MXPA99006939A - Fractionation trays - Google Patents

Abstract

A fractionating column (1) is provided which has perforated fractionating trays (2) and downcomers (7) allowing liquid to flow from one tray to the tray immediately below, said downcomers being provided with radial outflow ports (4) directing downflowing liquids towards the column wall rather than onto the surface of the tray directly below the downcomer. This permits at least a portion of the under-downcomer area to be perforated thereby increasing the capacity of the tray for vapor/liquid contact and ensuring that weeping of the liquid through the perforations is avoided without need for an increase in vapor pressure.

Description

CHARLES FOR FRACTIONATION BACKGROUND OF THE INVENTION This invention relates to equipment for chemical processing in which a liquid is brought into contact with a gas backflow. This can be due to a large number of purposes such as separating a component from a liquid stream or absorbing a component within a liquid stream. More generally, this invention relates to equipment designed to facilitate the transfer of mass and / or heat between the phases. The type of equipment to which this invention specifically refers employs trays for cross-flow fractionation connected by drop tubes. In this equipment, a tower is provided with a large number of fractionating trays generally arranged horizontally inside the tower. Each tower has a perforated platform and at least one channel, called a descent tube, in which a liquid that flows over the platform must be collected and channeled to the bottom tray. A gas or steam in use is introduced to the base of the tower and passes up through the perforations in the platforms of the trays for fractionation. Meanwhile, a liquid is introduced into the upper part of the tower and filtered down, passing over the trays for fractionation and below the descent tubes to the bottom tray. The liquid comes out of the drop tube in a typical design either through an open bottom and / or the front area of the drop tube (i.e., the side facing forward of the center of the tray). In some cases the down tube may have a lower tray where the liquid flows around and out through openings in the bottom. In some designs, a perforated area is provided under the drop tube that contacts the vapor and liquid prevented by a box over the perforated portion of the lower area of the drop tube. Normally there are no measures for the vapor contact with the liquid in the lower area of the descent tube and this reduces the capacity of the tower. Some modifications to address this problem have led to the use of grooved bottoms for the drop tubes, as in example JP-A-7 318 192, to distribute the liquid flow in the same way in all directions to allow perforations of the lower area of the descent tube but this is still a problem area from the point of view of the liquid passing directly down through the perforations intended for the upper steam passage. In the apparatus described in the USP document. 3,784,175, the runoff from the drop tube is directed towards the portion of the tray near the wall of the column by means of a curved member supported by springs that is sensitive to the weight of the liquid in the defense tube so as to open or close the outlet to the drop tube in response to said weight. According to the design of the ideal procedure, liquid should be prevented from passing through the perforations in the platform of the trays for fractionation by the pressure of the gas passing through the perforations in the upward direction. This is a finely balanced procedure since, if the pressure is too high, the gas will have a small run time inside the tower and a less efficient contact with the liquid flowing down. The high gas velocity can also cause leakage in the upper tray, thus reducing the separation efficiency as a result of remixing. On the other hand if the velocity of the gas flow is too low, the liquid will penetrate through the perforations in the platform of the tray (known as "drip") and will put out of circuit the flow patterns whose intention is to increase the maximum the liquid / gas contacts. In this way, in summary, the gas flow must be slow enough to allow efficient contact with the liquid flow but fast enough to minimize leakage. Although the pressure difference between the space above a tray for fractionation and the space below is necessaryIf the difference is too high, the gas flow will accelerate as it passes through the perforations and the efficient bubble contact will be lost. To maintain the same volume of gas flow but reduce the pressure difference, it is necessary to maximize the perforated area of the fractionating tray or provide some other efficient mechanism for the gas to come into contact with the liquid while passing through. of the tray for fractionation.

However, dripping is often a problem when the speed of the liquid flow is particularly heavy in a local perforated area, and particularly in the lower area of the drop tube. Therefore, to some extent, the desire to achieve the highest contact efficiency (which implies that less favorable pressure falls through the tower), by drilling a part of the surface of the platform as long as possible goes against the I want to avoid the drip. The present invention provides high efficiency (or high capacity), tray design for fractionation which ensures that the drip hazard is minimized.

