流化床中颗粒流化运动的直接数值模拟

流化床燃煤锅炉对环境污染小的原因之一是是燃烧时间炉内加入脱硫剂,脱硫剂与某颗粒一起沸腾流化,相互充分接触,脱硫剂对燃烧过程中产生的硫化物进行反应吸收。由于喷入炉内的脱硫物质在粒径和密度上通常与煤颗粒不同,在流化区域上也存在差异。为了了解不同粒径和密度颗粒在流化床内的运动规律,达到高效、经济的脱硫效果,采用直接数值模拟方法,对粒径和密度呈正态分布的物料在流化床内的流化运动区域进行了研究,得到了相关的结论。     

流动密封阀调节特性实验研究

流动密封阀可作为加压灰渣的排放控制装置,本研究在流动密封阀返料实验台上对流动密封阀的调节特点进行了实验研究。主要通过固定松动风量改变流化风量、固定流化风量改变松动风量的方式,分别研究了流化风和松动风对颗粒质量流率的调节特点。研究发现松动风对颗粒质量流率的调节作用更加明显,随着松动风的增加,颗粒质量流率近乎线性增加,最后达到最大值。实验使用了3种不同粒径石英砂,研究了颗粒粒径对颗粒质量流率的影响。随着粒径的增加,获得相同质量流率所需风量也增加了。同时改变流动密封阀前后压差,也能够较好调节质量流率,压差增大,质量流率也增加。     

双循环流化床颗粒循环流率的冷态实验研究与预测

在自行搭建的双循环流化床冷态实验系统上研究了鼓泡床静床层高度、颗粒平均粒径、鼓泡床流化风速、快速床总流化风速及一次风量比例等控制参数对颗粒循环流率的影响,提出了基于上述控制参数的颗粒循环流率计算关联式。结果表明:随着鼓泡床流化风速的增加,颗粒循环流率变化不明显;随着快速床中一次风量比例和总流化风速的增加,颗粒循环流率均增大,当一次风量比例和总流化风速达到一定值后,颗粒循环流率的增幅逐渐变缓;颗粒循环流率随着静床层高度的增加而增大,随颗粒平均粒径的增大而减小,且颗粒平均粒径的影响程度较大;所提出的关联式能够较好地预测颗粒循环流率。     

水分对CFB锅炉燃烧的影响

煤的全水分包括内在水分和外在水分,增大水分会增加着火热、降低低位发热量。煤炭颗粒进入炉膛后,水分吸热而汽化并过热,降低炉床料层温度,影响燃烧速度和强度,从而降低煤炭颗粒的燃烬度;水分变成水蒸气随烟气排出,将增加烟气量,升高排烟温度,降低锅炉运行热效率,并增大引风机电耗。外在水分增大,将增大煤炭筛分、破碎、输送的难度。     

流化床O_2_CO_2燃烧_氧浓度对粒径的影响

为研究氧浓度对燃料粒径的影响,在15 kW循环流化床试验系统和0.15 MW循环流化床试验系统上进行不同氧气浓度、不同燃料、不同粒径的燃烧试验。试验结果表明,燃烧高挥发分的煤时,氧气浓度对燃料的热破碎有较大影响,进而影响燃料粒径。50%左右氧气浓度下时,燃烧高挥发分燃料,平均粒径要比在常规空气下燃烧增加约35%。低挥发分的神木半焦在燃烧过程中热破碎较弱,氧气浓度对热破碎特性影响不大,粒径和空气燃烧条件下无明显差异。     

