Evaluation of wetting measures and capture efficiencies of fugitive dust emitted from a limestone pile: Experiments and artificial neural network

In windy conditions, dry bulk material storage sites for limestone fugitively emit dust, causing occupational hazards and posing harmful health effects to nearby residents. According to this investigation, the threshold friction velocity for the limestone was 7 m s−1. As wind speed increases from 7 to 10 m s−1, the concentrations of TSP, PM10, and PM2.5 rose by 148%, 121%, and 76%, respectively. Separate tests were conducted to evaluate fog cannons' and heavy-duty sprinklers' ability to capture TSP, PM10, and PM2.5 and prevent re-suspension from the pile's surface. Eight cases of parameter combinations were investigated, where PM2.5 had the lowest dust capture efficiencies in six instances, while TSP had the highest dust capture in all eight cases. Low spray angles and intermittent water flow regimes showed the best dust collection efficiency. For the fog cannon it was 85.3% and for the heavy-duty sprinkler, it was 79.5%, and they occurred at low and high wind velocities, respectively. The wettability of dust particles smaller than 4 µm in diameter was more difficult than that of larger particles, because the size differences between dust particles and wetting agent's droplets reduces the probability of collision. An artificial neural network was applied to predict dust capture efficiencies from model parameters such as wind speed, spray angle, and water supply regimes. The relative errors in the predicted capture efficiencies for TSP, PM10, and PM2.5 capture were 1.86–4.73%, 2.15–4.57%, and 1.99–6.53%, respectively, implying a good learning ability of the neural network. The results of different wind speed predictions were verified by the F test, where the P values for TSP, PM10, and PM2.5 ranged between 0.17–0.44, 0.18–0.45, and 0.16–0.48, respectively. Overall, intermittent waterflows and low wind speeds optimized the spread of the mist released from the fog cannon, while intermittent waterflows and higher wind speeds were necessary for the optimal performance of the heavy-duty sprinkler.