Fouling propensities of blended coals in pulverized coal-fired power station boilers

This paper presents the experimental results on the fouling propensity of five pairs of blended coals (19 coals and blends) tested in the Australian Coal Industry Research Laboratory (ACIRL) furnace. The results showed that the coal D has the highest fouling propensity among tested coals and blends. A parameter, growth rate (mm/h), is used to numerically rank the fouling propensity based on photos of fouling deposits taken over a period of test time. The growth rate correlates the fouling propensity better than the build up rate or the fouling coefficient. Five empirical fouling indices are examined against the fouling propensities of the above 19 coals and blends, and another 10 coals and blends previously tested in the Energy and Environmental Research Cooperation (EER) furnace. The linear correlation between the flue gas exit temperature/initial deformation temperature (FGET/IDT(ox.)), a measure of the overall heat transfer in the furnace, and the Na₂O, g/GJ, is proved to be a good tool for predicting the fouling propensity of coals. There is also a relationship between the FGET and the growth rate.     

Modification of boiler operating conditions for mercury emissions reductions in coal-fired utility boilers

US EPA's studies have determined that mercury emissions from coal-fired power plants pose significant hazards to public health and must be reduced. Coal-fired power plants represent a significant fraction of the anthropogenic emissions of mercury into the atmosphere. Mercury emissions are impacted by factors such as coal type, boiler operation, fly ash characteristics and type of environmental control equipment installed on the unit. Field data show a wide variation in the fraction of mercury that is emitted in the gaseous phase, as elemental and oxidized mercury vapor, and as particulate-bound mercury. Oxidized mercury is a preferable species because is less volatile at stack temperatures, water-soluble, and tends to interact with mineral matter and char, and cold-end air pollution control devices. There is also evidence that boiler-operating conditions could be used to influence mercury behavior in the boiler, since they affect the thermo-chemical conditions for mercury formation and reduction. However, operation of boiler control settings, which result in mercury removal benefits, should also consider the tradeoff between mercury reduction and other emissions (for example, NO_x and CO), the level of unburned carbon in the fly ash, unit efficiency and the performance of particulate control equipment.This paper reports fieldwork performed to investigate the feasibility of affecting mercury emissions from coal-fired plants by manipulating boiler control settings. Full-scale testing was performed at two units. One of the units is equipped with a back-end train that includes a rotary air preheater followed by two electrostatic precipitators in series. The other unit is equipped with hot and cold precipitators and a tubular air preheater. A strategy for mercury control by selectively manipulating boiler control settings, if used in combination with other control measures such as sorbent injection, should provide a cost-effective option for mercury control.     

Monitoring and prediction of fouling in coal-fired utility boilers using neural networks

This paper describes a systematic approach to predict ash deposits in coal-fired boilers by means of artificial neural networks. The approach is of a “grey box” nature, decomposing the problem into logical parts, and avoiding the use of sophisticated data. Although it is relative to the specific fuel and equipment, the prediction is very detailed and can be used on-line; it accounts not only for the deposition rate, but also for short-term cleaning occurrences, thus simulating a complex and chaotic time-evolution. The model is developed with the aid of a case-study, that of the fouling of a furnace, as detected by heat flux meters. Provided that an adequate amount of heat transfer measurements can be gathered, the procedure can be used to simulate the evolution of boiler heat absorption under realistic conditions of deposition. Applications include obviously new possibilities for automatic control of the equipment, as well as the optimization of operating set points to maximize thermal efficiency, such as the sequence and operation of on-load cleaning devices. It is thought that the method developed would be applicable to other instances of fouling or equipment degradation exhibiting similar behavior, specially with respect to on-line corrective measures.     

