CA1121986A - Fluid distributor for fixed-bed catalytic reaction zones - Google Patents

Abstract

"FLUID DISTRIBUTOR FOR FIXED-BED
CATALYTIC REACTION ZONES"

ABSTRACT
A distributor device for effecting uniform dis-tribution of a fluid stream to a a fixed-bed of catalyst particles. Distribution of a vaporous phase, liquid phase, or a mixed-phase is effected in a plurality of spaced-apart parallel conduits, each of which consists of two concentric and coaxial perforated pipes. Fluid for distribution is intro-duced into the inner conduit, while fluid from that portion of catalyst above the device flows into the outer conduit and is distributed therefrom into the catalyst particles below.

Description

198f~

"FLUID DISTRIBUTOR FOR FIXED-BEP
CATALYTIC R~ACTION Z~NES"

SPECIFICATI~N

The fluid distributor of the present invention is intended for utilization in processes widely practiced within the petroleum and petrochemical industries, and particularly those processes which are effected through the use of fixed bed catalytic reaction zones. The present fluid distribution device is applicable for the inner-catalyst distribution of a heating medium in aprincipaliy endothermic process, or a quench (cooling) stream in an exothermic process. Applicable to those processes effected in vapor phase, li~uid phase and mixed-phase, the distributor serves to introduce, into the reaction zone~ a liquid, vapor, or a mixed vapor/liquid stream. In the interest of clarity ~ j and brevity, but without the intent to so limit our inven-tion, further description and discussion will be directed toward the introduction of a vaporous quench stream in an exothermic process which is conducted in mixed-phase.
Mixed-phase hydrocarbon conversion reactions are generally effected in exothermic processes where the fresh feed charge stock predominates in hydrocarbons boil-ing above the gasoline, or naphtha boiling range -- i.e.
above a temperature of 204~C. at atmospheric pressure.
Often, the mixed-phase reactant stream will consist of liquid hydrocarbon constituents and a hydrogen-rich vapor-ous phase. Charge stocks include kerosene fractions, light and heavy gas oils ~both atmospheric and vacuum) and asphaltenic black oils containing constituents boil-ing above about 566C. Obviously, our invention does not rely for viability upon a particular hydrocarbonace-ous charge stock, nor upon the particular reaction, or reactions being effected. The lattex include hydrocrack-ing, hydrogenation, desulfurization and/or denitrogena-tion, hydrotreating and various combinations thereof, all of which are hydrogen-consuming and, therefore, principal-ly exothermic in nature. Although the distributor herein described is capable of uniformly distributing the reac-tant stream as the same is initially introduced into the cataly~ic reaction vessel, it is primarily intended for the inner-catalyst introduction of a fluid quench, or cooling stream.
Paramount to successful hydrogen~consuming, 98Çi mixed-phase processing, is the uniform distribution of - the reactant stream throu~hout the bed of catalyst parti-cles. This is especially true at those loci within the catalyst bed at which the quench stream is introduced.
Tantamount to hydrogen-consuming reactions is the continu-ous contact of the hydrocarbon phase with hydrogen through-out the bed of catalyst particles. At the points of quench stream introduction, whether liquid or vaporous, it is also important to distribute the quench stream uni-formly into the reactant stream to insure equally impor-tant uniform quenching of the reactant stream, or uniform heat transfer to the quench stream. The distributing de-vide encompassed by our inventive concept readily achieves these necssary results.
A principal object of our invention is to pro-vide a device ~or distributins a fluid uniformly to a bed of catalyst particles. A corollary objecti~e is to dis-tribute an external fluid stream uniformly int~ a reac-tant stream traversing a fixed-bed of catalyst particles.
More specificall~, in an exothermic reaction system, an object is to afford uniform heat transfer from the reactant stream to the fluid quench stream introdu~ed intermediate the bed of catalyst particles. Another ob-ject is to provide an intimate thorough mixture of an ex-ternal fluid stream with the internal reactant stream.
These, and other objects of the presen~ inven~

