高氯准东煤中典型矿物元素对颗粒物生成的影响

在高温沉降炉上,进行了高氯高碱准东煤、低氯低碱准东煤和由低氯准东煤处理制得的调质准东煤在含不同浓度HCl的模拟空气中的燃烧实验。利用DLPI进行了颗粒物的分级收集,对其质量粒径分布和矿物元素分布特性进行了讨论分析。结果表明,高氯高碱准东煤的超细模态颗粒物生成量和峰值粒径均明显大于其他两种煤,其主要成分为Na和Cl。Ca的迁移特性与其形态密切相关,原煤中的Ca主要以无机矿物形式存在,主要迁移进入粗颗粒物而对超细颗粒物生成贡献较小。气氛中加入不同浓度HCl气体后,低钠煤和调质煤产生细颗粒物中Cl含量均升高,但生成量无显著变化。表明HCl并未显著促进矿物的气化,但会促进NaCl形式矿物蒸气的形成,进而促进成核形成超细颗粒物。     

高碱煤燃烧过程中亚微米颗粒物PM1的生成特性

高碱煤中通常具有较高的碱金属含量,其是煤燃烧过程中形成亚微米颗粒物PM_1的主要前体。在一维高温沉降炉上,研究了不同反应温度和取样位置对高碱煤燃烧过程中PM_1生成特性的影响,并分析了其质量粒径分布、产量以及矿物元素组成。同时研究了不同反应温度下高岭土对PM_1高效吸附特性。结果表明:随着反应温度的增加,亚微米颗粒物PM_1生成量逐渐降低,颗粒粒径向小粒径偏移。PM_1生成主要受到Na、S等矿物元素的影响,随着温度升高,PM_1中Na、S相对含量降低,Ca、Fe、Si等相对含量增加。硅铝氧化物在高温条件下形成的氧活性位能够高效捕获Na蒸气,进而抑制PM_1生成。PM_1生成特性主要受到高浓度的矿物元素均相成核、异相凝结沉积以及矿物元素蒸气与一些中间产物的相互作用的影响。     

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。     

新疆准东高碱煤流态化气化过程中碱金属的迁移特性

在0.25 t/d高碱煤热化学转化热态实验台上对不同气化温度下神华准东高碱煤中碱金属的迁移分配特性进行了实验研究.结果表明,煤中Na主要以水溶态形式存在,K主要以不溶态形式存在.在不同气化温度下,底渣中的Na含量总体上高于循环灰中,气化温度越高对飞灰中Na,K的迁移分配特性影响越显著,Na,K迁移特性差异明显.在850?1 000℃气化条件下,煤中86.7%?93.1%的Na冷凝富集于飞灰中,主要以Na Cl晶相形态存在.     

H2O(g)对富氧燃烧超细颗粒物生成特性影响

为实现富氧燃烧技术的广泛推广,对煤粉燃烧在富氧气氛下的颗粒物排放特性进行了研究。在1800 K管式炉内进行煤焦燃烧试验,研究了富氧气氛下H₂O(g)体积分数(0、5%、10%、20%、30%)对煤焦燃烧超细颗粒物的影响;采用荷电低压撞击器(ELPI+)获得超细颗粒物质量和数量浓度粒径分布并进行分析。结果表明,H₂O(g)对超细颗粒物质量浓度和数量浓度粒径分布无影响,但会导致超细颗粒物的峰值波动。超细颗粒物总数量由最小粒径超细颗粒物决定,5种水蒸气浓度下EL?PI+第1级撞击器收集到的超细颗粒物数量占比均超过65%。超细颗粒物总质量由最大粒径超细颗粒物决定,5个水蒸气浓度下ELPI+第7级撞击器收集到的超细颗粒物质量占比均超过94%。低H₂O(g)浓度会抑制超细颗粒物生成,H₂O(g)体积分数为5%时的抑制作用最显著;高H₂O(g)浓度会促进超细颗粒物生成。这是因为一方面H₂O(g)与煤焦发生气化反应,使煤焦颗粒周围产生还原性气氛,促进矿物质还原为单质,进一步促进矿物质蒸发;另一方面气化反应是吸热反应,会降低煤焦颗粒燃烧温度,同时H₂O(g)加入也导致烟气热容增加进一步降低,煤焦燃烧温度抑制煤中矿物质的蒸发,导致超细颗粒物生成减少,是2种作用相互竞争的结果。此外,H₂O(g)的加入使超细颗粒物平均粒径增大,0~5%H₂O(g)时超细颗粒物平均粒径增大最迅速。     

