19-05-2014, 02:23 PM
Conductivity in power plants
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Introduction
A power plant with its steam/water cycle, raw water
treatment plant and, if used, district heating water system, is
an evident field for conductivity measurements.
Applications such as control of the water quality are nearby,
but also the ion-exchangers exhaust or wash-out after
regeneration is easily controlled.
Conductivity measurements are useful as supplement to
other kinds of measurements. If a correlation exists between
the pH-value and the ion-concentration, it is expected that a
correlation also exists between the conductivity and the pH-
value. That is the case of the boiler feedwater when
alkalized with ammonia.
A peculiar application is the detection of impurity anions,
where the water passes through a cation exchanger before
the conductivity measurement.
Indication of cooling water break-in
After having passed the turbine and produced the power,
the steam condenses in the condenser. In coast regions, the
condenser is often cooled by seawater, the break-in of
which has serious effects due to its contents of salt. A
leakage of the condenser (break-in of cooling water) will
give a rise of the conductivity at 1 and 2. Measurement of
specific conductivity 1 gives a response very fast, but the
sensitivity is not very high. When the cation exchanger
removes cations and increases the sensitivity, the
measurement of conductivity 2 will give an excellent
sensitivity. The cation filter will delay the response of
measurement. Thus, measurement 1 very fast indicates any
big in leakage and salt water and measurement 2 indicates
very small in leakage of salt water, though delayed for a
few minutes. The cation exchanger has to remove the
conductivity from the alkalinity of the raw condensate and
to increase the sensitivity of the measurement.
Control of the make-up water and of
the ion exchanger
After the mixed bed filter, the water is practically free of
impurity ions SiO2 and CO2, and ready for use as make-up
water. The mixed bed filter absorbs the impurity ions
passing through the precedent ion exchangers. The
conductivity at 16 controls the purity of the make-up water
when leaving the deionization plant; the measurement also
determines the exhaust of the mixed bed filter as well as the
end of the rinse after regeneration.