US2015420A - Method of cracking oil in the vapor phase - Google Patents

Description

Sept. A24, 1935. 'c. T. cHAvE ET AL 2,015,420

METHOD OF CRACKING OIL IN THE VAPOR PHASE Filed Feb. 1e, 1935 BEUS Ill

llll

ooooQQw A TTORNE Y.

Patented Sept. 2,4, 1935 PATENT .OFFICE METHOD oF CRACKING on. IN THE VAPOR PHASE Charles T. Chave, New York, and Hermann C. Schutt, North Tarrytown, N. Y., assignors to Gyro Process Company, Detroit, Mich., a corporation of Michigan Application February 16, 1935, Serial No. 6,838

11 Claims.

j Our invention relates to a method of cracking oil in the vapor phase and more particularly to a method for converting hydrocarbon oil into lower boiling hydrocarbons.

Our invention is directed to an improvement in that process of cracking oil which is known as the gyro process in which oil is heated to vaporizing temperatures, flashed into vapors and unvaporized oil, the vapors cracked in the vapor l0 phase and the products of the cracking reaction quenched to inhibit a continuance of the reaction, and the lower boiling point hydrocarbons separated.

In general, the objects of our invention are to 15 provide an improvement of the gyro process in which a reduced crude oil is used as a charging stock and is mildly cracked or subjected to a viscosity breaking operation to decompose the asphaltic material in the reduced crude charging stock to the greatest extent possible; to eliminate all refractory cycle stock from the viscosity breaking and vapor phase cracking operations and to enable higher pressures to be employed vat the inlet of the vapor phase cracking zone.

These proximate objects will result in the ultimate object of obtaining increased yields of desirable lower boiling hydrocarbons and will, further, enable longer cycles of operation t-o be practiced without the necessity of discontinuing the process for cleaning.

Other and further objects of our invention will appear hereinbelow.

The accompanying drawing is a schematic view 0f one form of apparatus capable of carrying out the process of our invention.

, In general, our invention contemplates heating the reduced crude and flashing it, with or without the presence of steam, in order to remove the light ends therefrom. These light ends should not be subjected to a viscosity breaking operation and they are passed to the main fractionating tower where they arecondensed and ultimately form part of the cycle stock. The removal of the light ends also serves to raise the initial boiling point of the oil being charged to the viscosity breaking operation. The oil thus treated is mildly cracked in a viscosity breaking step and flashed in a flash evaporator which is maintained under a pressure higher than that which exists in the main fractionating tower. Into the flash evaporator is passed, too, the cycle stock which is subjected to a heating step in a separate heating coil. All of the vapors from the flash evaporator pass to the f vapor `phase cracking zone in which they are heated to active vapor phase cracking temperatures. The unvaporized oil is withdrawn from the flash evaporator and passed into a flash tower, which is maintained at a lower pressure than the primary evaporator heretofore mentioned. The unvaporized oil from the flash evaporator is with- 5 drawn as fuel oil and the vapors are introduced into the fractionating tower. The cracked va-Y pors are contacted with a fraction withdrawn from the fractionating tower and reduced in temperature by heat exchange. 'lhis contacting step 10 is the quenching or arresting step in which the cracking action is inhibited by the reduction of temperature which ensues. The quenching oil and the quenched products of reaction are passed into a separating zone, from which the unvapor- 15 ized oil is withdrawn. The remaining vapors which contain the desirable low boiling hydrocarbons are passed to the main fractionating tower. More particularly referring now to the drawing, a hydrocarbon oil such as a reduced crude oil 20 from line I is pumped by pump 2 through line 3, through heat exchanger 4, through line 5, through heat exchanger 6, through line 1, which is controlled by valve 8, to reduced crude flash tower 9. The oil` in passing through heat eX- 25 changers 4 and 6, has been heated to such an extent that the light ends will vaporize in the flash tower 9. The vapors are removed from flash tower 9 through line I0 and pass into the main fractionating tower through line Il. The 30 crude oil thus denuded of the lighter ends is removed from flash tower 9 through line I I and is pumped by pump I2 through line I3 to thev viscosity breaking furnace I4. In the viscosity breaking furnace, heat is supplied by burning of 35 fuel in burners I5. The oil first passes through tube bank I6 where it is heated by convection heat imparted by the hot gases of combustion, generated by the burners I5. 'I'he oil is then heated by radiant heat in radiantly heated tube 40 bank I'I'. The furnace I4 is so controlled that a mild cracking or viscosity breaking will take place. The oil thus heated leaves the tube bank Il through line I8 which is controlled by valve I9 and is flashed into evaporator 20. Reflux con- 45 densate which collects in the bottom of fractionating tower 2| is withdrawn therefrom through line 22. A portion of the hot` reflux condensate passes through line 23 and is pumped by pump 24 through heat exchanger 6 in heat exchange 50 relation with the incoming fresh charge, and returns to the fractionating tower through line 25. Another portion of the reflux condensate passes through line 2B and is pumped by pump 21 through line 28, through heating coil 29, in which the reflux condensate is heated to vaporizing temperature by the hot gases of combustion generated in the fire chamber of the vapor phase cracking furnace. The oil thus heated leaves tube bank 29 through line 30, which is controlled by valve 3| and is flashed into the evaporator 20, together with the heated oil entering through line I8. The combined vapors are removed from the flash evaporator 20 through line 32 and pass to the convection tube bank 33 of the cracking furnace. 'Ihe vapors are then heated by radiant heat in tube bank 34 and finally, by convection heat in tube bank 35. The vapors thus heated to cracking temperature, and a sufficient time interval to permit the desired reaction to take place having been allowed, the vapors are withdrawn through line 36 and pass directly to an arresting zone 31. For convenience, the drawing has been made schematic. It will be understood, however, that the arresting zone is in close pro'ximity to the exit from the cracking zone.