1000MW燃煤机组负荷变化对飞灰特性的影响

燃煤机组变负荷调峰运行是提高可再生能源消纳能力的重要举措，但会对燃烧过程及系统产生重要影响。飞灰特性与锅炉结渣、除尘设备性能、颗粒物排放等密切相关，笔者研究了燃煤锅炉负荷变化对飞灰特性的影响规律，用于指导炉膛沾污结渣和颗粒物排放等相关问题的防控。针对1 000 MW燃煤锅炉，在60%和90%运行负荷下分别采集飞灰样品，利用先进的计算机自动控制扫描电镜(CCSEM)技术对飞灰化学和矿物成分、粒径分布以及形状特征进行深入表征，采用数字成像煤灰熔点分析仪对飞灰熔融温度进行分析，揭示了锅炉运行负荷变化对飞灰特性和熔融行为的影响。研究结果表明锅炉在不同运行负荷条件下飞灰化学成分相似。无机矿物元素交互作用是影响飞灰粒径分布的关键因素，低负荷运行工况下煤中含Ca和Fe的矿物与硅铝酸盐交互反应减弱，飞灰整体粒径分布向小粒径迁移，飞灰的D₅₀(小于该粒径的颗粒占50%)由约40μm减至约30μm。相比高负荷运行工况，低负荷运行工况下飞灰在炉膛中的熔融受抑制，熔融飞灰比例相比高负荷运行工况降低约10%,低负荷运行条件下燃烧温度降低是导致飞灰熔融比例降低的主要原因。     

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。     

准东煤高温燃烧过程中含钙矿物质的转化规律

采用3种萃取液（水、醋酸铵和盐酸）对准东煤进行逐级萃取实验,使用高温气氛炉对准东原煤及萃取后的煤样进行燃烧实验,使用电感耦合等离子体原子发射光谱仪和X射线衍射物相分析仪对萃取前后的固体煤样及燃烧后煤灰样品分别进行Ca元素分析和矿物检测。研究结果表明,准东煤中的钙元素主要以醋酸铵溶钙和盐酸溶钙形式存在。在燃烧过程中,准东煤中含钙矿物质与含硅、含铝矿物质反应生成硅钙石、斜硅钙石与钙铝石等;其中经水萃取后碱酸比减小,灰熔融温度升高,盐酸溶钙与含硅、含铝矿物质反应生成硅钙石、硅铝石等,不溶钙主要以稳定的硅铝酸盐形式存在。     

准东煤燃烧过程中钠迁移转化机制研究进展

近年来，中国西部准噶尔盆地发现的大量低阶准东煤田引起广泛关注。准东煤田是中国目前发现的最大整装煤田，已探明储量3 900多亿t,足够供应中国近100 a的煤炭消耗。准东煤具有低灰、低硫、反应活性好、储量大、易开采等特点，是未来煤化工、火力发电的优质燃料。然而准东煤中含有大量碱金属钠，钠在燃烧过程中极易挥发，致使锅炉受热面极易发生沾污、结渣等问题，特别是氯化钠和硫酸钠的迁移会引起一系列灰相关的问题，严重制约了准东煤的大规模、高效清洁利用。综述了准东煤的分布及煤质特征，以及钠的赋存形态及测量方法，详细探讨了钠的内部、外部转化机理，以及煤中无机元素如硅铝酸盐、氯、钙、钾等对钠转化的影响，总结了反应条件如温度、压力、反应气氛、颗粒尺度、添加剂对钠迁移特性的影响。尽管已进行了试验、热平衡计算、模拟等多项研究，但准东煤碱金属释放及迁移引起的灰相关问题仍未从根本上得到解决，对其原因的了解还不够全面，重点回顾研究进展，揭示其形成原因。     

