US1775052A - Treatment of petroleum oils and products derived therefrom - Google Patents

Description

Sept. 2, 1930. F, R ET AL 1,775,052

TREATMENT, or PITROLEUI OILS AND PRODUCTS DERIVED THEREFROM Filed July 3, 192 4 INVENTORS Wade/2Z1 -G- BY fe zy flea/361 0128.

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ATTO RNEY Patented Sept. 2, 1930 UNITED STATES PATENT OFFICE FREDERICK GARTHEWAITE RING, OF WINCHESTER, MASSACHUSETTS, AND PERCY GEORGE PARIS, OF BETHLEHEM, PENNSYLVANIA, ASSIGNORS T BETHLEHEM STEEL COMPANY, A CORPORATION OF PENNSYLVANIA TREATMENT OF PETROLEUM OILS AND PRODUCTS DERIVED THEREFROM Application filed July 3,

This invention relates to a process and apparatus for the treatment of petroleum oils and the products derived therefrom, whereby the conversion, by pressure distillation, of

' heavier hydrocarbons having higher boiling points to lighter condensible oils of lower boiling point, can be effected in a simple and efficient manner. More particularly it relates to the production of crude naphtha from the gas oil derived from the preliminary distillation of crude petroleum.

This invention has for an object a process and combination of apparatus whereby the control of condensation of the distilled vapors, and the fractional separation of the various condensible constituents of said vapors, can be readily effected.

A further object of this invention is to utilize the fractionated condensates in an eflicient manner, and to obtain a maximum yield of crude naphtha, with a substantially reduced consumption of fuel.

In the known processes of pressure distillation, for the conversion of heavy hydrocarbon oils to crude naphtha, the various methods of effecting primary condensation of the still vapors can be broadly divided into two classes: firstly, those embodying the well known principle of dephlegmation, whereby the combined functions of condensation and preheating are fulfilled, by virtue of the intimate contact between the outgoing still vapors and the incoming cold charging stock; and, secondly, those involving the principles of surface condensation, by which condensation and heat interchange also take place but without direct contact or mixing together of outgoing vapor and incoming stock.

In the first case, owing to the intermingling of the constituents, it is not possible to avoid the return to the still of all the more easily condensed components of the still vapors, together with the feed of fresh charging stock that has been partially preheated in the dephlegmator. In the second case, although condensate and condensing medium are, by the nature of the condenser, kept separate, it has been customary to return or reflux said condensates to the still, with the object of effecting some further conversion of 1924. Serial No. 723,899.

these early condensates of intermediate boiling point to crude naphtha, and in the expectation that said step of redistillation under pressure could be effected concurrently with, and under similar conditions to the conversion of the fresh charging stock.

We have found, however, and have demonstrated by experiment, that the return to the still of all the condensates obtained in the primary condensation of the pressure still vapors is not advantageous to the process and may in many cases prove a distinct deterrerlllt to the efficient operation of the pressure sti It has been recognized in the art that the pyrogenetic conversion of hydrocarbon oils becomes increasingly difficult the lower the boiling point and the molecular weight of the oil under treatment. This is known to be due to its simpler chemical structure and its consequent greater stability at high temperature. Further the controlling factors in the pyrogenesis of petroleum are known to be temperature, pressure and also time of contact. From this it follows that condensates from the pressure distillation of petroleum having an average boiling point intermediate between that of the charging stock (gas oil) and the final low boiling point product (crude naphtha), will not be as susceptible to conversion to crude naphtha as the fresh charging stock of hi h boiling point.

It is, there ore, evident that in the absence of means to effect a very careful control of primary condensation and fractionation, or if the whole of the primary condensate be returned to the still, there will be submitted continuously for redistillation and conversion, a body of oil containing appreciable quantities of a product that it is impossible to convert under the conditions of temperature and time of contact provided for in the still.

