Experimental Study On Performance Of Biomass Reburning For NO_X Reduction

NOx emission from coal-fired is one of main substances polluted atmosphere and environment,the control of NOx is imperative.The biomass reburning technology is a new low cost and high efficiency technology adapted to the situation, it integrates the two great subject-energy saving and emission reduction and has good technical advantages and development prospect.The experiment selected 6 kinds of biomass with typical feature as reburning fuel such as wheat,maize,cotton,phoenix tree,deal and poplar.Then distinguished them into herbage plants and woody plants and studyed on the basic property, pyrogenation property and combustion property.Biomass contains little nitrogen and sulfur,so biomass is green energy resource.Biomass contains less carbon but upper hydrogen and has lower heat value than coal.All biomass contain high volatilization more than 62%and easy to combust.The ash of biomass contains some kinds of alkaline metal salt which can promote the NOx reduction effect.The mass loss rate of pyrogenation and combustion is big,the pyrolysis temperature, ignition temperature and combustion temperature are lower than coal,so biomass is perfect reburning fuel.Although the volatilization and heat value of woody plants are higher than herbage plants,the woody plants is difficult to combust than herbage plants because its pyrolysis temperature and combustion temperature are higher about 30℃.The results of experience of biomass reburning for NOx reduction as follows:6 kinds of biomass are perfect reburning fuels and the NOx removal efficiencies can achieve about 65%-70%.There are differences between different biomass about NOx removal efficiencies.The efficiencies of wheat,cotton,deal and are high and can achieve over 67%.The optimum parameters for biomass reburning were researched and found.The higher reaction temperature is,the higher NOx removal efficiencies is,but a lot of thermal NOx will generate when the temperature reach a critical temperature,so the optimal temperature is 1000℃-1200℃.The low stoichiometric ratio can get strong deoxidation atmosphere but combustion incompletely and high ratio can make CH group oxidation,so the optimal ratio is 0.7-0.8.The low reburning ratio cannot meet the concentration of CH group needed to reduce NOx but high ratio can make combustion incompletely,so the optimal ratio is 20%.The long resident time can make deoxidation reaction completely but limited by practice space,so the optimal time is 0.7s-0.8s.The research also found that the particle size of biomass do not affect the NOx removal efficiencies.The denitration ability of woody plants is as good as herbage plants.The denitration ability is affected by volatilization,pyrolysis characteristics and combustion characteristics,and the pyrolysis characteristics has great influence on denitration temperature characteristics.The NOx removal efficiencies of biomass mixture is slightly less than the theoretical average,so the biomass mixture also is perfect reburning fuel and adapt to industrial application.The NOx removal efficiencies of biomass can achieve 81%-90%in advanced reburning experience.The efficiencies of wheat,cotton,deal and are high and can achieve over 86%.The optimum parameters for biomass advanced reburning were researched and found.The lower reaction temperature is,the slower reduction reaction rate is,but if the temperature is over 950℃,NH3 start to be oxided to NO, so the optimal temperature is about 1000℃.The low stoichiometric ratio against reduction reaction of ammonia agent,and the high ratio will oxide ammonia agent, so the optimal ratio is 0.7-0.8.The low NSR cannot get the optimal NOx removal efficiencies,the high NSR will be secondary pollution by ammonia escaping,so the optimal NSR is between 1.5-2.Reburning and SNCR process show synergistic reaction characteristics in advanced reburning.The higher efficiency of basic reburning results in the lower NOx reduction of SNCR.The final affect present as the same NOx removal efficiency of different biomass.The additive can promote the NOx reduction affect,and expand the temperature window to 950℃-1100℃.The synergism affect of Na₂CO₃,K₂CO₃,(CH₃COO)₂Ca,FeCl₃ decreased systematically,and the three former can achieve over 91.4%efficiencies.The synergism affect of salt group of Na,K,Ca,Fe decreased systematically,The Na,K group has higher synergism ability,and interior MCl,MNO₃,M₂CO₃,MOH(M=Na/K)increased systematically.