US1984522A - Process of distilling oils - Google Patents

Description

Dec. 18, 1934. H. DQHERTY 1,984,522

PROCESS OF DISTILLING OILS Original Filed Feb. 24. 1920 4 Sheets-Sheet 1 Jnvembm HEN RY L. DOHERTY Dec. 18,1934. DQHERTY 1984 522 PROCESS OF DISTILLING OILS Original Filed Feb. 24. 1920 4 Sheets-Sheet 2 @Ejg l if. F N if l as V! M W S guocmto'c HENRY L. DOHERTY 351 his 61mm,

Dec. 18, 1934. H. 1.. DOHERTY PROCESS OF DISTILLING OILS Original Filed Feb. 24. 1920 4 sheet's sheet 3 Dec. 18, 1934.

H. L. DOHERTY PROCESS OF DISTILLING OILS Original Filed Feb. 24, 1920 4 Shams-Sheet 4 Suva Mica HE NRY L-. DOH ERTY 35 his Patented Dec. 18, 1934 UNITED STATES PATEN'E FFICE PROCESS OF DISTILLING OILS Henry L. Doherty, NewYork, N. Y., assignor to Doherty Research Company, New York, N. Y., a corporation of Delaware Original application February 24, 1920, Serial No. 361,030. Divided and this application January 31, 1930, Serial No. 424,807

4 Claims. (01. 196-59) This invention relates to a process of distllling oil and more particularly to a process of and apparatus for cracking heavy hydrocarbon oils to form lighter hydrocarbon oils thereirom.

ing heavy hydrocarbon oils to produce lighter hydrocarbon oils, particularly gasoline, have em ployed a cylinder still in which the oil'is heated in a large body. The inherent nature of the cylinder still presents certain limitations in the process which hold down the character and quantity of gasoline which may be recovered. Among these limitations are the formation of hydrocarbons of higher and lower boiling points than the boiling points of the gasoline desired. Al-

- though oil may be cracked througha wide range of temperatures, the most advantageous cracking is obtained in a specific narrow range of temperatures. Experience has shown that at the higher temperatures, the rate of reaction is very rapid with a consequent formation of large amounts of fixed gases and carbon. With lower temperaturea'the reaction is slower and consequently the time element is an important factor. Since oil is such a poor conductor of heat, it is not practical to use the lower temperatures when distilling oil in a cylinder still and in fact the outside of the still is subjected to very high temperatures in order to drive the heat into the center of the body of oil. This causes a local overheating and a layer of coke is always formed around the inner surface of the still.

One object of the present invention is to provide a process by which oil may be uniformly heated to any desired temperature.

In accordance with this object, one feature of the invention contemplates rapidly circulating the oil through a heater in a comparatively small stream and carrying a stream of vaporizing and agitating inert gas in contact and parallel with the oil while it is being heated.

Another object of the invention is to provide a process of cracking oil by which the oil may be held under the most advantageous temperatures for cracking for an extended period of time to allow the cracking or decomposing reaction to be completely effected.

In accordance with this object, another feature of the invention contemplates separating vapors from an oil which has been heated to a cracking temperature and passing the Vapors and 011 through a cracking chamber in countercurrent paths. The oil entering the cracking chamber is uniformly heated throughout and is maintained at a comparatively uniform temperature throughout the body by being agitated with the gas and vapors passing through the oil. The agitation of the oil assists the cracking reaction and while the oil is being agitated by the vapors, the vapors are repeatedly brought into the reaction zone so that they can enter the reaction to form specific hydrocarbons in accordance with the temperature and pressure conditions in the cracking chamber. In this way the more desirable lower cracking temperatures may be maintained for cracking and the oil may be held for any desired period of time under the proper cracking conditions.

Accordingly, another object of the invention is to provide a process of cracking oils by which the cracking reaction may be effectively promoted at the lower temperatures.

A further object of the invention is to provide a process by which the reflux condensation of the higher boiling point vapors may be accurately controlled to bring back into the reaction zone products of any particular range of boiling points.

A further object of the invention is to provide an apparatus by which a hydrocarbon oil may be rapidly and eiiectively cracked.

With these and other objects in view, the invention consists in the improved process and apparatus of cracking oil hereinafter described and claimed.

