WO1993008907A1

WO1993008907A1 - Conveyor trough apparatus for loading catalyst pellets into vertical, tubular reactors

Info

Publication number: WO1993008907A1
Application number: PCT/US1992/009303
Authority: WO
Inventors: Kelly James Johnson
Original assignee: Catalyst Technology Inc
Current assignee: Catalyst Technology Inc
Priority date: 1991-11-08
Filing date: 1992-10-30
Publication date: 1993-05-13
Anticipated expiration: 1994-05-08
Also published as: CA2123125A1

Abstract

An apparatus and process are disclosed for loading flowable materials, specifically catalysts, into receivers, specifically multi-tube reactors, quickly, without bridging of the catalyst and with maximum control over the catalyst drop rate and, consequently, control over the packed density of the catalyst in the reactor tubes. The invention utilizes a specially designed conveyor trough having a polygonal cross section, preferably octagonal, to load reactors in a more rapid, consistent manner without bridging and with minimum catalyst breakage and dust production. The invention is particularly applicable to jacketed multi-tube reactors used in the production of vinyl chloride monomer (VCM), ethylene dichloride (EDC), vinyl acetate, acrylic acid, ethylene oxide, phthalic anhydride and maleic anhydride.

Description

DESCRIPTION

( ^' CONVEYOR TROUGH APPARATUS FOR LOADING CATALYST

PELLETS INTO VERTICAL. TUBULAR REACTORS

Technical Field

This invention relates broadly to the field of 5 loading receivers with a flowable material and specifically to the field of rapid loading of vertical process vessels with flowable catalysts without bridging of the catalyst material. Background Art

10 Some of the problems associated with the loading of flowable particulate catalyst material in catalytic reaction vessels and, in particular those having a multitude of small vertical tubes, have been addressed in U.S. Pat. Nos. 2,070,868; 2,690,267; 3,562,998; and

15 3,608,751. Generally, these patents disclosed inventions relating to the movement and protection of the catalyst during loading or unloading and for obtaining proper loading of the tubes in order to achieve desirable process operating conditions. Additionally, U.S. Pat. No.

20 3,223,490 recognized the need for rapid loading of the reactor tubes to improve reactor utilization time for improving production capacity and it employed a vertical vibrator to speed movement of the flowable catalyst into the tubes. And in U.S. Pat. No. 3,913,806, a predetermined

25 quantity of flowable catalyst material is placed in a plurality of containers mounted on a movable frame using a movable loading tray. Operation of a valve means enables

* flow of the catalyst material from the plurality of * containers into the reactor tubes in a predetermined

* 30 manner. In U.S. Patent No. 4,701,101, a modular multi- tube funnel is provided in which each funnel module contains a hopper m which a rotatable metering rod is mounted. Each of the metering rods is height adjustable, so that the end of the metering rod can be raised or lowered in the mouth of the funnel to either increase or decrease the catalyst drop rate. Additionally, each of the metering rods is driven by a single motor having a variable-speed reducer so that the speed of rotation of all of the metering rods can be decreased or increased as desired. Thus, once the metering rods have been set, it is possible to vary the catalyst drop rate without the tedious height adjustment of the metering rods by variably adjusting the speed of rotation of the metering rods. In U.S. Patent No. 4,402,643, a horizontal vibratory feeder tray feeds the catalyst through V-shaped open troughs to a discharge spout, thence to the reactor tubes.

Magin et al. , U.S. Patent No. 4,461,327 discloses a controllable belt-weigher device for charging a plurality of tubes.

All of these prior systems produced undesirable results such as excessive loading time required, inconsistency in loading including bridging of the material, catalyst breakage and production of dust. Disclosure of the Invention

This invention relates to an apparatus for loading flowable material, particularly catalysts, into multi-tube reactors quickly, without bridging and with maximum control over the catalyst drop rate and,

, consequently, control over the packed density of the catalyst in the reactor tubes. Specifically, the invention utilizes a specially shaped conveyor trough to load reactors in a more rapid, consistent manner without bridging of the reactor tubes and with minimum catalyst breakage and dust production. Brief Description of Drawings

FIG. 1 is a side elevation view of the preferred embodiment.

FIG. 2 is a plan view of the preferred embodiment taken along line 2 of FIG. 1.

