US 2952618 A
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Description (OCR text may contain errors)
Sept. 13, 1960 i D. D. M LAREN 2,952,618
DUAL ZONE FLUID COKING PROCESS Filed Feb. 15, 1957 TO PRODUCT RECOVERY 6 2| 'E FLUE GAS 2 ATTRITION GAS REACTORL 23L ZONE I JMJAMJJMJQ i 8; 125
3| I HEATER f 29 Donald D. MucLuren Inventor Y GM Arrorney United States Patent O DUAL ZONE FLUID COKING PROCESS Donald D. MacLaren, Scotch Plains, N.J., assignor to Esso Research and Engineering Company, a corporation of Delaware Filed Feb. 15, 1957, Ser. No. 640,517
8 Claims. (Cl. 208-149) The present invention relates to an improved process for converting heavy hydrocarbon oils into desirable lower boiling products. More particularly, it deals with a process wherein the product distribution of a thermal cracking operation is improved while utilizing a relatively simple reaction system. Specifically, it contemplates the use of large size catalytic solids as a means for both supplying heat to the conversion process and enhancing yields of more valuable products.
The desire for improving the efficiency and selectivity of converting heavy oils such as residua, crudes, asphalts and the like, to give high yields of valuable lighter products has long been felt in the'art. While direct catalytic cracking of the heavy oil has been proposed in the past, such an operation has been found to suffer from numerous difficulties. Heavier feed components tend to contaminate the catalyst particles by depositing metallic materials such as nickel or vanadium on their surfaces, thereby reducing their intrinsic activity and degrading their selectivity. Approximately one-fourth of the oil feed is converted to coke, the coke depositing on the surface of catalytic solids. In order to oxidize this large amount of coke, considerable quantities of oxidizing gas must be supplied to the regenerator, thus necessitating the use of expensive gas compression equipment. Further, the heat released in the regenerator is greatly in excess of that necessary to maintain the conversion system in thermal balance, and regenerator cooling coils are needed. Summarily, direct catalytic cracking of heavy oil feeds is too expensive a process to justify the increase in product values.
In an effort to solve the problem of treating such heavy oil feeds, the fluid coking process has been developed. In this process, the hydrocarbon oil is injected into a dense, fluidized mass of inert particles maintained at a temperature suitable for converting the feed to lighter vaporous products and coke, the coke normally depositing on the bed particles. The contact solids are usually coke granules averaging 40 to 400 microns in size, although ;and, ceramics, glass beads and the like may be readily employed. Generally, about 25% of the coke thus formed s withdrawn in the form of coating on the surface of :he contact solids, burned in a burner zone, and the solids hus heated recirculated to the coking reactor, thereby :erving to supply heat for the thermal cracking operation. the remainder of the coke produced in the process is imply withdrawn as product, finding use as boiler feed rr being subjected to further treatment for other applicaions. Since the quantity of coke circulated to the burner readily controlled in response to the heat requirements f the entire system, a relatively simple burner vessel rith a minimum of extraneous equipment may be emloyed.
However, in order to realize the advantages of the ase of heat control, and relatively inexpensive mode f operation characteristic of the fluid coking process, )me sacrifice has to be made in the product distribution btained. Compared with a reaction in a fresh bed of italytic solids, the fluid coking process produces lower valued products in terms of poorer quality gasoline, and lower yields of middle distillates and gas oil.
The present invention provides a means for obtaining the benefits of a fluid coking operation while improving the distribution of the products obtained.
More specifically, according to the present invention, large size catalytic solids are employed in a fluid coking reaction bed. The catalytic solids, readily separable from inert bed particles in response to the force of gravity, are circulated to a burner zone wherein oxidation of carbonaceous deposits serve to impart suflicient heat to the particles to enable them to supply the thermal requirements of the coking reaction. By adjusting the relative amounts and sizes of catalyst and inert solids, the quantity of coke deposited on the catalytic particles is approximately that required for oxidation to supply heat for the overall process. A portion of the circulating catalyst is treated in an attrition zone to remove contaminated surface layers, thus maintaining a relatively active and selective catalytic level in the reactor. The remaining coke produced is simply withdrawn as product in the form of coated, inert solids as is normally done in fluid coking operations. Hence, improved yields due to the presence of catalysts are realized while employing essentially the same operations and equipment as found in conventional fluid coking.
