1 reply to this topic

[drdave]

Hello All !!!

In stead of conventional water cooled Ammonia condensers for tank boil off recovery, Can we think of shell & tube intercooler where oil contaminated (say 100 ppm) vapour ammonia gets condensed by -33 deg_C liquid ammonia (10~25ppm oil content) from ammonia storage tank pump out.
I request comments on heat exchanger performance point of view considering following:
What are the effects of oil fouling on shell side & tube side?

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[Art Montemayor]

Dr Dave:

I consider this application an excellent example of energy conservation. If you have sufficient heat load to apply to the cold, liquid NH3, then do it, by all economically feasible means. This is a good, logical and practical engineering thought and application. This is also an excellent example of what we are supposed to be doing - or thingking about - 100% of the time.

The one outstanding problem I can foresee right away is the type of heat exchanger/condenser that you need. This exchanger will have to take a large temperature difference between streams and will require a self-compensating type of tube bundle expansion design. I doubt if you want to consider a standard TEMA type of exchanger design. You surely will require SS construction and a "spiral" - or other type - of tube bundle. This will run more expensive than the normal TEMA design - but is a prerequisite, in my opinion. I would not depend on using a TEMA shell with an expansion joint. There may be other problems that exist, but this one comes to mind immediately.

You should have no problem in handling the normal oil content present in the screw compressor's discharge. This is no different than if you were feeding liquid NH3 at -28 oF to an evaporator for refrigeration effect. The oil used in NH3 compressors is (or should be) of refrigeration grade and will not foul to a noticeable extent. It may place a slight coat on the tubes, but it still transfers heat with a negligible resistance.

Of course, your heat (or "cold") recovery will only be effective during those times when both streams are available at the design rates. And this, as you explained in another prior thread, is not 100% of the time. As long as the recovered cold refrigeration energy is sufficient to yield a return on the investment, the application is sound and represents energy savings and less pollution (as generated by the incremental electrical energy saved and not required).

Your sketch is a succinct and accurate description of your scope of work. It succeeds in transferring your basic data and scope in a very accurate fashion. I hope my comments are as accurate and understandable as your description.

Art Montemayor