6 replies to this topic

[Rudra]

Hi
I have a question regarding full support plates in X or kettle type shells. When we specify full spport plates, how the shell side flow takes place.

What i understand from a full support plate is a plate with holes drilled for tubes to pass through. The shell side flow will take place only though shell to baffle clearance. Now shell to baffle clearance will be only 4-5 mm. Is it enough for shell side flow to take place.

Coming to a typical problem i am facing is, i am designing one vertical exchanger where no mixing or turbulance is allowed on shell side. so i want so specify full support plates in place of baffles. Liquid will flow from bottom to top on shell side. My idea was to keep some empty space in tubesheets. Support will have some riser type of holes for shell side liquid to pass in the empty space where no tubes are there. Without having any such arrangement, will shell side liquid will flow and if yes how?

[Art Montemayor]

Rudra:

You title your post "Support Baffles" and then go on to describe what you call "full support plates". I fail to understand precisely what you are describing. I have never heard of what you call "full support plates". I am not saying that they don't exist or that they are not described as such in India; but they are not described in TEMA or in the USA. And that's why I have a problem understanding what you mean.

The term baffles are what are used to support the tubes in a heat exchanger bundle and also to direct the flow of shell-side fluid. Also, what is an "X" shell? Is this a TEMA description? Or is it a DIN description? Or is it an Indian description? Please be specific and draw us a sketch showing what you are trying to describe in a detailed drawing. Refer to my attached Excel Workbook for help.

 TEMA_Designations.xls   108KB   129 downloads

[jcazenave]

sorry but I think some clarification are necessary

X shell are cross flow exchanger,ie the shell side flow is perpendicular with the tube.

Full support baffle are baffle with no baffle cut. They are used in cross flow exchanger because they are parallel with the shell side flow.

1) the flow does not go through the hole or clearance with the shell, it is between the baffles.

2) you are describing a "normal" exchanger not a crossflow exchanger. In this case you can not use full support baffle. Vibration is a complexe issue, some idea would be to use crossflow with support baffle, no tube in window (with supports) etc...

I hope this helps.

[Art Montemayor]

jcazenave:

Thank you for the clarification. Yes, the TEMA "X" shell type is meant for total cross flow across the shell. As such, total support, blind (no baffle cut) baffles are used to isolate each of the cross flow sections. This design is particularly effective in reducing the shell-side pressure drop and is used in vacuum tower overheads condenser applications.

I was expecting Rudra to understand and acknowledge this point and thereby improve his communication or explanation of just what it is that he/she is describing.

A support baffle is nothing more than a circular plate with a diameter slightly less than the internal diameter of a TEMA cylindrical shell. It is drilled with holes aligned to allow for all the tubes in the shell. This simply means that such a "baffle" is, in reality, a bulkhead – since it does not allow for shell side flow, beyond its location, in the normal direction of the shell length. It can, however, allow for shell-side flow ACROSS the tube bank (& within its confines). This flow would have the shell entry and exit nozzles directly opposite each other (180 degrees apart). You would require a set of such nozzles for each section confined by a set of support baffles. This is such a laborious and lengthy description in order to accurately describe the system that I often resort to a simplified, common-sensical engineering sketch that says it all – efficiently and detailed.

Rudra is concerned with support baffle clearance causing a by-pass (I think…) and then writes about a vertical exchanger that has nothing to do with that. I hope he returns to set things straight and clear with full, detailed explanation of what he is concerned with. My issue is that we can't help when the post is difficult or impossible to understand. This is not caused by a language barrier; this is caused by a logic and communications barrier – which are dependent on clear, organized thinking.

I hope Rudra follows up with details and a sketch.

[Rudra]

First of all, i am sorry to confuse you because of a very brief and non elaborate post. I will keep in mind next time to write in a elaborate and better way.

I agree to both of you in a way the flow takes place in X type shell with full support plates. I just wanted to confirm that when we give full support plates, the shell side inlet/outlet nozzles will be provided for each section confined by the support plates.

Further, i am working on a different design, where the vertical shell and tube exchanger is essentially a plug flow reactor with exothermic reaction. The heat of exothermic reaction being very less, heat transfer area requirement is too low 30 m2. while from the reactor volume requirement, with tube side reaction, the exchanger area goes to 500 m2.

In order to reduce the size, i was thinking to provide the reaction on shell side with very low velocity and minimum required tubes placed at higher pitch. This will reduce the Shell side being the plug flow reaction, no back mixing is to be allowed. Baffles will not be useful in this case. But with 6 m tube lenght some kind of support is requred. I was thinking to provide full support plates. With some sort of orifice arrangement like a distributor to allow the upward flow of reacting liquid.

The full support plate will have holes drilled for tubes as well as larger size orifices for shell side liquid to pass.

My question was without giving such orifices for shell side liquid, will the vertical flow take place? I do not think the flow will take place vertically with full support plate.

Please throw some light on this.

Thank you

[coolman]

The x type shell as shown in TEMA type table normally shows only one inlet nozzle and two outlet nozzles. As per your explanation (and logically), there should be one nozzle each for every space between the two full support plates. Would appreciate if you could post the sketch that you were talking about.

[jcazenave]

I dont have the TEMA accessible but, I think that you are confusing with a J shell which is one inlet and 2 outlets.

For an X-shell, the number of inlet/outlet is not defined, you can have 1 to many.

Kind Regards