11 replies to this topic

[process_persia]

Dear Engineers,

I was wondering if anyone could give me some criteria for condenser TEMA Type selection. In fact, I did some investigation in my own project which was a petrochemical process (Propane Dehydrogenation).

What I saw was that for all water cooled condensers BXM TEMA type was chosen. I know by that by splitting the vapor flow pass in condensers, the presure drop can be reduced compared to an E Shell which is a positive point. But are there any other considerations for Condenser selection with respect to coolant medium type, fouling or other operating conditions and other factors? (something like the reboiler selection criteria stated in GPSA)

Thanks

[Art Montemayor]

Process:

I have never seen or heard of a TEMA "BXM" designation. That doesn't mean there isn't one; it just means I'm ignorant on that subject. Could you enlightment me by describing it? I am attaching a copy of what I know of TEMA designations and I would appreciate it if you could sketch out a similar drawing of the BXM type.

I believe you are looking for a "recipe" regarding the determination of how to select a condenser for a given service. I know of no such formula or instructions. With respect to condensers, I usually guide my selection and recomendation based on the Scope of Work and the Design Basis. I guide my recommendations by sticking to the basics: fluids handled and their properties, location, flow rates, condensate removal, orientation, materials of construction, pressure drops available, maintenance requirements, and economics. There may be other factors to consider.

Attached Files

•  Art\'s TEMA Designations.xls   84.5KB   239 downloads

[process_persia]

Dear Art,

First of all, I am so happy of having a reply from you for the first time. I am sure that by the end of this thread I will learn too much from your answers which are based on your valuable experiences.

I will try to furnish as much information as I can to give you a clear picture for judgment. I am attaching one of these condensers from a P&ID sheet. this is the depropanizer condenser which condenses a stream consisting mainly of propane. The conditions for process streams are:

Tube side: Cooling water (Supply temp: 35, Return Temp: 45)
Shell Side: Propane rich vapor (Inlet Temp: 52.1 Outlet Temp: 51.7)

I also got valuable info about X-Shell exchangers from a very great book about heat exchangers titled: "Heat Exchangers Selection, Rating, and Thermal Design, Second Edition 2nd Edition" Authors: Sadik Kakac; Anchasa Pramuanjaroenkij; Hongtan Liu. I found this book really instructive and I would like to share this with others.

I would be glad to get your feedback based on the above info

Attached Files

•  BXM Type exchanger.xls   193.5KB   175 downloads

[Art Montemayor]

Process:

I refer myself to your request for criteria on the selection of TEMA Type condensers.

I appreciate your response with an accurate P&ID description of a condenser. Although this doesn’t tell us anything of how the unit is fabricated, it tells a lot of how it is expected to operate in service. In trying to interpret the application, I find the P&ID nomenclature and its quality different and lacking from what I’m accustomed to working with. I specifically don’t like the lack of flow arrow heads. I note that the flow direction of the cooling water in the tube side is not even indicated by arrow heads. I would assume the water is flowing from the bottom nozzle towards the top. What I look for in a P&ID is an indication of what is taking place in the process. And here, I believe I can spot that what we have is a liquid propane vessel used to capture and hold liquid propane that is entering as a pumped liquid and also a gravity-fed, condensed stream from what seems to be an overhead propane vapor condenser that is shown as a pure “cross-flow” unit – but with clear and detailed instrumentation that is apparently designed to maintain (and possible vary) a liquid level inside the condenser.

Any effort to maintain a liquid within a condenser immediately should alert us to two possibilities in the scope of design of this unit:

• The condenser is meant to SUB-COOL the resultant product; this is a performance function beyond just condensing (removing latent heat); it also entails the removal of sensible heat.
• The condenser is meant to control its own condensing capacity by varying the liquid level in the shell side and, thereby, varying the effective condensing area and its capacity.

Although the P&ID doesn’t indicate it, I suspect the shell type could be a TEMA “H” – but then, it could also be devoid of any baffles – either vertical or horizontal. Only the Data sheet or the fabrication drawing would tell us the details.

I can only surmise that this condenser is meant to condense a varying capacity of propane-rich vapors and that the capacity is varied by varying its surface area with a liquid propane internal level.

Perhaps you can enlighten us more.

