Effect Of Additives On NO_x Emissions Of Typical Coals Under Different Combustion Conditions

Due to the development of China's economy and the needs of people's lives,thermal power will still occupy a dominant position in the future.Nitrogen oxides,one of the air pollutants emitted by coal combustion in power plants,can cause serious problems such as ozone layer destruction and the greenhouse effect.The control of nitrogen oxides has become an inevitable requirement for practicing the concept of green development.The advantages of using a circulating fluidized bed and reducing the emission of nitrogen oxides during the combustion process in power plants through additives are of great significance for environmental protection.According to the results of industrial analysis and elemental analysis of coal,five typical coals were selected according to the ash and sulfur content of the coal.Experiments on the effects of additives on nitrogen precipitation of typical coals under different combustion conditions were performed in a tube furnace.The experimental results showed that the addition of desulfurizers increased the concentration of NO_Xemissions from coal combustion,and further addition of TiO₂ could reduce the concentration of NO_X emissions.The effects of oxygen flow rate,combustion temperature,type of catalyst TiO₂,type of desulfurizer,and preparation conditions of catalyst TiO₂ on NO_X emission concentration were studied in the experiment.The lowest combustion conditions for NO_X emission concentration of typical coal were obtained.When the oxygen flow rate is 40ml/min,the combustion temperature is850?,the desulfurization additive is Mg O,and the catalyst is Zr-TiO₂(Zr 5%,impregnation method),the combustion NO emission concentration is the lowest and reaches the ultra-low emission standard.According to the principles of economics and efficiency in practical applications,further analysis of the suitability of coal types through experimental data showed that the combustion conditions are applicable to coal with sulfur content<3%and ash content<30%,and can achieve a denitration efficiency of more than 40%.In the experiment,Zr-TiO₂ was prepared by impregnation method and microwave-assisted sol-gel method.Combined with the results of various analysis and characterization of TiO₂,the preparation conditions of Zr-TiO₂ in the experiment were optimized.The characterization results showed that the Zr-TiO₂ prepared by the impregnation method had a uniform structure and a high specific surface area,pore size,and pore volume.The doping of Zr element strengthened the lattice oxygen peak of TiO₂,and the crystal structure was gradually complete,thereby improving the redox capacity of the TiO₂ surface.The experimental data were consistent with the characterization results.The denitrification effect of coal with sulfur content<3%and ash content<30%was better than other types of coal.According to coal combustion experiments,combined with the results of coal analysis and characterization,it can be found that TiO₂ can improve the combustion performance of coal and contribute to full combustion.TiO₂ accelerates the cracking reaction of coal itself and increases the volatile content of coal,thereby increasing the pore size and pore volume of char,which is beneficial to the permeation and diffusion of NO to the inner surface of char for heterogeneous reduction reaction.In addition,Zr-TiO₂(Zr 5%,impregnation method)has a higher specific surface area,pore size and pore volume,which improves the efficiency of reducing NO from coal coke in different phases.The metal oxides in the coal ash can catalyze the reduction of NO,and can also reduce the NO emission concentration in the actual operation of the circulating fluidized bed boiler,so as to reduce the operating cost of the boiler.