| Biomass plays an important role in dealing with global climate change,alleviating energy supply,demand contradiction and ecological environment protection.It is the fourth major energy source of the world,after coal,oil and natural gas.Speeding up the development and application of biomass energy is significant not only to promoting the production and consumption revolution but also improving the environmental quality.Biomass energy utility is a process of converting energy from burning organics into thermal energy,electricity,or other forms of stored energy that can be used more diversely than the conventional fossil fuels.Among them,gasification is the most commonly biomass energy conversion technology.However,during the conversion of the biomass,the produced tar not only corrodes the converting equipment and pipelines,resulting in pollution and potential hazards,but also reduces the efficiency of the conversion.It also limits the development and application of the gasification technology.To find a high efficiency,clean,easy to operate,stable and feasible method of tar treatment to solve the problem due to the produced biomass tar is the key objective of this Ph.D.project.It has been found that a unique discharge phenomenon can be produced during the interaction of microwave and special shaped(such as tip,sharp edge,etc.)metal.In the simultaneously,the process is accompanied by obvious heat release and plasma excitation.The effect of heat and plasma can promote the pyrolysis reaction of organism,thus improve the recovery efficiency and utilization of the resource.Therefore,the target of this thesis is the removal of tar in biomass gasification process by using the heat effect and plasma effect induced by special discharge mechanism between microwave and metal.to be noted,in this context,the toluene(the highest content in tar)are used as the model compounds of biomass tar..In particular,the influencing factors and mechanism of microwave-induced metal discharge to intensify the pyrolysis of biomass tar were systematically studied by using the research methods of from feasibility analysis to mechanism research,and from mechanism study to technology application.The main work carried out is as follows:First,the feasibility of microwave induced pyrolysis of biomass tar by microwave-induced metal discharge was carried out using experimental method,according to the concentration of toluene before and after the microwave metal discharge area.Meanwhile,the influence of the microwave electromagnetic parameters,metal dielectric properties and discharge gas on the strength of metal discharge and the efficiency of toluene cracking during the discharge process were investigated.The results show that the concentration of toluene of 950 ppm is obviously reduced after going through a certain intensity of microwave metal discharge area,and small molecule combustible gas is produced in the cracked gas.This conclusion confirms that the discharge phenomenon of metal medium is enhanced by the microwave irradiation.At the same time,it is found that the quantity and activity of metal medium both can enhance the toluene cracking efficiency,and the properties of inert gases also have a significant effect on the cracking efficiency.Based on the feasibility that the microwave metal discharge can strengthen the toluene pyrolysis,the characteristics of the gas,liquid and solid phase products of toluene pyrolysis under discharge conditions were studied.This clarified the advantages of both product and depth of the pyrolysis reaction of toluene under the action of microwave metal discharge.The results showed that the effect of the pyrolysis of toluene in an extremely simple microwave metal discharge could achieve or surpass the effect of traditional high temperature pyrolysis at 900℃.What’s more,the H2 selectivity and the graphitization of the solid carbon in the products were superior to the traditional pyrolysis method.Based on the heat-producing characteristics of microwave metal discharge,the effect of different variables on the thermal effects of metal discharge is discussed by the accurate measurement of precision microwave-medium calorimetry.Based on the quantitative determination of the total thermal effect,the local temperature and interfacial temperature gradient of the metal discharge induced high temperature under different conditions(metal type,irradiation time,etc.)are calculated by the ANSYS software,and the degree of hot spot caused by the microwave metal discharge is determined.The results show that the direct calorimetry method creatively realizes the quantitative evaluation of the whole heat effect in the process of metal discharge and revealed other factors such as metal dielectric properties and electromagnetic parameters have certain influence on the discharge heating as well.At the same time,the simulation results of the discharge temperature field confirm the existence of hot spot effect and reveal the mechanism of the microwave metal discharge cracking toluene from the discharge heat production.According to the luminescence characteristics of the metal discharge induced by microwave,a set of high sensitivity plasma spectroscopic analysis system was utilized to validate the existence of discharge plasma.A thorough study on the plasma of microwave metal discharge under different conditions was not only to enable reveal the microscopic physical process of the microwave induced metal discharge,but also have a better effect to explore the mechanism of the tar cracking.At the same time,the effects of physical parameters such as metal electrode materials(Fe,Ni,W),discharging medium(N2,He,Ar)and the power of external microwave field power were discussed.The mechanism of the plasma characteristics of metal discharge was also defined.The results show that the microwave induced metal discharge is produced by the electron transition of the atom in the metal medium and the ambient atmosphere gas atom,which is accompanied by the generation and quenching of high-energy particles and the release of plasma.The discharge gas medium fundamentally determines the spectral distribution region of the discharge plasma emission spectra,and the influence of metal species and microwave power is mainly embodied in the intensity of plasma emission spectra.Finally,based on the results of experimental and mechanism studies,this paper presents a new industrialized idea of combining biomass-pyrolyzed-gas generation with biomass tar pyrolysis by microwave metal discharge,and applies model of microwave and special shaped metal induced discharge tar pyrolysis to practical biomass continuous pyrolysis conditions.An experimental study on the removal of tar from traditional Chinese medicine residue in a series of discharge environments was carried out.The results show that the microwave metal discharge has a positive effect on the tar in the real biomass pyrolysis system.In addition,through the optimization of the process,the microwave irradiation power can be improved,the gas residence time can be prolonged,and the series of discharge device can be increased.The technology integration of microwave metal discharge and catalyst-assisted pyrolysis of traditional Chinese medicine residue was completed,the process of preparation and purification of heat converted fuel gas was developed,and a new technology for high efficient conversion of biomass was provided. |
