US1767298A - Process of fractionation and apparatus therefor - Google Patents

Description

June 24, 193).`

w. K. A I Ewlsl PROCESS OF FRACTIONATION AND APPARATUSTHEREFOR Filed Jan. 12. 1925 Tn/mmtoz Patented June 24, 1930 UNITED STATES PATENT OFFICE WARREN K. LEWIS, OF NEWTON, MASSACHUSETTS, ASSIGNOR T STANDARD OIL DEVELOPMENT COMPANY, A CORPORATION OF DELAWARE PROCESS OF FRACTIONATION AND APPARATUS THEREFOB Applicationv led January 12, 1925. Serial No. 1,781.

This inventionrelates to improvements in processes and apparatus for cracking hydrocarbon oil and fractionating the resulting product. The invention will be fully understood from the following description, refer ence being made to the accompanying drawing, in which the single figure is adiagrammatic View of one suitable apparatus.

In the drawing, reference numeral 1 dew notes cracking means arranged in a. furnace setting 2. lVhile a single coil is illustrated, it will be understood that one or more coils, pressure stills, or other suitable apparatus may be used. The stock to be treated .is fed in through pipe 8. The coil 1 discharges through pipe 4 into a heat-insulated drum 5, in which further cracking takes place. A pipe 6 is arranged to takeoff the contents of drum 5 to separating means 7 such as a fractionating 'or rectifying tower. It is preferred to use a drum of the type de-v scribed, but the invention is not limited in this respect.

The upper part of the separating means 7 is ordinarily designed to function as a rectifying column. It may be provided with a partial condenser, such as a coil 8, or the;

reflux may be obtained byv returning a part of the condensate from the final condenser, or otherwise. The reflux is drawn from the tower, preferably above the point at which the cracked material is introduced. A pan 9 and draw-oil pipe 10 are provided for this purpose with defiecting plates to direct the condensate from coil 8 into the pan. A bell-cap column may be used with good results. AI prefer, however, to employ some type of tower filling l1 and 12, as illustrated.

The cracked product ordinarily asses into the tower at substantially the ull pressure and temperature of the cracking unit, except for the pressure drop incidentL to overcoming rictional resistance to flow. it is usually desirable to introduce the material into the tower at a point about onethird or one-fourth of the distance from the bottomy to the top.

A stream of an aeriform fluid, preferably an inert gas or vapor, such as oxygen-free flue gas, producer gas, lscrubbed still gas,

' returned lto the moved' through line 23.

or the like, is introduced into the bottom of the tower through pipe 13y and suitable distributing means, such as a sprayhead 14. The gas or vapor strips low boiling hydrocarbonsl from the heavy residue or tar refluxing down the lower section l2 of the v tower and collecting at its base. When an eicient tower arrangement is used, the quantity of gas required to strip the tar is relatively' small.

The stripping gas or vapor may be recycled or not,'as desired. In the installation shown,v gasoline vapors mixed with the stripping fluid are taken off through line 15 to a condenser 16, `which discharges into a container 17. The liquid product is drawn olif through line 19 and part of the gas is distillation apparatus through line '20. Grasl is initially introduced at 21 or other suitable location, and its pressure ismaintained by pump y 22. Gases generated by the cracking process are released/from the drum 17 by line 21a. Tar may be continuously or intermittently re- The cycle stock may be received in a hot accumulator tank 24 and returned by pump 25 to coil 1 for further cracking. 1' A particular4 object of the invention is to obtain the effective removal of hydrocarbons having -a low or intermediate boiling point that tend to be retained by the tar. The material discharged from drum 5 comprises vapor and liqui portions, the liquid containing dissolved vapors of naphtha and gas oil which mu'st .be stripped from the heavy tarry residue.` The vapor immediately rises into section 11 while the liquid drops down on the filling material 'of section 12. The composition of said liquid depends on the temperature andv pressure conditions.

volatile products in the tar will not be vaporized and the remaining liquid will be vlighter in gravity and will contain to'o large a fraction of low boiling oils to be useful as fuel oil. For this reason it has been impractical heretofore f to operate fractionating towers yunder high pressures, since volatilel products could not be Aeffectively removed.

high pressure is held Ain -separator 7, the

The function of the gas admitted to the separator through sprayhead 14 is to reduce the partial pressure of the volatile constitui ents in the vapors, thus allowing those fractions 4to distill from the heavy tar. By'this `means the se aration is accomplished.

In view of) this fact, I may operate at pressures above those at which prior h drocarbon f ractionating apparatus can ordY- narily function properly. For example, I may maintain with advantage a pressure of morethan 200 lbs. per sq. in., say 250 lbs.' or more, on the fractionating apparatus orI separator and produce a tar substantiall free from naphtha or light oils Whc could not be obtained under the high pressure without the use of gas.

An important feature of my invention is the provision of effective` countercurrent flow of the gas introduced and the tar bein stripped by it. In the apparatus illustrate this is accomplished by causing thev heavy c condensate to flow downwardly over the porphase,the invention is: not limited in this respect.` The boil, drum, and condensing ous packing 12 placed above the spray-head 14.. Merely injecting steam or gas into a body of heavy condensate will not accomplish the result desired.l

The pressure in the separator 7 will ordinarily approach or equal that of the crack-p ing system for, althou h the temperature in 7 is less than in 5, t e gas-added at ,14 allows the vaporization of a large part of the material as liquid in 5. This has important advantages. For example, since the cycle stock is discharged under substantially `the full pressure of the cracking unit, little eX- -pense in pumping is required for the return of this stock to coil 1. Also, its temperature is materially higher when high pressure is maintained on Athe distillation means.

The extent to which the light fractions are removed from thetar'-may be readilyv the a'mount of in regulated by adjustin ert gas introduced. I the tar tends to become too viscous for easy handling, the gas stream should be'. reduced. The reflux through the tower may be re ated to secure the .desired quality of al product. The feed stock, or other suitable liquid, may be used as the cooling means in coil 8.

WhileI have illustrateda system inwhich means for returning said heavy condensate` to the-cracking coil.

. 2. Process of operating hydrocarbon cracking and fractionating systems, comprising conducting the cracking and fractionating operations in separate zones under substantially the same pressure, in excess of 200 lbs. per sq. in., such pressure in the fractionating operation being in part maintained by vaporization and evolution of volatile products from the stock treated, and in part by introduction of gas into the fractionating zone, under pressure from an external source in effective countercurrent relation to unvaporized stock, condensing heavy vaporized products and separately collecting them in the -fractionating zone and returning-the heavy condensate to the cracking system together with the fresh feed.

3. Process of operating hydrocarbon cracking and fractionating systems, comprising cracking hydrocarbons under superatmospheric pressure in a cracking zone, fractionating the cracked products into tar, cycle stock and overhead distillate in a fractlonating zone under superatmospheric pressure not exceeding the pressure in the cracking zone, furthering vaporization in the fractionating zone byintroducing inert'gas thereinto in effective counter current relatlon to Junvaporized cycle stock, and returning the cycle stockto the crackingxzone for further digestioncpf'che.- oil take-s place .in liquid system' may be operated in various ways in connection with the utiliz ion of of rem lual cracking is allowed to take place in thnejlar-strippng apparatus. Thev frac- -tionati'ng column maybe a part of the tar'- v as from 'o an extraneous source for maintaimng pres- "'sure. If desired, theinvention may be applied in a' unit Vin which a certain amount 1

Images