准东煤及其混煤燃烧与结渣特性

准东煤田是我国目前最大的整装煤田,煤质总体呈现中高水分、中高挥发分、低灰、低硫、低磷、中等热值、反应活性好等特点,是大规模煤化工、煤电气联产优质原料。但准东煤中较高的Na、Ca含量影响锅炉正常运行,限制了准东高钠煤的燃烧利用,目前电厂主要通过掺烧低钠煤方式加以利用。为考察准东煤及其混煤燃烧与结渣特性,在五彩湾电厂采集了准东煤(ZD)和乌东煤(WD)等2种原料煤。采用热重分析仪研究30%、50%和80%等不同配比下混煤燃烧特性,并分析响应配比下煤灰特性变化规律。结果表明,准东煤混煤燃烧的DTG曲线有2个特征峰。随准东煤配比增加,混煤燃烧TG和DTG曲线向低温区移动,DTG曲线特征峰更明显;混煤燃烧特征温度逐渐降低,最大燃烧速率与综合燃烧特性指数先降低后升高,混煤灰熔融温度逐渐降低。准东煤相对乌东煤具有较高的碱性氧化物和较低的酸性氧化物含量,准东煤配比越高相应的SO_3、CaO、Na_2O的含量越高结渣倾向性更强。但部分指标并不能准确预测结渣强弱,如准东煤硅铝比为1.67,而乌东煤硅铝比为3.02,依据硅铝比判断结渣倾向性与事实不吻合。另外,煤中CaO含量大于30%后继续增加则灰熔融温度升高,是准东煤比乌东煤具有更高灰熔融温度的原因,随准东煤配比增加,混煤灰熔融温度呈明显降低趋势。燃烧结渣与沾污倾向指标主要有基于煤灰成分和基于煤灰熔融温度的指标,总结分析以往结渣与沾污预测指标结合试验结果认为:基于煤灰成分的碱酸比以及基于煤灰熔融温度的特征温度差值(FT-DT)是判别准东煤及其混煤结渣与沾污倾向性的理想指标。     

Water-soluble chlorine and associated major cations from the coal and mudrocks of the Cannock and North Staffordshire coalfields

Samples of high-Cl coals and their immediate roof, floor and intraseam dirt bands were analysed for major water-soluble ions in order to predict Cl leachability. In organic-poor mudrocks the total CI is as NaCI groundwater solution which is 100% water-soluble. In the coals the absolute water-soluble CI levels are higher, but even with ultrafine grinding 100% extraction cannot be achieved. The relation of the water-soluble Cl to Na in the coarse fractions and Ca in the ultrafine samples suggests different mechanisms of Cl holding and release. Dull coal has a higher water-soluble Cl content that bright coal, which may be explained by the greater size of dull coal pores and greater accessibility of these pores to the groundwaters. The groundwater Cl is Na-associated and leached with relative ease from coarse samples; it accounts for approximately one-third of the total Cl. For ultrafine samples there is a close correlation between water-soluble Cl^?, Ca²⁺, HCO^?₃ and pH. This Cl^? is thought to be combined with the organic matter and released by ion exchange (OH^? for Cl^?), the acidity created being balanced by carbonate solution. Fine grinding is essential to create a maximum surface area for exchange reactions to take place. If the groundwater Cl concentrations are high enough, they may override the total Cl-coal type relationship, but if the water-soluble Cl is leached from coal thus affected, the ‘normal’ relationship of highest total Cl in bright coal and lowest in dull coal holds true.     

