Method of rotary precoat filtering

Claim 1

IN A ROTARY PRECOAT FILTRATION PROCEDURE WHEREIN THE REVOLVING FILTER MEANS COMPRISES A PRECOAT OF AN INITIAL SUBSTANTIAL DEPTH OF FILTER CAKE CONSISTING ESSENTIALLY OF A RELATIVELY COARSE PARTICULATE FILTER AID HAVING AT LEAST 75% OF ITS PARTICLES OF AN AVERAGE EFFECTIVE DIAMETER BETWEEN 5 MICRONS AND 20 MICRONS AND A CONSTANTLY ADVANCING DOCTOR KNIFE CONTINUOUSLY CUTS AWAY AND REMOVES THE PORTION OF THE SAID PRECOAT FILTER AID CONTAINING ENTRAPPED AND ACCUMULATED FILTERED SOLIDS SIMULTANEOUSLY WITH FILTRATION, THE IMPROVEMENT WHICH COMPRISES ADMIXING A RELATIVELY FINE PARTICULATE FILTER AID HAVING AT LEAST 45% OF ITS PARTICLES OF AN AVERAGE EFFECTIVE DIAMETER BETWEEN 0 AND 4 MICRONS WITH A SUSPENSION TO BE FILTERED IN AMOUNT OF APPROXIMATELY 25 TO 100 POUNDS OF FILTER AID PER THOUSAND GALLONS OF SUSPENSION, WHEREBY THE ACCRETION OF RELATIVELY FINE FILTER AID ON THE FILTER SURFACE COOPERATES WITH THE RELATIVELY COARSE PARTICLES OF THE PRECOAT TO MODIFY THE MECHANICAL ACTION OF THE FILTER CAKE AND REDUCES TOTAL OVER-ALL FILTER AID CONSUMPTION.