弱还原性气氛下Fe_2O_3对高灰熔点煤矿物变化行为影响的研究

利用XRD、SEM-EDX分析了添加Fe_2O_3的LNC煤灰在高温弱还原性气氛下的矿物组成、微观形貌及微区化学组成变化情况。结果表明,Fe_2O_3的引入抑制了灰渣中莫来石的生成,高温下含铁矿物的生成及低温共熔降低了煤灰熔点;在高Fe_2O_3添加量下,多余的赤铁矿转化为磁铁矿。在弱还原性气氛中,受CO浓度及渣中溶解[O]的影响,未出现单质铁的析出现象。     

弱还原性气氛下Fe_2O_3对高灰熔点煤矿物变化行为影响的研究

利用XRD、SEM-EDX分析了添加Fe_2O_3的LNC煤灰在高温弱还原性气氛下的矿物组成、微观形貌及微区化学组成变化情况。结果表明,Fe_2O_3的引入抑制了灰渣中莫来石的生成,高温下含铁矿物的生成及低温共熔降低了煤灰熔点;在高Fe_2O_3添加量下,多余的赤铁矿转化为磁铁矿。在弱还原性气氛中,受CO浓度及渣中溶解[O]的影响,未出现单质铁的析出现象。     

Main mineral melting behavior and mineral reaction mechanism at molecular level of blended coal ash under gasification condition

The main mineral melting behavior and mineral reaction mechanism at molecular level of Chinese blended coal ash under gasification condition (30% H₂, 66% CO, 4% CO₂) from 1073 K to 1573 K were studied through the ASTM test, X-ray diffraction (XRD), ternary phase diagram system and quantum chemistry calculation with ab-initio calculations. The results show that with increasing blending mass fraction of low ash fusion temperature (AFT) ash (ash B), the location of blended ash in ternary systems is transferred from the mullite region to the anorthite region, as the dominant crystal mineral of blended ash at around DT (XRD analysis) is also transferred from mullite to anorthite. The calcium-bearing minerals, such as anhydrite, calcite etc., can react with mullite and the precursors of mullite (metakaolinite etc.), which is one of the main refractory minerals in high AFT ash (ash A), and is converted into low-melting minerals (anorthite, gehlenite, and fayalite etc.) in the temperature range between 1273 K and 1403 K. The reaction between mullite and CaO to form anorthite plays a significant role in decreasing AFTs of blended coal ash A/B. It is because the chemical activity of the highest occupied molecular orbits (HOMO) in mullite cluster is stronger than that of the lowest unoccupied molecular orbits (LUMO) in mullite cluster, the Ca²⁺ as electron acceptor can easily enter into the crystal lattice of mullite mainly through O (7) and O (12) and cause the rupture of bonds Al (1)-O (13) (in the [AlO₆]⁹⁻-octahedron) and Al (8)-O (13) (in the [AlO₄]⁵⁻-tetrahedron), which are weaker than any other bonds in crystal lattice of mullite. Finally, the entrance of Ca²⁺ can force mullite to transform to anorthite by the effect of Ca²⁺, and the entered Ca²⁺ is located in the center of [SiO₄]⁴⁻-tetrahedron ring in the anorthite crystal lattice. Taking the [SiO₄]⁴⁻-tetrahedron, which is composed of Si (70), O (78), O (48), O (91), O (86) as an example, the Ca²⁺ can capture the partial electronics of O (86) and cause the bond length (B.L.) of bond Si (70)−O (86) to become longer and unstable.     

Effect of different reaction atmospheres on the sintering temperature of Jincheng coal ash under pressurized conditions

The sintering temperature of coal ash is studied to further understand ash behavior. The objective of this study is to obtain a detailed understanding of the effect of the reaction atmospheres on the sintering temperature under elevated pressure. A series of experiments and analyses have been completed using a pressurized pressure-drop measuring device and X-ray diffractometer (XRD) analyzer. The results show that the sintering temperatures decline markedly under all reaction atmospheres with the rise in pressure. The pressure influences the sintering temperatures by affecting the reaction rate and the mineral transformations undergone by the coal ash, as observed from the XRD patterns. The sintering temperatures measured under the reducing reaction atmospheres are lower than those for oxidizing atmospheres. The sintering temperature under N₂ is lower than those under other oxidizing atmospheres. The sintering temperature under the gasification atmosphere is close to those under H₂ and CO atmospheres, whereas the sintering temperature under a H₂ atmosphere is lower than that under a CO atmosphere.     

