US2951806A - Catalytic conversion of hydrocarbons in a moving bed reaction zone with the addition of steam to control reaction temperatures - Google Patents

Description

F. R. WALSER 9 1, N OF HYDROCARBONS IN A MOVING BED Sept. 6, 1960 CATALYTIC CONVERSIO REACTION ZONE] WITH THE ADDITION OF STEAM TO CONTROL REACTION TEMPERATURES Filed March 9, 1956 f 5 7 Z5 av av w am NW 66 4 d W INVENTOR. Freaewwk If. Wilder OLl/I/G tired tea Frederick R. Walser, Drexel Hill, Pa., assignor to Houdry Process Corporation, Wilmington, Del., a corporation of Delaware Filed Mar. 9, 1956, Ser. No. 570,459

4 Claims. (Cl. 208-167) This invention relates to a process for the catalytic conversion of hydrocarbon charge stocks to produce high-octane gasoline and light distillate fuels, and is particularly directed to improvements in the so-called moving-bed type of process wherein hot granular catalyst having an average diameter of about 2-13 mm. is continuously circulated as a compact moving mass through a treating system having alternate stages of hydrocarbon conversion and catalyst regeneration.

Typical of the processes to which the invention may advantageously be applied are those described in an article, entitled Houdn'fiowNew Design in Catalytic Cracking, appearing in the January 13, 1949, issue of The Oil and Gas Journal, and in an article, entitled How Houdresid Works on Heavy Stocks, appearing in the September 1955 issue of Petroleum Refiner.

Each of the aforementioned processes normally requires a cooling system to remove a portion of the heat evolved in the regeneration zone through the combustion of coke formed on the catalyst in the preceding conversion stage. In addition, steam is generally introduced into the conversion zone to attain the optimum conditions for cracking. However, substantially greater quantities of steam are usually employed in the cracking zone when the charge stock comprises heavy hydrocarbons, such as residuum cuts ranging from crude tower bottoms to vacuum bottoms, or comprises other heavy hydrocarbons of whatever nature and from whatever source obtained.

With respect to both heat removal from the overall system and steam addition in the conversion or cracking zone, the requirements are substantially higher in the processing of heavy charge stocks than they are in the processing of lighter hydrocarbon materials.

Although it is possible to overcome the problem of heat removal or of overheating within the system in vari ous ways, the usual commercial practice embodies: the use of indirect heat exchange between the catalyst and a circulating fluid coolant, as by means of cooling coils located within the mass of catalyst in the zone where the removal of heat is desired. Such cooling systems are complicated in structure and expensive to fabricate, and present a problem in the way of maintenance and re placement. For this reason, any means by which heat may be removed from the system as a whole without the use of cooling coils, whether it be in the catalyst regeneration section or in the hydrocarbon treating section, is potentially advantageous.

While it is recognized that at least part of the cooling requirement in the system can be taken care of by increasing the catalyst circulation rate or by increasing the throughput of relatively cool regenerating gas, or by decreasing the oxygen content of the regenerating gas, etc., it is not always practicable to effect the desired cooling in such manner, or to employ such methods for the purpose of maintaining a temperature control.

In each of the hydrocarbon conversion processes described in the aforementioned articles provision is made assist for introducing'liquid hydrocarbons into the reaction zone in a manner which Will effect a substantially uniform distribution of the liquid throughout the catalyst bed. To obtain the optimum contact between the liquid hydrocarbons and the granular catalyst, a portion of the total catalyst entering the reaction chamber is introduced thereto as a free-falling, circumferentially-complete curtain of catalyst. One or more annular curtains may be provided, and the arrangement is such as to deposit the liquid-coated catalyst particles in a symmetrical pattern upon the surface of the bed.

The liquid hydrocarbons are introduced into the reaction chamber at a location within the falling curtain of catalyst, and liquid feed means are provided so that the liquid may be discharged as an atomized liquid spray directed outwardly and downwardly from :a central location within said annular curtain, so as to intercept the curtain around its entire inner periphery. Method and means for effecting such contact between the liquid hydrocarbons and the catalyst are disclosed in US. patents to Savage, 2,548,912, and to Evans, 2,553,561, each of which is typical of the methods generally employed. Vaporous hydrocarbon materials or steam may accompany the liquid hydrocarbon charge or maybe introduced independently into the reaction chamber. Where the steam requirement in the reactor is relatively high, as where heavy hydrocarbons are being processed, separate steam introduction means may be provided in the reaction chamber.

