US2027862A - Process of converting hydrocarbons - Google Patents

Description

Jan.. M W36, N. GOODWIN r-:T A1.

v PROCESS OF CONVERTING HYDROCARBONS Original Filed No'v. 26, 192B 4 5 Zw z v X 0 N ww o 4 mi MV J Q fw J o l a 4 /c v \7/ 7 3k WW M 4 M, 29W u /o/ QJ f a Z 3 5 w w, 3 @n O o /QM 2 20 J M h y .x l 1A TTOQNEY Patented Jan. 14, 1936 UNITED STATES Z,0ZZ,852

PATENT OFICE Pnooass or ooNvna'riNG nYDRooARBoNs Application November 26, 1928, Serial No. 321,842 Renewed January 22, 1934 1 Claim.

This invention relates to improvements in the art of converting (cracking) heavy hydrocarbons into lighter hydrocarbons, and its principal object is to maintain a proper rate of cracking whereby a continuous cracking operation is effected. Y

The invention is particularly applicable to a process and apparatus described in our copending application, Serial Number 195,308, filed May 3l, 1927, of which this application is a continuation in part.

In cracking hydrocarbons according to the process of said copending application, we have determined that the fundamentals for the best results attained therefrom are based upon the rate at which cracking takes place in a cracking chamber.

This rate of cracking may be expressed in proportionate terms of the Production of lighter hydrocarbons per square foot of cracking chamber area per hour,

Production and/or removal of carbon per square foot of cracking chamber area. per hour,

Production of lighter hydrocarbons per pounds of carbon removed per square foot of cracking chamber area per hour.

The heat applied to a cracking chamber for converting hydrocarbons in the above proportionate terms is reflected in the temperature oi? products of the cracking phenomena therein and, in consequence, we maintain the temperature of cracked products within such limits that, from a,

given charging stock, optimum results will be obtained in accordance with an optimum cracking rate.

It is generally known in the art that carbon is a product of the conversion of hydrocarbons, but in the practice of various processes heretofore used, the deposition of carbon in tubes, pipes, tanks, stills, reaction chambers, and the like, and the inability to remove carbon from such apparatus while a process is in operation, has proved one of the most serious drawbacks to a continuous cracking operation.

In fact, the term continuous operation, as applied to present day cracking methods, is purely a relative one, such so-called continuous operation being conned generally to a comparatively few days run, after which time present known cracking plants must shut down for from one to several days to remove the coke which has continuously been deposited in the various portions of such plants.

In such plants, the term continuous opera` tion is more aptly applied to the continuous (Cl. 196-69) n deposition and' non-removal of carbon therefrom,

principally in the form of a solidified coke, whereby a continuous slowing up of the rate of production ensues, due to the continuous formation of solidified coke, until operation of the plant is entirely halted owing to the choking of treatment conduits by such coke.

On the other hand, in our process, we are able to so regulate the rate of cracking hydrocarbons that the operation is truly a continuous one and the only time when our cracking operations need cease is when a shutdown is necessary from such mechanical troubles as are entirely outside of our process. Accordingly, with a set rate of feed of any particular charging stock to a cracking chamber, we can so regulate the rate of cracking by removing all the conversion products continuously therefrom in the same amount (weight) as is fed thereto, that continuous operation is possible, optimum conversion percentages. are obtained, and minimum losses sustained.

This regulation is obtained by governing the degree of heat applied to a cracking chamber in accordance with the temperature of conversion products educed from the cracking chamber so that a predetermined ratio, in the proportionate terms hereinbefore recited, may be maintained.

Inasmuch as one of the prime objects of a cracking process is to produce gasoline, we will hereinafter refer, in our ratios, to lighter hydrocarbons as gasoline and by such we mean a standard gasoline according to the Standards of the American Petroleum Institute, comprising a mixture of hydrocarbons having an initial boiling point of 110 F. and an end point of 437 etc., gravity from 55 to 60 A.v P. I. l

The above iigures apply to gasolines derived from California residuums, the residuums from other sections varying in gravity with the same boiling range.

