准东煤循环流化床气化过程中的矿物质转化行为特性

基于0.25,t/d高碱煤热化学转化热态试验台,利用X射线衍射(XRD)、扫描电镜-X射线能谱(SEMEDX)和电感耦合等离子体-原子发射光谱(ICP-AES)等手段,研究了准东天池木垒煤在煤气化过程中的矿物质转化行为.结果表明,天池木垒煤中含有大量Ca和Na,且主要分别以CaSO_4和NaCl的形式存在,其他矿物质元素多以硅铝酸盐矿物形式存在;在煤气化过程中,Na的硅酸盐是引起底渣聚团的主要原因,K、Mg、Fe、Ca等元素组成的低温共熔体和复合硫酸盐对聚团起低温助熔剂的作用;挥发的Na会在飞灰颗粒表面富集,导致尾部受热面出现积灰沾污现象,同时飞灰中有富Ca絮状物生成.     

氯和灰分对大型燃煤锅炉烟气中汞形态的影响

采用安大略标准燃煤烟气汞采样分析方法,对大型燃煤锅炉出口烟气中汞形态的形成及分布机理进行了研究.分析了煤中Cl、灰分及采样位置对锅炉出口烟气中汞形态分布的影响.结果表明:烟气中的飞灰能够直接影响颗粒汞与气态汞之间的平衡比例;煤中灰分含量越多,锅炉出口烟气中颗粒汞所占比例越大;煤中Cl对气态汞中Hg0向Hg2 形态转变有促进作用;较高的烟气温度和较短的停留时间会严重阻碍飞灰对汞的吸附,影响颗粒汞的形成,同时也会阻碍Cl元素对Hg0的氧化作用.     

污泥与高碱煤协同燃烧中碱金属与重金属竞争机制研究

在CFB锅炉燃烧温度下研究了低品质燃料(高碱煤)与生物质燃料(污泥)协同燃烧中重金属元素Pb、Ni和As的迁移特性。结果表明:燃烧温度对重金属元素热力学平衡分布起到重要的作用,温度越高,Pb、Ni和As在气相中的摩尔分数越高;当温度超过1 300℃时,Pb将全部以单质形态迁移至气相中,在CFB锅炉燃烧温度区间里大部分以PbCl2(g)、少量以PbCl的形态固集于飞灰颗粒上;当温度高于1 800℃时,系统中主要成分为Ni(g);在整个燃烧温度区间,As以单质的形态存在于系统中,其摩尔分数随着温度的升高而上升;碱金属Na主要竞争燃料中的Cl和O元素,实现重金属化合物形态的转化;与Na相比,K的竞争是微弱的,在700℃时K竞争Ni化合物中的CrO_4~(2-),导致NiO摩尔分数下降,而在850℃时,K与Ni竞争系统中的O元素,这与700℃的反应过程不同。     

生物质炉排锅炉飞灰特性及影响因素分析

针对由燃煤锅炉改造的某生物质锅炉燃烧3种特殊燃料时出现的飞灰含碳量较高、有机物附着、阴燃等异常情况进行研究。利用扫描电镜(SEM)观察飞灰微观形貌特征、能谱(EDS)分析其元素组成、X射线衍射分析(XRD)和气相色谱质谱联用(GC-MS)分析飞灰晶相组成及有机物组分,为了分析飞灰中高温下的失重特性,还进行不同气氛下的热重、差示扫描量热(TG-DSC)分析。结果表明:飞灰中含有较高含量的KCl、CaCO_3、K_3Na(SO_4)_2及少量的SiO_2,同时还有一定量的芳香族化合物,并探讨锅炉设计与燃料对飞灰特性的影响,得出由于锅炉缺乏二次风的布置加之燃料高K、Ca、Cl、S,低Si等特性是导致飞灰特性出现的主要原因,并提出一种合理的二次风布置方案。     

O_2/CO_2气氛下鼓泡流化床多粒径煤与生物质混燃模拟

针对6,kW·h鼓泡流化床燃烧室,建立了流化床内煤与生物质混燃燃烧综合计算模型.模型中主要应用基于双欧拉方法的多组分KTGF子模型描述炉内颗粒流动状态,将煤与生物质分为粒径、密度及拟温参量不同的两相进行模拟计算,详细分析了流化床内流场、温度场和燃烧特性.结果表明,流动过程中炉内煤颗粒与生物质颗粒发生轻微分离;生物质颗粒在密相区上部分布较多,煤颗粒在密相区下部分布较多;生物质颗粒在近壁面处分布多于煤颗粒;煤与生物质混燃工况炉内的温度略高于单燃煤工况;炉内温度场及炉膛出口烟气浓度数值模拟结果与实验值吻合较好.     

