As of January 2015, a new technical guideline (VDI2047, Sheet 2) has been established for manufacturers and operators to safeguard the sanitary operation of evaporative cooling towers. In addition, a legislative initiative was proposed. This directive and the planned law make operators liable for hygienic maintenance, care, and operation. These regulations are meant to apply retrospectively for existing installations.
JUMO supplies suitable measurement and control devices for equipping new cooling towers - particularly so for the retrofitting and conversion of existing installations. The JUMO AQUIS touch modular multichannel measuring device designed for liquid analysis is designed to ideally suit the recommendations of the VDI Directive. In addition to the desalination of the cooling tower through conductivity measurement, the device also enables controlled dosing of biocides for cooling tower hygiene. The desalination lock during biocide dosing, the compliance with exposure time of the biocide, and limit value monitoring of all important parameters are also controllable.
Redox measurement in the cooling tower
The redox measurement of the cooling circulation, just like in drinking water or pool water, is used to get an impression of the overall sanitary condition of the water. Individual disinfecting agents such as free chlorine, ozone, chlorine dioxide, or bromine cannot be detected in the concentration. Typical measured values are not available because they can vary greatly due to local water quality and miscellaneous cooling water components. The ideal range for redox potential of a cooling tower is communicated to the user by either the cooling tower manufacturer or the chemical supplier.
Desalination through conductivity in the cooling tower
If water evaporates in the cooling tower water cycle then the concentration of remaining salts rises constantly. This increased salinity can be monitored with a measuring device for electrolytic conductivity. Example: the cooling tower is filled with water that has a conductivity of roughly 400 µS/cm. After a few weeks of operation this amount will increase to 1500 µS/cm (1.5 mS/cm) due to evaporation. With this increase in conductivity the corrosion of cooling water will rise while at the same time the cooling capacity will decrease. Desalination control therefore consists of at least one measuring device and sensor for electrolytic conductivity with an appropriate switching point for automatic desalination. As soon as an adjustable limit value is reached, a part of the thickened medium is released into the sewer system and fresh water is added. Although, for cost reasons, conductive conductivity sensors were used in the past (the principle: two conductive electrodes made from graphite or stainless steel in an insulator), today's technical standards recommend that only inductive conductivity measurement technology is used ("touch free" measurement without conductive materials in the medium; transformer principle). The inductive measurement is practically maintenance free as well as free from measured value drift through contamination. With the older, conductive measuring method, dirt or corrosion can lead to incorrect measurement results on the open electrodes and decrease the operating life of the sensor.