US 2874113 A
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B. 1. SMITH ET AL 2,874,113
PRODUCTS SEPARATING SYSTEM Filed Dec. 16, 1953 Primary Coker Product Feb. 17, 1959 a, w I l W e vl l 3 n 5 v .w 0 b B 5 9 F w n u s m u u b m I II M W .1. "I .m H 1 n I IV\. f u H 5 9 r 1 .IIHHHHHHUHH HHHI 4 O C d U n d 0 O a a r S n m V. W. m 5 w m I 5 9 9 3 w o w 7 3 3 LI d. s r d e w w S 3 M .m m 3 3 G W a A m u s 0 M .l G M v S I\ l E E 0 PW m m m T 6 3m 054 222 C 1 w a u M Q W I Solids (Product Coke) Air (Etc) Propellinq 7 6| 2| Gus 'INVENTOQS Brook [SI/viii; aI/ zl EdwardDBostow BY *ATTORNE Y Probelling Gcls United W Patent 6 PRODUCTS'SEPARATING SYSTEM Brook I. Smith, Elizabeth, and Edward D. Boston, Westfield, N. J., assignors to EssoResear'ch and Engineering Company, a corporation of Delaware Thepresent invention relates to an improved vapor products separating system and particularly to an improved system for separating. hydrocarbon and similar' vapors or gases from other 'productsof thermal reactionprocesses. The invention has particular application to the separation of primary, or superior, products-from secondarypor inferior, products resulting from thermal cracking of heavy hydrocarbonoils. The invention is especially applicable to the'fse'paration of primary vapors and gases froma high'temperature oil cokingoperation from secondary products of'lower quality, although it is not expressly limited thereto.
In the prior artg'it' has been known for some time that certain materials 'such' as medium or heavy hydrocarbon oils and related organic feed stocks'can be converted by thermal cracking to low molecular weight materials of considerabiygreater value thanthe feed. For-example, a heavy residual petroleum oil, ofrelativ'elylow economic value, may be converted by"cra'ckingat moderately hightemperatures, etg. 900 to 1100" F. of so, into motor fuel and gas oil. At higher"temperatures (and shorter contact times) the samefeed'may be converted into starting materials for manyiuseful chemicals; Thus at temperatures of 1200 to 1500 Fior'so, heavy residual petroleum oils may be convertedto ethylene, acetylene, propylene, butylenes'," butadiene, isoprene and benzene, along with other products. These low molecular weight unsaturates and related materials are of considerable value as starting materials in the manufacture ofsynthetic fibers, plastics, alcohols, ketones, aldehydes, and many other useful products of modern chemistry. Hence this general type of conversion 'of heavy petroleum hy'dr'ocarbon oils is commonly "referred'to as high temperature cracking or coking for chemicals. The processobviou'slyis applicable'to coal tars, pitches, resins," shale oils and other organicresidues, in some'degreel In high' temperature cracking or coking, orin destructive distillations of organic materials, it is frequently of considerable importance to carry out the thermal reaction to an optimum point and terminate the reaction abruptly when that point is reached. This'isparticularly trueiof high temperature coking of heavy oils and pitches to produce low molecular weight olefins 'and' related prod-' ucts. At the temperatures necessaryto produce these products in good yields," they are extr'emelyreactive. They tend rapidly to polymerize, alkylate; or otherwise react with each other and with some other materials with which they may come in contact. An object of the present invention is to facilitate the abrupt termination or quenching ofreaction when optimum products have been produced. p}
A preferred method of effecting thermal conversion of heavy oils, pitches, tars, etc., involves contact thereof with preheated solid particles. A mass of preheatedsolid particles of a size which can be fluidized, carried, and lifted by a gasiform stream is a particularly satisfactory thermal contacting medium, as is well known in the art. For cokingheavyoils and "pitchesat moderately high 2,874,113 1 Patented. Feb. 17, 1959 temperatures, a fluidized bed of solids with which the feed is contacted'in finely divided from is very satisfactory. For higher temperatures, for production of substantial proportions of olefins (e. g. acetylene, ethylene, etc.) and in other cases where contact times must be very short, the use of a transfer line or mobile disperse phase solids reactor is highly advantageous. In such a system, the products to be converted are brought into contact momentarily with a rapidly moving stream of hot solids propelled by and usually suspended in a propellant gas stream; At the end of the contact period, the solids must 'besepar'ated quickly from the products to terminate the thermal conversion. It is usually desirable to quench the products immediately after separation, i. e. to cool them to a temperature where they cease to react and form degradation products. An object of the present invention is to facilitate such quick separation and quenching.
The most common'and frequently the most efficient and satisfactory manner of separatingheat carrying particulate solids from gases and vapors is to pass them through a centrifugal separator such as a cyclone. The cyclone may be of the conventional commercial type or it may be of a special quick separation type such as shown, for example, in an application ofMatheson, Serial No. 323,972, filed December 4, 1952, now abandoned. While a substantial part of the vaporous or gaseous conversion products may be separated very quickly in a centrifugal separator, there is always some occlusion and entrapment inthe solids. Also, the reaction of feed that is only partially converted continues through the separator and into the solids line leading. out of the separator. The secondary productsthus occluded, trapped, and converted are usuallydegraded to a substantial extent by reason of their'relatively prolonged heating time. A further and particular object of the present inention is to facilitate thesepa'ration of primary products of better quality from these secondary'products of relatively inferior quality.
