GB1030467A - An improved pneumatic classifier - Google Patents

Abstract

1, 030, 467. Classifiers. INSINOORITOIMISTO-ENGINEERING BUREAU R.T. HUKKI. Feb. 16, 1965 [March, 28, 1964], No. 6611/65. Headings B2H and B2P. A continuous pneumatic classifier comprises a closed, vertical, stationary vessel having a cylindrical top portion 1 and a conical bottom portion 2, means for feeding material to be classified with or without gaseous medium into the middle zone situated at about the level of the junction between the portions 1 and 2, means for feeding gaseous medium separately or with the material to be classified into the middle and/or lower conical part of the vessel, means for imparting a circular, turbulent motion to the mixture of medium and material within the conical portion 2 and for causing the separated coarse fraction to move vertically downwards,a manually or automatically operated valve 7 for the discharge of the coarse fraction via the apex of the conical portion 2, and braking means situated in the cylindrical portion 1 of the vessel to convert the turbulent flow into an upwardly directed laminar flow having a Reynolds number less than 2000 whereby the suspended light fraction and the bulk of the medium are directed to the top 13 of the vessel for discharge through a tangential outlet 10 whilst the middlings entrained in the upper portion 1 of the vessel are allowed to settle by gravity back to the lower portion 2. In the embodiment of Fig. 1, the material to be classified is introduced by gravity with gaseous medium through a pipe 9 and flows down a stationary tube 8 on to a vaned distributor 4 mounted on a rotary shaft 3 which also carries one or more impellers 5, 6 for imparting the turbulent circular motion to the mixture of medium and material. Additional medium under pressure is admitted through tangential inlets 15 to wash the settling coarse fraction. The braking means comprise one or more sets of stationary radial vanes 10, 11 attached to the tube 8 and dividing the annular space between the tube 8 and the vessel portion 1 into vertical or inclined compartments depending on the position of the vanes. The annular spacing and the inclination of the vanes may be the same or different in each set. The angle of inclination may be adjustable. The braking means may be vertically adjustable and may be so designed as to provide a gradually narrowing annular channel between the tube 8 and the vessel portion 1. In another embodiment, Fig. 4 (not shown), the material and the gaseous medium are introduced through a tangential or involute inlet 16. The conical portion 2 of the vessel has a conical extension 17 providing an elutriation chamber 18 in which counter current cleaning of the coarse fraction is obtained by additional medium introduced at 15. Cleaning also takes place as the medium flows up the annular passage provided between the wall of the vessel portion 2 and a conical member 19 installed on the shaft 3 between the impeller 5 and 6. The discharge 14 of the classifier may be connected to one or more cyclones or to a dust filter for removing the fines from the gaseous medium which may be recirculated to the classifier. A number of classifiers may be arranged in series or parallel.