[process_persia]

Dear Art,

Attached please find the mechanical drawing of the abovementioned heat exchanger along with nozzle data. The P&ID also showed the reflux drum (10C001) and the Reflux pumps which pump this liquid back to the depropanizer. More info about this exchanger:

Number of passes (Shell/ tube): 1 / 8
Number of tubes: 3178
Tube length: 6m
Tube layout: 30 deg
Tube OD/ Wall thickness: 25.4 / 2.11 mm
Number of baffles/ supports: ---- / 8
Shell ID: 2000 mm
Area: 1478 m2
Velocity (Shell/tube)(m/s): 0.2 / 1.3
Pressure drop (Shell/tube)(bar): 0.1 / 1.0

Hope the data can clarify the idea behind this selection

By the way, If we want to select the condenser TEMA Type only based on coolant medium, what are the criteria?


Regards

Attached Files

•  BXM Type exchanger_Rev01.xls   759.5KB   130 downloads

Edited by process_persia, 23 August 2010 - 11:28 PM.

[jcazenave]

The X type is a pure cross flow exchanger. The shell side flow is coming from a number of nozzle (2 in your case) and leave the exchanger on the opposite side.

There are a number of support baffles (parallel to the flow)

This type of exchanger are mainly used when low pressure drop is required as the HTC are usually smaller than the other type of exchanger. I doubt that you can achieve the same low pressure drop with another type of exchanger.


Kind Regards

[srfish]

-

[djack77494]

Although the P&ID doesn't indicate it, I suspect the shell type could be a TEMA "H" – but then, it could also be devoid of any baffles – either vertical or horizontal. Only the Data sheet or the fabrication drawing would tell us the details.

I can only surmise that this condenser is meant to condense a varying capacity of propane-rich vapors and that the capacity is varied by varying its surface area with a liquid propane internal level.

Art, I think of a TEMA "X" shell as sort of an "H" shell on steroids. There should not be any horizontal baffles present. My past approaches to this type of exchanger were in Vacuum Tower jet condenser service. There pressure concerns of course dominate. We had (if I recall correctly) 4 inlet and outlet shell nozzles on the last one I worked on, so you're not limited to just 2 sections within the exchanger. I have no idea regarding how or why one would want to control the liquid level inside, especially since you're probably talking about more than one independent level control loop that would be needed.

Process, I have no idea how to answer your inquiry about selecting TEMA type based on coolant. I suspect you're falling into the trap of thinking all this design stuff is just about following some sort of "cookbook".

Edited by djack77494, 09 September 2010 - 09:06 AM.

[process_persia]

Dear Djack,

Maybe you are right about the trap I am about to fall into. But actually what I need are some simple hints regarding this selection based on some factors like (fouling tendency, pressure range as well as the available refrigerant).

Of course these criteria can be shaped during the years I get more experience in design but I just needed a clue from which I get started.

Anyway, thanks for the technical discussions that you, Art and other members contributed to this post.

[chemsac2]

TEMA type selection is a vast topic and few guidelines can not cover it. Also, I have seen TEMA selection contrary to guidelines as well.

TEMA designation specifies Front end, Shell and rear end of the exchanger.

Front end:

A - used for low tubeside pressure and fouling tubeside fluid
B - used for high tubeside pressure and relatively less fouling tubeside fluid
C and N - for toxic or hazardous fluids where intermixing of shell and tubeside fluids is to be avoided.

Shell:

E - general purpose shell, high HTC and pressure drop
G/H - for horizontal thermosyphon
F - for temperature cross, low shell DP utilization applications
J - for condensers where nozzle size is constraint w.r.t. shell diameter
X - condensers where pressure drop allowed on shellside is very low (typically vacuum condensers)
K - kettle exchangers

Rear end:

L - similar to A
M - similar to B
N - similar to N above
P/S/T - Floating head exchangers (S most common, T for kettles)
U - U-tube exchangers

Selection of fixed, U-tube and floating head exchangers affects TEMA selection as well.

Refer to Effectively Design shell and tube heat exchangers by Rajiv Mukherjee, CHEMICAL ENGINEERING PROGRESS, FEBRUARY 1998 (available on google).

Regards,

Sachin

[process_persia]

Dear Sachin,

Thank you for the reply and the paper you recommended. it was pretty instructive.

[Zauberberg]

This is a bit late reply, and related only to vacuum condensers, but it's worth reading for sure: http://www.graham-mf...bVacuum/217.PDF