US2039611A - Process and apparatus for cracking oil - Google Patents

Description

ay '5, 33%, i A. L. STHLL. 29@39,M

IROCESS AND APPARATUS FOR CRACKING OIL I Filed March 26, 1929 CONDENSER COMPress 0 frieze/7hr Patented May 5, 1936 UNITED STATES PATENT OFFICE PROCESS AND APPARATUS FOR CRACKING OIL charging stock is maintained in the liquid phase.

during heating to cracking temperatures, by high pressures, the carbon formed as the liquid oil is decomposed being of a gummy nature and tending to deposit on the heating surfaces of the apparatus and causing hot spots thereon as is commonly understood. In processes for cracking in the vapor phase, the carbon precipitant is more in the nature of a finely divided powder which may, to a certain extent, be carried from the heating zone by passing the vapors through at a high velocity, but prior to the heating of the oil in the vapor phase, considerable deposits of carbon are frequently formed in the initial heating and vaporization of the charging stock, as a certain amount of cracking may take place in this operation. In all processes of this nature heretofore employed, insofar as I am aware, heat supplied to the charging stock, either merely to vaporize the stock or to effect its thermal decomposition, is transmitted from the heat source through the walls of the heating elements.

In accordance with the present invention, hydrocarbon oils may be subjected to cracking and the system be kept comparatively free from deposited carbon, this being accomplished mainly due to the fact that instead of heating and vaporizing. the stock by heat transmitted from an external heat supply through the wallsof the heating elements of the equipment, the liquid charge is heated and vaporized by admixture with previously vaporized and superheated stock. The present method of distillation includes generally, the vaporization of an entire or predetermined portion of a feed liquid charge by mixing the charge with a portion of the superheated vapors from previously vaporized stock, the heat of superheat in these vapors being sufficient to vaporize and, if. it is desired, to partially crack the charging stock. The vaporous mixture from this operation is then superheated and a portion of the superheated vapors utilized in heating and vaporizing subsequent heated liquid. As viewed in another aspect, the heating of the charging stock may be considered as being effected by recycling through the system a predetermined portion of superheated vapor product, the heat of 5 superheat in said portion being suflicient to prodtuce the desired heating and vaporization of the s cc As a result of the initial heating and vaporization of the charging stock by admixture with 10, previously superheated vapors, whatever carbon is formed during this operation is precipitated in the vapor body as a powder and may be conveniently removed as will hereinafter be described. Carbon formed in the subsequent steps 15 of superheating the vapor mixture is also thrown into the vapor stream as a dry powder and may be easily settled out of the final superheated vapors.

The apparatus utilized in carrying out the method outlined lends itself particularly to the maintaining of high efliciency in operation and also in facilitating control of the system. One particular feature of advantage resides in the compressing of that portion of the superheated vapors to be used in heating the charge, and subsequently discharging the compressed vapors at high velocity along with the feed drawn by injector action into the vapor stream, into a reaction chamber wherein the feed is subjected to vaporization and wherein carbonaceous bodies and any unvaporized charge settle out. The arrangement of the system also permits accurate control of the recycled superheated vapors by merely controlling the pressure in the system, or as will later be pointed out, the amount of recycled superheated vapors may be predetermined by controlling, in effect, the density of the superheated vapors before their intake to the compressor.

The above and additional features and advantages of the invention will be best and most fully discussed in the following detailed description of the system, reference being had throughout the description to the accompanying drawing, in which the apparatus employed in carrying out my cracking process is illustrated diagrammatically.

The charging stock, which may be crude petroleum or any suitable fraction thereof such as fuel oil, is supplied to the feed pump [0 from a suitable source, for instance, feed line H, after having previously passed through the heat changer l2, in which the oil is brought into heat transferring relation with. cracked vap rs. passin t the reflux tower, as will hereinafter appear. The feed is discharged by the pump through line l3 into the supply tank I 4, the liquid in the latter preferably being maintained at a substantially constant level by means of the float controlled valve [5 which controls the flow of steam to the pump through line l6. The feed liquid line I8 extends from the interior of tank l4 beneath the liquid level therein, and opens into the discharge throat I9 ofthe compressor 26. drawn from the supply tank through line l8 into the compressor discharge I!) by the action of vapors being discharged from the compressor at a high velocity as will later be described.