氧化钙添加剂对烟气中汞分布的影响

在一个大气压下,273．15～l273．15K温度范围里,采用化学热力平衡分析方法研究了煤燃烧过程中CaO和HCl对痕量元素汞的形态及分布的影响。化学热力平衡分析结果表明,在煤燃烧的最高温度区域里,单质汞是汞的主要形式。随着在烟气中温度的降低,单质汞将发生化学反应而生成二价汞的化合物,其中主要是HgCl2(g);预测结果还表明氯元素的增加可以增强汞元素的蒸发、排放,而CaO(s)对汞元素在烟气中的行为特性的影响不大。尽管化学热力平衡分析结果与实验结果之间存在较大差异,但是通过与实验结果的比较,仍可以推断CaO(s)主要是通过减少灰粒表面积或改变飞灰矿物学和形态学特性影响烟气中汞元素分布特性。     

生物质锅炉中温过热器结渣机理研究

针对国内某生物质电厂锅炉中温过热器的结渣问题进行了分析研究.采用X射线荧光光谱仪(XRF)和X射线衍射(XRD)技术手段,在确定灰渣成分和结构的前提下,分析了结渣形成与发展的过程,并在此基础上详细探讨中温过热器结渣机理.研究发现,Si是渣块中含量最多的元素,且渣块中Si的含量比飞灰中的含量高了14%左右,在渣块中主要以硅酸复盐的形式存在;渣块中的碱金属主要是Ca、Al、Fe、K、Mg和Na元素,其中Al、Fe元素含量高于飞灰中的含量,说明其在结渣形成过程中富集,对结渣的形成起很大作用.     

循环流化床锅炉飞灰中碳的形成机理

通过对循环流化床(CFB)锅炉飞灰含碳量分布及飞灰残碳形态的测量、CFB燃烧温度下焦炭失活过程的试验研究以及流化床条件下煤颗粒燃烧过程的分析.探讨了循环流化床锅炉飞灰中碳的形成机理.结果表明:实际运行的CFB锅炉飞灰中含碳量具有明显的不均匀性,残碳集中于25～50 μm的飞灰颗粒内;真实密度和XRD测量均表明,焦炭失活的2个条件是温度和时间,温度高于800℃,焦炭失活开始发生,并且随着时间的增加,失活程度提高;焦炭颗粒长时间停留在主循环回路中,反应活性下降,由于颗粒的碎裂和磨耗,形成了飞灰中粒径较小的残碳;煤中的细小煤粒首次通过炉膛时未燃尽且未被分离器收集,形成了飞友中较大颗粒的残碳.     

循环流化床内污泥与煤混烧时汞的浓度和形态分布

在循环流化床燃烧试验台上进行了污泥与煤的混烧试验,研究了污泥与煤的质量掺混比、燃烧温度、Ca/S摩尔比、脱硫剂种类以及过量空气系数等对重金属汞在烟气、飞灰和炉渣中的形态、浓度分布的影响.结果表明,元素汞是烟气中汞的主要存在形态,运行参数对烟气和灰渣中汞的浓度和形态分布均有较大的影响.     

燃煤电厂飞灰碳含量与PAHs有机污染物吸附量之间相关性研究

以五家燃煤电厂为例,实验分析了飞灰总碳、元素碳、有机碳含量,并与飞灰中多环烃类（PAHs）有机污染物吸附量作了相关分析;此外研究了燃煤排放PAHs与炉前煤中PAHs的关联性,从煤化学、煤燃烧学角度探讨了PAHs的吸附反应机制,提出煤粉燃烧过程中PAHs的一种重要形成机制-未燃碳颗粒及吸附反应机制,指出飞灰中的碳位不仅是PAHs的重要吸附位,同时也是PAHs的重要反应位。     

Investigation on the effects of fly ash particles on the thermal radiation in biomass fired boilers

Ash is produced in combustion of biomass. Some part of this matter is called fly ash and is carried by the flow and causes not only air pollution and erosion, but also can affect the thermal radiation. The effects of fly ash particles on the thermal radiation are considered in this investigation. By analyzing sampled data in an electrostatic filter, a realistic particle size distribution is found. Although the optical data on biomass fly ash are not available, however, similarity between coal and biomass ash compositions showed that the optical constants of the low Fe coal fly ash can be applied for the biomass fly ash. The Mie theory is used to predict scattering and absorption coefficients and phase function. The mean Planck scattering and absorption coefficients and phase function are predicted by averaging over the particle size distribution and Planck function, respectively. The effects of fly ash particles on thermal radiation are evaluated by a three-dimensional test case. It is assumed that the medium is a mixture of non-grey gases and different level of particle loading. Predicted results from the test case showed that the fly ash can be influential on the thermal radiation. In addition, in selected fly ash volume fractions, the effect of scattering by particles is not so important on the radiative heat source and radiative heat flux to the wall whereas their absorption effect is important and can increase the radiative heat source and wall heat fluxes.     

