Our CDU overhead air cooled heeat exchanger is designed with 156 tubes and 3 passes. we have recently shutdown the unit to plug 32 leaked tubes:
- 20/52 tubes plugged in pass 1
- 12/52 tubes plugged in pass 2 .
We would like to estimate the effect of tubes plugging on the overhead ACHE performance by simulation (example wtih PRO II ).
How could we do that ?
Eric Vetters, ProCorr Consulting Services, email@example.com
You could treat each pass like a separate heat exchanger. That would make it like 3xchangers in series operating countercurrently with the CDU OH on one side and air on the other. You can then reduce the area of each pass by the number of tubes plugged. You should be able to do these calculations in a process simulator. A simpler but less accurate way is to reduce the total area appropriately and use Q=UAF(LMTD) to estimate the duty with the new area. A in this case is 124/156 * original area.
A bunch of leaking tubes is usually a sign of significant corrosion going on. Over time tubes will foul or plug with salts and/or corrosion products, so air cooler performance is likely to continue to decline after you start up with plugged tubes. You can qualitatively monitor fouling in the ACHE using infrared thermography. You can also monitor DP between the tower overhead and the accumulator.