4 replies to this topic

[curious_cat]

We have a 850 kg/hr light-organics stream (Fine Chem; not a refinery.  ) that needs to be heated from 30 C to 120 C. If I'm doing the calculations right, that's a duty of about 46 kW. 

 

What's the right equipment to do this in? Initially, I considered a small, off-the-shelf Shell & Tube HEX with ~3 barg steam on the shell side (~140 C)

 

Something like the ones here:

 

http://www.standard-...r=4&strMetaTag=

 

Problem is, for such a low flow rate of process fluid, even if I keep bare minimum velocities to prevent fouling (say 1 m/sec) I only need a 20 mm tube or so. Anything larger and my flow will stagnate. 

 

OTOH, my heat transfer area comes to around 1.8 m2 which needs quite a bit more than a single 20 mm tube. (I calculated a very conservative U of 500 W/m2 K; LMTD = 52 C) Longest tube I can get is ~2 m long. 

 

Even with 4-passes (plenty of head is available) it'd be hard to get the velocity of the light-organic up to an acceptable level. 

 

Am I doing something wrong or should I be thinking of a totally different kind of exchanger? What'd the more experienced guys suggest?  Or would (unconventionally) putting the steam on the tube side help? 

 

Additional Data:

Specific Heat ~2190 J/kg K

Density ~ 850 kg/m3 

Non corrossive

Process Fluid ~3 bar pressure

Edited by curious_cat, 10 August 2013 - 06:43 AM.

[Art Montemayor]

I would not use what you show.  It is nothing more than a low-priced, hydraulic or lubricating oil cooler, with no ability to clean out the shell side.  What I have always used in these relatively small duty applications is a Graham Helifow Spiral heat exchanger.  It has never let me down and is used quite extensively in industry for as long as I can recall.  Go to:

http://www.graham-mf...heat-exchangers

 

and you will find out about this unique and efficient unit.

[curious_cat]

Thanks. Agreed about the critique about fixed tubesheets. 

 

In general though, even if I went for a better mechanical design, a S&T is just not right for this application, right? Just confirming my understanding. 

[Art Montemayor]

Curious:

 

Why belabor the fact that you have a small heat duty?  There is no law against that - not is there any law that states that you MUST use a TEMA shell & tube heat exchanger.  Base yourself on engineering practicality.  If your basic scope of work calls for a heavy duty, shell & tube design, then so be it.  However, if you simply want to design for meeting the heat duty and are only ruled by the economics, the space, and the practicality of the application, then use whatever design suits your scope best.

 

Using a shell & tube doesn't make you a better heat transfer engineer, nor does it necessarily resolve your application in the best manner for you and your scope of work.  If a double-pipe unit suits your purpose and fits the scope, then by all means consider it an option.

[curious_cat]

Fair enough. Thanks.