Evaporating cross flow spray jets in gas-solid circulating fluidized bed
Department of Mechanical Engineering
Doctor of Philosophy
Ho, Teh C.
Geskin, E. S.
Dave, Rajesh N.
Multi phase flow
Three-phase flow of solid-gas suspension with liquid spray is found in many industrial applications, including fluidized catalytic cracking in petroleum refinery process, and wet scrubbing process. This dissertation study is aimed to understand the gas-solid-liquid three-phase flow structure, phase interactions and transport in a gas-solid circulating fluidized bed where an evaporating cross-flow liquid spray jet from a rectangular nozzle with a fan angle is injected. The investigation is based on both numerical and experimental approaches. The numerical study is for detailed field descriptions of the flow structure, phase interaction and distributions whereas the experimental study is for simulation validations. The numerical simulation further explores the parametric effects such as nozzle aspect ratio and solids loading on the spray structure, evaporation characteristics as well as local phase distributions of solid concentration, gas temperature and velocity. The governing equations of both gas and solids phases are solved by the Eulerian method while the droplet phase is modeled by the Lagrangian approach. For the experimental validation of numerical simulations, a circulating fluidized bed (CFB) has been set up with a thermocouple matrix system for phase temperature measurement. Cases of liquid nitrogen spray jets from rectangular nozzles with aspect ratio up to 4 in cross-flows of air-FCC suspensions with solids volumetric fraction up to 25% in the CFB system at ambient conditions were numerically investigated. Experimental validations for aspect ratio up to 4 and solids volumetric fraction up to 1.5% were performed.
The results show that the spray penetrates basically along its injection fan angle but deflected by the gas-solid cross-flow convection. The penetration length is significantly reduced by the increase in solids loading. Due to the strong cross-flow convection, most vaporized gas is blown away from the spray region, as indicated by the deviation of the gas and solids' velocity and temperature contours. The results also show that the spray evaporation leads to a very low solids concentration within the vapor region while there is a dense layer of solids surrounding the vapor region. Detailed droplet structure along the trajectory and field distributions of velocity, temperature and concentration of gas and solids were also obtained. With low solids concentrations, there exist flow similarities in velocity and temperature distributions in the spray region. As expected, the flow structure is also strongly dependent on the nozzle orientation, with a deeper penetration and less deflection of vertically-oriented rectangular nozzle than that of a horizontally-orientated nozzle. The simulation predictions agree reasonably well with the experimental measurements.
njit-etd2005-076 (100 pages ~ 8,993 KB pdf)
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Created November 17, 2005