A new semi-empirical model for predicting particulate collection efficiency in low-to-high temperature gas cyclone separators

A new semi-empirical model has been developed to predict particulate collection efficiency in low-to-high temperature gas cyclone separators. It has been tested at 20 and 600°C using various flow rates and dust loadings. The model is particularly suitable for efficiency predictions in cyclones attached to fluidized bed gasifiers using rice husk as feedstock, where de-volatilization, which occurs in the temperature range 300-600° C, is the major contributor to gasification of the feedstock, which is 70-90% volatile matter. To develop the particulate collection model, the cylinder-on-cone reverse-flow gas cyclone separator was geometrically modeled as an equivalent right circular cylinder, which was then divided into three zones, reflecting the main hydrodynamically distinct flow zones that result after dust-laden gas enters the device, i.e. inlet, outer (free) vortex and inner (forced) vortex zones. Mass balance computations were then carried out using residence time as the independent parameter, in order to determine the dust loadings in the various zones and subsequently compute the capture efficiency of each particle size in the polydisperse flow. This approach contrasts with ones in which the cyclone is either viewed as one cylindrical region or else, when multiple zones are employed, the axial location in the cyclone, as opposed to residence time, is utilized as the independent variable in mass balance computations. The effects of cyclone inlet temperature, gas flow rate and dust loading on particulate collection efficiency are incorporated in the model equations, along with the cycloneʹs geometric parameters. In validation of the model, comparisons were made with widely used models in the literature, the new model being shown to produce predictions of grade efficiencies in closer agreement with the experimental data than those by the other models. Thus, the current model constitutes a significant contribution to current knowledge of the particulate capture process in gas cyclone separators.