| Microwave discharge in liquid is a new plasma technology and becomes more and more concerned due to its large spatial distribution and high density of plasma. At present, there are few reports about the characteristics of plasma and application in the field of pollution treatment and hydrogen production. In this paper, the design method of electrode of microwave discharge in liquid, characteristic of electrode structure, mechanism and characteristic of microwave discharge in liquid, spectral characteristic of discharge, application of microwave discharge in liquid in the field of pollution treatment and hydrogen production are studied. The main results are as follows:First, a new style electrode of microwave discharge in liquid is designed, which consists of inner electrode, ceramic tube, silicone and outer electrode in turn from inside to outside. At the same time, the effects of physical and chemical properties of liquid in the reactor on matching properties of microwave discharge are studied. The results show that the SWR increases as the water temperature rise, while the pH, pressure and conductivity have no effects on the SWR. The main cause for the change of the SWR is the change of the relative dielectric constant of liquid.Second, the characteristic of microwave discharge in liquid is studied. The results show that:the change of plasma area is well corresponding with that of the emission intensity of OH radicals. The increase of microwave power and temperature is beneficial to maintain the generation of plasma, while the increase of external pressure and conductivity make the quenching of plasma more and more frequent. Suspension electrode can enhance the intensity of discharge effectively. The emission intensity of OH radicals decreases with the increase of pressure, but increases with the increase of power. The emission intensity of OH radicals is seen to attain the maximum value at the temperature of25℃. The emission intensity of OH radicals increases firstly and then decreases gradually with the increasing conductivity.Third, by studying the influence mechanism of loss factor on microwave discharge in liquid, it can be got that:when the microwave frequency is fixed, the relative dielectric constant of medium, temperature, conductivity are main factors of injection efficiency of microwave energy. The results of HFSS simulation show that when there is a bubble, the area of strongest electric field is located at the bottom of the bubble, instead of the gap between the inner electrode tip and the ceramic tube. By adjusting placed mode of the electrode, it is found that the movement of bubble has influence on the discharge. Combined with the simulation and theoretical analysis, it is concluded that the process of microwave discharge in liquid is actual the breakdown of bubble over the electrode tip by strong electric field.Fourth, in the paper, methylene blue is decolorized using plasma which is generated by microwave discharge in liquid. The results show that the decolorization rate of methylene blue increases with increasing of microwave power, but decreases with increasing pH in the range of6-8. A maximum decolorization rate of97.81%is obtained in the acidic solution with12minutes treatment. When the initial concentration is12.5mg/L, the decolorization of methylene blue reaches the maximum value, and the max energy efficiency can reach120mg/kWh.Fifth, hydrogen is produced from low carbon alcohol (methanol and ethanol) by microwave discharge in liquid. The results show that the gaseous product of discharging in methanol and ethanol solution mainly includes hydrogen, carbon monoxide, acetylene and carbon dioxide. The flow rates of total gaseous product and hydrogen in the process of discharge increase with the increase of power, while that increase firstly and then decrease with the increase of concentration of low carbon alcohol solution. The proportions of the hydrogen and carbon monoxide increase with the increase of power, but the proportion of other gases decreases significantly. When the concentration of low carbon alcohol solution is8%, the proportions of the hydrogen and carbon monoxide reach a maximum value, while the proportion of other gases have a minimum value. The energy efficiency of hydrogen production improves significantly as the power increase, and the energy efficiency of hydrogen produced from ethanol is higher than that from methanol in the condition of same power. The energy efficiency of hydrogen production increases firstly and then decreases with the increase of concentration of low carbon alcohol solution. When the concentration of low carbon alcohol solution is8%, the energy efficiency of hydrogen production reaches the maximum value. In this paper, the maximum flow rate of hydrogen, the maximum proportions of hydrogen and the maximum energy efficiency are215mL/min,64.55%and74.26NL/kWh respectively. |
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