US1769459A - Method of and apparatus for cracking petroleum oil - Google Patents

Description

July l, 19530. J. PRIMRosE 1,769,459

IETHOD OF AND APPARATUS FOR CRACKING P'ROLEUI OIL med Jan. 11, 192sv 2 sheets-sheet 1 I arf-n I l n Hu 1 1L I. ll

u 'zo J. PRIMRosE 1,769,459

uETHoD oF AND AgPARATUs FOR CRACING PETRoLEUM oIL Filed Jan. 1l. '1923 2 Sheets-Sheet 2 W.my 1, 1930.

. Lil., lllliwFMHH, I m u n w s f x products together Wit Patented July l, 1930 JOHNramBOsE, Or DONGAN HILLS, NEW YORK,

OOMPANY, OF NEW YORK, N. Y.,

A CORPORATION OF NEW YORK METHOD OF AND APPARAT'US lFOIE. CRACKING- PETROLEUM OIL applicati@ mea :ranuay 11, 192s. serial No. 611,332.

This invention relates to a novel method of destructive distillation of petroleum oils and apparatus therefor. Heretofore the process of cracking has been extensivel utilized for the production of lower from igher boiling point oils. One method of carrying out such a process has been to pass the petroleum oil through a tubular heater resembling an ordinary Water tube boiler and having a number of rows of tubes dis posed one above another. These tubes are disposed above a furnace and the hot gases of combustion sweep across the tubes and heat the oil contained therein to the desired cracking temperature. The cracking temperature employed varies with different processes but for purpose of explanation the temperature `of 765- F. can be taken as a typical one. When petroleum is subjected to a suiicient degree of heat the molecules ofoil are cracked into components which may be briefly stated to be free carbon, ixed gas and the desirableli htand intermediate afgproportion of heavier fractions. strated that the heat absorption and temperature conditions must be very `carefully controlled to provide for the maximum quantity of the desirableproducts. If the Oil passing through the tubes'absorbs heat at an excessive rate the oil` {iL-lim lying next to heating surface is cracked beyond the desired degree with the result of a loss in yield of lower boiling point products and an excessive formation of carbon and fixed gases. A portion of the carbon thus formed will adhere to the surface ofthe metal and will form a film upon the inside of the tubes particularly at the points where there is an excessively high rate of heat absorption, which film will act as a heat insulator betweenl the oil which acts to carry away the heat and the metal of the tube, allowing an overheating of the tube at such points. Eventually a point will be reached in which the tubes subject to the higher rates of heat absorption are excessively or even entirely clogged with carbon. Even before such a stage is reached the accumulation of carbon in the tubes may be such that hot spots Experience has demonwould .develop in the tubes if thel operation ASSIGNOR TO POWER SPIEK'JIAIL'YA` PATENT OFFICE' Then, in putting 'a From the foregoing it is seen that localized overheating must be avoided and the temperature of the metal tube maintained as low as possible if the 'desired maximum of elliciency and capacity are-to be obtained.

It has been further found that for the best results in the cracking processes that the range of temperature is very small. This point is covered by Bureau of Mines Technical Paper N o. 258 in whichv it is stated that this range is considerably less than 50 C. rThis again emphasizes the importance of accurate control of the temperature of the metal tube.

In absorbing heat by oil passing through a metallic tube the temperature of the metal tube bears an im rtant relation to the cracking results w ich are obtained within the tube. Conditions of rates of absor tion above those actually required for crac ing oil will cause an excessive formation of carbon and fixed gases. This condition is particularly aggravated in the treatment of distillates from asphaltic base oils such as fromv California crudes.

The ideal condition for crackingl oil would be to bring all points of the oil within the heatingvunit to a desired and uniform cracking temperature. This, however, is impossible where heat is supplied to the oil by hot metal surfaces such' as those in any heater having conduits through which oil is passing. practicable approach to the ideal condition, the heat must be so supplied to the oil as to maintaina substantially equal rate of heat: transfer from all portions of the unit In-order to realize the nearest temperature difference between the inside surface of the conduits and the oil in any section of the conduits anywhere within the heating unit.

