Solids mixing and residence time distribution in a horizontal rotary drum reactor

Abstract

For the design of a rotary drum reactor, knowledge of the mechanism of both heat transfer and the dispersion of the solids is important. In this contribution the movement of solids in a horizontal rotary drum is investigated. Residence time distribution measurements were performed in an industrial scale reactor. Also, in model sections of this reactor, the behaviour of solids was studied visually. In the model sections the rotational speed of the drum, the number and height of the strips on the reactor wall and the angle between strip and wall, as well as the degree of filling, were varied. Model sections 0.60 and 1.40 m in diameter were used: the length of the industrial scale drum was 9.0 m, its diameter 0.60 m. Potato starch, particle size range from 15 to 100 μm, was used as the solid material. It was shown that in a drum provided with strips for rotational speeds above 5 r.p.m. and a degree of filling less than 15%, the transverse mixing was virtually completed within 2 revolutions of the drum. At these speeds and degrees of filling the extent of axial mixing is still very low as was shown by the residence time distribution measurements, the length of a mixing unit being 0.1 m or less.