基于灰颗粒的物理特性为分类原则的试验研究

循环流化床(CFB)锅炉炉内的燃烧及传热与炉内床料的状态密切相关,而炉内床料主要是由燃煤含有的矿物组分经过燃烧、爆裂和磨耗过程形成的。文中对6种煤样在固定床燃烧后,使用可视化显微仪,获取了灰颗粒的微观形貌特征,根据灰颗粒的机械强度和耐磨性能的不同,将灰颗粒定义为3类不同性质的灰。以此为基点,采用固定床燃烧后冷态振动筛分和流化床实验台热态流化后筛分的方法,研究了不同燃烧温度下升温速率对灰颗粒粒径变化的影响,以及不同燃烧温度下燃烧时间对灰颗粒粒径变化的影响,推演了不同煤样在燃烧过程中的演化特征。结果表明:3类灰颗粒在不同的燃烧温度和时间的演化过程存在明显的不同,从而为预测循环流化床中的床料粒径分布提供了理论依据。     

鼓泡流化床风帽压力波动信号的小波局部奇异性检测

在冷态鼓泡流化床实验台上,针对不同流化数、静床高及床料颗粒粒径下测得的风帽压力波动信号,采用小波模极大值法获取信号的小波局部极大模线,分析了流化数、静床高及床料颗粒粒径对鼓泡流化床风帽压力波动信号奇异性的影响.结果表明:风帽压力波动信号的局部奇异性随着流化数的减小、静床高的增加和床料颗粒粒径的增大而有所增强,说明通过小波局部极大模线可以对风帽压力波动信号的局部奇异性进行描述,并且能够反映鼓泡流化床流化数、静床高和床料颗粒粒径变化时床内气固流动状态的变化.     

粒径对无烟煤颗粒在循环流化床锅炉中燃尽影响的研究

根据流体动力学理论分析了颗粒径与流化速度的关系，通过利用或建立简单的传热与燃烧模型，定量计算了不同粒径无烟煤颗粒的燃尽时间和一次通过炉膛时的停留时间。计算发现：颗粒燃尽所需时间和一次通过炉膛的停留时间均随颗粒径的增加而增长。但停留时间增长的幅度较缓慢。在较大颗粒径时，提高炉膛温度将大大缩短颗粒的燃尽时间。有利于提高颗粒燃尽率。对于一些较难着火的高变质无烟煤，当颗粒径较小时。预热时间对颗粒燃尽的影响不能忽略。图5表1参8     

柴油机缸内团聚态颗粒氧化过程中的破碎

基于全气缸取样系统采集不同燃烧时刻的柴油机碳烟,使用粒数粒径测试分析仪和透射电子显微镜测量了碳烟的粒径分布、数密度、分形维数和团聚度,进而获得团聚态颗粒的破碎速率,在上述工作的基础上,分析了柴油机缸内碳烟氧化主导阶段团聚态颗粒物的破碎现象.结果表明:碳烟氧化主导阶段初期,团聚态颗粒破碎速率高,碳烟颗粒总粒数密度和核态颗粒数密度增加,同时分形维数和团聚度明显减小.随氧化主导阶段燃烧反应的进行,破碎速率逐渐降低,总颗粒数密度逐渐减小,核态颗粒数密度先增加后减小,而分形维数和团聚度呈现上升的趋势.     

粉煤灰改性钙基吸收剂颗粒在流化床中的磨损特性研究

以粉煤灰改性钙基吸收剂作为研究对象,考察流化时间、颗粒粒径、煅烧温度、流化风速以及煅烧气氛对其磨损特性的影响,并与石灰石的磨损特性进行比较。结果表明:吸收剂颗粒磨损率随时间增加而减小;起始粒径、流化风速越大,磨损越严重,但磨损3h后粒径对吸收剂颗粒磨损特性的影响几乎可以忽略。吸收剂颗粒在起始的10min,950℃煅烧温度下的磨损程度要比850℃时严重,但随着时间延长,850℃下的吸收剂颗粒磨损程度反而要比950℃时严重。吸收剂颗粒在CO_2煅烧气氛下的磨损程度要比空气煅烧气氛下轻微,高浓度CO_2环境下抑制了煅烧反应的进行,某种程度上减弱了其磨损作用。粉煤灰改性钙基吸收剂颗粒的抗磨损能力明显较石灰石颗粒的强。     