The above briey indicates the desirability of the proper control of the rate of heat absorption by the oil, which is equal to the rate'of heat transfer through the tubes, and also the necessity and desirability of preventing overheating. Summarizing, it may be stated that a certain temperature and rate of'heat absorption must be reached before obtaining a proper yield of the desirableproducts. Secondly, this oil tempera'- ture and the corresponding rate of heat ab,-l

sorption should not be exceeded to any material degree otherwise the quantity of desirable products will be decreased and there will be an undesirable and deleterious formation of carbon and fixed gas. Third, the method and construction employed should be one which should permit a high over all heat efficiency. Fourth, the necessity for shut downs should be brought to a minimum. Q

In practice it has been demonstrated that when petroleum oil is cracked in a heater embodying a plurality of superimposed tubes, the tubes which are exposed to the direct or radiant heat of the fire or furnace absorb a far greater amount of heat than the tubes which absorb heat from the gases. by convection. The absorption of heat by the oil is attained in two ways: first, by absorption of direct and radiant heat energy and second, by absorption of heat by convection. With an ordinary type of heater the lower tubes are usually exposed to this direct or radiant heat. The furnace walls become highly radiant and this radiant energy impinges upon the lowermost halves of the lowermost tubes. In a given apparatus,

for example, provided with nine superim posed rows of tubes it was observed that of the heat absorbed, the lowermost row received so much heat by direct and radiant energy, that these tubes alone effected of the heat absorption, leaving the balance of eight rows of tubes together to absorb the remaining 30%. Consequently, when such a heater is used for cracking and the proper quantity of heat is supplied to the heater to eifect the cracking of oil at a given rate the lower tubes will absorb heat too rapidly and the rows of tubes above will not absorb heat at an efficient rate.v Furthermore with such a heater there will be an excessive deposition of carbon and an excessive formation of fixed gas in the lower tubes. In order to minimize such conditions arising it has been heretofore necessary to cut down the furnace tem erature and this has usually been accomplis ed by admitting excess air with the heating fuel( The .use

of this excess air has materially reduced the efficiency of such heaters since a large roportion of the heat of combustion is utillzed in raising the temperature of excess air. With the utilization of only sufficient air for complete combustion, much higher furnace or heating efficiency is attainable.

The present invention 'is directed to a novel method and apparatus for cracking petroleum oils to the general end that the rate of heat absorption in the various parts of the apparatus may be made substantially uniform and effectively controlled so that the ideal rate of heat absorption may be obtained in each part of the apparatus. The result is that the entire apparatus may be operated under ideal conditions for cracking, the production of the maximum quantity of the desirable products under which conditions a maximum length of run without shutting down of the apparatus is secured and with the obtaining of the maximum yieldy of the desirable products and a minimum of carbon and xed gas from a given oil. Further, such a regulation of the heat distribution will make lpossible high heat efficiency in the heating apparatus.

A further object of the invention is the control of the heat distribution in such a way as to compensate for both the intensity of the direct and radiant heat and for the comparative sluggishness of transfer of heat by convection from hot gases to the general end that the oil receiving heat by radiation will notl be overheated and that the oil receiving heat by convection will be heated to the properdegree.

The invention .can be best illustrated by reference to the drawings which illustrate a preferred embodiment of the apparatus by which the process can be carried out.

In the drawings,

Fig. 1 is a central vertical section of the apparatus.

Fig. 2 is a top plan view of the same.

Fig. 3 is a detail view of certain of the conduit casings.

Fig. lis a diagrammatic view of a complete ap aratus.

Accor ing to the present invention I provide an apparatus which generally consists of two chambers as shown in Fig. 1, one a furnace chamber 10 and the second a socalled heating chamber 11. This structure is built up in the usual way with fire brick and the furnace chamber is separated from the heating oharnberby a bridge wall 13 which is preferably hollow. The fuel for providing a source of heat is burned in the furnace chamber in any desired manner, as by a burner, indicated diagrammatically at 14. A suitable quantity of air to support combustion may be admitted from below and damper 15. The arrangement of the bridge i bers is such that the direct radiationsf'from the heated walls of the furnace chamber and from the iame are prevented from impinging upon the roof portion of the -heating chamber, either directly or by reflection. In order to secure this result the bridge wall is preferably made of a considerable thickness. When the furnace is in operation the hot gases of combustion pass over the bridge walls through the conduit 16 and thence downwardly into the heating chamber 11, finally emerging through the outlet duct 17 to the stack.

Furnace chamber During the operation the walls of the furnace chamber become highly heated, and eventuallyprattain a condition of radiance. In order to utilize this radiant energy in the furnace chamber without excessive absorption of heat by portions of the oil which are to be cracked, I provide a plurality of conduits 18. In practice these conduits may be placed in the roof of the furnace as well as the front or side walls or even in the bridge wall. The number of conduits which are to be used and their relative location in the furnace chamber or their omission from one-or more of the walls or roof-will depend upon the operating demands of the cracking process. If these conduits were directly exposed to the radiant heat of the furnace chamber itself and of the flame thereinfthe oil iowing through the conduits or tubes would absorb heat at an excessively high rate and there would be the undesirable results heretofore explained. To obviate such results I provide protecting casings 19 of refractory material surrounding these tubes. The thickness and character of these casings will be such that the high temperal ture heat radiations will be received upon the outer surface of the casings and the heat thereof conducted through the casings and imparted to the tubes at a reduced temperature whereby the oil within the tubes will not absorb heat at an excessive rate but at a rate which is suitable for the highest yield of the desirable products. v