In accordance with the invention, all or at least a substantial part of the cooling requirement. of the system may be satisfied by the direct introduction of water intosystem, so that a portion of the heat may be utilized for the vaporization of the water. Whether such water introduction is eifected within the kiln or within the reactor it serves to lessen, if not eliminate, the cooling coil requirement of the kiln. Where the nature of the charge stock is such that the beneficial effect of high steam concentration is desired in the reaction zone, such process steam requirement also may be satisfied by the injection of water into the reaction chamber with the purpose of generating the steam through contact between the water and the hot regenerated catalyst particles.

Thus, water introduction into the reactor serves a dual function in that it satisfies a portion of the cooling requirement While at the same time providing the desired process steam in the reaction zone.

In accordance with a preferred embodiment of the invention, water is introduced in the form of a fine mist into the reaction chamber, and is so directed as to contact the falling curtain of catalyst before the latter is contacted by the liquid hydrocarbons. Extremely fine spray or fog nozzles may be provided for this purpose, and they may be disposed within or without the falling catalyst curtain. Preferably they are located at: an elevation above the elevation of liquid hydrocarbon introduction.

In another preferred embodiment of the invention, water is similarly introduced into the air inlet conduit or duct-work associated with the regenerator or kiln. Such water is vaporized While being conveyed by the air stream through the air introduction system into the catalyst bed comprising the regenerating zone.

For a fuller understanding of the nature of the invention reference may be had to the copending application of George A. Mills, Serial No. 421,226, filed on April 6, 1954, now US. Patent No. 2,914,459. The advantages of the invention will be apparent from a consideration of the following specification and claims taken in connection with the accompanying drawings forming a part of this application, in which:

. Fig. 1 is a fragmentary section, in elevation, showing the upper end portion ofa typical reactor, and disclosing one embodiment of the means for introducing cooling water into the reaction zone;

Fig. 2 is a similar fragmentary section showing another embodiment of the means for introducing cooling water into the reaction zone; and

Fig. 3 is a fragmentary section of a kiln of known design, disclosing the means for introducing cooling water as a fine spray into the air inlet system of the kiln.

Fig. 1 shows the upper end portionof a catalytic reactor comprising a cylindrical vessel '11. Near its upper end the vessel 11 is provided with a tube-sheet 12 which divides the upper region of the unit into an upper catalyst distributing chamber 13 and a lower reaction chamber or zone 14. Only the upper end portion of the reaction chamber 14 is shown in the drawing, since illustration of the remaining portion thereof is not considered essential for a complete understanding of the invention. Catalyst supplied, for example, from the disengager of a pneumatic lift, or from the discharge chute of a mechanical bucket elevator, is introduced into the distributing chamber 13 through conduit 10. The catalyst is deposited upon the surface of a compact moving bed 15 of catalyst supported .by the tube-sheet 12. The peripheral area of the tube-sheet 12 is provided with a circumferential row of elongated downcomers 16 which continuously withraw catalyst from the peripheral region of the bed 15 and deposit the same directly upon the surface of a compact moving bed 17 of catalyst maintained within the reaction zone 14. In known manner, downcomers 16 serve to maintain the bed 17 at the desired level Within the reaction chamber 14.

Additional catalyst is continuously withdrawn from the central lower region of distributor bed 15 through suitable discharge means, such as a circumferential row of short closely-spaced nipples 18, adapted to discharge the withdrawn catalyst in the form of a circumferentiallycomplete free-falling curtain of catalyst 19.

A fluid feeding device 21 supported in tube-sheet 12 is adapted to introduce liquid or mixed-phase charge stock and Water into the reactor. It comprises a housing internally partitioned to provide upper chamber 22 and lower chamber 23. Charge stock enters chamber 22 through conduit 24. The charge is conveyed by conduit 25 from chamber 22, through chamber 23, into reaction chamber 14 where it is discharged through liquid feed nozzle 26 within the annular catalyst curtain 19. The liquid component of the hydrocarbon charge stock contacts the hot catalyst in the falling curtain and is partially vaporized. The vunvaporized portion coats the catalyst particles and is carried'thereby to the surface of the reactor bed 17.

Cooling Water is introduced into chamber 23 through the sides of vessel 11 and housing 21 by conduit 27. The lower end portion of member 21 is provided with a circumferential row of side openings 28 through which steam, generated within conduit 27 and chamber 23 by indirect heat exchange with the hot catalyst in bed 15, the hot charge stock flowing through conduit 25 and the reaction zone 14, is discharged as an outwardly-directed stream directed toward the entire inner peripheral surface of the fallingcurtain 19 as it descends from the short nipples 18.

The cool water is converted to steam either by indirect heat exchange while flowing through conduit 27 and chamber 23, or by direct heat exchange with the hot catalyst. The heat utilized for such vaporization substantially lowers the cooling requirement in the kiln, and may result in the elimination of some or all of the cooling coils.

