NUMERICAL-SIMULATION OF VAPOR AEROSOL DYNAMICS IN COMBUSTION PROCESSES

A computer model (ABC-code) has been constructed to describe the stead y one-dimensional aerosol dynamics in combustion processes for ps and particle interactions at post-combustion conditions. The aerosol gener al dynamic equation has been solved numerically using a discrete-nodal point method for describing the particle size distribution. In the pr esent model we consider those mechanisms that will affect the dynamics of alkali species after volatilisation, i.e. nucleation, condensation , coagulation, chemical reactions and deposition. The main features of the ABC code have been explained and an example calculation has been carried out for simulation of aerosol dynamics and alkali vapour behav iour in a real scale pulverised coal fired boiler. The results show th at for predicting the gas phase concentrations of alkali species at di fferent temperatures it is important to know the volatilisation of sod ium, potassium, chlorine and sulphur and the formation rate of alkali sulphates in the gas phase. The initial ash size distribution determin es the distribution of condensed alkalis between sub- and supermicron particle modes. The choice of the homogeneous nucleation model has som e importance for the calculated submicron number size distribution. Th e effect of heterogeneous nucleation to initiate condensation on ash p articles was negligible. The predictions of our simulation are in a qu alitative agreement with the experimental results. The utilisation of the present code will lead to a better understanding of aerosol behavi our which will be of great importance for the control of toxic flue ps emissions, slagging and fouling in commercial boilers.