By tlie provisionxof sultable oil conveying, heat receiving conduits in the furnace chamber, I not only reduce the temperature of the -gases passing from the furnace chamber through the conduit 16 but I also usefully recover the heat and utilize the same in the cracking process.- It will thus be seen that the temperature of the gases entering the heating chamber may be so reduced that the walls of the 'heating chamber do not attain a condition of radiance from the heat of the gases. tained therein, serve the purpose of absorbing radiant heat so that the tubes 20 to be hereafter described, and the oil therein will The conduits 18 with the oil con-Y not be subject to the combined cumulative ,effects of heat of radiation and heat of convection. p

Heating chamber The absorption of heat in the heating chamber is effected substantially only by convection. Consequently, as the gases impart heat to successive exposed surfaces the temperature of the gases will fall and less and less heat will be given up by them other conditions being equal. As it has been heretofore pointed out all parts and all heat absorbing surfaces `should receive heat'at substantially an equal rate. Itherefore lprovide a means for distributing and equalizing the rate of heat absorption in the heating 4 chamber as will'now be described.

Preferably within the heatingv chamber there are provided a series of superimposed wrought iron or steel tubes 20. The individual tubes are provided with suitable casings of cast iron. Preferablythe upper row of tubes which are subject to the hottest gases are provided with plain cylindrical casingsl 21. The tubes which are later traversed by the heat-ed gases are provided with corrugated ca-st iron casings 22 Details of the cast iron casings are shown in Fig. 3. I also vary the depth of the corrugations in such a manner that the exposed heat absorbing surfaces are substantially in inverse proportion ,to the temperature difference between the hot gases and the oil within the tubes. As shown, the corrugations are shallower on the tubes nearer the top of the heating chamber and become greater and greater in depth as they approach the lowermost rows. The exact arrangement of corv rugations and the number of rows of plain cylindrical' casings to be employed, if any, will depend upon the particular operating characteristics of the individual heater.`

Furthermore the ability of the hot gases to impart heatyis nearly directly proportional to the velocity of the gases themselves. This factor is of course taken into consideration in designing the corrugations of the casings to the general end that the desired transfer of heat will be made uniform on all of the tube sections of the heater.

Substantially uniform 4distribution of heat is obtained around the entire eriphery of the tubes subject to radiant heat y means of the refractory protective casings which not only cut down the transmission of heat to the oil within the tube but also serve to distribute the heat and the temperature equally about the tube periphery.

The smooth and corrugated metallic casings which are disposed upon the tubes which are traversed by the hot gases and hot gases and impart the sameto the tubey vend that the excessive formation of carbonl and fixed gas is minimized. Furthermore the distribution and transfer of heat to the oil may be so vcontrolled that all units of the-surfaces supply heat at substantially the same rate.

It is not deemed necessary here to describe in detail the arrangement of header connections for the various conduits. These can be arranged as individual conditions necessitate, and the oil can be arranged to flow through the conduits in series or in multiple or series-multiple paths as desired.

In the system herein illustrated it is contemplated that the oil enters the system in a highly heated condition. It will be understood, however, that the oil may be fed to the system in a cool or cold condition, in which case, certain heating surfaces in the sy-stem are employed forbringing the oil up to the cracking temperature and the maximum allowable temperature difference condition does not apply necessarily to that portion of the heat absorbing surface which is used for preheating the oil. No detrimental effects will result from the high rates of heat transfer in this preheating portion of the heating system because no cracking takes place until certain critical temperatures are reached.

In certain instances it may be desirable to operate with such high temperatures of the gases entering the heating chamber that the exposed walls will become slightly radiant. Inlsuch instances the effect of this radiant hea-t upon the uppermost tubes within the heating chamber-may produce slight overheating of the oil contained therein unless provision is made for eliminating destructive heat radiations. For this purpose I may provide oil conveying tubes or conduits 23 in the .roof of the heating chamber 11. These tubes are preferably provided with cast iron protective casings 24 which cooperate to prevent a transfer of radiant yheat energy from the roof to the upper tiers of tubes 20. Similar oil conveying tubes 25 may be placed in the walls of the heating chamber above the transverse heating elements and these tubes 25 may be covered` with refractory or cast iron casings 26 depending upon the individual prevailing conditions. In the drawings, refractory casings areillustrated'and they serve the purpose of protecting the tubes in the wall from the possibility of being over-heated when operating under su'ch high temperatures as .would cause the exposed walls of the fur- `nace chamber to become radiant. A The principal destructive heat radiation with high temperature conditions in the heating `chamber is between the opposed heat absorbing surfaces. By' providmg the opposing heating surfaces 21 and 24 destructive heat radiations are prevented from impinging upon either the upper row of tubes 20 or tubes 23 in the roof. These tubes 23 are here shown as extended from and forming a continuation of the tubes or conduits 18 in the roof of the upper o conduits 20. The present application is a continuation in part of the' subject matter of my copending application Serial No. 482,135 led January 2, 1921 and now patented, Patent No. 1,568,182 dated January 5, 1926.

