流化床燃烧煤的成灰磨耗特性

循环流化床燃烧条件下，煤的成灰磨耗特性是影响床的流化特性和锅炉整体性能的重要因素之一。将煤在床内爆裂和燃尽引起的尺寸减损和颗粒的磨耗视为相互独立的两个过程，利用静态燃烧然后冷态流化的方法，得到成灰与磨耗参数，提出煤种的本征成灰数据概念，认为煤种的本征成灰数据应视为只与煤种本身特性有关的燃料特性参数，建议将其作为设计循环流化床锅炉的燃料数据。     

生物质与煤混合燃烧成灰特性研究进展

基于能源与环境的双重压力以及生物质与煤单独燃用存在的问题,生物质与煤混燃已成为一种发展趋势.生物质与煤混燃存在的结渣积灰等问题制约着混燃技术的推广利用,因此研究生物质与煤混合燃烧的成灰特性具有现实意义.文章详细介绍了生物质与煤混合燃烧成灰特性的影响因素和分析方法,认为温度是影响生物质与煤混合燃烧成灰特性的主要因素;生物质与煤的混合比例对灰渣成分有一定影响,但二者间不存在明显的线性关系.燃料中的碱金属、氯、硫是引起结渣积灰的主要物质.由于生物质与煤的成灰特性相近,只是灰渣成分的含量差异较大,因此可以利用已有的煤结渣特性研究成果,分析混燃的成灰特性,但须要考虑生物质灰分的特征.     

燃煤的一次破碎_成灰和燃烬特性实验研究

煤的一次破碎、成灰和燃烬特性对循环流化床的物料平衡和燃烧有着重要的影响。本研究通过实验,研究了内蒙褐煤、平朔混煤、朔州贫煤和郑州烟煤的一次破碎、成灰和燃烬特性,给出了各煤种破碎前后、成灰后的颗粒粒度分布和燃烬曲线。计算了各煤质的粒度变化率,得到了能够满足工业预测的煤颗粒一次破碎后的平均粒径的关联式。实验结果显示,不同煤种的一次破碎、成灰和燃烬特性差别较大。挥发分高、灰分低和固定碳含量高的煤种的一次破碎程度高;给煤中粗颗粒质量份额越多,一次破碎程度越高,粒度分布率越小;挥发分较大的煤质,其成灰中的细灰质量份额较大;内蒙褐煤的燃烧速率最大,燃烬时间较短,约为30 min;郑州烟煤的燃烬时间约25 min;平朔混煤和朔州贫煤的燃烬时间约为45 min。     

300MW锅炉掺烧低灰熔点煤种的应用研究

为了研究低灰熔点、高挥发分蔚州煤的可用性,根据灰成分对其灰渣类型、粘度和强度特性进行了分析,得出其结渣性仅为"中等偏强",而非"强结渣".通过在300 MW锅炉上掺烧70%以上蔚州煤,连续满负荷运行184 h的掺烧试验,验证了蔚州煤的结渣特性和可用性.结果表明:煤种结渣性不仅取决于灰熔点,还与粘度特性与强度特性有关;确定新煤种结渣性要排除炉内空气动力场的影响;解决锅炉结渣问题需要根据不同的结渣特点对结渣原因进行分析.     

一种研究飞灰粒径分布和磨耗的简单方法

基于对流化床燃烧条件下煤的成灰磨耗过程的分析,提出了用静床燃烧和振动筛分研究煤燃烧成灰磨耗的简化方法,以代替复杂的流化床热态实验,将该方法的实验结果与冷态流化进行比较,并进行了理论分析,表明该方法与流态化方法是完全相似的,通过这种方法可以方便地得到可靠的流化床条件下的煤燃烧成灰磨耗参数。     

神华煤配煤的试验研究

介绍了选用榆林D矿区神华煤和平朔煤进行配煤试验,通过工业分析、灰熔点和灰成分测试分析研究混煤的灰熔融特性。掺入平朔煤能有效地改变神华煤高钙高铁的灰成分特点,提高神华煤的灰熔点。不同混配比例混煤的沉降炉燃烧结渣试验结果表明,平朔煤能降低神华煤的粘结性、熔融性和结渣趋势,且灰渣易吹落。     

