Effect of coal slag on the wear rate and microstructure of the ZrO2-bearing chromia refractories

The typical properties of slag and refractories for slagging coal gasifier were investigated. In the range of 0–25% CaO/ash, the characteristic ash-fusion temperatures (AFTs) and viscosity of a coal-ash slag decreased with an increase of CaO additive. When the CaO/ash ratio was greater than 25% in the mixture of the coal and limestone, AFTs no longer reduced. The slag viscosity for limestone addition with CaO/ash = 25% was very low and in a narrow range (4–13 Pa.s) at coal gasification temperatures between 1300 °C and 1500 °C. However, corrosion resistance of the ZrO₂-bearing chromia refractories reduced with increasing CaO content in coal slag, especially for a slag with more than 30% CaO content. Increased chromia in three kinds of the ZrO₂-bearing chromia refractories resulted in increased corrosion resistance. The higher the Cr₂O₃ content and the lower the SiO₂ content, the less the deterioration of microstructures in the materials. Thermochemical spalling of the ZrO₂-bearing 80% Cr₂O₃ refractory after 807 operating hours of a coal gasifier was considered as the primary attack mechanism.     

Viscosity of Molten Na2O─B2O3 Slags

The viscosity of sodium borate slags at high Na₂O concentrations (37.3 to 49.4 mol%) and high temperatures (1000° to 1300°C) follows an Arrhenius-type relationship. This relationship was also observed for sodium borate slags (mass% Na₂O/mass% B₂O₃= 0.86) containing CaO and CaF₂ for the same temperature range. There has been a reduction in viscosity of the sodium borate slags (mass% Na₂O₃mass% B₂O = 0.53 to 0.86) with increase in Na₂O concentration. On adding CaO (10 to 50 mass%) to the sodium borate slag (mass% Na₂O/mass% B₂O₃= 0.86), the viscosity increased considerably, while an addition of CaF₂ (S to 15 mass%) to the slag (30.9 mass% Na₂O₃ 35.8 mass% B₂O₃, 33.3 mass% CaO) decreased the viscosity. The average activation energies of Na₂O─B₂O₃, Na₂O─B₂O₃─CaO₃ and Na₂O─B₂O₃─CaO─CaF₂ slag systems have been estimated as 14.6, 124.7, and 41.4 kJ/mol, respectively, for the given composition ranges and 1000° to 1300°C temperature range.     

基于晶体生长及形貌的煤灰渣黏温模型

采用高温热台显微镜研究了非牛顿煤灰渣结晶过程的晶体生长规律及形貌特征,获得不同化学组成煤渣晶体的种类转变和长宽比变化等参数。基于实验获得的晶体生长规律,耦合晶体形貌、长宽比及熔渣固相随温度的变化关系式,修正悬浮液的黏度模型,建立了适用于非牛顿熔渣的黏温预测模型,并与实测黏温曲线对比和验证。该模型考虑了主要析出以单斜晶系或三斜晶系特征的长石类、黄长石、钙长石和镁硅钙石等单相和多相晶体形貌特征,并结合煤渣固相分数（范围0≤?≤0.8）和长宽比（1.0~16.0）等参数修正。结果发现,模型对于煤渣酸碱比范围为0.5~3.0,煤渣硅铝含量总和35%~70%（质量）范围,CaO含量低于30%（质量）、MgO含量为0~10%（质量）以及Fe₂O₃含量范围低于16%（质量）的煤渣黏度预测适用性较好。     

Dissolution of MgO in CaO–"FeO"–CaF2–SiO2 Slags under Static Conditions

The dissolution of MgO in CaO–"FeO"–CaF₂–SiO₂ slags has been studied in the temperature range 1573°–1673° K under static conditions. The concentration profiles of Mg in the product Mg_1-xFe_xO solid-solution layer as well as slag were determined by EDS analysis. From this, the diffusivities of MgO in the slag and the. interdiffusivities in solid solution were estimated. The dissolution of MgO in CaO–"FeO"–CaF₂–SiO₂ slags increased with CaF₂ content.     