In addition to gasoline, we produce by our process a valuable fuel oil having a high heat value due to.. a suspension oi nely divided carbon therein, and an intermediate product resembling gas oil, whose properties lie between the gasoline and the fuel residuum, and which is quite free from suspended' carbon, or free carbon.

By reference to the appended drawing, in which Fig. l is a diagrammatic ow sheet through apparatus adapted for use with our process,

Fig. 2 is an elevation of a revolvable cracking chamber, and

Fig. 3 is a vertical sectional view of Fig. 2.

Fig. 4 is a cross-sectional view of the line 4 4 of Fig. 3.

It will be seen that heavy hydrocarbons are supplied from a storage through pipe I to a pump 2 which forces the same through a preheater 3. Pre-heater 3 may be any of the present day well known structures, but is preferably a pipe still, and is enclosed in a furnace 4 heated by a burner 5.

A valve controls the passage of pre-heated hydrocarbons from pre-heater 3 to a charging pipe 1, the last coil of pre-heater 3 being slidably joined to pipe 1 through a stuing-box 8 wherein charging pipe 1 may be longitudinally reciprocated.

The outer end of the charging pipe 1 has a thread I cut thereon meshed with a wheel II for reciprocating said pipe and is suitably journaled in a support I2, the inner end of pipe 1 extending into and through a revolvable cracking chamber I3, set in a furnace i3d and heated by burners I3b, wherein conversion of the heavy hydrocarbons into gasoline takes place.

The cracking chamber I3 is fitted with flanges I4 and I5, a hollow member I6 being bolted to ilange I4, one end of which extends into cracking chamber I3 to form a valve seat I1, the other end extending into an expansion chamber I8 and being maintained therein by a stufling-box I9.

Expansion chamber I 8 centrally supports the charging pipe 1, which is movably held therein by a stuffing-box 28, and the inner end of pipe 1 is held in a spider 2E, placed in a recess 2'?. bored in a hollow member 23, which hollow member 23 is bolted to ange I5 and has geared drive wheel 24 keyed thereto, its outer end being closed by a valve 25.

The flow of heavy hydrocarbons from preheater 3 to the interior of cracking chamber i3 is thus through the inner end of pipe 1 to recess 22 and spider 2|, and the liquid level maintained in cracking chamber I3 is substantially that shown at the dotted lines A-A, or the center line of chamber I3 and charging pipe '5. This liquid level may vary slightly (due to variations in mechanical or manual control) and therefore is referred to as an average predetermined level.

Cracking chamber l3 is filled to substantially the dotted line B-B with a plurality of loose attrition members 21, the line B-B being just below pipe 1, this level being maintained in order that balls 21 may keep pipe 1 free of carbon by their attrition effects, and such attrition members are preferably steel, or iron, balls of about one inch diameter, ground to a proper sphericity as used in ball bearings and like precision mechanisms.

We prefer to use metallic balls because of minimum corrosion and erosion effects and to take advantage of any inherent catalytic properties, such as are particularly noted in the use of nickel balls, but we do not limit ourselves either to the use of iron or nickel balls, but may employ any of the alloys thereof, or other metals, having the desired properties for a particular operation or a particular charging stock.

`An expansion valve 25 is secured to chargingr pipe 1 and is adapted to be seated on valve seat I1 for controlling, in conjunction with valve S and pump 2, the outflow of conversion products from cracking chamber I3 to expansion chamber I 8, and thereby the rate of cracking hydrocarbons according to their time of residence in cracking chamber I3, the whole operation being governed by the indications of a pyrometer 28 set in expansion chamber I8.

By residence we mean the period of time it takes a unit amount (weight) of hydrocarbons to pass from the inlet end of pipe 1 through chamber 3, where it is subjected to cracking conditions, to yield the same unit amount (weight) of conversion products.