As a quenching medium, a fraction of reflux condensate is withdrawn from the fractionating tower 2| through line 38 and is pumped by pump 39 through line 40, through heat exchanger 4 in which the hot reflux condensate imparts some of its heat to the incoming charge, through line 4|, through cooler 42, through valve 43, into the arresting zone 31, in which the hot products from the cracking zone are contacted with the oil thus cooled. The process is such that the quenching oil is of sufllcient quantity and temperature to inhibit the cracking reaction and prevent the formation of excess carbon and fixed gas. The products of the quenching step leave the quenching zone 31 through line 44 and pass into a separating zone 45, from which the vapors are withdrawn through line 46 and pass to the fractionating tower 2|. The unvaporized oil is withdrawn through line 41 and is pumped by pump 48 through cooler 49 into line 50. This unvaporized oil may be termed "refractory fuel oil and contains hydrocarbons having a low hydrogen to carbon ratio. If this oil were permitted to form part of the cycle stock, it would tend to deposit carbon in the cracking zone. If this oil were permitted to enter the viscosity breaking operation, it would deposit carbon in the viscosity breaking zone. The unvaporized oil in the flash evaporator 20 may be termed primary fuel oil. This oil contains valuable hydrocarbons having such hydrogen to carbon ratio that it is suitable for cracking. 'Ihe higher boiling hydrocarbons contained in the primary fuel oil are poorer in hydrogen and, if permitted to pass through the cracking zone as part of the cycle stock, will occasion carbon deposition. Accordingly, in order to maintain the yields. it is desirable to separate the higher boiling hydrocarbons having a poorer hydrogen to carbon ratio from the lower boiling hydrocarbons which can be utilized as part of the recycle stock. This is done by passing the primary fuel oil to a zone of lower pressureland flashing it into vapors and unvaporized oil, en-

abling a separation to be made. The primary fuel oil is withdrawn from the flash evaporator 20, which is maintained under the pressure which it is desired to employ at the entrance to the vapor phase cracking zone, through line 5|, which is controlled by valve 52 Aand flashed into the fuel oil flash tower 53. In order to enable a better separation to be made in flash tower 53 a branch line 80, controlled by a suitable valve, communicates with line 40 and is adapted to introduce reflux condensate into the flash tower as reflux. In order to provide for recirculation of part of the viscosity breaker charge which has not been cracked, a line 80 controlled by valve 82 is adapted to withdrdaw a portion of liquid from the fuel oil flash tower 53 from an internal 5 drawoff section for introduction into the reduced crude flash tower 9. A steam pipe 83 may be provided in flash tower 53 to assist in the separation of desirable low boiling constituents from the primary fuel oil. The vapors are removed 10 from the fuel oil flash tower through line 54 and join the vapors from the reduced crude flash tower in line and pass to the fractionating tower 2|. 'I'he unvaporized residue is withdrawn from the fuel oil flash tower through line 55 and is pumped 15 by pump 56 through cooler 51 and passes through line 58 to storage. The refractory fuel oil may be commingled with the fuel oil withdrawn through line 58 by means of a cross connecting line 59 which is controlled by valve 60. 20 It will be observed that we have accomplished the objects of our invention. The fresh feed entering the system is flashed or distilled by means of heating and flashing. A steam pipe 6|, controlled by* valve 62 is provided in the 25 reduced crude flash tower 9 so that light ends may be removed by stripping with superheated steam. The vapors thus removed are passed to the main fractionating tower where they are subsequently condensed and form part of the cycle 30 stock which is passed to the heating zone 29. By thus removing the light ends from the charging stock, the initial boiling point of the charge is raised. This boiling point may be controlled very readily by the extent of heat exchange and by the extent of open steam employed, which obviously is easily controlled.