钙基对煤灰熔融特性影响的研究

炉内喷钙脱硫技术增加了烟气的飞灰含量和灰中钙的含量,对煤灰的熔融特性有一定影响.在几种动力用煤中添加钙基吸着剂,对灰渣的成分及其熔融特性进行研究,并对添加钙基吸着剂后的灰熔点进行拟合计算,为添加钙基吸着剂后灰熔点的计算提供一种计算方法.结果表明:不同煤种的含硫成分不同,随着Ca/S的不同,煤灰熔融特性变化也不相同.根据20组试验数据,用回归方法拟合出适合添加钙基的灰熔融特性方程,拟合结果显著性高,既充分证明了不同煤的灰熔融特性随添加钙基的变化不同,又可预测添加钙基吸着剂后灰熔点的变化.     

煤在燃烧过程中灰层有效扩散系数的实验研究与应用

搭建了大颗粒热重实验台,通过测量焦炭反应速率得出有效扩散系数的变化规律.将有效扩散系数的实验拟合表达式应用于整体层燃模型,得到改进的层燃模型,并对改进前后层燃模型的预测结果与实炉测量结果进行了比较.结果表明:不同煤种的有效扩散系数均随着反应的进行而减小,且与灰层厚度之间符合指数关系;煤种和温度是有效扩散系数的重要影响因素,无烟煤的初始有效扩散系数比烟煤的小,有效扩散系数的下降速率比烟煤快;反应温度高于灰熔点时会引起烧结现象,使有效扩散系数减小;考虑灰层生长对有效扩散系数影响的模型可以更准确地预测床层燃烧的气体产物分布和燃烧速率.     

恒温下准东煤粉燃烧特性研究

针对准东煤碱金属含量高导致灰熔融温度低、在燃烧过程中容易造成沾污及结焦等问题,利用恒温热重实验系统,研究了准东煤的燃烧特性及温度、煤种掺混等对燃烧特性的影响。实验结果表明：单煤煤种燃烧过程中,不同煤种燃尽时间、燃烧速率存在显著差异,其中路茂通坎乡煤种和永华金泰煤种差异最大,路茂通坎乡煤种易着火,燃烧速率快,燃尽时间短;随着温度升高,单煤燃烧失重曲线发生左移,燃尽时间缩短,燃烧速率上升,表明温度升高会加速煤粉燃烧,并且1 000℃后提高温度对焦碳燃尽的促进作用更明显;掺混燃烧过程中,掺烧高挥发分的煤种可以有效改善煤粉燃烧初期着火特性,而掺烧高固定碳煤种可使燃尽时间延长,从而降低燃尽率;混煤掺烧能够提高灰熔点,有效改善准东煤熔融特性,从而在煤源方面减少或者避免炉膛受热面沾污、结渣,确保锅炉运行的安全性和经济性。     

煤种对循环流化床焦炭燃烧速率的影响

建立了循环流化床锅炉整体数学模型,模型中考虑了循环流化床锅炉给煤和床料的宽筛分特性,特别在燃烧模型中引入了煤种通用理论,数值分析了煤种对焦炭燃烧反应速率的影响.数值分析得到温度和煤种热态实验的温度吻合良好,改进后的模型能够准确反应不同煤种在不同粒径下的焦炭反应速率.     

不同煤种下循环流化床灰渣特性的试验研究

在一台 0 .5MW的循环流化床燃烧炉上对 4种不同煤种分别进行燃烧试验 ,对燃烧产生的灰渣的分析结果表明了煤种特性如挥发分、灰分和含碳量等对循环流化床燃烧过程的灰渣形成及其排放特性有很大影响 ,并获得了煤中挥发分、灰分及含碳量对底渣粒径及其含碳量、飞灰粒径及其含碳量、飞灰份额及燃烧效率等影响特性 ,对循环流化床锅炉的设计和运行有一定的指导意义。     

Experimental studies of ash film fractions based on measurement of cenospheres geometry in pulverized coal combustion

