Fundamental Research Of Decomposition Of Tar Compounds From The Gasification Of Municipal Solid Waste By Rotating Gliding Arc Plasma

Tar is produced as a harmful byproduct in the gasification process inevitably and hard to deal with,which drastically hampers the development and application of gasification technology.With the major merits of fast ignition,compact design and high efficiency,a non-equilibrium plasma is regarded as an elegant alternative for realizing thorough tar elimination.In this study,a novel rotating gliding arc(RGA)plasma co-driven by a swirling flow and a Lorentz force was used for the decomposition of tar compounds.The physical characteristics of the RGA discharge were sufficiently analysed.Based on which,experimental study and mechanism analysis of tar decomposition by using the RGA were performed,which could provide fundamental support for the potential industrial application.In addition,dry reforming of methane for the production of syngas by using the RGA plasma was carried out as a supplementary study.The main contents and conclusions of this dissertation are as follows.(1)Technological means such as high-speed camera,oscilloscope,optical emission spectroscopy(OES)and numerical simulations were employed to investigate the arc dynamic behaviors,electrical parameters,arc force and spectroscopic properties of the RGA plasma.Under the synergistic effect of a swirling flow and a Lorentz force,the arc can be stabilized at the non-equilibrium region and there rotates rapidly,generating a stable three-dimensional plasma arc zone for chemical reactions.The external magnetic field play s a dominant role in the maintenance of the arc rotation.Additionally,the discharge gas composition has an important influence on the arc dynamic behaviors,electrical parameters and reactive species.(2)Toluene was chosen as a typical tar surrogate.The effects of input toluene concentration,gas flow rate,steam concentration and CO2 concentration on toluene destruction were investigated.As a result,the highest destruction efficiency and energy efficiency could achieve 95.2%and 16.61g/kWh,respectively,and the two major gaseous products were H2 and C2H2,when using pure nitrogen as a carrier gas.The presence of CO2 in the process suppressed the conversion of toluene.By contrast,adding appropriate amount of steam could enhance the destruction of toluene.In the presence of steam and CO2,the problem of solid carbon precipitation was well solved and the major gas products turned into H2 and CO.In a simulated producer gas,a maximum toluene destruction efficiency of 95.6%was achieved.Meanwhile,the concentration of the useful components of syngas(CO and H2)was significantly enhanced compared to the initial producer gas.After plasma treatment,the lower heating value(LHV)of the effluent gas was enhanced by up to 6.9%.(3)Toluene,naphthalene and phenol were used as monocyclic,bicyclic and heterocyclic tar model compounds,respectively.The application of RGA discharge to tar decomposition was investigated at different steam concentration,tar concentration,CO2 concentration and pre-heating temperature.In nitrogen,the destruction efficiency of toluene,naphthalene and phenol first increased and then declined with rising steam concentration.Besides,increasing tar concentration or CO2 concentration decreased tar destruction.The maximum destruction efficiency of toluene,naphthalene and phenol were 95.9%,86.2%and 96.3%,respectively,with a highest energy efficiency of 21.31 g/kWh.Under all test conditions,the destruction efficiency of the three components followed the order:phenol>toluene>naphthalene.In producer gas,the maximum destruction efficiency achieved at a steam concentration of 12%.After plasma treatment,the CO2 conversion could reach 52.9%and the CH4 conversion could maintain above 65%.Meanwhile,the heating value of the producer gas could be enhanced by up to 5.1%.(4)The reaction pathways and mechanisms in the plasma reforming of tar model compounds have been proposed and discussed based on the analysis of gas and liquid products combined with optical emission spectroscopy(OES)diagnostics.The results from theoretical thermodynamic balance calculation indicated that the input energy to the RGA was not used to heat the gas but to form reactive species to fulfill tar destruction.The initial decomposition product of toluene,naphthalene and phenol were benzyl,naphthyl,and phenoxyl,respectively,which would fragmentize by stepwise breaking of C-C-bonds to final products(H2 and CO)through the interaction with excited nitrogen molecules and hydroxyl radicals.(5)Plasma-catalytic dry reforming of methane(DRM)for the production of syngas was carried out over Ni/?-Al2O3 catalysts with different Ni loadings(6 wt.%,8 wt.%and 10 wt.%Ni)in the RGA plasma reactor.In the plasma reforming without a catalyst,the highest conversion of GH4 and CO2 can reach up to 52.6%and 39.2%,respectively,and the major gas products were H2 and CO.In the presence of catalysts,increasing Ni loading enhanced both the CH4 conversion and H2 yield.The maximum CH4 conversion of 58.5%was achieved while the H2 yield was risen to 20.7%from 17.6%.Compared to DRM using other non-thermal plasmas,the RGA reforming process offers a significantly reduced energy cost for syngas production.