By way of clarifying nomenclature, it should be understood that the term catalytic shot is used to denote the large sized catalytic particles of the present invention. The expression seed solids refers to the inventory of small sized inert particles, normally necessary in a fluid coking reaction to maintain average bed solids size sufiiciently small so as to prevent excessive bogging and loss of fluidity.
The present invention will be more clearly understood by referring to the following description, drawing and accompanying example.
The drawing, illustrating a preferred embodiment of the present process, depicts a conversion system consisting essentially of reactor 1 and heater 2. A relatively dense turbulent conversion bed 3 is maintained in reactor 1 at a temperature of about 950 F. The bed is composed primarily of coke particles averaging 40 to 400 microns in size, although other suitable inert solids may be readily employed. Admixed with the coke particles are large sized catalytic solids, such as silica-alumina cracking catalyst, generally ranging between 1000 and 4000, preferably 2000 to 2500, microns in size. Other conventional cracking catalysts such as activated clay, silicamagnesia, or mixtures thereof, may be alternatively utilized. A supply of these catalytic shot particles is continuously circulated to reactor 1 from heater vessel 2 by means of line 22 at a catalyst to oil weight ratio of about 8 to 9. The catalysts enter the reactor at a temperature of about 1100 F. At these conditions the catalytic shot supplies requisite thermal energy for the conversion of the oil feed. The catalytic particles are preferably introduced into the lower portion of bed 3, thereby providing a space velocity of about 12 to 20 wt. of feed/hr./wt. of catalyst based on total reactor feed, about 3 to 5 wt./hr./wt. based on the portion of the feed which the shot catalyst contacts while settling.
A heavy hydrocarbon oilfeed such as a West Texas 1100 F.+residuum, preheated to a temperature of about 700 F., passes from line 4 into multiple feed nozzle 5 whencefrom it is injected into fluidized bed 3. Upon contact with the hot mixture of inert and catalytic solids, the oil feed is converted into lighter vaporous products and carbonaceous material. Gaseous products,
by means of line 10 and jets 11, 12, and 32, as will be further described, pass upwardly from the conversion bed and are withdrawn overhead. Entrained solids are removed in cyclone-separator 6, and returned to the conversion zone by means of dipleg 7, generally extendingbelow' the level of bed 3. The gases withdrawn through conduit 8 are then sent to further product recovery treatments, not shown. Generally the gases undergo scrubbing, fractionation, and other conventional processing steps, to recover product streams of gasoline, light and heavy gasoils and other valuable materials.
About 20 to 30% by weight of the oil feed is converted to coke, approximately one-fourth of which is deposited on the surface of the large size shot catalyst, the remaining portion coating the inert contact solids. Shot catalysts, thus coated with carbon, settles downwardly to form bed 9.in the lower portion of the reactor. Fluidizing steam is advantageously supplied upwardly through bed 9 by means of line 10 for a number of reasons. First, it serves to strip coke particles from between the large catalytic shot particles. Second, it strips occluded hydrocarbons from the catalyst particles. Third, the steam is substantially uniformly distributed'in the lower portion of the reactor prior to fluidizing the reaction zone. tially that quantity of coke deposited on the inert solids, is withdrawn by line 14 after passing through zone 13 where it is stripped with steam from line 32. Since the inert contact solids are coke granules, the coke prpduct is obtained as a relatively pure carbon material ofi'ering comparatively few problems with regards to the removal of contaminants.
To reduce the size of the coke particles, high velocity steam jets 11 and 12 effect attrition of the coke particles larger than about 250-300 microns to produce particles ranging from 75-250 microns. As will be appreciated by. those skilled in the art, the necessary seed coke for the conversion process is thus supplied. While a jet gas attritor has been shown as a preferred mode for supplying seed coke, a grinder or similar conventional means may be readily employed.
, Shot catalyst is removed from the reactor through line 15 and conveyed by means of inclined conduit 17 and.
vertical riser 18 into heater vessel 2. Air, injected into the conveying passageway by means of lines 16 and 19, serves to propel the shot catalyst, and additionally acts asa secondary source of oxygen for the burning operation. While a fluid bed heater is shown, a transfer-line burner, or a moving bed burner may be alternatively utilized.
