Faschingleitner, J. (2008). Model verification of water spray suppression of fugitive dust emission using different bulk solids and droplet sizes [Diploma Thesis, Technische Universität Wien]. reposiTUm. http://hdl.handle.net/20.500.12708/183814
depth-filtration; fugitive dust emission; PM10; water-spray; bulk good manipulation; air humidification model; dust suppression; PM5; two-phase nozzle; droplet size distribution
en
Abstract:
Fugitive dust pollution is an issue for human health. Bulk handling in quarries or mines, in particular from bulk materials falling from a hopper or a conveyor belt are one of the main sources of fugitive dust emissions. Methods to suppress such dust emissions are water sprays with two-phase nozzles for instance. In previous studies [1],[2] mathematical modelling of such suppression action where derived from deep-bed filter equations just for yellow-river sand and using one nozzle air pressure. In order to improve the application and efficiency of water spraying systems this model was verified bringing different droplet size distributions (using different nozzle air pressure) different saturation states of the air inside and outside the chamber and different bulk good characteristics into play. Since 11 years there exists a scientific cooperation of TU-Vienna (Professor Höflinger) with Jinan Jangzhu University (Peoples Republic of China, Shandong Province) (Professor Liu) where studies of fugitive dust suppression [1],[2] were performed. Using the developed dust suppression assembly of previous studies [1],[2] at Jinan Jangzhu University construction dust and steel slag dust was dropped from a conveyor belt into a dust chamber, wherefrom the emitted dust was sucked off and quantified via a cascade impactor. The different particle size distributions of the two examined bulk solids were analyzed using a laser particle sizer. A two-phase nozzle was installed in the dust chamber to perform dust suppression.<br />The model adopted from depth-filtration equations was verified using different bulk solids and at different nozzle air pressures and clarified if the dust suppression gets improved. Different water volume flows and nozzle-air pressures were used creating different dust suppression conditions which are characterized by different water spray assimilated moisture by the air inside the chamber (=different evaporating water volume flows) and different droplet size distributions. To examine the different water spray conditions a droplet size measurement assembly was built using a laser particle sizer at TU-Vienna. The droplet size of the spray was found to decrease by rising nozzle air pressure and to increase by exceeding a water-flux (depending on nozzle air pressure) of 4-6L/h. Using the measured conditions inside and outside the dust chamber (relative humidity and temperature) and the Mollier-diagram a mathematical model equation was developed to describe the dependence of evaporating water volume flow on nozzle water-flux as the air in the chamber isn't saturated completely. The natural variation of outside air humidity was ruled out using linear interpolation of evaporating water-flux at different outside air humidities. The dust suppression dependence on bulk solid and nozzle air pressure was examined using the adapted deep-bed filter equations from previous works and the developed humidication model. The natural variation of outside air humidity was ruled out using linear interpolation of dust emission at different outside air humidities. It could get proven that the dust suppression model is applicable for different bulk solids and nozzle air pressures in equal quality. Also different dust suppression characteristics of PM5, PM10 and TSP where clarified. It was found out that TSP is suppressed with highest efficiency. The nozzle air pressure dependence of remaining emission after suppression was studied and found that lower remaining emission is more likely at lower nozzle air pressures even tough higher dust suppression efficiency is reached using higher nozzle air pressures.