Electrostatic Dust Collection of Sub-micron Particles with the Aid of Electrostatic Agglomeration Promoted by Particle Vibration

2001 Fiscal Year Final Research Report Summary

• Project/Area Number: 12650261
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: 電力工学・電気機器工学
• Research Institution: HOKKAIDO UNIVERSITY
• Principal Investigator: NAKAJIMA Yoji Hokkaido Univ., Grad. School of Eng., Assoc. Prof., 大学院・工学研究科, 助教授 (70002029)
• Co-Investigator(Kenkyū-buntansha): SATO Takashi Hokkaido Inst. Tech., Prof., 電気工学科, 教授 (90048025)
• Project Period (FY): 2000 – 2001
• Keywords: electrostatic agglomeration / acoustic agglomeration / sub-micron particles / agglomeration rate constant / agglomeration volume / polarization force / dust collection / SPM

Research Abstract

Detrimental sub-micron particles in flue gas are to be agglomerated electrostatically on charged core particles so that they can be effectively removed with conventional dust collectors.
Sub-micron particles suspended in gas receive an attraction due to electrostatic polarization to the charged core particles. Our recent calculations by the re-expansion method have proved that the attraction is much pronounced by the higher order polarizations. In order to make use of the higher order polarizations effectively, however, it is necessary to convey the sub-micron particles very close to the charged core particles. A strong vibration of core particles or application of intense acoustic wave with suitable frequency produces the acoustic streaming, which entrains the sub-micron particles around the core particles to enhance the rate of agglomeration. To evaluate such an effect of vibration, we have used the method of matched asymptotic expansion to find a perturbation solution to Navier-Stoke s equation, the solution that predicts the induced acoustic streaming around a core particle vibrating with large amplitude. It is shown that the acoustic streaming greatly promotes the efficacy of polarization forces to capture sub-micron particles. Then the motion of a sub-micron particle around a vibrating core particle has been precisely simulated to obtain the agglomeration rate constant.
For measuring the agglomeration constant, a newly invented apparatus tracks the changes in size and electrostatic charge of a single core particle, which agglomerates sub-micron particles supplied around the core particle from a mono-disperse aerosol generator. The measured results show that the practical agglomeration constants are very high ; they are typically twice the simulated values. This is because turbulence in the agglomeration cell takes the same role as the acoustic streaming and enhances considerably the agglomeration rate. This implies that the present method will provide a powerful means for collecting sub-micron particles in practical situations.