Study On Structural Denitrification Design Of New Rural Biomass Boilers

Nowadays,the extensive use of fossil energy such as coal and oil leads to more and more gas pollutants and dust being discharged into the atmospheric environment,resulting in the decline of air quality and increasingly serious environmental problems.In order to find new energy which can replace it,clean energy such as wind energy,solar energy,tidal energy and biomass energy has been widely studied and used because of its advantages of small pollution and renewable.In rural areas of China,biomass resources are particularly abundant.Many crop straws are directly burned or discarded,which not only wastes a lot of biomass resources,but also causes additional environmental pollution.The biomass pellet fuel made from these straw crops has the advantages of convenient storage and transportation,high combustion thermal efficiency,and because of the less sulfur element in plants,the sulfur oxides emitted from combustion are much less than coal,which can be used to replace coal as the main energy for rural household cooking and winter heating.However,biomass combustion will emit more nitrogen oxides.Biomass denitrification is mainly used in large industrial furnaces.There is no nitrogen oxide treatment device in rural household biomass boilers.In this project,an hourglass type furnace structure of rural household biomass boiler is designed.on the basis of it,a set of urea spray system is designed to remove nitrogen oxides generated by fuel during combustion,so as to realize the clean combustion of small biomass boiler.According to the combustion characteristics of biomass fuel,this paper first introduces the structure and characteristics of the designed household biomass boiler,and explains why urea is selected as the additive of nitrogen removal.Through building the boiler experimental platform,the combustion experiments of three kinds of biomass fuel,namely,mahogany particles,poplar particles and corn straw particles,are carried out.Km9106 flue gas analyzer was used to measure the content of NO,NO₂ and oxygen in flue gas during combustion,and multi-channel temperature tester was used to measure the combustion temperature in the boiler.Combined with the formation mechanism of nitrogen oxides,the effects of different urea spraying strategies and combustion conditions on the concentration of nitrogen oxides emitted from biomass combustion were analyzed in detail.The results show that spraying urea solution with mass concentration of 10%in the secondary combustion zone of the furnace has little effect on the combustion of biomass particles,and has significant denitrification effect.Too high or too low mass concentration of urea solution will increase the emission concentration of nitrogen oxides;changing the excess air coefficient and the ratio of primary and secondary air volume will affect the combustion temperature of biomass particles,thus changing the emission concentration of nitrogen oxides.According to the experimental data,when the excess air coefficient is 1.1 and the ratio of primary and secondary air is 6:4,the combustion temperature of biomass particles is the highest,and the NOx emission can be reduced to the national standard limit by using the best urea spray strategy.After analysis,it is considered that the environmental benefits of the new type of household biomass boiler with this urea spray strategy and combustion conditions are far higher than that of coal-fired boiler,which makes a certain contribution to the use and promotion of rural biomass boiler.