As the boiler water begins to evaporate, the concentration of non-volatile dissolved solids left behind in the boiler increases as a function of the steam demand. If the dissolved solids content exceeds a fixed set point, foaming and priming occurs as the density of the boiler water increases, resulting in a carry-over of solids with vapour into steam lines and superheaters. This adversely affects safety in operation and inflicts serious damage on the steam generating unit and pipelines. To prevent this, boiler water with a high dissolved solids content is evacuated as necessary with the aid of a blowdown controller, conductivity electrode and continuous blowdown valve. If the maximum permitted conductivity exceeds the max. limit set in the controller, an alarm is triggered and the burner shut down and locked, to protect the boiler plant.
However, the controlled excess of phosphates or the complexing of residual hardness in the boiler water also produce sludge, which settles as a fine layer on heating surfaces and the floor of the steam generating unit.
This has an insulating effect, which poses a serious threat of damage to boiler plates due to overheating. Use of an automatic intermittent blowdown control, a solenoid valve and an intermittent blowdown valve enables the best possible evacuation of this boiler sludge.