EXPERIMENTAL-STUDY OF A CYCLONE WITH TANGENTIAL SECONDARY AIR INJECTION

In some applications, injection of secondary air into the cyclone could provide process advantages. For example, advanced concepts for circulating fluidized bed combustion (CFBC) utilizes the cyclone for secondary stage combustion, thus requiring the addition of secondary air. The purpose of this experimental investigation was to determine the effect of secondary air injection upon the particulate collection efficiency of a cyclone. A high efficiency cyclone of standard design was modified with the addition of eight nozzles for tangential injection of air into the cyclone barrel. Tests were carried out with the cyclone in a CFB system operating at atmospheric pressure and room temperature. With the primary air flow rate held constant (inlet velocity of 12 m s-1), the secondary air injection was varied from 0 to 3 times the magnitude of primary air flow (ratio of mass flux). Total and fractional-grade efficiencies for the cyclone were determined, using sand particles with a mean diameter of 125 micrometers. The results indicated that total cyclone efficiency remained unaffected by the secondary air injection up to equal mass flow rates of secondary to primary air. For flow ratios above unity, the total efficiency decreased slightly but still maintained a value greater than 0.99 at an air flow ratio of 3. The conclusion is that secondary air injection into high efficiency cyclones is feasible, without causing significant deterioration of particle collection efficiency.