Experimental Study Of Bubble Size Distribution And Flocculants Compatibility In Flocculating Flotation

Flotation is an efficient and economical water treatment technology. In this thesis, EDUR multiphase pump is used as the main flotation device, and high speed photography system and laser diffraction system are constructed for the measurement of bubble and particle sizes. Based on these experimental apparatus, the factors that influence the flotation efficiency are studied in depth.Bubble size distribution (BSD) is of great importance for the removal efficiency of suspended particles during sewage treatment. Present study focused on the size distribution of the bubbles generated by a new type of bubble generator—EDUR multiphase pump, and the factors that influenced the BSD such as saturation pressure, gas-liquid ratio, salinity and surface tension were also investigated. Measurements of bubble size were conducted by high speed photography system and laser diffraction system. The results show that both methods consist well with each other. The increase of saturation pressure causes the decrease of bubble size. However, pressures higher than 0.50MPa have no effect. Bubble size decreases with the increase of gas-liquid ratio until the liquid is completely saturated. The change of flow rate affects the air-dissolving time and turbulent intensity of the fluid in pipe, and therefore influences the bubble sizes. Salinity has a positive effect on the reduction of bubble size. Surfactant can significantly inhibit the coalescence of bubbles by reducing surface tension.Flocculant-effluent quality compatibility is the key factor for demulsification of oily water and the effective adhesion of bubbles and oil droplet/flock. Based on deep investigation of wastewater quality in oil field, different kinds of oily water are prepared, and the compatibility of flocculants with water qualities such as pH, temperature, surfactant concentration, salinity and oil droplet size are studied. The results show that water qualities affect the growth of flock, demulsification of flocculant and coalescence of oil droplet during flotation. The optimum combination of organic and inorganic flocculants is that the dosage of APAM is 6mg/L and the dosage of PAC or PAFC is 30mg/L. Oily water can be treated efficiently and economically under this ratio. It is difficult for the adhesion of bubbles and oil droplets. Oil droplets are mainly removed by the wake flow of bubbles when they float upward. After demulsification by flocculants, bubbles and oil droplet/flock can form single-bubble/droplets/flock copolymer and multi-bubble/droplets/flock copolymer, which will enhance separation efficiency.