Gas-Solid Interaction, Flow Behavior analysis and Development of a Design Basis equation for the Dense Entry Region of an Asymmetrically Loaded Cold Flow CFB Riser.

摘要

The dispersion of a gas tracer was used to indicate the effectiveness of the mixing process of an injected flow of solids into the dense bed region of NETL's cold flow CFB riser in three distinctly different fluidization regimes. NETL's cold flow test facility mimics commercial scale transport reactors with side entry of solids into the vertical riser. Pure CO2 was used as the tracer gas and was introduced continuously into the injected flow of solids and it was assumed to essentially remain in the injected flow stream. The tracer gas would be released from the injected flow stream as the as the flow stream begins to disintegrate. As the stream loses its identity the remaining tracer gas would be released. The tracer gas distribution was measured using inline IR CO2 detectors across the cross-sectional area of the riser at four different elevations, two near the injection point and two further downstream. Due to the high solids hold up and high reactant concentrations, a significant portion of the reaction can take place in the dense bed region. The effectiveness of a Transport Reactor depends on its ability to adequately mix the incoming flows of reactants: fuel, sorbent and air. These reactants have to be dispersed across the reactor's cross-sectional area by the different mixing mechanisms. A good description of the flow behavior is also essential in developing and validating predictor reactor models as well as in developing crucial gas and solids mixing relationships that will can be incorporated and validated for CFD codes (MFIX). In addition there are several operational variables (independent variables) that influence this mixing behavior. Multivariable analysis of variance (MANOVA) model were developed for the NETL cold flow CFB riser based on the dispersion data. The mixing process as a function of the operating parameters is empirically proposed outlining the independent variables (operating and system parameters) which significantly influenced the dispersion of the tracer gas. Since the contacting between the gas and solid phases in a fluidized bed is mainly governed by the degree of gas mixing, the equations governing the gas mixing in fast-fluidized beds is useful in reactor design. The results from this work have been presented at the 2010 Multiphase Flow Workshop organized by NETL at Pittsburgh.