Study On The Characteristics Of HgCl₂ Continuous Production By Non-thermal Plasma

Energy resources distribution imbalance caused the coal as the main energy consumption predicament.The problem of mercury pollution caused by coal has received increasing attention.Accurate determination of mercury concentration in various forms is the guarantee for the implementation of mercury emission standards.However,conventional Hg continuous emission mornitoring system（Hg-CEMS）can only detect Hg⁰ signal,and the core technology for determination of Hg²⁺is blocked by relevant enterprises.The production of Hg²⁺standard gas and calibration gas is one of the core technologies for the determination of Hg²⁺.In order to meet the requirements of the development of mercury emission control,our research group proposes to realize the HgCl₂ continuous production in chlorination reaction by dielectric barrier discharge,providing a new idea for realizing the production method of Hg²⁺standard gas.Therefore,determining the influencing law of the parameters of HgCl₂ continuous production by non-thermal plasma（NTP）and selecting the control range of the parameters are the focus of this paper.Firstly,EPA method 30B was selected as the method to determine the content of HgCl₂ in this paper.Subsequently,combined with relevant theoretical knowledge,the effects of reactor structure parameters such as single and double dielectric layers,dielectric material and thickness,discharge gap on HgCl₂ continuous production by non-thermal plasma were studied.The results show that although the dielectric barrier discharge（DBD）reaction under the condition of double dielectric layers can ensure the efficiency of HgCl₂ continuous production for a long time.When Al₂O₃ ceramics is used as the dielectric,due to the relationship between its excellent characteristics of physico-chemical,it exhibits better performance than quartz glass in the experiment of HgCl₂ continuous production by non-thermal plasma.Both the reduction of air gap thickness and dielectric thickness is conducive to the improvement of efficiency of HgCl₂ continuous production,as well as the risk of reactor breakdown.In addition,under the condition of low Cl concentration,the adverse effect of high temperature on the high-energy electron deposition in the near-wall reaction zone leads to a decrease in the generation rate of HgCl₂.However,with the increase of Cl concentration,the influence of temperature decreases continuously.Under the condition of higher Cl concentration,the promotion effect of temperature rise on the excitation and ionization of particles is far greater than the adverse effect on the near-wall reaction zone.Increasing the gas velocity promotes the production of HgCl₂ when the heat dissipation of the reactor is poor.However,when the reactor has good heat dissipation,increasing the gas velocity is not conducive to the efficient production of HgCl₂。According to the influence rule of the parameters obtained,combined with the requirement of long-term stable generation rate of HgCl₂,the parameters condition of double dielectric layers,dielectric thickness of 2.5 mm,gas gap width of 3.5 mm and gas velocity of 2 L/min were selected for further study.Secondly,through a series of studies on the influence of Cl source of chlorination reaction and output voltage on the efficient generation of HgCl₂,the following conclusions are drawn:Compared with HCl as Cl source of chlorination reaction,Cl₂as Cl source can achieve high efficiency generation of HgCl₂（more than 95%）at lower power supply output voltage（16 kV）and Cl source concentration（10 ppm）;DBD chlorination can be carried out in an atmosphere of N₂+1.25 ppmCl₂+50ppm HCl at 16kV power supply output voltage,taking into account the excellent HgCl₂production rate over 90%.In addition,in order to determine the weight of two influential factors for the HgCl₂ continuous production by NTP under different Cl source conditions,the experiments of Cl radical injection were carried out.According to the results,it is concluded that the collision of particles in DBD reaction zone is the main factor affecting the generation of HgCl₂ when Cl₂ is used as Cl source of chlorination reaction,while the number of Cl radicals in DBD reaction zone is the main factor affecting the generation of HgCl₂ when HCl is used as Cl source of chlorination reaction.Finally,the effects of other gases on HgCl₂ continuous production by non-thermal plasma were studied.The importance of gas purity for HgCl₂ continuous production by NTP was clarified.The theoretical and experimental analysis lays a foundation for the generation of HgCl₂ standard gas by NTP,and is of great significance for promoting the R&D of Hg⁰/Hg²⁺Hg-CEMS.