It may be noted at this point that the vapors discharged from the. compressor are superheated considerably above their saturation temperatures, the heat of superheat of the vapors being sufficient to vaporize all or a predetermined portion of the charging stock mixed with the vapors. The liquid and vapor mixture from throat l9 passes into the mixing chamber 2| wherein the liquid and vapor are thoroughly mixed and in which partial vaporization of the feed liquid may take place. The mixture within passage 2| is discharged into the reaction chamber 22, the latter preferably being of increased volume in order that the fluid stream may be slowed down and any carbonaceous bodies resulting from the heating of the feed, and alsoa'ny unvaporized portions of the feed, may settle out in the bottom of the chamber. In the reaction chamber the heating and vaporization of the feed is carried to completion, and upon complete vaporization of the chargea certain amount of cracking may take place, this however being dependent upon the nature'of the stock and also the available superheat in the vapors discharged from the compressor. In certain instances it may not be desirable to vaporize all of the feed liquid taken into the chamber through line IS, in which event the amount of superheat inthe vapormay be predetermined as will later be described, to vaporize only the desired portion of the feed. The reaction chamber 22 may be of any suitable design, preferably however of such nature as to assure the removal of carbon particles from the vapors discharged from the chamber. V

The vapors in line 23 leading from the reaction chamber are passed through the pipe coil 24 in the superheater 25, the superheater serving to complete the cracking of the vapors and to heat the vapors to provide suilicient available superheat for vaporizing subsequent feed liquid. The heated vapors from the superheater are conducted through line 26 into the carbon trap 21 wheree in the powdery carbon particlesformed during the passage of the vapors through the superheater are settled out in the bottom of thetrap. The residual carbonaceous materials in the bottoms of the reaction chamber and carbon'trap are removed by means of suitable ejectors 29 and 30, respectively. Outlet lines 3| and 32 lead into the ejectors and materials settling in the bottoms of the reaction chamber and carbon trap are drawn through the outlet lines into the ejectors and subsequently discharged along with the ejector operating fluid.

A portion of the superheated vapors in chamber 2l is delivered through line 34 to the com: pressor 20, the latter being driven by motor 35 and being positioned at any suitable height above the feed liquid in the supply tank. The vapors are compressed in compressor 20 to such an extent as to enable their being discharged through the The feed is outlet throat l9 at a high velocity and at a rate such as to draw the feed liquid from line l8 into the vapor stream as heretofore mentioned. It may be noted that the vapors also are further superheated somewhat by virtue of their being compressed. In addition to the injector action for drawing the feed through line It! into the mixing chamber, there is a certain amount of pressure applied to the surface of the liquid in supply tank M. The pressure of the superheated vapors discharged from the heater 25 is communicated to space Na in the supply tank by line 3! leading into the discharge vapor line 36, the application of pressure to the liquid surface in. the supply tank serving not only to assist in the delivery of feed through line l8 but also to maintain an even pressure in the tank regardless of possible irregular operation of the supply pump Ill. The invention contemplates, in a broad sense, the use of any 7 suitable means for effecting recirculation of a portion of the superheated vapors in the system and for mixing the recycled vapor with feed liquid, the use of a compressor and in the manner described, as well as the introduction of feed liquid by injector action into the vapor stream after compression, however, being preferred.

That portion of the superheated vapors not recycled to the compressor line 34, passes through the outline line 36 through apparatus, generally indicated at 38, for separating the cracked vapors into the desired constituents. Any suitable equipment may be used in subjecting the vapors to fractionation, or separation, the illustrated apparatus being typical only. The vapors in line 36 are first conducted through the heat exchanger l2, wherein the superheat in the vapors may be transferred to the feed liquid in line II, the vapors then flowing through line 38a into the reflux tower 39. The heavier and undesirable fractions in the product vapors are separated 'within the reflux tower, and are drawn from the base of the tower through line 39a, the separated vapors flowing from the top of the column through line 40 into the condenser 4|. The fractions condensed in condenser 4| being separated from the uncondensible or fixed gases in the gas trap 42 are discharged from the system through line 43. "The pressure conditions in the system preferably are regulated by means of the back pressure valve 44 in the discharge line 43.

By adjusting the back pressure'valve 44 to control the pressure of the vapor in the system beyond the superheater, the amount of vapors recycled through the compressor, and therefore the amount of heat contained in these vapors, is likewise controlled. For instance, by adjusting valve 44 to build up the pressure in the system, the resulting effect on the vapors is to increase their density and therefore the heat content of a given volume-of the vapors. Assuming the compressor to operate at constant volumetric displacement, although this may not necessarily be the case, the effect had by increasing the pressure of the vapors and therefore their density, is to increase accordingly the heat contents of the vapors admixed with the feed liquid. The amount of recycled vapors and therefore the degree of heating of the feed liquid thus being controllable by the back pressure valve 44, the latter may be adjusted to effect any predetermined degree of heating of the feed. Substantially the same effect may be gained by placing the back pressure valves in the system at any desired location beyond the point of taking oif the vapors to be recycled, for instance by back pressure valves 10- catedin the vapor lines at 45 or 46 beyond the carbon trap, although it is preferred that the control valve be located at 44/ in order to maintain more even pressure conditions throughout the entire system.