Although every effort may be made, and usually is, to disperse the feed evenly'ont'o or among the heat carrying solidparticles, some particles always pick up more feed, e. g. a heavier coating. of oil, than others. As a result,
some solid particles are still relatively moist or beara though'primary-products should be-drawn off after an optimum contact time, some of the solids must go on giving off heat and converting the partially coked feed to'sorne sort of product after the primary products have been withdrawn. It is desirableto prevent substantial admixture of these secondary and inferior products-with the primary products which ordinarily are of higher quality. Such is'another object of the invention. In the preferred embodiment, this 'is accomplished by establishing a gas or vapor seal or barrier between the primary and secondary products. The'solids' continue to dry and to vaporize or crack the adherent oil, but the long contact time products, though often useful forother purposes, are desirably separated from the primary products Therefore, they are sealed against reverse flow through the separator and are separately withdrawn.
The above features and objects of the invention and others not expressly mentioned will be more fully and clearly understood by reference to a specific embodiment of the invention. For this purpose, reference will next be made to the attached drawing showing, somewhat diagrammatically, an apparatus for carrying out the process of the invention.
Atransfer line reactor 11 leads from a burner or heater 13'to a gas-solids separator 15' Hot particulate solids, which meet suitable particle size for suspension in a gas stream, such as sand, metal shot or other metal particles, Carborundum, alumina, silica, glass beads, ceramics, etc., or coke particles derived from coal or petroleum, or even spent catalyst particles may be used. These serve as the heat carrying media. The particles most suitable for entrainment in a gasiform stream through the reactor 11, are usually between about 40 and 500 microns average particle diameter but may be as small as 20 or as large as about 2000 microns. Coke particles produced in the process are commonly preferred, although the invention is not limited thereto. The particles preferably are substantially non-catalytic for high temperature coking for chemicals.
The oil or like feed to be converted is fed into the reactor through a line 17, preferably being atomized by introduction through a plurality of nozzles 19 or by introduction at the throat of a venturi in the stream of suspended solids to achieve good distribution. Steam may be introduced with the feed if desired. The upflowing hot solid particles, preferably preheated to a temperature of l250 to 1600 F. or more, are propelled by steam, hydrocarbon gas or other inert gas, introduced through lines 21, 23, 25 in such volume as to carry the solids in the desired degree of dispersion, e. g. at a density of 0.1 to 20 pounds per cubic foot. Steam is preferably used. The reactor temperature may be 1200-l600 F., preferably l3001400 F. The reactor pressure may vary from atmospheric to 50 p. s. i. g. or so, but is preferably 5 to 15 p. s. i. g. The steam used may vary from 5 to 100% by weight of feed, preferably 20 to The velocity of the solids-laden gasiform fluid stream through reactor 11 is preferably at least 8 feet per second and may be as much as 100 feet per second or more. The oil spray is vaporized and rapidly cracked to the desired low molecular weight unsaturates. The vapors so produced are quickly separated from the solids in separator 15. The total contact time in reactor 11 and separator 15 is 0.001 to about 1 second, preferably 0.05 to about 0.5 second.
The primary vapor products separated in centrifugal separator or cyclone 15 are taken upwardly through an outlet line 27 and are immediately quenched by injecting into line 27 a stream of relatively cooler liquid such as water or oil through a line 29. The oil feed itself may be used as quenching medium, if desired, being recycled to the coking line later. Cool solids, such as coke particles, may be used in lieu of or with the liquid coolant. In this case, the quenching material may be entrained in the product and separated therefrom in a later separation stage, not shown. Some of the quenching material may flow down line 27, if desired, to join the downflowing separated solids.
The separated solids pass downwardly from the separator through a constricted passageway 31 of the vena contracta or venturi type into a drying zone 33 of larger cross-section. Here the occluded gases and vapors and the later cracked products, not separated in the primary stage, are stripped by an upflowing stream of stripping fluid such as steam or other inert gas introduced through a line 35. The stripped and spent solids, under control of a valve 37, are returned through a reverse bend 39 to the burner or reheater 13, previously mentioned.
The burner or reheater 13 is shown to be of the fluid bed type for purposes of illustration. The solids, e. g. coke particles, which have grown by accretion of coke in the coking operation, flow upwardly through inlet line 41, under the propelling and/or buoyant effect of a lifting gas such as air, introduced through one or more lines 43, 45. A bafile member 47 spreads out and distributes the solids entering the burner bed. A fluidizing and/ or burning gas, such as air or air plus a fuel, is introduced through inlet 49 and grid 51 at the bottom of the burner or reheater to fluidize and burn or reheat the solids. When their temperature has been raised sufliciently, the solids overflow a partition member 53 defining a separating zone 55, from which flue gases separate and pass upwardly.