Characterization of low-temperature coal ash behaviors at high temperatures under reducing atmosphere

The coal ash obtained at 815 °C under oxidizing atmosphere was further treated at 1300 °C and 1400 °C under reducing atmosphere. The resultant ashes were examined by XRD, SEM/EDX and FTIR. The results show that the residence time of coal ash at high temperatures has considerable influences on the compositions of coal ash and little effect on the amounts of unburned carbon. The amorphous phase of mineral matters increases with the increasing temperature. The FTIR peaks due to presence of different functional groups of minerals support the findings of XRD, and supply additional information of amorphous phase which cannot be detected in XRD. The ash samples generated from a fixed bed reactor during char gasification were also studied with FTIR. The temperatures of char preparation are responsible for the different transformation of minerals during high temperature gasification.     

红外光谱分析淮南煤灰中矿物组成

选取淮南矿区HN115与HN119两种煤样,在氧化性气氛下,制成815℃煤灰。利用红外光谱研究了其矿物质组成以及煤中添加不同比例助熔剂CA后矿物组成的变化。结果表明:淮南煤灰中,矿物质组成为石英、硬石膏、方解石、高岭土和赤铁矿,其中硬石膏和方解石含量较低。煤中添加助熔剂CA后,煤灰中硬石膏含量增加,并且随着助熔剂CA量的不断增加,方解石含量在不断减少,硬石膏含量在不断增加。     

Fundamental ash deposition characteristics in pulverized coal reaction under high temperature conditions

Three types of coal with the different melting temperature and ash content were burned under the condition of high-temperature air pulverized coal reaction. A water-cooled tube was inserted into the furnace to make the ash adhere. Particle size and composition distributions of ash particles in both reacting coal particles and depositing layer were analyzed, using a Computer Controlled Scanning Electron Microscope, to study the deposition behaviors of ash particles. As a result, quantity of the ash deposition on the tube surface increases with a decrease of the melting temperature of coal ash. Index of fraction of the ash deposition depended on the coal type. For structure of the deposit layer, fine particles of size less than 3 μm mainly consisted of the initial layer for three types of coal, and the thickness was about 30 μm. Deposition of fine particulates of about 3 μm became a trigger of initial deposition at the stagnation point of tube even if irrespective of coal type is burned. The chemical compositions of ash particles in the reacting particles differed from those in the initial deposition layer. The deposition phenomenon relates to the particle size distribution of ash formed, the flow dynamics surrounding the probe, the chemical compositions in each ash particle and so forth.     

改性粉煤灰矿物组成变化特性试验研究

以低硫兖州煤为试验煤种,开展了低硫煤增钙粉煤灰矿物组成特性试验研究。试验结果表明：改性粉煤灰矿物组成接近贝利特水泥熟料矿物组成,但矿物组成中没有硅酸盐水泥熟料矿物3CaO·SiO2。     

Oxygen in coal ash: a simplified approach to the analysis of ash and mineral matter in coal

Oxygen was determined accurately in eight U.S. Bureau of Mines coal ash samples A, B, D, F, G, I, and J, NBS coal fly ash 1633 reference material, and two low-temperature ashes (LTA) from lllinois State Geological Survey. The method uses fast-neutron activation (FNA) analysis employing a dual counting and irradiation system which is essentially free from interferences. The stoichiometric balance based on analyses of the ashes performed by the USBM is calculated and summations given in oxide and element percent. Excellent agreement is found with the chemical data obtained by classical silicate analysis methods. Accurate oxygen determination for coal ash and LT-ash (or mineral matter) is important for calculation of data in the ultimate analysis of coal as such. Knowledge is required for recalculation of the data on a dry and dry-ash-free basis. The routinely used ‘oxygen by difference’ values are inadequate for accurate work. In order to determine the organic oxygen in coal one also has to correct for oxygen in mineral matter and oxygen in the water removed as moisture. The Parr formula and other methods of empirical estimation are inadequate and may be replaced in some cases by the oxygen determination. The complete data provide a quantitative basis for stoichiometric interpretation of coal analyses. It was found that the eight coal-ash samples analysed contained 45.5 ± 3% oxygen. Since these ashes represent a large variety of U.S. coals, this figure can be used as an estimate for recalculation and evaluation of the proximate and ultimate coal analyses. It is better, however, to use values actually determined in ash by the rapid fast-neutron activation method. This permits a better estimation of the sum of cations plus sulphates in the ash.     

