Trays are used for mass transfer operations where the pressure drop limit is not critical. They are mainly used in high pressure distillation operations. However, in the case of a tray tower, there are some atmospheric, medium and vacuum operations. The trays are available in multiple configurations to meet customer requirements.
The valve tray typically has a cover that provides perforations of the sieve trays. The valve can be moved (conventional) or fixed. The valves provide additional resistance to the rising vapor phase, which can be discharged out. This helps to better interact with the liquid on the tray and increase efficiency. The valve tray has a better adjustment range. The valve is circular or rectangular in shape and can be moved vertically up/down to form a variable lateral opening that allows vapor phase to bubble in the liquid pool. When the vapor energy is very low, an increase in vapor energy will cause the valve to move up and the valve to be on the deck. The cage valve has a locking structure and a lighter movable disc located on the perforations. The disk provides a lower pressure drop because it provides less resistance to rising vapor phase.
The sieve tray is a flat perforated plate with no moving parts. The vapor rises from the perforations to the upper tray and crosses to the liquid stream. The vapor energy keeps the liquid from flowing down the hole. The latter moves through the tray and travels downstream through the tray below the tray. Sieve trays have better capacity and medium efficiency than valve discs and blister lid trays, but have limited flexibility over the operating range. Compared with other conventional trays, the main advantages of the sieve tray are low maintenance costs and low tendency to scale. In addition, Sieve trays are simple and easy to manufacture and relatively cheap compared to other mass transfer trays.
The fixed valve tray is a valve tray with a valve unit that is fixed in a fully open position and is a low cost fixed assembly that mimics the shape of the valve. They have a better turndown ratio than the sieve tray. Non-moving discs eliminate wear and sticking, but at the expense of lowering other valve trays. The valve can be flat dome shaped, triangular or rectangular.
The bubble cap tray is a flat perforated plate with a riser (e.g., a tube) around the perforations and a lid in the form of a cup over the riser. The lid is usually fitted with a slot or hole and the vapor comes out. The cover is mounted such that there is a space between the riser and the cover to allow vapor to pass. The vapor rises through the riser and is directed downward through the slot in the lid through the lid and finally bubbling through the liquid on the tray. Since vapor must pass through many channels, this results in higher pressure drop and lower capacity than other conventional trays. This kind of tray is used for reaction applications.
This deck-type vane liquid collector can be used in all towers. The liquid volume and residence time are controlled by using a high riser (round) on the pallet deck. A sump can be added on one side, both sides or at the center to facilitate liquid withdrawal. The risers can be made in sections/components to allow installation through manholes, which can then be welded to the seal welded deck.