7 replies to this topic

[Azzurro]

What is the actual purpose of using chimney tray in distillation/stripping column?Can anyone explain more details about chimney tray in hysys..i try to find it in tray sizing but i couldn't find it..

[Zauberberg]

Yes, there is a chimney tray in the Tray Sizing utility in Hysys. See attached snapshot and a chimney tray in the drop-down list.

As for the purpose of chimney trays, please refer to any distillation textbook - "Distillation Design" by H. Kister, "Applied Process Design" from E. Ludwig, or similar. I also believe that plenty of information can be found on the internet as well. Have you tried?

Attached Files

•  Chimney.jpg   134.09KB   214 downloads

[Zauberberg]

See attached.

Attached Files

•  Chimney Trays.pdf   54.65KB   945 downloads

[Azzurro]

yes, of course, there are plenty of information about chimney tray in internet n i already find it..thanks for your explanation and also for the attachments .

For the previous post, u said that the chimney tray can be excluded in thermo/mass transfer modelling the absorber because it does not contribute to the overall mass transfer process..it means we doesn't need to use the chimney tray in stripper column?

[Art Montemayor]

“What is the actual purpose of using chimney tray in distillation/stripping column?”

Azzurro:

Allow me to attempt to answer the basic question.

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.

However, there are some tradeoffs to consider in any chimney tray installation – as would be expected.

[Zauberberg]

For the previous post, u said that the chimney tray can be excluded in thermo/mass transfer modelling the absorber because it does not contribute to the overall mass transfer process..it means we doesn't need to use the chimney tray in stripper column?

If you look at the layout of a chimney tray, you can see that there is no direct contact between vapor and liquid phase as they flow/pass through the tray - meaning that there cannot be mass transfer as well. However, some of the mass transfer takes place due to heat transfer effects: colder liquid tends to condense small portion of uprising vapor as it hits the colder chimney tray metal, and also some small portion of liquid evaporates as well due to the fact that the tray metal is being heated by the uprising vapors. For practical/design purposes both these effects can be neglected.

From that point of view, you certainly do not need chimney tray as a mass transfer device inside the column. But you need it for other reasons, explained by Art in his post: as a liquid collector, and also as a vapor (re)distributor.

[Azzurro]

Thanks for all explanations about this topic and it's really2 help me for better understanding about the chimney tray.

[Padmakar Katre]

Dear Art and Zauberberg,
Great replies on the topic. Thanks really good to see such kind of perfect explanations.