Carryover with steam, in steam technology, refers to transport of moisture and impurities with steam.
The moisture carryover with steam is quantified by the mass flow rate of liquid water per mass flow rate of steam. In
boiler
A boiler is a closed vessel in which fluid (generally water) is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, central h ...
s producing
saturated steam
Steam is a substance containing water in the gas phase, and sometimes also an aerosol of liquid water droplets, or air. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporization ...
, it is typically about 0.1% but may increase with
fouling
Fouling is the accumulation of unwanted material on solid surfaces. The fouling materials can consist of either living organisms (biofouling) or a non-living substance (inorganic or organic). Fouling is usually distinguished from other surf ...
and boiler impurities.
The carryover of impurities (for example, sodium, chloride, copper, silica) with steam can be divided into two parts:
[Procedure for the Measurement of Carryover Boiler Water into Steam, The International Association for the Properties of Water and Steam, Technical Guidance Document, Berlin, September, 2008]
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# mechanical carryover of the impurity with liquid water droplets entrained with the steam, and
# vaporous carryover of the impurity in steam.
The total carryover is a sum of the mechanical and vaporous carryover. The vaporous carryover generally increases with increasing steam pressure. In low pressure boilers, the mechanical carryover of impurities prevails, possibly with the exception of more volatile impurities, like silica.
The impurity carryover can cause corrosion and fouling of steam turbines, reheaters, and superheaters.
See also
* Priming (steam engine), Priming
References
{{reflist
Boilers