Study On Heterogeneous Reduction Mechanism Of NO By Biochar And Its Modified Char

NOx is the main pollutant of flue gas emission from thermal power plants.The heterogeneous reduction of NOx by activated carbon with biochar as reducing agent has the characteristics of abundant raw materials,low cost and no ammonia leakage.Among the three components of biomass,lignin is the main component to form biochar.The physical and chemical properties of biochar produced by different lignin species are diverse,which affects the reduction efficiency of NOx.Residual O₂（2～5%）in flue gas will consume biochar and reduce NOx removal efficiency.Therefore,in this article,physical and chemical adsorption apparatus（BET）,Fourier transform infrared spectroscopy（FTIR）,Raman spectrometer（Raman）,X-ray fluorescence spectroscopy（XRF）and self-built fixed bed denitration device are used,and Chinese fir（G-type lignin）,elm（G-S lignin）and bamboo（G-S-H lignin）are used as raw materials,which are developed in turn:（1）Characteristics and mechanism of heterogeneous reduction of NO by biochar of three lignin species;（2）Effects of pickling and nitriding treatment on pore structure,surface functional groups distribution and denitration characteristics of three lignin biomass chars and their mechanism.Biochar was prepared on a self-built biochar-making test-bed with variable heating rate,and its surface physical and chemical structure was characterized.The results show that the Chinese fir biochar（FB）obtained from biomass with G-type lignin has developed pore structure,and the surface of elm biochar（EB）prepared from G-S lignin biomass has the most oxygen-containing functional groups（COOH,C=O）and hydroxyl groups（O-H）.The effects of reaction temperature and oxygen concentration on denitration characteristics of three kinds of biochar were studied under temperature programmed condition.The results show that the developed pore structure of FB is the main reason for the continuous decrease of NO curve in diffusion control zone（low temperature zone）.EB has the highest NO removal efficiency and the strongest oxidation resistance in the C-NO reaction kinetics control zone（high temperature zone）.In addition,a small amount of oxygen can promote the formation of complex（C（O））,thus forming active sites（C（））and increasing the reduction efficiency of NO.However,at higher oxygen concentration,too much C（O）produced on the surface of biochar will occupy active sites,which is not conducive to NO reduction.The effects of acid washing and nitriding on pore structure and surface functional groups distribution of three kinds of biochar were studied.The results showed that acid washing changed the pore structure of biochar,increased the specific surface areas and pores structure of FB and EB,and nitriding effectively introduced nitrogen-containing functional groups on the surfaces of the three biochar.The denitration characteristics and mechanism of three kinds of modified biochar were studied in constant temperature experiment.The results showed that acid washing and nitriding treatment of Chinese fir biochar（FB）with high density of microcrystalline carbon defects could slightly improve its denitrogenation performance.Acid washing and nitriding of elm biochar（EB）with low density of microcrystal carbon defects can improve the denitrification efficiency and reaction selectivity,and the effect of acid washing and nitriding is the best.Acid washing and nitriding of herbal bamboo biochar（BB）with high Si element content in ash is not conducive to the improvement of denitration performance.Transition metals and alkali metals are the key components of Chinese fir biochar（FB）and acid washed Chinese fir biochar（FB-S）（elm biochar（EB）and acid washed elm biochar（EB-S））in denitrification process,respectively.The key components of bamboo biochar（BB）and acid-washed bamboo biochar（BB-S）in denitration process are Si and alkali metals.The affinity of these metal elements to oxygen atoms and the difficulty of reducing metal oxides affect the nitriding and denitration process of biochar.