In the embodiment shown in Fig. 2 the liquid or mixedphase charge stock is introduced through connected conduits 31 and 32 and feed nozzle 33 to the space within the annular falling curtain of catalyst 19. The cooling water may be supplied to the reaction zone through a plurality of conduits 34 having their discharge ends loatomized spray of water.

cated in a circle concentrically surrounding the falling curtain of catalyst 19. The lower ends of conduits 34 are arranged to discharge the water and/or steam inwardly toward the axis of the vessel so as to be intercepted by the outer peripheral surface of the falling curtain 15.

Thus, whereas the modification of Pig. 1 discloses the introduction of both charge stock and process steam from locations within the falling curtain 19, the modification of Fig. 2 discloses charge stock introduction from within the curtain and steam introduction outside the curtain. While the foregoing means for introducing cooling water into the reaction zone and for effecting contact between the liquid charge and the catalyst are considered to be especially desirable, it is contemplated that other arrangements for introducin cooling water and charge stock, within the broad scope of the invention, will in some cases be more suitable, so that the broad invention is 'to be considered as limited to the specific means illustrated in Figs. 1 and 2. In any case, however, it is preferred that the water contact the catalyst before the latter is contacted by the liquid hydrocarbon charge.

Fig. 3 discloses an arrangement of apparatus whereby all or at least a substantial portion of the cooling require ment of the kiln may be provided by direct injection of cooling Water in the form of a finely-divided spray or mist. The drawing illustrates a fragmentary portion of a two stage countercurrent-flow regenerator or kiln which, for the purpose of illustrating the application of the invention, may be considered as being contained within a lower portion of the cylindrical vessel 11. In other words, either reactor portion illustrated in Figs. 1 and 2 together with the portion of the kiln illustrated in Fig. 3 maybe considered as parts of a single catalytic cracking unit having superimposed reaction and regeneration zones. Such arrangement being known to the art, further illustration is not considered necessary for an adequate understanding of the invention. In Fig. 3 the kiln portion of vessel 11 is provided with spaced tube-sheets 35 and 36 which separate the kiln into first and second regeneration stages containing compact moving beds of catalyst 37 and 38, respectively, undergoing regeneration by combustion in the presence of oxygen-containing gas, such as air.

Within the space between the tube-sheets 35 and 36 a relatively-shallow compact moving bed of catalyst 39 is maintained. Bed 39 only partially fills the space between the tube-sheets, so that a solids-free space or plenum 31 is provided above the surface of the bed 39. The catalyst is passed from thebottom of bed 1 L0 the surface of'bed 39 and from the bottom of bed 3% to the surface of bed 38 through successive levels of nipples or downcomers 42 and 43, respectively.

Tube-sheet 35 is provided also with a plurality of nipples 44 which have their lower ends located at a highlevel within the plenum 41 and their upper endsiocated within the lower region of bed 37 at a level above the uppermost ends of nipples 42. Nipples 44, singly or in rows, may be provided with inverted caps or channel members 45 which are rigidly supported in known manner above the upper ends of the nipples so as to provide a means for introducing air into the lower region of bed 37. A stream of regeneration air is introduced into the plenum 41 through conduit 46 supplied under pressure from a source, not shown. Within the conduit as and at a 10c"- tion near the point of introduction to the plenum 41 there is located a spray or fog nozzle 47 which is supplied with cooling water from conduit 46 extending through the wall of conduit 45. The nozzle 47 is arranged to discharge a fine mist-like spray of cooling water into the stream of regeneration air in the direction of air flow, so that the stream of air entering the plenum d1 carries with it the The moisture-laden regeneration air passes upwardly through nipples 44 into the catalyst-free spaces beneath the members 45 and passes therefrom into the lower region of the bed 37. While a portion of the water will be vaporized in passing through the plenum 41 and the nipples 44, the major portion of the vaporization is expected to occur Within the region of bed 37 surrounding and directly above the members 45, which region forms a cooling zone within the bed 37. The air and the steam formed by the vaporization of the water pass countercurrently through the descending catalyst bed 37 to a region of disengagement at the upper end of the bed, from which the gaseous regeneration products are discharged.

In similar manner, air and cooling water is introduced at the bottom of bed 38 so as to flow countercurrently to the catalyst in the second regeneration stage. The gaseous regeneration products are disengaged from the catalyst at the surface of bed 38 and collected within the plenum 49 formed between the surface of the bed and the tubesheet 36. The disengaged gaseous material, or flue gas, is discharged from plenum 49 through outlet conduit 51.

