Experimental Research Of Degradation Of Typical MSW Tar Components By Rotating Gliding Arc And Cathode Spot Formation Mechanism

Tar is an inevitable harmful by-product in the process of MSW and biomass gasification,which is difficult to remove and limits the development and application of MSW gasification technology.In this paper,a rotating gliding arc plasma driven by air flow and magnetic field is used to destroy tar components.This article focuses on the destruction of fused ring aromatics in the tar.For the first time this reactor is used for the real tar reforming,showing good results.The physical characteristics of the rotating gliding arc reactor were studied.A new reaction system was developed to enable the reactor to destroy fused ring substances and real tar.The physical characteristics of the rotating gliding arc reactor were studied in order to solve the problem of carbon deposits.In addition,cathode spotting phenomenon,a common phenomenon of gliding arc reactor,is studied to provide guidance for the design of similar reactors.Main content of this article is as follows:(1)A high-speed camera and a high-precision oscilloscope were used to study the arc movement characteristics and electrical parameter characteristics of the rotating gliding arc plasma.Two discharge modes(the restrike mode and the takeover mode)of the reactor is focused on.The takeover mode discharges stably,and the reaction efficiency is raletively higher.The reflux of the gas in the reactor is an important factor for the carbon deposit on the electrode.Although the gas flow with a low degree of swirling will reduce the arc speed,it can avoid the carbon deposit ong the electrode.The continuity of tar injection as well as the vapor content will also affect the carbon deposit in the reactor.(2)Naphthalene and toluene as well as the mixture of naphthalene,toluene and phenanthrene were selected as tar surrogates.Influence of flow rate,tar concentration,H₂O concentration,CO₂ concentration and discharge current on the degradation rate of several components and the energy efficiency were studied.The by-products of tar were analyzed.Rotating gliding arc plasma coupled catalyst to deal with tar was tested.In the experiment of naphthalene and toluene mixture,the highest destruction efficiency of the two reached up to 89.1%and 94.2%,respectively.The energy efficiency can reach up to 20 g/k W·h.In the experiments of toluene,naphthalene and phenanthrene,the destruction efficiencies of the three reached 95.2%,88.9%and 83.9%,respectively.The addition of vapor greatly increases the production of hydrogen and increases the selectivity of CO and CO₂.However,Excess or insufficient vapor will cause the decreasing of destruction efficiency.The increase in discharge current will increase the production of hydrogen and the selectivity of carbon-containing gases.The Ni/?-Al₂O₃ catalyst can produce certain effects at high gas flow rates.(3)Optical emission spectroscopy(OES)diagnostics is used to analyze the effects of vapor concentration,tar concentration and carbon dioxide concentration on the relative concentration,vibration temperature,rotation temperature,and electron excitation temperature of typical active particles in the plasma reaction process.3%argon is added to calculate the electron excitation temperature.The electronic temperature of the rotating gliding arc is generally about 20000 K in the experiment.The vibration temperature is usually higher than the rotation temperature.The vibration temperature is mostly 4000-6000K and the rotation temperature is mostly 3500-4500 K.Vibration temperature and rotation temperature are highly correlated with the intensity of the argon line.(4)A reaction system to destroy the real tar using a rotating gliding arc reactor was proposed.The composition of domestic waste and biomass tar was compared.The effects of vapor concentration,carbon dioxide concentration and discharge current on the tar components destuction rate as well as gas products were studied.The destruction efficiency of the main components in MSW and biomass tar can reach over 90%.The fused ring substances are more difficult to destroy.Substances with oxygen-containing functional groups such as-OH are more easily to destroy.The destruction efficiency of MSW and tar is slightly different attributed to the differences of element and group content.(5)Electrical characteristics,OES characteristics,arc shape and movement characteristics,of wheather the cathode spot exist or not,was compared.Cathode material,H₂O concentration,tube furnace temperature,flow rate,CO₂ concentration and reactor preheating time were adjusted to obtain the critical conditions for the appearance of cathode spots,analysing the reasons for the occurrence and disappearance of cathode spots in the experiment.Cathode materials with low roughness and high melting point are less likely to produce cathode spots.The higher the concentration of H₂O,the easier it is to produce cathode spots.Various other factors affect the generation of cathode spots by affecting the temperature of the cathode discharge position.Within a certain range,the higher the cathode temperature,the less likely cathode spots occour.