Temperature effect on the pressure drop across the cake of coal gasification ash formed on a ceramic filter

In order to predict the pressure drop across the cake of coal gasification (CG) ash formed on ceramic filter, an empirical equation was developed taking into account several factors, such as the face velocity, ash load, shape factor and size of particles, and especially the operating temperature. The hot air stream of well classified fine particles of CG ash was simulated as the syngas derived from the coal gasification process. The pressure drop behavior and cleaning efficiency of the filter were carefully investigated within the temperature range from room temperature to 673 K. The pressure drop across the ash cake was dominantly governed by the air viscosity, which increased with temperature. It was well expressed by the previously reported-empirical equation [J.H. Choi, Y.C. Bak, H.J. Jang, J.H. Kim, and J.H. Kim, Korean J. Chem. Eng., 21(3) (2004) 726.] with the modification of the viscosity term in the equation for different temperatures. The residual pressure drop rate across the ash cake also increased while the cleaning efficiency of the ceramic filter decreased as temperature increased.     

粒度对煤灰熔融特性的影响及作用机理初探

利用计算机控制扫描电镜(CCSEM)和5E-AFⅡ型智能灰熔点测试仪分别研究了A和B两种典型煤样的矿物组成及粒径分布和煤灰熔融温度。结果表明,煤灰熔融温度随粒径增大呈直线上升的趋势,当粒径大于100μm时,煤灰流动温度大于1 450℃。A、B煤中高岭石、石英、硅铝酸钾、蒙脱石矿物均以中小颗粒的形式存在,方解石分别以小颗粒、粗大颗粒的形式存在,铁氧化物则反之,且内在、外在矿物颗粒分布存在非均一性,这些是导致煤灰熔融特性产生重大变化的根本原因。     

Kinetics of mineral matter transformation during coal combustion

The transformation of individual minerals was investigated based on TG and DTG analysis at temperature up to 1700 K in inert and oxidizing atmospheres. The decomposition of minerals in inert atmosphere and the reaction with gaseous atmosphere was described by first order reactions for which the kinetic data were found. The evaluated kinetic parameters were then tested on a complex mineral matter of coals. It has been demonstrated on example of two different compositions that the mass loss during the transformation of coal mineral matter during combustion can be modelled as a mixture of individual minerals.     

矿物质对煤转化过程中含氮物迁移的影响

综述了煤本身所固有的矿物质和外来添加物在煤热解、气化过程中的作用,主要针对煤中氮的形态变化和迁移规律进行了讨论.煤中的含氮物在热解气化过程中以HCN、NH3 N2等形式释放于气相产物之中,还是以大分子杂环化合物形式残留于煤焦和焦油之中,煤中固有的矿物质和添加剂对其在各形态间的分配比例具有较大影响.含Fe、Ca等金属元素的化合物是对含氮物迁移转化存在明显作用的代表性物质,同时对Fe、Ca在煤氮催化转化生成N2中的可能机理和在氮氧化物形成之前进行其前驱体的抑制进行了分析.     

高灰分煤煤灰对硅酸盐水泥熟料烧成的影响

通过在水泥生料中掺加不同品质高灰分煤的煤灰,研究了灰分对硅酸盐水泥熟料液相变化、矿物形成及岩相结构的影响.结果表明,灰分含量的升高是降低液相初析温度的主要原因,随着灰分含量的升高,C3S的含量降低,C2S的含量增加.同时,灰分使生料中酸碱矿物比例改变,造成熟料矿物分布的均匀性更差,熔蚀现象更多.     

