Simulation Of Sampling Method For Condensable Particles In Flue Gas By Homogeneous Nucleation

As an important part of the global energy system,coal combustion often releases particles with small particle sizes and attachment of rare metal elements,causing serious harm to the air environment and human health.Total particulate matter(TPM)in coalfired power plants can be divided into condensable particulate matter(CPM)and filterable particulate matter(FPM).With the continuous promotion of national environmental protection,the emission of FPM from coal-fired power plants has been effectively controlled by near zero emission technology,and the study of the formation characteristics of CPM has gradually been put on the agenda.Up to now,the sampling methods for CPM are mainly divided into impulse condensation sampling method and direct dilution sampling method.However,due to the different sampling methods,data inconsistency may occur under the same working condition.Therefore,accurately collecting the quality and quantity concentration of CPM has become a difficult point in the research of CPM today.In this paper,quantum chemical calculations and cluster dynamics simulations were used to study the nucleation mechanism of(NH3)x(HCl)y(SO3)z(NO2)m(H2O)n(0≤x,y,z,m≤5,0≤n≤2).The structural and thermodynamic analysis of B3LYP/def2-SVP dft-d3 dispersion correction theory shows that the different working conditions of CPM during the formation process will affect CPM nucleation.The theoretical calculation used B3LYP/def2-SVP level to optimize the structure and determine the stable configuration of each adsorption structure.In order to accurately calculate the adsorption energy,B3LYP/def2-SVP was used to calculate the energy of the system with a single point energy.D3 dispersion correction was performed.The calculation is carried out using the Gaussian 16 software package,and the wave function analysis is based on the multifunctional wave function analysis software Multiwfn picture using VMD software for plotting.In binary structures,two binary structures,(NH3)x(SO3)y and(NH3)x(HCl)y,are the main drivers of nucleation.In particular,the escape amount of NH3 contained in flue gas has a significant impact on CPM nucleation.Therefore,the content of escaping NH3,and the concentration of other SO42-and Cl-are the basic conditions for CPM nucleation,and water and nitrogen oxides play a promoting role.NOx cannot effectively nucleate when combined with a single type of molecule,but can participate in the binary structure of other effective nucleation,and together with H2O,it acts as a bridge reinforcement.In the simulation of the molecular weight participating in nucleation as the changing trend of reaction concentration,it is found that there is an increase in the molecular weight of both binary and ternary structures,which effectively promotes the trend of nucleation.Water molecules also play a key role in nucleation.sometimes acting as a bridge to strengthen other binary structures,and sometimes directly fixing some molecules such as SO3.NH3 plays an important role in the formation of CPM,where protonated ammonia molecules may be located at the center of the cluster structure and form stable bridge complexes between surrounding molecules.In the experimental aspect,ELPI+ method combined with EPA 202 method and direct dilution method were used to collect the concentration of CPM in the flue gas generated by the combustion of a dropper furnace to study the impact of different sampling methods on the collection results and the distribution of CPM particle size concentration.The data collected by the dry impact method improved by ELPI+is higher than the data collected by the improved direct dilution method.That is,different measurement methods can have an impact on CPM data,which is caused by different condensation methods.ELPI+equipment also distributes CPM data by particle size,and finds that there is a significant difference between the two methods on small particle sizes.It is believed that the significant difference in CPM with small particle sizes is due to positive and negative deviations caused by environmental changes on homogeneous nucleation in small particle sizes,while there is no impact on nucleation with large particle sizes.Changes in flue gas concentration,humidity,and nitrogen oxide concentration are the main factors affecting homogeneous nucleation in small particle sizes.