Pretreatment of straw for power production by pyrolysis and char wash

Co-firing of straw and coal in existing pulverised coal-fired boilers is an option for biomass based power generation. However, the high chlorine and potassium content of straw may cause problems. Experiments with co-combustion of straw and coal in power plants have shown that when a moderate amount of straw is applied (up to 20% on a thermal basis), the most serious problems are deactivation of SCR catalysts applied for NO reduction and deterioration of the fly ash quality caused by potassium. To prevent these problems a pretreatment process is required in which the heating value of the straw is supplied to the boiler without introducing potassium into the furnace chamber. A pretreatment process based on pyrolysis and char wash was investigated. Straw is pyrolysed at moderate temperatures at which the potassium is retained in the char. Potassium and residual chlorine are then extracted from the char by water, and char and pyrolysis gases may be co-fired with coal. Fundamental laboratory studies and technical investigations were conducted to evaluate the pretreatment concept. The investigations indicate, that the low temperature pyrolysis of straw can be performed in a circulating fluid bed reactor applying only straw and straw char as bed material. With a bed temperature of approximately 550°C no significant amount of potassium is released to the gas phase. Applying a counter current moving bed to the char potassium extraction with water will probably be advantageous.     

燃煤机组耦合固废焚烧关键技术研究进展

[目的]燃煤与固体废弃物混合掺烧不仅可以实现固废的能量回收利用,也是实现燃煤发电的碳减排的路径之一。[方法]文章综述讨论了燃煤电站掺混固废的研究工作,主要介绍了基于目前主流的电站锅炉为反应器开展燃煤与不同固废掺混的燃烧应用与技术发展;从燃料经济性、混合燃料的飞灰特征、污染物排放以及碳税角度评价燃煤掺混固废的燃烧技术发展;最后讨论了直接掺混和间接掺混的技术的特点。[结果]燃煤直接掺混固废燃烧时需要尽可能减少对锅炉运行的影响,特别是气体污染物的排放以及飞灰对换热面的影响和飞灰无害化处置。间接掺混可以避免混合燃料燃烧对炉膛的影响,但是需要较高的硬件成本投资且耦合技术较为复杂。富氧燃烧技术依旧需要对现有锅炉结构优化来提高该技术的适用性。[结论]直接掺混可实现性与成本优于间接掺混,且循环流化床燃料适应广的特点有利于燃煤直接掺混固废燃烧技术的应用,随着基于循环流化床的富氧燃烧技术的发展将更有利于实现火电厂的碳减排。     

掺烧稻壳对煤粉炉飞灰特性的影响

在某300MW机组煤粉锅炉上进行稻壳掺烧试验,掺烧后飞灰的性质发生变化。对掺烧后锅炉飞灰的微观形貌、化学性质和稻壳灰的孔隙结构等性质进行试验分析。发现:掺烧稻壳后飞灰的物相中出现鳞石英和方石英晶形,飞灰中稻壳灰呈现熔融后块状的不规则颗粒物和黑色的大粒径的不规则片状灰粒,SiO2的含量从掺烧前的55.93%增加到75.05%。利用压汞仪对稻壳灰的孔隙特性进行分析。稻壳和煤共燃的飞灰的利用方式需要重新评估,而分离的稻壳灰可用作多孔材料。     

Distribution of mineral matter in pulverized coal

Mineral transformations, and therefore fly ash evolution, during pulverized coal combustion, depend on the amount, composition and spatial distribution of the inorganic matter within individual pulverized coal particles. Thus, it is necessary to have information on the mineral composition of individual particles, as well as that of the raw pulverized coal. A model is proposed based on the assumption that mineral inclusions of size and composition determined using a CCSEM are distributed randomly in the coal. From this distribution it is possible to generate distributions of mineral content for any particle size and density fraction of coal. The model has been checked by comparing computed results with data on the compositional variations of narrowly and density classified fractions of an Upper Freeport bituminous coal. The results of individual coal particle compositions are used to generate information on the variability of the composition of the fly ash generated during combustion.     

