US1917705A - Cracking hydrocarbon oils - Google Patents

Description

July 11, 1933. H. L. DOHE RTY 1,917,705

CRACKING HYDROCARBON OILS Original Filed Feb. 24, 1920 2 Sheets-Sheet l |NVENTOR HENRY L. DOHERTY Juiy H, 1933. H L: DOHERTY 1,917,705

CRACKING HYDROCARBON OILS Original Filed Feb. 24, 1920 2 Sheets-Sheet 2 INVENTOR .HENRY DOHERTY BY ATTORNEY Patented July i1, 1933 1 UNITED STATES, PATENT o,Fi-"icsjjf nanny L. DOI-IEBTY, or ivnw rAnY, or NEW cneoxme HYDROCARBON orns Original application filed February 34, 1920, serial No. 361,030. Divided and this application filed October 1, 1931. Serial No. 566,268, i I

lhis invention relates to a process of distilling oil and more particularly to a process for cracking heavy hydrocarbon oils to form lighter hydrocarbon oils therefrom. a

This application is a division ofpending application arv 24, 1920, for Process of distilling oils.

Heretofore the commercial processes for.

cracking heavy hydrocarbon o ls to produce lighter hydrocarbon oils, particularly gasoline, have employed a cylinder still in which the oil is heated in a large body.- The inherent nature of the cylinder still presents certain limitations 'inthelprocess' hich hold down the character and quantityofgascline'which may be recovered. Among these limitations arethe formation of hydrocarbonstof higher andlower boiling points points of the gasoline desired. Although oil may be cracked through a wide range of temperatures, the most advantageouscracking is obtained in a specific narrow rangeof temperatures. Experience has shown that agthe higher temperatures, the rate of reaction 1s very rapid with a-cons'equent-formation of large amounts of fixed gases and carbon. With lower temperatures, the reaction is slower and consequently the time element is an-important factor. Since oil is suchapoor conductor of heat, it is not practical to use the lower temperatures when distillingoilin' a cylinder still and in fact the outside of the still is subjectedto in order to drive the heat into the center of the body ofoil. This causes a local overheating and a layer of coke isalways formed around 7 the inner" surface'of the still.

Cine object of the present nvention isto provide aprocess by which oil may begu liformly heated to any desiredtemperature. l A further object of the invention is to provide a pressure cracking process in which the concentration oftarry materials in the oil in the cracking zone may be eifectivelycontrolled. v V Accordingly, as feature of the nvention comprises the withdrawal of oil residuum from the pressure cracking system through the. withdrawal lines, intermittently with a pulsating operation to prevent the stoppage Serial No. 361,030, filed Febru'- than the boiling boiling'point' oils;

in the drawn in through a pipe 10to a pump 12 and very high temperatures shi ith 11 vapors,

' the oil has ling chamber to a tray 42 (Fig. 1), it meets of these lines due to the deposition of carbon and coke fromthe oilresiduum; i

lVith these and other objects in view, the invention consists in the improved process for cracking .oil hereinafter described and claimed. V

York; N. Y., Assmnon To nonnarynnsnnncncoivrvonx, N.'Y., a oonrons'rron or DELAWARE.

The various features ofthe invention are illustrated in which: 7 V l I I l is a view side elevation, partly in section, showing a cracking still embodying the preferred formeof the invention; Fig. 2 is a top plan view of the cracking still shown in Fig. c i

