Influence of the pump type on the parameters of the pneumatic-hydraulic aeration system in flotation apparatus

Summary

Flotation has been one of the efficient water treatment technologies. Flotation treatment is based on small gas bubbles generated by different methods, pneumatic-hydraulic, in particular. A case is considered of air feeding before the pump and subsequent water-air mixture passing through the aerator, and air being broken to small bubbles. Possible operation in the presence of air determines the choice of self-priming pumps (centrifugal and vortex). Experiments were carried out on determining two of the most important aeration parameters: bubbling rate and average size of generated air bubbles that determine the efficiency of water flotation treatment. Based on the data obtained it is shown that in most cases centrifugal pumps have the advantages: considerable part of the air entering the pumps is dispersed at the outlet of the aerator to 30–100 μm bubbles; whereas in case a vortex pump is used air bubbles of more than 200 μm size are generated which is ineffective for water flotation. It is stated that for some wastewater types the use of vortex self-priming pumps can be more reasonable.

Key words

water treatment , centrifugal pump , aeration system , pneumatic-hydraulic flotation , aeration intensity , air bubble size

Process concentrate treatment by flotation at CHP plants

Summary

The problem of processing oily wastewater generated at power plants is discussed. Much attention is paid to the purification of process concentrate that is characterized by higher temperature (55–70 °С). A pneumatic flotation unit used for the process concentrate treatment at the South CHP plant operated by Lenenergo OJSC is considered. The major drawback of the unit is pointed out: the changes in the rubber properties result in the changes in air bubble dimensions, and the efficiency decreases. A possible solution to the problem can be the use of an ejection aeration system with a disperser. The experiments in a laboratory unit on determining the size distribution of the bubbles generated by the ejection aeration system at 55°С were conducted. In addition, model oily wastewater was subject to purification in a unit with the pneumatic and ejection aeration systems. The average size of the finely dispersed bubbles generated by the ejection aeration system with a disperser was 60 μm, and that of the coarse bubbles was 105 μm. It is shown that the use of the ejection aeration system with a disperser provides for reducing the residual concentration of oil products from 4 to 1 mg/l or reducing the purification time from 25 to 15 minutes.

Key words

flotation , ejector , pneumatic aeration system , air bubble size , dispersant , process condensate

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