水蒸汽对黄铁矿热转化的影响

发布时间：2019-06-22 19:35

【摘要】：巨大的CO2减排压力导致对氧/燃料燃烧技术的浓厚兴趣,在该技术应用过程中,锅炉受热面的结渣是一个亟待解决的问题。在煤粉燃烧过程中,含铁矿物的转化被认为是影响锅炉受热面结渣的重要因素,黄铁矿作为煤中的主要含铁矿物,其在传统空气燃烧气氛下的转化过程和模型已经有了广泛的研究,但是对其在氧/燃料燃烧方式下转化行为的研究还相当缺乏。相比于传统空气燃烧,在湿式循环氧/燃料燃烧方式下,烟气中高浓度的H2O可能对黄铁矿的转化行为产生重要影响,从而影响到煤灰的结渣行为。因此亟需开展黄铁矿在含水蒸汽条件下转化的动力学过程和机理的研究,以为湿式循环氧/燃料燃烧方式下锅炉的结渣倾向的预测及模型的建立提供重要的理论及实验基础。本文围绕黄铁矿在含水蒸汽条件下的转化行为,利用纯黄铁矿样品在热重反应器上进行了不同工况下的实验研究。首先,进行了不同温度、不同水蒸汽浓度条件下黄铁矿的恒温热重实验,并运用X射线衍射仪(XRD)、X射线荧光光谱仪(XRF)等分析了反应固体产物。结果表明水蒸汽促进了黄铁矿的分解,温度越低,促进作用越明显。随着温度的升高,水蒸汽对磁黄铁矿的氧化作用增强。不同停留时间转化产物的XRD分析表明,黄铁矿先分解生成磁黄铁矿,之后被分步氧化,先生成磁铁矿,随后被水蒸汽继续氧化生成赤铁矿。其次,对黄铁矿分解的动力学过程进行了分析。黄铁矿在水蒸汽气氛下转化的动力学模型和在N2气氛下的相似,先遵循未反应收缩核模型,随着反应的进行,过度到三维扩散模型。但是两个阶段反应的活化能比N2气氛下分别小16.83 kJ/mol和18.51 kJ/mol。最后,研究了黄铁矿在模拟氧/燃料燃烧气氛下的转化过程。发现黄铁矿在3%O2中的转化与在3%O2+20%H2O中的转化不同。O2气氛下先转化生成铁的硫酸盐,再分解氧化生成铁的氧化物,有水蒸汽存在时,黄铁矿直接被氧化为赤铁矿。相同温度下,H2O对黄铁矿分解的促进作用大于CO2,CO2和H2O同时存在时,H2O对其分解的促进作用占主导,而对磁黄铁矿的氧化能力二者相当。H2O/O2/CO2共存时CO2对黄铁矿转化的影响不明显。
[Abstract]:The huge pressure of CO2 emission reduction leads to a strong interest in oxygen / fuel combustion technology. in the process of application of this technology, slagging of boiler heating surface is an urgent problem to be solved. In the process of pulverized coal combustion, the transformation of iron-bearing minerals is considered to be an important factor affecting the slagging of boiler heating surface. Pyrite, as the main iron-bearing mineral in coal, has been widely studied in the transformation process and model in traditional air combustion atmosphere, but the research on its transformation behavior under oxygen / fuel combustion mode is still quite scarce. Compared with the traditional air combustion, the high concentration of H _ 2O in flue gas may have an important impact on the transformation behavior of pyrite under the wet circulating oxygen / fuel combustion mode, thus affecting the slagging behavior of coal ash. Therefore, it is urgent to study the kinetic process and mechanism of pyrite transformation under the condition of steam, so as to provide an important theoretical and experimental basis for the prediction of slagging tendency of boiler under wet circulating oxygen / fuel combustion mode and the establishment of the model. In this paper, based on the transformation behavior of pyrite under the condition of water vapor, the pure pyrite samples were used in thermogravimetric reactor to carry out the experimental study under different working conditions. Firstly, the thermogravimetric experiments of pyrite at different temperatures and different water vapor concentrations were carried out, and the reaction solid products were analyzed by X-ray diffractometer (XRD), X-ray fluorescence spectrometer (XRF) et al. The results show that steam promotes the decomposition of pyrite, and the lower the temperature is, the more obvious the promoting effect is. With the increase of temperature, the oxidation of pyrite by steam increases. XRD analysis of conversion products with different residence time shows that pyrite first decomposes to form magnetite, then is oxidized step by step to form magnetite, and then further oxidized by steam to form hemite. Secondly, the kinetic process of pyrite decomposition is analyzed. The kinetic model of pyrite transformation in steam atmosphere is similar to that in N2 atmosphere. First, the unreacted shrinkage nuclear model is followed, and with the progress of the reaction, the transition to the three-dimensional diffusion model. However, the activation energy of the two stages is 16.83 kJ/mol and 18.51 kJ/mol. lower than that in N2 atmosphere, respectively. Finally, the conversion process of pyrite in simulated oxygen / fuel combustion atmosphere was studied. It is found that the transformation of pyrite in 3%O2 is different from that in 3%O2 20%H2O. The sulfate of iron is first transformed into iron sulfate in O _ 2 atmosphere, and then the oxide of iron is decomposed and oxidized to iron oxide. In the presence of steam, pyrite is directly oxidized to hematite. At the same temperature, the promoting effect of H _ 2O on the decomposition of pyrite is greater than that of CO2,CO2 and H _ 2O at the same temperature, while the oxidation ability of magneto pyrite is the same as that of H _ 2O / O2/CO2. When H _ 2O / O2/CO2 coexists, the effect of CO2 on pyrite transformation is not obvious.
【学位授予单位】：华中科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TD951

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