Particle fractionator employing multiple fluidized bed modules

A multi-module particle fractionator for separating particles by size from a feedstock of multi-sized particles comprising:

• a plurality of particle separating modules arranged in succession, serially connected and in fluid communication with one another, each of said succeeding particle separating modules being similar to a first particle separating module, said first particle separating module including a fluidized bed chamber having an end wall, a support grid through which a gas passes to fluidize particles supported on the grid, an inlet port for feeding particles to be fractionated to said support grid, and an outlet port for discharging a fluidizing gas and elutriated particles from said bed chamber, a gas plenum below said support grid, gas supply means for delivering gas to said gas plenum at a rate to fluidize particles supported on said support grid and elutriate the smaller of said particles, cyclone means connected to said outlet port for separating and collecting elutriated particles discharged through said outlet port, said end wall including a weir and a baffle forming a downcomer for feeding particles overflowing from said fluidized bed chamber of said first particle separating module to the fluidized bed chamber of an adjacent downstream particle separating module;
• the support grid of said adjacent downstream particle separating module having an imperforate section below said downcomer so that particles are de-fluidized as they are fed into said fluidized bed chamber of said adjacent downstream particle separating module and act as a seal to reduce the flow of fluidizing gas from said adjacent downstream particle separating module fluidized bed chamber to said first particle separating module, and wherein the cyclone means of at least one of said plurality of particle separating modules is connected to the inlet port of a preceding particle separating module for returning particles collected in said cyclone means to a fluidizing bed chamber of a preceding particle separating module, so that smaller particles moving downstream in the overflowing fluid particle stream are recycled to the preceding particle separating module for elutriation therein, the arrangement of particle separating modules being such that initially fine particles and then larger and larger particles are elutriated and collected from the particle stream as it flows downstream through said succession of particle separating modules whereby the particles in the feedstock are fractionated into desired ranges of particle sizes.