Furthermore, the constant addition of oil, of boiling point appreciably lower than that of the charging stock, will lower the average boiling point of the mass and upset the temperature and pressure equilibrium in the still. Also having a boiling point, under the pressure existing in the still, lower than the critical cracking temperature maintained therein, it is evident that said addition of pre viously distilled oil will only result in the prompt vaporization of the latter without any conversion whatsoever, and greatly increase the fuel consumption. In the presentinvention, we avoid this condition by not returning the primary condensates to the still. We further separate the said condensates obtained from primary condensation by the use of a fractionating condenser that facilitates said separation and enables us to use each of the separated products to the best advantage. By this means we are enabled to Work our pressure still at a high degree of efl iciency, by continuously feeding to it only fresh preheated charging stock, continuously removing therefrom under predetermined conditions of temperature and pressure and with a reasonable time of contact, the vapors resulting from these conditions, without impairing the efficiency of the still by continued additions of material previously distilled under pressure in the same still, and which can only be efficiently .converted to hydrocarbons of lower boiling point by means and under conditions particularly suited to it.

We prefer to separate the oil condensed in our primary condenser into two fractions, which for purposes of comparison we may call (1) and (2). The fraction (1) of heavier specific gravity and higher boiling point can be used for combustion in the refinery, the lighter fraction (2),can be blended with certain other heavy products of the refinery as for instance, with fuel oil of high viscosity, so as to decrease the specific gravity and improve the viscosity of the latter. Alternatively either or both fractions, when the size of the refining plant warrants, can be treated in an auxiliary or secondary still in which they can be submitted to treatment peculiarly suitable to them and can be therein converted to hydrocarbons of low boiling point. In practice, however, it will be found preferable to. confine this treatment of the fractional condensates to those of higher boiling points.

Apparatus suitable for carrying out our improved process is illustrated in the accompanying drawings, forming a part of this application, in which:

Figs. 1, 2 and 3, are diagrammatic views of our improved oil refinery apparatus.

Referring to the drawing, in Fig. 1, We show a vertical still A.- of suitable construction having a feed pipe B for the first filling of the still with an initial charge of heavy oil and for the occasional injection of steam for cleaning purposes, said injection of steam, however, having no part in the process of distillation. After this preliminary charging, and when distillation is in progress,further additions of preheated charging stock are made through the pipe D, said pipe being constructed so as to deliver the preheated oil under pressure near the surface of the still charge and at a point preferably near the central axis of the still. The lower part of the vertical still where carbon deposit may accumulate, is protected from the direct heat of the furnace gases by an apron wall A A vapor pipe F conducts the distillation gases to the vapor belt of a combined preheater and fractionating condenser 'G by means of inlet H and leaves said condenser by an outlet H \Vithin the condenser (Figs. 1 and 2), is a nest of return tubes J communicating with distributing manifolds J In said manifolds are partitions J to effect the passage of the fresh charging stock through all the tubes J in the preheating system in four passes. The stock enters the preheater under pressure, at inlet I, and leaves it at L, thence passing to the still A by means of pipe D. In order to effect the passage of the distillation gases up and down the vapor belt of the combined preheater and fractionating condenser G and in the closest possible contact with the tubes J vertical baffle plates K are inserted within the condenser casing in such a way as to cause the said gases to flow in a direction counter-current to that of the charging stock within the tubes J. Bleeder pipes L, L L L3 in direct communication with the vapor belt, separately collect the portions of the distillation gases that have been condensed on either side of the baille plates K. By means of pipes M and N and suitable valves, these condensates or fractions can be readily removed from the system separately or collectively.

The vapor belt outlet H communicates by the vkpor pipe P with the pressure relief valve so that the distillation gases, which up to this point are at the pressure prevailing in the still, may be reduced to atmospheric pressure The pipe l connects said pressure relief valve 0 with the final condenser Q. i

The final condenser Q is in construction similar to the condenser i'already described. The distillation gases at atmospheric pressure enter the. condenser by the inlet R, and the finally incondensible or permanent gases pass out through the outlet 11,. The bafiie plates S insure the EiilCtlClOllS circulation of the gases in the condenser. The cooling medium, which may be water or oil, enters the tube system at T and leaves it at T The upper distributing manifold U and the lower distributing manifold U provide for the passage of the cooling medium through the condensing system, in a manner somewhat similar to that already described in the case of the condenser G.

