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颗粒煤拔头工艺的基础研究
Alternative TitleThe Fundamental Study on Coal Particles Topping Process
杨翠广
Subtype博士
Thesis Advisor林伟刚
2013-05-01
Degree Grantor中国科学院研究生院
Degree Discipline化学工程
Keyword颗粒煤   大称量热重   热解时间   颗粒碎裂   颗粒内外二次反应
Abstract颗粒煤拔头工艺是正在开发的低阶煤提质、热解工艺中的一种。工艺中使用了粗筛分的毫米级的颗粒碎煤为原料,降低了前期原料煤的处理成本;此外,颗粒煤热解时细半焦颗粒少,降低了细粉与焦油产物混合堵塞管路的几率。颗粒煤拔头工艺技术方案之一是利用循环流化床(CFB)锅炉的高温循环灰作为热载体将粗筛分后的颗粒煤在鼓泡流化床热解反应器内进行热解,生成热解煤气和焦油,热解半焦返回CFB锅炉燃继续燃烧发电,从而实现热、电、油、气的联合生产。该工艺将热解、燃烧过程耦合,是提高煤炭资源利用率的有效手段之一。本论文就颗粒煤拔头工艺相关的颗粒煤热解特性进行了实验及计算模拟研究。论文选取了2mm、6mm、10mm及14mm四种不同粒径的颗粒煤为研究对象,在大称量热重天平中考察了煤粒的热解失重特性;在小型鼓泡流化床及固定床实验装置中分别考察了热解产物产率分布、气体产物组成及焦油特性的变化规律;建立一综合的传热-热解模型以模拟考察颗粒煤在鼓泡流化床中的热解特征;基于实验结果进行了10t/h的颗粒煤拔头工艺的方案设计。主要的研究内容及结果如下:首先,在大称量热重分析仪(MTG)中对导致颗粒煤热解滞后效应的粒径、升温速率、物料量等因素进行了考察。研究表明:升温速率的提高及粒径的增大加重了煤粒热解的滞后性;物料量的增大提高了颗粒外二次反应程度;单个颗粒煤的热解失重量要高于小颗粒煤的。此外,在对热解动力学进行的分析表明,由于热解挥发分在颗粒煤的热解过程中存在显著的颗粒内二次反应(放热反应),使得颗粒煤热解反应的活化能值低于粉煤的热解反应活化能值。其次,对颗粒煤在实验室规模小型鼓泡流化床中模拟考察颗粒煤拔头工艺的颗粒粒径及热解温度对产物分布及热解时间的影响。在煤粒热解过程中观测到了煤颗粒的碎裂,实验发现颗粒煤在高温下的碎裂程度更加严重。热解挥发分的二次反应及颗粒煤高温条件下碎裂、裂纹的产生将导致大小颗粒煤热解产物产率随温度变化趋势的不同,在低热解温度下由于热解挥发分几乎不发生二次反应,观测不到颗粒粒径效应。研究结果表明:①挥发分产率随粒径增大呈现先降低到最低值(6mm煤粒所对应的值)而后升高的趋势,在高温下此现象更为明显;②随温度升高,2mm及6mm煤粒液体产率分别在600℃及700℃时达到最大值,粒径增大使得最大液体产率所对应的温度值向低温区偏移,10mm及14mm煤粒液体产率随温度升高呈现先降低而后增大的变化趋势;③液体产率随粒径增大呈现先降低到最小值而后升高的变化趋势,500℃及600℃热解温度下10mm粒径煤粒液体产率最小,700℃及800℃热解温度下则是6mm粒径煤粒液体产率最小;④煤粒的热解脱挥发分时间与煤粒之间的关系可以使用经典的幂函数关系式来描述,与前人高温环境下测得的幂指数n值相比,本实验中的数值要低许多,这可能归因于煤粒的碎裂及实验中所采用的流化比下对流传热系数较高的缘故。第三,论文在固定床中考察了中速/慢速加热条件下颗粒煤的热解产物分布,对热解过程中所捕集的焦油进行了系统的组分及元素分析。研究结果表明:①实验研究进一步证实鼓泡流化床实验中的粒径增大会使颗粒煤最大液体产率向低温区偏移的结论;②中速加热条件下,就所考察的粒径,在700℃的热解温度下,热解液体中焦油/热解水产率的比值能达到最大;③中速加热速率下焦油中PAHs的含量要高于慢速加热速率下焦油中的;④通过与府谷粉煤的焦油特性对比发现,颗粒煤的热解能够在基本不降低焦油产率的情况下,改善焦油的品质:如提升H/C原子比率,降低组分中PAHs的含量等;⑤与快速加热情况下6mm煤粒液体的H/C比率最大,中速加热下液体的H/C比率变化不太明显,这是由于中速加热液体中水分含量较高的缘故。第四,就颗粒煤鼓泡流化床内热解实验所关心的热解时间、颗粒煤碎裂的问题本论文还进行了流化床内单颗粒煤的传热-热解模型的计算。模型计算了颗粒内所形成的压力梯度,考察了床层温度、煤颗粒粒径等因素对颗粒内压力梯度形成及变迁过程的影响。计算结果表明,①流化床加热条件下,颗粒煤热解反应热是不能忽略的;②颗粒内挥发分的对流冷却效应是可以忽略的。最后,论文还进行了热解规模在10t/h的双流化床颗粒煤拔头工艺系统方案的初步设计,确定了工艺中主要设备的尺寸及关键的操作参数如循环倍率、流化气体积流量、燃烧空气量等。为下一步进行的工艺放大了提供参考依据。
Other AbstractThe coal particles topping is one pyrolysis process of quality upgrading and utilization of low rank coal. Using rough sizing mm-sized coal particles in the process, it will be helpful to reducing the cost of raw coal pretreatment. Furthermore, utilization large coal particles will largely reduce the probability of pipeline-blocking owing to the blending of tar and fly ash in venting. One technical solution for large coal particles topping is coupling the Bubbling Fluidized Bed (BFB) and Circulating Fluidized Bed (CFB). Large coal particles are heated by the high temperature circulating ash from CFB and then coal gas and tar are released, solid residue matters, i.e. char, are returned to the CFB. With this method, the poly-generation application of heat, power, tar and coal gas can be realized. Large coal particles topping process is an effective method to improve the coal source utilization efficiency. In the topping process, tar as the aimed products, are collected and broadly used for industrial raw materials. The thesis make particular researches, including computing simulations and experimental studies, on the large coal particles’ fundamental pyrolysis characteristics, the pyrolysis products distribution and composition. The effects of large coal particles size, heating rate and quantity are tested in a Macro-Thermogravimetric (MTG). Some valuable results were obtained: 1. The weight loss of large coal particles are larger than that of small coal particles due to the former contains more maceral than the latter;
Pages204
Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/8242
Collection研究所(批量导入)
Recommended Citation
GB/T 7714
杨翠广. 颗粒煤拔头工艺的基础研究[D]. 中国科学院研究生院,2013.
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