US 2608527 A
Description (OCR text may contain errors)
w. w. HOLLAND 2,608,527 TEMPERATURE CONTROL IN SHOCK-CHILLING PETROLEUM VAPOR PHASE CONVERSION PRODUCTS Filed Aug.. l, 1947 Aug. 2G, 1952 .N .mi
Patented Aug. 26, 1952 TEMPERATURE CONTROL IN SHOCK-CHILL- ING PETROLEUM VAPOR PHASE CONVER- SION PRODUCTS William Holland, Baltimore, Md., assignor to The Gyro Process Company, Detroit, Mich., a
corporation of Michigan Application August 1, 1947, Serial No. 765,438
(Cl. 19E-61) 12 Claims.
This invention is directed to the cracking of hydrocarbons in the vapor phase, and particularly to the therrnolytic conversion of relatively heavy `liquid hydrocarbons into products boiling temperatures involved that the reaction will proi ceed too far or secondary reactions occur unless Aadequate precautions are taken to check the progress of the reaction suddenly and at precisely the correct point. There is also the ever-present danger of excessive coke formation unless the reaction conditions are under definite and positive control.
The practice of shock-chilling the products of conversion reactions has been followed in some vapor phase cracking` processes by directly contacting the hot vapors emerging from the conversion zone with a relatively cool oil in a quenching zone, thus reducing the temperature to a point where the cracking reaction ceases, but the results have been only measurably satisfactory because of the absence of any deiinite means ci exact temperature control at this critical stage of the conversion operation. If the temperature is not substantially instantaneously reduced to the proper degree at this stage, and maintained relatively constant, not only will the cracking reaction continue beyond the desired point but coke will be formed in the quenching Zone, causing a premature shut-down of the equipment and the lo'ss of valuable operating time. Also if the temperature is reduced only to a point below that required for cracking or below the critical coking temperature, the chilled products have a marked tendency to deposit granular carbon in the transfer lines between the quenching Zone and the `after equipment, eventually plugging the lines and necessitating major repairs. On the other hand, if the temperature is reduced to too W a degree, undesirable condensation results and the It is, therefore, an object of this invention to provide efficient and reliable means of controlling the temperature of the vapor phase cracking operation at the critical stage between the period of maximum cracking and that at which cracking has ceased-altogether, and to reduce the time element at this stage to the shortest possible interval.
It is also an object of this invention to provide means whereby the deposition of coke in the transfer lines between the quenching zone and the fractionating column is reduced to; a minimum, and such granular coke as may be held in suspension in the oil is collectedin a-conned Varea and removed from the system without interfering with the continuous operation ofthe process'- Y It isa further object of this invention to `retain sufficient residual heat in the products -of the quenching operation to cause the fractionating column to function properly andefciently in effecting the desired separation of the light and heavy fractions resulting from the pyrolytic conversion operation. i i l w Other objects ofthis invention will'become apparent as further details ofthe process are set forth. Y l `inthe vapor phase conversion of .liquid hydrocarbons for the production of high grademotor fuel, temperatures in excess of 1100 Rare-usually required, and for particularly refractory charging stocks, suchas cycle stocksproduced in previous cracking operations, temperaturesof the order oi 1250 to 1350 F. are-not infrequently required. In the case of gaseous charging stocks, however, such as, for example, the saturated C2, C3 and C4 compounds generally used in the pyrolysis of gases for the production of unsaturated hydrocarbons for chemical synthesis, the conversion temperatures may range from 1350 to 1550" F. But "inl, `either case, whetherthe charge is normally in the liquid or gaseous state, the temperature of the products of the conversion reaction must be reduced as nearly instantaneously as possible, immediately upon emergence from the cracking zone, to a degree where cracking ceases altogether. Several factors may govern the optimum temperature at this point, the mostimportant of which is that it must be below lthe temperature at which further pyrolytic decomposition can take place or coke can be formed, and it must be below the temperature at which secondary reactions occur. On the other hand, the vapors preferably must retain sufiicient residual heat for the required fractionating purposes, which is governed by the degree of separation desired, which in turn is dependent upon the height of and the number and emciency of the bubble trays in the fractionating column. Generally speaking, quenching temperatures not substantially in excess of 600 F. are suitable for the purpose; but Ythe exact temperature best suited to an individual operation should be calculated from theoretical considerations or preferably determined by experimental methods.
