www.nature.com/scientificreports OPEN Study on the characteristics of nitrogen dioxide adsorption and storage of coal residue in coal‑fred power plants in goaf Xuefeng Wang1*, Ling Qiao1, Cunbao Deng1, Ge Chu2, Xiaofeng Li2, Qi Zhao3 & Guoli Wang4 In order to realize the storage of the residual coal in the goaf on the fue gas of the power plant, the adsorption characteristics of nitrogen dioxide in the fue gas of the power plant were studied. The Gaussian09 was used to study the adsorption process of NO2 molecules on coal at the density functional (DFT) B3LYP/6‑311G level, and the model of NO2 adsorption by coal was established. Diferent quantities were obtained using orbital energy changes and molecular bond length changes. According to the principle of molecular adsorption, the adsorption of NO2 by coal is considered to be physical adsorption with endothermic heat. On the basis of simulation, using self‑organized experimental devices, the single‑component NO2 gas and the simulated coal‑fred power plant fue gas were introduced into anthracite, bituminous coal and lignite. In single‑component adsorption, the adsorption of NO2 by lignite increases with time. The time to reach equilibrium is related to the properties of the coal itself. In the process of simulated fue gas adsorption, the order of the adsorption amount of coal to fue gas is CO2 > NO 2 > N 2 > ­O2. In the simulated fue gas, coal is easy to absorb NO2 and CO2, and the competition between gases reduces the frequency of contact between NO2 and the coal surface. Simulation and experimental results show that coal has obvious adsorption characteristics for NO2, and it is feasible for the residual coal in the goaf to adsorb NO2 in the fue gas of power plants. Te presence of nitrogen oxides in the fue gas is an important gas that causes the ozone layer, and particle pol- lution and related pollution are also the main cause of acid rain, which will destroy the ozone layer. Te nitro- gen oxides in human production and life mainly come from the burning of fossil fuels, and the content in the air increases year by year. Te nitrogen oxide content in the fue gas of coal-fred power plants is about 0.05%. According to relevant reports and studies, the amount of NOX emissions from fuel combustion in thermal power plants, iron smelters, and chemical plants accounts for more than 90% of total man-made emissions1–4. In order to deal with NOX in the fue gas of power plants, dry fue gas denitration and wet fue gas denitration are ofen used to reduce NOX in fue gas. In the dry fue gas denitration, the SCR catalyst is difcult to choose and the cost is high; the SNCR denitration rate is low and the temperature is difcult to control. Te NH3 and fue gas produced by the combined denitrifcation technology of the two methods in the SNCR area cannot meet the denitrifcation demand of the SCR area. Te catalytic decomposition method has a low denitration rate. Te adsorption method is susceptible to interference from external conditions and has high requirements for NO X. Wet fue gas denitration technologies include reduction adsorption, oxidation adsorption and lye absorption. Te use of lye adsorption is limited because of its high cost and complex products. Te oxidation absorption method requires the equipment to have anti-corrosion ability, and the conversion material is still polluting the environment. Although the reduction and absorption method is harmless, the denitrifcation rate is low and cannot meet the atmospheric emission standards. Te above-mentioned methods have serious disadvantages and cannot be promoted vigorously. Terefore, the denitration of fue gas in power plants is still an urgent problem to be solved5–10. In the 1970s, the United States took the lead in researching coal-bed methane as a resource and achieved success. Later, the research on coal adsorbed gas gradually deepened. Experiments show that there are 12 many types of coal adsorbed gases, including CH4, N2, CO2, O2, H2, and NO2 . 1College of Safety and Emergency Management Engineering, Taiyuan University of Technology, Taiyuan 030024, China. 2College of Safety Science & Engineering, Liaoning Technical University, Fuxin 123000, China. 3China Coal Society, Beijing 100000, China. 