(74c) Experimental And Computational Study Of T- And L-Outlet Effects In A Dilute Circulating Fluidized Bed Riser

Outlet effects induced by an L-outlet and T-outlets with different extension heights and outlet surfaces are studied experimentally and computationally. Experiments are carried out in a cold flow riser. The mean and fluctuating particle velocities are measured using a 3D Laser Doppler Anemometer (LDA). The riser has a diameter of 0.1m and a height of 8.765 m and is operated in the dilute regime with a superficial gas velocity of 2.65-7.43 m/s and a solids flux of 3.0 kg/m2/s. A T-outlet configuration induces recirculation by vortex formation in the extension part of the riser above the outlet, resulting in steep velocity gradients and off-centre maxima in the velocity field. The vortex has a 3D nature, but recirculates the flow along the wall opposite of the outlet, inducing reflux down to about 0.1m upstream of the outlet. High Root Mean Square (RMS) fluctuating particle velocities are observed at the vortex boundaries. The vortex is affected by the extension height of the T-outlet and stretches with growing extension. The use of an L-outlet significantly reduces vortex formation. With decreasing outlet surface area, the over-all solids hold-up in an abrupt T-outlet increases and the recirculation zone at the opposite of the outlet broadens. The experimental measurements are used to validate an Eulerian-Eulerian and Kinetic Theory of Granular Flow (KTGF) based gas-solid flow model. In general, the 3D simulation results are in agreement with the experimentally observed phenomena, that is 3D vortex formation is simulated, but the exact length, shape and position of the vortex are not always accurately predicted.