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tion, are readily achieved in a fixed-bed catalytic reaction chamber throu~h the use of a fluid distribution device which, in one embodiment, comprises in cooperative relationship (a) a fluid inlet conduit; (b) a first plurality of spaced-apart, perforated fluid distribution conduits in open communication with the fluid inlet conduit and disposed in a plane perpendicular to the vertical plane containing the axis of the fluid inlet conduit; (c) a second plurality of perforated fluid distribution conduits, having a nominal diameter greater than the first distribution conduits, one each of which is coaxially and concentrically disposed around each of the first distribution conduits; and (d) annular-form, spaced-apart stabilizing discs, having a major diameter substantially the same as the internal diameter o~ the second distribution conduits, surrounding the first distribution conduits and disposed substantially perpendicular to the longitudinal axis thereof, the adjacent pairs of -~ the stabilizing discs forming individual internal chambers, containing both first and second distribution conduit perforations, along the length of the first and second conduits, and the discs also providing for annular stagnant internal chambers between perforations to impede transfer of heat to the quench fluid. This embodiment may be additionally characterized in that the fluid distribution device occupies from about 60.0% to about 90.0% of the horizontal cross-sectional area of the reaction chamber.

dm~ _ 5 _ , Other objects and embodiments of the presen-t invention will become evident from the following detailed description thereof, particularly when read in conjunction with the several accompanying drawings in which:
FIG. 1 is a plan view of the present fluid distributor, indicated generally by the numeral 1, disposed within a reaction chamber 2.
FIG. 2 is a sectioned elevation of distributor 1 taken substantially along the line 2--2 of FIG. 1.
10 ` FIG. 3 is a partially-sectioned enlarged end view of the distribution conduits; FIG. 4 is iden-tical, but shows the outer conduit 5 encased in a cylindrical perforated screen 11.
FIG. 5 is a side elevation of inner conduit 6, show-ing the relationship between stabilizing washers 10 and apertures 6a.
FIG. 6 is a partially-sectioned side elevation of a portion of one of the distribution conduits, illustrating the spacial relationship of the various elements.
In one such embodiment, annular-form, spaced-apart discs, or washers, having a major diameter substantially the same as the internal diameter of the second (larger) distribution conduits, surround the first distribution conduits (smaller) and are disposed substantially perpen-dicular to the longitudinal axis thereof.
It must be recogn-ized and acknowledged that the dm~ - 5a -9~

prior art CQntainS a variety of fluid distribution devices to introduce (1) a mixed-phase, or single phase reactant stream into a catalytic reaction zone, (2) a vaporous and/or liquid quench, or heating stream a~ one or more intermediate loci within a fixed-bed of catalyst particles and, (3) the mixed-phase effluent from an upper catalyst bed into the next succeeding lower catalyst bed. Many of the prior art fluid distributing devices utilize a horizontal plate through which a plurality of downcomers extend. This technique is illus-trated by United States Patent Nos. 3,146,189; 3,378,3497 and 3,524,731.
Distributor devices similar to the present inventionare found in the prior art as shown by United States P~tent No. 2,632,692. Here the distributor device is situated in a catalyst-free area between two horizontal, perforated plates.
In this instance, the device consists of a pair of concentric, perforated t~roidal rings connected to each other by a cross conduit which, in turn, communicates with the inlet conduit which supplies the quenching fluid. It will be noted that each toroidal ring is unitary in and of itself; that is, the device does not contemplate a second such ring totally within the confines of the first.
The distributor device shown in United States Patent No. 2,860,955 more closely resembles our fluid dis-tribution device (the plan view shown in FIGURE 2.) Here,the inlet conduit tangentially introduces the mixed-phase fluid stream into a separation zone. ~iquid components flow downwardly into a horizontal header which in turn feeds a plurality of perpendicularly-disposed, perforated distribution conduits. Again, each of the distribution conduits is unitary in construction.

