Study On Discharge Characteristics Of Coaxial DBD And Its Application For Toluene Degradation

As an important way to generate low-temperature plasma,because it can discharge under normal temperature and pressure,the reaction device has a simple structure,the discharge space is controllable,and the discharge process has a high electron energy,which is easy to break molecular chemical bonds,dielectric barrier discharge(DBD)has been widely used in many fields.In recent years,with the deepening of the research on DBD,improving the energy utilization efficiency of discharge device has become the focus of attention.In order to further explore the energy utilization of different discharge systems,this paper designed tube-tube and rod-cylinder coaxial discharge devices.The effects of the variation of power supply parameters and reactor parameters on the discharge power and power factor of the two DBDs were studied,and the discharge parameters were optimized by response surface analysis.The electron density of the plasma were calculated by simulation.On this basis,the experimental study of DBD degradation of toluene was carried out,and the gas products were analyzed.The main research contents of this paper are as follows:(1)The discharge mode of tube-tube DBD and rod-cylinder DBD were filamentous discharge,and a large amount of pulse current was generated in the positive and negative half cycles of DBD device.With the increase of discharge voltage,the discharge intensity and the current density increased.The discharge initiation time was advanced,at the same time showed the discharge initiation voltage decreased.The number of discharge filaments in positive half period and negative half period of tube-tube DBD were 23 and 17,respectively.The number of discharge filaments in negative half period was about 26%less than that in positive half period.The number of discharge filaments in the rod-cylinder DBD were 24 and22 respectively,while the number of discharge filaments in the negative half period of the rod-cylinder DBD was reduced by about 8%.The discharge intensity of rod-cylinder DBD was higher than that of tube-tube DBD.(2)The discharge power of DBD increases exponentially with the increase of discharge voltage and linearly with the increase of discharge frequency.The discharge power will be increased by decreasing the gas velocity and increasing the discharge length.The discharge parameters were optimized by response surface.The maximum discharge power of the tube-tube DBD and rod-cylinder DBD were obtained under the following conditions:discharge voltage of 10 k V,discharge frequency of 9 k Hz,discharge length of 18 cm and gas flow rate of 1 L/min.(3)When the discharge voltage and discharge length are increased,the power factor increases gradually.With the increase of gas flow rate,the power factor decreased,which proved that the discharge energy used to generate plasma decreases gradually.The power factor increased first and then decreased with the increase of the discharge frequency.The discharge frequency of the reactor with different discharge lengths was different when reaching the maximum power factor.The longer the length was,the lower the frequency value was.But the maximum power factor has little difference.After optimizing the discharge parameters,the discharge conditions of the tube-tube DBD to reach the maximum power factor are as follows:the discharge voltage is 10 k V,the discharge frequency is about 8.5 k Hz,the discharge length is 18 cm,and the gas flow rate is 1 L/min.The discharge conditions of the rod-cylinder DBD to reach the maximum power factor are 10 k V discharge voltage,about8.7 k Hz discharge frequency,12 cm discharge length and 1.5 L/min gas flow rate.(4)The toluene degradation experiments were carried out with two kinds of discharge devices to explore the influence of discharge parameters and gas parameters on toluene degradation performance.The degradation rate of toluene was improved by increasing the discharge voltage and decreasing the gas flow rate and initial concentration of toluene.The toluene degradation rate of rod-cylinder DBD was higher than that of tube-tube DBD.When the gas flow rate was 70 m L/min,the toluene concentration was 50 ppm,and the discharge voltage increased from 8 k V to 10 k V,the degradation rate of the rod-cylinder DBD reached61.3%-81.3%,which was 1.03-1.55 times that of the tube-tube DBD.With the increase of gas flow rate,the energy efficiency of toluene increased first and then decreased.When the gas flow rate was 90 m L/min,the energy utilization efficiency of both devices reached the optimum.The maximum energy efficiency of tube-tube DBD and rod-cylinder DBD were0.025 g/k W·h and 0.029 g/k W·h,respectively.After the degradation of toluene products were mainly HCOOH,CO,N₂O,CO₂,H₂O.