Bed temperature and torque forces effects on abrasion of oil shale particle during pyrolysis and combustion in granular medium

Abstract

In the present work, measurements of oil shale solid particle abrasion due to rotation in silica granular media are reported for different bed temperatures. Operating angular rotations ω used were 1.95, 2.6, 4.28, 5.5, 7, 10, 22.5, 60, 100, 120, 150, 200 and 250rpm. The experimental procedure was based on the measurement of the amount of detached reacting matter from the surface of the oil shale particle when it rotates about its axis. Bed temperatures investigated varies from 450 to 800°C. At each test condition the mass of oil shale particle was determined. Granular media was characterized by its rheological properties: Strain rate γ (0.41–4.62s−1), particle frequency ω (rpm), η bed sand viscosity and shear stress τ (1.84–20.79Pa). The largest propensity to undergo important abrasion by rotation was observed for experimental temperatures greater than 600°C for all experimented angular rotations. Rates of abrasion were determined for the different angular velocities and compared each other. A clear distinction was observed between thermal degradation processes and rotational effects as is shown in all the figures. Increases in the strain rate increased the abrasion by rotation and contributes to the particle weight loss if bed temperature exceeds 700°C. More than 5% of the particle mass loss is due to the simple fact that particle rotated at angular velocities greater than 7rpm in granular media heated to 800°C and expanding shear stress exceeded 2s−1. The course of abrasion of oil shale particles is described as a function of the elapsed time, particle rotation velocity and bed temperature. Experimental results show that there is a competition between abrasion due to particle rotation and thermal particle decomposition depending on bed temperature and angular rotation velocity. This competition reveals the existence of an Inversion point(ti,T,αi)ωi where abrasion activity decline after a certain period ti if compared to the thermal degradation activity. αi refers to the extent of oil shale particle thermal degradation if silica bed is hold at temperature T.