Development of a New High Effective Flotation Device Used for Water Treatment
Authors: Zhu Youyi 
Published: December 2007

A new high effective flotation device used for water treatment was introduced in this paper. Its separation efficiency is 5–10 times as much as that of conventional separation device. Jet pump being used as aerator, the gas hold-up of this flotation column could reach up to 50%, 4–5 times as much as that of conventional separation device. The factors of structural and operating parameter affecting gas hold-up of the flotation column were discussed. Measurement of bubble size indicated that the bubble sizes in separating column were affected by fluid physical-chemical parameters and structure parameter, and the addition of forthers or other surfactants was the most important factor to gain small bubble size. Pollution water of Shengli oil field was treated using this device, and the ratio of crude oil separation reached up to 97%.

Introduction

The development of column flotation is the most significant achievement in the area of water treatment and mineral processing in the last few decades. Column flotation has the following advantages compared with conventional flotation separation device:high flotation efficiency;low capital operational and maintenance casts;small floor space requirements and a simple design;low reagent dosage;more suitable for fine particles separation;easy optimization of the process.

These considerable advantages stimulated active research work on the development and introduction of the apparatus. Today columns produced by Cominco Ltd.(Canada), Column Flotation Co. of Canada Ltd., Deister Concentrator Co. (USA), Control International Co. Inc.(USA), Holdings Ltd.(Australia), etc. are supplied to different countries.

Judged from the references, low height column of high efficiency is the most possible trends of further development of column flotation.

Development of the LHJ column

Process and design advantages promoted development of a great number of different designs of column apparatus. During the last two decades, about 100 patents for different modifica-tions of the column apparatus and aerators were granted. Jameson flotation column was one of new concept column (1988). Based on Jameson column, A low height Jet (LHJ) column was developed by Professor Zhang Qiang and Doctor Zhu Youyi etc. in the USTB. A general design of column apparatus is given in Figure 1.

A brief description of this device was given as follows: A high velocity slurry jet issues from the nozzle, entraining air which was then sheared into bubbles upon plunging into the separating vessel. This entrainment also provides the slight vacuum, which helped elevate slurry to downcomer by elevating pipe of liquid level. Hydrophobic particles were collected by the bubbles. The three-phase mixture descended and discharged into a separating vessel, where the bubble-particle aggregates disengaged (separate) from the slurry and rose to form the overflow while the uncollected particles and water from the underflow.

The advantages of LHJ column are:The collision between particles and gas bubbles take place in the downflow pipe, while the separating process take place in the vessel, thus ideal condition of particle-bubble interaction in the turbulent flow, while separating process under a quiescent flow was achieved.Jet pump being used as aerator, the structure of jet pump was optimized using the technology of water jet flow, the mixing efficiency of slurry and air was enhanced.As elevating pipe being used, the downflow pipe filled with the slurry became easy, the liquid level and air content in downcomer were stable, while they were instability or remained oscillatory in Jameson column.The height of LHJ column was about 2m, much lower than the conventional column (more than 10m), it was easy to operate and to maintain.