The process of the presentoinvention provides a treat-mentfof heavy or high boiling the accompanying drawings, in

hydrocarbon oils to produce light or low 7 I p ,The raw material for treatment may be kerosene-,1 gas oil, fuel oil, l or a mixture of two ormore of these, and the treatment always produces lower boiling point hydrocarbons therefrom. Underthe presentcommercial conditions the treatment is conducted to produce gasoline, In carrying out the process in the apparatus-shown drawlngs, the raw oil from storage is carriedby means of a pipe 14 into the first condenser 16 of a series of surface condensers 1e,1s,20,22,24:,2e,2s and 30, (Fig. 2). n then advances throughthecondensers while being passed in heat-transferring relationwhich are formed in; the cracking operation and flow through the sur+ face condensers c'ountercurrent to the flow of oil. The oil is preheated by the vapors at 300-450 F., depending upon the temperature of the vapors, and flows fromthe condenser 30 through a pipe 3 f (Fig. 2), and enters the upper portiontof a cracking chamber 36. In the cracking chamber, the oil isiformed into a series of bodies which are separated traysfor horizontal partitions 38 and the oil overflows by gravity. from one tray to the next tray below through overflow pipes 40. .When

flowed downwardly in the cracka body ofioil which is'introduced through a pipe 44:. The oil introduced through thepipe d i 'has been previously treated inthe crack;

ing operation and has been heated to the most advantageous cracking temperature. By the time the incoming raw oil reaches the tray 42, its temperature is raised to substantially the cracking temperature by the hot vapors and gas passing therethrough. The mixture of preheated raw oil and the heated oil admitted through the pipe 44 is then held at 'a cracking temperature as it flows downwardly to the bottom of the cracking chamber to an outlet pipe 46.

The incoming raw oil and the mixture of raw oil and cracked oil which flow downwardly through the cracking chamber are constantly agitated by means .of gas and oil vapors which are admitted to the bottom of the still through a pipe 48. To accomplish this, the plates 38 which form the bottom of the trays are preferably provided with perforations which have such asize that the gas is permitted to pass upwardly therethrough while the oil is prevented from passing down-.

wardly therethrough. Inthis way, the gas and vapors entering through the pipe 48 pass upwardly through .the bodies of oil on. the trays to actively agitate the oil and to transfer to the oil any superheat which they may possess. Further, the oil vapors leaving one tray encounter the oil on the tray above and there is always an interminglingof oil and vapor and an interchange of heat between the vapors and oil. This causes a continual change of state from liquid to the higher boiling point vapors and vice versa, which is inducive of cracking and increases the percentage oflow boilin'g point products in the vapors leaving the cracking chamber.

A portion of the raw oil entering the body of oil in the cracking chamber is cracked in its passage through the cracking chamber from the tray 42- to the bottom of the cracking chamber. The uncracked portion of the oil, together with any uncracked oil which remains from the oil introduced through the pipe 44, after it passes downwardly through the cracking chamber, flows out through the pipe 46 to a pump 50 which forces it through a pipe 52 to a'pipe still 54. As the oil'flowsthrough the'pip'e 52, a gas is introduced'into the oil through a pipe 56 by means of a pump 58. 'Thegas flows in contact and in parallel currentwith the oil and serves to actively agitate and'accelerate the velocityQof the oil passing through'the pipe still 54:- Further, theoil vapors which are formed in the pipe still are absorbed by the gas flowing in parallel curent therewithand at the time .the oil and gas have passed through the coil of the pipe still, they are heated to a cracking tem perature and the gas is saturated with vapors which are also heated to a cracking tem;

perature. T he oil leaving the cracking cham-' 1 her to pass to the pipe still is heated to substantially a cracking temperature and therefore onlya small amount of heat willhave to be supplied in the pipe'still to vaporize the oil and to provide for any heat of reaction in cracking the oil.

The mixture of gas, oil and vapors leaving the pipe still flows through a pipe 60 into a separator 62 where the oil is separated from? the gas and vapors, and the gas and vapors then flow through a pipe 64 to the pipe 48 positioned at the bottom of the cracking chamber. The oil collected in the separator 62 flows out through a pipe 66 to a float valve 68 and then passes into the pipe 44 connected with the upper portion of the cracking chamber. As described above, the oil introduced through the pipe 4L4 together with incoming oil flowing downwardly through the upper portion of the cracking chamber are heated tothe cracking temperature and pass in a countercurrent path through the gas and vapors which are also heated to a cracking temperature. By the cotmtercurrent movement of the oil and vapors, the oil bodies in the cracking chamber are maintained at substantially a uniform temperature, which temperature can be accurately controlled to be the most desirable'temperature for cracking oil in order togive a maximum yield of gasoline. The heated gas passing upwardly through the oil, along with the vapors, acts as an absorbent for the gasoline vapors and helps to sweep them out of the reaction zone and carry them out of the cracking chamber.

