煤样不同密度组分中致渣矿物特性的CCSEM研究

将一种典型的易结渣烟煤分为低(1.3 g·cm-3)、中(1.3~1.6 g·cm-3)、高(1.6 g·cm-3)3个密度煤样。利用先进计算机控制扫描电镜(CCSEM)技术对原煤及分密度煤样中的致渣矿物进行了深入研究。结果表明,Na与K在煤中无机矿主要以硅铝酸盐的形式存在;粒径大于22μm的外在(独立于炭基质)黄铁矿、磁黄铁矿主要分布在高密度煤中;未识别矿物(复杂硅铝酸盐)在高密度煤矿物中所占的比例最小,但其中Fe含量为20%~90%的颗粒所占比例最高;不同密度煤样中,内在(与炭基质结合)矿的硅铝比和碱酸比不同,低密度煤中内在矿的碱酸比最大,结渣倾向最严重,而中密度煤内在矿的碱酸比和硅铝比均小于原煤。     

准东煤燃烧中矿物质转化行为的CCSEM研究

在沉降炉中进行了准东煤的燃烧实验,利用计算机控制扫描电镜技术(computer controlled scanning electron microscopy,CCSEM)研究了煤中矿物质的转化行为。研究表明煤中主要矿物为方解石、高岭石、含铁类物质以及未分类矿物,燃烧后灰中石英、铁的氧化物、白云石的含量急剧增加,未分类矿物和方解石的含量下降。同时对3种重要致渣元素Na、Fe、Ca在燃烧前后的矿物转化行为及颗粒粒径分布进行了详细研究。     

新疆高钙煤混烧对灰中含钙矿物熔融特性影响

选用一种高钙和一种高硅铝新疆煤,在沉降炉中进行不同比例的混煤和单煤燃烧实验。采用计算机控制扫描电镜(CCSEM)分别对燃烧后总灰矿物成分和粒径分布进行分析。基于CCSEM分析获取单颗粒灰成分数据,采用热力学平衡方法对灰中矿物液相比例进行计算,分析混煤燃烧对灰中含钙矿物熔融特性影响。结果表明,煤中有机结合态Ca极易与煤中其他矿物元素发生交互反应,交互反应后含钙矿物种类取决于煤中内在矿种类。混煤燃烧会促进灰中含钙硅铝酸盐向含钙复杂硅铝酸盐转化,同时促进含钙矿物的熔融。在低温条件下,混烧煤灰中熔融含钙矿物粒径分布受碱金属粒径分布影响;但是高温条件下,混烧促进熔融含钙矿物向大粒径煤灰迁移。     

煤中含铁矿物在煤粉燃烧过程中行为的研究进展

综述了国内外关于煤中煤中含铁矿物在煤粉燃烧过程中行为及其在结渣过程中作用的研究进展,着重对硫铁矿（ＦｅＳ２）菱铁矿和伊利石在燃烧过程中行为的研究结果进行了评述,并指出了这方面值得进一步研究的内容。     

煤粉密度对燃煤过程中颗粒物形成特性的影响

通过浮选实验先将典型烟煤分成高、中、低3个密度段,然后对3种不同密度原煤在沉降炉内进行热解和燃烧实验,研究原煤密度对颗粒物形成机理和特性的影响。实验采用低压撞击器（LPI）把颗粒物按不同粒径大小从0.03～10.0 μm共分13级,分别采集燃烧后的可吸入颗粒物。实验结果显示：低密度原煤对颗粒物形成的贡献最大,中密度次之,高密度最小,低密度原煤所含矿物质粒度最小,形成的焦的膨胀率、总孔体积和BET表面积最大,高密度原煤所含矿物质粒度最大,形成的焦的膨胀率、总孔体积和BET表面积最小,中密度原煤介于两者之间,3种密度原煤燃烧后形成的PM10颗粒物元素构成的相同点是：对于亚微米颗粒物,元素S＋碱金属元素＋其他元素>难熔元素,对于超微米颗粒物,难熔元素占80%以上,远远大于其他三类元素。     

生物质燃烧过程中结渣行为的研究进展

生物质是一种清洁、低廉、可再生的新能源,其利用过程中二氧化碳的排放几乎为零,对于我国实现“双碳”目标具有非常重要的意义。直接燃烧是生物质利用的主要方式之一,然而生物质在燃烧过程中存在的结渣问题限制了其进一步的应用。本文从结渣现象的概念入手,介绍了生物质结渣判别和预测的指标,概述了常见的结渣研究方法和技术,然后从燃料特性、运行条件和锅炉结构等方面重点分析了生物质燃烧过程中结渣行为的影响因素并总结了结渣机理,最后就目前生物质结渣行为研究中存在的问题提出了展望。     