4Dananhu No.1 Mine of Guoshen Group, Hami 839000, China. *email: [email protected] Scientifc Reports | (2021) 11:8822 | https://doi.org/10.1038/s41598-021-87855-y 1 Vol.:(0123456789) www.nature.com/scientificreports/ Coal adsorbs gas through van der Waals force, and the van der Waals force is related to the properties of the coal itself. In recent years, the research on the afnity of coal to various gases has achieved many remarkable results in the aspects of experiment and simulation calculation13. Te competitive adsorption and difusion mechanism of CO2/CH4/H2O mixture in lignite was studied by using Monte Carlo method and molecular dynamics. Te efects of temperature and pressure on competitive adsorption and difusion behavior were discussed. Te results show that the adsorption capacity of lignite to CO2 is greater than that of CH4, and the adsorption of moisture on gas is inhibited. Xu et al. conducted a grand canonical Monte Carlo simulation on the bituminous coal model, studied the adsorption behavior of CO 2, CH4 and their mixtures, and believed that CO2 showed preferential adsorption over CH4. Li et al. established 3 models of diferent coal ranks and studied the competitive adsorption of CO2/CH4 on coal. Te results show that from low-rank coal to high-rank coal, the total pore volume, porosity and efective pore ratio of coal increase, which leads to an increase in the adsorption capacity of coal. With the increase of coal rank, the choice of CO 2/CH4 adsorption Sexual decrease. Yang et al. established a gas–solid coupling test system and performed uniaxial load- ing tests on coal samples adsorbed with diferent gases, indicating that under the same adsorption pressure, the adsorption capacity and degradation rate of coal for CO2, CH4, N2 and He decreased in turn. Kui et al. proposed that when the coal body expands with the increase of water content, the adsorption capacity and adsorption rate of CH4 both decrease. Lin et al. studied the adsorption behavior of bituminous coal in mixed gases with difer- ent ratios, and established a coal adsorption experimental system to conduct experiments. Te results showed that the adsorption of bituminous coal to CO2 is stronger than that of N2, and there is a competitive adsorption relationship between the two. Stevenson et al. used dry coal samples to perform adsorption tests on CH 4, N2, and CO2 mixed gases. Arri and Yee used wet coal samples to study the adsorption experiment of CH4, CO2 and CH4, N2, and obtained that the adsorption of coal to multiple gases was achieved by competing for the same adsorption sites. Cui et al. studied the isothermal adsorption experiment of binary mixed gas of CH4, CO2, N2 with diferent ratio concentrations, and obtained the diferent adsorption capacity of each component gas under diferent conditions. Gu et al. simulated the adsorption process of coalbed methane (CH 4, N2), and the quanti- tative relationship between the concentration of the component in the free phase and its concentration in the adsorbed phase was determined by the adsorption competition. Yu et al. studied the adsorption characteristics of CH4 and CO2 and their mixed gas under high pressure, and found that the adsorption capacity of coal for the mixed gas is between that of pure CH 4 and pure CO 2. Wang et al. applied quantitative calculations to study the mixed adsorption process of multiple gases on the surface of coal, and concluded that the afnity order of adsorption on the surface of coal with various gases is: O2 > ­H2O > ­CO2 > ­N2 > CO > ­CH4. However, most of the current researches focus on the competitive adsorption between CO2, N2 and coalbed methane, and there are few studies on the adsorption of NO2. Te adsorption of coal and gas is not only on the surface, but also on the surface of the pores in the coal. In this study, the simplifed structure of the coal surface and the physical adsorption of gas were selected. However, the adsorption of gas in coal pores also includes physical adsorption, associative chemical adsorption and dissociative chemical adsorption. In addition, the adsorption may cause deformation of the pores, and the phenomenon of pore blockage, which leads to a decrease in pore volume, will afect the adsorption. Tis paper only studies the physical adsorption process of coal and gas. Gaussian simulated coal adsorption of NO 2 Te calculation was completed with the Gaussian09 program. Te adsorption process of coal molecules and NO 2 molecules was studied at the level of density functional (DFT)B3LYP/6-311G. Simplify model building. It is generally believed that coal is a polymer structure, which is based on con- densed aromatic ring and connected with various alkyl side chains, oxygen-containing functional groups and bridge bonds. Te composition of coal is also relatively complex, mainly composed of carbon, hydrogen, oxy- gen, nitrogen and sulfur, and many kinds of trace elements. Te composition and structure of coal vary greatly according to its metamorphic degree and geological conditions. In the simulation calculation, the more complex the coal structure model, the less representative it is. In the artical, the model of molecular fragments on the surface of coal is simplifed as a characteristic structure of coal composed of two benzene rings. A side chain con- taining 1 C atom, 1 N atom and a side chain containing 2 C atoms extend from the skeleton.