A classifier system for separating coarser particles from finer particles entrained in an upward air stream comprising: a housing having a general circular cross section; a truncated cone inside of the housing having a larger section at its top and a small cone outlet at its bottom, the cone defining an inner chamber; an outer chamber between the housing and the cone adapted to receive coarser and finer particles entrained in the upward air stream; a fuel tube outlet above a classifier ring adapted to allow the air stream to exit the classifier system;the classifier ring at the top of the cone having a frame with a plurality of windows with vanes hinged adjacent to each window; wherein the vanes are adjustable to partially or fully close the windows thereby affecting the size of particles allowed through them and into the inner chamber; characterized in an adjustment system having: at least one pressure sensor upstream of the classifier ring to measure air pressure entering the classifier ring; at least one pressure sensor downstream of the classifier ring to measure air pressure exiting the classifier ring; a coarseness sensing device adapted to sense particle size exiting the fuel tube outlet; and, a control unit adapted to receive signals from the sensors (263, 261, 269), and iteratively adjust the setting of the vanes to determine an optimum particle coarseness and pressure drop. a housing having a general circular cross section; a truncated cone inside of the housing having a larger section at its top and a small cone outlet at its bottom, the cone defining an inner chamber; an outer chamber between the housing and the cone adapted to receive coarser and finer particles entrained in the upward air stream; a fuel tube outlet above a classifier ring adapted to allow the air stream to exit the classifier system;the classifier ring at the top of the cone having a frame with a plurality of windows with vanes hinged adjacent to each window; wherein the vanes are adjustable to partially or fully close the windows thereby affecting the size of particles allowed through them and into the inner chamber; characterized in an adjustment system having: at least one pressure sensor upstream of the classifier ring to measure air pressure entering the classifier ring; at least one pressure sensor downstream of the classifier ring to measure air pressure exiting the classifier ring; a coarseness sensing device adapted to sense particle size exiting the fuel tube outlet; and, a control unit adapted to receive signals from the sensors (263, 261, 269), and iteratively adjust the setting of the vanes to determine an optimum particle coarseness and pressure drop. at least one pressure sensor upstream of the classifier ring to measure air pressure entering the classifier ring; at least one pressure sensor downstream of the classifier ring to measure air pressure exiting the classifier ring; a coarseness sensing device adapted to sense particle size exiting the fuel tube outlet; and, a control unit adapted to receive signals from the sensors (263, 261, 269), and iteratively adjust the setting of the vanes to determine an optimum particle coarseness and pressure drop.