新疆高碱煤四喷嘴气化炉结渣特性研究

针对新疆高碱煤为气化原料造成气化炉堵渣的问题,以四喷嘴气化炉实际运行过程中产生的渣块为研究对象,采用扫描电子显微镜结合X射线电子能谱(SEM-EDX)、X射线荧光光谱(XRF)和灰熔点测试仪等分析了灰渣物化及矿物学特性。对新疆北山煤和牧场煤以及2种煤的混煤进行气化试验,考察了煤中矿物质高温演变行为规律。结果表明,新疆煤中矿物质具有不均一性,在高温热转化过程中,矿物质相互作用发生一系列复杂的物理化学反应,导致形成的矿物质灰渣具有多样性。采用新疆煤为气化原料时,大量灰渣在气化炉渣口处积累,形成了层状灰渣,主要由Na、Ca、Mg和Fe的硅酸盐或硅铝酸盐共熔物和Na-Al-Si-O构成。新疆煤气化后不同形态灰渣中Na含量差别较大,Na含量差异导致矿物质灰渣的黏温特性及固化温度不同。通过热力学模拟发现,Na-Si-O体系中其初始液相形成温度仅为800℃左右,随着Na_2O含量升高,其初始液相形成温度基本保持不变;混入一定量Al_2Si_2O_7后,其液相初始形成温度迅速升高至1 050℃左右。矿物质高温下发生熔融形成组分复杂的共熔物,随温度降低液态灰渣中具有高熔点的矿物质体系将结晶形成晶核,晶核迅速生长形成结晶颗粒而析出。在高温热转化过程,煤中活性Na可与石英黏土类矿物质发生反应生成低熔点的NaAlSiO_4;而Ca、Mg和Fe等与酸性矿物质反应生成具有高熔点的硅铝酸盐矿物质,在降温过程中首先从熔渣中析出,导致堵渣的发生。通过选取或调配煤种的熔渣黏温特性和灰熔融温度与气化运行参数一致可预防煤灰结渣发生。     

粉煤燃烧过程的熔融煤灰在刚玉上的结渣特性

采用光学显微镜、X射线衍射等方法对煤粉气流燃烧过程中在刚玉质耐火板上结渣的渣样进行了测试,并就渣样的形貌及结晶特性、渣样成分与刚玉之间的高温烧结特性进行了分析研究. 结果表明,煤粉气流焦炭颗粒着火燃烧时释放出的CO使焦炭颗粒处于还原性气氛中,降低了灰渣熔融温度,增强了熔融煤灰与耐火板之间的粘结作用;耐火板中的Cr2O3和煤灰中的Fe2O3, CaO, TiO2等晶核剂在煤粉燃烧过程中对刚玉质耐火板上的灰渣结晶程度的影响明显,Al2O3对刚玉质耐火板上熔融煤灰冷却过程的成核结晶作用不明显;灰渣的结晶度较好地反映了灰渣与刚玉质耐火板的粘结作用,在焦炭颗粒着火燃烧区域,煤样I和II灰渣的结晶度最小,分别为49%和32%左右.     

Effects of Xinjiang high calcium coal co-firing on melting characteristics of Ca-bearing minerals in ash

In this study, a high-calcium coal, a high-silicon-aluminum Xinjiang coal and their blends were burnt in a drop tube furnace. The computer-controlled scanning electron microscope (CCSEM) was used to analyze the total ash mineral composition and particle size distribution after combustion. Based on CCSEM analysis, the composition data of single particle ash was obtained. The thermodynamic equilibrium method was used to calculate the liquid phase ratio of minerals in the ash, and the effect of coal blending on the melting characteristics of calcium-containing minerals in the ash was analyzed. The results show that the organically bound Ca easily interacts with other minerals in the coal. The mineral species of Ca-bearing minerals in the bulk ash mainly depend on the included minerals in coal. Co-firing will promote the conversion of calcium-containing aluminosilicate in the ash to calcium-containing complex aluminosilicate, and at the same time promote the melting of calcium-containing minerals. Under low temperature conditions, the particle size distribution of molten calcium-containing minerals in co-fired coal ash is affected by the particle size distribution of the alkali metal; however, under high temperature conditions, co-firing promotes the migration of molten calcium-containing minerals to large particle size ash.     

