Quantum Chemical Calculation of the Effect of NH₃ on CO₂ Adsorption and Storage in Goaf
2022
Hao, Chao-yu | Zhang, Ya-chao | He, Wen-hao | Deng, Cun-bao
The injection into a goaf of a flue gas issuing from a power plant and containing highly polluting CO₂ as inert gas can allow, at the same time, disaster prevention and greenhouse gas emission reduction. However, it can happen that unreacted ammonia present in the power plant flue gas is injected underground, and ammonia is present in the coal seam itself. At present, it is unclear how NH₃ can affect disaster prevention and storage. To explore the influence of NH₃ on CO₂ storage and coal spontaneous combustion, the micromechanism of adsorption between a coal model molecule and NH₃/CO₂ (taken separately or as a mixture) was studied using the density functional theory of quantum chemistry, including the dispersion correction method (DFT-D3). Results show that the lowest adsorption energy of CO₂ adsorbed on the surface of the coal molecule is significantly lower than that of NH₃, which indicates that the adsorption of CO₂ on coal is preferred to that of NH₃. In the mixed adsorption state, the adsorption stability of NH₃ on the coal–CO₂ system is lower than that of NH₃ on the coal molecular surface alone. On the contrary, the adsorption stability of CO₂ on the coal–NH₃ system at the same location is higher than that of CO₂ on the coal molecule alone; that is, the presence of NH₃ promotes the adsorption of CO₂ on coal, while the presence of CO₂ promotes the desorption of NH₃. Therefore, the presence of NH₃ is positive in terms of CO₂ storage in the goaf, reducing the environmental pollution caused by flue gas from a power plant and inhibiting the occurrence of coal spontaneous combustion.
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