r 6 United States Patent No. 3~208~833 ~ffers a fluid distribution device which resembles that of 2,632,692 discussed above. Here, however, the device, consisting of a multiplicity of concentric, perforated rings, rectangular in cross-section, is capable of being back-flushed for removal of a retained fluid. These ring sections are interconnected through a plurality of short hollow tubular members which distribute the feed fluid throu~h all of the spaced-apart distributing rings. It is again noted that all of the distributing rings are of unitary construction~
As hereinbefore set forth, the fluid distribution device of the present invention is adaptable for utilization in those fixed-bed catalytic systems in which the reactions are effected in vapor phase, liquid phase or in mixed phase.
Additionally, the device may be utilized to distribute the reactant stream initially into the xeaction chamber, or to dis-ribute a heating medium or quenching stream at one or more intermediate loci within the bed of catalyst particles. The following discussion will be directed toward a mixed-~kase exothermic reaction chamber wherein the exothermicity of reaction is controlled, or tempered through the use of a vaporous hydrogen quench. Distribution of a quench stream to a fixed-bed of catalyst particles, in accordance with the present invention, is founded upon recognition of the fact that provisions have not heretofore been afforded which will alleviate the diff-iculties and probIems associated with (13 uniform and tborough mixing of the quench stream with the flowing reactant stream and, (2) uniform transfer 8f~

of heat to the quench s~eam throughout the cross-sectional area of the catalyst particles at the various quench introduction loci.
In ~urther describing our invention, both ranges of and specific dimensions will be given. It is under-stood that these are presented solely for illustration purposes, and not with the intent to limit the present in-vention, the scope and spirit of which is defined by the appended claims. The precise design o~ a fluid distribution device is dependent upon many conslderations pertinent to the particular process with which the de~ice is to be integrated r These include at least the following:
the physical and chemical characteristics of the charge stock, or reactant stream; the character of the reactions being effected, and the intended product quality, the charge stock feed rate; the dimensions of the catalytlc reaction chamber; the quantity o~ the catalyst disposed therein; and, the degree of exothermic reaction experienced.
In accordance ~ith the present invention, the quench stream is introduced into the reaction chamber through an inlet conduit which is in open communication with a plurality of perforated distribution conduits, each of which is encased within an outer perforated con-duit having a laryer nominal internal diameter. Each quench distribution conduit consists of a pair of co-axially and concentrically disposed perforated pipes.
The quench inlet conduit is in direct communication only with the smaller, or inner distribution conduit, and is disposed, or aligned with the diameter of the reaction chamber~ Double-pipe distributi~n conduits are spaced apart, and disposed in a plane which is perpendicular to the vertical plane containing the central axis of the quench inlet conduit. The quench distribution conduits may take the form of toroidal rings, similar to those shown in the art, or of individual conduits closed at both ends. In the latter config~ration, the central axes of the distribution conduits will be parallel chords of the reaction chamber~
In the more conventional quench distribution de-vices, difficulties have arisen as a result of heat dis~
tortion of the device or uneven catalyst loading and distribution. This results in discharge from the conduits into various portions of the catalyst bed which are func~
tioning at variant pressures, and thus leads to non-uni-form heat distribution. Furthermore, distortion of the device permits flow fxom high pressure areas to lower pressure areas, again contributing to poor heat distribu-tion, as well as non-uniform mixing throughout the bed of catalyst particles. The co-tubular, double-pipe distribu-tion conduits of the present device readily afford the solutions to these problems. Distortlon under high-sev-erity operating conditions is vlrtually non-existent ~y virtue of the provision of the large~ outer conduit.
Distortion of the device with resulting non~
unlform flow is additionally eliminated by providing annular-form, spaced-apart stabilizing discs, or washers, around the inner pipe, which washers have a m~jor diameter sub-stantially the same as the internal diameter of the outer r g~6 larger conduit, and which are disposed substantially per-pendicular to the longitudinal axis thereof. Perforations in the inner and outer conduits are contained wlth~n indi-vidual internal chambers formed between a pair of stabil-izing discs. Thus, the quench fluid discharging from agiven perforation in the inner pipe can only be admitted - into the catalyst through those perforations in the outer conduit which are between the same pair of stabilizing discs. Also provided thereby are annular stagnant areas lQ between perforations which tend to impede the transfer of heat to the quench fluid. In other words, the quench fluid is not heated as it tra~erses the inner distribu-tion conduit towards the extremities thereof.
Fluid distribu ion de~ices wi11 be designed for a pressure drop of about 0.3 to about 1.0 atm, through the perforat:Lons in the smaller, inner conduit which have a diameter in the r~nge of from about 0.8 to about 4,0 mm. The perforations in the inner ~onduit are dis-posed 90 with respect to the vertical axis, and general-ly two such apertures are confined within each individualinternal chamber formed by a pair of the stabilizing wash-ers. The perforations in the larger, outer distribution conduit have a nominal diameter of from 16 mm, to about 22 mm. and are preferably chamfered inwardly (toward the center of the conduit). These are disposed 30 ~ith respect to the vertical axis, and from two to about four are confined within each individual internal chamber.
Thus, the smaller ape~tures are positioned such that they discharge from the inner conduit onto an imperforate in-ner surface of the outer conduit, The entire fluld dis-tribution devic~ will occupy from about 6.0% to about 90.0% of the horizontal cross-sectional area of the bed of catalyst particles. The ratio of the diametex of the outer conduit to that of the inner c~nduit will be in the range of about 2.0:1.0 to about 4.0:1Ø
In passing the quench vapors at high velocity into the catalyst bed, precautions are required to pre-~ent excessive attrition of the catalyst particles. With respect to the present fluid distribution device, the velocity of the vapors emanating from the apertures in the inner conduit is broken by discharging against an im-perforate area of the outer conduit. By encircling the outer pipe with a perforated screen member~ the velocity is again broken as the vapors discharge into the catalyst bed. Intimate, uniform mixing of the fluid guench and the internal reactant stream is accomplished by locating the outer conduit perforations 30 with respect to the top and bottom of the vertical axisO This promotes the flow of the reactant stream at the precise points of quench introduction. The design utillzes the jet effect of the quench vapors exiting through the small perfora-tions to effectively pump the reactant stream through the individual internal chambers between the pairs of stabil~
izing washers. Additionally, the entire quench apparatus blocks a significant portion of the catalyst bed cross-section, such that t~ere is a relatively high pressure drop through th~ catalyst bed in the spaces between indi-G