In the embodiments of the invention illustrated in Figs. 1 and 2, in which the treating zone is the reactor, the increased partial pressure of steam is beneficial to the conversion of the heavy hydrocarbons and the steam may therefore be considered as process steam, even though it performs the also important function of cooling the catalyst. In the embodiment of Fig. 3, however, the increased partial pressure of steam correspondingly decreases the partial pressure of the combustion-supporting gas, such as air, which, of itself and additional to the cooling provided by the vaporization of the water, tends to keep down the temperature of the catalyst undergoing regeneration.

In further explanation of what is contemplated as desirable charge stock in the herein described process, within the definition of heavy hydrocarbons as referred to in the appended claims, the described operation may be applied to petroleum distillation residues composed essentially of high-boiling hydrocarbons, such as those boiling above normal cracking temperature (about 850 F.) as well as to wider cut hydrocarbon fractions containing unremoved or added lower-boiling hydrocarbons in addition to the higher-boiling material comprising all of, or part of, the asphaltic materials, metallic components and other contaminants found in the crude oils from which these fractions are derived. They may comprise, for example, reduced crude from a crude distillation tower, the bottoms fraction from an atmospheric flash tower, or the bottoms fraction from a vacuum distillation unit. The process is therefore adapted for the catalytic cracking of residua containing the tar and asphalt-like material which heretofore required separation and removal in the preparation of charge stock for catalystic cracking, and which were disposed of as low grade fuels, road surfacing agents, etc. It is, of course, to be understood that the invention is not limited to the treatment of hydrocarbon materials obtained solely from the aforementioned sources, but embraces also the treatment ofheavy hydrocarbon stock, however obtained.

As to the matter of the quantity of process steam to be employed in the reaction zone, it may of course vary by reason of the nature of the charge stock to be treated, or for other reasons. It is contemplated, however, that the process steam requirement will be in excess of about 15 wt. percent based upon total feed (including recycle stock), with higher percentages, up to about 100 wt. percent, being required for the heavier stocks.

What is claimed is:

1. In a moving bed process for the catalytic conversion of hydrocarbon charge stocks in the presence of more than 15 wt. percent of water based upon total charge, wherein hot granular catalyst continuously circulates between conversion and catalyst regeneration zones and is contacted by liquid phase portions of said charge stock within said conversion zone while falling freely as an annular curtain of solids onto the surface of a compact moving bed of catalyst maintained therein, and wherein, as a result of heat imbalance in the system, the temperature of the catalyst entering said conversion zone tends to exceed that which is required to vaporize the liquid phase portions of the charge stock and supply the endothermic heat of conversion, the improvement which comprises the steps of: spraying water into the upper region of said conversion zone in the form of a mist directed laterally onto said free-falling curtain of hot catalyst to complete the vaporization of said water, the quantity of sprayed water being sufiicient to provide the desired amount of process steam and, by withdrawal of the heat utilized for water vaporization, to cool said catalyst to the extent required to maintain a condition of heat balance within said system; and passing the gaseous hydrocarbons and the total steam through said bed of catalyst.

2. In a moving bed process for the catalytic conversion of hydrocarbon charge stocks in the presence of more than 15 wt. percent of water based upon the total charge, wherein hot granular catalyst continuously circulates between conversion and catalyst regeneration zones and is contacted by liquid phase portions of said charge stock within said conversion zone while falling freely as an annular curtain of solids onto the surface of a compact moving bed of catalyst maintained therein, and wherein,

as a result of heat imbalance in the system, the temperature of the regenerated catalyst tends to exceed that which is required to both vaporize the liquid phase portions of the charge stock and supply the endothermic heat of conversion within said conversion zone, the improvement which comprises the steps of: spraying water into the upper region of said conversion zone in the form of a mist directed laterally onto said free-falling curtain of hot catalyst to complete the vaporization of said water, the quantity of sprayed water being sufiicient to provide the desired amount of process steam; passing additional water in the form of a mist directly into a compact moving bed of catalyst in the lower region of said regenenation zone to complete the vaporization of said additional water, the withdrawal of the total heat utilized for water vaporization in both said zones being effective to cool said catalyst to the extent required to maintain a condition of heat balance within said system; and passing the steam formed in each of said conversion and regeneration zones through their respective compact moving beds of catalyst.

3. A process as in claim 2, wherein said additional water in the form of a mist accompanies a stream of regeneration air into said regeneration zone.

4. A process as in claim 3, wherein said additional water is initially sprayed into said air stream out of contact with said catalyst.

References Cited in the file of this patent UNITED STATES PATENTS 2,331,343 Phillips Oct. 12, 1943 2,661,321 Schutte Dec. 1, 1953 2,726,938 Lassiat Dec. 13, 1955 2,729,548 Forkel Jan. 3, 1956 2,794,771 Evans June 4, 1957 2,837,467 McClure June 3, 1958

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