An investigation on the heterogeneous nature of mineral matters in Assam (India) coal by CCSEM technique

This is a very first preliminary investigation on the distribution of heterogeneous nature of mineral matter in one of the industrially important Assam (India) pulverized coal using computer-controlled scanning electron microscopy (CCSEM). The results show that clay minerals, quartz, pyrite, and pyrrhotite form the bulk of the mineral matter. Minor minerals, such as calcite, dolomite, ankerite, barite, oxidized pyrrhotite, and gypsum, are also observed in the sample. The particle size distribution (PSD) of the included minerals is generally observed to be finer than that of the excluded ones in the coal. As a consequence, the coal rich in included minerals has more small mineral particles, which may affect its reactivity. Regarding the association of individual mineral species, the proportion of included to excluded is found to be higher in major cases. With regard to the modes of occurrence of major inorganic elements, it is found that Si mostly occurs as quartz and clay minerals, while Al mostly occurs as silicate minerals. Fe is primarily present as iron sulfides, iron oxide, and Fe-Al-silicate. S is partitioned into iron sulfides and gypsum. Most Ca occurs as carbonates and gypsum, with a minor fraction associated with clay minerals. Mg is mainly present as dolomite and clay minerals, with a very minor fraction present as ankerite. The majority of alkali elements are associated with aluminosilicates. P is mostly associated with kaolinite and/or present as more complex compounds containing Al, Si, and other elements as apatite is found to be absent in the coal studied. Ti is mainly present as rutile and kaolinite.     

O2/CO2燃烧对神华煤Ca和Fe交互反应影响

选用高Ca、高Fe含量的神华煤,在沉降炉系统中进行空气以及O₂/CO₂燃烧实验。利用X射线荧光探针(XRF)、X射线衍射仪(XRD)、先进计算机控制扫描电镜(CCSEM)分别对总灰元素、晶相组成以及主要矿物元素的共生特性进行深入表征。结果表明氧/燃料燃烧促进了Fe、Ca与其他矿物元素的交互反应,总灰中Fe在Fe-rich类矿物分布减少,而在铁铝硅酸盐(Fe-alsil),尤其是在Fe与Ca发生交互反应的Fe+Ca类矿物的分布增加,同时Ca也存在类似的分布规律。对总灰中Fe+Ca类矿物深入分析发现,氧/燃料燃烧条件下总灰中Fe+Ca类矿物结渣倾向更严重(Fe₂O₃/CaO摩尔比为0.5～3)。     

Flotation and sulphur selectivity of a bituminous coal with different degrees of oxidation

The relation between the surface oxidation of a bituminous coal and its floatability and sulphur selectivity was analysed, using creosote as the flotation agent. The variations in electrokinetic potential and contact angle were found to be poor indicators.     

锅炉全烧准东煤沾污结渣特性分析

针对燃烧新疆准东煤存在结渣、沾污等问题,在新疆宜化150 t/h锅炉全烧准东煤进行实炉测试试验。在全烧准东煤期间,对锅炉炉膛水冷壁、过热器、低温受热面、底渣的结渣形态观测,对以上各部位渣样取样分析。结果显示,锅炉全部燃烧准东煤时存在严重的结渣与沾污问题。结合实验室试验研究及本次实炉测试试验,认为结渣、沾污主要原因是由于煤中钠的氯化物、氧化物、单质气化后形式挥发到烟气中冷凝在高温管壁,与烟气SO_2、Fe_2O_3等化合生成硫酸盐沉积,煤中铁矿石分解后与CaO、Al_2O_3等形成低温共融化合物,降低灰熔融性温度,增加准东煤灰结渣、沉积倾向,煤中高钙、高水分加速了烟气低温段的积灰。     

Experimental investigation of the combustion of bituminous coal in air and O2/CO2 mixtures: 2. Variation of the transformation behaviour of mineral matter with bulk gas composition

