configured in the annular space so that gas does not travel axially through the annular space except along the spiral path shown there may be some escape of air but this should be negligible in fig1 a drum 10 has a substantially cylindrical interior wall rotatable around a horizontal longitudinal axis the gas entry zone 140 and the solids entry point 130 are proximate opposite ends of the drum with respect to the longitudinal axis so that the movement of gas from gas supply 90 to gas exit 94 is substantially countercurrent to the movement of solids through the drum countercurrent operation is preferable in an application such as coating confectionery centers with liquid syrup combined with drying the liquid syrup to form a sugar shell because the drying air having the lowest humidity is expected to contact the solids toward the end of the processing where more intense drying is required also as dust from the particulate solids and dried coating material becomes suspended in the gas dust laden gas is carried toward the solids entry point where the coating on the solids is more liquid such that the gas is contacted with liquid coating material and dust is removed from the gas by adherence to the particles a screen 120 or other suitable partition with apertures prevents particles from being entrained by the gas into the entrance shroud 24 in other embodiments the drum is rotatable around a horizontal longitudinal axis as shown in fig1 a but the gas entry zone and the solids.