Abstract
A physical-mathematical model has been designed to estimate the emission of dust from the surface of granular materials exposed to wind erosion. The emission model implements the Monte Carlo probabilistic approach, which for a given wind velocity (i.e., shear stress velocity) ascribes the probability of saltation to the particle aggregates composing the erodible surface and calculates the emission of dust aerosol based on the main laws governing the physics of wind-blown particles. The article discusses the application of the emission code to the surfaces of two metal sulphides (PbS and ZnS), which are typically stored in stockpiles in the open yards of industrial plants that operate in the commodity sector, to be used as raw materials for the production of lead and zinc (non-ferrous metals). The results of the simulation were found to be in agreement with the indication provided by the technical literature about the emission potential of the two metal sulphides. The emission model hereby proposed intends to provide an analytical integration to the experimental and empirical Emission Factors (EF) already suggested by the technical and scientific literature about industrial wind erosion.
Highlights
This article deals with the definition of a physical-mathematical model which explains the emission of dust aerosol from the surfaces of granular materials exposed to wind erosion
The particulate matter (PM) produced by saltation remains suspended in the air to travel to variable distances depending on its aerodynamic characteristics: according to the schematizations proposed by the scientific literature, short-term suspension and subsequent deposition near the emission source occur for particles/particles aggregates with aerodynamic diameters in the range of 20 μm and 70 μm, while PM with an aerodynamic diameter
The values of fine dust (FD) calculated with the damage ratio suggested by Thornton [26] were found to be about one order of magnitude higher than those determined with the DR equation of Deng and Davé [28] (FD Thornton ≅ 10 ∙ FD Deng and Davé)
Summary
This article deals with the definition of a physical-mathematical model which explains the emission of dust aerosol from the surfaces of granular materials exposed to wind erosion (i.e., industrial wind erosion). The impact of the bouncing aggregates (i.e., saltators) on the granular surface, from which they are originally ejected by direct entrainment (i.e., direct effect of the drag forces exerted by the wind), causes the breakage of both the saltators and the splashed aggregates (i.e., aggregates hit by saltators) and the emission of dust aerosol (i.e., finer particles aggregates or elementary particles) [5,6,7]. A physical-mathematical model has been designed to estimate the emission of the fine fraction of dust aerosol (d < 20 μm) by implementing a probabilistic approach (Monte Carlo method), which, for a given value of the wind friction velocity, ascribes the saltation probability to each saltator laying on the surface and simulates the entire emission mechanism: aggregates saltation, impact onto the granular surface and rupture of both saltators and splashed aggregates, with consequent ejection of fine particles into the atmosphere. The results of the simulation were found to be consistent to the indication of USEPA (US Environmental Protection Agency) [15] regarding the two materials under investigation, as well as to the dispersiveness classification reported by the Reference Document on Best Available Techniques (BREF)-Emissions from Storage [16] (paragraph 5)
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