FIG. 3 is an isometric view of the loading system shown without a dust cover. FIG. 4 is an isometric view of an embodiment of the specially shaped feed chutes. Best Mode for Carrying Out the Invention

While the invention is useful in moving and loading any flowable material into vertical receiving tubes of a multiple-tube receiver, the following description is directed to multi-tube vertical catalyst reactors. Each of the reactions for producing ethylene oxide, or for the production of phthalic anhydride, aleic anhydride, or acrylic acid is highly exothermic, involving the controlled oxidation of organic substances. Thus, it is necessary that the heat generated by the reaction be removed as efficiently as possible so as to prevent a run-away reaction in which undesirable products are produced and in which expensive raw materials are wasted. Accordingly, it has been the practice to utilize catalytic tubes of extremely narrow diameter. Thus, for example, it is not unusual for a catalyst tube to have an inside diameter of 0.75-2.00 inches (1.91-5.08 centimeters) and to be 10-60 feet (3-18 meters) long, and the reactor may contain as many as 25,000 such tubes. Each of the tubes is connected at each end to a tube sheet, and the entire bundle of tubes and tube sheets is jacketed and filled with a heat transfer fluid or medium, as, for example, water or kerosene. Due to the heat given off by the reaction, the space velocity is maintained at an extremely high rate so that there can be considerable abrasion of the catalytic particles within the small diameter tubes if the particles are loosely packed. Additionally , high space velocities can result in relatively high pressure drops across the tubes and, if the tubes are not packed to uniform densities, a poor distribution of feed gas is obtained across the reactor. Additionally, hot spots can occur within the reactor. When this occurs, the catalyst bridges over and that particular tube may be lost from service due to coke formation. This, of course, depends upon the severity of the spot. Additionally, in the case of ethylene oxide, for example, one patentee points out that the optimum temperature for the reaction is in the range of 225°C-250°C. If the temperature falls below 225°C, the conversion rate is insufficient to be economically feasible. If the temperature goes above 250°C, the ethylene oxide selectivity decreases significantly with the concomitant loss of the desired end product. It is obvious, of course, that, if the reaction gets too far out of hand, the end product is carbon dioxide and the catalyst becomes fused throughout the length of the small-diameter tubes. Also, since, in the case of ethylene oxide, the catalyst comprises silver on alumina pellets, minimization of dust production is in itself a worthwhile goal since the dust contains valuable metals.

Referring to the Figures which show preferred embodiments, a catalyst loading apparatus is generally designated at 10 and comprises a catalyst supply hopper 12 for receiving a catalyst for loading into a reactor tube 14 through loading funnel 15. The catalyst pellets are received in the supply hopper 12 and may be alumina impregnated with silver and other chemicals. Variously shaped pellets may be used. Preferably, the catalyst is silver-based ethylene oxide pellets having a mean shortest dimension of about 0.25 inch (0.64 centimeter) and a mean longest dimension of about 0.375 inch (0.953 centimeter). Of utmost importance is a continuous, uniform supply of catalyst through the loading funnel 15 and into the reactor tubes 14. Any catalyst dust generated by the operation may be drawn off, for example, by a vacuum line or tube 13 located at the top of the hopper 12 and at the end of the discharge tray 20. In operation, the reactor comprises a plurality of catalyst tubes 14 which are secured to a reactor tray or tube sheet 17. The catalyst loader 10 is located above, or may rest on, the reactor tray 17 and is moved from tube to tube as each tube 14 is loaded. Normally, several loaders, 10 may be used at one time. Alternatively, or additionally, multi-tube loaders 10 may be used. Supply hopper 12 may actually be partitioned to provide a plurality of supply hoppers, for example 12a, 12b, and 12c, so that each separate hopper may be loaded with the desired amount for filling one catalyst tube 14. Each hopper compartment, for example 12a, 12b and 12c, may be loaded with a pre-measured bag of catalyst sufficient to fill one tube 14.

