A new device, the pneumatic escalator, for conveying solids pneumatically was examined from the viewpoint of solids mixing or residence time distribution of particles within a continuous gas-solid contacting apparatus. According to experimental results by tracer technique, the residence time of particles passing through the device could be adjusted by operational variables like solids feed rate, air velocity and inclination angle of the device in addition to material properties of particles and

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... dimensions of the device. Amongthem, air velocity was found to be effective in controlling the shape of the distribution curve and the meanresidence time of particles. The distribution function of residence time was mathematically expressed by applying a complete-mixing model to solids within a cell of the device and a binomial distribution model to solids bypassing flow through the cells. Thus, an appropriate distribution curve of residence time required in each case of gas-solid contact operation can be simulated by changing the operational conditions as well as the dimensions of the pneu-escalator.