Abstract:

High alkali coal generally has a high alkali metal content, which is the main precursor for the formation of submicron particulate matter PM₁ during coal combustion. However, the alkali and alkaline earth metals (AAEMs), especially Na, result in a large amount of fine particulate matter (PM₁) formation during coal combustion. In this work, two kinds of typical Zhundong coal are selected, namely, ZD-1 and ZD-2. The pulverized coal is burned in an electrical heated drop-tube furnace with different temperature (1273 K, 1373 K, and 1473 K). The mass size distribution and concentration of the particulates are analyzed by low pressure impactor (LPI), and compositions are determined by energy dispersive spectrometry (EDS). The results indicate that the amounts of PM₁ produced by the submicron particles gradually decreases with increasing the reaction temperature. The size of PM₁ shifts to a smaller size. The formation of PM₁ is mainly affected by mineral elements such as Na and S. As the temperature increased, the relative contents of Na and S decreases in PM₁, and the relative contents of Ca, Fe and Si increase. The mass concentrations of Na and S in the collected particles depend upon the particle size, which are proportional to \mathrm{1} / D_{\mathrm{p}}^{\mathrm{0}} for the particle sizes less than 0.4 μm. The PM₁ formation characteristics are mainly affected by the homogeneous nucleation and heterogeneous condensation of high concentrations of mineral elements, and the interaction between mineral elements with intermediate products during combustion. Active sites of oxygen formed by silicon-aluminum oxides at high temperature can efficiently capture Na vapor, thereby inhibiting PM₁ formation. This is one of the main reasons for the reduction of PM₁ at higher temperature.

Key words: coal combustion, alkali and alkaline earth metals, PM₁, precursor, mass size distribution, sorbents

摘要：

高碱煤中通常具有较高的碱金属含量，其是煤燃烧过程中形成亚微米颗粒物PM₁的主要前体。在一维高温沉降炉上，研究了不同反应温度和取样位置对高碱煤燃烧过程中PM₁生成特性的影响，并分析了其质量粒径分布、产量以及矿物元素组成。同时研究了不同反应温度下高岭土对PM₁高效吸附特性。结果表明：随着反应温度的增加，亚微米颗粒物PM₁生成量逐渐降低，颗粒粒径向小粒径偏移。PM₁生成主要受到Na、S等矿物元素的影响，随着温度升高，PM₁中Na、S相对含量降低，Ca、Fe、Si等相对含量增加。硅铝氧化物在高温条件下形成的氧活性位能够高效捕获Na蒸气，进而抑制PM₁生成。PM₁生成特性主要受到高浓度的矿物元素均相成核、异相凝结沉积以及矿物元素蒸气与一些中间产物的相互作用的影响。

关键词: 煤燃烧, 碱金属, PM₁, 前体, 质量粒径分布, 吸附剂