CaO/MgO对花岗岩尾矿微晶玻璃物相和性能的影响

以花岗岩尾矿为主要原料(掺入质量分数:56%),TiO₂为主晶核剂,适量Na₂SiF₆为助熔剂和晶核剂,添加部分辅助原料,采用整体析晶法,制备了R₂O-CaO-MgO-Al₂O₃-SiO₂系花岗岩尾矿建筑微晶玻璃。研究了CaO/MgO质量比对微晶玻璃析晶能力、物相、微观结构及性能的影响。结果表明:CaO/MgO质量比的增加有利于增强基础玻璃的析晶能力,当CaO/MgO质量比≤0.88时,微晶玻璃的主晶相为钙长石和角闪石,当CaO/MgO质量比＞0.88时,主晶相转变为钙长石,且钙长石衍射峰的强度随着CaO/MgO质量比的增加而增大;随CaO/MgO质量比的增加,晶体数量逐渐增多,晶粒尺寸增大;微晶玻璃的体积密度和显微硬度随CaO/MgO质量比的增加呈先增大后减小的趋势,当CaO/MgO质量比为0.57时,体积密度达到最大值2.752 5 g/cm³,当CaO/MgO质量比为0.71时,显微硬度达到最大值为8.6 GPa。     

Flow properties of low-rank coal ash slags: Implications for slagging gasification

For predicting satisfactory operation in slagging fixed-bed gasification, a slag should have a viscosity of < 10 Pa s at 1300 °C when measured in a reducing atmosphere. Various phenomena related to slag flow observed qualitatively in pilot plant testing can be explained or predicted from results obtained in the laboratory. Hysteresis between cooling cycle and heating cycle viscosities requires that slag must be reheated well above its initial temperature to resume slag tapping that was interrupted by a temperature fluctuation. A transition from a reducing to an oxidizing atmosphere in the gasifier hearth, such as may be caused by fuel bed bridging, will raise slag viscosity enough to impair or stop flow even in the absence of hearth cooling. Formation of metallic iron by partial reduction of the slag will raise viscosity, but for low-silica slags which give good slagging operation in the gasifier this effect is not usually serious.     

温度对精炼渣碳酸化效果影响分析

为了有效改善精炼渣的安定性及致密性问题,采用正交试验探讨精炼渣碳酸化过程,以温度为单一影响因素,考察碳酸化粒度分布,结合XRD,SEM,FT-IR,TG-DTA等手段对精炼渣碳酸化效果进行探讨。结果表明,精炼渣碳酸化各因素主次关系为:粒径>CO₂通气量>反应温度>转速>液固比;碳酸化后精炼渣中f-CaO、Ca₂SiO₄、Ca₃SiO₅、12CaO·7Al₂O₃消失,CaCO₃晶型增加明显,且以方解石为主;不同温度(20 ℃、40 ℃、60 ℃、80 ℃)碳酸化后精炼渣总的热分解失重百分率分别为:35.26%、35.24%、34.36%和27.29%。     

水泥结合铬刚玉浇注料抗危废炉渣侵蚀行为研究

铬刚玉浇注料是重要的危废焚烧炉炉衬材料之一,但危废来源广泛,成分复杂,导致炉渣的成分存在差异,从而影响炉衬的使用寿命。本文以铝酸钙水泥结合铬刚玉浇注料为研究对象,选取了富含CaO、Fe₂O₃和SiO₂的三种典型危废炉渣,研究了上述危废炉渣对铬刚玉浇注料烧成前后的侵蚀/渗透行为和Cr(Ⅵ)形成的影响。结果表明,材料的抗渣侵蚀和渗透性能与渣的黏度、渣与材料的界面反应以及材料的孔隙结构有关。就渗透性而言,高SiO₂渣和高Fe₂O₃渣与材料界面反应后形成了低熔点的霞石等物相,促进了渣渗透;高CaO渣与材料反应后形成了高熔点的六铝酸钙等物相,减缓了渣渗透,造成渣渗透深度顺序为高SiO₂渣>高Fe₂O₃渣>高CaO渣。相比之下,将材料进行烧成处理可以显著降低基质中CaO的反应活性,而且可以实现微孔化,渣的渗透行为受到抑制,尤其是高SiO₂渣的渗透显著降低。静态坩埚抗渣侵蚀性与渣液的渗透行为有关,由于渣的显著渗透行为,反而降低了渣的侵蚀指数。高CaO渣与试样反应后渣液黏度上升,且生成高熔点的铝酸钙相减缓渣液渗透,渣作用在材料界面时间增长,导致高CaO渣的侵蚀指数略高。     

Effect of Al2O3/CaO on the melting and mineral transformation of Ningdong coal ash