Influence of coal co-firing on the particulate matter formation during pulverized biomass combustion

Biomass is regarded as CO₂-neutral, while the high contents of potassium and chlorine in biomass induce severe particulate matter emission, ash deposition, and corrosion in combustion facilities. Co-firing biomass with coal in pulverized-combustion (PC) furnaces is able to solve these problems, as well as achieve a much higher generating efficiency than grate furnaces. In this work, the particulate matter (PM) emission from biomass co-firing with coal was studied in an entrained flow reactor at a temperature of 1623 K simulating PC furnace condition. PMs were sampled through a 13-stage impactor, and their morphology and elemental composition were characterized by scanning electron microscopy and electron dispersive X-ray spectroscopy. SO₂ emissions were measured to interpret the possibility of potassium sulfation during co-firing. Results show that PMs from the separated combustion of both biomass and coal present a bimodal particle size distribution (PSD). The concentration and size of fine-mode submicron particles (PM_1.0) from biomass combustion are much higher than those from coal combustion because of the high potassium content in biomass. For the co-firing cases, with the coal ratio increasing from 0% to 50%, the PM_1.0 yield is reduced by more than half and the PM_1.0 size becomes smaller, in contrast, the concentration of coarse-mode particles with the size of 1.0–10 μm (PM_1.0-10) increases. The measured PM_1.0 yields of co-firing are lower than the theoretically weight-averaged ones, which proves that during the biomass and coal co-firing in PC furnaces, the vaporized potassium from biomass can be efficiently captured by these silicon-aluminate oxides in coal ash. In the studied range of coal co-firing ratio (≤50 wt.%), the chlorides and sulfates of alkali metals from biomass burning are the dominating components in PM_1.0, and a certain amount of silicon is observed in PM_0.1-1. The analysis of chemical composition in PM_1.0, together with that of SO₂ emission, indicates a marginal sulfation of alkali metal chloride occurring at high temperatures in PC furnaces.     

循环流化床锅炉的飞灰含碳量问题

循环流化床锅炉的飞灰含碳量问题近年来受到关注。对实际运行的多台燃烧各种燃料的220t／h锅炉的飞灰样品测定表明：飞灰的含碳量具有明显的不均匀性。分析了煤质、分离器及运行条件对飞灰含碳量的影响。结果表明：循环流化床锅炉燃烧过程中焦炭反应性逐渐下降;焦炭燃烧过程中发生的爆裂、磨损、失活等行为与煤种有关,对循环流化床锅炉飞灰碳燃尽有很大影响。气固混和不均匀是导致较高的飞灰含碳量的原因之一。图7表2参13     

Characteristics of co-combustion of anthracite with bituminous coal in a 200-MWe circulating fluidized bed boiler

The effect of co-combustion of Vietnamese anthracite with Australian bituminous coal on the performance of a commercial circulating fluidized bed boiler was observed in the Tonghae thermal power plant.The temperature in the cyclone exit of the boiler increased slightly, which caused a decrease in the desulfurization efficiency as the co-combustion ratio of the bituminous coal increased from 40 to 100%. The unburned carbon fraction also increased. Consequently, the fine particles of the bituminous coal had lower combustion reactivity than those of the anthracite.NO_x emissions decreased as the bituminous coal ratio increased, although the fraction of nitrogen in the bituminous coal was higher than that in the anthracite. However, the emission of dust was found to increase due to an increase in the amount of CaO and MgO in the fly ash, which could lower the efficiency of the electrostatic precipitator.From these results, we concluded that the complete switch from the anthracite to Australian bituminous coal was possible, although the efficiency and the operation stability became lower than before. Additionally, as a future study, it is necessary to monitor the instability of the temperature increase and its effect on the prolonged clinker formation in the boiler.     

Effects of calcium chloride and sodium chloride on the flotation removal of unburned carbon from coal fly ash

The effects of calcium chloride and sodium chloride on the coal fly ash flotation were investigated by studying the surface properties of coal fly ash. X-ray photoelectron spectroscopy and scanning electron microscopy showed the presence of many lime particles in the coal fly ash, which, together with Ca(OH)₂(s), could be adsorbed on the rough surface of unburned carbon particles. The flotation results indicated that calcium chloride reduced the performance of unburned carbon removal from the coal fly ash, whereas sodium chloride increased froth stability thereby improving the flotation performance.     

硫铁矿在炉内结渣中所起作用的数值研究

以某台有结渣现象的国产300MW机组的1025t／h锅炉为对象,采用数值模拟对其中硫铁矿和煤粉及其飞灰颗粒的运动进行数值计算,通过对两者在炉内的运动和水冷壁附近颗粒浓度的比较,探讨结渣产生的机理和原因,并对与结渣有关的含硫量、FeS2密度、硫铁矿颗粒尺寸分布、缩小切圆直径的影响进行了数值研究。