Experimental Study Of NO Reduction By Biomass Gasification Tar

Gasification is a main conversion technology of biomass energy, but tar produced in gasification process cause some problems to the technology. Tar is undesirable due to condensation, formation of tar aerosols and polymerization to form more complex structures, which cause blockage in transporting pipe and damage to engines and turbines. Then, tar is still the bottleneck of the technology. Though many researchers have been working on tar removal, the efficient and cheap removal of tar is still immature and the main technical barrier for the successful commercialization of biomass gasification technology. Some research indicate that oxidation of tar produces light C1-2 hydrocarbons that can reduce NO, which means that tar can reduce NO. So, a technical routine of biomass gasification gas reburning with tar, or biogas reburning without tar removal, is put forth to deal with the comprehensive utilization of tar in the present work. The work is to investigate some basic issues of NO reduction by biomass gasification tar and by biogas with tar. The research results have the guiding role for the engineering application of the technology of biomass gasification gas reburning with tar.Tar compositions are so complex that some typical tar model compounds are selected to study. TG-MS apparatus is used to analyze the tar compositions produced in pyrolysis and gasification of several typical biomasses. The TG-MS analyses indicate that the cumulated ion intensity area of benzene, toluene, styrene and phenol is large. The four compounds are main compositions of tar, and they cover from the primary tar to the tertiary tar. Then, those four hydrocarbons are selected as the typical tar model compounds for the further research.The chemical kinetic modeling of NO reduction by a typical tar model compound is studied, in order to discover the mechanism of NO reduction by tar. Base on the mechanism of NO reduction by hydrocarbon and non-hydrocarbon intermediates produced in the tar oxidative decomposition, the chemical kinetic modeling of NO reduction by toluene is studied. The chemical kinetic model of NO reduction by a mixture of light hydrocarbon and non-hydrocarbon fuels (NRMF) is developed at first. Then, the chemical kinetic model of NO reduction by toluene (NRT) is developed, after some reactions of toluene oxidative decomposition are added into the NRMF model. The validity of the NRMF model and the NRT model is proved, experimentally. The reaction pathway of NO reduction is analyzed. The study indicates that tar tends to yield HCCO and C2H radicals. The reaction activity of the two radicals is higher than CHi (i=1, 2, 3) radicals, so that the two radicals are more important in NO reduction.Experimental study of NO reduction by the four typical tar model compounds, benzene, toluene, styrene and phenol, is carried out to analysis the experimental characteristics of them. The results of the experiments indicate that the bulk equivalence ratio,φ, and temperature are the main factors in NO reduction; the NO reduction ability of tar model compound with substituent is higher than benzene; toluene and styrene, which have hydrocarbon substituent, can reduce more amount of NO than acetylene under suitable conditions. Then more tar with hydrocarbon substituent is expected than benzene in the engineering application of biomass gasification gas reburning with tar. The experiment of the four typical model tar compounds simultaneous reburning indicates that the NO reduction efficiency increases at 900-1100℃, and increases at 1300-1400℃, as the content of oxygen decreases. It is a transition stage as 1200℃.Tar is mixed in biogas from gasifier, and NO reduction by biogas with tar is investigated, experimentally. The experimental results show that tar can improve the NO reduction by biogas with tar with comparison to by biogas without tar. The bulk equivalence ratio,φ, and temperature are the main factors in biogas reburning with tar. Then, remaining proper oxygen concentration and controlling tar polymerization even to yield soot is needed to maximize the ability of NO reduction by biogas reburning with tar.