Simulation of a Wet Scrubber Using a Combined Eulerian-Lagrangian Model in OpenFOAM®

In a wet scrubber water droplets are introduced into the dust laden off-gas in order to capture the fine dust particles. If the off-gas stream is additionally guided through a contraction (e.g. a Venturi nozzle), the dust capturing efficiency is further increased because of the larger relative velocities and the reduced droplet sizes. From a physical point of view the wet scrubbing process comprises a whole set of phenomena starting from droplet break-up and coalescence to the behavior of the wall film and the dust capturing mechanism itself. The aim of this study is to investigate the scrubbing performance, mainly characterized by pressure drop and dust capturing efficiency, of a Venturi scrubber using open source software. Therefore, a comprehensive simulation model, comprising sub-models for liquid droplets, liquid wall film and dust fractions, is used. Thereby, representative droplets are traced in a Lagrangian frame of reference while the fine dust particles are treated as additional passive Eulerian phases which are allowed to drift with respect to the gas phase due to gravitational and centrifugal forces. The dust phases’ diffusivity is derived using a model considering the dust particle diameter and the local turbulence characteristics. Droplet deformation and break-up is considered by the Taylor Analogy Breakup (TAB) model. Furthermore, dust capturing is triggered by impaction, interception and diffusion mechanism. In a further step the influence of a wall film is considered by a model extension solving the shallow water equations at wall boundaries. It is shown that on principle incorporating water deposition from the droplets to the film is feasible as well as droplet entrainment from the film due to film separation and droplet entrainment.