I The downflowing solids may be stripped of occluded combustion gases, if desired, by a suitable stripping fluid introduced through a line 57. The reheated solids return to the transfer line reactor through a standpipe 59 and reverse bends 61, 63, under the propelling elTect of gas introduced through lines 21, 23, 25, as previously mentioned.
A branch line 65 is provided for withdrawing hot product coke from standpipe 59, under control of valves 67, 69. Heat may be recovered from the withdrawn product by passing it through a suitable heat exchanger, not shown. If desired, product coke also may be withdrawn at a lower temperature from the outlet line 39 of the solids dryer through a branch line 71, under control of a valve 73.
Combustion gas may be withdrawn from burner vessel 13 through a gas-solids separator 75 which may be of the conventional cyclone type. Separated solids are returned to the bed through solids return line 77. The flue gases pass overhead through outlet line 79.
The quantity of coke produced in most coking processes is much greater than is needed to supply the process heat requirements. If desired, a heat exchange coil 81 may be placed in the fluid bed 83 in the burner vessel to generate steam or to provide heat for other uses, in which case a larger portion or all of the coke product may be burned. Where coke values are low, this may be very desirable.
The secondary products accompanying the solids from separator 15 and those produced in drying the solids in the solids drying zone 33 are withdrawn through a secondary product line 85. The respective pressures in separator 15 and dryer 33 are kept fairly well in balance by a control valve 87 operated by a differential pressure controller 89 connected thereto by a control line 91. The controller 89 is also connected respectively to the separator and the upper part of the solids drying zone by leads 93, 95 which terminate in pressure sensing devices 97, 99.
In order to maintain a clean separation of primary and secondary products, a separating gas that is inert and is easily separated, when condensed, from injected at the vena contracta or through a line 101. The preferred separating gas usually is steam, although light hydrocarbon gases such as ethane or propane may be used if desired. The quantity is regulated by a variable valve 103 and is preferably just enough to maintain a seal between vapors in the separator 15 and vapors in the dryer 33. Furthermore the velocity of the upfiowing separating gas through the constricted passageway 31 is held at a value which will allow the separated solids to pass downwardly through the constricted passageway 31, e. g. a velocity about 0.5 feet per second or less, preferably about 0.1 feet per second. The dilferential vapor or gas pressure between separator and drying zone is kept between about 5 and +5 inches of water, a differential not greater than :1 inch being preferred.
It will be understood that the fluid bed burner may be replaced by a fluidized transfer line type burner, if desired. For instance, at temperatures above about 1400 F., a transfer line burner could be used to hold residence time and carbon monoxide formation to a minimum. The reactor may, in some cases, be replaced by a fluid bed reactor, although for very short contact times this is not very satisfactory, a transfer line system being preferable. Various other arrangements and modifications may be made by those skilled in the art without departing from the spirit and purpose of the invention. It will be understood that the terms vapor and gas or gasiform material, as used in the claims, are synonymous, since the primary and secondary products, and the sealing gas or vapor, may be either gas or vapor.
What is claimed is:
l. The process of converting a heavy hydrocarbon oil to low molecular weight products including unsaturates and aromatics, having a tendency to degenerate at high the products, is the venturi constriction,
5 temperatures, and coke, which comprises contacting said oil momentarily with hot particulate solids in the disperse phase at a temperature of about l200 to 1600 F. for a period of time in the range of 0.001 to 1 second to form primary products in vapor form and coke, quickly separating in a primary separation stage the primary vapors from said solids and coke while some further conversion of oil is still taking place on said solids to form secondary products, quenching and separately recovering the primary products immediately to prevent degeneration, quickly passing the separated solids downwardly from said primary separation stage through a passage having a sharply constricted section therein into a solids drying zone where said further conversion is completed to form said secondary products, establishing a vapor seal in said sharply constricted section of said passage between said primary and said secondary products by introducing a sealing gas into said constricted section by injection of an inert gas which has a maximum upflow velocity of about 0.5 ft./sec. so as to permit the separated solids to flow downwardly and to prevent substantial mixture of the secondary products with the primary vapor products while keeping the pressure in the 6 1 primary separating stage and the drying zone substantially in balance and separately recovering secondary products.
2. Process according to claim 1 wherein the pressure differential is between -1 and +1 inch of water.
3. Process according to claim 1 wherein the particulate solids are coke particles.
4. Process according to claim 1 wherein the vapor seal is a steam seal.
5. Process according'to claim 1 wherein the vapor seal is a low molecular weight hydrocarbon seal.
References Cited in the file of this patent UNITED STATES PATENTS 1,825,707 Wagner Oct. 6, 1931 2,443,180 Bergstrom June 15, 1948 2,489,925 Omwake Nov. 29, 1949 2,543,884 Weikart Mar. 6, 1951 2,560,356 Liedholm July 10, 1951 2,587,554 Weikart Feb. 26, 1952 2,598,058 Hunter May 27, 1952 2,772,225 Bergstrom et a1. Nov. 27, 1956