The flanges I4 and I5 of cracking chamber I 3 are adapted to rest on two pairs of rollers 29 and 38 respectively and drive-wheel 24 is meshed with a pinion actuated by any suitable prime mover through drive shaft 32.

'Ihe conversion products move from cracking chamber I3 past valve 26 and through the annular space between pipe 1 and hollow member I6 to expansion chamber I8 (which may be an enlarged pipe) and thence through pipe 33 to a separator 34 wherein a separation of vapors, fuel oil, and carbon is effected and, in order to hasten such separation, dry or superheated steam may be injected into pipe 33 through a pipe 33a and valve 33h. The residue from separator 34 may be withdrawn through pipe 35 controlled by valve 36.

Vaporized hydrocarbons (with or without steam) are conducted from separator 34 through a pipe 31 to a fractionating column 38 wherein a carbon free residuum (gas oil) is condensed and withdrawn through pipe 39 and valve 40 for storage or otherwise.

The proper temperature and other conditions are maintained in column 38 whereby the desired out for lighter hydrocarbons (gasoline) is made and such cut is conducted from column 38 through a pipe 4I to a condenser 42, wherein such cut is liqueed and passes (together with any fixed gases) through a pipe 43 to a trap 44.

If steam has been employed, the same is liquefied in condenser 42 and passes into trap 44 wherein a separation of water and gasoline is effected, the water being drawn off through pipe 45 and valve 45 while gasoline is withdrawn through pipe 41 and valve 48.

Any fixed gases pass through pipe 49 and valve 58 to burners 5 and i311. or otherwise, and pipe I controlled by valve 52 serves to reflux a desired amount of condensate back into column 38 to aid in securing the desired cut.

In cracking operations generally, it has been observed by the operators of cracking plants that the rate of cracking is greatly increased by the presence of free carbon in the oil being cracked. This free carbon is ordinarily produced as the cracking reaction proceeds and its presence is highly desirable insofar as the production of cracked products is concerned. In the ordinary types of cracking apparatus its presence is a potential source of danger and ineiciency due to its tendency to clog up the apparatus and to deposit upon the heating surfaces.

It is a further object of our invention to provide a cracking apparatus in which heavy concentrations of free carbon may be carried in the oil without danger of clogging the apparatus or depositing upon the heating surfaces.

We have further discovered that the condition in which the individual carbon particles are present in the oil has a marked iniiuence on the cracking reaction. For example, in the practical operation of our process we have found it possible to greatly increase the rate of cracking by introducing into the oil, carbon which has been previously ground to the desired degree of flneness; that is to say, the cracking reaction is apparently greatly accelerated if the free carbon in the o-il has been previously broken up by mechanical attrition. This is perhaps due to the shape and/or the catalytic influence of the indvidual particles of carbon but is more probably due to the fact that the carbon is present in the form of angular masses having sharp corners and edges. It is probable that the free carbon produced by cracking tends to build up in masses which may perhaps be spherical but which in any event are free from sharp angles. By subjecting the carbon previously produced in the cracking operation to the action of mechanical attrition, we produce ne particles of carbon which are extremely eicient in promoting the cracking reaction.

It is therefore an object of our invention to provide an apparatus in which the oil is mixed with ne particles of free carbon which have been previously broken up by mechanical attrition.

The cracking chamber I3 is preferably so constructed that it can safely carry a pressure in the neighborhood of 1500 pounds per square inch even when the oil therein is heated to a temperature of 900 F. Pressures and temperatures considerably below these limits are usually sufficient for the cracking of petroleum.I oils, and We provide the proper pressure and temperature as herein described and vary the same with the character of the oil to be cracked and the desired product.

