【作者】 纪明俊；

【导师】 董众兵；

【作者基本信息】 安徽理工大学 ， 环境工程， 2013， 博士

【摘要】 燃煤颗粒物是大气可吸入颗粒物的重要来源之一,危害人体健康。淮南是我国重要的能源电力基地之一,淮南煤作为高灰熔点煤的典型代表,深入研究其矿物分布特征及其在燃烧过程中的转化行为,探讨配煤、添加剂对淮南煤燃烧细微颗粒物生成的影响,对于研究高灰熔点煤燃烧细微颗粒物生成及排放控制具有重要意义。本文利用计算机控制扫描电镜(CCSEM)分析了高灰熔点煤(淮南煤)的矿物种类、含量、粒度分布,并对内在矿物和外在矿物进行了区分；在滴管炉中分别进行了高灰熔点煤(淮南煤)单煤燃烧、与低灰熔点煤配煤燃烧、淮南煤与添加剂的混合燃烧实验,产生的细微颗粒物用低压撞击器(LPI)进行收集,采用高分辨率透射电子显微镜(HRTEM-EDS)、CCSEM、扫描电子显微镜(SEM-EDS、X射线荧光光谱(XRF)等对收集的细微颗粒物进行分析,考查了高灰熔点煤(淮南煤)单一燃烧无机矿物向细微颗粒物的转化行为,分别探讨了低灰熔点煤配煤、添加剂对高灰熔点煤(淮南煤)燃烧细微颗粒物生成的影响；最后,利用合并-破碎模型,对高灰熔点煤(淮南煤)与添加剂混合燃烧细微颗粒物的粒度分布和化学组成进行了模拟计算。主要内容如下：高灰熔点煤(淮南煤)中矿物主要由高岭石、石英、蒙脱石、未知矿物(成分更为复杂的硅铝酸盐矿物)组成,粘土矿物和石英约占到矿物总量的85%以上,其灰熔融温度大于1500℃。淮南煤中内在高岭石和外在高岭石含量接近,内在石英和外在石英含量也接近；选用的配煤HT煤中高岭石、石英含量相对较少,高岭石和石英约占到矿物总量的60%,而方解石、白云石和黄铁矿含量较高,约占到矿物总量的21%,其灰熔融温度在1278℃左右。矿物颗粒的粒度对燃煤细微颗粒物的形成有重要的影响。淮南ZJ、XQ煤与低灰熔点煤HT煤中<1.0μm的外在矿物含量分别约为5.95%、2.00%、1.86%；淮南ZJ、XQ煤与HT煤中1.0μm-2.5μm的外在矿物含量分别约为15.09%、5.52%、4.44%；淮南ZJ、XQ煤与低灰熔点煤HT煤中<1.0μm的内在矿物含量分别约为3.67%、5.79%、6.20%；淮南ZJ、XQ煤与HT煤中1.0μm-2.5μm的内在矿物含量分别约为13.86%、14.52%、17.29%,矿物颗粒粒度分布的差异进一步表明了煤中不同的矿物分布特征。高灰熔点煤(淮南煤)单一燃烧排放的细微颗粒物有一个双峰分布,大约分别在0.05μm和2.5μm。高灰熔点煤(淮南煤)单一燃烧排放的PM1和PM2.5浓度均高于外地HT煤燃烧排放的PMl和PM2.5浓度,其中淮南ZJ煤燃烧排放的PM1和PM2.5浓度最高,这与淮南ZJ煤中<1.0μm和1.0μm-2.5μm的外在矿物颗粒含量最高有关,一部分细小外在矿物在燃烧过程中可直接转化形成细微颗粒物。高灰熔点煤(淮南煤)燃烧产生的PM1有两种典型的矿物学形态,一是大约由20nm的基本粒子分形聚合形成的粒径≤1.0μm的颗粒,富含易挥发性的元素包括S,P,碱金属元素和少量的难挥发性的元素Si,Fe,由蒸发-冷凝形成；另一种是粒径大约在0.1-0.2μm软化的含Si,A1的单颗粒,由淮南煤中<1.Oμm硅铝酸盐矿物颗粒在燃烧过程中熔融自由释放形成。同样,高灰熔点煤(淮南煤)中一部分1.0μm-2.5μm不纯净的硅铝酸盐矿物也熔融转化形成PN1-2.5\。HT煤富含Ca和Fe,灰熔点较低,在燃烧过程中矿物间的融合降低了PM1和PM2.5的生成。与低灰熔点煤配煤燃烧能减少高灰熔点煤(淮南煤)PM1和PM2.5的生成。S,P,Si和Al从亚微米级颗粒转化到PM1+,减少了PM1排放。Ca、Fe、Al和Si从PM1-2.5转化到PM2.5+,减少了PM1-2.5排放。由于Ca和Fe在混煤中浓度较高,在燃烧过程中产生液相量增加,挥发的S,P更容易粘附到铝硅酸盐的粘性表面,形成超微米颗粒物,减少了PM,生成；液相量的增加,矿物颗粒在燃烧过程中碰撞熔融合并的几率增大,亚微米或微米颗粒的熔融合并生成粗颗粒的钙铝硅酸盐、铁铝硅酸盐和钙铁铝硅酸盐,这样Ca、Fe、Al和Si元素从PM2.5转化到PM2.5+,相应PM1和PM1-2.5排放减少。添加Ca基,Mg基,Fe基添加剂均能有效减少高灰熔点煤(淮南煤)煤PM1和PM2.5的生成。高灰熔点煤(淮南煤)与添加剂混合燃烧,导致矿物高温下熔融产生的液相量增加。在燃烧过程中,高灰熔点煤(淮南煤)中细小的Al-Si颗粒分别与添加的Ca基,Mg基,Fe基添加剂发生了反应,熔融形成相应的钙铝硅酸盐、镁铝硅酸盐和铁铝硅酸盐粗颗粒；同时,熔融的钙铝硅酸盐、镁铝硅酸盐和铁铝硅酸盐的颗粒,能捕获蒸发和冷凝形成的亚微米颗粒物,控制和减少了PM1和PM1-2.5的生成。高灰熔点煤(淮南煤)与添加剂混合燃烧显著影响了细微颗粒物的粒度分布。SiO2和Al2O3有一个单峰分布,可能由煤中难挥发性元素直接转化形成,固体-颗粒的模式控制着它们的转化。CaO在PM1中含量很低,表明Ca的蒸发很少,CaO主要与硅铝酸盐反应熔融进入PMl+；而MgO和Fe2O3呈现多峰分布,说明Fe元素的蒸发同Ca元素相比更高。Fe2O3的转化由两个模式控制,一部分与铝硅酸盐反应熔融进入PM1+,一部分经过蒸发、冷凝进入PM1。对于Mg元素,其存在PM1的原因可能是其蒸气吸附在亚微米颗粒上。基于高灰熔点煤(淮南煤)原煤、高灰熔点煤与添加剂混合样、以及燃烧产生细微颗粒物的CCSEM分析数据,利用合并-破碎模型,对高灰熔点煤(淮南煤)与添加剂混合燃烧细微颗粒物的粒度分布和化学组成进行了模拟计算。预测的结果与实验结果的一致性表明：由于添加剂与高灰熔点煤(淮南煤)混合燃烧,导致矿物高温下熔融产生的液相量增加,内在矿物的平均合并率也呈增加的趋势,从而有效减少高灰熔点煤燃烧细微颗粒物的生成。更多还原

【Abstract】 Particulate matter (PM) having an aerodynamic diameter of smaller than2.5μm and coming from the coal combustion is generally considered to contribute to air pollution and a threat to human health. Huainan city is one of the important energy power base in China. Huainan coal is a typical representative of the high ash fusion temperature coal, it is essential and significantly important to know the mineralogical properties in raw coal. To reduce the PM2.5emissions from coal combustion, a good understanding of the transformation of minerals in the combustion process is required. The mineral composition, size and their association with organic materials in the raw coal samples were analyzed by Computer-controlled scanning electron microscope (CCSEM). Singel Coal、coal blending and coal with additives was burnt in a laboratory-scale drop tube furnace(DTF) respectively. The