In pulverized coal particle combustion, part of the ash forms the ash film and exerts an inhibitory influence on combustion by impeding the diffusion of oxygen to the encapsulated char core, while part of the ash diffuses toward the char core. Despite the considerable ash effects on combustion, the fraction of ash film still remains unclear. However, the research of the properties of cenospheres can be an appropriate choice for the fraction determination, being aware that the formation of cenospheres is based on the model of coal particles with the visco-plastic ash film and a solid core. The fraction of ash film X is the ratio of the measuring mass of ash film and the total ash in coal particle. In this paper, the Huangling bituminous coal with different sizes was burnt in a drop-tube furnace at 1273, 1473, and 1673 K with air as oxidizer. A scanning electron microscope (SEM) and cross-section analysis have been used to study the geometry of the collected cenospheres and the effects of combustion parameters on the fraction of ash film. The results show that the ash film fraction increases with increasing temperature and carbon conversion ratio but decreases with larger sizes of coal particles. The high fraction of ash film provides a reasonable explanation for the extinction event at the late burnout stage. The varied values of ash film fractions under different conditions during the dynamic combustion process are necessary for further development of kinetic models.     

Mathematical modeling of gasification of high‐ash Indian coals in moving bed gasification system

Simulation of gasification of high‐ash Indian coal in an updraft moving bed gasification system is presented in this paper. A steady one‐dimensional numerical model, which takes into account of drying, devolatilization, combustion and gasification processes, is used to solve the mass and energy balances in the gasification system. The results from the model have been validated against the experimental data available in literature for various types of coals. The predicted product gas composition, its calorific value and the exit temperature are in agreement with the reported results. The validated model is used to study the effect of input parameters such as oxygen content in air stream, steam flow rates and the pressure of the gasification system. Results indicate that the value of oxygen mole fraction around 0.42 in the oxidizer stream can provide optimum performance in oxygen‐based gasification systems. There is a range of steam‐to‐coal ratio that is dependent on the oxygen content in oxidizer stream. For air‐based systems, this value is around 0.4 and for oxygen‐based systems it is 1.5. The gasification performance improves with operating pressure significantly. An operating pressure of around 8 bar and higher, based on the application, can be used for achieving the required performance with high‐ash coals. The model is useful for predicting the performance of high‐ash Indian coals in a moving bed gasification system under different operating parameters. Copyright © 2013 John Wiley & Sons, Ltd.     

Computer-controlled scanning electron microscopy of minerals in coal-Implications for ash deposition

The nature of mineral matter in coal determines its transformation into ash during combustion and the nature of resulting ash (e.g. chemical composition and particle size distribution), and subsequently influences the ash deposition behaviour. The behaviour of mineral matter is primarily influenced by two parameters: the mineral grain size, and whether the mineral grains are within the coal matrix or not. Computer-controlled scanning electron microscopy (CCSEM) of coal provides such information on mineral matter in coal. CCSEM data are, therefore, processed to predict the fouling and slagging characteristics of several coals. The fraction of basic oxides in each mineral grain may be considered as an indicator of stickiness of the corresponding ash particle due to formation of low melting compounds. The cumulative mass fraction of mineral grains with certain basic oxides or viscosity of resulting ash particles from included and excluded minerals are proposed as alternative indices for ash deposition.

The excluded mineral matter is in equilibrium with the combustion flue gases at the gas temperatures, whereas the included minerals are in equilibrium with the atmosphere within char at the burning char particle temperature. It is predicted from thermodynamic calculations based on this understanding that almost all the evaporation is either from the included mineral matter or from the atomically dispersed minerals in coal. This is due to the high temperature and reducing atmosphere inside the char particle. The release of the evaporated species is controlled by diffusion through the burning char particle and, therefore, may be estimated theoretically. The amount of mineral matter that is vaporized may then be related to fouling, whereas the melt phase present on the surface of large ash particles may be related to slagging. The theoretical speculations on the physical character of ash derived from these indices are compared with the experimental data obtained from combustion of coals in a drop-tube furnace.     

