Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Including heat exchanger for reaction chamber or reactants...
Reexamination Certificate
1998-12-21
2001-02-06
Beck, Shrive (Department: 1764)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Including heat exchanger for reaction chamber or reactants...
C422S198000, C422S198000, C422S220000, C422S224000, C261S114500
Reexamination Certificate
active
06183702
ABSTRACT:
I. FIELD OF THE INVENTION
This invention relates to a distributor assembly for multi-bed, down-flow catalytic reactors, that is, reactors which include vertically superimposed packed beds of particulate catalytic material and where a liquid or liquid and gas mixture is processed as it flows down through the packed beds. This type of reactor is used in the petroleum and chemical processing industries for carrying out various catalytic reactions, such as hydrotreating, hydrofinishing, hydrocracking, and dewaxing.
II. BACKGROUND OF THE INVENTION
Multi-bed, down-flow catalytic reactors are used in the petroleum and chemical industries for a variety of processes. In the petroleum refining industry, multi-bed, down-flow reactors are used in processes for hydrotreating, hydrodesulfurization, hydrofinishing, hydrocracking, and dewaxing. In these processes, the process liquid is mixed with a gas or vapor and this multiple phase mixture is passed through the packed catalyst beds. In exothermic reactions, large amounts of heat may be generated in the catalyst beds. Quench media may be added to regulate the temperature in the reactor. Typically, the quench media is also a reactant, e.g., hydrogen. As the liquid and gas mixture flows through a catalyst bed, some maldistribution of temperature and reactant concentration often develops across each bed. Unless this is mitigated, the reactor operation would be inefficient and hot spots may develop that could potentially shorten catalyst life and force premature reactor shutdown and therefore plant shutdown. It is, therefore, necessary to provide reactor internals for collecting and mixing the liquid and gas exiting from one bed before distribution to the next bed, so that any such maldistribution is not propagated from one catalyst bed to the next. To accomplish this, distributor assemblies are used between the catalyst beds to ensure that the distribution of the liquid and gas mixture (and as the case may be, the vaporous reactant or quench gas) across each bed is as uniform as possible in both composition and temperature. To make the corrections of temperature and concentration maldistributions, the distributor assembly should provide for good liquid-liquid, gas-gas, and gas-liquid mixing. In addition to providing good mixing, it is desirable that the distributor assembly be compact and impose only a low pressure drop.
By providing such uniform distribution, each bed will be efficiently utilized and the desired catalytic reactions will take place in a more predictable manner. Numerous types of distributor assemblies for multi-bed, down-flow reactors are known in the prior art. One example is shown in U.S. Pat. No. 4,836,989, in which the distributor assembly includes a collector tray arranged below a catalyst bed and a distributor tray is mounted under the collector tray. The distributor tray is fed by spillways which provide passageways for the liquid collected on the collector tray, as well as quench gas injected between the distributor tray and the catalyst bed. The spillways have outlets below the collector tray which face sideways and tangentially into an annular second mixing zone located under the collector tray. This second mixing zone has a high liquid holdup. The outlets are described as imparting a swirling motion to the liquid in the annular second mixing zone that promotes good mixing and temperature equilibrium. Further mixing and redistribution apparatus is provided below the second mixing zone to collect and distribute liquid over the underlying catalyst bed. The design also requires a high pressure drop to be effective.
Another type of a distributor assembly, as shown in U.S. Pat. No. 4,960,571, includes a collector plate that has a central opening therein. A quench mixing zone is provided under the collector plate, in which a second plate having openings formed in an annular outer portion thereof is mounted under the collector plate, with the annular portion thereof being situated radially outwardly of the central opening in the collector plate. Baffles are affixed to the annular portion and arranged at a tangential angles and in concentric rings to induce current eddies in the liquid and gas flowing through the annular portion. The design does not provide as extensive radial mixing as is usually desirable.
Another distributor assembly for multi-bed, down-flow reactors is described in U.S. Pat. No. 5,690,896 ('896 patent). The '896 patent teaches a mixing box arrangement were all fluid collected on a tray flow in a spiral pattern to a single mixing zone leading to a single outlet. This design has drawbacks in that the degree of correction of temperature and composition distributions may depend upon the origin of the distribution relative to the single opening to the mixing zone. Also, because of the single opening and mixing zone, the required height of the assembly could be high in order to accommodate a sufficient liquid throughput. The design also requires a high pressure drop to be effective.
Examples of other types of distributor assemblies for multi-bed, down-flow reactors are described in U.S. Pat. Nos. 3,705,016, 3,977,834, and 4,182,741. It would be advantageous to have a distribution assembly that overcame the deficiencies of known designs. The distributor assembly of the invention provides this improved design.
III. SUMMARY OF THE INVENTION
The invention, in one embodiment, is a distributor assembly for a multi-bed, downflow catalytic reactor including: a collection plate configured for substantially horizontally disposal between the walls of a cylindrical reactor, configured for collecting liquid flowing down from a higher catalyst bed contained in the reactor. The collection plate having of an outlet in a center portion thereof configured for allowing a passageway for liquid and gas from the higher catalyst bed to flow toward a lower catalyst bed contained in the reactor.
A plurality of generally arc-shaped elongated baffles: disposed in a staggered, substantially symmetrical pattern about the collection plate, each baffle having a bottom edge portion fixably attached to the collection plate and a top edge portion extending substantially vertically upward to a height sufficient to substantially prevent liquid flowing over the top edge portion. Each baffle having a head portion proximal to perimeter portions of the collection plate and having an opposite tail portion proximal to a center portion of the collection plate, wherein the head portion of each of the elongated baffles overlaps a tail portion of another of the elongated baffles.
The elongated baffles configured for directing the liquid from an outer portion of the collection plate toward a center portion of the collection plate and configured to cause mixing between liquid passing out of the tail portion of each elongated baffle with the liquid passing into the head portion of the adjacent overlapping elongated baffle. A first mixing zone configured to be bounded on the bottom by the collection plate, on one side by a wall of the cylindrical reactor, on the opposite side by the outer surface of the elongated baffles.
A cylindrical weir fixably attached to the collection plate about the outlet, configured for causing the liquid and gas to rise up and over the first cylindrical weir before flowing through the outlet toward the lower catalyst bed. A second mixing zone: bounded on the bottom by the collection plate, on one side by the outer surface of the cap and the first cylindrical weir, and on the opposite side by the inner surface of the elongated baffles; having a plurality of entrances bound on one side by the interior surface of a head portion of one elongated baffle and on an opposite side by the outer surface of a tail portion of an overlapping elongated baffle. Optionally, a plurality of quench gas ports is disposed in the second mixing zone; each port having an outlet disposed proximal to the collecting collection plate and configured for ejecting a quench gas beneath the surface of a liquid collected in the second mixing zone and towa
Cash Dennis R.
Nguyen Duyen T.
Parimi Krishniah
Beck Shrive
Bradin David S.
Chevron U.S.A. Inc.
Hadlock Timothy J.
Ohorodnik Susan
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