The lower manifold U1, however, has an additional partition V across the center thereof and in line with the central vapor battle S, A by-pass and valves X, X X connects the two compartments on each side of the said central partition. By suitable manipulation of the valves X, X X the cooling functions can be effected entirely by cooling water or they can be effected partly by cooling water and partly by cold charging stock. That is to say, with valve X open and valves X and X closed, the cooling water entering at T can be caused to flow through the whole of the condensing system in four passes, and leave the system at T On theother hand, with valve X closed and valves X and X open, the cooling water can be caused to leave the system at X after only two passes while cold charging stock can be caused to enter the system at X and after two passes leave the system at T The charging stock thereby receives a preliminary heating and by means of pipe connections T and suitable valves, it can be pumped by pump into the main preheater G for further heating. The pressure distillates obtained from the final condenser are recovered by the bleeder pipes Y, Y Y Y and passed by pipes Z and Z to cooling and storage.

In practice the operation of our pressure distillation system is as follows:

An initial charge of gas oil is pumped into still A through pipe B until the still is filled to the charging level. Heat is then applied until an oil temperature not exceeding 600 C. is obtained, the pressure due to evolved gases being likewise permitted to rise to 7 or 8 atmospheres by appropriate setting of the pressure relief valve 0. Fresh charging stock is pumped into the coils of the primary condenser and preheater G and then, through pipe D, into the still charge, at which point it will have attained a temperature of about 250 C. below that of the mass in the still. The preheated charging stock enters the still charge at a point slightly below the level of the charge and at the axial center of the still.

The charging stock being of specific gravity heavier than the average specific gravity of the still passes downwards in the center of the mass and induces thereby a regular circulation of material down the center and up the sides of the still. The avoidance of erratic or unbalanced currents facilitates sedimentation of the carbon formed, towards the bottom and cooler Zone of the still.

The distillation gases from the still pass by vapor pipe F and inlet H to the vapor belt of the combined preheater and primary fractionating condenser G, where, owing to the circulation of the gases up and down the outside of the condenser tubes, the portions more readily condensible at the cooling temperatures provided, canbeseparatelyremoved by the lilecder pipes L. L L L At the same time the charging stock introduced by the inlet ,1 traverses in four passes the full length of the condenser within the cooling tubes J above mentioned. The dual functions of condensing portions of the still vapors and at the same time preheating the fresh charging stock are thereby efficiently performed. The now heated charging stock passes out by outlet I to the still by the feed pipe D above described.

We prefer to use this primary condenser so as to obtain therefrom two separate condensates. One condensate which for purposes of description we will call fraction (1) is an oil that will have an average specific gravity of 34 B. or thereabouts, the second condensate called fraction (2) will have an average specific gravity of 39 or thereabouts. Each of these is separable by virtue of the arrangement of bleeder pipes and valves and can be run to suitable storage tanks. .The heavier fraction (1) is suitable for fuel purposes in and about the refining plant. The lighter fraction can be used for reducing the gravity and improving the viscosity of heavier oils. as for example those obtained from the asphaltic bottoms produced in the lubricant section of a refining plant. Alternatively either or both fractions can be submitted to further distillation in a recracking still. lVe prefer, however, to confine said further distillation to the heavier fraction (1) using the lighter fraction (2) for the purpose of improving. the viscosity of the heavier oils of a refining plant, as will be described in a later part of this specification.

The distillation gases, after separation of the primary condensates therefrom, consist of a large proportion of gases condensible to liquid hydrocarbons of low boiling point which make up the pressure distillate or crude naphtha. 'We consider it advantageous to effect this further condensation under atmospheric pressure by the use of pressure relief valve 0. From this valve the uncondensed gases pass to the final condenser which is of a type similar in construction to that used for primary condensation. The gases entering the vapor belt of said condenser pass up and. down the vertical length of the con-- denser, their path being guided by suitable baffle plates. Through the condensing element consisting of a series of return tubes. a cooling medium is continuously circulated from inlet T to outlet T,. Said cooling medium may be water, or water may be passed through a certain proportion of the tubes, and cold fresh charging stock through the remainder, thereby assisting in the preheating of said stock. The means, whereby the proper distribution can be attained. of either the cooling Water alone or of the cooling water and of the cold charging stock. has already been described in a previous part of this specification. The final condensates are collected by the bleeder pipes Y. Y Y Y and run to storage for further refining.

llji

Should the capacity of the refinery be sufficiently large to furnish adequate quantities of fraction (1), it is preferable to convert the said fraction to crude naphtha and add the converted product to the main yield of pressure distillate. Ashas already been ex-' plained, the boiling point of this fraction (1) being lower than that of the charging stock, we prefer to feed this-fraction to a secondary pressure still AA where the conditions of its conversion can be met without interference with the normal operation of the main still.