particulate matter were collected by a Low Pressure Impactor (LPI). PM were analyzed by High-resolution transmission electron microscopy (HRTEM)、CCSEM、Scanning electron microscopy energy dispersive spectroscopy (SEM-EDS) and X-ray florescence (XRF). Properties of fine particulate matter generated from single coal were investigated, firstly. Then, effect of coal blending and additives on fine PM emissions were studied. The particle size distributions and chemical composition of PM2.5were also compared to that predicted by an advanced coalescence and fragmentation model, finally. The main conclusions are shown as below.Huainan coal is rich in kaolinite, quartz, montmorillonite and unknown (a complicated compound containing Si, Al, Ca/Fe, P, and O together). The mineral matter was dominated by clay minerals with quartz(more than85%of the total mineral), The ash fusion temperature(AFT) of Huainan coal ash samples is higher than1500℃, while in the HT coal, only about60%of clay minerals with quartz is found, and there are about21%of calcite, dolomite and pyrite in HT coal,which are beneficial to ash melting (FT=1278℃). The contents of excluded kaolinite are comparable with that of included kaolinite in the Huainan coal, so is quartz. The size distribution of minerals in coal is one of the most important factors in determining ash size during combustion. The content of excluded minerals (<1.0μm) in Huainan ZJ、 XQ coal and HT Coal is approximately5.95%、2.00%、1.86%, respectively, and the content of excluded minerals (1.0μm-2.5μm) in Huainan ZJ、XQ coal and HT Coal is approximately15.09%,5.52%,4.44%, respectively. The content of included minerals (<1.0μm) in Huainan ZJ, XQ coal and HT Coal is approximately3.67%,5.79%,6.20%, respectively, and the content of included minerals (1.0μm-2.5μm) in Huainan ZJ, XQ coal and HT Coal is approximately13.86%,14.52%,17.29%, respectively.It further indicates the different distributions of the minerals in three coals.A bimodal distribution was obtained for the emission of PM10from the combustion of the Huainan coals and HT coal. The large mode is around2.5um and the small one around0.05μm.The amount of PM1and PM2.5produced from Huainan coal is much higher than that from coal HT. The amount of PM1and PM25generated from Huainan ZJ coal combustion is highest among three coals, which is due to the Huainan ZJ coal is riched in fine excluded minerals (<1.0μm and1.0μm-2.5μm) And a small amount of fine excluded minerals might contribute to the formation of fine PM. With regard to the morphology of PM1, it is composed of two typical structures. A portion of particulates, having a diameter<0.1μm, is formed as fractal aggregates consisting of a primary particle around20nm. EDS analysis proves the abundance of volatile metals including S, P, and alkali elements and a small amount of Fe as well. They should be caused by the vaporization-condensation pathway. Moreover, the molten single particles around0.1-0.2μm were also observed, which mainly consist of refractory elements such as Si,Al, and Fe as detected by EDS. Clearly, liberation of the fine minerals and their liquid droplets contributes to the formation of this kind of particles in PM1. PM1.2.5is also the case, liberation of the fine Al-Si minerals(1.0μm-2.5μm) and their liquid droplets contributes to the formation of this kind of particles in