The choice of a cooling medium for use in quenching operations or for shockech'illing the cracked vapors issuing from the conversion zone is a matter of convenience rather than exact specifications. Any relatively light distillate that is clean and free from sediment and that Will not be completely vaporized when brought into contact with the hot vapors will serve the purpose. However, it should contain no heavy fractions subject to cooking under the temrerature conditions prevailing in the quenching zone. It is preferable, of course, to select a distillate fraction produced within the operation itself, rather' than from an extraneous source. For this` purpose, thereforer a suitable stream of oil may be withdrawnfrom a tray at an intermediate point in the fractionating column. This material, after cooling, is collected in a working tank 'from which it is delivered to the top of the temfperature arrester or quenching chamber where by suitable mechanical means, such as atomizing spray nozzles, it is intimately mixed in direct contact with the hot vapors issuing from the conversion zone.
vThe novelty of this invention resides primarily in the design of the quenching chamber and means of controlling the temperature therein, together with its relation to the fractionating column, with respect to the disposition of coke lduringA the passage of the products of conversion from one tothe other.
Since the temperature maintainedv in the quenching chamber is dependent upon the quantity of oil delivered thereto from the working `tank, itl is obviously vdesirable vthat the' Vrate of 'oil now should be governed by the temperature.
It r should be stated in this connection that the ilsmoothne'ss of the entire conversion operation, "as well as the uniformity in quality' of the nal 'products'. isY more largely dependent upon acculrate temperature control throughout the system than any other single factor. Heretofore "little importance has been attached to the maintenance of Van exact degree of temperature in the 'quenching zone, a feature which has contributed :to the varying character of the nal products and vinconsistent yields, as well as promoting the formation of coke under fluctuating temperature conditions. It is therefore a primary object of 'this invention to provide positive means of controlling the temperature at this point and completely checking the rapid pyrolytic decomposivvtion of thev hydrocarbon charge at the proper ners, extensive experimental work and the care- .ful study of 'heating problems by designing en- Igineers, but the samel attention, soA far as I am `aware, has never been directed tothe simpler -yetl equally important problem of dealing with the decomposition products of hydrocarbons as they leavethe conversion zone.
It is neither practical nor economical to maintain the quenching oil in the Working tank at a constant temperature because of its relatively large volume and the varying atmospheric and cooling water temperatures, yet any substantial variation` in the temperature of the oil delivered to the quenching chamber is reflected immediately in the character of the cracked products leaving the chamber, as is clearly shown by fr-equent analyses of the end products. On the other hand, it has been observed that if the quenching chamber is maintained at a reasonably constant temperature, the character of the conversion products is uniform and the yields consistent, and little or no coke is formed in the quenching operation.
To thisend a temperature control system is provided, the mechanism of which consists essentially of a thermostatic element inserted through the wall of the quenching chamber, electrically connected with a source of current and means for automatically controlling the delivery of a stream of cool oil from the working tank to the quenching chamber as the thermostatic circuit is established or broken. This arrangement aifords ample means of maintaining a constant temperature in the quenching chamber or of regulating the temperature in accordance with If Y the temperatur-e in the chamber rises, a larger quantity of cooling oil is admitted thereto; if the temperature falls, the supply of oil is diminished.
