Study On Non-equilibrium Plasma For Methane Reforming

Non-equilibrium plasma is a partially ionized gas.Since the non-equilibrium plasma has obvious non-thermodynamic equilibrium characteristics,its electron temperature can reach1-10 eV,which can easily break the chemical bond to promote the reaction,while the gas temperature is kept at room temperature,effectively reducing the heat loss during the experiment.Non-equilibrium plasma provides a new way for methane reforming under normal temperature and pressure.The device of dielectric barrier discharge is simple and the plasma is suitable for working in a large space for a long time;gliding arc discharge has the characteristics of both hot plasma and cold plasma,high electron temperature and electron density,and good selectivity to chemical reaction.Therefore,these two discharge ways have been widely concerned by domestic and foreign scholars in the field of methane reforming.In order to further improve the effect of methane reforming,it is necessary to compare the characteristics of the two non-equilibrium plasmas.Therefore,the coaxial cylinder dielectric barrier discharge device and rotating gliding arc discharge device were built in the experiment.The electrical and physical characteristics of the two discharge ways were investigated by comparative experiments,and the experimental study of methane reforming was carried out on the basis of these experiments.The results are as follows:?1?Coaxial cylinder dielectric barrier discharge and rotating gliding arc discharge are two different gas discharge ways and discharge characteristic difference of the two discharge ways is obvious.The coaxial cylinder DBD driven by the high frequency ac power supply generates a large amount of pulse current in the positive and negative half period.Since the existing dielectric capacitance limits the free growth of the current in the discharge space,The peak value of the current pulse is about 150 mA.The rotating gliding arc discharge adopts an electrode structure with a conical spiral wire as inner electrode and a stainless steel cylinder as outer electrode,which realizes stable discharge under the drive of a high-frequency AC power supply.According to the characteristics of the current signal,the rotational sliding arc discharge can be divided into the breakdown gliding mode?B-G?and the stable arc gliding mode?A-G?:The peak value of the discharge current pulse in B-G mode is large,which is close to 2 A.No breakdown occurred in the discharge gap of A-G mode,and the peak current varied between±900 mA.?2?There is a big difference in the plasma morphology between the coaxial cylinder dielectric barrier discharge and the rotating gliding arc discharge.Coaxial cylinder DBD is a typical filamentary discharge,and the microdischarge channels are densely distributed in the discharge space;The arc is a dynamic process of continuous change in rotating gliding arc discharge.The range of plasma regions is small,with only a single discharge channel.The temperature distribution of the two discharge ways is not uniform:Due to the heat transfer of the airflow,the coaxial cylinder DBD temperature distribution is characterized by gradient descent from the left inlet to the right outlet;The energy of rotating gliding arc discharge is concentrated in the plasma area,which makes the temperature of stable rotating position of arc much higher than other positions.The emission spectra of coaxial cylinder DBD are mainly composed of N₂?C³?_u?B³?_g?and excited argon atoms in the air?add less than5%argon?.The emission spectra of rotating gliding arc discharge are mainly composed NO?B²??X²??,N₂?C³?_u?B³?_g?and excited argon atoms in the same atmosphere.According to the calculation,the electron density of coaxial cylinder DBD is 1.65×10¹⁴ cm^-3and the electron density of rotating gliding arc discharge is 1.07×10¹⁵ cm^-3.The degree of gas ionization of rotating gliding arc discharge is much higher than that of coaxial cylinder DBD.?3?The feasibility of two discharge ways for methane reforming reaction was studied.The experimental results show that the conversion rates of CH₄ and CO₂ are not much different in two discharge ways.The reaction gas flow rate?2 L/min?of rotating gliding arc discharge used for methane reforming is much higher than that of coaxial cylinder DBD?0.08L/min?,and the energy efficiency of rotating gliding arc discharge is 3.58 mmol/kJ,which is dozens of times higher than that of coaxial cylinder DBD?0.14 mmol/kJ?.The experimental effect of methane reforming to syngas is better than that of coaxial cylinder DBD.