Name: AFONSO DE JESUS CORDEIRO
Publication date: 23/10/2024
Examining board:
Name |
Role |
|---|---|
| ANDRÉ LUIZ AMARANTE MESQUITA | Examinador Externo |
| ARTHUR VIEIRA DA SILVA OLIVEIRA | Examinador Externo |
| MARCIO FERREIRA MARTINS | Presidente |
Summary: Air pollution from dust suspension during the handling of bulk solids, such as iron ore pellets, presents significant challenges for the mining industry, including Vale S.A. The dispersion of fine particles into the air can lead to urban and health issues, as these particles are capable of traveling long distances driven by wind. To comply with air quality standards set by the National Environmental Council, Vale utilizes technologies to reduce environmental impacts, one of which includes the use of glycerin and water-based dust suppressants. These are applied through large nozzles designed to saturate the ore pellets and suppress dust during the storage yard’s stacking and retrieval processes. Despite the effectiveness of the current system, challenges associated with glycerin waste have prompted the exploration of alternative methods, such as deploying spray nozzles at strategic locations within the plant. Implementing these methods necessitates quantifying the coverage fraction of the suppressant solution on the pellet surfaces post-spray and understanding the wettability mechanisms stemming from the interactions at liquid-solid and liquid-liquid interfaces. Consequently, methodologies have been developed to characterize both the morphological and physical properties of the pellets—such as average diameter, surface area of the spherical cap, porosity, average volume, apparent density, roughness, and shape factors—as well as properties of the suppressant, including viscosity and density. Techniques utilized include image analysis via ImageJ software, advanced 3D profilometry, density determination by fluid immersion, drop penetration tests, and mathematical analyses of empirical equations using MATLAB programming. The results were statistically validated with a 10% confidence level and revealed a distinction between open and closed pores relative to the pellets’ porosity. Although the total porosity was high, only about 5% of the pores were available to accommodate the volume of the suppressant. It was observed during the drop penetration experiments that the effectively open pores were predominantly on the surface of the pellets. Once these pores were filled, the pellets ceased to absorb further liquid, leading to the formation of a liquid film on the surface. This film altered the liquid-solid interface to a liquid-liquid interface, thereby defining a saturation point. A dimensionless average saturation number was developed, calculated as the ratio of the current dry mass of the pellet plus the mass of solution applied dropwise to saturation against the total average mass of solution absorbed by the pellet samples. This dimensionless number facilitates the calibration of spray nozzle systems to optimize the quantity of suppressant required to achieve complete coverage of the pellets with the suppressant solution. Additionally, it sets the stage for a novel field measurement methodology that can quantify the amount of suppressant solution present in groups of pellets after they pass through the application system.
