil from the pool downwardly to one end of `heating tubes,-

thence through the heating tubes,'and upwardly back from the other end of the heating tubes to the said pool, heating the oil to a cracking temperature in the said heating tubes, and promoting circulation of the oil vthrough the heating tubes by introducing a current or currents of gas, acting on the air-lift principle, into the oil at a point .in

its passageupwardly between the heating` tubes and said pool.

2. The method of cracking oils in a pressure still, which comprises circulating the oil from and to-a drum through tubes heated to al cracking temperature and promoting the circulation of oil through the heated tubes of the still by introducing current or currents of gas, acting on the air-lift principle, into the oil at a point in its passage upwardly between the tubes and the drum.

3. The method of cracking oils in a pressure still, which comprises circulating the oil from and to a drum through tubes heated to a cracking temperature and promotin the circulation of. oil through the lieate tubes of the still by`introducing a current or currents of gas from the still', acting on .the air-lift principle, into the oil at a point in its passage upwardly between the tubes s' and the drum.

4. The method of cracking oils in a pressure still, which comprises vcirculating the oil from and to a drum through tubes heated to a cracking temperature and promoting the circulation of oilthrough the heate tubes of the still by introducing arurrent or currents of gas and vapor from the still and at substantially thestill temperature,

acting on'the air-lift principle, into thev oil at a point infits. passage upwardly bef,

tween the tubes and the. drum. l

5. The process of -pyrogenetically distilling lower boiling point hydrocarbon oils from higher boiling point hydrocarbons which consists in maintaining a bulk supply thereof under pressure, withdrawing oil therefrom, passing it in a stream through a heated zone and returning it to said bulk supply, and injeeting u gaseous medium into it in the direction of its iow in its passage between the heated zone und the bulk sup- Plyl 6. The process of pyrogenetloully distilling lower boiling point hydrocarbon oils from higher boiling point hydrocarbons which consists in maintaining a bulk supply thereof under pressure, withdrawing oil therefrom, passing it in an upwardly directed stream thru a heated zone and back to the bulk supply, whereby circulation of the oil is thermally maintained, and injecting steam upwardly into the oil in its pas-- sage between the heated zone and the bulk supply.

ln testimony whereof We affix our signa- 20v tures.

WARREN F. FARAGHER. WILLIAM ARTHUR GRUSE.

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