Dynamic flowsheet simulation of re-entrainment from particle layers formed inside electrostatic precipitators

Electrostatic precipitators clean away the particulate matter of exhaust gases in manifold industrial processes.Parameter studies of particle separation in the size range of several 100 nm to 25μm is of particular interest for the prediction of precipitation efficiencies and emissions.Models typically cover the transport of particles towards walls of the precipitator.However,no model yet covers the possible re-entrainment of particles from layers formed at the walls back into the gas flow.This study presents the implementation of a new time-resolving model for electrostatic precipitation utilizing a re-entrainment model.Experimental data support the results of modelling.The model uses a statistical approach based on properties of the particulate layer forming at the precipitator walls.The model is used for the analysis of the redispersion of particles in a laboratory-scale electrostatic precipitator(Sander,Gawor,&Fritsching,2018).Results show reduced precipitation efficiencies for particles larger than 5μm as particles have higher kinetic impact energies and lower bounding energy at the layer surface.Time dynamics reveal a steady-state behavior of the separation for CaCO3(limestone,trademark"Ulmer WeissR")while Al2O3(trademark"Pural NFR")precipitation is affected by layer buildup at the walls increasing over several minutes.

INVESTIGATIONS INTO THE DETACHMENT OF DIFFERENTLY STRUCTURED DUST LAYERS FROM SURFACES

A technique is presented for creating surface-adhering dust layers under defined conditions, and characterizing and stressing the layers created. The procedure described is shown to be suitable for the quantitative evaluation of the effects of different parameters such as particle size, porosity and surface roughness etc. on the stability of particle layers.

Coefficient of restitution for particles impacting on wet surfaces： An improved experimental approach

The coefficient of restitution is widely used to characterize the energy dissipation rate in numerical simulations involving particle collisions. The challenge in measuring the coefficient of restitution is the strong scatter seen in experimental data that results from varying particle properties, i.e. shape and surface roughness, and from imperfections in the experimental technique. To minimize this scattering, a novel experimental setup was developed based on two synchronized high-speed cameras capturing the collision behaviour of a particle in three dimensions. To measure the wet restitution coefficient, which describes particle impact in the presence of a liquid layer in the contact region, additional accuracy can be achieved by measuring the liquid layer thickness by a high-precision optical confocal sensor. The coefficient of restitution was measured for glass particles with two different diameters, at different relative velocities and liquid layer thicknesses, with a focus on small collision velocities and thin liquid layers, using both the improved （three dimensional） and the conventional （two dimensional） approaches to quantify the improvement of the new method＇s accuracy.

Scalable gas-phase processes to create nanostructured particles

The properties of nanoparticles are often different from those of larger grains of the same solid material because of their very large specific surface area. This enables many novel applications, but properties such as agglomeration can also hinder their potential use. By creating nanostructured particles one can take optimum benefit from the desired properties while minimizing the adverse effects. We aim at developing high-precision routes for scalable production of nanostructured particles. Two gas-phase synthesis routes are explored. The first one - covering nanoparticles with a continuous layer - is carried out using atomic layer deposition in a fluidized bed. Through fluidization, the full surface area of the nanoparticles becomes available. With this process, particles can be coated with an ultra-thin film of constant and well-tunable thickness. For the second route - attaching nanoparticles to larger particles - a novel approach using electrostatic forces is demonstrated. The micron-sized particles are charged with one polarity using tribocharging. Using electrospraying, a spray of charged nanoparticles with opposite polarity is generated. Their charge prevents agglomeration, while it enhances efficient deposition at the surface of the host particle. While the proposed processes offer good potential for scale-up, further work is needed to realize large-scale processes.