The quenched products of conversion, now reduced in temperature to about 600 F., usually include a small amount of iinely divided carbon or soot which should be removed from the system before the other products enter the iractionating tower. This is accomplished by means of a flash drum, acting as a trapY for the solid materials which settle to the bottom because of their higher specific gravity and greatly reduced velocity at this point of the operation; while the liquid, vapors and gases are flashed off with the aid of steam under partial pressure conditions, leaving the top of the flash tower and passingA directly to the fractionating column. The solid materials, along with arsmall amount of Vtar formed in the cracking operation, are withdrawn from the bottom of the flash. tower and diverted from the system.A
In vapor phase cracking operations, there is always the possibility of the deposition of finely divided coke in horizontal transfer linesV of any considerable length between the quenching chamber and the fractionating column. This invention is particularly directed to the avoidance of such a condition. To thisend, the quenching chamber is provided with a conical bottom constructed on about a sixty degree angle'to facilitate the complete and rapid exit of the quenched products from the bottom of the chamber, the turbulence within washing the walls of the cone free of carbon. Immediately below the cone is a pipe tters spool about twelve inches in length in which a helical vane is placed. Because of` the high velocity of the materials passing through the spooL this vane imparts a-rapid spiral or swirling motion to the liquid and vapors which eiectively scrub the inner walls; of the comparatively short line leading to the ash drum, thus avoiding the deposition of coke before it is trapped at the desired point in the bottom of the ash drum, from which it is withdrawn in the form of a suspension in the liquid residue. The placing of bailies in the flash drum vane; and
.tobstruct theyupward passage of the finely idivided -co'ke particles is optional, although experience indicates that the increased velocity resultig therefrom renders the advantage of bailles questionable.` i i v This invention will be clearly understood by `'referenceto `the accompanying simplied flow diagram forming a part of these specications, in which Fig. l represents in partial section and 'side elevation apparatus and equipment adapted tothe `continuous performance of the functions `and operationsV herein described;
f' l Vlig. `is anenlarged longitudinal section of the pipe viitters spool containing the helical Fig. 3 is a transverse cross section of the spool .Referring t0 the drawing, the numeral l repre- A-sents a tank containing a liquid hydrocarbon charging stock such as crude oil, topped crude,
gas oil, kerosene or the like, which is delivered by pump 2 through line 3 to an intermediate point .in the fractionating column iwhere it frst serves as a reflux for, and is preheated by,
the hot ascending cracked products of the conversion operation.A The preheating `ci? the charge or,V feed stock,` however, vis not limited to this means alone, since itis customary to `take ladvantage' of any economical source of heat exchange wherever possible in such systems, especially when charging crude oil, in which event the natural gasoline is usually removed through heat exchange with hot products, such as residuum from the evaporator, before entering the cracking coils in the furnace.
The` preheated feedstock, mixed with condensate produced within the .fractionating column, is withdrawn from .the `bottom of the column through `line 5, controlled by valve 6, and is de- `liveredby pump 'l to a vaporization coil 8 `lo- `catedpreferably in the convection section of a furnace 9 where it is substantially converted into vapor.` The vaporized and unvaporiaed portions of the charge or feed then pass vthrough line Hi into an evaporator lIl where Vaporization is effected with the aid of steam under partial pressure conditions, the unvaporized heavy residue being withdrawn fromthe bottom of the evaporator through line l2, controlled by valve i3, and divertedvfromthe system.` This residue may be 'subjected to a-viscosity-breaking operation, run
to coke or processed by any suitableY means for the production of road oil, bunker C iuel or other desirable products.v
The oil vapors leaving the top of the evaporator, commingled :with steam, pass through line i4 and enter the cracking coil i5 Where the con- `lversion` into i lighter products is effected.
V.Any suitable arrangement of preheatingcoils, drying coils or cracking elements may befused for .this purpose, depending upon the character` of the charging stock and the endproducts desired, That is to say, whether the charge is normally in the liquid or gaseous state, or `whether the `final ,products are to beused primarilyiforthe purpose of `motor fuel or `asunsaturated hydrocar-` bons for the synthesis of chemical compounds, or for both purposes. w
The process herein described is adapted to the conversion of either liquid Aor gaseous `hydrocarbons, although in the latter case, a somewhat different `arrangement ofA equipment is required and higher conversion temperatures are employed. For` example, when chargingl a liquid Ahydrocarbon according to Fig. 1 of the accompanying drawing, conversion temperatures of the rl 6 order of 1000 to 1350" F. maybe adequate `for the'desired conversion; While if the :chargeisin the` gaseous state underrnormal' temperature and pressure conditions, theconversion temperatures 'quenching chamber I1 where by direct and intimate contact with relatively cool atomized oil,
the temperature of the highly heated vapors is substantially instantaneously reduced to adegree below that at which further decomposition.
