Preheating of oil-shale

Claim 1

IN THE DISTILLATION OF OIL SHALE IN THE FORM OF A DENSE TURBULENT MASS OF SUBDIVIDED SOLID PARTICLES FLUIDIZED BY AN UPWARDLY FLOWING GAS, THE IMPROVEMENT WHICH COMPRISES SUPPLYING COARSE FRESH SHALE PARTICLES RANGING IN SIZE FROM ABOUT 0.5 TO 1.5 INCHES AT SUBSTANTIALLY ATMOSPHERIC TEMPERATURE TO THE TOP OF A SUBSTANTIALLY VERTICAL PREHEATING COLUMN OF FINELY DIVIDED SHALE HAVING A COLUMN RATIO OF LENGTH-TO-DIAMETER OF AT LEAST 3:1, INTRODUCING HOT SPENT SHALE FINES INTO THE BOTTOM PORTION OF SAID PREHEATING COLUMN AT A RATE SUFFICIENT TO MAINTAIN SAID BOTTOM PORTION AT A PREHEATING TEMPERATURE OF ABOUT 700 TO 800* F. AND CONDUCIVE TO ONLY INSIGNIFICANT SHALE DISTILLATION, SAID SHALE FINES HAVING A PARTICLE SIZE ELUTRIATABLE FROM SAID COARSE SHALE PARTICLES, PASSING A FLUIDIZING GAS UPWARDLY THROUGH SAID COLUMN AT A LINEAR SUPERFICIAL VELOCITY OF ABOUT 0.5 TO 3 FT. PER SECOND SO AS TO FLUIDIZE THE FINES WHILE PERMITTING THE SAID COARSE SHALE PARTICLES TO SETTLE DOWNWARDLY THROUGH SAID COLUMN, PASSING THE FLUIDIZED SHALE FINES UPWARDLY THROUGH SAID COLUMN IN DIRECT COUNTER-CURRENT CONTACT WITH SAID DOWNWARDLY MOVING COARSE SHALE PARTICLES, SAID COLUMN BEING HIGH ENOUGH TO ESTABLISH A SUBSTAN-