Experimental Studies Of Submicrometer Particle Formation And Control During Pulverized Coal Combustion

Submicrometer particles (PM2.5) are main pollutants to atmosphere in current China. These submicrometer particles would enrich some kinds of trace elements and would do harm to environment when they are emitted into atmosphere. The formation mechanism and control method are chief problems need to be timely solved. Abundant experimental studies are performed in the article to investigate the formation mechanism and control method of submicrometer particles. Two important controlling factors: coal type and temperature are detailed discussed. Also the effectiveness of vapor-phase sorbent injection on suppression the nucleation mode of the ash particles is examined. Finally, the mechanism of As release is primarily experimentally discussed and the distribution of As in slag is predicated by thermodynamic equilibrium simulations.Experiments indicate that percent of submicrometer particles in fly ash is increasing with the increase of temperature; also it increases with the higher content of S in coals. The fly ash particle size distributions are typically bimodal. On the one hand submicrometer fly ash particles are formed by vaporization and nucleation, and they grow by condensation and coagulation. On the other hand submicrometer particles are formed by ash particles detached from the surface of high temperature C particles. These ash particles are formed by congregation, nucleation and agglomeration of melted Si, Al compound, which detach from the surface of C particles by effect of eccentric force and form a large amount of submicrometer particles. An in-suit vapor phase sorbent precursor injection methodology is experimentally testified to be effective in controlling the submivrometer particles. The sorbent is demonstrated to decrease the nucleation rates and increase the resultant mean size of coal combustion aerosol by promoting condensation on agglomerated aerosol particles. However the capture effectiveness of sorbent is affect greatly by temperature, which is to be more validate for titanium sorbent at temperature from 850℃ to 1100℃. Also As can be captured by titanium sorbent effectively at such temperatures. The equilibrium distribution of As in thermal field predicated by thermodynamic equilibrium simulations is in accordance with experimental results, that is the volatility of trace element As would increase with the increasing of temperature during the pulverized coal combustion. At reduced environment the content of As increases from 51.82% at temperature of 1300K to 97.28% at 1600K, while the content of As is only 0.19% in melted oxides. At oxided environment, the content of As in gas at 1300K is 1.48%. It increases to 11.26% at 1400K, and to 68.43% at 1600K, then to 98.70% at 1900K. It can be predicated that at reduced environment approximately 48.48%~2.72% As exists in condensation between 1300K and 1600K.