Experimental Research On The Influence Factors Of Dissolved Air Flotation Micro Bubble Generation

In the area of water treatment,flotation method has been one of the most widespread and effective oil-removal method.Flotation method achieves the separation through the principle of buoyancy.Composite particles whose density is much less than water are formed by a large number of micro bubbles surrounding the impurity particles and oil droplets.Thus,the generating technique of micro bubble is the key of floatation method.The current theory of micro bubble generation is obviously insufficient and the research on the release nozzle structure and gas holdup is also limited.Aiming at the generation technique of micro bubble flotation,this paper investigated the characterization parameters such as the gas holdup,Sauter mean diameter,the micro bubble size distribution uniformity and micro bubble number density according to the law of gas dissolution in the dissolved air vessel and dissolved air floatation micro bubble formation.The experiment conducted many groups of parallel experiments about the operating parameters and structure parameters such as the dissolved air pressure,the air column height in the dissolved air vessel,the hole ratio of the releasing nozzle,the hole size and distribution.The gas hold-up is obtained using the self-designed experimental device while the micro bubble photos are captured by electron microscope and the Sauter mean diameter and the bubble size distribution are calculated by matlab procedure.A formula about the relationship between water flow and the releasing nozzle hole area as well as dissolved gas pressure was deduced according to dimensional analysis after measuring the flux of different release nozzle under a series of pressure.The experiment shows that the mass transfer between gas and liquid mainly happens in the air column.And the increase of the gas hold-up along with the air column height turns slow gradually,besides the effect of pressure on bubble formation changes with the difference of release nozzle,thus we can know that the interaction between different parameters is obvious.The above research results provide theory basis for optimizing the structure and process parameters of pressurized dissolved-air flotation system.