The Normalpractice is to use a downcomer clearance of 1/2 inch less than the overflow weir height to provide a static liquid seal This is the vertical distance between the tray floor and the bottom edge of the downcomer apron. As the liquid leaves the contacting area of the tray, it flows over the tray weir to enter into the downcomer. Cryogenic columns have tray spacing of 200-300 mm.Īn outlet weir maintains a desired liquid level on the tray. Prime factor in setting tray spacing is the economic trade-off between column height and column diameter. Generally tray spacing ranges from 8 to 36 inches (200 mm to 900 mm). Tray spacing is the distance between two trays. If the weir loading exceeds this the tray needs redesign with higher number of passes. The maximum allowable weir loading is 13 gpm/in of weir length. From a capacity viewpoint, a liquid rate greater than 6 gpm / inch of weir (weir loading), is the rate at which a higher number of flow paths should be considered. The numbers of flowpaths of liquid on tray are 1, 2, 3 or 4 as per liquid capacity requirement of column. Valve trays combine high capacity and excellent efficiency with a wide operating range.Ĭomparison between Common Conventional Trays. The vapour flows through valves which are installed parallel to the outlet weir. Valve trays are perforated sheet metal decks on which round, liftable valves are mounted. Each tray should be designed so as to give as efficient a contact between the vapour and liquid as possible, within reasonable economic limits. The particular tray selection and its design can materially affect the performance of a given distillation, absorption, or stripping system. If this reference is not available the guideline as per Appendix 1 are to be used The industry, based on its experience, has standardised the type to be used in certain services. As these are guidelines for selection of trays or packings for a particular service, it is recommended to analyze each design case on its own merit for selection. The factors discussed below influence the choice between trays & packings. This zone has two functions, first moving liquid from one contacting tray to another and second disengaging vapour from liquid.Įach of these zones takes up vertical and horizontal space in the tower. Vapour space above the active area: This is the zone in which liquid is separated from vapour.Active area for mixing vapour and liquid: This is the zone where mass transfer occurs.Liquid enters the tray from a downcomer above and leaves via a downcomer below.Ĭonventional Tray has three functional zones: In any conventional tray vapour rises through the liquid pool on the tray deck and then disengages from the liquid in the space above the deck. All the simulation results, which predict a certain number of theoretical stages, can be converted to actual trays depending upon tray efficiency for a particular service. Tray columns are widely used in various types of mass transfer operations. One of the most prominent hardwares used for mass transfer is tray. This stage of design converts process requirements into actual hardware. Once the process design stage ends, the equipment design begins.