脉动流化床内干燥特性研究

发布时间：2018-03-04 15:25

  本文选题：流化床　切入点：脉动气流　出处：《东北电力大学》2017年硕士论文　论文类型：学位论文

【摘要】：流化床在工业中具有广泛的应用范围,它在工业应用中可以将固态颗粒等属性物质进行流态化处理从而实现大规模、高效率的工业应用。流化床与传统的反应器及设备相比较,流化床设备具有设备大型化、过程易于控制、传热传质效率较高、床内温度分布较均匀等优点,并且能够改善气固两相间的接触效率,减少传热热阻,从而提高传热效率。但是在处理一些较细颗粒、比重较低的生物质和含水较大原料时容易出现沟流、结块等非正常流化现象。所以应对流化床进行部分改进。我们针对上述流化床所出现的运行非正常现象进行了技术探讨和改进,提出了脉动流化床的解决方案,并针对此种方案的可行性以及同普通流化床的运行特性进行了对比,对脉动流化床的运行特征进行了分析,尝试找到其合理的运行工况参数。为此我们进行了以下几方面的探究:本次试验系统在原有常规流化床的基础上增加脉动气流,这种情况下在脉动气流停止加入时也会有一股稳定的气流进入对流化床对原料进行流化。并且在总进气流量不变的情况下来研究稳定气流和脉动气流不同比例分配对流化床流动特性及传热传质效果带来的影响,通过实验探究了在总气流量一定的情况下,改变稳定气流和脉动气流流量分配比例并利用采集的温度、压力、湿度等参数对流化床的流化情况以及传热传质效果进行分析,尝试利用气流波动图以及空气焓值进行分析。发现在较低脉动气体流量下低频率的0.25Hz脉动气流适合流化内传热传质的进行,而在脉动气流流量加大后则高频率的3.3Hz更为适合;并且在加入脉动气体之后会提高气固两相间的传热传质,但在频率提升到一定高度之后优势减弱。而温度参数对物料最终的干燥程度即最终湿含量影响最大,在进行了多个温度的实验之后发现,在90℃时流化床内传热传质速度最快干燥效果最好,并且能量消耗较少;在进气配比方面,进气比例的大小具有一定的影响,在进气流量较小时应提高脉动气流流量,而在流量较大时应使稳定气流保持在最小流化风速流量附近。在对相关实验结果进行分析后,提出利用脉动气流波动曲线图合理的解释了相关结论;利用湿空气焓值变化来分析并合理解释了相关实验现象,提出了一种合理的解释方法。
[Abstract]:Fluidized bed has a wide range of applications in industry, it can fluidize solid particles and other attribute matter to realize large-scale, high-efficiency industrial application. Fluidized bed equipment has the advantages of large-scale equipment, easy control of the process, high efficiency of heat and mass transfer, uniform temperature distribution in the bed, and can improve the contact efficiency between the gas-solid phases and reduce the heat transfer resistance. So as to improve the heat transfer efficiency. But it is easy to appear ditch flow when dealing with some fine particles, low specific gravity biomass and higher water content raw materials. Therefore, some improvements should be made to the fluidized bed. We discussed and improved the operation abnormal phenomenon of the fluidized bed mentioned above, and put forward the solution of the pulsating fluidized bed. In view of the feasibility of the scheme and the operation characteristics of the conventional fluidized bed, the operating characteristics of the pulsating fluidized bed are analyzed. We try to find out the reasonable operating condition parameters. For this reason, we have carried out the following research: this test system increases pulsating air flow on the basis of the original conventional fluidized bed, In this case, there will also be a steady flow of air entering the fluidized bed to fluidize the feedstock when the pulsating flow stops to be added, and the different proportion of stable and pulsating airflow will be studied under the condition of constant total intake air flow. The effect of flow characteristics and heat and mass transfer in fluidized bed, The fluidization and heat and mass transfer effect of fluidized bed are analyzed by changing the distribution ratio of steady and pulsating air flow and using the parameters of temperature, pressure, humidity and so on under the condition of constant total gas flow. It is found that 0.25Hz pulsatile flow at low frequency is suitable for heat and mass transfer in fluidization, but 3.3Hz at high frequency when the flow rate of pulsating gas is increased. After adding pulsating gas, the heat and mass transfer between the gas and solid phases will be improved, but the advantage will be weakened after the frequency is raised to a certain height, and the temperature parameters will have the greatest influence on the final drying degree of the material, that is, the final wet content. After several temperature experiments, it is found that the fastest heat and mass transfer speed in fluidized bed is the best at 90 鈩，

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