Large rotary processors such like rotary dryers, rotary calciners and kilns are difficult to seal properly because of their large diameter, their low precision methods of fabrication and their severe operating conditions. Those factors result in several types of imperfection at the sealing surface. This work explores the possibility to seal large rotary processors to positive pressure up to 1 atmosphere (14.7 psig).
First, an extensive theoretical analysis combined with on-site measurements evaluation was conducted to quantify the magnitude of each type of surface imperfection at the seal location. Against these results, the current typical seals used in the industry were evaluated and compared. The seals that featured compressed packing seals seem to show great possibility as they are already used in successful positive pressure large seal arrangement. A typical packing seal arrangement with a stuffing-box was studied thoroughly in order to understand its particularities.
The data collected and calculated in the previous steps was gathered and settled the new seal requirements. A new seal arrangement is proposed and it features as principal characteristics: radial compression and adaptive flexible housing. Based on the stuffing-box available mathematical relations, the equations are re-evaluated to account for the new radially oriented arrangement. Meanwhile, a test rig is designed and built to measure the seal performance and observe its behaviour. The effect of several parameters can be studied such as temperature, gas pressure, magnitude of sealing surface imperfection, magnitude of radial compression and drum rotation speed.
Finally, tests are conducted and the results are discussed in order to make a recommendation for the possible industrial application. In the light of this study the new proposed seal meets or surpasses the industrial application requirements. The performance of the full scale 1.952 m (76.875 in) seal are projected as follow; a leak rate of 114 ml/sec (0.24 scfm) at 0.69 MPag (10 psig), 4 kW (5 HP) of power loss in friction, half a year of longevity before maintenance and a deformations absorption greater than 3.15 mm (0.125 in) in the radial direction
