The conductivity and pH value of boiler water in No.1unit of Midong Thermal Power Plant were over standard.So the water wall tubes suffered the risk of alkaline corrosion and boiler water concentrate corrosion.Detection finds a larger number of free sodium hydroxide appears in the boiler water.This is because the heat-supply network drain which is used as the feed water supplement water was polluted by leakage of circulating water of district heating system heater. The check valve between the steam separated from continuous blow-down flash vessel and the deaerator had some defects

leading to invalid blow down

so the boiler water were over concentrated

a larger number of free sodium hydroxide appeared in the boiler water

resulting in boiler water abnormality eventually.Finally

after improving continuous blow down

the boiler water turned back to normal.