Separation characteristics of swirl-tube dust separators



Experimental results for the overall efficiency, pressure drop, and grade efficiency curves (GECs) in a laboratory cylindrical swirl tube with inlet vanes are given and compared with experimental data and model predictions for a tangential-inlet, cylinder-on-cone cyclone, tested in the same rig. The results show that the performance of swirl tubes is comparable with that of cyclones in spite of the simpler body shape, and also that swirl tubes are more compact than cyclones when operating at the same pressure drop and capacity and with the same cut point (efficiency). The S shape of the GEC in swirl tubes, however, differs in steepness from that of conventional cyclones. That steepness m (larger m, steeper GEC, that is, sharper cut) had values between 2.5 and 3 in the swirl tube and around 4 in the cyclone. The values found for the swirl tube are still well within the range of 2–4 often seen in industrial cyclones. The swirl tube GEC, while less steep around the 50% mark, is steeper at larger particle sizes. Using Stokesian scaling, the GECs from the laboratory swirl tube, which was working alone, are also compared with experimental GECs from a commercial swirl-tube installation, in which the swirl tubes work in parallel. The commercial GEC is found to be slightly less steep: this, in fact, favors the separation of “microfines” (responsible for equipment fouling), while the separation of coarse particles remains sufficiently large. Underperformance of the commercial installation due to cross talk could not be detected. © 2004 American Institute of Chemical Engineers AIChE J, 50:87–96, 2004