Experimental Study On The Reduction Of NO By Nitriding Modified Coconut Shell Char And Its Reaction Mechanism

Coal char direct heterogeneous reduction NO_X technology（CARBONO_X technology）is one of technologies to effectively eliminate nitrogen oxides in combustion flue gas.It has the characteristics of abundant raw materials and low cost.However,residual oxygen in the flue gas will consume coal char and reduce the reduction efficiency of NO.Biomass coking properties have many similarities with coal char,such as low price,higher chemical activity and alkali metal content.Therefore,this paper proposes a scheme for modifying biomass char by nitriding treatment to increase its reaction selectivity for NO.By using self-built fixed bed reactors,Fourier infrared（FT-IR）,pyrolysis-mass spectrometry（Py-GC-MS）and photoelectron spectroscopy（XPS）,the research is carried out with using the Hainan coconut shells as a raw material in turn:（1）Study on the influence of preparation conditions on the chemical structure of coconut shell char and the reaction characteristics of heterogeneous reduction of NO by coconut shell char;（2）The denitrification characteristics of modified coconut shell char by nitriding condition,the change process in cracking compound composition of coconut shell char before and after nitriding,and the change rules of carbon,oxygen and nitrogen-containing functional groups were studied.Coconut shell char was prepared on a self-built variable heating rate Coking bench,and its surface chemical structure was studied by Fourier infrared spectrometer.Research indicates:The length of the aliphatic chain（I₁）,the carbonyl group and other C=O increase with the increase of pyrolysis temperature,relative to the aromatic macromolecule（I₂）and the relative content of C=O（I₃）in the coconut shell char;The ratio of aromatic carbon to total carbon（fa）decreases with the increase of pyrolysis temperature.The effects of coking conditions and reaction conditions on the denitration rate of coconut shell char were studied under simulated flue gas conditions.Research indicates:The denitration rate of coconut shell char increases first and then decreases with the increase of pyrolysis temperature and oxygen content;it increases with the increase of reaction temperature and feed rate;the direct heterogeneous reduction of NO has a good effect by coconut shell char when the heating rate was 15K.The denitrification characteristics of nitriding modified coconut shell char,the change process of pyrolysis compound composition of coconut shell char and the change rules of carbon,oxygen and nitrogen-containing functional groups were studied in a fixed bed reactor.Research indicates:The denitration rate of coconut shell char decreases first and then increases with the increase of nitriding time.The longer the nitriding time,the higher the reaction selectivity and the higher the denitration rate.The components in the thermal cracking product are more complicated.After nitriding treatment,the content of various compounds in coconut shell char can be increased,the activity of coconut shell char can be enhanced,and the ability of coconut shell char to reduce NO can be promoted.The content of C-C functional groups in coconut shell char decreases with the increase of nitriding time,and the content of C=O/C-N,COOH andπ-π*functional groups increase first and then decrease with the increase of nitriding time.The content of C=O functional group decreases with the increase of nitriding time,and the content of C-OH/C-O-C functional group and chemisorbed H₂O/O₂ decrease with the increase of nitriding time.The surface nitrogen-containing functional groups of the modified coconut shell char mainly include N-6,N-5,N-Q and N-X;the contents of N-6 and N-X functional groups increase with the nitriding time;the content of N-Q functional groups decrease with the nitriding time;the change on the content of N-5 functional groups is not significant with the increase of nitriding time.