'I'he charging stock is then subjected to a viscosity breaking operation. It will be noted that this viscosity breaking operation is independent of 'the recycle stock. By thus performing the viscosity breaking step without the presence of recycle stock, the concentration of the heavy bottoms which are generally asphaltic in nature, is increased. This results in a greater reduction of these asphaltic bottoms to usable cracking stock than would otherwise be possible. At the same time, the elimination of the light ends from the charging stock reduces the amount of still lighter products such as gasoline and fixed gases in the viscosity breaking step. Then, too, there is no danger of cracked material being circulated through the viscosity breaking operation. As cracked material has a low hydrogen to carbon ratio, if it is circulated through the viscosity breaking step, coke and fixed gas will be formed. By thus eliminating cracked material from the viscosity breaking operation, it may be carried on efficiently. This, in turn, results in a high yield of gas oil which is excellent material to be 60 vaporized and subjected to a vapor phase cracking operation. This, in turn, results in a high yield of lower boiling hydrocarbons suitable for use as motor fuel. By heating the cycle stock independently from the fresh feed, we are enabled to heat the cycle stock to a temperature suitable to vaporize the same without the danger of coke deposition. The cycle stock is somewhat refractory -in character, that is, it has a lower hydrogen to carbon ratio than the virgin material being charged. If it is subjected to thev same viscosity breaking operation as the virgin material, coke depositions and fixed gas will result. The separation of the viscosity breaking step from the cycle stock heating step enables 'I5 higher evaporator temperatures to be employed. This permits the use of higher pressures in the vapor phase cracking coil which, in turn, enables a high outlet temperature from the vapor phase cracking operation to be obtained without the necessity of soaking and with little or no danger of forming coke in the evaporator. The control of the charging stock which we are enabled to obtain, results in a partial control of the cycle stock. Extensive stripping of the lighter ends from the charging stock will increase the amount of vapors which in turn will increase the amount of cycle stock going to the cycle stock heating step. It will be obvious that the greater the amount of cycle stock passing through the furnace under given conditions, the lower the temperature of the vapors of the vaporized charging stock entering the flash evaporator.

The primary fuel oil is removed from the flash evaporator which is maintained at a higher pressure than the fuel oil flash tower and is passed to the fuel oil flash tower, which is maintained at a pressure approximately equal to that of the main fractionating tower. If desired, a steam stripping coil may be employed in the fuel oil flash tower. In the present design of the gyro process, a user is limited in the pressure which may be maintained on the evaporator since it is not possible to recover all the crackable stock as overhead vapor, unless such temperatures are employed which are excessive. By thus flashing the primary fuel oil under reduced pressure, a heavier fuel will be produced and valuable crackable material is added to the cycle stock. The primary fuel oil flash tower is independent of the refractory fuel oil flash tower so that no contamination of the vapors from the'primary fuel oil flash tower by highly refractory material will occur.

The desired low boiling hydrocarbons are removed from the main fractionating tower through line 63 and are passed through condenser 85 into reflux accumulator 61, from which reflux condensate is removed through line 68, and pumped by line 69 through line 10 to the main fractionating tower. Unvaporized hydrocarbons and fixed gases are removed from the reflux accumulator through line 1I and subjected to f urther condensation in condenser 66. The condensate and uncondensed materials pass through line 12 to line 13 where they are joined by condensate passing from the reflux accumulator through line 1I. The condensed material and gases pass into the separator 15, whence the fixed gases areV removed through line 16, the desirable motor fuel through line 11, and water, which results from the use of steam, through line 18.

A portion of the quenching medium withdrawn through line 38 may be passedthrough line I9 to the evaporator 20, where it assists in making a separation of the vapors from unvaporized oil. Likewise, the quenching medium may be bled from line 4| through line 80 and passed to the cracked fuel oil separator to assist in making a separation of the vapors from unvaporized oil.

' It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of our claims. It is further obvious that various changes may be made in details within the scope of our claims without departing from the spirit of our invention. It is,

is not to be limited to the specific details shown and described.

