Molecular Simulation Research On The Effect Of Microwave On The Gasification Of Char-steam

In recent years,microwave heating technology has been introduced into gasification technology due to its high efficiency and easy control characteristics.Microwave heating can provide heat from inside the fuel,avoiding additional air combustion.However,the understanding of the interaction mechanism and related basic issues between microwaves and chemical reaction systems is not yet deeply understood.The special effects（non-thermal effects）generated during their interaction process are the current focus and difficulty of understanding.This article discusses some special effects generated during the interaction process between microwaves and char-water vapor gasification reaction systems,from molecular dynamics simulation and density functional theory calculation to theoretical analysis,providing a scientific basis for further understanding the mechanism of microwave-chemical reaction interaction,exploring its special effects,and further engineering applications.The main research contents are as follows:（1）The effects of microwave gasification at different temperatures（2500K,2750K,3000K,3250K,3500K）,different waveforms（constant,square,sine）,and different field strengths（0V/（?）,0.01V/（?）,0.015V/（?）,0.02V/（?））on the gasification reaction were researched through non-equilibrium molecular dynamics simulation（NEMD）.It is found that the lower the temperature,the more obvious the promoting effect of microwave,and the introduction of microwave significantly reduces the activation energy of the gasification reaction.The waveform and field intensity of the electric field had a significant impact on the gasification reaction,and the impact of the waveform on the gasification reaction is in the order of constant<square<sine.It can be seen that the change in the direction of the electric field and the instantaneous change in the field intensity both promote the gasification reaction,and the effects of both can be superimposed.As the electric field intensity increases,the carbon conversion rate during the gasification reaction increases exponentially,and the growth rate is still in the order of constant<square<sine.（2）The research on the morphological changes of char during the gasification reaction showed that the introduction of the electric field promotes the destruction of the carbon ring and destroys the stability of the carbon edge.The visualization of the reaction trajectory also showed that the morphology of char in the electric field system is looser,providing more active sites and inhibiting the formation of graphite carbon.（3）The individual reactions in the gasification reaction were studied by extracting reactants from the reaction system.It is found that the introduction of the electric field significantly increased the content of oxygen-containing free radicals during the adsorption process;in the desorption reaction simulation,it is found that the electric field had a significant promotion effect on the desorption reaction,but the difference between the waveforms is reduced,and the desorption rate under the sine wave system could reach about10 times that under the non-microwave system.The simulation results of the gasification secondary reaction showed that the introduction of microwaves promoted the forward reaction of water gas reaction,played an important role in the production of H₂ in the system,and found that the constant electric field in the system may have a better effect on water dissociation.（4）Quantum chemical calculations were performed on a simplified model（PAH）to analyze the potential distribution,multi-center bond order,and conjugatedπelectron orbitals of carbon-oxygen composite PAHs.The results showed that the introduction of the electric field significantly promoted the polarization of PAHs,and the degree increased with the increase of the electric field strength,promoting the adsorption process.The multi-center bond order had a sudden change phenomenon with the increase of the electric field strength,making the carbon ring easier to be destroyed.The analysis of the conjugatedπelectron orbitals also showed that with the increase of the electric field strength,the aromaticity of the carbon edge is gradually destroyed.In addition,it is found that the electric field had a dynamic stretching effect on carbon-oxygen complexes,promoting the desorption process.