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循环流化床U阀(Loop Seal)动力学研究
Alternative TitleHydrodynamics of the U Valve (Loop Seal)for a Circulating Fluidized Bed
李昌进
Subtype博士
Thesis Advisor李洪钟
2014-04
Degree Grantor中国科学院研究生院
Degree Discipline化学工程
Keyword循环流化床 U阀 动力学模型
Abstract循环流化床以其特有的优越性能己经在化工、石油、冶金、能源、材料、制药等领域得到日益广泛的应用。循环流化床主体部分由提升管、气固分离装置(如旋风分离器)、返料装置(包括立管及返料阀)等构成。返料阀用来控制床体的返料量,目前应用于循环流化床装置的返料阀主要包括L阀、J阀、V阀、U阀等,其中U阀是应用的最为广泛的一种非机械返料阀。 许多研究者对U阀的运行进行了详细的考察。但他们的研究往往停留在单纯的实验研究,或得出一些固体返料量的经验关联式,或者像Basu等人提出的压力平衡模型,需要对循环流化床各个部分的压力进行分析,这些研究都增进了对U阀的理解。但需要进一步提出更加普适性的理论方法来预测设备结构、物料性质和各种操作条件对U阀排料速率的影响。 针对上述问题,本文建立了一个包含U阀的循环流化床实验平台,对循环流化床系统U型阀的排料特性进行系统的实验研究。研究流化风Q2、松动风 Q1、孔口高度和提升管气速等调控手段对于U阀排料特性的影响。对单独配流化风Q2、单独配松动风Q1、联合调整流化风Q2和松动风Q1,以及改变提升管气速等进行研究,考察各送风量对返料量调节的影响。在实验的基础上,通过对U型阀的动力学分析,针对不同的排料形式,提出不同的动力学模型来预测固体循环量和各种操作条件对U阀运行的影响。 实验得出了以下结论:流化风量Q2是U型阀返料装置调节和控制固体颗粒循环量的主要运行参数, 对其运行具有相当大的影响。当固定松动风量Q1, 通过改变流化风量Q2时, 可稳定地调节与控制通过返料装置的固体颗粒循环量。松动风量Q1 对U型阀返料装置的运行也具有相当大的作用, 它也为固体颗粒通过U型阀水平孔口时提供了有效的驱动力。但过大的松动风量Q1会引起返料立管内物料流化,此时进一步增加底部充气量,固体返料量几乎不再增大。提升管底部流化风风速 Ur虽然不是U型阀自身的一个特性参数,但是在不同的底部流化风下, 整个循环压力回路是不同的。提升管底部流化风风速Ur通过影响整个压力回路来影响 U 型阀进口和出口处的压力以及立管的料高, 进而来影响循环物料量Gp。无论哪种排料形式,排料室中颗粒一般处于流化床状态,而立管及供料室中颗粒可能为流化床状态,也可能为移动床状态。 针对排料室中为流态化状态,而立管及供料室中为移动床状态的排料模式,提出了流态化控制排料动力学模型。对于U阀在这种操作条件下,建立了一个包含三个方程的动力学模型,此模型可以用来预测排料室中的实际气体速度、实际颗粒速度和床层空隙率,进一步得到固体颗粒的返料量、立管中气体流率和排料室及立管中的压力降等。将模型预测的结果和实验测量值对比,两者基本相符,从而验证了此模型的正确性。 针对立管及供料室中的物料和排料室中物料均处于流态化的排料模式,提出了一个包含13个方程的协调控制排料动力学模型,此时返料量的大小由孔口两端及孔口本身的动力及阻力平衡决定。此模型可以用来预测底部充气、提升管气速、系统物料总量和孔口高度等对物料流率及U阀运行的影响,结果表明提升管气速和系统物料总量对物料流率有重要影响,而底部充气和孔口高度对物料流率影响不大。同时将模型预测的结果和实验测量值进行对比,两者基本相符,表明了该模型的正确性。
Other AbstractCirculating fluidized bed (CFB) has been successfully used in many fields such as chemical industry, petroleum, metallurgy, energy, material, medicine and so on due to its many intrinsic properties. A typical circulating fluidized bed system normally consists of a riser, a gas–solid cyclone, a recycle device (a standpipe and a solids recycle valve). The recycle valves are used to control the solids flow rate, several types of recycle valves, like L-valve, J-valve, V-valve and loop-seal, have been developed and used successfully in industrial CFB units, loop-seal is one of the most common non-mechanical valves used in CFB system. Loop-seal has been investigated by many scientists. Their research focused on pure experimental study, or proposed an empirical equation to correlate the solids flow rate, Basu et al. developed a model based on the pressure drops blance, needed to analyse the pressure drops of each section of the circulation loop. These investigations improve greatly the understanding of loop-seal performance. It is therefore necessary to develop more general theory and method for prediction of the solids flow rate and the effect of operation conditions on loop-seal peformance. In the present thesis, a CFB system including loop-seal, (i.e. U valve) has been set up, the recycle characteristics of loop-seal are studied by experiments. The effect of fluidization wind, loose wind, opening height and riser gas velocity on regulation characteristics are studied. The effect of bottom aeration on Gp are studied by using fluidization wind Q2 alone, using loose wind Q1 alone and using Q1 and Q2 both. On the base of experimental study, through hydrodynamic analysis, different hydrodynamic models have been established for different recycle mode. The solids flow rate Gp and effect of operation conditions on loop-seal performance can be predicted by the hydrodynamic models. The results of experimental study are: the fluidization wind Q2 is the influencing factor of regulation operations for loop-seal, has great influence on its operations. At a given Q1, Gp can be regulated steadily by changing Q2. The loose wind Q1 also has great influence on loop-seal’s operations, it drives the solids to pass through the opening. Loose too much wind, the particles in the standpipe would be fluidized, Gp will not increase anymore when increasing the bottom aeration. Although the riser air velocity, Ur , is not a feature of loop-seal itself, but under different air velocities at the bottom of the riser, the entire cycle pressure loops are different. The Ur affect the entire pressure loop,then the air pressure at the entrance and exit of the loop-seal and the height of solids in the standpipe change with Ur, so Gp also changes. No matter what kinds of recycle models, the solids flow mode in recycle chamber is fluidized bed, and the solids flow mode in the standpipe and supply chamber may be moving bed or fluidized bed. For the case of in recycle chamber is fluidized bed and in the standpipe and supply chamber is moving bed, a fluidized recycle hydrodynamic model has been proposed. This hydrodynamic model consisting of three equations has been established to predict the actual gas velocity, particle velocity and bed voidage in the recycle chamber as well as the solids flow rate, gas flow rate, and pressure drops in both recycle chamber and standpipe. The predicted results are compared with experimental data, they show good agreement. It proves the validity of the model. For the case of the solids flow in both sides across the opening of the loop-seal are fluidized bed, a integrate controlling hydrodynamic model including 13 equations has been proposed, the solids flow rate is determined by the blance of driving force and resistance across the opening. The effect of operating conditions such as aeration rate, fluidizing gas velocity in the riser, total solid inventory, opening height on solids flow rate and the performance of loop-seal was stud
Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/15537
Collection研究所(批量导入)
Recommended Citation
GB/T 7714
李昌进. 循环流化床U阀(Loop Seal)动力学研究[D]. 中国科学院研究生院,2014.
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