GENERAL DESCRIPTION OF THE INVENTION The present invention provides a fractionation column consisting of a first fractionation tray perforated with at least one drop tube to channel a runoff from the first tray to a second perforation tray directly below the first one in which each Drop tube channels descending circulation liquid from the first tray to a portion of the second tray next to the junction of the tray and the wall of the column. The drop tube preferably has a restricted outlet area designed to ensure that the runoff therefrom is directed exclusively to a peripheral, non-perforated portion of the second tray. For example, the liquid has to be discharged from the descent tubes by means of radial openings, rectangular openings, crenellated landfills or flat landfills specifically designed to direct the flow to a wall / tray splice area from which it can be equally distributed before to make contact with the perforated area of the tray for fractionation. It has been found that if runoff from the drop tube extends into the second tray in this manner before coming into contact with the perforations, it is possible to avoid localized heavy flow situations which can lead to dripping. From the junctions of the wall / tray, the flow naturally extends around the wall and enters the perforated area. Since the flow is initially directed to the wall, a substantial portion of the lower area of the drop tube can now be drilled with either single or valve holes, thus increasing the efficiency of the trays. In a preferred embodiment, a perforated barrier separates the contact area of the initial fluid from the perforated portion of the tray so that the flow in the perforated area is distributed if possible in the same manner.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-section of a portion of a tower containing trays for fractionation and an individually enclosed drop tube in accordance with the invention.

Figure 2 is a plan view of the fractionation trays shown at the bottom shown in Figure 1. The perforations are shown in the lower area of the drop tube.

DETAILED DESCRIPTION OF THE INVENTION The invention is now described in more detail with respect to the drawings which are intended to illustrate the invention but should not be taken to imply any essential limitations on the scope of the invention. The apparatus illustrated in Figures 1 and 2, comprises a container, 1, wherein two trays for fractionation, 2, are located one above the other, usually in horizontal positions. The fractionating trays are provided with a large number of perforations, 6, and a descent tube, 7, which has an inlet port, 3, and an exit port, 4. In figure 1, only the tube is shown. of descent for the upper tray but it is understood that all the trays have similar descent tubes although the location is usually on the opposite side of the tray to that which receives a flow of the descent tube related to the tray that is immediately above. This maximizes the path of the liquid flow and the opportunities to get in touch with the vapor.

The liquid exiting the descent tube through the exit port, 4, is directed to the lower area of the descent tube, 5, which is next to the container wall and is not perforated. From there the liquid extends in the manner shown by the arrows in Figure 2 so that no part of the tray receives enough liquid to drip through the perforations in that part. The upper structure is very advantageous since it ensures that the liquid flowing out of the down tube is not channeled to the perforations in the platform of the fractionating tray in amounts such as to prevent steam from flowing through the perforations and causing dripping . Preferably, in order to ensure that the flow is first pounded in contact with non-perforated areas and extends in the same manner in the direction of all the perforated areas, a highly uniform degree of liquid / vapor contact is maintained.

Claims (2)

NOVELTY OF THE INVENTION CLAIMS

1. - A column for fractionation having an interior wall and consisting of a large number of horizontally arranged perforated fractionation trays, located one above the other within said column including a first fractionating tray drilled with at least one drop tube located next to the periphery of the tray to channel a run-off of the first tray through at least one outlet port disposed radially to a second tray for fractionation perforated directly below the first, said second tray comprises a lower area of the drop tube located directly below the descent tube of the first fractionation tray, characterized in that the outlet port of each descent tube is located in such a way that the flow from it is initially directed exclusively towards the inner wall of the column next to the drop tube, and at least one portion n the bottom area of the downcomer of the second tray is provided with a large number of perforations.

2. A column for fractionation according to claim 1, comprising a perforated barrier between the perforated area of the second perforated tray and the area immediately contacted by the liquid exiting the descent tube.