The direction of .iow of oil through the various sections, stages and zones of the heater is largely a matter of selection and design. As here illustrated the radiant heat absorbing stage or zone is divided. Oil entering the system Hows through the walls of the furnace chamber absorbing radiant heat, thence through the conduits 2O where heat is absorbed by convection from the hot gases and finally flows back through the roof tubes 18 where further radiant heat is absorbed. The particular flow conditions may be reversed or the order changed as desired. From the heater the oil Hows to a suitable condenser and evaporator.

Fig. 4 shows dia rammatically a complete system including eater H, evaporator E, dephlegmator D, circulatin pump. P and condenser C. These parts o the system may be of any desired type. I

lThe direction of flow of the oil through` the various sections of the furnace is largely a matter of selection and design. If desired l the oil can flow through the tubes in the heating chamber first and thence through the other tubes or if desired the iow conditions may be reversed.

It will be apparent that there will be a zone in the heating system where the radiant and direct heat as well as the heat by convection are factors in the heat absorption.

Substantially. however, the heating system is divided into the two distinct zones or stages as described, and this invention is not limited by lack of a complete analysis of such obvious conditions or inessential details which would only tend toburden the .specifications and obscure the important elements .in the process.

What I claim is 1. A. method of )cracking petroleum oil which comprises passing the oil through a plurality of conduits, subjecting the oil to cracking temperature in a multistage heating process, inone stage supplyin heat to the oil by radiant heat and in anot er stagev supplying heat to the oil primarily by heat of convection, and maintaining substantially uniform and equal the rate of heat absorption iii the various stages.

2.' In the method of cracking petroleum oils, the improvement which-consists in conducting oil to be cracked through a plurality of metallic conduits, heating the oil progressively to cracking temperature by radiant heat in certain of said conduits and heat of convection in other of the conduits, and providing a substantially uniform rate of heat absorption throughout to give a substantial .uniformity of the cracking action by limiting the heating effect by convection in some parts of the system and limiting the 'heating effect by radiation in other parts 4of the system.

3. The method .of cracking petroleum oil which comprises passing the oil to be cracked through a plurality of conduits, heating the oil to crack the same by absorbing heat by the conduits from gases of diminishing temperatures and thereby heatin 'the oil which is to be cracked, and in provi ing substantial uniformity of thecracking action by substantially equalizing the rate of heat transfer to the oil from the gases of various temperatures. .l

4. An apparatus for lcracking petroleum oil comprising in combination, a lurality of conduits, means for conducting t e oil to be cracked therethrough, certain of said conduits being disposed toreceive heat by radiation, means comprising refractory, protective coverings on said last mentioned confduits for limiting the rate of heat transl being disposed to receive heat by convection mission to avoid temperatures in the metal towhich thoil is exposed, of such degree as to cause excessive formation of carbon and xed gases', certain others of said conduits from hot gases, said first mentioned conduits adapted to absorb suiiicient heat to decrease the temperatures/of the gases `-of combustion' iowing to the second mentioned conduitsbelow a temperature at which exincreasing in exterior area as the gas temperatures decrease.

5. In'an apparatus for cracking petroleum oil, a' source of heat, a plurality of oil con-V taining conduits subject to the heat from said source, certain of said conduits being disposed in the path of hot'gases from said source, outside corrugations on said) last mentioned conduits having' extended heat absorbing surfaces so proportioned as to vcompensate for diminishing temperatures of the hot gases whereby a substantially uni,- fo'rm rate of heat transfer wi-ll occur in all parts of said conduits, certain other con.-

the rate of heat 'transfer tlfereto, other of I said conduits being disposed in the path of hot gases, the outside surface of said conduits having exterior corrugations constituting an extended heat absorbing surface, said surface, being so proportioned .as to compensate for diminishing gas temperatures and to substantially equalize the rate of heat transfer to the various conduits which receive heat from thehot gases still other of said conduits being oppostely disposed to the last4 mentioned set of conduits so as to substantially prevent destructive' effects of radiantheat on the opposing surfaces. l

In testimony whereof I hereto aiiix. myv

signature.

^ JOHN PRIMROSE.

cessive carbon and fixed gases form, and

meanscomprising smooth and corrugated metallic casings on said second mentioned conduits to distribute the heat completely around' the periphery of the conduits, said smooth fcasings bein disposed in the region ofho'ttest gases an the corrugated casmgs

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