The catalyst material falls onto the conveyor tray 20 and the vibrator 22 forces the catalyst to move along tray 20 comprising specially-designed conveyor troughs or chutes 24 (better shown in FIG. 4) . The output of troughs 24 is fed by gravity into individual loading funnels 15 and each funnel 15 fills an individual tube 14. The troughs 24, are specially designed to be polygonal in complete cross-section having one side of the polygon on the bottom (flat-bottomed) , preferably to have an octagonal cross-section but with three sides truncated so that the troughs 24 comprise only five sides of the octagon. This design has proved to be preferable to a V-shaped trough because the V-shaped trough allows only one catalyst particle at a time to flow into a tube 14, thereby greatly increasing the loading time required. Alternatively, the troughs 24 may have, e.g. a hexagonal cross-section truncated so as to form a three-sided trough or a pentagonal cross-section truncated so as to form a three- sided trough. The vibrator 22, when attached to a loading tray 20 being fed by multiple feeding hoppers 12, allows each compartment, e.g. 12a, 12b, 12c, etc. to uniformly empty at the same time. This gives the same loaded length of catalyst and thus the same pressure drop across the tubes 14.

FIG. 3 shows an isometric view of the loader 10 without the dust cover. In this view the individual hoppers 12a, 12b, and 12c are shown, each supplying catalyst to individual troughs or^c chutes 24 and ultimately into loading funnels 15 for loading an individual catalyst tube 14 with a measured quantity of catalyst. The catalyst loader 10, as described above, thus assures that less catalyst breakage occurs (therefore minimizing dust production) and more uniform loading time of the catalyst loaders 10 which may be used at one time is obtained (all loaders 10 may be adjusted to fill the individual tubes 14 within about ten seconds of each other.) The preferred loading time per tube varies with the type and size of material.

Industrial Applicability

The invention is particularly applicable to jacketed multi-tube reactors used in the production of ethylene oxide, phthalic anhydride, maleic anhydride, acrylic acid, vinyl chloride monomer (VCM) , ethylene dichloride (EDC) , and vinyl acetate, but is not limited to such uses.

Claims

1. Apparatus for loading a flowable material into the vertical receiving tubes of a multi-tube receiver, said apparatus comprising: a supply hopper (12) for receiving a charge of flowable material; a conveyor trough (24) open at the top for receiving the output of said supply hopper, said conveyor trough comprising part of a truncated generally polygonal complete cross-section; means (22) for conveying said flowable material to the end of said conveyor trough; a loading funnel (15) located below said conveyor trough for receiving the output of said conveyor trough; and means for supplying the output of said loading funnel to an individual receiving tube.

2. Loading apparatus as claimed in claim 1, wherein said means for conveying includes a vibrator (22) for vibrating said conveyor trough.

3. Loading apparatus as claimed in claim 1 or claims 2, wherein the complete cross-section of which said conveyor trough (24) comprises a part is generally hexagonal, octagonal or pentagonal.

4. Loading apparatus as claimed in claim 3, wherein the complete cross-section is truncated such that when the complete cross-section is generally hexagonal or pentagonal the trough (24) is three-sided and when the complete cross-section is generally octagonal the trough is five-sided.

5. Apparatus is claimed in any of the preceding claims, wherein the conveyor trough (24) is flat-bottomed in cross-section, said flat bottom being formed by one side of said generally polygonal complete cross-section.

6. Loading apparatus as claimed in any of the preceding claims, wherein the apparatus is a catalyst loader for loading vertical reactor tubes of a multi-tube reactor.

7. Loading apparatus as claimed in claim 6, wherein the apparatus is arranged to rest on an upper tube sheet of the reactor, the tubes of the reactor being securely attached at one end to said upper tube sheet.

8. Loading apparatus as claimed in claim 6 or claim 7 in combination with the multi-tube reactor.

9. A process for loading catalyst to a reactor tube, comprising the steps of: providing a flowable catalyst in a supply hopper

(12) ; passing the catalyst to a conveyor tray (20) comprising a conveyor trough (24) , said conveyor trough comprising part of a truncated generally polygonal complete cross-section; moving the catalyst in the conveyor tray along the conveyor trough toward a loading funnel (15) by vibrating the conveyor trough; passing the catalyst to the loading funnel; and passing the catalyst from the loading funnel to the reactor tube (14) .

10. A process as claimed in claim 9, wherein said complete cross-section of which said conveyor trough

(24) comprises a part is generally octagonal, hexagonal, or pentagonal.