In cold storage and food processing facilities, evaporative condensers are frequently utilized for heat rejection, in low temperature ammonia refrigeration applications. Evaporative condensers and the cooling tower systems utilized in HVAC applications have several significant distinctions, despite the fact that they are sometimes confused with conventional cooling towers.
For water treatment programmes to be successful, it's crucial to comprehend these variations and the problems they pose.
What are the Water treatment processes in Evaporative Condensers?
Design variations
Evaporative condensers and cooling towers both reject heat through evaporative cooling. The dissolved solids in the recirculating water concentrate as fresh makeup water, is supplied to make up for evaporation losses. Scale deposits will develop if the dissolved solids are allowed to over-concentrate.
In cooling tower systems, the cooling water is re-circulated from the basin to the heat exchanger, through a maze of piping before being sent back to the tower's top to cool again. The cooling water in an evaporative condenser is re-circulated from the basin to the top of the device, where it is sprayed over the condenser coil housing the refrigerant.
The value of a smooth flow
For deposit management in evaporative condensers, a smooth flow through the spray nozzles that apply cooling water, to the tightly packed condenser tube bundle is essential. Dry spots and bridging deposits will develop in the presence of uneven, erratic, or blocked flow, which can significantly lower refrigeration efficiency and raise operating costs.
It is the owner's duty to regularly check the spray nozzles and tube bundle, while the pumps are running for any indications of dry patches, obstructions, or missing nozzles. Seasonal problems with plants and bugs may call for more frequent inspections. Condenser tube bundles are exceedingly tough to clean, once bridging deposits have formed.
Additionally, care must be taken to prevent any dry spots on the condenser tubes, if the supply water for the water treatment control loop is removed from the spray pump discharge. To sustain flow to the water treatment control loop, it could be necessary to add an inline circulation pump or an isolated circulation line.
The intention is to guarantee that there is flow across the spray nozzles and to the chemical feed controller, whenever the system is in operation.
Volume of Water System
Evaporative condensers function as the heat exchanger and cooling tower at the same time, and they frequently have much less water in them than HVAC cooling tower systems. Due to the reduced water volume, the dissolved solids concentration in an evaporative condenser can change extremely quickly, necessitating improved management to avoid waterside issues brought on by over-concentration or loss of treatment.
Typical Sumps
A common sump design can considerably reduce the possibility for upsets, and improve management in facilities with many evaporative condensers. True common sumps have individual or shared recirculating pumps that supply the spray nozzles in each unit.
Water from the separate evaporative condensers drains directly into the remote sump, in these systems. The outside basins are left dry when the spray pumps are not in use, since all the water drains into the shared sump. In cold climates, true common sump systems are required to meet freeze prevention issues.
It is frequently possible to retrofit a forced common sump system into plants with numerous isolated evaporative condensers, to assist streamline water treatment and enhance management. In a forced common sump system, the water in each individual evaporative condenser is forced to mingle using a sump tank, and specialized recirculating pump.
As a result, there is no longer a need to build chemical feed and control equipment on each evaporative condenser, increasing the water volume. For consistent mixing, forced common sump systems must be appropriately planned, scaled, and balanced.
White rust
Evaporative condensers commonly use galvanised steel coils as heat transfer surfaces, in contrast to HVAC cooling towers. The bright zinc coating on freshly galvanised steel will eventually develop a non-porous, protective film under the correct circumstances. White rust, a porous, white coating that can form if the right water chemistry is not maintained, particularly during starting, reduces the corrosion resistance of galvanised steel.
Since, condenser tube corrosion can cause ammonia leaks and production losses in evaporative condensers, white rust is a particularly important concern in these systems.
Additionally, to lessen the possibility of white rust forming on newly galvanised steel surfaces, passivation must be done properly. This calls for stringent water quality control throughout the first 8 to 12 weeks, which might be challenging to achieve. The most important component in passivation is good pH control. Operating at decreased cycles rather than using acid feed, should be used whenever possible to maintain the appropriate pH range. In order to retain > 50 ppm of calcium hardness during passivation, softened cosmetics should also be combined.
It's crucial to perform routine visual inspections to look for white rust indicators. Galvanized surfaces may require re-passivation after cleanings, pH changes, chemical cleanings, and starting procedures.
Conclusion
When it comes to water treatment, evaporative condensers provide a number of particular difficulties. White rust can be challenging to avoid because to variations in makeup water quality, and the effects of operating circumstances outside of the water treatment program's control.
Netsol Water can assist you in overcoming these obstacles, with its distinctive blend of knowledge and specialist products. For each application, we can offer many water treatment solutions.
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