No abstract

The influence of cone angle on solids circulation was investigated using a computational fluid dynamics (CFD) Euler–Euler multiphase model. The solids mass flow rate in the spout and the average particle cycle time were used to evaluate the solids circulation rate for seven cone angles with different loads of solids. A factorial design was applied to evaluate the effects of cone angle, solids load, and inlet air velocity on particle circulation. The proposed CFD method for measurement of the particle cycle time showed good agreement with experimental data reported in the literature and could be applied to investigate solids circulation for other particles and spouted bed geometries The solids load had the greatest effect on the particle cycle time, followed by the cone angle. Simulation results showed that lower cone angles favored solids circulation in spouted beds and could be used to improve the drying of sorghum in the equipment.

RESUMOA sedimentação é um processo no qual um sólido suspenso em um líquido é separado devido à diferença entre as densidades e concentrações das fases presentes na suspensão, por ação do campo gravitacional. Os métodos existentes para dimensionamento de sedimentadores são empregados para equipamentos de alta capacidade, de uso industrial ou em estações de tratamento de água e esgoto. Neste trabalho, foi projetado e construído um sedimentador em escala de laboratório (piloto) pelos métodos de Biscaia Jr e Kynch. O sedimentador contínuo foi projetado e construído de acordo com as dimensões fornecidas pelo método citado de Biscaia Jr., pelo qual uma concentração de alimentação de suspensão de cal hidratada de 70 g L -1 foi selecionada, com tanque sedimentador de 52 cm de diâmetro e altura total de 31 cm. A concentração do lodo obtida experimentalmente foi superior ao predito pelo método de Biscaia Jr., resultando em espessado de 425 g L -1 . O líquido clarificado obtido apresentou baixas turbidez e concentração de sólidos. A eficiência de separação sólido-líquido obtida foi de 95,7%. Assim, considerou-se o equipamento construído com ótima eficiência de separação.

Heating and drying are important in order to meet pellet specifications in the steel making industry. Besides, the drying of iron ore for trading may be effected by the intermittent formation of agglomerates. As a consequence, it is important to understand the drying of such materials. Drying assays of spherical pellets suspended in an oven at 50 o C were developed. We analyzed and compared the drying kinetics of two pellets (2.0 cm and 1.4 cm). A discussion was presented about the drying behavior. Moreover, the critical moisture content, constant drying rate, and effective diffusivity for the hindered drying were estimated.

Drying operations in iron ore processing plants have a particularly high energy demand due to the massive solid flow rates employed in this industry. A 33 full-factorial design was applied to investigate the effects of air temperature, airflow velocity, and solids load on the drying time and the specific energy consumption (SEC) of the convective drying of iron ore fines in a fixed bed. The results demonstrated that each drying air condition was associated with an optimal solids load that minimized the SEC. A load of 73 g (bed height of about 0.8 cm) was identified and validated as the optimal condition in terms of energy consumption for the configuration with the highest air temperature (90?C) and airflow velocity (4.5 m/s). This condition resulted in a drying time of 29.0 s and a corresponding SEC of 12.8 MJ/kg to reduce the solids moisture content from 0.11 to a target of 0.05 kg water/kg dry solids. The approach presented here for identifying the optimum values for the process variables should assist in the design and operation of energy efficient convective dryers for iron ore fines.