As the gas and vapors pass upwardly from the tra'y42 through the incoming oil, a certain portion of the higher boiling constituents is condensed in the oil and returned to the cracking zone. The sensible heat of these gases and vapors and the heat of vaporization ofv the vapors condensed serve to preheat the raw incoming oil to a cracking temperature. These vapors leaving the uppermost vtray of the cracking chamber pass through a reflux ondenser 70 mounted on and communicating with-the upper portion of the cracking chamber. The temperature of the reflux condenser 70 is regulated by means of water which is introduced through a pipe 72. The introduction of water is controlled by a thermostatic valve 74 which in turn is controlled by a thermostat 7 6 mounted in the upper portion ofthe condenser. With the thermostatic control, vapors of any desired boiling point may be condensed and carried back'into the cracking chamber so asto permit only vapors having a predetermined temperature 'to pass into the condensers 30-16. Steam produced in conilglgel' 70 may bedischarged through a pipe 7 The gas and vapors leaving the reflux condenser pass through a pipe 7 8 and enter the ast surface condenser 30. These gases and vapors then pass in series through the condensers 3016 and finally flow out through a pipe 80, (Figs. 1 and 2) to a water-cooled condenser 82 where thelowest boiling point hydrocarbons are condensed. The fixed gases formed in theprocess, together with the gases introduced into the-circuit through thepipe 56,1low from the condenser through a trap 83 to a pipe 84 by which they [are introduced into the lower portion of an oil scrubber 86. In the scrubber 86 the gases are treated with a mineraljoil to remove the uncondensed vapors and the gases leaving the upper portion of the scrubber 86 flow through a pipe 88 to the pump 58. 'Any excess of gas over that necesssary in the processmay beremoved throughthe pipe 90.. If desired, gas from an external source for starting the process or for any other purpose,-may'be introduced through the pipe 90.;

As the mixture of. gas and vapors advances 7 through the condensers 301-6, it is gradually cooled by'the incoming raw oil advancing through the condensers 16'30. The gradual interchange of heat'between the incoming oil and the gasand vapors permits the condensation of fractions-with sharply defined boiling points, which may vary only by a few degrees of temperature. This intensified fractionation of vapors permits the recovery of'avnumber of products of substantially the desiredboiling points and thus avoids the necessity of several redistillations in recovering themarketable products. The fractions condensed in the condensers 30-16 are removed through outlet pipes 92- (Fig. 1) to look-boxes 9% and flow into traps 96 from which they are conducted through pipes 98 to their respective cooling coils 100. The coils 100 are supported in a water-cooling tank 102 and each coil has a connection 104: by which the condensates may be conducted to their respective collecting tanks. If desired, any or all through the traps 96 may be returned to the cracking chamber by closing valves 106 in the pipes 98 and opening valves 108 in a run-back line 109, which connects with the raw inlet pipe 34k. NVith'the apparatus outlined above,'the process maybeso conducted hat allof'the heavy fractions of the oil may be held back by the reflux condenser and'the incoming oil in the upper portion of the cracking chamber and only the vapors of the desired oil fractions to be recovered are allowed to pass through the surface condensers 30-'16. Also,"some of the surface condensers may be used in-conjunction with the reflux condenser in carrying back any desired fraction to the cracking chamber. Furthen'if any of the fractions, in the surface condensers donot meet the desired specifications, they may be returned to the cracking chamber through the run-back line 109 for retreatinent. To promote the positive circulation of the vapors and gasin the condensers and to maintain the proper pressure conditions throughout the apparatus, a pressure-equalof the condensates passing.