The various features of the invention are illustrated in the accompanying drawings, in which:

Fig. 1 is a view in side elevation, partly in section, showing a cracking still embodying the preferred form of the invention;

Fig. 2 is a top plan View of the cracking still shown in Fig. 1;

Fig. 3 is a vertical sectional view of the oil heater and furnace therefor taken on the line 33 of Fig. 1;

Fig. 4 is a vertical sectional view of the reflux condenser which is mounted on the top of the 4 cracking chamber; and 5 The raw material for treatment may be kerosene, gas oil, fuel oil, or a mixture of two or more of these, and the treatment always produces lower boiling point hydrocarbons therefrom. Under the present commercial conditions the treatment is conducted to produce gasoline. In carrying out the processirr the apparatus shown in the drawings, the raw oil' from storage is drawn in through a pipe 10 to a pump 12 and carried by means of a pipe 14 into the first condenser 16 of a series of surface condensers, 16, 18, 20,. 22', 24,. 26,, 28 and 30 (Fig. 2). It then advances through the condensers while being passed in heat-transferring relationship with oil vapors, which are formed in the cracking operation and flow through the surface condensers countercurren-t to the flow of oil. The oil is preheated by the vapors at 300-450 F., depending upon the tem-' perature of the vapors, and flows from the condenser 30 through a pipe 34 (Fig. 2), and enters the upper portion of a'cracking. chamber 36 In. the cracking chamber, the oil is formed into: a series of bodies which. are separated by trays or horizontal partitions 38 and the oil overflows by gravity from one tray to the next tray below through overflow pipes 40. When the oil has flowed downward-1y inthecracking chamber to a tray 42 (Fig. 1), it meets a body of. oil which is introduced through a pipe 44. The oil introduced through'the pipe 44; has been previously treated in the cracking 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 a size i. that the gas is permitted to pass upwardly therethrough while the oil is prevented from passing downwardly therethrough. In this way, the gas and vapors entering through the pipe 48 pass up.- wardly through the bodies of oil on the trays. to

actively agitate the oils 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 intermingling of 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 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, how out through the pipe 46 to a pump 50 which forces it through a pipe 52 to a pipe still 54. As the oil flows through the pipe 52, a gas is introduced into the oil through a pipe 56 by means of a pump 58. The gas flows in contact and in parallel current with the oil and serves to actively agitate and accelerate the velocity of the oil passing through the pipe still 54. Further, the oil vapors whichv are formed in the pipe still are absorbed by the gas flowing in parallel current therewith and at the time the oil and gas have passed through the coil of the pipe still, they are heated to a cracking temperature and the gas is saturated with vapors which are also heated to a crack in-g; temperature. The oil leaving the cracking chamber to pass to the pipe still is heated to substantially a cracking temperature and therefore only a. small amount of heat will have 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 69 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 44 together with incoming oil flowing downwardly through the upper portion of the cracking chamber are heated to the cracking temperature and pass in a countercurrent path through the gas and vapors which are also heated to a cracking. temperature. By the countercurrent 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 to. give 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 tray 42 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 of the vapors condensed serve to preheat the raw incoming oil to a crack ing temperature. These vapors leaving the uppermost tray of the cracking chamber pass through a reflux condenser 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 '76 (Fig. 4) mounted in the upper portion of the condenser. With the thermostatic control, vapors of any desired boiling point may be condensed and carried back into the cracking chamber so as to permit only vapors having a predetermined temperature to pass into the condensers 30-46.

The gas and vapors leaving the reflux condenser pass through a pipe '78 and enter the last surface condenser 30. These gases and vapors then pass in series through the condensers 30-16 and finally flow out through a pipe (Figs. 1 and 2) to a water-cooled condenser 82 where the lowest boiling point hydrocarbons are condensed. The fixed gases formed in the process, together with the gases introduced into the circuit through the pipe 56, flow 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 mineral oil to remove the uncondensed vapors and the gases leavin the upper portion of the scrubber 86 flow through a pipe 88 to the pump '58. Any excess of gas over that necessary in the process may be removed through the pipe 90. If desired, gas from an external source for starting the proc ass or for any other purpose, may be introduced through the pipe 90.

As the mixture of gas and vapors advances through the condensers 30--16, it is gradually cooled by the incoming raw oil advancing through the condensers 1630. The gradual interchange of heat between the incoming oil and the gas and vapors permits the condensation of fractions with I sharply defined boiling points, which may vary only by a few degrees of temperature. This intensified fractionation of vapors permits the recovery of a number of products of substantially the desired boiling points and thus avoids the necessity of several redistillations in recovering the marketable products. The fractions condensed in the condensers 30-46 are removed through outlet pipes 92 (Fig. 1) to look boxes 94 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 watercooling tank 102 and each coil hasa connection 104 by which the condensates may be conducted to their respective collecting tanks. If desired, any or all of the condensates passing 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 oil inlet pipe 3 1. With the apparatus outlined above, the process may be so conducted that all of 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 3016. 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. Further, if any of the fractions in the surface condensers do not meet the desired specifications, they may be returned to the cracking chamber ,xthrough the run-back line 109 for retreatment.

To promote the positive circulation of the vapors and gas in the condensers and to maintain the proper pressure conditions throughout the apparatus, a pressure-equalizing pipe 110 (Fig. 1)

connected between the vapor-pipe 78 and the oil-inlet pipe 34.