In one method of operating our process, we`

take a heavy oil, for instance a renery residuum comprising heavy hydrocarbons remaining from the distillation of crude oil, having a grav- (version products is eifected past valve ity of from 12 to 17 Baum, and pass the same through pre-heater 3, wherein the temperature of the oil is raised to say 750 F. or just) below the cracking temperature thereof, into cracking chamber I3, which is filled therewith substantially to the level A-A. Burners I3b are lighted and cracking chamber I3 is revolved at a predetermined rate of speed, until pyrometer 28 indicates the temperature of the converted and expanded products to be from 780 F. to 800 F., the temperature of the material interiorly of chamber I3 at this time, and with the above charging stock, ranging from '790 F. to 820 F.

Cracking chamber I3 is maintained under about 300 lbs. pressure and the continuous revolution thereof causes the prevention of any deposition of carbon on the walls thereof due to the attrition action of balls 27. Such carbon is-held in suspension in the fluid products of chamber I 3 and is in such finely divided condition that it flows freely out of chamber I3 together with other conversion products.

Expansion valve I1 is regulated by means of wheel II to maintain the desired pressure in chamber I3 and is of such size that the maximum. annular space, under a maximum desired pressure, between it and seat I7 is insufficient to permit the passage of any of the balls 27.

The liquid level in chamber I3 being maintained substantially at A-A and the heavy oil being continuouslysupplied to chamber I3 through pipe 7, a continuous withdrawal of coni7, through member I 6 to expansion chamber I8, wherein the pressure of the evolved products is greatly reduced. v

For a particular charging stock of the chari acte-r before described (residuum of from 12 to 17 Baume gravity), we obtain good results by maintaining the pressure in the system, from expansion valve 26 to the various points of discharge therefrom, at atmospheric pressure, or just suicient pressure to cause the various evolved products to pass through the system, which pressure is regarded in the art as atmospheric pressure because it is negligible, ranging from one to ve pounds or just enough to overcome the skin friction of the pipes, co1- umn, etc.

The temperature of from '780 F. to 800 F. maintained in expansion chamber I8 is highly desirable for, if such temperature drops to r770 F., no cracking takes place with such charging stock, while if such temperature is permitted to increase to 810 F., the loss in fixed gases increases and in consequence the yield of carbon increases, whereby the rate of cracking is varied.

It should be noted that this range of temperatures is dependent on the distance of pyrometer 28 from valve 26, and upon the amount and nature of the intervening pipe surfaces.

We have noted such range at a distance of from two feet to six feet from valve 26, but the temperatures indicated at these points are relative and may be taken at other points in chamber I8 or pipe 33, to the end that there is not more than a range of approximately 20 F., which is the working range.

Such a range of 20 F. enables us to determine the rate of cracking in chamber I3, one of the features of which is to permit no cracking vto take place after passing valve 26 and at one point in particular, about three feet from Valve 26, we iind an indicated temperature of 775 F. sufcient to maintain the rate of cracking.

In order to maintain our process in a balanced condition, to the end that the loss in xed gases and carbon will be a minimum and the yield of valuable conversion products a maximum (with the above charging stockdescribed), it is necessary to maintain the temperature of the conversion products within a range of temperature diierence of 20 F., and such range may be indicated at a point close to or distant from the expansion valve of chainber I3.

By a balanced condition we mean that the process is in equilibrium whereby a predetermined rate of cracking is maintained to yieldY optimum results and thus the hot cil being constantly fed into the chamber I3, mixes with the cracked and partially cracked oil which precededV it, while concurrently and automatically there is removed through pipe 33 an equivalent mixture of gaseous, liquid, and solid products resulting from the cracking taking place within the chamber. When operating in a balanced condition, the stream of material removed through pipe 33 is identical in ultimate chemical content with the untreated material fed through the pipe 7.

