Candle Filters work on the famous principle of mechanical trapping and adsorption of toxic particles in the pores of candles. The candle filter work in three stages: filling, filtration, and discharge. But depending upon the circumstances, the following steps are included in most of the operations.
Pre-coating is not usually performed. This step occurs only in the following circumstances:
When the product is sticky or gelatinous. The pre-coat layer will act as a barrier that avoids cloth binding. In this way, the interface between cloth and pre-coat departs quickly, and the cake discharges, leaving the clean cloth behind.
When the clear filtrate is immediately required after one filtration cycle. Otherwise, recirculation must be needed until a clear filtrate is obtained.
As described previously, the slurry will enter the vessel from the bottom, release the air above the candles and headers.
After pre-coating and filling, the filtration will occur in the candles. The pressure is used to separate the forming cake from the filtrate. This forming cake will retain on candles, and filtrate will pass through headers for further processing.
If the filtration process is slow, you can add body-aid to enhance the cake permeability. But this addition may cause an increased formation of cake for disposal.
Spray bars are present near the headers. These spray bars clean the cake down the length of the candles.
The air or gas will pass through the cake until the moisture content becomes minimum. At this point, the cake will be considered dry. Moreover, this process may filter any leftover filtrate into the candles.
After the completion of the filtration cycle, the air or gas will blow through the vessel. Under the influence of air, the slurry heel around the candles will be pushed and displaced downwards until it reaches the lowest region of the candle stack. From here, the remaining heel slurry will go back to the evacuated tank by a special dip pipe. The dip pipe is located at the end of the vessel. The sole purpose of this pipe is to empty the vessel from any slurry.
The cake outlet will open during this step, and the candle will vibrate to discharge the cake. But keep in mind that the cake outlet opening must be integrated with the pressure sensors to avoid opening under pressure. In some cases, you might be required to clean the candles if any residue cake is present. If absent, then the filter is ready for another cycle.