A method of determining thermal parameters of granular coal particles during devolatilization

Fluidized bed combustion offers great potential for the utilization of high-sulphur coal and low-grade coal in an environmentally acceptable manner. Utilization of fluidized bed technology, especially for the combustion of low quality lignites, enables pollutant emission control as well as efficient combustion. The most important stage during the combustion of coal particles is devolatilization, in which various factors such as heat transfer from the surroundings to the particle surface, heat conduction within the particle, the chemicals involved, the kinetics and the transport of volatile compounds within the particle play significant roles. The heat transfer coefficient, thermal diffusivity, thermal conductivity, heating coefficient and lag factor are the most significant thermal parameters in this process. In this study, a 1-D transient heat transfer analysis is carried out for a granular coal particle during devolatilization in a fluidized bed. The particle is idealized as a spherical solid body. Models are developed to determine the thermal parameters of such particles, and are verified using experimental centre temperatures of a 10 mm granular coal particle subjected to devolatilization at a medium temperature of 960 K. The data are taken from the literature. The results show that the thermal parameters determined here are in good agreement with experimental findings.     

煤颗粒热膨胀破碎特性的试验研究

煤颗粒的热膨胀破碎特性直接影响流化床锅炉的运行效率。利用热机械分析仪(TM A)测定了不同种类不同密度的型煤受热膨胀的特性,并对部分破碎微观形貌利用场发射扫描电子显微镜(FSEM)进行了观察;通过马弗炉内的燃烧试验研究了热膨胀特性和燃烧破碎的关系。研究表明,煤颗粒在燃烧过程中其热膨胀破碎主要发生在挥发分析出阶段;内部挥发分的析出会使颗粒内压增大而产生膨胀,进而产生细小裂纹并破碎;挥发分越高,颗粒密度越大,其热膨胀形变率越大,越容易发生破碎现象;主要挥发分析出后热膨胀引起的破碎可以忽略。     

粉煤流化床燃烧_PC_FBC_炉膛烟温试验研究

针对新型高效、清洁煤燃烧方式,即粉煤流化床（ＰＣ－ＦＢ）,在一座０．３ＭＷ的试验台上,系统而详细地研究了ＰＣ－ＦＢ炉膛空间烟气温度的分布特性。主要研究内容包括：ＰＣ－ＦＢ炉膛空间内烟流的稳定性与均匀性;床层温度、流化速度、床料的平均粒径、二次风率、二次风的投入位置对炉膛内烟温分布的影响,并总结出合理的炉膛烟温分布。     

The influence of alkaline catalysts on combustion of coal particles

With increasingly stringent environmental limitations, it is essential to develop and study low-emission combustion techniques such as fluidized bed combustion. In this work, an experimental work was carried out to study the influence of minerals on combustion characteristics of Tabas coal in a one-stage fluidized bed. The results showed that the alkaline minerals have a significant influence on the combustion behavior of coal particles, especially at higher temperatures. It was also found that the residence time has a significant role in both the higher thermal energy and char conversion, due to a considerable increase in the rate of reactions especially at the beginning of the process.     

运行参数对粉煤流化床_PC_FB_燃烧效率的影响

在一座 0 3MW热输入的PC -FBC试验台上进行了试验研究 ,获得了不同操作参数下PC -FB燃烧效率的试验数据 ,详细讨论了这些参数对PC -FB燃烧效率的影响规律。研究结果表明 ,粉煤流化床的燃烧效率最高达 98%～ 99% ,可与煤粉炉相媲美。本试验研究亦首次提出 ,只要燃烧温度、颗粒停留时间、火焰湍流度 (3T)及炉内氧浓度、颗粒浓度(2C)合理匹配 ,就能够实现煤粉的低温高效燃烧。     