Coal ash melting characteristics has a direct impact on the smooth operation of entrained gasifier. Mineral conversion of coal ash is very significant to be investigated, because the mineral can affect the melting temperature and viscosity under high temperature conditions. In this paper, the effects of different Al₂O₃/CaO on the mineral conversion, melting temperature and viscosity of Ningdong coal ash are studied by the combination of experiment and simulation. The trend of melting temperature decreases firstly and rises with increasing Al₂O₃/CaO. The ash melting point reached to the lowest when the ratio is 1.23. XRD and Factsage software are used to analyze crystallization behavior of samples. The results show that the content of anorthite, albite and corundum increases and subsequently decreases, while the content of mullite decreases firstly and then rises with increasing Al₂O₃/CaO. High content with CaO can contribute to form albite and anorthite of low-melting. Besides, high content with Al₂O₃ can tend to produce mullite of high-melting. The results of experimental and simulation are basically the same, which lays a foundation for the melting characteristics of Ningdong coal ash and can provide technical support for the smooth operation of the entrained-gasifier.     

基于气流床气化炉熔渣结构的黏度预测

在煤气化工艺中,煤灰高温黏度特性是影响熔渣流动特性重要参数之一。以NBO/T、P/M为结构参数,建立熔渣高温黏度预测模型,对结构参数、熔渣黏度的关系进行了研究,并通过文献的实验数据验证了模型的准确性。研究发现随着NBO/T的增大,熔体聚合程度降低,熔体流动时内摩擦力减小,黏度降低;随着P/M增大,熔体结构强度减弱,熔体流动所需要克服的阻力增加,熔渣黏度逐渐升高。引入结构参数后的熔渣黏度预测模型对一定范围内的熔渣黏度具有良好的预测效果,在NBO/T < 0.5时,黏度预测值和实验值误差在10%以内,采用两种结构参数均可;在NBO/T > 0.5时,黏度预测值和实验值误差在25%以内,采用结构参数P/M更合适。     

Crystallization of MgO-CaO-SiO2-P2O5 Glass

The crystallization behavior of a glass with a composition of 40 wt% 3CaO · P₂O₅−60 wt% CaO · MgO · 2SiO₂ was investigated. The primary crystalline phase was apatite with a dendritic form and ellipsoidal shape. β-(3CaO · P₂O₅) and CaO · MgO · 2SiO₂ were crystallized as samples heated to 990°C, and a three-layer structure was obtained. The development and morphology of this construction were explained by both the surface crystallization of the apatite and CaO · MgO · 2SiO₂ and the bulk crystallization of apatite and the CaO · MgO · 2SiO₂-β-(3CaO · P₂O₅) composite.     

碱性氧化物对煤灰熔融特征行为的影响

利用分析纯试剂制备了酸碱比为0.82,但Na₂O、CaO、MgO和Fe₂O₃含量不同的合成灰,并在815℃下在马弗炉中进行灼烧后,对其熔融温度进行测定。同时利用扫描电子显微镜-能谱仪（SEM-EDS）和X射线衍射仪（XRD）对样品微观形貌和矿物组成进行表征。结果表明：随着Na₂O质量分数从4%升高到12%,合成灰变形温度（DT）、软化温度（ST）、半球温度（HT）和流动温度（FT）分别从1225℃、1233℃、1255℃和1297℃下降为1162℃、1174℃、1181℃和1189℃,意味着Na₂O对合成灰具有较强的助熔效果;随着CaO和MgO含量在合成灰中分别增加,DT、ST和HT均单调上升,而FT则呈先下降后上升趋势,说明二者含量变化与合成灰熔融温度呈非线性关系;随着Fe₂O₃质量分数由5%增加至30%,FT由1215℃上升至1308℃,而其他3个熔融特征温度并无显著变化。通过SEM-EDS和XRD表征发现,合成灰中耐熔矿物（SiO₂和CaAl₂Si₂O₈等）和助熔矿物（CaMgSi₂O₆和NaAlSiO₄等）的比例变化和含钠矿物、含钙矿物之间低温共熔反应程度是影响其熔融温度的主要原因。综合对比所有合成煤灰熔融特征温度和化学组成发现,对于具有相同酸碱比的煤灰,DT主要与样品中Na₂O含量和碱土金属总量（CaO+MgO）密切相关影响,而FT主要受Na₂O和Fe₂O₃含量影响。     

