2 replies to this topic

[EAGLE80]

Hi
I am new member and want to discuss one process development problem.

We are in the phase of developing some type of process to utilize excess liquid nitrogen to cool utility water. Can liquid nitogen be used to cool water from 110 degF to 41 degF in S&T type Heat Exchanger? Due to very low temperature of N2 i.e. -283degF, water in tubes of exchanger can freeze.

Actually this is existing facility and existing intercoolers (2+1) are not compatible for cryogenic conditions. That's why we hace to cool sea water going to intercoolers. Sea water can be cooled in S&T type HE or in vaporizer as other options like using glycol or mixture of water & glycol as a media, is not economical.
Is there any one who did the same of type of study.How can I confirm that wich option is sutiable?

[Majid-Process]

Hi
There are some issues for such application:
1) You will need special materials for such low operating temperatures and available equipments will not be applicable.

2) Due to high temperaure gradiant (about 400 F) available HE can not tolerate this new condition.

3) Similar operating temperatures are applicable in LNG industry. Normally Plate HE is used for this application.

4) Flow control of such system will be extremly difficult as in case of flow decrease below minimum required flow to prevent ice formation, the water will be freezed and all relevent connections and equipments will be damaged due to water expansion.

Cheers

[Art Montemayor]

Even if you comply with the correct, expensive cryogenic materials of construction, you will not succeed in using liquid nitrogen to cool utility water with a shell & tube heat exchanger. What you are contemplating is simply not a practical, controllable process. You have already stated the most practical reason for my assertion: The utility water will freeze, unless you can ensure a sufficient amount of water flow rate to continually avoid a local "cryogenic cold spot". Any flow excursion in your cooling water will expose the exchanger to a total freeze up and subsequent shut down. Additionally, you will find that you will be exposing your exchanger to extreme potential contraction and expansion forces that will ultimately change the mechanical design and fabrication of your exchanger. You will most certainly be force to used to use a "U" tube bundle (a TEMA type BEU, probably) in order to protect the bundle and the shell from contraction/expansion failure.

There are other problems – such as the insulation required on the shell side (to conserve the heat transfer and protect personnel). Not only will you find this type of insulation application hard to design, but also very expensive to install and maintain. Normally, liquid Nitrogen (LIN) is insulated with a vacuum jacket or by a "cold box" – both costly and complex.

Your idea is not a new one; many others, including myself, have found ourselves in a situation where we had a cryogenic fluid in need of vaporization and a cooling process in need of colder water. The idea of resolving both needs by combining them is an old one. The only time I have applied it successfully is with an excess of cooling water flow rate and utilizing a totally submerged cooling coil in an open water "box". This scheme worked for me, but only as an energy savings project and one that could not be maintained steadily due to the intermittent introduction of the LIN. The LIN is vaporized inside the coiled tube bundle. Operation is kept safe due to the visual and physical availability to test the flowing water. Any potential freezing of the water can be mitigated or corrected externally. This method is bulky and, although low in capital cost and simple, has little or no temperature controls. You take whatever cooling you can get and that's all you can ask for.