Water Slugs Reaching the Dryer — Protecting Molecular Sieve Beds with a Catch Pot and Coalescer
An adsorption dryer is built to remove water vapour — not liquid water. When condensate from a cooler or cold pipework reaches the bed as a slug or as aerosol, the adsorbent is loaded far faster than planned and the outlet dew point rises.
Recognise the Symptoms
- Outlet dew point of the dryer rises much earlier than expected after a media change
- Adsorbent has to be replaced or regenerated far more often than planned
- Wet, clumped or discoloured adsorbent found when the dryer is opened
- Visible liquid in the line between cooler and dryer, especially after start-up
- Pressure drop across the dryer increases because the bed is wetted or fouled
Root Causes
No bulk liquid separation after the cooler
condensate formed in the cooler is carried directly to the dryer
Coalescer used as the only liquid stage
a coalescing element is designed for aerosol, not for slugs of liquid; bulk water floods the element and passes through
No coalescing stage
fine water aerosol that a simple separator cannot catch is carried into the adsorbent bed
Drain not emptied
the liquid collected in the separator or filter bowl is re-entrained once the bowl is full
Start-up transients
condensate collects in cold lines during shutdown and is swept into the dryer when flow starts
Diagnostic Checklist
- 1Is there a catch pot (bulk liquid separator) directly after the cooler?
- 2Is a coalescing filter installed between catch pot and dryer?
- 3How often are the drains emptied — and is the interval matched to the amount of condensate?
- 4What are the gas temperature and pressure before and after the cooler?
- 5Is the dew point measured downstream of the dryer, and how quickly does it rise after a media change?
- 6Does liquid appear at start-up after a longer shutdown?
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