秸秆烘焙过程氯、硫释放及AAEMs迁徙转化特性研究

利用固定床管式炉研究了玉米秆中氯、硫、碱及碱土金属（AAEMs）在不同烘焙温度下的释放和迁徙转化规律。研究发现氯、硫的释放率随烘焙温度升高呈递增趋势，在220~300℃范围内氯和硫的释放率分别为10%~40%和27%~60%。烘焙后样品中氯的绝对含量相比原样有所增加，并且以碱金属氯化物形式存在的无机氯占比减少，有机氯占比增加；硫的绝对含量显著降低，烘焙后可达到Ⅰ级成型燃料中硫含量要求。AAEMs在烘焙过程中释放率均较低，但赋存形态发生一定变化，主要表现为水溶性AAEMs含量降低，有机结合态AAEMs含量增加，此外盐酸酸溶性和不溶性Ca、Mg的占比也有一定程度增加。     

Release and transformation characteristics of chlorine,sulfur and AAEMs during cornstalk torrefaction

A fixed-bed tube furnace was used to study the release and migration and transformation of chlorine, sulfur, alkali and alkaline earth metals (AAEMs) in corn stalks at different baking temperatures. It was found that the release ratios of chlorine and sulfur, which increased continuously with temperature in the range of 220—300℃, were 10%—40% and 27%—60%, respectively. However, the absolute content of chlorine increased after torrefaction with the decreased ratio of alkali metal chloride and increased ratio of organochlorine (C—Cl). The absolute content of sulfur decreased significantly after torrefaction, meeting the sulfur requirement of commercial biomass pellets. In addition, the proportion of acid-soluble and insoluble Ca and Mg in hydrochloric acid also increased to a certain extent.     

Effects of chlorine and sulphur on particle formation in wood combustion performed in a laboratory scale reactor

Fine particle formation in wood combustion was studied in a laboratory scale laminar flow reactor at various flue gas chlorine and sulphur concentrations. Aerosol samples were quenched at around 850 °C using a porous tube diluter. Fine particle number concentrations, mass concentrations, size distributions and chemical compositions were measured. In addition, flue gas composition, including SO₂ and HCl, was monitored. Experimental results were interpreted by thermodynamic equilibrium calculations.Addition of HCl clearly raised fine particle mass concentration (PM1.0) which was because of increased release of ash-forming material to fine particles. Especially the release of K, Na, Zn and Cd to fine particles increased. These species form chlorides which apparently increases their volatilization from the fuel. When a sufficient amount of SO₂ was supplied in a chlorine rich combustion (S/Cl molar ratio from 4.7 to 7.5), most of the HCl stayed in the gas phase, release of ash-forming elements decreased and also fine particle concentrations dropped significantly. The sulphation of alkali metals is suggested to play a key role in the observed decrease in the fine particle concentration. It seems that the formation of sulphates leads to alkali metal retention in the coarse particle fraction.     

Importance of coal ash composition in protecting the boiler against chlorine deposition during combustion of chlorine-rich biomass

Experiments were carried out in a pilot scale CFB reactor with Meat and Bone Meal (MBM) blended with three coals. MBM has high Cl content, which produces fouling and corrosion in superheaters. Coal ash contains protective elements (Al, Si and S) that are able to trap alkalies, and the HCl that is released does not condense on superheaters. The goal of the study was to select the most protective coal so that the portion of MBM in the feedstock could be maximised. South African coal, with highest content of reactive aluminosilicate, provided more protection against chlorine deposition than did Polish and German coals. Alkali aluminosilicate formation was the main alkali sequestration path, dominating over sulfation.     

Volatilisation and catalytic effects of alkali and alkaline earth metallic species during the pyrolysis and gasification of Victorian brown coal. Part I. Volatilisation of Na and Cl from a set of NaCl-loaded samples

