WATER TREATMENT OF THE EVAPORATIVE CONDENSERS
Evaporation sprayed with water is the dominant process of heat transfer in the evapoartive capacitors. The volume of heat transfer attributible difference in the dry bulb temperature between the condenser tubes and air is minor. Because of make-up water contains some minerals and other chemicals, and because water vapor leaves the condenser, that none of these impurities, the concentration of foreign materials sprays of water has a tendency to increase. To save the concentration of impurities under control, purging some water spray should be given whenever capacitor works. Manufacturers evaporative condensers, as a rule, we recommend the blowdown rate is approximately equal to the rate of evaporation. Speed of make-up water, so double-reset speed.
Almost all sources of feed water should be considered in any way to avoid the situation when one or more of the problems faced by the surface of the capacitor, which are in contact with water. These difficulties include scaling, fouling and corrosion. Scaling Deposit hard layer of minerals, as a rule, calcium carbonate (CaCO3), on the surface of the tube.
A layer of scum 0.8mm (1/32) on the thick tubes can be expectecd reduce the capacity of the condenser on 30%. This layer scale is usually due to the high concentration of minerals in the make-up water and, if calcium carbonate precipitated, this could form of scum on the pipes. In General CaCO3 concentration of less than 170 ppm will be satisfactory. It should not be implied, however, that softened water with mineral concentration (for example, 30 ppm desirable. Softened water can lead to excessive corrosion. Fouling, as a rule, represents the accumulation of nonscale solid substances such as dirt, sludge, sand, algae, fungi, and bacteria.
Corrosion is a painful problem in galvanized steel, because it often takes the form of deterioration of the zinc coating, which provides steel oxidation. Electrochemical corrosion is a process, in which the electric potential of developing between two different metals. When current flows in the result of this voltage difference in the presence of an electrolyte, such as the water with dissolved solids, one of the dissolved metals. Particularly sensitive situation where the zinc coating on steel deteriorated, because between those points that the current will flow. PH control spray of water, will be especially useful in corrosion inhibition. The PH value of the acidity or alkalinity of a solution with pH value of 7 is defined as neutral. Maintenance of pH from 6 up to 8, as a rule, recommended19. Corrosion inhibitors, approved by the capacitor manufacturer procedures to prevent corrosion.
A problem called white rust appeared in the last ten years and may be associated with the prohibition on the use of chromate corrosion protection. White rust is an accumulation of white, waxy, nonprotective zinc corrosion products galvanized surfaces20. It normally occurs suddenly and rapidly progress within the wetted, galvanized steel, components of the capacitor. If not corrected, white rust can lead to premature failure of the galvanized coating. One of the most effective methods for the prevention of white rust is to assure the passivation of the capacitor during commissioning. The passivation of the natural formation of protective, light crystalline film on the surface of zinc. A recent trend in water treatment towards more high alkaline (high pH), which some experts suspect contributes to white rust. Indications for soft water (less than 30 ppm total hardness) in combination with high pH valves exacerbate the problem. Passivation contributes to the initial use of untreated water, as well as the use of phosphates. Water treatment expert should be consulted for a unique approach applicable to the local conditions...
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