i'zing pipe 110 (Fig. 1) is connected between the vapor-pipe 78 and the oil-inlet pipe 34. I

ln all'cracking processes a certain amount 7 of carbon and tarry sludge is always formed and if this material is notreniov'ed from the still or oil circuit, it will soon interfere with the cracking operation. Due to the high velocity with which the oil and gas go through the coil of the pipe still 54:, the carbon deposited therein is reduced to a minimum.

The principal portion of the carbon and tar'is set 16186'111 the separator 62. The carbon and tar set free in the separator 62 pass down with the oil through a tube 111 (Fig. 1) to; a settling chamber 112 where the oil slowly 9.

rises to the top and the carbon and tar settle to the bottom. This carbon and tar is intermittently drawn off from the chamber 112 through a pipe 113 and passes through "a valve ll l to a still 116. Since the oil in the settling chamber 112 is heated to a cracking temperature while under a high pressure, it contains a large amount of potential energy or suflicient sensible heat to vaporize apprbximately 50 of the oil when it is reduced to atmospheric pressure. 7 116 is maintained at atmospheric pressure and the carbon and tarry sludge isintermittently drawn off from the settling ch amber 112fby opening up the valve 114. The still 116 is not heated but the sensible heat in the sludge will vaporize the lighter constituents at atmospheric'pressure and thesevapors will pass out of the still through a pipe- 118 to a condenser 120. The vapors collected in the condenser 120 may then be added through the line 121 to the raw oil entering the pump 12 for retreatment in the cracking still.

Since the cracking operation is completed Accordingly, the still ice in the cracking chamber 36, considerable carbon and tar sludge will be formed therein.

To remove thiscarbon and tar from the oil circuit, the lower end of the cracking chamber is provided with .a conical collecting charm ber 1) which isconnected through a valve 12 and pipe12;6 with-the still 116: The oilcontaining carbon and tar mav be drawn from the cracking chamber 30 iii the same manner that it is withdrawnfrom the collecting chamber 112 and passed into the still 116 to recover any light oil vapors therefrom. The heavy tar sludge which doesnot I vaporize in the still 116 is withdrawn through (an-outlet 127. Although the distillation op? eration is continuous, it is preferred to operate the valves 11 and 12- 1- for withdraw,-

ing sludge from the oilcircuit alternately and intermittently since an intermittent pulsating operation tends to clear theheavy sludge from the pipes 113 and126 due to the rapid rush of the high pressure oil into the low pressure still 116.

Of the high boiling point vapors are formed in an oil cracking operation,

which se at temperatures above 400 to 450 F. carry a large-amount of carbon and tarry material. If these vapors are condensed in contact with cooling surfaces, this tarry material is, deposited and clogs the condensers as well as seriously interfering with the heattransfer of the eondenser. f Vfith a cracking chamber constructcd as described above, this difliculty is overcome since the vapors are cooled to the desired minimum temperature for removing carbon and tarry material by passin them through the incomingoil in the. upper portion oi. the cracking chamber before the heavy vapors come into contact with the cooling surface of the reflux condenser. lVhen the heavy vapors are condensed within the oil the carbon and tarry material is caugh in the oil and carried downwardly to the collectin chamber at the bottom of the cracking chamber. v

r The cracking chamber 36 described above may consist of any approved form of apparatus in which the. oil may be supported in a body to permit the to pass countercu-rrent thercthrough. The function of the cracking chamber is to provide a means by which the oil may be held at a cracking temperature tor an extended period of time to permit the those vapors which conden cracking and conversion reaction to take place. By means of the apparatus shown in the drawings, the oil is supported in comparatively thin bodies. and the and vapors passing through the oil act to thoroughly agitate the oil so as to maintain a uniform temperature and to repeatedlybring the vapors into contact with the heated oil to assist in the heat reactions.