Requisite air or other oxygen-containing gas for combusting the carbonaceous material deposited upon the shot catalyst particles is primarily supplied through line 20. Solids, thus heated by combustion to a temperature of about 1100 F., are withdrawn and returned ,to the conversion bed through line 22. Propellant gas such as steam or nitrogen is normally injected by line 23 to aid in circulating the relatively large sized particles back to the coking reactor. Gaseous products of combustion are removed from the heater by line 21. The unit can be maintained in heat balance by varying the circulation'rate of the shot catalyst. For example, if more heat is required, the catalyst to oil ratio 'is increased.
This'increase in shot catalyst to the reactor increases the overall catalyst holdup, thereby depositing a greater amount of carbon on'the catalyst and thus supplying the added fuel needed in the burner. However, it maybe desirable under certain conditions of operation'to supply an extraneous fuel to the'combustion zone? In order to maintain the'activity and selectivity level of the catalyst in the -conversion zone 3, normally a portion of the circulating shot catalyst is subjected to treatment for the removal of its more contaminated surface'layers. While the drawing illustrates'the use of a jet 'a'ttritor 25 operating in conjunction with heater 2, otherfmeans well known in the art, such as a ball mill type grinder, for accomplishing surface layer removal should be understood as falling within the scope of the present invention. Similarly, such a step may be employed at other points in the overall conversion process. As shown, catalyst particles pass from heater 2 through line 24 to attrition zone '25. A high velocity gas jet, preferably heated steam, is injected by line 27 and serves to wear away the outer layers off the catalytic solids thereby exposing fresh catalytic contacting surface. The openings of grid 26 are adjusted in size topermit the downflow of removed contaminants and catalytic solids less than 1000 microns in diameter, such particles passing out of the system through exit 29. Fines, entrained in expended attrition gas, are withdrawn by line 28.
In order to maintain a relatively constant supply of catalytic solids, a fairly small amount of fresh shot catalyst may be added by line 31' into the stream of treated particles circulated back to heater 2 through line 30. Of course, unreacted catalysts may be introduced at other points in the process.
Thus, oil feed is subjected to a conversion treatment intermediate in nature between fluid coking and catalytic I cracking.
The following summary illustrates the improved product distribution obtained by the present process when compared with conventional fluid coking operations.
The feed in both cases is an l F.+West Texas residuum, having a Conradson carbon content of 24.7, and an A.P.I. gravity of 5.4.
Table 1 Products Conventional Example Fluid Coking 0 Wt. Percent 9. 7 8.5 C Vol. Percent 3. 6 4. 2 05-430 F., Vol. Percent 19. 5 20.2 430 F. to 650 F. Gas Oil, Vol. Percent--- 14.1 15. 6 650+ F. Gas Oil, Vol. Pcrcent. 36. 9 37. 7 Coke, Wt. Percent 27. 2 24.4 Product Qualities:
C5 to 430 F. Research Clear Octane-.. 74. 5 79 430 F. to 650 API 27. 7 27. 3
As shown above, the present invention produces less gas and coke (low valued products) and more gasoline and gas oil of equal or better quality (high valued products) than conventional fluid coking.
The table below presents a compilation of pertinent ranges of conditions with regards to the process described:
While the above description has been limited to the use of a dense fluidized bed as the conversion zone, it should beunderstcod that the application of large sized catalytic solids may be readily extended to dilute phase reaction systems such as a transfer line reactor. Additionally, it may be desirable to reactivate the surfaces, of the catalytic particles and provide seed coke for ther reaction bed in a' single attrition system. Other modifications, apparent to those skilled in. the art, may be applied to the system described without departing from the spirit'of the present invention. V i
By using shot catalyst as'the'primary means for directly supplying 'heat'to a fluid coking process, numerous advantages are realized. Product quality and distribution are improved while utilizing conventional equipment and coking procedures. The relatively large size of the heat-carrying catalytic particles provides for easy separation from inert bed solids. Additionally, contaminated surface layers may be readily removed while still maintaining a reasonably large catalytic surface area.
Having described the invention what is sought to be protected by Letters Patent is succinctly set forth in the following claims.