We desire to maintain such a balanced condition for a particular charging stock, and within the optimum predetermined limits of heat and pressure because if too much heat is transferred to the oil being converted, the rate of crackingis disturbed, with consequent increased loss in xed gases and also increased yield of carbon, which carbon detrimentally affects the action of balls 27 and reduces their attrition eiciency. as well as the rate of heat transfer from the walls of chamber I3, because a balanced condition demands the removal of carbon in suspension as quickly as formed.

Such balanced condition includes maintaining the space above the liquid level in chamber I3 under the pressure of evolved fixed gases, with a minimum content of condensable vapors, such vapors not forming to any great extent within the chamber I3, but being maintained in liquid form therein, whereby the hydrocarbon material is held in such fluid condition by solvent action that the attrition action of balls 21 is a maximum.

In other words, from optimum results secured, we believe the rate of cracking should be such that light hydrocarbons in liquid form are removed from chamber I3 substantially as quickly as formed, thus performing a solvent action on the remaining concurrently formed heavy hydrocarbons. From a residuum charging stock (above described) optimum results yield 80% of the charging stock to the column 33 and 20% to the separator 34.

These percentages are divided as follows:

Separator l5 to 25% tar (asphalt and carbon) The residuum from column 38 is quite free from suspended, free, or comminuted carbon.

In order to obtain such results and to obtain maximum efficiency from the apparatus, the time of residence of the charging stock in cracking chamber I3 should be a minimum and the rate of cracking should produce from two to three (2 to 3) U. S. gallons of untreated gasoline per square foot of area of chamber I3 per hour. In terms of carbon, this signifies that approximately two to three (2 to 3) pounds of carbon are formed (and removed) per hour per square foot of area of chamber I3, and in both the above proportionate terms the area of chamber I3 referred to is the interior area.

The carbon above obtained is a solid material insoluble in the body of the conversion products, or any of them, and which may be a mixture of fine elementary carbon with undened percentages of asphaltic matter, the gravity of which carbon material is below 2.0.

With a cracking chamber I3 having an interior area of square feet, we can remove carbon as fast as formed at the rate of 3 pounds of carbon per square foot of area per hour, and we maintain this maximum rate and optimum results therefrom by the controls already described.

With different charging stocks, particularly on hydrocarbons lighter than residuums, such as gas oil or a kerosene, different controls in' like proportionate terms will be maintained up to the limit to which carbon will be removed by balls 2l as quickly as formed, so that continuous operation in a balanced condition shall result, but inasmuch as increasing temperatures are required for cracking hydrocarbons as their gravity (Baume) increases, it is apparent that charging stocks should be used in their entities, because the temperatures and pressures required for cracking a gas oil will be much higher than those required for cracking a crude oil, or residuums. However, with a higher maintained pressure, a greater proportion of gasoline fractions remains in liquid phase, whereby the increased amount of carbon formed (at higher temperatures) is removed by increased solvent action and in this manner the rate of cracking (or eiciency of the process) is increased.

Obviously then, if a crude oil, or residuum, is being cracked in chamber I3, the temperatures and pressures required would have a relatively small conversion effect on a gas oil mixed therewith, but at times it is advisable to pass gas oil from column 33 through pipe 39, pipe 53, and pump 54, whence it is forced into charging pipe l, the amount being controlled by valve 55.

Such mixing of gas oil with a residuum, or crude oil, charging stock works as a solvent, or suspending medium, only to help maintain the iiuid condition of material in chamber I3, whereby equilibrium is assisted by keeping the carbon in suspension. On the other hand, if a gas oil is the charging stock being cracked in chamber I3, it would be disadvantageous to mix a crude oil, or residuum, therewith, because, on account of the higher temperatures and pressures required for cracking a gas oil, the rate of cracking the crude oil, or residuum, would be so greatly increased that the balanced condition for the gas oil would be upset due to the increased rate of carbon formation.

The use of mixtures of resduums or like charging stocks with gas oil or like charging stocks for cracking purposes should be avoided as being detrimental to a balanced condition,

except that a lighter charging stock may be b added to heavier charging stock as a solvent, whereby substantially no cracking of the solvent stock takes place.