In all cracking processes a certain amount of carbon and tarry sludge is always formed and if this material is not removed 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 free in 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 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 114 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 sufficie-nt sensible heat to vaporize approximately 50% of the oil when it is reduced to atmospheric pressure. Accordingly, the still 116 is maintained at atmospheric pressure and the carbon and tarry sludge is intermittently drawn oil from the settling chamber 112 by 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 these vapors 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 in the cracking chamber 36, considerable carbon and tar sludge will be formed therein. To remove this carbon and tar from the oil circuit, the lower end of the cracking chamber is provided with a conical collecting chamber 122' (Fig. 1), which is connected through a valve 124 and pipe 126 with the still 116. The oil containing carbon and tar may be drawn from the cracking chamber 36 in the same manner that it is withdrawn from the collecting chamber 112 and passed into the still 116 to recover any light oil vapors therefrom. The heavy tar sludge which does not vaporize in the still 116 is withdrawn through an outlet 127. Although the distillation operation is continuous, it is preferred to operate the valves 114 and 124 for withdrawing sludge from the oil circuit alternately and intermittently since an intermittent pulsating operation tends to clear the heavy sludge from the pipes 113 and 126 due to the rapid rush of i the high pressure oil into the low pressure still 116.

Of the high boiling point vapors which are formed in an oil cracking operation, those vapors which condense 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 aswell as seriously interfering with the heat transfer of the condenser. With a cracking chamber constructed as described above, this difficulty is overcome since the vapors are cooled to the desired minimum temperature for removing carbon and tarry material by passing them through the incoming oil in the upper portion of the cracking chamber before the heavy vapors come into contact with the cooling surface of the reflux condenser. When the heavy vapors are condensed within the oil, the carbon and tarry material is caught in the oil and carried downwardly to the collecting chamber at the bottom of the cracking chamber.

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 gas to pass countercurrent therethrough. The function of the cracking chamber is to provide a means by which the oil may be held at a cracking temperature for an extended period of time to permit the 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 gas and vapors passing through the oil act chamber.

1 as described hereinafter.

to thoroughly agitate the oil so as to maintain a uniform temperature and to repeatedly bring the vapors into contact with the heated oil to assist in the heatreactions.

To effect the countercurrent treatment of the oil and vapors in the cracking chamber with the apparatus illustrated in the drawings, it is necessary to maintain alower 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 reduced, however, depends upon the difference in vertical head between the pipes 44 and 48 and is controlled to allow the oil to be admitted into the upper portion of the cracking chamber while the gas is being introduced at the bottom of the chamber. A ten to fifteen pound pressure differential will ordinarily protime an active circulation of the gases and vapors up through the body of the oil in the cracking 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. While the pressure of the gas and vapors is reduced by means 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 frictional losses in the pressure of the oil passing therethrough.

The pipe still 54 is shown more particularly in Figs. 1- and 3. The still consists of a series of pipes 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 chamber130 of a furnace 132 and the opposite ends of the pipe project through side walls 134 of the furnace. The ends of the pipes 128 are connected by means of return bends 136 (Fig. 3), which arelocated on the outside of the walls 134 to permit the return bends to be readily removed for cleaning and repairing the pipes. The ordinary tube cleaner which is used for cleaning water tube boilers may be effectively used for cleaning the tubes 128. A division wall 137 (Fig. 3) is placed in the heating chamber 130 to support the central portion of the pipes 128 and prevent them from sagging while being heated. The pipe still is preferably heated by means of an oil or gaseous fuel, which is ignited in a combustion chamber .138 positioned outside of the heating chamber 130. The fuel is introduced into the combustion chamber 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, or may be used 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 heated up to the cracking temperature in passing through the pipe still.

