CARRYOVER CONTROL

TYPES OF CARRYOVER

Carryover is caused by two mechanisms, priming and foaming.

Priming is the sudden violent eruption of boiler water, which is carried along with steam out of the Boiler, usually caused by mechanical conditions.

One of the major causes is a sudden increase in the steam demand. This creates a rapid lowering of pressure on the water surface.

The surface erupts, much like the water in a bottle of soda. Nothing can be done about this chemically. It is controlled mechanically, either by using slow-opening valves, or by moderating charges in steam load.

PRIMING

Priming can cause deposits in the main steam head, and around main steam header valve in a short period of time, since it usually involves the deposition of relatively large amounts of solids when it happens.

FOAMING

Boiler water foaming causes carryover by forming a stable froth on the boiler water. This is easily carried out of the boiler along with the steam. Foaming increases with the amount and nature of the impurities in the boiler water.

Higher alkalinity, higher conductivity and impurities, which affect the surface tension of the water, all increase foaming. Over a period of time, foaming can completely plug a steam or condensate line.

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