Relationship between pore structure and hydration activity of CaO from carbide slag

CaO needs to show high activity to be used as Ca-sorbent and slagging agent. Hydration activity is an important characteristic to evaluate the activity of CaO. In this study, carbide slag from polyvinyl chloride (PVC) industry was utilized as precursor for preparing high activity CaO. The roles of crystallite grain, average pore diameter (APD) and volume fraction of pore < 200 nm in diameter (VF200) in hydration activity of CaO from carbide slag (CS-CaO) were respectively investigated. The hydrolysis kinetics model of CaO shows a three-dimensional spherically symmetric diffusion model (D4), which suggests that hydration activity was mainly associated with APD and VF200 of CS-CaO with limited correlation to the crystal size. Specifically, the hydration activity of CS-CaO is increased with increasing VF200, while decreased with increasing APD. Under the invariable calcination temperature, the core-shell structure formed by the addition of graphite or CaCO₃ to CS effectively inhibits the sintering of CS-CaO and improves VF200. Consequently, the hydration activity of CS-CaO increased from 22.79℃·min^-1 to 27.19℃·min^-1 and to 29.27℃·min^-1, with addition of 5% graphite or 5% CaCO₃ into carbide slag, respectively.     

硅铁还原菱镁矿制镁的热力学分析与实验研究

对硅铁还原氧化镁进行了热力学分析,计算出硅铁还原氧化镁的化学反应自由能和临界反应温度,表明造渣反应和真空条件可使临界反应温度由3846 K降到1358 K. 实验得出还原温度1473 K、10.13 Pa真空度、还原时间1 h及CaO/MgO摩尔比1.4时,镁还原率达94.42%,还原金属镁纯度达98.36%,渣团物相主要为Ca2SiO4和SiO2.     

Liquidus Relationships on 10% MgO Plane of the System Lime-Magnesia-Alumina-Silica

The system CaO-MgO-Al₂O₃-SiO₂ is well known for its importance in many fields of ceramic technology, especially in the field of industrial refractories. The present study, although providing additional data on the liquid phases in basic refractory materials, was undertaken primarily to determine the composition-melting- point behavior of iron blast-furnace slags. About 95% of the composition of blast-furnace slags generally can be expressed in terms of CaO, MgO, Al₂O₃, and SO₂, the additional constituents being FeO, MnO, and S. The MgO content of these slags depends on the type of "stone" used as a flux, which may be essentially pure limestone, dolomitic limestone, or a mixture of limestone and dolomite as determined by economic factors related to sources of raw materials. The amount of MgO usually varies between 2 and 10% in the final slag, and it is often important to know the effect on the melting point of a substitution of MgO for CaO. In the present study one hundred and two glass compositions were prepared for liquidus and in some cases secondary-phase temperature determinations by the quenching method. The investigation was confined chiefly to the central part of the plane adjacent to the lime-silica-magnesia face of the tetrahedron. Primary fields of s'lica, diopside, anorthite, pseudowollastonite, cordierite, melilite, spinel, mullite, merwinite, dicalcium silicate, periclase, and corundum were encountered in the course of the work. Liquidus temperatures ranged from a minimum of 1230°C. at the diopside-anorthite-tridymite intersection to a maximum of about 1650°C. in the dicalcium silicate field, which was the upper safe limit for the equipment. Petrographic and X-ray diffraction methods were used to identify phases.     

Shell气化炉中灰渣的熔融特性与流动特性

分析了Shell气化炉中灰渣的物理性质,同时利用灰熔点测定仪、高温黏度计测定了添加适量助熔剂CaO的灰渣熔融温度和黏度,并利用热力学软件FactSage计算了灰渣在不同温度下对应的固液相的相对含量及全液相温度。研究结果表明：由于灰渣中主要结晶矿物中熔点较高矿物质如莫来石的含量在不断减少而熔点较低矿物质如钙长石的含量在不断增加,使得灰渣的熔融温度随着CaO含量的增加先降低而后升高。同时从灰渣的微观结构中可知,随着CaO含量的增加,灰渣的液相区面积先增大而后减少,这使得气化炉的最低排渣温度和高温下的灰渣黏度也随着CaO含量的增加呈先降低而后升高的变化趋势。同时由热力学软件FactSage计算出的灰渣全液相温度和相对固含量随CaO含量的变化趋势与灰渣的熔融温度、黏度的变化趋势一致。     

