Dissolved air (pressure) flotation

Bratby, John Raymond

Dissolved air (pressure) flotation

Master Thesis

1973

Abstract

It appears that, in the past, little attempt has been made to establish the basic parameters influencing the flotation process, or their inter-relationships, on a quantitative basis for the purpose of developing rational design procedures. This thesis investigates those parameters influencing solids removal and thickening by dissolved-air (pressure) flotation and the criteria pertaining to the design of flotation tanks for solids removal and thickening. A review of pertinent literature on flotation is presented. The historical development of flotation is given together with the theory of bubble-particle adhesion. Four common methods of flotation are compared and their inherent advantages and disadvantages are discussed. Dissolved-air (pressure) flotation, the method used in this investigation, is considered in greater detail by presenting established practical considerations for design. A pressure-saturation unit was developed in which all the compressed air supplied is dissolved into the saturator feed by continously recycling the air through a sparger, i.e. there is no air wastage. The air circulating pump operates within the pressurized circuit so that it pumps only against the hydrostatic head of water in the saturator. A vertical flow type flotation unit was developed which provides a counter current flow regime and a stable interface between the clear liquid and rising agglomerates. The accumulated agglomerates discharge freely and without mechanical assistance at the top of the unit.

Keywords

civil engineering

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