Technical note reconciliation of bubble size estimation methods using drift flux analysis

Banisi, S.; Finch, J.A.

doi:10.1016/0892-6875(94)90046-9

Cited by 40 publications

(12 citation statements)

References 5 publications

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“…The g gas rate by drift fl ux analysis (Banisi and Finch, 1994). The ε g ), the latter being preferred as it is fundamentally related to the rate of fl otation (Finch et al, g fundamentally related to the rate of fl otation (Finch et al, g 2000).…”

Section: Methodsmentioning

confidence: 98%

Comparison of Internal and External Mixer Spargers in a Laboratory De‐inking Flotation Column

2004

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Paper recycling is assuming increased importance in response to growing concerns over waste disposal and conservation of natural resources. The paper recycling process aims to remove contaminants while retaining the valuable fi bers. This is accomplished through a variety of separation processes including screening, cycloning, fl otation and washing.Today, fl otation dominates the removal of printing inks from recycled paper. A typical composition of a feed pulp is given in Table 1. De-inking is a reverse fl otation process where the fl oat product is the waste rejects and the non-fl oat is the valuable accepts. The increasing volume of recycled paper and the rising quality requirements of de-inked fi bers drive development of fl otation technologies. This has led to trials using column fl otation.Column fl otation in mineral processing has been introduced over the last two decades. Columns offer advantages in terms of reduced fl oor space, reduced operating and capital costs, simplifi ed circuits and greater selectivity (Luttrell et al., 1993). Unfortunately, these advantages are not always fully realized in practice, frequently due to defi ciencies in the design, scale-up and operation of the bubble generating system.The air sparging system should be capable of producing small (ca. 0.5 -2.5 mm), relatively uniform sized bubbles at the required aeration rate (Huls et al., 1991). Small bubbles enhance the capture of fi ne particles (Yoon and Miller, 1982;Dobby and Finch, 1986) and increase the fl otation rate and carrying capacity by increasing the bubble surface area rate (or fl ux) (Finch and Dobby, 1990;Gorain et al., 1996). Too small a bubble (e.g., < 0.2 mm) should be avoided as when loaded they can be swept in to the underfl ow stream (Uribe-Salas, et al., 2003). Many bubble-generating systems are available (Al Taweel, 1989;Dobby and Finch, 1991;Rubinstein, 1995); they can be broadly divided into two types, internal and external.* Author to whom correspondence may be addressed. E-mail address: jim.fi nch@mcgill.ca jim.fi nch@mcgill.ca Column fl otation has been introduced for waste paper de-inking to take advantage of low capital cost and excellent separation performance. Bubble generation employs a variety of systems, broadly divided into two types: internal and external. An external in-line static mixer sparger was tested against an internal porous stainless steel sparger. They were compared in an industrial de-inking facility using a 10 cm diameter column. Operating conditions were defi ned and the effect of gas rate, retention time, wash water rate, and froth height on de-inking was investigated. Both spargers gave similar ink recovery and fi ber loss as a function of bubble surface area fl ux. However, the static mixer gave stable operation while the porous sparger showed evidence of plugging over a 6h test. Combined with some ability to control bubble size, overall the in-line static mixer gave superior performance.La fl ottation en colonne a été adaptée pour le désencrage du papier recyclé afi n de ...

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Section: Methodsmentioning

confidence: 98%

Comparison of Internal and External Mixer Spargers in a Laboratory De‐inking Flotation Column

2004

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“…Thus, Equation (1 1 Kumar (1970). The model assumes the following: (i) The resistance offered by the porous material i s so large that bubble formation takes place under essentially constant flow conditions; (ii) The sparger contains an extremely large number of potential pores for bubble formation, only a fraction of which are operative or active pores; (iii) The gas flow rate through each of the active pores is the same and no flow occurs through the non-active pores; and (iv) The number as well as the location of active pores adjust as the flow rate varies.…”

Section: Molerus Modelmentioning

confidence: 98%

Determining equivalent pore diameter for rigid porous spargers

2000

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eactors in a variety of engineering fields from mineral to food processing employ a dispersion of gas bubbles. The technology of R bubble generation and dispersion (or sparging) is central to the operation of these reactors. A case in point are flotation columns used in the de-inking of recycled paper and de-oiling of effluents from refineries and metal rolling mills. In these applications one current method of sparging gas (usually air) is through porous spargers made from sintered stainless steel powder.There is no accepted procedure for selecting the type (e.g., porosity), size and number of these spargers for a given duty. There is a methodology for scaling-up a flotation column based on parameters such as flotation rate constant determined experimentally at the laboratory scale (Finch and Dobby, 1990). One assumption is that the gas holdup-gas rate relationship operative at the laboratory scale is preserved a t full scale. The means to achieve this, however, are not well defined. A rule of thumb is to maintain the same column cross-sectional area to surface area of sparger (AJA, = R,). There is some support for the rule (Xu and Finch, 1990) but a more engineered approach would be preferable.The preservation of the gas holdup-gas rate relationship is tantamount to preserving the bubble size-gas rate relationship or, borrowing from a current approach to flotation modelling, to preserving the bubble surface area flux-gas rate relationship (Corain et al., 1996). Thus, if the bubble size could be predicted for the stream of interest from the sparger characteristics as a function of the gas rate, this would be a key step towards developing a sparger selection procedure. Several models claim to predict bubble size but they require knowledge of the pore diameter. Figure 1 is a SEM secondary electron micrograph of a stainless steel sparger supplied by Mott Industrial. It is difficult to identify the pore size, thus some means to estimate an equivalent pore diameter (D,) is required (the nominal pore diameter quoted by the manufacturer is based on the particle size of the powder prior to sintering).One possibility is to use a model to predict bubble size, compare with the measured and search on D, until a match between measured and predicted is achieved. This is examined in the first part of the paper. We will show that, by using the model of Kumar and Kuloor (1 970), a D, can be fitted to the mean diameter of a bubble swarm measured photographically.The procedure, while successful as shown, is limited by the measurement technique to low bubble concentrations and transparent systems (i.e., no solids present) as well as requiring the collection and analysis of photographic images. (Automated image analyzers do alleviate some of the effort but this is balanced by the surprising level of vigilance needed to maintain data integrity.) Previous work has shown that bubble size can be estimated from drift flux analysis using measurements of gas holdup and gas and liquid rates (Dobby et al., 1988;Yianatos et al., 1988). It is ...

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“…BSD can be used to predict flotation performance, and it is commonly used for process control (Gorain et al, 1995). Between the techniques and approaches for bubble size determination, the following are highlighted: (i) conductivity probes (Barigou and Greaves, 1992); (ii) drift flux analysis using gas rate and gas holdup measurements (Banisi and Finch, 1994;Yianatos and Levy, 1989); (iii) optical sensors (Randall et al, 1989); and (iv) image analysis of recorded bubbles (Grau and Heinskanen, 2002;Hernandez-Aguilar et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

Indirect estimation of bubble size using visual techniques and superficial gas rate

Vinnett

Álvarez-Silva

2015

Minerals Engineering

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Technical note reconciliation of bubble size estimation methods using drift flux analysis

Cited by 40 publications

References 5 publications

Comparison of Internal and External Mixer Spargers in a Laboratory De‐inking Flotation Column

Comparison of Internal and External Mixer Spargers in a Laboratory De‐inking Flotation Column

Determining equivalent pore diameter for rigid porous spargers

Indirect estimation of bubble size using visual techniques and superficial gas rate

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