. from all the final condensers Q and also EE are combined and sent to pressure distillate storage tank FF, as shown in Fig. 3 by suitable pipe lines. For reasons of clarity and to avoid confusion in this figure the feed of fresh charging stock to the several stills A, after preheating in G, or in G and Q, has not been shown,*but is to be understood as taking place exactly as has already been described. Furthermore, by using the type of final condenser herein described, we can, should we desire, divide the final condensate into two fractions. Of these the lighter fraction will be the pressure distillate or crude naphtha. the heavier will be similar in gravity and boiling point to our primary :ondensate fraction (2) above described, and can be treated in conjunction therewith, for

reducing the viscosity of heavier oils in a rev fining plant.

By following the preferred method of treatment above described, we have been able to effect a maximum yield of crude naphtha with a substantially reduced consumption of fuel. For example, two identically similar samples of gas oil of 32.4" 13 3. were submitted to pressure. distillation under identical conditions of temperature and pressure. In the first case the usual methods of primary condensation were used and all the condensates from said primary condensation were refluxed to the still. In the second case our method of fractional condensation was; used and only the selected portion of the primary condensate was submitted to redistillation. As a result of the last named method of treatment the fuel consumption was reduced between 19 and 20%, while the total yield of naphtha was increased 1.75%.

These comparative tests indicate that the return to the still of all the primary condenit is evident, that sates is not advantageous because of the presence therein of material not amenable to conversion under the same conditions of distillation that are being applied to the main bulk of the oil. It is further evident that the return to the still of any portion of the primary condensate will result in a decreased capacity of the still for fresh charging stock. As long as that portion of the returned condensate is not substantially different in gravity to the original charging stock, the yield of pressure distillate per unit of time will be approximately the same as would be the case if entirely fresh stock were used in the still. But, as the average boiling point of the'return condensate becomes lower, this equivalence in capacity will not be maintained.

For this reason we prefer to eliminate all return of condensate to the still and submit a substantial portion of the primary condensate to a further process of conversion, in an auxiliary still under conditions of temperature, pressure and time best suited to it.

. Having thus described the invention what we claim as new and desire to secure by Letters Patent is:

1. An improvement in the artof converting high boiling point petroleum products to low boiling point hydrocarbon oils by pressure distillation, which consists in preheating the high boiling point product under pressure to a temperature approximately 250 C. below the distillation temperature in the still, introducing this fresh preheated stock to the still at a point below the surface of the still charge and at substantially the central axis thereof, submitting the said stock to pressure distillation in the still at temperatures not exceeding 600 C. and pressures not exceeding 8 atmospheres, submitting the gasesevolved from said pressure distillation, to fractional separation by pressure condensation, in order to obtain products of intermediate boiling point, then passing the uncondensed gases to final condensation at atmospheric pressure to obtain products of low boiling point.

2. An improvement in the art of treating the distillation gases evolved in the pressure distillation of high boiling point hydrocar-' bon oils for the purpose of obtaining crude naphtha, which consists in fractionally condensing at substantially distillation pressure the more readily condensible constituents of said gases so as to obtain a series of fractions of intermediate boiling point, submitting the heavier fractions of said series to a separate process of pressure redistillation and pressure condensation, and separately submitting to fractional condensation under reduced pressure the condensible gases remaining from the original distillation and from the redistillation of the heavier condensates.

3. An improvement in apparatus for the conversion of high boiling point petroleum harness products to low boiling point hydrocarbon oils comprising, a furnace, a vertical pressure still disposed therein, a vapor pipe connected to the still, a combined preheater and frac- I tionating condenser in open communication therewith, said condenser including a bafied for the recovery of the low boiling point hydrocarbon oils.