`can take place, secondary reactions occur `or coke be formed. Yet the vapors must retain sufficient residual heat to cause the fractionating column to function iproperly.- These requisite conditions can be met only by accurate temperature `controlof the quenching chamber, upon which the ultimate yields and quality of the finished products largely depend. Y
The fractionating column, which is preferably of the bubble tower design, provides a suitable source of oil for the quenching opera-tion, a selccted stream being withdrawn from an .inteme- `diate `bubble tray for thisA purpose, Vleaving the tower through line i8 and passing through a water cooler I 8 into-the Working tank `20,'from which itis deliveredby pump 2| through line 22, controlled by valve 23, into the top of the quenching chamber I1 where it is atomized by nozzles 24, contacting the heated vapors at this pointas previously stated. i A
Somewhat less cooling oil is supplied thrQllgh valve 23 than the total amount required for the i complete quen-ching operation, the remaindenbeling routed through a by-pass 25, around valve 23.
It is this portion of the cooling oil that is used for regulating the temperature in the quenching chamber, Yits rate of flow being governed auto- `matically by thermostatic control of a ,quick- 1opening-and,-closing valve 26, or any other means `design-ed for the accomplishment of the same purpose. The by-pass provides more `delicate and accuratetemperature adjustment than if the entire volume of cooling oil were placedV under thermostatic control. It also insures a suiiicient quantity of oil reaching the quenching chamber at all times, since the major portion of the oil iiowin-g continuously through `valve 23 may be manuallycontrolled in the event of failure of the automatic system through mechanical defects or otherwise. i f
Various mechanical devices involving theuse Vof motors, pumps, valves and the like are availfing oil, in addition to that passing continuously through valve 23, for the complete quenching` of able for automatic temperature control `under thermostatic conditions, any of which may be us-ed for the purpose at hand; but for reasons of simplicity and reliability, with no intention of limiting the scopeof this invention, I prefer the quick-opening-and-closng valve in the bypass 25 to supply the regulatory quantity of coolthe hotvapor issuing from the cracking coil i5. Valve 26 may be magnetically actuated to the open or closed position as the` thermostatic cirfecit. Ais' established or broken by the rise or fall of the `temperature in the quenching chamber.
vThe thermostatic element 21 inserted through the Wall of the chamber is electrically connected with the, magnets 29 through conduit 28 and with a source of current (not shown) in such .a manner as to control the movem-en-t of the valve mechanism 30 to the open or closed position in response to the uctuationof temperature in the chamber. When the temperature rises above the desired point, valve 26 is opened automatically, admitting more oil to the chamber; when the temperature falls, the valve is closed, diminishing the iiow of oil, thus maintaining an even temperature in the quenching chamber.
The bottom of the quenching chamber is constructed in the form of a cone 30, the walls oi which are built on an angle of approximately sixty degrees to facilitate the ready eXit of the materials from Ithe bottom of the chamber, espeoially `any coke particles held in suspension in the oil. Immediately below the cone, and hanged thereto, is a pipe iitters spool 3|, in which is placed a helical vane 32, more clearly shown in the enlarged sectional drawings, Figs. 2 and 3, which imparts a rapid spiral or swirling motion tothe oil and vapors as they enter the comparatively short pipe 33 leading to the flash tower 34, scrubbing the inner walls of the pipe free of carbon in transit.
Reaching the hash tower at reduced pressure, the vaporous fractions are dashed oi, preferably with the aidv of steam injected into the lower sec- `tionV ofthe tower,l while the residue holding the carbon in suspension is diverted from the system through line 3'5, controlled by valve 3G. The
-flashed Vvapors leaving the top of the tower throughline 31 enter the fractionating column 4 where separation of theV light and heavy fractions is eiected, also, if desired, with the aid of steam injected into the bottom of the column. The overhead vapors and gases leaving the fractionvating column through line 38 are conducted through a condenser 39 and collected in a receiver or separator 40, from the bottom of which Athe cracked distillate is withdrawn through line 4|-, controlled by Valve 42, .and sent to the treating system; while the uncondensed gases leaving the top of the receiver through line 43, controlled by valve 44, go to the gas recovery system.
