25 May 2005
Reasons and Criteria for Treating Makeup Water
Reasons for Treating Makeup Water. Makeup water is treated to
remove or reduce the concentration of any unwanted impurity, including impurities that
will cause corrosion, create a deposit or scale in the system, or otherwise interfere with
the operation of the industrial water system or limit the use of the original water. The
process of treating makeup water often results in water conservation, which minimizes
the chemical treatments in terms of frequency and amount of use and the resulting cost.
Criteria for Treating Makeup Water
Makeup Water for Cooling Tower Systems. To allow the system to
operate at a minimum of 3 COC, the makeup water needs to be of a minimum standard
of quality. Pretreatment of makeup water for cooling towers is not required if the levels
of impurities in the water are not excessive. Refer to Chapter 4 for factors limiting COC,
including mineral limitations.
Makeup Water for Steam Boilers. The quality requirement for makeup
water often necessitates using water softeners (zeolite or ion-exchange units) to remove
water hardness before use. Dealkalizers can be used to remove alkalinity. High-quality
steam applications require demineralization or RO, or both. Refer to Chapter 3 for
Makeup Water for High-Temperature Hot Water Systems. The makeup
water for high-temperature (177 C [350 F]), high-pressure hot water systems should
be softened when its total hardness exceeds 10 parts per million (ppm) as calcium
carbonate (CaCO3). See Chapter 5 for specific requirements.
Other Systems. Soften the makeup water for chilled water systems and
for dual-purpose (hot and chilled) systems if its total hardness exceeds 250 ppm (as
calcium carbonate [CaCO3]). For hot water boilers, treat makeup water with sodium
sulfite and caustic soda, and soften makeup water used for diesel jacket systems if the
total hardness of the raw makeup water exceeds 50 ppm (as CaCO3). Refer to Chapter
5 for specific requirements.
Measurement of Makeup Water Rates. Knowing the use rates of
makeup water is essential for calculating proper operating data on cooling towers and
steam boilers. You may estimate makeup water use rates by recording the time it takes
to fill a container of known volume with water obtained from a blowdown line or,
preferably, measured with an appropriately sized makeup meter to provide more
accurate values. Filling a container is not a recommended method for measuring hot
water streams such as boiler blowdown.
MAKEUP WATER TREATMENT METHODS. Treatment of industrial
makeup water is a process of external water treatment. External treatment involves the
treatment, by various processes, of makeup water to remove or reduce hardness,
alkalinity, dissolved gases, or other impurities before the water enters the water system