The temperature to which the vapors are heated in the super-heater may be determined in accordance with the nature of the charging stock and also the extent to which it is desired to carry the cracking reaction. As a typical temperature range to which the vapors may be superheated, I may state that using a charging stock of fuel oil, the outlet vapor temperature at the superheater may be in the neighborhood of from 1200 F. to 1400 F. It will be understood that instead of superheating the vapors excessively to have available sufficient heat for subsequently vaporizing the feed by admixture with a portion of the heated vapors, the available heat may be increased or decreased by correspondingly controlling the flow of recycled vapors. And although the quantity of recycled vapors might be regulated by controlling the speed of operation of the compressor, a more simplified and accurate control is maintained, as hereinabove described, merely by regulating the pressure of the vapors. The operating pressure in the system therefore may vary within such limits as may be necessary to effect the necessary heat supply to the feed, a typical pressure range, however, may be given as from 5 to 200 pounds per square inch. It will be understood, of course, that the operating temperatures and pressures in the system are not limited to the typical values given.

Due to the nature of the successive operations of initially heating and vaporizing the feed", and subsequently subjecting the vapors to superheating, it is assured that whatever carbon is formed resulting from the heating of the oil is of such nature, and is precipitated under such conditions, as to render it readily removable from the system. Carbon initially formed upon vaporization of the feed in the reaction chamber is efiectively removed as heretofore described, and during the subsequent heating stage within the pipe coils of the superheater a powdery carbon precipitant is formed which is readily entrained in the high velocity vapor stream and carried into the carbon trap wherein final settling out and separation of the carbonaceous bodies takes place.

In starting operations the apparatus may be brought up to near the normal operating temperatures before putting oil into the system, by firing the superheater and introducing vapors or gases into the system through inlet II to prevent overheating of the superhater tubes as the apparatus is preliminarily heated. Natural gas or steam may for example be used for this purpose. Valve 45 may at first be kept nearly closed so that the gas taken into the supply tank l4 through lines I l and I3 will be recycled by the compressor through lines l8 and I9 into the reaction chamber and thence through the superheater. During the preliminary heating period it will only be necessary to maintain a circulation of gases through the superheater sufficient to prevent overheating until the superheater is brought up to temperature. The heated gases will also serve to preheat the reaction chamber and carbon trap. After the apparatus has been heated to the desired temperatures, feed liquid will be introduced to the system through inlet line H, and valve 45 gradually opened as the feed is subjected to vaporization and the oil vapors displace the previously entered gases. As will be readily understood, the presence of the heated gases within the system will serve to effect the delivery of feed oil from the supply tank to the compressor outlet, and to initially vaporize the feed, as well as oil vapors.

It will be'understood the drawing and description are to be considered merely as illustrative of and not restrictive on the broader claims appended hereto, for various changes in design, structure and arrangement may be made without departing from the spirit and scope of said claims.

l. The method of distilling petroleum oil that includes injecting feed oil into a chamber with superheated vapors from previously vaporized feed oil thereby vaporizing a portion of said feed oil, withdrawing and separating from the resulting mixture the unvaporized residual liquid, superheating and cracking vapors discharged from said chamber, returning a portion only of the superheatedand cracked vapors to said chamber together with subsequent feed oil to be vaporized and subjecting the remaining superheated and cracked vapors to condensation.

2'. The method of distilling petroleum oil that includes drawing feed oil into a stream of superheated vapors from previously vaporized feed oil thereby vaporizing a portion of said feed oil and discharging the mixture so formed into a chamber, withdrawing and separating from the resulting mixture the unvaporized residual liquid, superheating and cracking vapors discharged from said chamber, returning a portion only of the superheated and cracked vapors to said chamber together with subsequent feed oil to be vaporized and subjecting the remaining superheated and cracked vapors to condensation.

3- The method of distilling petroleum oil that includes drawing feed on into a stream of super heated vapors from previously vaporized feed oil thereby vaporizing a portion of said feed oil and discharging the mixture so formed into a chamber, withdrawing and separating from the resulting mixture the unvaporized residual superheating and cracking all of the vapors discharged from said chamber, returning a portion only of the superheated and cracked vapors to said chamber together with subsequent feed oil to be vaporized, and subjecting the remaining superheated and cracked vapors to condensation, and regulating the degree of heating of the feed by controlling the quantity of superheated vapors returned to the chamber.

