Gas and liquid contact apparatus – Contact devices – Porous mass
Reexamination Certificate
2001-03-07
2003-01-07
Bushey, C. Scott (Department: 1724)
Gas and liquid contact apparatus
Contact devices
Porous mass
C261S110000
Reexamination Certificate
active
06502806
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to liquid distributors for vapor-liquid contact columns and, more particularly, to a liquid distributor assembly for packed columns wherein counter-current, vapor-liquid flow is employed.
2. The State of the Prior Art
It is well known in the prior art to utilize various types of exchange columns or towers, in which a gas and a liquid are brought into contact with one another, preferably in counter-current flow for purposes of mass and/or heat transfer, close fractionation and/or separation of feedstock constituents, and other unit operations. The overall process generally involves mass transfer, heat transfer, fluid vaporization and/or fluid condensation. To conduct these operations efficiently, intimate contact between the gas and the liquid must be achieved and yet the pressure drop within and the physical dimensions of the contact zone desirably is minimized. For these reasons, counter-current flow of vapor and liquid within the exchange column has become the preferred method for bringing the vapor and the liquid into the desired intimate contact. Moreover, the preferred means for achieving this desired contact is a so-called packed bed positioned within the column. Such beds are well known. Some are packed with a multiplicity of packing elements designed to maximize the vapor/liquid interface. Others may be in the form of a structured packing.
Liquid is distributed on top of these packed beds in the most feasible manner, while vapor is distributed beneath the beds in the lower regions of the column. In this manner, liquid trickling downwardly through the packing bed is spread out over the surfaces of the packing elements so as to maximize the surface area of the liquid that is exposed to vapor ascending through the bed.
It is well established that the configuration of the packing bed determines the pressure drop, efficiency of the vapor-liquid interface and the concomitant mass and energy transfer occurring in the process column. The means for effective and even distribution of the vapor and the liquid on opposite sides of the packing bed as well as maintenance of that distribution as the fluids move through the packing are critical to the efficient operation of the column. Only with efficient initial vapor and liquid distribution and the maintenance of such distribution throughout the packing, will homogenous mixing zones be created so as to maximize the efficiency of the overall contact operation. Efficiency is readily convertible to cost of operation and production quality. For this reason, a myriad of prior art packing designs have been prevalent in conventional exchange columns.
The efficiency of the packing, however, is limited to a large extent by the efficiency of the methodology used to distribute the vapor and liquid across the bed. For example, failure of either vapor or liquid to be evenly distributed over the entire cross-section of the bed effectively eliminates the utility of the part of the packing where there is poor or no distribution. This in turn adversely directly affects the overall cost effectiveness and efficiency of the contact operation. The packing bed depths are critical in establishing production criteria and operational costs, and failure to evenly distribute both the vapor and the liquid across the packing and/or to maintain homogeneity within the packing can lead to serious consequences, particularly in the petroleum refining industry.
Aside from the packing beds, the liquid distributors are the most important components of the column. Failure in performance of a packed column sometimes stems from liquid distribution problems such as clogging or uneven distribution. Hence, the selection of a proper liquid distributor is critical for uninterrupted continuous operation. Operational considerations thus include the functional aspects of the distributor, such as how level the distributor troughs are maintained, how well the flow is equalized therethrough, and the means through which the liquid is distributed from the troughs to the packing beds positioned beneath the distributor. Also considered is the effect which the ascending vapor has on the liquid being distributed. When vapor flow areas are restricted, flow velocity can increase to the point of interrupting the descending flow pattern. The liquid is, in essence, “blown” around, and this condition can lead to uneven distribution and inefficiency in the operation of the column.
Conventional liquid distributors generally include the multi-orifice spray head variety adapted for dispersing liquid in the form of a spray atop a packing bed. In the utilization of dump packing wherein a plurality of randomly oriented packing elements are disposed, within the exchange column, such liquid distribution technique is sometimes effective. This is particularly true when high efficiency parameters are not of critical significance. However, in the event of high efficiency packing such as that which is described in U.S. Pat. No. 4,604,247, means for homogenous liquid and gas distribution is of extreme importance.
The cost of high efficiency packing of the type described in the '247 patent mentioned above commands attention to proper vapor-liquid distribution. Even small regions of non-homogenous interaction between the vapor and liquid is an expensive and wasteful loss not consistent with the utilization of high efficiency packing, where space and homogeneity in vapor-liquid interface is both expected and necessary for proper operation. High efficiency packings of the state of the art varieties shown in the '247 patent require counter-current vapor-liquid flow through the channels defined by the opposed corrugations of sheets. If the initial liquid or gas distribution fails to enter a particular corrugation pattern, then precious surface area is lost in the packing until the liquid and vapor are urged to migrate into and interact through the unfilled regions of the packing. Only by utilizing proper vapor and liquid distribution means may effective and efficient utilization of high efficiency packing as well as conventional dumped packing be assured.
The development of systems for adequate liquid distribution in process towers has been limited as set forth above. In the main, it is known to discharge and distribute liquids with spray orifices, pipes, perforated plates, apertured troughs and nozzles. Gas is concomitantly discharged in an ascending turbulent configuration to provide adequate vapor distribution. Although many prior art systems are generally effective in distributing some vapor and some liquid to most portions of the packing bed, uniform distribution across the entire bed is usually not obtained without more sophisticated distribution apparatus. For example, unless gas is injected into a myriad of contiguous areas beneath the packing bed with equal pressure in each area, the mass flow of vapor upwardly through the packing bed cannot be uniform. Random vapor discharge simply distributes unequal amounts of vapor across the lower regions of the packing bed but does not in any way assure equality in the distribution. Likewise the simple spray of liquid atop the packing bed, though intended to be effective in wetting all surface areas, often results in high concentrations of liquid flow in certain packing bed areas and less flow in others. This, of course, depends on the spray device. Orifice distributors are generally more susceptible to plugging than other types of distributors, and plugging is generally non-uniform to uneven irrigation within the tower. Surface irregularities in a distributor pan occurring during manufacture likewise increase flow resistance of some perforations or induce liquid flow along the bottom of the pan which is a distinct disadvantage. Any flow irregularity which focuses the flow in one area while reducing flow in other areas is deleterious.
When pipe distributors consisting of headers equipped with tributary pipes or laterals that have holes or nozzles to spray liquid are used, t
Bushey C. Scott
Koch-Glitsch, Inc.
Shook Hardy & Bacon L.L.P.
LandOfFree
Liquid distributor assembly for use in packed column does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Liquid distributor assembly for use in packed column, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Liquid distributor assembly for use in packed column will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3019291