To effect the countercurrent treatment of the oil and vapors in the cracking chamber with the apparatus illustrated in the draw- 'ings, it is necessary to maintaina lower pressure in the cracking chamber from that in the separator in order-that the oil may flow in a continuous circuit throughout the still. The oil entering the separator 62 preferably has a pressure of from to pounds per square inch and this pressure is reduced from 10 to 15 pounds in the cracking chamber. The amount by. which the pressure is re duced, however, depends upon the difference in vertical head between the pipes 44 and 48 and is controlledto allow the oil .to be ad mitted into the upper portion of the cracking 'chamber while the gas is befngintroduced at the bottom of the chamber. A ten to fitteen pound pressure differential will ordinarily produce an active circulation ofthe gases and vapors up through the body of the oil in the cracking chamber. To obtain this pressure differential, the oil flows through a float valve and is introduced into the cracking chamber under the pressure prevailing in the separator with only frictional losses. VVhilethe pressure of the gas and vapors isreduced bymeans of a valve 47 in the pipe 48 (Fig. 1), the float valve 68 acts merely to maintain a predetermined level in the separator and only causes slight trio tional losses in the pressure of the oil passing therethroughQ c v The pipe. still 54 is shown more particularly in Fig. 1. The still consists of a series ofpipes 128 which are connected to form a long continuous coil in which the oil is heated. The pipes are mounted in a horizontal position in a heating chamber 130 of a furnace 132 and the opposite ends of the pipe project through side walls of the vfurnace. The ends of the pipes 128 are connected by means of return bends, which are located on the outside of the walls to permit the return bends to be readily removed for cleaning-and repairing the pipes. The pipe still is preferably heated by means of an oil or gaseous fuel, which is ignitedin a c0mbustion chamber 138 positioned outside of the heating chamber 130. The'fuel is introduced intothe combustionchamber 138 by means of a burner 140 and the products of combustion are deflected around an ignition arch 142 (Fig. 1) in passing to the upper portion of the heating chamber 130 through a flue 144. The products of combustion pass downwardly through the heating chamber 130 around the pipes 128 to a flue 146 and flow out to the atmosphere through a stack 148. By this arrangement, the heat is supplied to the pipe still coil in a direction countercurrent to the direction of movement of the oil therein, that is, the highest temperature is developed adjacent the outlet end of the heating coil and the lowest temperature developed adjacent the inlet end of the coil. In this way, the oil and gas are gradually heat-ed up to the cracking temperature in passing through the pipe still.

'lVith the apparatus outlined above, it will be seen that practically any desired combination of pressure and temperature may be maintained in the pipe still 54, separator 62, and cracking chamber 36. Temperatures of from GOO-900 F. and pressures of from 60 to 125 pounds per square inch are the usual working temperatures and pressures which are employed'in accordance with the end productes desired. The form of pipe still shown in the drawings affords a means by which a large amountof heat may be rapidly placed in the oil and the separator and cracking chamber give a means by which a large body of oil may be maintained at a uniform temperature during the cracking operation. The separator and cracking chamber may be insulated as illustrated at 200 to prevent radiation losses and these parts may be heated in'the usual manner by means of exhaust flue gases.

While it is preferred to introduce gas under pressure into the oil entering the pipe still, to furnish a carrying medium for the oil vapors andto induce a positive, rapid, circulation of the oil and vapors, this addition of gas is not essential. Some gases are always formed while cracking oil, and this gas, together with the vapors formed in the pipe still 54 and separator 62, will always produce an active countercurrent circulation of the oil and vapors in the cracking chamber 36.

In the process outlined above, the gas introduced is still-head gas which is hydrocarbon that may enter into and assist in chemical reaction or cracking in the still. For many purposes, natural gas is preferred to still-head gas because it contains more of the heavy hydrocarbons that may be useful in the formation of gasoline. Also, inert gases such as flue gas, air, etc., may be used as an agitating and vapor-carrying medium, but it is preferred to use a hydrocarbon gas.