A set of NaCl-loaded coal samples was prepared by physically impregnating NaCl into a Victorian (Loy Yang) brown coal. This set of brown coal samples was pyrolysed in a thermogravimetric analyser and in a novel fluidised-bed/fixed-bed reactor. The latter reactor has some features of both a fluidised-bed reactor and a fixed-bed reactor. The reactor configuration allowed the volatilised Na to be swept away by carrier gas from the bed of char particles, avoiding the re-condensation of the volatilised Na on the char particles at lower temperatures. The volatilisation of Na and of Cl during pyrolysis was quantified simultaneously. The results indicated that a significant proportion of Cl could be volatilised at temperatures around 200°C. The volatilisation of Cl increased drastically with increasing temperature, from 200 to about 500°C. At higher temperatures with a fast heating rate, Cl could interact with the nascent char to be retained in the char. The volatilisation of Na followed a different trend from that of Cl and increased monotonically with increasing temperature. The loading of NaCl into the brown coal had negligible effects on the total volatile yields and on the volatilisation of Mg and Ca during pyrolysis. It is concluded that NaCl in the brown coal was mainly released as Na and Cl separately rather than as NaCl molecules. Reactions involving radicals play important roles in the volatilisation of Na and Cl.     

Properties of water-soluble and insoluble particulate matter emitted from dewatered sewage sludge incineration in a pilot-scale ash melting furnace

Emission of inorganic particulate matter (PM) from the incineration of dewatered sewage sludge has been investigated in a novel ash melting furnace. The sludge containing 79 wt% water was incinerated in an oxygen-enriched atmosphere at the primary temperature of 1400 °C, and its unburned volatile was combusted at 1100 °C in a secondary combustion chamber. A 13-stage low-pressure-impactor and the conventional impinger methods were employed for PM sampling at the outlet of the secondary combustion chamber. The results indicate that, PM is dominated by volatile and semi-volatile elements including Br, Cl, P, S, Na, K, Zn, As, Cu, Mn and Ni. Less refractory elements were found. PM has two major fractions: <0.22 and ?0.22 μm. Their chemical forms as well as water solubility are different between two fractions. The majority of Br, nearly half of Cl, and 40% of S and P are present in the small fraction. They are mostly water-soluble due to the association with alkali elements and heavy metals. The water-insoluble calcium sulfate and calcium/iron phosphate were, however, found in the large fraction of PM. Regarding the cations, the water solubilities of Na, K, Mn and Ni are close to their proportions partitioned into the small fraction of PM, since their water-soluble species were preferentially formed in this fraction. A relatively weak correlation for Al, Ca and As, while no such a correlation were found for Cu, Zn and Fe, due to the complex compounds formed for them.     

A pilot-scale fireside deposit study of co-firing Cynara with two coals in a fluidised bed

Costs of biofuel production from energy crops can be reduced by applying the crop residues in heat and power production. Perennial herbaceous crops like Cynara cardunculus L. are challenging fuels because they tend to have high ash and chlorine contents. Coals, however, are often rich in aluminium silicates and sulphur, and co-firing of these biofuels with coal could be expected to reduce operational problems. In addition, CO₂ emissions are lower than during coal firing alone. Blends of Cynara and two coals, South African bituminous and Spanish sub-bituminous coal, were combusted in a 20 kW bubbling bed pilot reactor to ascertain the ability of the coals to reduce operational problems by alkali capture. The Cynara fuel sample contained almost 2 wt% chlorine. The South African coal was rich in kaolinite capable of capturing alkalies from chlorides to produce alkali aluminium silicate and HCl. The Spanish coal was rich in sulphur (mostly present as FeS₂), and produced high concentrations of SO₂ that partially oxidised to SO₃. The SO₃ can capture alkalies from chlorides by sulphation. Up to 30% Cynara, on energy basis, could be co-fired with Spanish coal without operational problems, whereas the same percentage of Cynara with South African coal led to strong Cl deposition. Co-firing of Cynara with both coals resulted in high HCl emissions (up to 1500 mg/Nm³ in 6% O₂). In addition, co-firing of the Spanish coal led to very high SO₂ emissions (up to about 16,000 mg/N m³ in 6% O₂). Thus, a power plant capable of firing such blends must be equipped with flue gas cleaning equipment for effective SO₂ and HCl capture in the flue gas channel after the superheaters, or else the quality of the Cynara must be markedly improved by changing the harvesting technology and fertilisers, which could be major sources of high ash and chlorine content in the fuel.     

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。