Prills are most often cooled in ambient air, which is readily available. However, certain products may require an inert atmosphere for safety reasons or because they react with oxygen.
In such cases, nitrogen or CO2 can be applied. Using these inert gas solutions require the application of closed-loop systems to keep operational expenses at a minimum.
We use several types of de-dusting units to remove dust from the cooling medium and meet the most stringent emissions quotas. The prilling fan and de-dusting unit are located at ground level, immediately downstream and next to the prilling tower. The variable speed induced draft fan draws the required amount of cooling medium through the tower and the de-dusting unit, discharging the filtered air into the atmosphere or to a heat exchanger for the closed-loop process.
The most common way of de-dusting the cooling medium is to use a dry filter. Filter bags are cleaned by an automatic jet pulse blowback system, with the blowback being controlled by an adjustable timer on a differential pressure basis to achieve maximum bag life.
Bag cleaning is done with instrument air. Level detection and sonic horns are provided to prevent excess build-up of dust on the de-dusting unit hopper walls. The design ensures that filter elements can be changed during operation. In addition to dry filters, scrubbers and cyclones are used to reduce emissions and regenerate the cooling medium.