Classifier and method of classifying

A method of classifying particles of a feedstock according to size and density in a fluidised bed, the method including the steps of:

• providing an elongate classifier having:
• an underflow outlet;
• a fluidising means;
• a settling chamber which is in fluid flow communication with the fluidising means and the underflow outlet;
• a reflux chamber which is in fluid flow communication with the settling chamber, the reflux chamber having a cross-sectional area larger than a cross-sectional area of the settling chamber and wherein the reflux chamber comprises a lower chamber and an upper chamber, and wherein a cross-sectional area of the lower chamber increases gradually towards the upper chamber;
• a vibrator or agitator;
• a launder which is in fluid flow communication with the reflux chamber;
• and
• an inlet conduit which projects into the elongate chamber;
• feeding the feedstock via the inlet conduit into the elongate classifier;
• introducing a fluidisation fluid into the elongate chamber via the fluidising means;
• permitting the fluidisation fluid to rise within the elongate chamber towards the reflux chamber;
• forming a fluidised bed in the elongate classifier, the fluidised bed comprising the feedstock and the rising fluidisation fluid;
• vibrating or agitating the elongate classifier for encouraging particles that have a density greater than that of other particles in the fluidised bed to settle faster within the rising fluidising fluid;
• forming a hindered-settling zone in the settling chamber for increasing the effect of particle density on the separation of the particles in the fluidised bed;
• forming a free-settling zone in the reflux chamber for increasing the effect of particle size on the separation of the particles in the fluidised bed;
• conveying a first product out of the elongate classifier via the underflow outlet;
• and
• conveying a second product from the classifier via the launder.