Primary froth

The primary froth contains air and is therefore compressible and more viscous than bitumen (38). To make it easier to pump, it is deaerated in towers by causing it to cascade over a series of cones, flowing against the upward flow of steam. The froth from the secondary flotation is cleaned in stirred thickeners to remove some of the water and solids, and then deaerated. After deaeration, the primary and secondary froths are combined into a single feed for a froth treatment process. This deaerated froth contains about 65% oil, 25% water, and 10% solids. 

Composition and Density. Density is of fundamental importance to any flotation process. The density of bitumen is much less variable and less dependent on temperature than on its viscosity. Thus, the density data reported by Ward and Clark (41) and Camp (22) shows slight temperature dependence for Athabasca bitumens. However, the density of froth is strongly influenced by the gas phase and also the entrained solid particles. Primary froth typically has a composition of 66% bitumen, 25% water, and 9% solids, and secondary froth typically contains 24% bitumen, 59% water, and 17% solids. Table II shows a series of freshly formed primary froth densities that vary from 0.7 to 0.9 g/cm3 at about 70 °C (the experimental conditions are described later). 

Table n. Viscosities, Densities, and Compositions of Some Fresh Primary Froths by On-Line Measurements... 

Fresh froth viscosities can be quite high compared to that of bitumen at the same temperature, primary froth having a viscosity of typically 1.8 to 3.0 x 103 mPa-s at about 80 °C (shear rate of 58 s-1), compared to a bitumen viscosity of 495 mPa s under the same conditions. 

In an attempt to obtain more reproducible, more representative data for freshly produced froth, some on-line measurements for continuously produced primary froth have also been made. The processing was carried... 

Figure 9. Flow curve for primary froth at 70 °C, measured in situ in the continuous pilot plant flotation vessel...

When plotted on triangular coordinates, primary froth assays from commercial operation typically lie on a straight line and indicate an upper limit of 67.5% bitumen concentration. This observation adds credence to... 

Figure 17. The structure of primary froth and the role of the variable G. G = 267 corresponds to the intersection of the two lines given by Vfl = 0.56 and VM = 0.23.

Schramm, L.L. and Smith, R.G. (1990) Monitoring electrophoretic mobility of bitumen in hot water extraction process plant water to maximize primary froth recovery. Canadian Patent 1,265,463,... 

Foams and emulsions may also be encountered simultaneously [114]. Figure 1.5 shows an example of an aqueous foam with oil droplets residing in its Plateau borders (see Section 5.6.7). In addition to containing gas, an aqueous phase, and an oleic phase, foams can also contain dispersed solid particles. Oil-assisted flotation of mineral particles provides one example (Chapter 10). Oil-sand flotation of bitumen provides another (Chapter 11). In the case of oil-sands flotation, an emulsion of oil dispersed in water is created and then further separated by a flotation process, the products of which are bituminous froths that may be either air (and water) dispersed in oil (from primary flotation) or air (and oil) dispersed in water (from secondary flotation). In either case, the froths must be broken and de-aerated before the bitumen can be upgraded to synthetic crude oil. (See Section 11.3.2). 

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