Numerically Simulating the Parameters of Submicron Particles Generated in Coals Burning

Аннотация

Bulk condensation of substance vapors releasing from the mineral part of coals in burning them is regarded to be the possible mechanism through which environmentally dangerous submicron particles are generated. The possibility of certain toxic microelements contained in coals to condense on the surface of particles is an additional negative factor associated with the generation of particles during coal combustion. To set up a particle trapping process that would make it possible to decrease the emission of submicron particles into the atmosphere in burning coals, information on the parameters of condensation aerosols generated during the combustion is necessary. The required data, in particular about the concentration of particles and their distribution by sizes, can be obtained through numerically simulating the bulk condensation process. A condensation model describing the generation of submicron particles of potassium and sodium sulfate in burning coals is proposed. The proposed model is based on applying a combined approach (involving the use of thermodynamic and kinetic analysis) to describing the bulk condensation process in the coal combustion products. It is assumed that the generation of potassium and sodium aluminosilicates in the volume of a burning coal particles “freezes” after the particle burning process terminates and the particle temperature decreases; part of potassium and sodium in the composition of aluminosilicates is removed from the combustion products with slag and fly ash, and the other part that was not included in the aluminosilicates remains in the gaseous phase and forms sulfate condensation aerosol as the temperature decreases. The proposed model implemented by means of software was used to numerically simulate the bulk condensation of potassium sulfate vapors in the coal combustion products as they are cooled in the process path. Data on the concentration of the generated particles and on their distribution by sizes are obtained. The calculated and experimental data on the fractional composition of particles are compared with each other.