外甩油浆温度高的要因分析和对策

介绍了应用MIP技术改造后催化裂化装置外甩油浆温度高的要因和对策。工业实施表明,通过平稳原料和操作、提高外甩油浆流速和合理选择冷却介质和冷却温度等对策,能够将外甩油浆温度由高于110℃、超出工艺指标上限,降低到85℃左右、在工艺指标范围内,满足了装置安全生产的需要。     

Further study of the gas temperature deviation in large-scale tangentially coal-fired boilers

Gas temperature deviation in upper furnace is an important but a less reported issue in large-scale tangentially fired boilers, since they endanger largely boilers operation. Simulations are conducted in this paper to study the deviation. Perfect agreement between the simulation results and key boiler design values and available site operation records indicates that the calculations are reliable. Based on the simulations, effect of some factors, including residual airflow swirling at furnace exit, super-heaters panels, coal particle trajectories and their combustion histories, on temperature deviations are studied in details. The most important cause and how it affects the temperature deviation are located. Two new methods, a nose on front-wall and re-arranged super-heater panels, are put forward unprecedentedly to alleviate the deviations.     

关于燃气加热炉低温腐蚀的原因与对策

低温腐蚀是困扰燃气加热炉安全运行与炉效提高的主要问题。以某石化公司120万t/a焦化加热炉为例进行了换热计算和腐蚀原因分析,提出了以下改进方法:①提高脱硫工艺温度,降低燃料中的H2S含量;②增加吹灰器;③降低烟气中的水含量;④调整好烟道挡板的位置;⑤控制烟气酸露点温度。     

粗苯低温气相加氢结焦原因分析及对策

介绍了粗苯低温气相加氢易发生结焦的部位。通过工艺参数判断结焦堵塞情况,并对结焦原因做了分析,提出了针对性的措施。通过增加预处理装置和加入阻聚剂以及加强生产管理,能够极大缓解结焦进程。     

Computational modeling of furnace sorbent injection for SO2 removal from coal-fired utility boilers

Furnace sorbent injection (FSI) is used to remove SO₂ formed during coal combustion by injecting sorbent into the high temperature zone of a furnace above the fireball. FSI is cost effective for older coal-fired boilers, especially when space or capital budgets are limited. To optimize the design and performance of FSI, an SO₂/sorbent modeling scheme that simultaneously considers calcination (or dehydration), sintering, and sulfation has been developed and implemented. It is coupled with a three-dimensional combustion model based on computational fluid dynamics to determine the most desirable locations for sorbent injection and to optimize the amount of sorbent needed to achieve a targeted SO₂ removal efficiency. A sensitivity analysis was conducted to determine the effect of flue gas temperature, particle diameter, and SO₂ concentration on the extent of sulfation. This SO₂/sorbent sub-model was applied to a 126-MW front-wall fired boiler firing eastern bituminous coal. The SO₂ removal efficiencies predicted by the model agreed well with those measured in the field. The modeling results indicated that sorbent injected directly into the furnace through boosted over-fired air ports is more effective at removing SO₂, due to longer residence time and better mixing, relative to ports higher in the furnace with poor mixing. This modeling approach is optimized for full-furnace application to facilitate the design process.     

燃煤电站锅炉水冷壁壁面高温腐蚀问题分析与对策

以对冲燃烧方式的电站锅炉水冷壁壁面高温腐蚀问题为研究对象,从腐蚀机理与燃烧特性角度对水冷壁燃烧区域进行腐蚀特性建模分析,研究水冷壁近壁区域还原性和腐蚀性气氛作用下的硫化物型熔盐腐蚀部位分布规律,腐蚀发生严重的区域将集中在两侧墙的燃烧器周围区域、下层冷灰斗区域、上层燃烧器与顶层燃尽风喷口之间的两侧墙中间区域。现场实测数据验证可知,燃煤电站锅炉水冷壁近壁区域在氧浓度极低情况下,H₂S、CO等物质浓度严重超出腐蚀判定指标要求,水冷壁壁面腐蚀严重,腐蚀发生部位与数值模型结果吻合。结合工程经验,给出了水冷壁壁面高温腐蚀防治的具体措施。     

换热设备污垢监测及预测研究进展

重点阐述了近年来国内外学者对换热设备污垢预测和监测的研究工作,并提出了污垢预测和监测研究的新方向。同时,也对污垢机理做了概述,对污垢典型模型做了总结。