Effect of Glass Composition on the Dielectric Properties of a Liquid-Phase-Sintered MgO-Doped BaTiO3

A series of BaTiO₃–MgO–glass mixtures has been sintered via liquid-phase sintering in a reducing atmosphere at 1280°C by controlling MgO/CaO ratio in an aluminum borosilicate glass composition, and the subsequent microstructure, phase evolution, and dielectric properties have been investigated. The growth of BaTiO₃ grains was inhibited in all of the prepared specimens with the evidence of Mg incorporation to the BaTiO₃ lattice from the glass. The change in MgO/CaO ratio in the glass notably modified the dielectric properties: a high MgO/CaO ratio in the glass resulted in a decreased dielectric constant, a decreased phase transition temperature, a broadened temperature range of phase transition, a decreased temperature coefficient of capacitance, and increased electrical resistivity.     

新疆淖毛湖煤中钠在CO2气化过程的迁移行为

针对新疆淖毛湖煤矿煤中Na含量高,在气化过程中可能会导致气化炉内壁腐蚀、沾污等问题,本文通过开展实验室气化实验和Factsage热力学模拟实验,研究了淖毛湖煤中钠在CO₂气化过程时的迁移行为。通过热重实验研究了淖毛湖煤的气化反应特性;利用扫描电镜-能谱（SEM-EDS）、X射线衍射（XRD）及电感耦合等离子体-原子发射光谱（ICP-OES）等手段,对淖毛湖煤在800～1100℃下CO₂气化条件下得到的残渣进行了分析表征,研究了不同温度下得到的残渣形貌以及残渣中Na的赋存形态、含量变化等;同时,结合化学热力学平衡计算方法,研究了CO₂气化过程中淖毛湖煤中Na在气相中的分布情况,分析了气化过程中Na的析出特性。结果表明,在一定的反应时间内,随着气化温度的逐渐升高, 在温度为900~1100℃下淖毛湖煤中Na的析出量逐渐增加。在煤气中钠元素主要以NaCl（g）、NaOH（g）和Na（g）的形态存在,这部分形态的Na随着煤气排出而未富集于残渣中。800℃时残渣中主要成分为CaCO₃,当气化温度高于900℃时,残渣开始熔融,且随温度的升高残渣中共熔物增加。当温度在800～1100℃时,淖毛湖煤中Na主要以硅铝酸盐的形式存在。     

制备高品质磷石膏的湿法磷酸新工艺的开发

采用三级磷酸逆流萃取,然后加硫酸结晶的方法制备出高品质的磷酸和磷石膏。利用单因素实验法考察了温度、液固比、反应时间以及硫酸的用量对P₂O₅和各杂质萃取率的影响;通过实验确定最佳反应温度90℃,最佳反应时间2h,最佳液固比12:1,第三级硫酸的最佳用量为1.2%;萃取率达到98%以上;产品磷酸中的杂质CaO、Al₂O₃、Fe₂O₃、MgO含量分别下降到0.29%、0.11%、0.24%、0.431%;制备出白色的磷石膏,所得石膏采用水热法制备出晶形好和长径比较大的晶须;此法能运用到其他低品位的矿,适应性强,能够实现经济附加值,有广阔的推广前景。     

Na2O-TiO2-SiO2-CaO-Al2O3-V2O5-MnO-MgO-FeO渣系渣铁间硫分配比热力学模型

基于离子分子共存理论(IMCT)建立了Na₂O-TiO₂-SiO₂-CaO-Al₂O₃-V₂O₅-MnO-MgO-FeO九元渣系的结构单元作用浓度模型和渣铁间硫分配比热力学模型,并对模型进行实验验证。通过模型计算出1200℃下渣系主要结构单元组成和渣中Na₂O,CaO,MnO,MgO和FeO的活度,发现Na₂O的加入可促进渣中低熔点物质的生成,降低渣系熔化性温度,改善脱硫反应的动力学条件;同时随着Na₂O加入量的增加,渣中Na₂O和CaO的活度增加,进而降低渣中S^2?离子活度,强化渣铁间脱硫反应。实验结果表明,增加碱矿比提高了渣铁间硫分配比,有利于铁水深度脱硫,铁水中硫含量可降至0.0005wt%以下,硫分配比的理论计算值与实验结果吻合极好。渣中各碱性氧化物的硫分配比随碱矿比R_N/C增加逐渐增大,各碱性氧...