The reflux condenser 70 is shown more particularly in Figs. 1 and 4. This reflux condenser is in the form of a steam boiler and. converts all of the heat liberated by the condensing vapors into useful steam energy which may be used to drive the pumps or other apparatus. The temperature of the reflux condenser is controlled by varying the steam pressure to produce the products desired and variations in the operating temperatures are regulated by means of the water which is introduced through the pipe 72. The condenser consists of a cylindrical shell 150, the lower end of which is mounted on the upper end of the cracking chamber and the upper end of which is closed by a vapor-collecting dome 152. Tube sheets 154 and 156 are mounted respectively near the upper and lower ends of the shell and a series of long vapor tubes 158 are connected between the tube sheets. The vapors and gas passing out of the cracking chamber flow through the tubes 158 and are cooled by means of water and steam which is positioned around the tubes. By means of the thermostatic control -of the water entering the condenser through the pipe '72, the vapors passing up through the dome 152 may be maintained at any desired temperature. To accomplish this, the steam formed from the water in the condenser by the heated vapors, is permitted to flow out of the condenser through a pipe 160 to maintain a uniform pressure within the condenser. The transfer of heat in the lower portion of the condenser from the vapors to water is very rapid as compared to the transfer of heat from the vapors to superheated steam in the upper portion of the condenser. If the temperature of the vapors passing the thermostat 76 tends to rise, the thermostatic valve will be opened to permit more water to flow into the condenser and this influx of water will continue until the vapors are sufficiently cooled by rapid heat transfer to the water to close or partly close the valve 74. On the contrary, if the vapors fall below the desired temperature, the valve '74 will be closed to stop the influx of water into the condenser, and the longer path of travel of the vapors in contact with steam with the consequent low rate of heat transfer will allow the vapor temperature to be raised to the desired point before the valve will be opened. With this construction, the water level in the condenser 70 will automatically vary to maintain the desired temperature of vapors flowing out of the condenser through the pipe 78. In case there is a very large volume of vapors having a specific boiling point such that it would overtax the cooling capacity of the condenser 70, these vapors may be partially condensed in the surface condensers 30-16 and returned to the cracking chamber without interfering with the collection of the desired end product in the surface condensers. The reflux condenser 70, however, permits of a wide range of operation and can be used with a comparatively small number of fractional condensers to recover any desired end product.

The details of construction of the surface condensers 30--16 are shown more particularly in Fig. 5. These condensers consist of cylindrical drums 162 which have tube sheets 164 and 166 mounted at their opposite ends. Tubes 168 are connected between the sheets 164 and 166 and the oil is caused to pass through the tubes in effecting a heat interchange with the vapors and gas. Oil-collecting chambers 169 and 170 are formed respectively between the ends of the cylinders 162 and the tube sheets 164 and 166. The chambers 169 and 170 of adjacent condensers are connected by pipes 171 which are arranged to connect the condensers in series so that the oil flows therethrough in a continuous stream. The vapors are introduced into and leave the vapor chambers of the cylinders 162 through pipes 172, the pipes 172 being arranged to connect the ends of the vapor chambers for series circulation. In passing through the vapor chamber, the vapors flow around baiilcs 174 which effect a uniform distribution of the heat into the oil passing through the tubes 168. Any vapors which are condensed in the shell 162 and on the tubes and baiiles are collected at the bottom of the shell 162 and withdrawn through the pipes 92 (Figs. 1 and 5).

With 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 products desired. The form of pipe still shown in the drawings affords a means by which a large amount of 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 (Fig. l) to prevent radiation losses, and these parts may be heated in the usual manner by means of exhaust flue gases.

When exhaust flue gases are to be used for the purpose of heating the separator and cracking chamber suitable apparatus elements may be provided as shown in Fig. 6. As shown in this figure the hot flue gases conducted from the furnace 132 by means of the stack 143, are bypassed from the stack into a flue 149, which discharges into a heating jacket around the chamber 112 formed by a refractory enclosing wall 151. The flue gases after passing around and heating the chamber 112 are then conducted through a flue 153 into a refractory jacket 155 which surrounds the portion of the tower 36 used as a cracking chamber. The spent fiue gases are conducted from the jacket 155 to the atmosphere through an outlet 157. If desired a portion of the hottest flue gases may be passed directly from the stack 148 into the jacket 155 surrounding tower 36.

In order to control the amount of flue gases diverted from the stack 148 for heating chambers 112 and 36 a damper or valve 159 has been provided therein above the flue 149.

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 and to 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.

I claim:

1. The process of converting hydrocarbon oils into hydrocarbon oils of lower boiling point which comprises forcing the oil to be converted through a highly heated confined passage-way with sufiicient velocity to prevent substantial deposition of coke the oil being thereby brought to conversion temperature, discharging the oil into and through a succession of enlarged chambers, the contained heat of the oil being confined in the earlier of said chambers to maintain the oil therein at conversion temperature and the later of said chambers being heated only sufiiciently to maintain the oil at conversion temperature.

2. The process of converting hydrocarbon oils into hydrocarbon oils of lower boiling-point which comprises forcing the oil through a confined passage, heating the passage so that the oil discharged thereirom has a temperature of 750 to 900 F., the velocity of the oil in the confined passage being such that no substantial amount of coke is deposited therein, discharging the oil into an enlarged chamber while confining therein the contained heat of the oil to maintain it at a conversion temperature and passing the products from said enlarged chamber, into a second enlarged chamber supplying heat to said second chamber sufiicient to maintain the oil at conversion temperature and not more than sufficient to maintain the temperature of the oil at its entrance temperature.

3. The process defined by claim 1 in which a gas is introduced into the later of said chambers to aid in the conversion of the oil therein.

4. The process defined by claim 2 in which the vapors produced in the conversion operation are conducted from. said enlarged chambers, subjected to reflux condensing conditions, and reflux condensate resulting therefrom returned to the conversion operation for retreatment.

HENRY L. DOHERTY.

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