【作者】 陈军；

【导师】 于敦喜；

【作者基本信息】 华中科技大学 ， 热能工程， 2015， 硕士

【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。更多还原

【Abstract】 Oxy-fuel combustion continues to be of great interest all round the word because of the enormous pressure on carbon dioxide reduction. During the technology is applied to industrial application, ash deposition and slagging is a desiderate problem for coal-fired boilers on the heat exchanger. The transformations of iron-bearing minerals have long been recognized as an important factor for ash deposition and slagging. In further pyrite the main iron-bearing mineral in coal. So lots of studied have been done on the transformation of pyrite and its relationship with ash deposition and slagging under air combustion. The transformation model has also been built under air combustion. However, under oxy-fuel combustion, the transformation of pyrite and its relationship with ash deposition and slagging has little been investigated. Compared to conditional air combustion, high concentration of steam would impact the transformation of pyrite, which will further influence impact the characteristic of deposition and slagging on the heat exchanger. Therefore, it is urgent to study the conversion of pyrite and its mechanism under steam containing atmosphere to offer theoretical and experimental basis for the tendency of ash deposition under oxy-fuel wet recycle combustion.In this work, the conversion behavior of pyrite in steam containing atmosphere is investigated. Pure pyrite is used as raw material on the TGA under different experimental conditions. And XRD and XRF are used to analysis the composition of conversion products and the results show that steam promotes the decomposition of pyrite at lower temperature. With the increasing of temperature, the ability of steam to oxidize pyrrhotine becomes stronger. Pyrrhotine is oxidized to form magnetite first and further to be oxidized to hematite by steam. The kinetic model of pyrite transformation is also investigated and the results indicate that the model that described the decomposition process was shrinking core and three-dimensional diffusion, almost the same with that in nitrogen. But apparent activation energy was 16.83 k J/mol and 18.51 k J/mol respectively lower than that in nitrogen atmosphere. At last, the transformation behavior of pyrite under simulant oxy-fuel atmosphere is studied. It is revealed that the final products of pyrite under 3%O2 and O2/H2 O atmosphere are hematite. But the transformation process is not the same. Under 3%O2 atmosphere, pyrite first to form iron sulfate and then to form hematite(high purity nitrogen as balance gas). While under O2/H2 O atmosphere, pyrite is oxidized to form hematite directly. Steam dominates the promoting of pyrite decomposition under CO2/H2 O at low atmosphere and they have almost the same ability to oxidize pyrrhotine. The effect of CO2 on pyrite transformation is not obvious under O2/CO2/H2 O atmosphere compared with O2/H2 O.更多还原