We have used pressures from 100 lbs. to 1,000 lbs. per square inch in chamber I3, but find that the optimum temperatures '780 F. to 800 F. in the expansion chamber E 8, close to the cracking chamber I3, for the residuum charging stock described, are maintained irrespective of the pressures used.

The residue from separator 34 may be withdrawn through valve 3 and used as an asphalt containing from to 85% coke or carbon. Such asphalt is fluid above 350 F. and may be used directly as a liquid fuel or may be chilled and powdered for use as a powdered fuel, or the same may be treated with steam, whereby the more volatile constituents are passed into column 38, leaving a substantially dry carbon residue in separator 34, which can be used as briquettes, etc.

Upon initially starting the process, part of the carbon formed may build up approximately to the dotted lines C-C at the discharge end of chamber I3, but thereafter when equilibrium has been reached, the carbon is removed in suspension substantially and proportionately as formed. Of course, if chamber I3 is originally built to the dotted lines C-C, no carbon will collect and all will be discharged as described.

At times it is desirable to place the entire process of conversion, separation, and condensation, under pressure, which may be done by manipulation of valves 36, 40, 46, 48, and 50, and in this respect we have used pressures up to 250 lbs. exterior of chamber I3. In all cases, however, there is a pressure drop between the interior and exterior of chamber I3 to provide for temperature control in expansion chamber i8 and this pressure difference may vary from 100 lbs. to 600 lbs.

It is, of course, understood that we do not limit ourselves to the exact structures shown in the drawing but may use many alternative structures for the same effects. For instance, valve 6 aoavgsee chamber I 3 is comparatively brief, being neces- Y sarily so in order that a balanced condition shall be maintained and also to obtain economic operation throiugh maximum throughput.

In a cracking chamber I3, having an interior diameter of twelve inches and about iive feet long between flanges, interior area about lifteen square feet, and containing about four hundred and eighty (480) pounds of steel balls one inch in diameter, the fluid capacity thereof to the center line A-A is about eight (8) U. S. gallons.

On operating the described process continuously, by passing through chamber I3 is a heavy residuum at the rate of ve thousand gallons per twenty-four hours, it will be seen that hydrocarbons flow therethrough at the rate of three and three-tenths (3,3) gallons per minute.

'I'he time of residence of hydrocarbons is therefore short and may be'increased or decreased, but in any event the application of cracking heat per gallon of charge should not endure beyond a few minutes (ten minutes or less), otherwise the continuity of the process will be disturbed for optimum, or desired results.

Thus, while the velocity of the hydrocarbons must be greatly reduced upon entry into chamber I 3 in order to obtain the proper residence therein, their too prolonged exposure to the cracking temperature is undesirable.

We claim as our invention:

A continuous process of producing gasoline from a heavier hydrocarbon oil by super-atmospheric-pressure cracking, which consists in continuously pre-heating a stream of hydrocarbon oil; passing such pre-heated hydrocarbon oil into a revolving still forming a single chamber the diameter of which is at least twice that of the stream while being pre-heated, in order to diminish the velocity of flow through the chamber; subjecting the liquid in the chamber to a cracking temperature in the presence of a quantity of metal balls, the liquid and the balls together continuously filling approximately half of the chainber; continuously withdrawing all the products of cracking in a single stream from a point near the liquid level in the chamber at a rate of from two to three gallons of gasoline and/or two to three pounds of carbon per square foot of heated inner surface of the chamber per hour; whereby to avoid incrustation of the wall of the chamber by reason of the presence of the balls which break up the carbon and keep it in suspension, and the rate of withdrawal being the same as the rate of flow of the pre-heated liquid so that there is maintained in the chamber at all times the said quantity of hydrocarbon oil impregnated with carbon particles to accelerate the cracking action. Y

NORRIS GOODWIN.V ROBERT WADE POINDEXTER.

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