Cleaning a feedwater economiser
Feedwater economiser cleaning is the removal of gas-side fouling and any water-side deposits from the economiser that recovers flue-gas heat into boiler feedwater. Restoring its clean surfaces recovers the stack-gas heat the economiser is meant to capture and lowers the final flue-gas temperature back toward design.
What it is
An economiser is a flue-gas-to-feedwater heat exchanger in the boiler's exit gas path, and over time its gas-side surfaces foul with soot, ash and — if the metal runs below the acid dew point — sticky acidic deposits, while the water side can scale. Cleaning removes that fouling so heat transfers freely again. The goal is to bring the leaving flue-gas temperature and feedwater rise back to the clean-condition values.
Why it is done
A fouled economiser transfers less flue-gas heat to the feedwater, so the stack temperature rises and the heat that should have preheated the feed is lost up the chimney — a direct, continuous fuel penalty. Acidic deposits also corrode the tubes, threatening leaks. Because the loss shows only as a slowly rising stack temperature, fouling accumulates unnoticed. Cleaning on the right trigger restores the heat recovery, protects the tubes and keeps the boiler's overall efficiency where commissioning set it.
How it is done
The economiser's health is trended from the flue-gas temperature drop across it and the feedwater temperature rise, compared with clean-condition values, so cleaning is triggered on performance rather than calendar. The gas side is cleaned by soot-blowing, water washing or mechanical means appropriate to the deposit, with washing managed to neutralise acidic effluent and protect the metal. The water side is checked for scale and descaled if feedwater chemistry has allowed deposits. Causes are addressed — keeping metal above acid dew point and feedwater within limits — and performance is re-measured to confirm recovery.
- Trend temperature drop
- Trigger on performance
- Clean gas side
- Manage wash effluent
- Check & descale water side
- Address fouling cause
What to watch for
Cleaning on a fixed calendar rather than on the measured temperature drop either wastes outages or lets fouling cost fuel between cleans. Letting the economiser metal fall below the flue-gas acid dew point at low load creates sticky, corrosive deposits that foul fast and thin the tubes. Aggressive water washing without neutralising the acidic run-off corrodes the very surfaces it cleans and the downstream ductwork.
Related practices
Retrofitting removable insulation to hot equipment
Conducting a hot-surface temperature survey
Maintaining a thermal oil heating system
Related topics
Waste Heat Recovery in Industry: Methods and Where It Pays · Economiser · Flue Gas Loss
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