vidual quench con~uits~ This pressure drop also encour-ages the flow of the reactant stream through the annulus at the quench point, rather than through the catalyst.
In further descrlbing the fluid distribution de-vice encompassed by our inventive concept, reference will be made to the several accompanying drawings which illus-trate the various embodiments thereof. Since the draw-ings are presented for ~he sole purpose of providing a clear understanding of the distributor, its construction and its operation, they have not been drawn to a precise scale. As previously stated herein, the dimensions of a particular device are dependent upon a wide variety of processing considerations as well as the particular di-mensions of the catalytic reaction chamb~r.
In one specific design, for use in a catalytic reaction chamber having an effecti~e internal diameter of about 3.7 meters, twenty-five double-pipe distribution conduits are utilized. These are disposed on approximate 1.27 cm. centers with approximately 3.8 cm. between adjacent conduits. The inner conduit has a dia-meter of about 2.54 cm~, and the aperture therein are 1.6 mm in diameter; the outer conduit has a diameter of 7.6 cm., and the apertures therein are 1.9 cm. in diameter. Within each of the individual internal chambers formed by a pair of stabilizing discs 2.54 cm. apart, there are two 1.6 mm. apertures and four 1.9 cm. aper~
tures. The apertures are 7.6 cm. apart, measured center to center along the axis of the conduit.

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DETAI~ED DESCRIPTION OF D~AWINGS

