The conductivity-controlled bleed-off device will be used for the automatic control of the max. salt-concentration in the circulating water of the cooling tower.
The main components: A conductivity measuring cell, a electronic controller and a bleed-off ball valve.Description and technical data see enclosure A.
The bleed-off water automatic controls the maximum salt concentration in the water circuit of the cooling tower. During plant operation water is continuously evaporating, thus the salt concentration in the remaining circulating water increasing. Therefore the part of the circulating water has to be replaced by fresh water when the salt concentration exceeds a certain limit value. The electric conductivity of the circulating water is proportional to its salt concentration. Therefore it can be used as the controlled variable for the bleed-off water.
The conductivity is determined by a measuring cell and serves as an input signal for the regulator. In addition the measured value will be shown on a display of the regulator. When the set desired value is exceeded, the regulator opens the electrically driven ball-type cock and part of the circulating water can flow off. The discharged water volume is replaced by fresh water (via a float valve or a float switch in combination with a solenoid valve). The ball-type cock will be closed by the regulator when the desired value for the salt concentration is about 3 % less.
