| Compared with traditional low nitrogen oxide(NOx)burner,porous media burner is featured by simple structure,high combustion efficiency,large operation range and low pollutant emission.However,current researches on porous media burner mainly focus on low power burner at the stage of laboratory,and there is no research on industrial-scale porous media burner until now.In present thesis,an industrial two-layer porous media burner which power range from 50kW to 100kW was designed based on the research of combustion mechanism of porous media in preliminary work,and it was experimentally and numerically studied,the guidance for the design and application of industrial porous media burner is provided by the research.The investigation work is as follows:1.Based on the results of combustion mechanism of small-scale porous media burner in literatures and industrial burner design requirements,the guidelines for the design of industrial porous media burner was raised.A two-layer porous media burner with power range of 50?1 OOkW was designed based on the guideline.An experimental system with porous media combustion was developed.The influence of disturbing device structure and the diameter of porous media on the emission characteristics of the burner was studied.Results show that compared with honeycomb ceramics,placing foamed ceramics in front of premixed chamber can significantly improve the mixing effect of fuel gas and air,as well as reduce carbon monoxide(CO)emission.The CO emission can be reduced from 136.3mg/m3 to 17.5mg/m3 when honeycomb ceramics is replaced by foamed ceramics at burner rating 50kW and equivalence ratio 0.8.2.The stability limits and pollutant emissions when natural gas/air premixed gas combusted in the industrial porous media burner were experimentally studied.The results show that the stable operating range extended and shifted to larger values when the equivalence ratio increase.NO is the main component of oxynitride when natural gas combust in porous media burner.The NOx emission increased with the burner rating and the equivalence ration.The maximum NOx emission of the burner was below 30mg/m3 for all operating conditions.It demonstrates that the industrial porous burner still has low NOx emission characteristics.CO emission of the burner was first decrease then increase with the equivalence ratio and inlet velocity,and it was lower than 56 mg/m3 when the equivalence ratio was not bigger than 0.9.In order to control the pollutant emission of the burner at low level,the suggested equivalence ratio is between 0.6 and 0.8.3.Combustion characteristic of natural gas in two-layer porous media burner was numerically simulated using CFD software Fluent 6.3.The simulation conforms to the industrial porous media burner prototype designed in this thesis.Two-dimensional,two-energy model,while considering detailed chemical kinetics mechanism was developed to simulate the radiation efficiency,gas-solid temperature,component distribution and pollutant emission when natural gas/air premixed gas combustion in the porous media burner in typical conditions.The thickness of porous media was used for parametric analysis.The general trend of temperature profiles and emission for various operating conditions are well predicted.The radiation efficiency of the burner decreases with the increase of burner load,and it ranges from 15.6%to 25%in the studied conditions.The flame surface is stable near the interface of the porous media,and the difference of gas phase temperature and solid phase temperature is within 300K.The emission concentrations of CO,NO and NO2 increase with the equivalence ratio and burner rating,and the value is basically in line with the experimental results.Considering the pollutant emission of the burner and the cost,the thickness of the upstream porous media is recommended 40mm,while the thickness of the downstream section is recommended 80mm. |
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