Evaporative towers are thermal machines employed for water cooling in industrial production processes, for outdoor installation. Very often in Tempco we did applications in geographical areas with extreme climate conditions, with wide thermal excursions and therefore hot summers and very cold winters. We’re speaking of applications such as steel industries, in areas where temperatures go widely down 0° C, even at temperatures of -20° C, -30° C or -40° C. Aimed to serve industrial production processes, cooling towers must always ensure the best performances in every condition. That’s why they are designed and built upon the worst possible conditions, meaning the hot season as they are intended to produce cold water.
In order to ensure the proper functioning during the winter season, the main issue is represented by the temperatures going down to very extreme temperature levels. There are some tricks that are employed in these cases, the first being the employ of anti freeze resistances to maintain a certain minimum temperature of the water inside the tank, preventing it to freeze in case the tower gets arrested.
In fact, while the plant and the tower are working, water continually comes from the production process at temperatures of 30-40° C, and circulating within the tower it’s difficult for it to freeze. But it could occur that the process gets stopped, or the tower must be shut down for maintenance, or even due to vacation periods. The water inside the tank could then freeze.
When having big sized tanks, the anti freeze resistances are no more enough. An expedient is to insert some steam pipings, draining exhaust steam inside the tank coming from secondary processes, with an operation called ‘barbotage’. Further tricks are referred to the circulation of the water within the tower: as far as the temperature goes down, fans can be stopped, because the thermal transfer efficiency required decreases. Fans can then be stopped, or in case of EC fans equipped with inverters it’s possible to slow down the speed up to the complete arrest of the fans, as long as the natural ‘chimney effect’ of the tower will be enough to cool the water.
The more the water temperature goes down, the more the ‘chimney effect’ becomes exceeding, also for the thermal duties on the outlet of the tower. The next step is to stop the water from passing through the tower and directly bypassing it to the tank, in order to avoid that the water freezes inside the filling packs, clogging the tower. And also avoiding them to get heavy, with the severe risk they collapse inside the tower.
In case of prolonged cold temperatures, bulkheads can be installed to close the air inlet, limiting the air incoming which could freeze the water passing through or percolating from filling packs.
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