A New Improved Dissolved Air Flotation, 1998 Pulping Conference Proceedings

Today more than 200 installations of an older type of Dissolved Air Flotation (DAF) clarifier are running in mills. This older DAF design incorporated a tile tank, a long scraper assembly, and an inefficient air saturation tank. This system had some operational drawbacks. These included problems with the scraper assembly, heavy solids build up in the bottom of the clarifier, problems with the air saturation tank and, at times, poor effluent quality. Also, this system had a low hydraulic loading rate of only 2-3 gpm/ft2, which resulted in the use of a large floor area for a given flow demand.

In the attempt to improve on this design, a new DAF system was designed. The goal of the new design was to increase capacity, improve effluent quality, eliminate operating problems and reduce the size of the footprint. This process began in early 1996 and after a short design review period, a prototype unit was built and delivered to the Beloit Research and Development Center in Pittsfield, Massachusetts later in that same year. This system was tested for its operational integrity and removal efficiency. It was determined, after small modifications, that the system was mechanically sound, provided excellent removal rates, provided high sludge discharge consistency and operated at a hydraulic loading rate of 5-8 gpm/ft2.

After the successful pilot installation, a full scale system was designed and offered to the marketplace for use as savealls and process water clarifiers. This paper details some of the changes incorporated into this design and provides some data on the efficiency of the new DAF clarifier system.