Effect Of Expanding Modification On Reactivity Of Coal Char In Reducing NO

Industrial boilers have become an important source of atmospheric pollutants,and achieving low NOx emissions from coal-fired industrial boiler is imminent.The previous study found that using high-temperature semi-char cycle technology can effectively reduce the original NOx emissions from the layer burning furnace.However,the long-term high temperature environment makes the coal char structure develop towards the graphitization direction,which leads to the deterioration of the reactivity of coal char.Considering that the coal char contains polar groups and graphite-like microcrystalline structure,this paper proposes the technical idea of using graphite intercalation,expansion and microwave chemistry related methods to regulate the physical structure of coal char,and carries out research in terms of the preparation and expansion of intercalated char,the analysis of physical and chemical characterization,the evaluation and analysis of reaction capability.Firstly,Ningxia smokeless char with different pyrolysis temperatures is prepared by high temperature settling furnace.The expansible char is prepared using potassium permanganate as oxidant and concentrated sulfuric acid as intercalation agent.Finally,the expansible char is subjected to different conditions of high temperature expanding or microwave expanding.The pore structure,type of hybrid carbon structure and the distribution of surface functional groups of each sample are tested by nitrogen adsorption,Raman,and FTIR.The results show that the original pore structure of char is improved after different conditions of hightemperature expanding or microwave expanding.After the expansion,the specific surface area and pore volume of each sample increases,and the average pore size decreases;the relative content of ordered carbon structure of coal char decreases,and various defect structures increase.Besides,a large number of pore structures of2~12 nm will be newly generated by microwave expanding.However,excessively high expanding temperature,too large expanding power,and excessively long expanding time all lead to ablation and collapse of the pores of char,and the order of carbon structure increases again,resulting in deterioration of the modification effect.Oxidation can form polar groups such as conjugated C=O on the surface of coal char.After microwave expanding,C-O-C,C=O will oscillate and form large amounts of aromatic C=C unsaturated carbon atoms,increasing the number of surface active point of char,thereby increasing its reactivity.The experimental results of NO reduction by coal char show that the higher the temperature of preparing coal char,the more obvious the effect of high-temperature puffing on the modification of coal char.And the reactivity of all kinds of modified char is obviously stronger than that of the original char.With the increase ofexpanding temperature,expanding time and expanding power,the reactivity of coal char increases first and then decreases.The optimum temperature for hightemperature expanding is 800°C,the best expanding time is 90s;the optimal power for microwave expanding is 960 W,and the best expanding time is 90 s.Combined with the analysis results of samples,it can be seen that NO reactivity of coal char is mainly determined by the degree of pore structure development and the relative content of defect structure.The experimental results of isothermal reduction of NO by coal char show that the higher the NO inlet concentration is,the lower the reduction ratio of NO of raw char and microwave expanding char becomes.However,the reactivity of microwave expanding char is stronger.With the increase of the concentration of CO,the reduction rate of NO by raw char and microwave expanding char gradually increases.Coal char is inevitably in contact with the oxidizing atmosphere during the cycle in the furnace.Thus,this article has carried out the constant temperature combustion experiment of coal char,and the results show that the combustion process of char is significantly shortened and the NO release time is shortened after the pretreatment of microwave expanding,but the release peak of NO and the conversion rate of char-N to NO increases.However,the expanding treatment has a positive effect on the overall nitrogen reduction effect of recycled coal char.At low temperature of 600°C,the microwave field can increase the combustion rate of char,but it will not affect the conversion rate of char-N to NO.At high temperature of 900°C,the microwave field can reduce the release peak of NO and the conversion rate of char-N to NO,the higher the power,the greater the decrease.But applying microwave field can not further shorten the combustion process,namely,and NO release time is basically unchanged.