Presidential Young Investigator Award: Large Particle Fluidization

简介：在总统研究员奖的5年中，将研究以下方面：(I)小颗粒对大颗粒沸腾床的润滑作用。添加非常少量的细小颗粒固体润滑剂，如石墨或硫化钼，可以显著减少较大的脆性颗粒流态化时发生的磨损量。这种颗粒的例子是具有低粘结剂材料比例的沸石。通过使用更多的粘结剂，一些沸石催化剂可以用于移动床操作，例如，流态床催化裂化。然而，由于使用更多的粘结剂，颗粒内扩散会受到影响，这可能是不可取的。如果低粘结剂含量的沸石催化剂的烧损能显著减少，那么一系列固定床工艺就可以在沸腾床反应器中实现。(2)利用示踪剂颗粒磁性的变化来表征气固热传递和颗粒混合。当固体进料到流态化床中时，无论是分批操作还是连续操作，重要的是要知道这些固体相混合的速度，并与床达到热平衡。对于小颗粒系统，这一信息很难获得，因为过程发生得很快，而且颗粒太小，无法插入温度传感探头。已经开发了一种技术，通过使用示踪剂材料的磁性变化来测量这些过程，该技术将允许获得关于颗粒加热和混合的详细信息。(3)大颗粒流态化系统的建模。在过去的15年里，沸腾床垃圾焚烧炉和燃烧器的广泛使用重新引起了人们对大颗粒流态化系统的兴趣。在这些系统上有大量的实验信息，但到目前为止，几乎没有可靠的流动模型来预测这些系统的行为。固气两相湍流搅拌流态化与气液两相搅拌流动有许多相似之处。后者已经用现象学方法进行了相当成功的模拟，人们认为对气-固系统采用类似的方法可能是卓有成效的。

Narrative: During the 5 years of this Presidential Investigator Award, the following areas wil be investigated: (i) The lubricating effect of small particles on large particle fluidized beds. The addition of a very small amount of fine particle solid lubricant such as graphite or molybdenum sulfide can significantly reduce the amount of attrition that occurs when larger brittle particles are fluidized. Examples of such particles are zeolites with low proportions of binder material. By utilizing greater amounts of binder some zeolite catalysts can be used in moving bed operations, e.g., fluid bed catalytic cracking. However, by using more binder, intraparticle diffusion is affected and this may be undesirable. If the erosion of low binder content zeolite catalysts can be significantly reduced, then a whole family of fixed bed processes could be implemented in fluidized bed reactors. (ii) The characterization of gas-solid heat transfer and particle mixing using changes in magnetic properties of tracer particles. When solids are fed to a fluidized bed, either in batch or continuous operations, it is important to know how quickly these solids mix and obtain thermal equilibrium with the bed. For small particle systems this information is difficult to obtain since the processes occur quickly and the particles are too small for temperature sensing probes to be inserted in them. A technique has been developed to measure these processes by using the change in magnetic properties of a tracer material and this technique will allow detailed information about the heating and mixing of particles to be obtained. (iii) Modeling large particle fluidized systems. The widespread use of fluidized bed waste incinerators and combustors in the last 15 years has given rise to a renewed interest in large particle fluidized systems. Considerable experimental information is available on these systems but as yet there are few reliable flow models to predict the behavior of such systems. There are several similarities between solid-gas turbulent churning fluidization and liquid-gas churning flow. The latter has been modeled quite successfully using a phenomenological approach and it is believed that a similar approach to gas-solid systems could be fruitful.