چكيده به لاتين
Due to the importance of the impacts of spraying a liquid into the riser reactors, the hydrodynamic characteristics of risers have been numerically and experimentally investigated. Based on a 3D transient model with Eulerian approach, a cold simulation was carried out in conditions similar to flow in a FCC riser reactor. The governing equations for the phases and an equation based on the kinetic theory of granular flow (KTGF), as well as the dispersed turbulence model were applied. The governing equations were numerically solved by FVM for all of phases. Beside volume fraction distribution of the phases(by infrared sensor), solid particle velocity was determined by utilizing a fast digital image capturing system and particle image velocimetry (PIV) technique. In addition, the solid velocity profile in each height of the riser was obtained via image processing and the cross-correlation algorithm. Therefore; based on pneumatic conveying regime, the three phase flow pattern in CFB riser operating at a solid mass flux up to 300 kg/m2s and a superficial gas velocity in the range of 4-10 m/s was evaluated. The inlet zone of the riser reactor, where the solid particle is accelerated by the evaporating liquid, is the most complex part of the reactor.In the liquid injection area intense turbulence and flow inhomogeneities exist, while the hot solid particles exchange large amounts of heat with liquids to balance the needs of heat of vaporization of liquid phase. The area where liquid vaporization takes place inside the riser was predicted and the evolution of atomized droplet size was illustrated. The atomization modeling scheme took into account the liquid droplet size at nozzle's exit, as well as droplet size reduction along with vaporization. To evaluate the degree of atomization effects of a evaporating liquid on riser reactor performance, a parametric study is carried out considering different independent variables. Meanwhile, affecting some independent variables comprising the gas superficial velocity (m/s), the solid particle mass flow rate (kg/s), and the evaporating liquid volume flow rate (l/s) on the solids velocity are investigated. The results of two-phase simulations show that in most axial levels of the riser, there is a parabola-shaped velocity profile so that the particle velocity near the bed walls is lower than that in the central regions. The results of three-phase simulations revealed that the injection of the third phase into the bed leads to phenomenal changes of the flow pattern. The simulation results based on CFD are in good agreements with the experimental data.