Effects of ash fouling on heat transfer during combustion of cattle biomass in a small‐scale boiler burner facility under unsteady transition conditions

Combustion of cattle biomass (CB) as a supplementary fuel has been proposed for reducing emissions of NO_x, Hg, SO₂, and nonrenewable CO₂ in large coal‐fired power plants; however, its high ash content resulted in fouling and slagging problems when the CB was co‐fired with coals during small‐ and pilot‐scale tests. Ash depositions during combustion of the CB as a reburn fuel were investigated using a 30 kW_t (100 000 Btu h^?1) boiler burner facility with water‐cooled heat exchangers (HEXs) under unsteady transition conditions and short‐term operations. Two parameters were used to characterize the effects of the ash deposition: (1) Overall heat transfer coefficient (U) and (2) Burnt fraction (BF). A methodology was presented and empirically demonstrated for the effects of ash deposition on heat transfer under unsteady transition conditions. Experiments involving ash deposition during reburning the CB with coals were compared with experiments involving only ash‐less natural gas. It was found that the growth of the ash layer during reburning the CB and coals lowered the heat transfer rate to water in the HEXs. In low‐temperature regions, the thin layer of the ash deposition promoted radiation effects, while the thick layer of the ash deposition promoted the thermal resistance of the ash layer. A chemical analysis of the heavy ash indicated that the BF increased when a larger fraction of the CB was used in the reburn fuels, indicating better performance compared with coal combustion alone. However, the results of ash fusion temperature indicated the ash deposited during combustion of the CB and coals was more difficult to remove than the ash deposited during coal combustion alone. Copyright © 2010 John Wiley & Sons, Ltd.     

Movable injection point–based syngas production in the context of underground coal gasification

Underground coal gasification (UCG) has been proven as a viable technology for the generation of high calorific value syngas using deep mine coal seams. The use of multiple injection points/movable injection point method could be an alternate technique for efficient gasification of high ash Indian coals. In this context, the present study is focused on evaluating the heating value of syngas using a variety of gasifying agents such as pure O₂, air, humidified O₂, and CO₂-O₂ dual-stage gasification under movable injection method for high ash coals. It is found that the use of movable injection point method had significantly increased the heating value of the product gas, compared with the fixed point injection method. For high and low ash coal under pure O₂ gasification, the calorific value of syngas obtained using movable injection point is 123.2 and 153.9 kJ/mol, which are 33.5% and 24.3% higher than the syngas calorific value obtained using fixed injection point, respectively. Further, the air as a gasification agent for high ash coals had increased the gross calorific value of the syngas by 24%, using this technology. The results of high ash coal gasification using humidified oxygen at optimum conditions (0.027-kg moisture/kg dry O₂) and CO₂-O₂ gas had enhanced the syngas calorific value by 12.6% and 5%, respectively. Humidified O₂ and CO₂-O₂ gasifying agents produced a high-quality syngas with the calorific value of 190 kJ/mol, among the gasifying agents used. The experimental results had shown that the movable injection point method is found to be a better alternative for the generation of calorific value-enriched syngas using high ash-based Indian coals.     

Influence of coal nature and structure on ash size formation characteristic and related pollutant emissions during CFB combustion

IntroductionOne of the advantages of CFB boiler is its ability touse different kinds of fuels. Theoretically, all types ofcoals may be used in a CFB boiler. Nevertheless, allcoals do not have the same behavior in a CFB boiler.Furthermore, we know now that the size distribution ofcoal particles circulating in a CFB boiler plays a crucialrole in the complicated combustion, heat exchange andpollutant formation mechanisms. Therefore, it is of primeinterest to know better the link between the…     

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.     

Mercury capture by native fly ash carbons in coal-fired power plants

The control of mercury in the air emissions from coal-fired power plants is an ongoing challenge. The native unburned carbons in fly ash can capture varying amounts of Hg depending upon the temperature and composition of the flue gas at the air pollution control device, with Hg capture increasing with a decrease in temperature; the amount of carbon in the fly ash, with Hg capture increasing with an increase in carbon; and the form of the carbon and the consequent surface area of the carbon, with Hg capture increasing with an increase in surface area. The latter is influenced by the rank of the feed coal, with carbons derived from the combustion of low-rank coals having a greater surface area than carbons from bituminous- and anthracite-rank coals.     

Impact of heavy metals in Indian fly ashes on its application as soil ameliorant

Coal contains various organic and inorganic substances including trace quantities of the heavy metals. Therefore, the combustion of coals releases some of the ultimately to the environment of some heavy metals elements in the form of their oxides and in a redistribution of these heavy metals in the surface soil and water bodies, particularly in the vicinity of coal-fired power plants. The fly ash and pond ash of different thermal power stations of India were mixed with soil at different doses separately to compare their impact on crop produce and soil. The present study deals with the presence of the heavy metals in the coal ash and its movement through the amendment of coal ash to the soil and crop produce.