With specific reference now to the accompanying drawings, FIGURE 1 shows a plan view of the fluid distribut-ing device 1 within a catalytic reaction chamber 2. The fluid quench stream is introduced by way of inlet port 3 and inlet conduit 4. In this illustration of a preferred embodiment, fluid inlet conduit 4 is shown as traversing the reaction zone through the center, and as being substantially the same length as the diameter thereof. A plurality of fluid distribution conduits, consists of an outer pipe 5 and a smaller inner pipe 6, are disposed below inlet conduit 4, and lie in a common plane which is perpendicular to the vertical planes containing the central axis of the inlet conduit. As more clearly shown in FIGURE 2, fluid inlet conduit 4 communicates directly only with inner distribution conduit 6 by way of reducing couplings (or unions) 7. In the plan view of FIGURE 1, ~he entire device occupies approxi-mately 80.0% of the cross-sectional area o~ catalytic reac-tion chamber 2.
FIGURE 2 is a partially sectioned side elevation taken substantially along the line 2-2 of FIGUR2 1. The fluid quench stream passes from inlet conduit 4 through short vertical pipes 8, reducing coupling 7 and pipes 9 into inner distribution conduit 6; vertical pipes 9 are generally of the same size as conduits 6. A pair of aper-tures 6a, disposed 180 with respect to each other, dis-charge the quench stream onto an imperforate portion of outer distribution conduit 5 which contains four apertures 5a, each of which is disposed 30 with respect to the ver-tical axis, ~ he spacial relationships of distribution con-duits 5 and 6, as well as apertures 5a and 6a, are illus-trated in FIGURES 3 and 4, enlarged for clarity. Alsoshown in these views is a stabilizing disc 10 and the per-forated screen member 11 which surrounds outer distribu-tion conduit 5. The jet action of the quench fluid dis-charging through apertures 6a effectively pumps the reac-tant stream through apertures 5a, and intimately admixestherewith by virture of discharging against the imperfor-ate portion of outer conduit 5. The apertures lla in per-forated screen member 11 are sized to inhibit the passage of catalyst particles therethrough.
FIGURE 5 is a side elevation of ~he inner dis-tribution conduit 6 having the stabilizing discs, or wash=
ers 10 in place. As shown, adjacent pairs thereof effec-tively separate apertures 6a from each other~ ~IGURE 6 illustrates more clearly the individual internal chambers 13 which are formed by the pairs of stabilizing discs 10.
Stabilizing disc lOa is installed as shown in order to di~
vert the fluid quench stream in conduit 9 such that ~he same traverses the entire length of inner dlstribution conduit 6. Between pairs of stabilizing discs 10 are the stagnant areas 12.

Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a catalytic reaction chamber, containing a fixed-bed of catalyst particles, an inner catalyst fluid distribution device which comprises, in cooperative relationship:
(a) a fluid inlet conduit;
(b) a first plurality of spaced-apart, perforated fluid distribution conduits in open communication with said fluid inlet conduit and disposed in a plane perpendicular to the vertical plane containing the axis of said fluid inlet conduit;
(c) a second plurality of perforated fluid distribution conduits, having a nominal diameter greater than said first distribution conduits, one each of which is coaxially and concentrically disposed around each of said first distribution conduits; and (d) annular-form, spaced-apart stabilizing discs, having a major diameter substantially the same as the internal diameter of said second distribution conduits, surrounding said first distribution conduits and disposed substantially perpendicular to the longitudinal axis thereof, said adjacent pair of said stabilizing discs forming individual internal chambers, containing both first and second distribution conduit perforations, along the length of said first and second conduits, and said discs also providing for annular stagnant internal chambers between perforations to impede transfer of heat to the quench fluid.

2. The fluid distribution device of claim 1 further characterized in that said first and second fluid distribution conduits are disposed below said fluid inlet conduit.

3. The fluid distribution device of claim 1 further characterized in that the perforations in said second plurality of conduits have a greater nominal diameter than the perforations in-said first plurality of conduits.

4. The fluid distribution device of claim 1, 2 or 3 further characterized in that each of said second distribution conduits is encased in a cylindrical, per-forated screen member.

5. The fluid distribution device of claim 1, 2 or 3 further characterized in that the perforations in said second distribution conduits are inwardly chamfered.

6. The fluid distribution device of claim 1 further characterized in that the perforations in said first distribution conduits are disposed to discharge against an imperforate portion of said second distribution conduits.

7, The fluid distribution device of claim 6 further characterized in that the perforations in said first distribution conduits are disposed 90° with respect to the vertical axis and the perforations in said second distribution conduits are disposed 30° with respect to the vertical axis.

8. The fluid distribution device of claim 1, 2 or 3 further characterized in that it occupies from about 60.0%
to about 90.0% of the horizontal cross-sectional area of said reaction chamber.