【作者】 王春梅；

【导师】 张军营； 周英彪； 郑楚光；

【作者基本信息】 华中科技大学 ， 热能工程， 2004， 硕士

【摘要】 超细颗粒物(PM2.5)是目前我国城市大气环境的首要污染物。煤燃烧产生的超细颗粒表面富集了部分痕量重金属元素,进入大气后,对环境的危害更大。超细颗粒物的生成机理和排放控制是我国面临的亟待解决的问题。本文对煤燃烧超细颗粒物的生成机理和排放控制进行了系统的实验研究,探讨煤种和燃烧温度对超细颗粒物生成和排放量的影响,验证钛吸附剂对超细颗粒物生成和团聚的促进作用,以及对煤燃烧过程中痕量元素砷的释放规律和污染性抑制进行了分析。实验结果表明随着燃烧温度的升高,超细颗粒物的排放量是趋于增加的,并且随着S含量的增加,超细颗粒物的排放量也是呈增长的趋势。煤燃烧飞灰粒子的粒度分布呈典型的双峰分布,实验分析发现超细颗粒物不仅是金属元素通过气化成核形成,并通过冷凝和团聚过程长大,还发现超细颗粒物的形成主要是高温的C粒表面,分散的熔融的Si、Al化合物不断聚集,成核、凝聚,在C粒表面形成球形颗粒,随着C粒的不断燃烧,这些表面形成的灰粒在离心力的作用下,从C粒表面脱落,形成大量的超细颗粒物。钛吸附剂可以有效抑制超细颗粒物的生成,这是由于吸附剂在燃烧的高温条件下具有较大的表面积,可以有效地吸附重金属元素蒸气,形成较大粒度的吸附剂-重金属元素聚团。但是吸附剂的效力受温度的影响很大,实验发现钛吸附剂在850～1100℃吸附效果最好,并能有效的控制烟气中As的排放。利用实验和热力学平衡模拟分析了痕量元素As在热场中的转化迁徙规律,模拟结果与实验结果一致,即随着温度的升高,As的排放量增加。在还原气氛下,在1300~1600K温度范围内,As在气相的含量由1300K时的51.82%升高至1600K时的97.28%,而在氧化物熔融体中的含量只有0.19%。在氧化气氛下,在1300K时As在气相中的含量为1.48%,在1400K升高为11.26,在1600K升高68.43%,在1900K时升高为98.79%,而在还原性气氛中1300~1600K可以预测48.48~2.72%的As在凝聚相中。更多还原

【Abstract】 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 <WP=5>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.更多还原