Kinetic free mathematical model for the prediction of Kst values for organic dusts with arbitrary particle size distribution

Risk mitigation in production facilities has been an issue of great interest for decades, especially in activities which represent a serious hazard to human health, environment and industrial plants. Dust explosions are a major hazard in many industrial processes: only in the first part of 2019 (January–June) 34 dust explosions, mainly due to organic powders, occurred worldwide. An explosion may take place whenever there is the presence of combustible dusts, which are frequently generated by activities such as grinding, crushing, conveying and storage. Currently, a relatively expensive experimental test, carried out into a 20-L Siwek apparatus, is used to address the order of magnitude (class) of explosive dust: this piece of information is referred to as the deflagration index, K_st. At the current state, only a few pioneering models have been developed in order to predict the value of the K_st as a function of some relevant properties of the dust: e.g. particle size distribution (PSD), humidity, thermal conductivity, etc‥ Most of these models condense the information about the PSD of a given dust into an average value, referred to as D₅₀. In this work, a kinetic free mathematical model aimed at predicting the deflagration index for organic dusts is presented. This model, unlike the older ones, considers the whole particle size distribution for the computation of the deflagration index. In order to be implemented, only a single experimental K_st value (which works as a reference) and a particle size analysis on the dust are required. The model was validated using the whole granulometric distribution of three different organic powders (fosfomycin, sugar and niacin). In addition, the same estimations were done by considering only the D₅₀ data. It was noticed that, for highly polydispersed dusts, results were less accurate with respect to those obtained using the complete PSD, highlighting the importance of considering a complete granulometric distribution for process safety purposes.     

Photochemical alteration of the molecular weight of dissolved organic matter

Molecular weight (MW) is a key control on the physical, chemical, and biological characteristics of dissolved organic mater (DOM). This study investigated the effect of photooxidation on the average MW of DOM by exposing DOM of diverse origins to simulated solar radiation at varying levels of dissolved oxygen and under different incident light wavelength regimes. During irradiation, high-molecular-weight fractions were destroyed and low-molecular-weight constituents were formed. The average MW decreased with irradiation time in all treatments in a manner that can be described by a quasi-exponential function, which suggests that solar radiation is incapable of completely mineralizing DOM even after prolonged exposure. Increasing the oxygen concentration accelerated the MW reduction while the removal of oxygen strongly suppressed this process. The fractional contributions from UV-B, UV-A, and visible radiations to full-spectrum photoinduced MW reduction varied considerably among the DOM samples examined, ranging from 19% to 60%, 17% to 36%, and 15% to 46%, respectively. The MW changes in time-series irradiations were inversely correlated with the ratio of the absorbance at 250 nm to that at 365 nm (i.e., the E₂/E₃ quotient). Photoinduced MW reduction was accompanied by a decrease of polydispersity, which is indicative of a reduced DOM heterogeneity.