表面曝气反应器中气泡尺寸分布测量

Measurement of Bubble Size Distribution in Surface Aeration Reactor

合理处置矿山开采过程中产生的废水是绿色矿山建设中必要且重要环节,表面曝气处理废水有助于节约能耗。本研究开展了表面曝气反应器内气泡局部性质分布的测量,将为反应器准确设计奠定基础。采用新研制的侵入式远心照相多相测量仪,对表面曝气反应器内气泡直径分布进行了系统测量,进一步获得了相界面积和气含率分布,重点考察了轴向位置和搅拌转速2个因素。研究结果表明:与相同转速下分布器供气的气液搅拌反应器相比,表面曝气反应器中气泡尺寸更小;沿轴向逐渐远离液面,气泡尺寸逐渐减小,同时气泡数量也逐渐变少;随着转速增大,吸入气泡增多,平均气泡尺寸变大。为了强化表面曝气反应器内气液分散过程,采用浅层床设计,同时在功率允许范围内可适当提高转速。本研究将为绿色矿山废水高效处理提供一种新的选择。

It is necessary to do well the waste water produced by mining in green mines.In the surface aeration reactor,the unreacted gas is entrained from the space above the liquid level and dispersed again through the violent turbulence formed by the surface aeration paddle on the liquid surface.Therefore,a series of processes such as separation,purification,compression and recycling of unreacted gas can be omitted by using surface aeration,which is of great significance to reduce equipment investment and operation cost. Waste water treatment using surface aeration is helpful to save energy consumption.At present,there is no research reported on the local property distribution of bubbles in the surface aeration reactor,which is the necessary basis for the accurate design of the reactor. Sharp pictures of bubble motion can be obtained by using the newly developed multi-phase measuring instrument based on the telecentric photography. Then,a series of image processes including enoising,filtering(Gaussian filtering and Median filtering),binarization and in-focus bubbles detection are conducted. Thus,bubble size distribution is obtained and consequently,the specific surface area and bubble holdup distribution are further obtained. Using this method,bubble hydrodynamics in the surface aeration reactor is systematically measured. The axial position and stirring speed are mainly investigated. The results show that the bubble size in the surface aeration reactor is smaller than that in the gas-liquid agitated reactor supplied by the gas distributor.Along the axial direction downwards,the bubble size gradually decreases and the number of bubbles decreases on the whole. This can be explained qualitatively by the different gas dispersion model in surface aeration reactor and gas-liquid stirred tank.The effect of impeller speed is studied on B position.With the increase of the impeller speed from 350 r/min to 450 r/min,the number of suction bubbles increases and the average bubble size increases. In order to strengthen the gas-liquid dispersion process in the surface aeration reactor,two advices are provided:In a shallow bed,zones with fewer bubbles will be greatly reduced.So,such design is more advantageous,and the increase of impeller speed can strengthen the turbulence near the liquid surface and the overall fluid circulation. Thus,it is also appropriate to increase impeller speed within the allowable range of power. This study will provide a new choice for the efficient treatment of green mine wastewater.