| 题名 | 溢流管式多层流化床稳定操作 |
| 作者 | 许徐飞 |
| 学位类别 | 硕士 |
| 答辩日期 | 2012-05-25 |
| 授予单位 | 中国科学院研究生院 |
| 导师 | 高士秋 ; 许光文 |
| 关键词 | 多层流化床 溢流管 稳定操作气速 压力降 煤热解 |
| 其他题名 | Stable Operating Gas Velocity and Pressure Drop in a Multistage Fluidized Bed with Overflow Standpipes |
| 学位专业 | 化学工程 |
| 中文摘要 | 热解是一种从煤中直接获取低碳燃料及高值化学品的温和转化工艺。基于多层流化床工艺的煤热解技术可有效地发挥流化床的高气固传热传质速率和多层流化床梯级升温的优势，可沿床层建立温度梯度以满足对煤热解反应的调控要求，实现多段分级热解，达到提高热解油气品质的目的。但多层流化床的稳定操作范围比单层流化床窄，且与结构参数、操作条件密切相关。目前有关分布板和溢流管的结构参数对稳定操作气速的影响还不十分清楚，如何针对不同物料确定合适的稳定操作范围，并选择最优的操作参数及结构参数有待进一步研究。本文在床径为100 mm的溢流式4层流化床冷态装置上，研究了颗粒加料速率、颗粒密度及粒径、气体分布板的开孔率及孔径、溢流管内径及位置、堰高等操作和结构参数对多层流化床稳定操作气速范围以及压力平衡特性的影响。结果表明，这些影响因素的变化改变了多层流化床的压力分布状况，影响了流化气体在分布板和溢流管间的流量分配，从而影响到稳定操作气速范围。通过系统的实验研究，得到以下主要结果： (1) 最小稳定操作气速随颗粒加料速率、颗粒粒度、分布板开孔率及溢流管下端口距分布板高度的增大而增大，随溢流管管径、堰高的增大而减小，与分布板孔径大小无关。最大稳定操作气速随颗粒粒度、堰高、分布板开孔率和孔径的增大而增大，随溢流管管径和溢流管下端口距分布板高度的增大而减小。石英砂和煤颗粒的最大稳定操作气速均先随加料速率增加而增加，超过某一加料速率(表观颗粒速度约为1.0×10-4 m?s-1)之后基本保持不变。石英砂的最大与最小稳定操作气速的比大约是煤颗粒该比的3倍，石英砂的更大操作弹性可能是因为实验中使用的褐煤含水量高、流动性差所致。在本文的实验条件下，煤颗粒的稳定操作气速范围为4.5Umf~0.30Ut，石英砂的稳定操作气速范围为2Umf~0.65Ut。根据实验数据拟合得到了稳定操作气速范围的经验关联式，相对误差范围在±15%以内。 (2) 多层流化床分布板压降与单层流化床不同，由于气流夹带细小颗粒上行对分布板小孔的堵塞作用，多层流化床有床料时的分布板压降明显高于空塔的分布板压降，其差值随着分布板开孔率和孔径的减小而增大。对溢流管式多层流化床，床层压降随流化气速的增加而减小，随加料速率、颗粒密度及粒径的增大而增大。与单层流化床不同，由于分布板和溢流管的尺寸改变会影响气流在分布板和溢流管间的流量分配，因而床层压降也受到这些结构因素的影响。实验发现，床层压降随分布板开孔率及孔径、溢流管下端口距分布板高度的增大而降低；随溢流管管径及堰高的增大而增大。通过对多层流化床进行压力平衡分析，建立了计算溢流管料封高度的流体力学模型，通过与实验数据对比发现该模型应用于石英砂时相对误差可控制在±15%之内。 |
| 英文摘要 | Pyrolysis is considered to be a mild conversion process to obtain low carbon fuels and valuable chemical products from coal directly. Coal pyrolysis in multistage fluidized bed possesses the advantages of high heat and mass transfer rates and cascade heating performance，which can establish temperature gradient along the height of the bed to realize multistage cascade prolysis for improving the quality of pyrolysis oil and gas. However, the stable operating gas velocity range of multistage fluidized bed is more narrow than that of single-stage fluidized bed and is closely related to the configuration of the multistage bed and operating parameters. At present, the effect of structural parameters of gas distributor and overflow standpipe on the stable operating gas velocity range is still unclear. Thus, further study is needed to determine the suitable stable operating range for different particles and whereby optimize the operating conditions and structural parameters. This dissertation studied experimentally the variations of the stable operating gas velocity range and pressure drop with major configuration and operating parameters in a four-stage fluidized bed of 100 mm in diameter with overflow standpipes. The tested parameters included the particle feeding rate，density and size of different particles, opening ratio and orifice size of gas distributor, inner diameter and position of the overflow standpipes, and height of the weir in each stage. The results showed that the variation of pressure drop with those influencing factors in multistage fluidized bed changed the gas flow distribution between the distributor and the overflow standpipe, and thereby affected the stable operating gas velocity range. The following major results were obtained from this work. (1) The minimal gas velocity (Umin) for stable operation increased with increases in the particle feeding rate, particle size, opening ratio of gas distributor, height of the overflow standpipe bottom from distributor, while it decreased with increases of the inner diameter of the overflow standpipe and the height of the weir, and was independent of the orifice size of gas distributor. The maximal stable operating gas velocity (Umax) was found to increase with increasing the particle size, height of weir, opening ratio and orifices size of gas distributor，but it decreased with increases in the inner diameter of the overflow standpipe and also the height of the standpipe above the distributor. For the tested silica sand and coal particles, Umax increased with increasing particle feeding rate, but it was almost a constant when the superficial particle velocity was higher than 1.0×10-4 m/s. The threshold gas velocity ratio Umax/Umin of silica sand was about 3 times of that of coal, indicating that the operation flexibility for silica sand was larger than that of coal, probably due to the poor particle fluidity of coal with high moisture content. In our experimental conditions，the gas velocity range of stable operation are 4.5Umf ~ 0.3Ut for coal and 2Umf ~ 0.65Ut for silica sand, respectively. Based on experimental data, an empirical correlation was proposed to predict the gas velocity range of stable operation with relative errors of ±15%. (2) The pressure drop of distributor in a multistage fluidized bed is different from that in a single stage fluidized bed. In multistage fluidized bed, the pressure drop of gas distributor with particles above it was obviously larger than that of empty bed due to the clogging of the distributor orifices by entrained fine particles. The difference in pressure drops for such two cases increased with decreasing the opening ratio and orifice size of the gas distributor. For multistage fluidized bed with overflow standpipes, the pressure drop of the entire bed increased with increases in feeding rate, density and size of particles, and decreased with increasing the gas velocity. The pressure drop of the bed varied also with the structural parameters of gas distributor and overflow standpipe because of the consequent change in gas flow distribution. The pressure drop also decreased with the increases in opening ratio and orifice size of gas distributor, height of the overflow standpipe above the gas distributor, but it increased with increasing the inner diameter of the overflow standpipe and the height of the weir. A model for predicting the particle bed height in the overflow standpipe was developed and the predicted value was in close agreement with the experimental data for silica sand, and the relative error was within ±15%. |
| 语种 | 中文 |
| 公开日期 | 2013-09-25 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/1826]  |
| 专题 | 过程工程研究所_研究所（批量导入） |
| 推荐引用方式 GB/T 7714 | 许徐飞. 溢流管式多层流化床稳定操作[D]. 中国科学院研究生院. 2012. |
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