化学药剂对粉煤灰改性作用的研究

用CaO,Na2CO3,NaOH等物质对粉煤灰进行干、湿法联合改性,并引入热冲击程序,通过XRD衍射分析粉煤灰改性前后的物相变化,研究其改性效果。结果表明：加CaO焚烧-硫酸浸泡和加Na2CO3焚烧所得样品的衍射峰较多;而在加CaO焚烧-酸浸泡中引入热冲击则出现了更多紧密的衍射峰,最终确定用加有CaO高温焙烧,经热冲击后用（1＋4）酸浸泡得到的改性粉煤灰吸附性能较好。     

镇雄煤中含铁矿物在还原性气氛下的转化行为研究

利用超声逐级化学提取法研究镇雄(ZX)煤中铁元素的赋存状态,而后灰化煤样,在还原性气氛下(CO∶N2=160∶40)继续热处理煤灰,制得不同温度下的渣样。借助X-射线衍射(XRD)和带能谱的扫描电镜(SEM-EDX)分析煤、煤灰及渣样的矿物组成和微观形貌。结果显示,ZX煤中的铁元素主要是硫化物结合态铁和铝硅酸盐结合态铁。煤灰中含铁矿物主要是赤铁矿,其含量随温度升高逐渐降低。在还原性气氛中,温度升至900℃,渣样中产生铁单质,1 000℃的渣样中析出陨硫铁。温度达到1 450℃时,渣体系无序性增加,铁质玻璃体是主要的含铁成分。     

镇雄煤中含铁矿物在还原性气氛下的转化行为研究

利用超声逐级化学提取法研究镇雄(ZX)煤中铁元素的赋存状态,而后灰化煤样,在还原性气氛下(CO∶N2=160∶40)继续热处理煤灰,制得不同温度下的渣样。借助X-射线衍射(XRD)和带能谱的扫描电镜(SEM-EDX)分析煤、煤灰及渣样的矿物组成和微观形貌。结果显示,ZX煤中的铁元素主要是硫化物结合态铁和铝硅酸盐结合态铁。煤灰中含铁矿物主要是赤铁矿,其含量随温度升高逐渐降低。在还原性气氛中,温度升至900℃,渣样中产生铁单质,1 000℃的渣样中析出陨硫铁。温度达到1 450℃时,渣体系无序性增加,铁质玻璃体是主要的含铁成分。     

反应气氛对煤热解过程中硫变迁与释放的影响

通过固定床、流化床热解脱硫过程,重点对比分析反应气氛对煤中硫变迁与释放行为的影响.研究结果表明:还原性气氛较惰性气氛和氧化性气氛更有利于煤中硫的释放.较高的热解温度有利于有机硫和硫酸盐硫的脱除,较长的热解时间可以使更多种类的硫发生分解反应.选择合适的热解条件参数是实现煤热解预脱硫、有效提高脱硫效率的关键.     

煤中矿物质对神府煤快速液化的影响

利用共振搅拌反应器研究了煤中矿物质对神府煤高温快速液化的影响。原料煤经酸洗去除煤中大部分矿物质,脱灰率可达84．83％。脱灰后的煤在490℃进行加氢液化,结果表明,煤中矿物质的降低对神府煤高温快速液化有较大的影响,尤其影响了煤的初始高活性,煤转化率及液化产物的产率都降低,且煤中矿物质的降低会使矿物质自催化作用减弱,影响了神府煤液化产物质量。     

The effect of different flotation operating parameters on the froth properties and their relation to clean coal ash content

Froth properties and their relation to the concentrate grade play an important role in monitoring flotation running conditions and predicting flotation concentrate quality. In this paper, the correlation between the froth properties and clean coal ash content was investigated under complicated conditions where the frother dosage, gas velocity, and froth height were changed together. For the froth properties under study, their degree of correlation with clean coal ash content decreased in the order of homogeneity, water recovery, gray value, and froth velocity. The coefficient of determination (R²) of the fitting relationship between homogeneity and clean coal ash content was as high as 0.9028, because homogeneity has a close correlation with the foam structure and foam destabilization behaviors.