Fundamental Study Of The Destruction Of Aromatic Hydrocarbon Organic Pollutants By Gliding Arc Plasma

With the development of industry and improvement of life quality, release of kinds of pollutants to the environment is inevitable, which results in threats to the whole environment. Among of them, pollutions by Aromatic Hydrocarbon Organic Pollutants (AHOPs) are very serous. Scientists dedicate to invent and develop different technologies to control AHOPs emission. Compared with traditional methods, nonthermal plasma has some unique advantages that providing numerous free radicals and energetic electrons, low gas temperature and so on. Therefore, nonthermal plasma is received lots of concern and considered as a promising technology for environmental decontamination. In this thesis, a novel kind of nonthermal plasma, namely gliding arc gas discharge, is utilized for the destruction of three kinds of AHOPs. Based on the knowledge of gliding arc physical characteristics, the destruction processes and mechanisms of Polycyclic Aromatic Hydrocarbons (PAHs),1,2-dicholorobenzene, polychlorinated dibenzo-p-dioxines (PCDDs) and polychlorinated dibenzofuran (PCDFs) are investigated. The main research contents are as followed:1. Background introduction and literatures review. The treatment targets, PAHs, Chlorobenzenes and PCDD/Fs, are introduced from their chemical and physical properties and impactions to environment. And the decontamination methods are also reviewed. In addition, the definition, classification of plasma, generation methods of nonthermal plasma and its environmental applications are reviewed. Finally, the literatures and reports about gliding arc gas discharge are comprehensively reviewed from several aspects including its physical and chemical properties as well as its applications on environmental improvement, energy conversion and materials treatment.2. Studies on physical properties of gliding arc plasma. Firstly, electrical characteristics of gliding arc at different operation condtions are investigated. Then, arc fluctuation is studied by analyzing arc voltage signals by using Fast Fourier Transform (FFT) method. Furthermore, main radical species in nitrogen, oxygen and air discharges were determined by means of optical emission spectroscopy. In this chapter, characteristics of an advanced type of gliding arc plasma:gliding arc in tornado (GAT) are also investigated. In order to study its electrical properties and fluctuation, arc voltage and current signals are measured at different experimental conditions. And the effect of gas input configuration on GAT physical properties is studied. Three working modes and the stable working mode of GAT are concluded based on the foregoing experimental results.3. Studies on PAHs destruction by gliding arc plasma. Firstly, naphthalene is used as the target pollutant. The influence of external resistor of plasma generation circuit, gas type and naphthalene initial concentration on naphthalene destruction rate and process energy efficiency is investigated. The experiment results indicate that the destruction rate, which rises with increasing of concentration in carrier gas and decreasing of external resistance, can be achieved up to92.3%. The highest destruction process energy efficiency is3.6g/kWh which increases with rising external resistance. Secondly, the naphthalene destruction mechanism is proposed by analyzing all detected products. Finally, the simultaneous destruction process of four kinds of PAHs i.e. acenaphthene, fluorene, anthracene and pyrene is studied to increase the energy efficiency.4. Studies on1,2-dichlorobenzene destruction by combined using gliding arc plasma and ozone. Firstly, the effect of key factors of experimental condition on1,2-dichlorobenzene destruction process is investigated and the results indicate that the destruction rate of1,2-dichlorobenzen can be achieved up to74.1%when external resistance is50kΩ and working gas is oxygen. The destruction main mechanisms in different carrier gas are proposed by analyzing gas products. Most of organic chlorine in1,2-dichlorobenzene is converted to inorganic chlorine, which is proved by study of chorine balance in destruction processes. In order to improve the gliding arc reactor performance for1,2-dichlorobenzene destruction, a novel method that combing gliding arc and ozone is utilized in this study. The effects of ozone injection place (in plasma area or in post-plasma area) and carrier gas type on the destruction process are studied. And the results indicate that the1,2-dichlorobenzene destruction process is enhanced significantly when the carrier gas is nitrogen or oxygen and ozone is injected in post-plasma area.5. Studies on the destruction of PCDD/Fs in fly ash by using gliding arc in tornado. Solid waste fly ash is treated by GAT and its high concentration PCDD/Fs are destructed. The experimental results indicate that the mass destruction rate and I-TEQ destruction rate of PCDD/Fs can be achieved up to67.7%and72.3%, respectively, when oxygen is used as working gas. The I-TEQ concentrations of PCDD/Fs in the treated fly ash and in the off-gas are638pg-TEQ/g and342pg-TEQ/Nm3, respectively. Based on analysis of PCDD/Fs congeners distributions in original fly ash, treated fly ash and off-gas, two major PCDD/Fs destruction routes are proposed primarily:(1) PCDD/Fs are destructed by the direct interaction between GAT and fly ash surface;(2) PCDD/Fs are evaporated to gas phase and then destructed in the GAT by gas phase reactions.