Microscopic Properties And Removal Of Harmful Byproducts In Multi-Needle To Plate Corona Discharge

Indoor air pollutants are characterized by their mutil-components, long period, low concentrations, and etc. Most pollutants can be effectively and rapidly removed by plasma air cleaning. Although corona discharge is adopted as a main plasma technology in indoor air cleaning, some harmful byproducts such as ozone and NOx are generated, and the corresponding secondary pollution is formed. Based on the laboratory earlier work, this thesis analyzes the properties in ionization region of multi-needle-to plate corona discharge systematically, and well studies the optimization of Excited state OH radical yield in the corona discharge by OES, which will provide design principles for needle matrix to plate DC corona discharge as the core technology of indoor air cleaning device. Taking the removal of harmful byproducts generated by corona discharge as the research goal, the generation of NO2 and O3 in corona discharge as well as their decomposition by MnO2 is studied experimentally. The relative roles of generation and removal of the byproducts are abtained by bench-scale experiements in a closed chamber and application tests. Meanwhile, the design principles and running parameters of the air cleaning device have been determined.Firstly, according to the measured experimenatal results of multi-needle-to-plate corona discharge by OES, the statistics, fitting and theoretical analyses are carried out. The isophote equations of N2 second positive band intensity (ISPB) are obtained. The distribution of ISPB and the variation of micro electrical parameters including ISPB×S, the average speed of electrons and current density in ionization region have been known. The micro physical properties in ionization and drift regions of multi-needle-to-plate positive-negative corona discharge are analysed systematically.Secondly, taking excited state OH radical as study object, the influences of discharge parameters including discharge power, electrode gap and relative humidity on OH generation in the corona discharge by OES are well studied. Under stable discharge condition, the optimized running parameters of excited OH yield have been abtained, and the relative roles between macro parameters and OH radical have been determined.In this thesis, in order to make the technology of needle matrix to plate corona discharge suitable for indoor air cleaning, safety problem caused by harmful byproducts generated in corona discharge is considered in detail. The relative roles of NO2 generated by the corona discharge are studied, especially on the influences of discharge power, discharge polarity, electrode gap and relative humidity on NO2 generation. Some principles of the parameter design as well as of qualitative running conditions have been obtained. On this basis, removal experiments of NO2 with catalyst containing MnO2 as active ingredients and SiO2-active Carbon as vector have been conducted. The relationship between MnO2 content and NO2 removal efficiency is studied under different discharge conditions such as discharge power P, relative humidity RH, discharge polarity, and etc. The method of effective removal of NO2 by MnO2 and relative running roles have been obtained.The generation of O3 and its removal with catalyst in needle matrix to plate corona discharge are also studied. The generation roles of O3 have been summarized by observing concentration variation of O3 in a closed chamber. Removal experiments of O3 with catalyst containing MnO2 as active ingredients and SiO2-active Carbon as vector have been conducted. The relationship between MnO2 content and O3 removal efficiency is studied under different discharge conditions including discharge power P and discharge polarity. The roles of O3 removal by MnO2 catalyst have been obtained.Finally, on the basis of the above work, the application tests of the noval air cleaning device with needle matrix to plate corona discharge have been conducted under different discharge polarities in a closed room of 84m3. MnO2 catalyst is set on the exit of the discharge reactor to study the removal effects of harmful byproducts of NO2 and O3 generated by the discharge. Meanwhile, the catalyst functional pattern is also studied by catalyst analysis. In the end, it has been known that the values of concentrations of NO2 and O3 generated by the corona discharge satisfy the demand of Standard of Indoor Air Quality(GB/T18883-2002). Hence, this work has provided powerful technology support for practical application of indoor air cleaning.