Having thus described our invention, what we claim is:

1. The method of cracking hydrocarbon oil in order to convert high boiling hydrocarbons into lower boiling hydrocarbons which includes the steps of subjecting hydrocarbon oil to mild cracking conditions to break its viscosity by decomposing some of the high boiling hydrocarbons, flashing the oil from the viscosity breaking step into vapors and unvaporized oil in a first evaporating done maintained under pressure, separately withdrawing the unvaporized oil from said evaporating zone and flashing it into vapors and unvaporized oil in a second evaporating zione maintained at a pressure lower than said first evaporating zone, withdrawing said last mentioned unvaporized oil from the process, separately withdrawing said last mentioned vapors from the second evaporating zone, fractionating said vapors in a fractionating zone, withdrawing reflux condensate from said fractionating zone, heating said reflux condensate to vaporizing temperatures, and flashing the heated reflux condensate into vapors and unvaporized oil in said first evaporating zone, withdrawing the vapors from said first evaporating zone and subjecting the same to vapor phase cracking conditions, inhibiting the cracking reaction by contacting the reacting vapors with a cool hydrocarbon oil, separating the products of the inhibiting step into vapors and unvaporized oil, withdrawing said unvaporized cil from thev process, separately withdrawing the vapors, fractionating the vapors in said fractionating zone,

' withdrawing vapors from the fractionating zone and condensing the same to recover low boiling hydrocarbons.

2. In a process of cracking hydrocarbon oil to produce lower boiling hydrocarbons in which a hydrocarbon oil is subjected to mild cracking conditions to break its. viscosity and flashed into vapors and unvaporized oil in an evaporating zone, the unvaporized oil separately withdrawn from the evaporating zone and flashed into vapors and unvaporized oil in a zone of reduced pressure,

i the unvaporized oil withdrawn from the process,

the vapors fractionated in a fractionating zone in which reflux condensate is formed, reflux condensate is withdrawn from said fractionating zone as cycle stock and heated to vaporizing temperature, flashed in said first mentioned evaporating zone into vapors and unvaporized oil, the vapors withdrawn from said evaporating zone and subjected to vapor phase cracking temperature, in a conversion zone, the vapors withdrawn from the conversion zone and contacted with a cool hydrocarbon oil in an arresting zone to inhibit the conversion reaction, the products of the inhibiting step withdrawn from the arresting zone and separated into vapors and unvaporized oil, the vapors fractionated in the fractionating zone and the unvaporized oil withdrawn from the process; heating the hydrocarbon oil being charged to the process to vaporizing temperature and flashing it in a rst separating zone to vaporize some of the lower' boiling hydrocarbons, passing the vapors to the fractionating zone, passing the unvaporized oil to the viscosity breaking step, and performing the heating of the cycle stock separately from the viscosity breaking heating.

3. In a method of cracking hydrocarbon oil to produce lower boiling hydrocarbons in which a hydrocarbon oil is subjected to mild cracking conditions in a viscosity breaking zone and the oil thus subjected flashed into vapors and unvaporized oil in a iirst evaporating zone maintained under pressure, the vapors withdrawn from said evaporating zone and subjected to vapor phase cracking conditions whereby a portion of the vapors are converted into lower boiling hydrocarbons in a conversion zone, the vapors withdrawn from the conversion zone and contacted with a cool hydrocarbon oil in an arresting zone in which the conversion reaction is inhibited, the products of the inhibiting step withdrawn from the arrest from said second and third evaporating zones into said fractionating tower, withdrawing the remainder of the unvaporized oil from said second evaporating zone as primary fuel oil, introducing the unvaporized oil from said third evaporating zone to the viscosity breaking step, withdrawing vapors from said i'ractionating zone, condensing said vapors and recovering lower boiling hydrocarbons.

4. A process as in claim 3 in which the fresh oil being introduced to the process is heated and fiashed,into vapors and unvaporized oil in said third evaporating zone.

5. A process as in claim 3 in which a portion v of reflux condensate from the fractionating tower is withdrawn, cooled, and contacted with the cracked vapors as the arresting medium.

6. A process as in claim 3 in which reux condensate is withdrawn from the fractionating 5 tower, heated to vaporizingconditions and ashed into said first flash evaporator together with the oil coming from the viscosity breaking zone. r

7. A process as in claim 3 in which superheated steam is introduced into said second evaporating 10 zone to strip the primary fuel oil of lighter constituents suitable as cracking stock.

8. A process as in claim 3 wherein superheated steam is introduced into the separating zone in which the refractory fuel oil is separated from 15 the products of the cracking reaction in order to control the ash point of the cracked residue.

9. A process as in claim 3 in which a fraction of reflux condensate is withdrawn from the fractionating tower and introduced into said rst 20 evaporating zone as reflux to assist in separating vapors from unvaporized oil.

10. A process as in claim 3 in which a fraction of reflux condensate is withdrawn from the fractionating tower and introduced into said sec-v 25 ond evaporating zone as reflux to assist in separating vapors froni unvaporized oil.

11. A process as in claim 3 in which a portion of reflux condensate is withdrawn from the fractionating zone and introduced into the cracked 30 fuel oil separating zone as reflux to assist in the separation of the cracked products from the cracked residue.

CHARLES T. CHAVE. HERMANN C. SCHU'I'I. 35

Images