A Review of Flotation Physical Froth Flow Modifiers

Over the past few decades, the need to process more minerals while lowering capital costs has led to an increase in the size of flotation cells, e.g., 0.03 m3 to 1000 m3. However, this increase has created new challenges in the operation and design of industrial flotation cells, particularly in terms of froth removal, because the distance the froth must travel increases with an increase in the flotation cell diameter. This has a negative impact on recovery. Physical froth flow modifiers can be used to improve froth removal. Their major functions are to modify and optimise the flow of the froth, improve froth drainage, reduce dead zones, and improve froth flow and removal dynamics. Therefore, physical froth flow modifiers are discussed, evaluated, and compared in this paper. The literature indicates that physical froth flow modifiers such as crowders and launders are used extensively as industrial solutions to enhance froth transport and recovery in large flotation cells. Other modifiers (including froth baffles and froth scrapers) have been found to have a profound effect on local froth phase sub-processes, including drainage and bubble coalescence. However, industrial uptake is either dwindling or limited to small-volume rectangular/U-shaped cells in the case of scrapers, or, there is no uptake at all in the case of froth baffles. Further research on how some of the physical modifiers (e.g., baffles and launders) impact the selectivity of particles is required.

Study on the Vibrational Characteristics of a Tube Array Caused by Two-Phase Flow—Part 2: Fluidelastic Vibration

Fluidelastic vibration of a tube array caused by two-phase flow has been reported in some papers. The critical flow velocity is usually estimated with a simple Connors-type criterion which is based on average flow velocity, average fluid mass density and damping in two-phase flow. However, there is no explanation why this simple criterion can be used or how the fluidelastic instability occurs by two-phase flow. This paper shows the experimental results on the fluidelastic vibration both by air-water two-phase flow and by steam-water flow in the condition of up to 7.0 MPa in pressure and to 284°C in temperature, and a new criterion based on an assumption of energy balance is here introduced using a “true” flow velocity. However, the comparison with the experimental data indicates that an intermittently rising slug speed, which has been introduced in Part 1, in slug or in froth flow region, should be used, and a modified new criteria for slug or froth flow region is derived. In addition, the new criteria is compared with the usual Connors-type criteria, which greatly depend on the estimation of the damping in two-phase flow. The agreement of both criteria is revealed to be in the vicinity of the variance of the unknown parameters in the usual criteria.