VThe temperature of the top tray in the frac- Ai'sionating column, which governs the end point of the distillate produced, is controlled by the quantity of distillate returned to the top of the column y' through line 45Y by means of pump 46.
I. In a vapor phase cracking apparatus for the conversion of hydrocarbons, a conversion arrester comprising a quenching chamber, means in the upper part of said chamber forfintroducing therein a quenching agent in a lnely divided form, means for introducing converted hydrocarbonsintosaid chamber for contact with said quenching agent, the chamber being formed with a conical bottom, a ilash tower, a transfer line leading from the conical bottom of said quenching chamber to the lower part of said flash tower,
'helical means disposed in said transfer line to impart a rapid swirling motion to the materials passing therethrough, a vapor line leading from the top of said flash tower, and means for diverting from the system liquid residues and -suspended' carbon trapped in the bottom of the iash tower.
2. In a vapor phase cracking apparatus for hydrocarbon products, -a converter for converting hydrocarbons therein,` a conversion arrester comprising a hollow body dening an internal quenching chamber, means for transferring converted hydrocarbons from said converter to said chamber, means in said chamber for contacting the convertedy products introduced therein with a quenching agent in a nely divided form, a flash tower, a transfer line leading from the bottom o1' the quenching chamber of said arrester to said tower, means in said transfer line `for imparting a rapid swirling motion to the materials passing therethrough, Vapor outlet means leading from the top of said flash tower, and means for withdrawing from the bottom of said tower liquids and solids present therein.
3. In a vapor phase cracking apparatus. for the conversion of hydrocarbons as deiined in claim 2, wherein the` bottom of the flash tower is provided with means4 for introducing steam therein.
Ll. A conversion arrester for use in vapor phase cracking systems for the molecular conversion of hydrocarbons, said arrester comprising a receptacle formed with an internal quenching chamber, means for introducing converted hydrocarbons into the upper part of said chamber, spray means arranged in the upper part of said chamber for bringing a quenching agent in a nely divided form into direct and intimate contact with the converted hydrocarbons to reduce the temperature of the latter sufficiently to substantially arrest conversion reactions, said quenching chamber being formed with a substantially conical bottom terminating in a flanged outlet, a flanged spool secured to said fdanged outlet to form a continuation thereof, and a helical vane means disposed in said spool and operative to impart a` rapid swirling motion to materials passing therethrough from said quenching chamber.
5. In a vapor phase cracking system for the conversion of hydrocarbons, means for heating hydrocarbons, a conversion arrester having an internal quenching chamber into which the converted hydrocarbons are introduced, spray devices in said chamber, means for forcing a relatively cool hydrocarbon distillate through said spray devices to bring the distillate in a finely divided form into direct and intimate contact with said hydrocarbon vapors, means constituting a iiash chamber, transfer conduit means of reduced cross-sectional area in relation to that of said chambers for transferring hydrocarbons from the bottom of said quenching chamber to said flash chamber, helical vane. means arranged in said conduit means for imparting a rapid swirling motion to the hydrocarbons passing therethrough, vapor outlet means leading from the upper part of said ash chamber, and means diverting from the system residual hydrocarbons contained in the bottom of the flash tower.