PM1.2.5. during the combusting of Huainan coal. For the HT coal, the coalescence among mineral particles reduce the emission of PM1and PM2.5, due to its low ash melting point.HT coal with low ash melting point is mixed with Huaian coal to investigate effect of coal blending on reduction of PM emissions during Huainan coal combustion. The results indicate that emissions of PM1and PM25are reduced compared to their calculated linear results during combustion. The transformation of S, P, Si, and Al from submicron particles to PM1+reduces PM1emissions. The transformation of Ca, Fe, Al, and Si from PM2.5to PM2.5+reduce PM1-2.5emissions. The high concentration of Ca and Fe in coal blends enhances the liquid phase percentage produced during combustion, and as a result, improves both the adhesion of volatilized S, P on the sticky surface of large particles to be transformed to PM1+, and the probability of collision and coalescence of particles to form larger particles of Ca-Fe-Al-Si, Ca-Al-Si, or Fe-Al-Si. Thus, as Ca, Fe, Al, and Si are transformed into PM2.5+.PM1and PM1-2.5emissions are reduced accordingly. PM1and PM25are reduced by two pathways:vapors adhesion to the larger liquid particles and the coalescence among submicrometer mineral particles.The addition of the Ca-or Mg-or Fe-based additives can affect the mineral transformation process, and thus, control the emissions of PM1and PM2.5during combustion. Because the additive is able to reduce the ash melting point via the formation of low-melting eutectic compounds. Several fine Al-Si particles adhering to large Ca Al-Si particles or Fe Al-Si particles or Mg Al-Si particles. These particles derive from the liquid or partial liquid phase according to the shape-related structure. Therefore, the collision of primary particles and their subsequent coalescence is a reasonable agglomeration route for particle growth. The addition of the Ca-or Mg-or Fe-based additive increased the coarse ash fraction and substantially reduced the amount of ash particles smaller than2.5μm (PM2.5). The additive has a pronounced impact on particle size distribution of PM. CaO, SiO2, Al2O3have a single mode distribution, which is prevalent in PM1+, and its low content in PM1implies negligible vaporization of calcium. The transformation of CaO, SiO2,Al2O3was likely caused by the direct transformation of inherent refractory metals within the mixtures. A solid-to-particles pathway governs their transformation. MgO and Fe2O3have a bimodal distribution. The transformation of Fe2O3should be governed by two pathways. A portion of it undergo direct transformation whereas the remaining portion vaporizes and condenses into ultrafine particles. For the MgO, its presence in PM1is likely caused by adsorption of its vapors on the submicrometer particles.The particle size distributions and chemical composition of PM10were also compared to that predicted by an advanced coalescence and fragmentation model during the combustion Huainan coal added with additives. The comparisons indicate that the model can satisfactorily predict ash formation and properties, taking into account both coalescence of included minerals and fragmentation of excluded minerals at high temperature. With the liquidus amount increasing, the average coalescence number of minerals in raw coal and coal mixed with additives increases.更多还原