What is function of tray?

Answer 1

The basic reason for having a chimney tray is to segregate two (2) different Unit Operations within the same piece of equipment - usually a pressure vessel. This technique is used in a variety of processes.

For example, let's consider a TEG absorber (contactor). The basic process requirements for a TEG absorber call for the incoming feed gas to be totally devoid of any liquids - particularly water and/or hydrocarbons. In order to comply with this important specification, special, efficient vapor-liquid separators are installed upstream of the contactor. However, in certain situations - such as in offshore platforms - space and volume come at a premium and as a consequence, process engineers make use of a chimney tray to combine a vapor-liquid separator in the bottom section of the contactor tower and the actual, absorber section on the remaining top section of the same tower. By introducing a chimney tray between both section, the process engineer ensures that there will be vapor-liquid separation (one Unit Operation) in the bottom section and only the product moist gas stream will be injected into the bottom of the absorber section (another Unit Operation).

Another example can be found in strippers or distillation columns. Sometimes there are needs in either of these two types of Unit Operations to introduce side-stream drawoffs or to selectively take a liquid portion and impose another Unit Operation on it (such as heating or reboiling). Taking a drawoff and diverting it to a reboiler while returning the reboiler vapor product back into the top section of the drawoff is done in many distillation towers and strippers. This is done by incorporating a chimney tray and gives the operation a more realistic credit of having one additional theoretical separation tray because the chimney tray segregates the feed liquid and the product vapors to-and-from the reboiler.

The chimney tray does this without any moving parts.