Characteristics of boiler feed water
Water absorbs more heat for a given temperature rise than any other common inorganic substance. It expands 1600 times as it evaporates to form steam at atmospheric pressure. The steam is capable of carrying large quantities of heat. These unique properties of water make it an ideal raw material for heating and power generating processes.
Feed-water purity is a matter both of quantity of impurities and nature of impurities: some impurities such as hardness, iron and silica are of more concern, for example, than sodium salts. The purity requirements for any feed-water depend on how much feed water is used as well as what the particular boiler design (pressure, heat transfer rate, etc.) can tolerate. Feed-water purity requirements therefore can vary widely. A low-pressure fire-tube boiler can usually tolerate high feed-water hardness with proper treatment while virtually all impurities must be removed from water used in some modern, high-pressure boilers.
The following tables are extracts of recommended levels from APAVE (Association of electrical and steam unit owners), up to pressures of 100 bar for medium steaming rates and for volumes of water in the chambers sufficient to properly control the blow down rates, and from ABMA (American Boiler Manufacturers Association) in its standard guarantee of steam purity.
Find information about the main problems occurring in boilers: scaling, foaming and priming, and corrosion.