Effects of high intensity acoustic fields on sulfur dioxide capture and particle agglomeration in pulverized coal combustors.

摘要

A technique whereby a high intensity acoustic field at low to moderate frequencies may be used to enhance sulfur dioxide capture by limestone sorbent, as well as promote agglomeration of flyash sized particles, among themselves, or by the use of a bimodal distribution, is presented. A comprehensive sulfation model detailing the important processes of calcination, sintering and sulfation is discussed and implemented. Comparisons of model results to experimental data are undertaken and the results show a fairly good match. The key factors that influence sulfation were identified with respect to particle size using a parametric study. Pore diffusivity and mass transfer play an important role in the sulfation of large particles (100 {dollar}mu{dollar}m) as compared to small particles (10 {dollar}mu{dollar}m). The sulfation model was then incorporated into a comprehensive code for coal combustion to study sulfur dioxide capture by sorbent injection in a pulverized coal pulse combustor. Acoustic effects on particles were implemented by correlations for enhanced heat and mass transfer coefficients that were obtained from previous studies. Predictions of exit concentrations of SO{dollar}sb2{dollar} for cases with and without sorbent injection compared well to experimental data obtained from pulse combustor tests.; Finally, expressions for the relative convergent velocity for two particles in an acoustic field are derived based on the so-called "acoustic wake" effect to study the rate of agglomeration of particles. Parametric studies were carried out to identify effects of major parameters like acoustic velocity amplitude, frequency, separation distance and particle diameter both for on-axis orientations as well as arbitrary orientations of the line-of-centers with respect to the acoustical axis. The expressions for the relative convergent velocity were utilized to obtain a so-called agglomeration frequency function. The agglomeration frequency function was used to predict final particle size distributions for both unimodal and bimodal initial size distributions in a pulverized coal combustor. Analysis of results revealed a significant shift of the mean particle diameter from the lower sizes to higher sizes.