1. Type of technology
2. Contaminants which can be removed
Dusts in general.
3. Emission limits possible
Collection efficiency very much depends on the particle size and specific gravity of the dusts to be handled. Normally it lies between 85 and 95%.
4. Description of the equipment and/or process
These cyclone separators are suitable only for dusts with specific gravity greater than 300 kg/m3 with fairly coarse particles (more than 10 micron for dusts with specific gravity greater than 1000-1500 kg/m3 and more than 50 micron for dusts specific gravity exceeding 500 kg/m3), present in the air in fairly high concentrations (a few grams per m3.). Collection efficiencies of the cyclones can range between 85% and 95%. When very high collection efficiencies are Required, the cyclones serve merely as precleaners to more efficient final filters.
Where there are very high concentrations of dusts it is always useful to install a cyclone for precleaning in order to obtain appreciable reduction in the dust load sent to the final filter, as well as to increase the dust collection efficiency and to avoid hazardous plugging in the more efficient filter which could cause trouble to the entire plant.
Such case is typical of pneumatic conveyors where there are extremely high dust concentrations in the air and where sometimes just the cyclone is sufficient to obtain an acceptable collection efficiency.
On the other hands cyclones offer certain appreciable advantages, namely:
l) low resistance or pressure drop (60-70 mm H2O);
2) no maintenance costs;
3) very low running costs;
4) low installation cost.
Sometimes the material conveyed and sent to the cyclone exerts an abrasive action on coming into contact with the walls. In this case the cyclone (like the elbows in the plant ductwork) represents the points most affected by the abrasive action. In fact, the dusts entering the cyclone settle with a spiralling movement along the inner walls of the cyclone and here they exert their abrasive action.
In this case certain precautions can be adopted:
The cylindrical housing of the cyclone should be made of heavy gauge metal sheet with the top body flanged and bolted to allow replacement without having to replace the entire cyclone, likewise built of heavy gauge metal sheet (4-6 mm).
The same system can be used for the elbows and fans.