Hello Everyone,
Thanks in advance for helping me in this matter.
I am a process engineer at a salt evaporating plant. We have a multiple effect evaporators here. The general heat exchanger and evaporator's drawing is attached. We are basically using the steam generated from the previous evaporator to heat the brine in the next evaporator. This steam will have some non-condensable gas in it. Currently, we have been fighting with a heat exchanger that constantly have an increase in its LMTD, whereas other heat exchangers are not.
We have been looking at the possibility of fouling tubes, non-condensible gas blocking the heat transfer surface, condensate flooding in the shell side and steam side scale formation.
Fouling tubes: Since it is a mixure of CaSO4 and salt slurry going through the tubes, I expect there would be plugged tubes or scale fomation inside the tubes, but each time during the shutdown, we open the manway to check, there are minmum amount of plugged tubes and I do not really see any scale on the tubes.
Non-condensable gas: We have two nozzles locating at the top and bottom of the heat exchanger (shell side) to get rid of the non-condensable gas.
Condensate flooding: The condensate drain line is just located a few inches above the bottom of the tube sheet, so whatever it is condensed, it should be removed. There should be minimum amount of condensate in the shell side. The condensate drain line is connected to the side of a condensate pot. where the condensate level within the pot is higher than the drain line.
Steam side scale formation: Never considered before. Not sure if this is causing the problem.
Another fact is that this evaporator and circulation loop is much smaller than the other 3 evaporators. I know the circulation loop is 24'' whereas others are 30''. I am wondering if the vapor release area (evaporation surface area) is restricted that it cannot release the steam in the evaporator that caused this increased LMTD?
I am trying to figure out what really causing this increased LMTD and I am wondering if anyone here has some experience on solving this issue?
Thanks a lot in advance.