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Abstract: Numerical technology has been widely used for the study of the electrostatic precipitators (ESP) and the bag filters. This paper presents a numerical model for a scale hybrid particulate collector (HPC), which combines the ESP technology and the filtration technology together. The collection process of the HPC is unsteady as the pressure drop across the bag filter increases with the deposition of the particles. The physical processes of the model include the corona discharge, the fluid flow, the particle charging and the filtration. The corona discharge field is solved by using a finite volume method. For the fluid field, the unsteady and incompressible Navier–Stokes equations with the RNG κ–ε turbulence equations are solved. The effect of the electric field on the fluid field named electro-hydrodynamic is also considered. For the particle charging, the filed-diffusing combined model of Lawless (1996) is adopted. For the filtration, an unsteady cake formation model is proposed. The pressure drop across the cake is calculated according to the mass density of the cake. The coefficient between the pressure drop and the mass density of the cake comes from the experimental data. Applying the numerical model to the HPC, the influence of the hole diameter of the perforated-plate on the collection efficiency of the electrostatic zone is analyzed. Numerical results show that the collection efficiency of the electrostatic zone of the HPC has no certain relation with the hole diameter of the perforated plate. The effect of the hole diameter of the perforated-plate on the collection efficiency of the electrostatic zone becomes weaker with increasing the applied voltage. [Copyright &y& Elsevier]

The ash fouling during coal combustion is initialized by a deposition of ‘sticky’ inner layer composed of fine particulate matter (PM). In this work, we present a quantitative investigation on the built-up of the initial deposit layer and its roles in the capture of coarse fly ash particles. The fly ash and ash deposit are sampled in a 25 kW self-sustained pulverized coal combustor for various lignite samples including Zhundong and Hami lignites. The ash collection efficiency onto the probe is positively correlated to the ultrafine particle formation fraction. The deposition rate of fine particle PM 10 is modeled in a combined Eulerian-Lagrangian scheme, with an input particle concentration measured at the entrance of boundary layer. The predicted results divulge that the thermophoresis enhances the impaction efficiencies of submicron and micron sized particles by 1–2 orders. The deposited particles are more concentrated on the central top region of the probe, and the trend is even more remarkable for larger particles, consistent with experimental observations. For both Zhundong and Hami lignites, the deposits are largely composed of fine PM 10 and condensed matter during the initial stage of one minute, but the weight percentages of fine particle deposits over the total deposit mass decrease significantly in the subsequent 5–10 min. Consequently, the average sticking efficiency of the coarse mode PM 10 + increases asymptotically as the deposited PM 10 grows to ~ 1.5 g/m 2 . Zhundong lignite shows higher saturated sticking efficiency of PM 10 + than Hami lignite, which is possibly attributed to the different surface properties of the bulk ash particles. [ABSTRACT FROM AUTHOR]

Introducing airflow into the low-intensity dry magnetic separator (LIDMS) is an effective means to improve the separating efficiency of ferromagnetic particles under dry conditions. In this study, a multi-physical coupling model was established to compare the separating performance of LIDMS under four typical air supply modes. The result shows that Mode D can maximize the competing force along the normal direction of the drum due to the vertically outward air supply mode, and its separating performance is the best, especially for the particles with a fine diameter. The mechanism of airflow under different modes which enhances the LIDMS is expounded by analyzing the characteristics of the magnetic field and the flow field and calculating the forces on particles with various properties. We expect that this study could provide a reference for the dry separation of magnetic minerals and the development or optimization of LIDMS under airflow conditions. [Display omitted] • The performance of magnetic separation under different air supply modes is compared. • A multi-physical model is established to simulate the magnetic separation process. • The difference in separation performance is explained by analyzing the flow field and forces on particles. • The airflow in a normal direction can maximize the dry magnetic separation efficiency. [ABSTRACT FROM AUTHOR]