Having thus described the preferred form of the invention, what is claimed as new is:

1. A process of distilling oil comprising continuously circulating oil under pressure in a stream through a heater to raise it toa crackingtemperature, passing the oil from the heater into an enlarged chamber and holding the oil under superatmospheric pressure and at a cracking temperature for su cient period of-time to promote cracking reactions, subjecting the vapors from the chamber to reflux condensation and then final condensation and withdrawing concentrated residuum oil from said chamber under a surging action by intermittently at frequent intervals withdrawing the residue under sudden reduction of pressure to control the concentration of the oil in the chamber.

2. A process of distilling oil comprising continuously circulating oil under pressure in a stream through a heater to raise it to a cracking temperature, passing the oil from the heater into an enlarged chamber maintaining the oil in the chamber under superatmospheric pressure and at crackingtemperatures, holding the oil in the chamber for a suiilcient period of time to promote cracking reactions, withdrawing and condensing vapors from the chamber, removing residuum oil from the chamber by a surging action by intermittently and quickly withdrawing residuum oil from the chamber to control the oil concentration therein, releasing the pressure of the withdrawn oil to vaporize it and condensing vapors formed from the residuum to recover oil suitable for recracking.

3. The process of cracking hydrocarbon oils, which comprises continuously passing hydrocarbon oil to be cracked through a heating zone, heating the oil in said zone to a cracking temperature, passing the heated oil while at a cracking temperature into an enlarged chamber in which a body of oil is collected, maintaining the oil in said zone den reduction of pressure,

and chamber under a superatmospheric pressure, withdrawing oil from said chamber while in a highly heated condition into an externally unheated distilling chamber in which a lower pressure is maintained and in vwhich a substantial proportion of said withdrawn oil is vaporized, said oil residuum withdrawal being carried out under a surging action by intermittently at frequent intervals withdrawing the oil residuum from said enlarged chamber under a sudden reduction in pressure, and collecting a distillate from the vapors produced from the oil withdrawn into said distilling chamber.

4. The process of cracking hydrocarbon oils, which comprises heating the oil to be cracked to a cracking temperature while passing a continuous stream of the same through a heating zone, passing the heated oil while at a cracking temperature into a plurality of enlarged cracking zones wherein the oil is maintained under cracking conditions of temperature under a superatmospheric pressure, and withdrawing oil from each of said cracking Zones while at a high temperature with a surging action into a distilling zone of'lower pressure in which no further heat is applied to the oil and in which substantial vaporization of the withdrawn oil occurs, by intermittently at frequent intervals withdrawing said oil under a sudand collecting a distillate from the vapors produced from the oil withdrawn into said distilling zone.

: 5. The process of cracking hydrocarbon oils, which comprises continuously passing hydrocarbon oil to be cracked through a heating zone in which the oil is heated to a cracking temperature under a superatmospheric pressure, passing the heated oil while at a cracking temperature through a series of enlarged cracking zones in each of'which a body of oil is collected, maintaining the oil in said crackingzones under a superatmospheric pressure, enlarged zone to separate an oil residuum therein, alternately withdrawing oil residuum from said cracking zones while in a highly heated state into an externally unheated distilling chamber in which a lower pressure is maintained than that maintained on the oil in said cracking zones and in which substantial portions of said withdrawn oil residuum is vaporized, said oil' residuum withdrawal being carried out with a surging action by intermittently withdrawing the oil residuum from each cracking zone with a rapid rush under a sudden reduction in pressure, and collecting a distillate suitable as a cracking stock from the vapors evolved from the oil residuum withdrawn into said distilling chamber.

In testimony whereof I afliX my signature.

HENRY L. DOHERTY.

stratifying the oil in each p

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