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Gold Science and Technology ›› 2020, Vol. 28 ›› Issue (2): 188-194.doi: 10.11872/j.issn.1005-2518.2020.02.198

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Measurement of Bubble Size Distribution in Surface Aeration Reactor

Yixiao HAO1(),Xuefeng ZHENG1,Yiting XIAO2,3,Haoliang WANG2,3,Xiangyang LI2()   

  1. 1.Wuhuan Engineering Co. ，Ltd，Wuhan 430223，Hubei，China
    2.CAS Key Laboratory of Green Process and Engineering，Institute of Process Engineering，Chinese Academy of Sciences，Beijing 100190，China
    3.School of Chemical Engieering，University of Chinese Academy of Sciences，Beijing 100049，China
  • Received:2019-12-31 Revised:2020-02-25 Online:2020-04-30 Published:2020-05-07
  • Contact: Xiangyang LI E-mail:haoyixiao@cwcec.com;xyli@ipe.ac.cn

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Abstract:

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.

Key words: surface aeration reactor, bubble size distribution, telecentric photography, wastewater disposal, green mines

CLC Number: 

  • X703

Fig.1

Surface aerating reactor and telecentric vision instrument"

Fig.2

Comparison of typical bubble images in different aerating modes"

Fig.3

Typical bubble images on different axial locations （N=400 r/min）"

Fig.4

Bubble size distribution on different axial locations"

Table 1

Statistical result of bubble properties on different axial locations"

h/mmdm/μmd32/μms/μmαg/%a/(×10-5 μm-1)
503905741850.212.2
1504156612200.262.3
2504467832560.393.0
3504307172400.433.6

Fig.5

Typical bubble images at different impeller speeds（a）N=350 r/min；（b）N=400 r/min；（c）N=450 r/min"

Fig.6

Bubble size distribution at different impeller speeds"

Table 2

Statistical result of bubble properties at different impeller speeds"

N/(r·min-1)dm/μmd32/μms/μmαg/%a/(×10-5 μm-1)
3503735511720.141.5
4004467832560.393.0
4505241 0983870.925.0
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