AN EXPERIMENTAL STUDY ON RESIDENCE TIME OF TOBACCO PARTICLES IN ROTARY DRYERS

摘要

Rotary dryer has been widely used because of its strong adaptability to various materials, easy operation and reliability. The mean residence time (MRT) of the particles for particle transportation in the rotary drum is of importance due to the mass and heat exchange of particles with the hot medium during this time. And the influence of operational variables on MRT, the mass flow rate (MFR) and particle hold-up of the materials in rotary drum has been investigated by many researchers. But their reports on the influence of the material flow rate on MRT, for example, are very limited due to the different experimental materials and some of their reports are not consistent with one another. In this paper, the influences of operational and structural parameters on the particle hold-up and MRT of tobacco particles in rotary dryers are presented on an experimental rotary drum. The influences of rotation velocity, drum slop, gas flow rate, material flow rate and material moisture content were discussed, and a revised correlation of the former four variables was proposed to estimate MRT of the investigation. Experimental results show that MRT is proportional to particle hold-up, and the increases of rotation velocity, gas flow rate and drum slope reduce MRT and MRT increases with the increasing of material feed rate and moisture content if other variables are fixed. It is also found that the proposed estimation is accurate for the experimental system. The results could give good predictions over the range of parameters considered for rotary dryers used in the tobacco industry.