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Backup Vaporization against Circulating CW Disclosure Number: IPCOM000132290D
Publication Date: 2005-Dec-06
Document File: 2 page(s) / 251K

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The Prior Art Database

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Backup Vaporization against Circulating CW

An ASU (air separation unit) generally uses recirculating CW (cooling water) as the cooling medium in the intercoolers and aftercoolers of the air and product compressors. The heated CW is then recooled in a CT (cooling tower) by warming and humidifying air drawn through the tower by CT fans, before being pumped back to the compressor coolers.

In the event that the ASU trips, there is often a requirement that the normal ASU gaseous product supply be maintained by vaporizing stored backup cryogenic liquid.  A variety of heat sources have been used in the past for such backup vaporization.

It is known to use ambairs, where the backup liquid is vaporized against ambient air. This is particularly suitable for relatively small backup flows and has the advantage the heating source (ambient air) is secure.

For larger backup flows it is advantageous to use steam as the heat source for the backup vaporizer as steam driven vaporizers are relatively small due to the high heat transfer coefficients they have. However, at some ASU sites there may be no steam utility available.

While electrical backup vaporizers could be employed, the very large backup vaporization duty would result in very high power requirements unless the backup flows were low (when ambairs would be more economic and reliable).

It is known to route the returning heated recirculating CW through a backup vaporizer to provide the necessary vaporization heat. If  one or more of the ASU compressors still operated during the trip period, then the circulating CW would still be being heated in the machine coolers before it reached the backup vaporizer. i.e. it is indirectly compression heat which vaporizes the backup liquid.

A particular difficulty for the supply of vaporization heat applies to a situation when firstly high vaporized backup flows are required, secondly there is no steam utility and thirdly that it has to be assumed that no ASU compressor will operate during the backup period. The options for backup vaporization heat are then more limited:

1) The use of ambair vaporization would be uneconomic and require an enormous plot area due to the high backup flows.

2) Electrical vaporization would be uneconomic and the necessary electrical supply may not be available during the trip.

3) One could...