Boilers and cooling towers share two major water related problems: deposits and corrosion. As steam is generated by a boiler or water evaporating from a cooling tower, dissolved minerals are left behind, increasing the concentration of these minerals. Additional minerals are introduced via the water added to makeup the water lost to steam/evaporation. Eventually, the minerals reach a level (or cycle) of concentration that will cause either loss of efficiency due to scale or damage from corrosion. This level can be determined by the Ryznar or Langelier indices and correlated to a conductivity or TDS range. Most people recognize problems associated with corrosion. Effects from scale deposits, however, are equally important. For example, as little as 1/8" of scale can reduce the efficiency of a boiler by 18% or a cooling tower heat exchanger by 40%!
A variety of water treatment methods
are employed in an effort to control these problems. Even with water treatment,
it is still necessary to regularly blow down or bleed off part of the concentrated
water and make up with lower salinity water to reduce the overall mineral
To conserve water and treatment
chemicals, it is desirable to allow the dissolved minerals to reach a maximum
cycle of concentration while still avoiding problems. Because feed water/make-up
waters vary in the types and amounts of minerals present, the allowable cycles
of concentration will vary. As a result, regular testing of boiler and cooling
waters is essential to optimize water treatment programs and blow down schedules.
Tests commonly performed include conductivity or TDS, pH and ORP. Myron L®
Company instrumentation provides you with a simple, fast, and accurate means of
testing these parameters.
Many cooling towers and boilers have
inline controllers used to release water from the tower or boiler and feed
chemical(s) into the system. The controllers must be calibrated regularly to
ensure fouling or drift of the sensor has not occurred. Our portable instruments
in conjunction with NIST traceable standard solutions provide rapid verification
of the accuracy of inline controllers. This method reduces manpower and the
likelihood of disturbing or damaging sensors.
Conductivity is the measurement of a
solution's ability to transmit an electrical current. It is usually expressed in
microsiemens/cm (micromhos/cm). Pure water is actually a poor electrical
conductor (18,200,000 ohms/cm of resistance). It is the amount of ionized
substances (or salts) dissolved in water which determines the conductivity.
Because the vast majority of the dissolved minerals in water are these
conductive inorganic impurities, conductivity measurement is an excellent
indicator of mineral concentration.
The Myron L® Instruments were
developed for just this purpose. Models are available which display conductivity
and/or ppm of TDS. For detailed information regarding the relationship between
conductivity and TDS, please see the Myron L® Application Bulletin:
Solutions and Buffers.
pH, the measurement of acidity or
basicity, is one of the most important factors affecting scale formation or
corrosion in a boiler or cooling system. The types of impurities comprising the
mineral concentration behave differently at various pHs. Low pH waters have a
tendency to cause corrosion, while high pH waters may cause scale formation.
Boiler water requirements can range
from very pure to more than 6500 microsiemens, depending on size, pressure,
application, and feed water. Once the maximum cycles of concentration has been
established, a conductivity instrument can conveniently help you to determine if
the blow down schedule is adequate. Samples should be cooled to at least
160°F/71°C to ensure accurate temperature compensated readings.
Boiler condensate samples are often
tested to determine if there area any carry over of boiler water solids or
contaminants entering from outside the system. Condensate is relatively pure
water, and values of 2-100 microsiemens are common. Because of these low values,
a multiple-range instrument is recommended to increase the resolution and
accuracy of the reading. Monitoring the pH of condensate is also important since
condensate is very corrosive at low pHs. Treatment additives are often added to
elevate the pH to minimize corrosion in condensate lines.
Cooling tower water
Cooling tower water has become more
challenging since the reduced use of acid and the elimination of chromate.
Monitoring conductivity and pH has become imperative to maintain a proper
treatment program. Although many systems have controls on these parameters, the
possibility of a system upset is always present. Even slight upsets can cause
rapid scaling of heat exchangers.
Biological growth is another
extremely important facet to proper cooling water management. Microbes can cause
corrosion, fouling, and disease. Oxidizing biocides (chlorine, chlorine dioxide,
ozone and bromine) have been employed to keep bacteria under control. Monitoring
of the ORP (Oxidation Reduction Potential)/redox is very useful in its ability
to correlate millivolt readings to sanitization strength of the water. The
Ultrameter™ 6PIIFCE and the 9PTK include this parameter for quick on-site determinations.
The following tables list recommended Myron L® instruments
for boilers and cooling towers. For additional information, please refer to Myron L® data sheets, visit our website at www.myronl.com, or contact us by phone, fax, or email (email@example.com).
The following tables list
recommended Myron L® instruments for boilers and cooling towers. For additional
information, please refer to Myron L® data sheets, or
Contact us by phone, fax, or email