6. In apparatus for the molecular conversion of hydrocarbons in the vapor or gaseous phase, a'converter through which vaporous hydrocarbons are passed and heated to reaction temperatures, drum structures providing separated quenching, flashing and fractionation chambers. means for passing the heated products of said converter to said quenching chamber, means for introducing into the top ofV said chamber a liquid hydrocarbon distillate in a finely divided form for direct and intimate contact with said converted products to effect a substantially instantaneous reduction in temperature of the converted products to non-reacting temperatures, means for transferring the quenched products from the bottom of said quenching chamber to the lower part of said flash chamber, vapor outlet means leading from the top o said flash chamber to the lower part of said fractionating chamber, liquid outlet Ineans for the withdrawal of a heavy residual from the bottom of said iash chamber, fractionating trays provided in said fractionating chamber in vertically superposed order, vapor outlet means in the top of said fractionating column, vapor liquid outlet means leading from the top of said fractionating chamber above said trays, liquid outlet means leading 1from said fractionating chamber intermediately of the height thereof for advancing the same as the cooling distillate into the top of said quenching chamber, thermostat means associated with said quenching chamber, and means governed automatically by said thermostat means and the operating temperatures' within said quenching chamber for increasing or diminishing the flow of the cooling distillate to said quenching chamber, whereby to maintain a constant temperature in the quenching chamber.
7. In apparatus for the molecular conversion of hydrocarbons in the vapor or gaseous phase as specified in claim 6 in combination with means for introducing steam under regulated now into the bottoms of said flash and fractionating chambers.
8. In a vapor phase system for the molecular conversion of hydrocarbons, a conversion arrester dening an enclosed quenching chamber, means for introducing converted hydrocarbons into said chamber, spraymeans in said chamber for bringing a relatively cool hydrocarbon distillate in a iinely divided form into intimate and direct Contact with the converted hydrocarbons, vapor fractionating means, a transfer conduit leading from the bottom of said quenching chamber to said iractionating means, means for withdrawing at an intermediate point from said fractionating means a quenching distillate, pipe means for advancing said quenching distillate` to the spray means in said quenching chamber, an electro-responsive valve in said pipe means for increasing and decreasing the rate of ow of the distillate through said pipe means, an operating circuit for said valve, and a switch in said circuit responsive to the internal temperatures of said quenching chamber to open and close said valve, n
9. In a process of converting hydrocarbons in the vapor phase, the steps of converting hydro-` carbons at temperatures between 1000 F'. and 1550 F., introducing the converted hydrocarbons into a conversion arrester, spraying the converted hydrocarbons with a cool hydrocarbon distillate in said arrester to Substantially instantaneously reduce the temperature of said hydrocarbons to reaction-arresting temperatures of the order of 600 F., and maintaining the arrester at a constant temperature, by regulating the rate of flow of hydrocarbon distillate thereto in response to valve means thermostatically controlled by the temperature in said arrester.
10. In a process of converting hydrocarbons in the vapor phase, the steps of converting hydrocarbone at temperatures between 1000 F. and 1550o F., introducing the converted hydrocarbons into a conversion arrester, spraying the converted hydrocarbons with a cool hydrocarbon quenching medium in said arrester to substantially instan taneously reduce the temperature of said hydrocarbons to reaction-arresting temperatures of the order of 690 F., and continuously controlling the quantity of quenching medium to be sprayed and maintaining the temperature in the arrester constant by bypassing a quantity of the said quenching medium in response to thermos-tatie control by the temperature in the arrester.
11. In a process of converting hydrocarbons in the vapor phase, the steps of arresting the conversion reactions with a quenching medium in a quenching zone maintained at a constant temperature, transferring the arrested reaction products to a flashing zone, and imparting a rapidly swirling motion to the arrested reaction products during such transfer.
12. In a vapor phase cracking system forthe conversion of hydrocarbons, the combination including a quenching chamber, said chamber being provided with a conical bottom, a spool flanged to the lower end of said conical bottom, a helical vane disposed in said spool, a tower, a conduit connecting said spool to said tower, a thermostat associated with said quenching chamber, a conduit entering said quenching chamber for providing a fluid quenching medium thereto, valve means associated with said last named conduit for controlling the flow of fluid quenching medium to said chamber, and means controlled by said thermostat operable to increase or decrease the ow of iiuid quenching medium through said valve means to the quenching chamber, whereby the temperature in said chamber is maintained constant by automatic control.
WILLIAM W. HOLLAND.
REFERENCES CITED The following references are of record in the file of this patent:
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