循环流化床锅炉物料平衡分析

循环流化床物料平衡是循环流化床燃烧的核心和基础,它影响到循环流化床燃烧效率和脱硫效率,并决定燃烧室内的热负荷分布。循环流化床“一进二出”的物料平衡系统是循环流化床的核心概念,也是理解循环流化床物料平衡的关键。本文介绍并分析了循环床物料平衡的某些问题,如循环流化床定态设计、床料质量和物料平衡模型等。循环流化床运行需要高的“床料质量”和较大物料循环量,要求流化床锅炉分离器分离效率曲线存在一个清晰的100％分离粒径截止点。循环流化床内物料平衡除了受分离器效率影响外,还受到给煤成灰及磨耗特性、床内颗粒分层、排渣方式及效率等因素的影响。     

Comminution of carbons in fluidized bed combustion

The study surveys fifteen years of research on carbon comminution in bubbling fluidized bed combustors. It is carried out on the premise that comminution can be seen as the result of at least four phenomena occurring in series-parallel with each other and with combustion, namely: the primary fragmentation of coals or other carbonaceous materials, the secondary fragmentation, the fragmentation by uniform percolation and the attrition of chars, cokes and graphite. In combination with combustion, these phenomena control size reduction of feed carbon particles into fines of elutriable size and, as a consequence, combustion efficiency and particulate emissions.

Information on fragmentation and attrition behaviour is conveniently obtained by means of laboratory and pre-pilot scale combustors when carbon is charged batchwise to the bed. Some of the literature data separately reported in the paper for each of the four phenomena taken into consideration can be used, as they are, or after appropriate modification, in the design of larger units. To this end, submodels directed to extrapolate comminution data beyond the ranges of experimental conditions in which they have been determined are thoroughly examined.

The paper also discusses how comminution parameters are embodied into the equation model of bubbling fluidized bed combustors. The starting point is the carbon particle population balance. Depending on whether secondary fragmentation is or is not relevant, the population balance is expressed by means of an integro-differential or an ordinary differential equation. Reference is also made to a simplified model which contains essential comminution effects and adequately describes the performance of combustors charged with coals of different rank.     

The devolatilization of coal and a comparison of chars produced in oxidizing and inert atmospheres in fluidized beds

This is a study of the devolatilization of coal in a laboratory-scale bed of silica sand, fluidized with either air or N₂ and electrically heated to 750 or 900°C. Coal particles (diameter 1.4–1.7 or 2.0–2.36 mm) were fed in batches to the surface of the bed and allowed to devolatilize in either an oxidizing atmosphere of air or inert N₂. In the first case, combustion of the volatiles occurred, but there was only thermal decomposition (pyrolysis) in the second situation. The resulting chars were recovered and analyzed for composition and structure, so that comparisons could be made between the effects of devolatilization with combustion and of pyrolysis in an inert atmosphere. It was found that the fractions of C and H in the char were only slightly sensitive to the type of fluidizing gas used. The amount of nitrogen in the recovered char and also the devolatilization time showed no dependence on the type of fluidizing gas, whereas BET areas were slightly larger after combustion in air. It is concluded that these effects are small relative to other errors, inherent in experiments on coal combustion, so that chars prepared in a bed fluidized by hot N₂ are very similar to those formed during coal combustion at nominally the same temperature. Equally, the overall composition of the volatile matter released during combustion in a fluidized bed is the same as in pyrolysis in nitrogen. The effects of other parameters, such as the temperature of the bed, the flow rate of the fluidizing gas and the size of the coal particles are also discussed in detail. It is concluded that most of the volatiles burn in a fluidized bed (at or less than 900°C) far away from the original coal particle. Also, NO_x is in effect a primary product of devolatilization, being produced in appreciable amounts when coal is heated in inert N₂. The ratio of C/N in the volatiles is found to be a constant during the latter stages of devolatilization, but beforehand at lower temperatures, carbon species are preferentially released. Overall, devolatilization of small particles (< 2.4 mm) in a fluidized bed at 900°C is kinetically controlled. The activation energy is small, being 15 ± 6 kJ/mol.