The Influence Of Suspension Viscosity On Bitumen Rise Velocity And Potential Recovery In The Hot Water Flotation Process For Oil Sands

In the continuous hot water flotation process for extracting bitumen from oil sands, one a/the important steps involves a separation vessel in which aerated bitumen is floated while coarse sand is settled. These two separating processes must take place through a zone of dispersed clay constituents, mainly illite and kaolinite. Due to the clay content of the oil sand feed, and to the possibility of local solids concentration build-up in the continuous process, local viscosity can increase to the point where it markedly reduces the bitumen rise velocity and hence flotation efficiency. It is shown that the viscosity is significantly solids concentration and pH dependent. This is probably one of the reasons that the fines content of oil sandfeed and the amount of alkaline process aid employed are important variables in the hot water process. Introduction Hot Water Processing Of the many processes which have been developed for extracting bitumen from oil sands, the only recovery process to be applied in a large-scale commercial operation is the hot water flotation process. The original hot water process was developed by Clark et al.(1–3) for Athabasca oil sands. With modifications, it has been improved and implemented by Suncor and Syncrude for commercial use. The objective is to separate the bitumen in oil sand from the water, quartz sand, and the fines. (In this work fines are defined as the fraction of solids having an equivalent spherical diameter less than 44 µm and is expressed as a percentage of total solids). A typical continuous process sequence for bitumen extraction is indicated in Figure 1. The process can be considered in two stages. First, the mined oil sand is conditioned in a rotating drum (tumbler). Here hot water, steam and sodium hydroxide, added as necessary, form a slurry having about 7% bitumen and 70% solids. In this step the bitumen is disengaged from solids and becomes aerated. Falling screening to remove rocks and lumps of unconditioned oil sand the slurry is diluted with further hot water, and advanced to a flotation vessel. In this separatory stage the flotation vessel contents are held under nearly quiescent conditions to allow the aerated bitumen globules to float to the surface and the coarse sand to settle to the bottom. The bituminous froth is skimmed off at the top while the sand slurry is withdrawn from the bottom as tailings. In the middle part of the vessel there is always a finite hold-up of both bitumen globules and well dispersed fine solids. A stream, termed middlings, is drawn off from this region and pumped to a secondary (scavenging) flotation-recovery circuit. Secondary flotation, froth collection and a combination of gravity settling and dilution (with naphtha) centrifuging of the froth complete the continuous hot water extraction process. Further etails can be found elsewhere(5–7). Because secondary recovery involves sparging with air to float the bitumen, the flotation of solids is promoted as well; the secondary froth is high in solids and water. This poor quality froth requires further cleaning.