Combustion of a Chinese bituminous coal was carried out in a laboratory-scale drop tube furnace (DTF) to clarify the variation of ash properties with bulk gas composition. The combustion conditions tested include three bulk gases, air, 21% O₂/79% CO₂ and 27% O₂/73% CO₂, two furnace/gas temperatures close to the fluidized bed reactor temperature range, 1073 K and 1273 K, and three particle residence times. Apart from bulk properties analysis, individual ash particles and the original mineral species in coal were characterized using Computer - Controlled Scanning Electron Microscopy (CCSEM). The results indicate that, under the given experimental conditions, shifting bulk gas from air to O₂/CO₂ mixtures is insignificant in terms of the elemental composition of bulk ash, in agreement with the literature. However, changes in the properties of individual species/metals are noticeable, including the extent of the vaporization of volatile elements, ash particle-size distribution (PSD), crystallization extent of K alumino-silicate associate, pyrite decomposition and oxidation rate and formation propensity of liquidus in ash. These changes were mostly considered to be caused by the evolution of included mineral grains in the distinct char particles in the O₂/CO₂ environment. Reduction in char particle temperature with bulk gas shifting from air to O₂/CO₂ mixtures was primarily crucial, which, however, could be overweighed by the existence of a fairly strong local reducing condition on the char surface in O₂/CO₂. Consequently, vaporization of the volatile elements such as Na and P was promoted; formation of the crystalline leucite in air was in contrast inhibited. Furthermore, the extent of coalescence of included minerals and oxidation rate of pyrite (or its derivative, pyrrhotite) were also influenced by char consumption rate, i.e. the receding extent of char surface. These parameters exerted a combined effect on ash formation, requiring detailed mathematical modeling to describe the dynamics of the formation of oxy-fuel ash. This study also indicated that the differences of ash properties formed between air and O₂/CO₂ mixtures can be greatly reduced and eventually eliminated by increasing furnace temperature. Increase in the turbulence of gas flow should also benefit the elimination of the side effects of local reducing gases on char surface.     

烟煤与无烟煤混合煤粉燃烧过程的动力学研究

利用热重分析(TGA)方法系统研究了配加烟煤对无烟煤燃烧特性的影响。结果表明:煤粉燃烧主要由3个阶段组成,烟煤配加量和升温速率对燃烧过程有重要影响,随着烟煤配加量的增加,燃烧DTG曲线向低温区移动;实验所用煤种中的主要矿物元素是Si,Ca,Al,Fe,S,P,其中Mg,Zn,K,Na,Cl等含量较低,这些元素主要以氧化物、硅酸盐、碳酸盐、硫酸盐、氯化物和磷酸盐等形态存在,在低温燃烧过程中,矿物质挥发损失量对煤粉燃烧率的影响较小。采用非等温模型Flynn-Wall-Ozawa(FWO)对主要燃烧过程进行动力学分析,当烟煤配加量从0增加到100%时,煤粉燃烧活化能从133.94 kJ/mol降低到78.03 kJ/mol,且烟煤的配加量低于60%时,能够显著降低煤粉燃烧的活化能。     

煤种性质对煤粉工业锅炉结焦的影响

燃煤锅炉内结焦会对锅炉运行的安全性和经济性造成极大损害,因而分析影响燃煤锅炉结焦的因素,进而有效预防燃煤锅炉结焦至关重要。在实际应用中,针对影响燃煤锅炉结焦的不同因素,可采取不同的预防措施。研究发现煤的灰熔融性温度、煤粉颗粒大小、锅炉燃烧气氛、一二次风动力场、锅炉截面热负荷和锅炉热负荷等都会影响燃煤锅炉结焦。为了解决某地区煤粉工业锅炉预燃室、炉膛、对流受热面大面积燃烧结焦问题,笔者结合燃煤锅炉燃烧结焦的机理,先后采取调整燃烧气氛、增大二次风刚性、减小煤粉颗粒粒径、更换孙家岔煤粉等措施对不同条件下的结焦现象进行对比分析,发现煤种、煤粉粒径大小是影响某地区煤粉工业锅炉燃烧结焦的因素。通过SEM-EDS(扫描电镜和能谱分析)对锅炉焦块进行微观形貌与元素组成分析,现场取样锅炉现用煤粉和孙家岔煤粉进行煤质及灰成分对比分析,并根据灰成分进行结渣性判别指标计算,结果表明锅炉燃烧现用煤种灰熔融性温度较低,煤灰软化温度Ts为1 170℃,小于1 200℃,为易熔煤,容易结渣,属于典型的易结焦煤种;结渣性判别指标计算结果显示,4项指标评价为"严重",1项指标评价为"中等",结渣性严重。综合分析认为:锅炉燃烧煤种发生改变,煤的灰熔融温度较低是影响某地区煤粉工业锅炉燃烧结焦的最本质因素。为进一步解决现场实际问题,采取破坏煤灰中酸碱平衡,提升煤的灰熔融温度,配合调节煤粉粒径等措施,如对锅炉现用煤种掺混5%的石英,提高煤灰中Si O2含量,掺混后煤粉的灰熔融温度达到1 280℃,提高了110℃;调大煤粉磨机频率,从19 Hz增大到22 Hz,煤粉粒度(200目,0.075 mm)过筛率从70%增大到85%。经过上述调整后,锅炉运行平稳,结焦状况显著改善,燃烧调整措施取得了较好的效果。