4. The method of distilling petroleum oil that includes drawing feed oil into a stream of superheated vapors from previously vaporized feed oil thereby vaporizing a portion of said feed oil and discharging the mixture so formed into a chamber, withdrawing and separating from the resulting mixture the unvaporized residual liquid, superheating and cracking all of the vapors discharged from said chamber, compressing a portion only of the superheated vapors, and subjecting the remaining superheated and cracked vapors to condensation, and returning the compressed vapors to said chamber with feed oil to be vaporized.

5. A petroleum distillation system embodying a reaction chamber, a superheater communicating with said chamber and adapted to receive and crack vapors removed from the chamber, means for compressing a portion only of the superheated vapors removed from said superheater,

means for subjecting the remaining superheated vapors to condensation, means for withdrawing from said chamber the residual unvaporized feed, separately from the vapors, as such residuum'is formed, and means for mixing the vapors after compression with feed liquid and for delivering the mixture to said reaction chamber.

6. A distillation system embodying a reaction chamber, a heater communicating with said chamber and adapted to receive and superheat vapors from the chamber, means for withdrawing residuum from said chamber separately from the vapors, a vapor passage leading from said heater, a compressor communicating with said passage and adapted to compress a portion of the superheated vapors from said heater, a liquid feed supply chamber communicating with said passage and the pressure in the passage being applied to the surface of the liquid in said supply chamber, means for delivering feed liquid to the supply chamber, a compressor outlet line communicating with the reaction chamber, the compressed vapors being discharged at high velocity through the outlet line, a feed line extending from beneath the liquid level in said supply chamber and opening into said compressor outlet line, the feed liquid being drawn into the last mentioned line by the high velocity vapors.

7. A distillation system embodying a reaction chamber, a heater communicating with said chamber and adapted to receive and super-heat vapors from the chamber, means for withdrawing residuum from said chamber separately from the vapors, a vapor passage leading from said heater, a compressor communicating with said passage and adapted to compress a portion of the superheated vapors from said heater, adjustable means for regulating the pressure in said vapor passage, a liquid feed supply chamber communicating with said passage and the pressure in the passage being applied to the surface of the liquid in said supply chamber, meansfor delivering feed liquid to the supply chamber, a compressor outlet line communicating with the reaction chamber, the compressed vapors being discharged at high velocity through the outlet line, a feed line extending from beneath the liquid level in said supply chamber and opening into said compressor outlet line, the feed liquid being drawn into the last mentioned line by the high velocity vapors.

8. A distillation system embodying a reaction chamber, a heater communicating with said chamber and adapted to receive and superheat vapors from the chamber, a separating chamber into which the vapors from said heater are discharged, a compressor communicating with said separating chamber and adapted to compress a portion of the superheated vapors discharged into the separating chamber, a liquid feed supply chamber, the'pressure of the superheated vapors from the heater, being applied to the surface of the liquid in said supply chamber, means for delivering feed liquid to the supply chamber, a compressor outlet line communicating with the reaction chamber, the compressed vapors being discharged at high velocity through the outlet line, and a feed line extending from beneath the liquid level in said supply chamber and opening into said compressor outlet line, the feed liquid being drawn into the last mentioned line by the high velocity vapors.

9. A petroleum distillation system embodying a reaction chamber, a superheater communicating with said chamber and adapted to receive and crack all of the vapors from the chamber, a compressor communicating with said heater and adapted to compress one portion only of the vapors discharged from the heater, means for mixing the compressed vapors after compression with feed liquid and for delivering the mixture to said reaction chamber, means for removing unvaporized residual liquid from the chamber, means communicating with said heater and adapted to separate another portion of the superheated vapors discharged from the heater into liquid and gaseous fractions.

10. A petroleum distillation system embodying a reaction chamber, a heater communicating with said chamber and adapted to receive and crack all of the vapors from the chamber, acompressor communicating with said heater and adapted to compress one portion only of the vapors discharged from the heater, means for mixing the compressed vapors after compression with feed liquid and for delivering the mixture to said reaction chamber, means for removing unvaporized residual liquid from the chamber, apparatus communicating with said heater and adapted to separate another portion of the superheated vapors discharged from the heater into liquid and gaseous fractions, and means for regulating the pressure in said apparatus, thereby controlling the pressure of the superheated vapors in the system.

ANDREW L. STILL.

Images