What is claimed is:
1. In a hydrocarbon conversion process wherein a residual hydrocarbon oil is introduced into a dense turbulent fluidized bed of inert particles averaging 40 to 400 microns in size and maintained in a conversion zone at a temperature in the range of 900 to 1200 F. for cracking said oil to vapors and carbonaceous material which deposits on said inert particles and solid cracking metal oxide-containing catalyst particles to be mentioned later on herein and wherein fluidizing gas passes upwardly through said conversion zone to maintain said inert particles in a dense turbulent fluidized condition and wherein said vapors pass upwardly and are withdrawn overhead, the improvement which comprises introducing solid cracking metal oxide containing catalyst particles heated to a higher temperature than said inert solids into the lower portion of said dense turbulent fluidized bed for supplying heat and catalyst for cracking said oil, said solid cracking catalyst particles being larger than said inert particles and being in the range between about 1000 and 4000 microns in size, said solid cracking catalyst particles contacting said inert solids in the lower portion of said dense fluidized bed of inert particles in heat exchange relationship and settling downwardly therethrough to form a bed of solid cracking catayst particles below said inert particles in the bottom of said conversion zone, passing said solid cracking catalyst particles from said bed of solid cracking catalytic particles to a regeneration zone to burn ofl carbonaceous leposits and to heat said solid cracking catalyst particles, and returning regenerated solid cracking catalyst partizles thus heated to the lower portion of said fluidized bed )f inert solids so as to supply necessary heat and solid :racking catalyst particles for converting said residual lydrocarbon oil introduced into said fluidized bed of nert solids.
2. A process according to claim 1 which includes passlg a portion of the regenerated solid cracking catalyst articles to an attrition zone for removing the deactivatlg contaminants from the surface of the solid cracking atalyst particles and returning the thus reactivated solid racking catalyst particles to said coking zone.
3. The process of claim 1 wherein said solid cracking rtalyst particles are selected from the group consisting E activated clay, silica-alumina, silica-magnesia, and mixlres thereof.
4. A method according to claim 1 wherein the inert uticles comprise coke particles and coke particles are ithdrawn as product from the upper portion of said :nse fluidized bed above the region of introduction of said larger solid cracking catalyst particles into said fluidized bed.
5. The process of claim 1, which further comprises passing steam upwardly through the bed of solid cracking catalyst particles in the lower portion of the coking zone, the steam being uniformly distributed for entry into the upper portions of said coking zone while stripping occluded hydrocarbons and admixed inert particles from said solid cracking catalyst particles.
6. An improved hydrocarbon oil conversion process for thermally and catalytically cracking residual hydrocarbon oil which comprises injecting a residual oil feed into a cracking and coking zone containing a fluidized bed of particulate inert solids averaging 40 to 400 microns in size and larger size solid cracking catalyst particles ranging from 1000 to 4000 microns in size maintained at a temperature in the range of about 900 to 1200 F. to convert the residual oil feed thermally and catalytically to gaseous products and coke which deposits on said bed inert and cracking catalyst particles, passing a fluidizing gas upwardly through said fluidized bed at a velocity sulficient to maintain a turbulent fluidized bed of inert and cracking catalyst particles while permitting said larger solid cracking catalyst particles to settle down into the lower portion of said cracking and coking zone, withdrawing and circulating a portion of said cracking catalyst particles to a regeneration zone to burn ofi coke deposits and heat the solid cracking catalyst particles to a temperature to 400 F. hotter than said fluidized bed, and recycling the regenerated solid cracking catalyst particles thus heated to said cracking and coking zone to supply thermal energy for the thermal and catalytic conversion process.
7. The process of claim 6 which further comprises passing a portion of said withdrawn regenerated solid cracking catalyst particles to an attrition zone to remove contaminated outside layers from the surface of said solid cracking catalyst particles and to expose relatively fresh catalytic surfaces and circulating thus reactivated solid cracking catalyst particles back to said cracking and coking zone.
8. The process of claim 6 which further comprises passing a portion of said withdrawn cracking catalyst particles to an attrition zone wherein contaminated outside solids layers are removed and relatively fresh catalytic surfaces exposed, and circulating thus reactivated cracking catalyst particles back to said coking zone.
References Cited in the file of this patent