4. Animprovement in apparatus for theconversion of high boiling point petroleum products to low boiling point hydrocarbon oils, which consists of a furnace, a vertical pressure still disposed therein, a vapor pipe connected to the still, a combined preheater and fractionating condenser in open communication therewith, said condenser including a multipass assembly of tubes, disposed within a bafied vapor space, means for red 7 moving the separate condensates of intermediate boiling points, means for further treating' said condensates, a pressure relief valve, and a final condenser for the recovery of the low boiling point hydrocarbon oilsf 5 An improvement in apparatus for the conversion of hi ,h boiling vpoint etroleum to products to low oiling point by rocarbon oils, which consists of apressure still, m'ans for continuously feeding fresh preheated high-boiling point oils to the still near its vertical axis and below the-surface of the still charge, a combined preheater and fractionating condenser in open communication with said still, means forremoving the separate.

condensates of intermediate boiling point, means for further treating said condensates, a pres re relief valve, and a final condenser for the recovery of the low boiling point hydrocarbon oils.

6 An improvement in the art of converting hi h boiling point hydrocarbonsto hydrocar ons of lower boiling point, which consists in, heatingthe first'named under pressure in a vertical still, submitting the vaporized products of conversion to a primary fractionation under pressure, by passing them about the tubes of a multipass surface'condenser through'which is passed .in tortuous flow a controlled amount of a cooling liquid,

' releasing the pressure on the residual gases from the primary fractionation, submitting said gases to a final fractionation in a similar condenser, and selectively removing all the fractions of both condensations.

7 An improvement in the art of converting high boiling point hydrocarbons to hydrocarbons of lower boiling point, which consists in, heating the-first named under pressure in a v'rticaL-still to a temperature at which the conversion maybe eifected, submittingthe vaporized products of conversion to a primary fractionatlon under pressure,

rent tov the flow of the vaporized products effecting va orization of any portion thereof,

feeding sai preheated oil to the still, releasing the pressure on the residual ases from the primary fractionation, subm tting said denser under reduced pressure and selectively removing all the fractions of both condensations. 8. A. process forthe conversion of hydrocarbon -oils of high boiling point to those of lower boiling point which consists in, heating a body of the oils to decomposing temperature while maintaining thereupon suificient pressure to raise the normal boiling point of the mass to a point above said decom osing temperature, removing from the sur ace of the mass the mixed vapors evolved as products of decomposition, effecting a plurality of selective partial condensations of said vapors without loss of pressure thereupon by passing them countercurrently into heat interchanging immiscible relation with high boiling point oil before submitting the latter to decomposing temperature, selectively assembling the condensates of higher boiling point, submitting the latter to further decomposition and condensation underpressure, said decomposition being effected independently of the initial decom osition first mentioned, expanding theremaining vuncondensed vapof conversion so as to preheat the oil without gases to a final fractlonatlon in a similar contoo ors of both decompositions into heat interefiect a urther series of selective partial condensations of said vapors and selecting the condensates of lowest boiling point therefromfor the recovery of crude naphtha.

9. In apparatusfor the conversion of high boiling point hydrocarbons to those of lower boiling point, the combination of vertical pressure stills adapted to contain a substantial body of oil for conversion, heating furnaces for the stills, means to protect the lower zones of the stills from direct furnace heat, vapor chambers connected to the stills, vertical bafiles in the chambers to confine the vapor flow in alternately ascending and descending streams, groups of condenslng members disposed in the streams, upper and lower manifolds connecting adjacent groups to eifect a cyclic passage of fresh oil through the chambers countercurrently to the flow of vapor, bleeder'pipes to withdraw condensate charge near the vertical axis of the stills, vapor lines connecting the vapor chambers with further chambers of similarconstruction, means to supply cooling fluid thereto, reducing valves in the va or lines between the first and second cham ers, means to re- 4 move condensates of decreasing boiling point from the system, an auxiliary vertical pressure still, independent vapor chambers connected thereto, and means to conduct to the auxiliary still all the heavier primary condensates derived from the main stills.

10. In apparatus for the pyrolysis of petroleum distillates including main pressure stills, an auxiliary ressure still, primary condensers open to sti l pressures and secondary condensers open to pressures substantially lower than the still pressures, the combination of means to circulate a cooling fluid through the latter, means to force fresh oil through the former against the still pressure,

p and means to convey a selected portion of the prfinary condensates to the auxiliary pressure sti In testimony whereof we hereunto aflix our signatures this 26th and 30th days of June, respectively, 1924.

- FREDERICK GARTHEWAITE RING.

PERCY GEORGE PARIS.

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