污泥与煤泥混燃过程中颗粒物的排放特性及汞成核机理

Emission characteristics of inhalable particles and mercury nucleation mechanism during mixed combustion of sewage sludge and coal washery tailing

为实现城市污泥协同低热值煤泥的高效资源化利用,以单组分污泥、煤泥以及耦合燃料作为研究对象,针对燃烧过程中所生成的可吸入颗粒物,利用多种表征手段及自行建立的流化床实验系统,结合耦合燃料以及燃烧产物的微观特性及元素分布,并基于成核控制理论,在揭示多参数耦合条件下颗粒物排放特性以及粒径分布的基础上,研究混烧条件下Hg在颗粒物表面的成核机理。研究结果表明:样品所含挥发分与矿物质在燃烧过程中存在交互作用,主要包括焦炭、无机矿物质与易气化元素之间的反应,对颗粒物的形成具有较大影响。所生成颗粒物的粒径均呈双峰分布的特征,其中燃烧温度对排放特性的影响存在临界值(800℃)。随着粒径的减小,粗细2种模态颗粒物的分布范围均呈现减小的趋势,且对应峰值均逐渐增大(800℃燃烧条件所对应峰值分别可达3.6%和18.0%)。PM1与PM1~10的组成元素分别主要为易气化元素(如K、Mg、S、Cl和P等)与难熔性元素(如Si、Al、Fe和Ca等)。均相成核和异相凝结是Hg由气相向粒子成核转变的基本途径,并存在不同的成核控制机制,其中异相凝结过程又包含扩散控制与表面反应控制2种机制。

To realize the efficient resource utilization of sewage sludge and low calorific value coal washery tailing,the single-component sewage sludge,coal washery tailing and coupled fuel were selected as the research objects.Aiming at the generated particulate matter during combustion process,using multiple characterization means and the fluidized bed experimental system,the micro-characteristics and elemental distribution of coupled fuel and combustion products were obtained,and the theory based on the nucleation control was analyzed to reveal particulate matter emission characteristics under multi-parameter coupling conditions.The nucleation mechanism of Hg on the surface of the particulate matter under mixed combustion conditions was clarified on the basis of particle size distribution.The results show that the interaction between the volatile and minerals contained in the samples during the combustion process,mainly including the reaction between coke,inorganic minerals and easily gasified elements,has a large impact on the formation of the particulate matter.The particle size of the generated particulate matter is characterized by a bimodal distribution,and the influence of combustion temperature on the emission characteristics has a critical value(800℃).With the decrease of particle size,the distribution range of both coarse and fine modal particulate matter shows a decreasing trend,and the corresponding peaks gradually increase up to 3.6%and 18.0%,respectively,for the combustion conditions at 800℃.The constituent elements of PM1 and PM1−10 are mainly easily gaseous elements(such as K,Mg,S,Cl and P,etc.)and refractory elements(such as Si,Al,Fe and Ca,etc.)respectively.Homogeneous nucleation and heterogeneous condensation are the basic ways for Hg trans formation from gas phase to particle nucleation,and there are different nucleation control mechanisms,among which the heterogeneous condensation process includes diffusion control and surface reaction control.