微波加热强化煤泥低温干燥的机理研究

The dehydration and drying of coal slime is a key method to enhance its quality. The increase of processing time and energy consumption due to the decreasing drying rate at the falling-rate drying period have become a bottleneck for the effective and fast drying of coal slime by the traditional drying technology. In this project, a new method was put forward. This method is to adopt the traditional heating in the front zone and microwave heating at the rear to enhance the low-temperature drying of slime. The internal heating mechanism can be applied to improve the heat and mass transfer of moisture in the slime, which is promising to increase the heating rate at the falling-rate drying period with the assistance of microwave, and then promotion of coal slime drying effect can be achieved. The feasibility of this method was verified by our previous research work. Based on the acquisition of physical, chemical and structural properties of the coal slime, and the occurrence mode and distribution pattern of moisture, we can obtained the drying curves at different heating mode and operating parameters, and the critical moisture content of slime. And then, the moisture type and migration process under microwave enhanced drying condition can be revealed; the effect of microwave drying process on the coal quality, moisture suck-back property and equilibrium moisture content of the dried sample can also be explained; the interaction of microwave with mineral composition in the slime and its effect on the temperature rise and drying process can also be investigated. Finally, a drying model can be established to predict the temperature field and moisture migration pattern. The project can provide support for the exploration of new drying methods and the improvement of basic drying theory of coal slime.

脱水干燥是高含水率煤泥品质提升的关键手段。在传统热干燥工艺的降速干燥段，随着干燥速率的降低，干燥时间和能耗显著增加，成为制约煤泥高效、快速干燥的一大瓶颈。本项目提出在常规干燥降速段辅以微波照射对煤泥进行低温强化干燥的新方法，应用微波“内部加热”机制优化水汽传热传质，有望大幅提升煤泥整体干燥速率和干燥性能，项目组前期的研究已初步证明了其可行性。拟在获取煤泥性质及水分赋存形态、类型及分布特性的基础上，研究不同干燥方式和操作参数下煤泥干燥的演变过程及相应的临界含水率范围，揭示经过常规预干燥的煤泥在微波深度干燥条件下的水分迁移规律。探索微波干燥对煤质的影响、干燥后样品的返潮特性及平衡含水率范围，阐明微波与煤泥中矿物的耦合作用对煤泥升温、干燥过程的影响。建立煤泥微波干燥模型，对煤泥中的温度场和水分迁移扩散规律进行预测。本项目研究将为探索煤泥干燥新方法、丰富煤泥干燥基础理论提供支撑。

脱水干燥是高含水率煤泥品质提升的关键手段。在传统热干燥工艺的降速干燥段，随着干燥速率的降低，干燥时间和能耗显著增加，成为制约煤泥高效、快速干燥的一大瓶颈。本项目提出在常规干燥降速段辅以微波照射对煤泥进行低温强化干燥的新方法，应用微波“内部加热”机制优化水汽传热传质，有望大幅提升煤泥整体干燥速率和干燥性能。提出的热风/微波联合干燥方式一方面通过热风干燥方式降低干燥过程总能耗，另一方面通过微波干燥的强化提升作用达到缩短干燥总时间的目的。.在对煤泥理化特性进行详细分析的基础上，本项目分别研究了热风和微波加热下的煤泥干燥特性及水分迁移规律，考察了不同干燥方式和操作参数下的干燥曲线，并分别进行了动力学及能耗分析，得到了常规干燥和微波干燥的最佳组合工艺参数及临界含水率范围，发现常规干燥后的煤泥含水率为15%时再辅以微波快速干燥，其总体能耗最低；通过与热风干燥的对比，揭示了具有特定内部孔隙结构的煤炭在特定的微波干燥条件下，内部的水分可能会以液态形式向表面快速释放的现象。由此大幅减少了水分气化时大量吸收汽化潜热带来的高能耗，为进一步降低微波干燥系统的总能耗提供了可能。考察了干燥对煤质的影响、干燥后样品的返潮特性及平衡含水率范围，评价了微波干燥对产品提质特性的综合效果；出于应用考虑，煤泥微波干燥的中试研究表明微波干燥低阶煤技术可行，是一种实现高含水率物料快速、有效干燥的新方法。本项目研究为开发煤泥新型干燥方式，探索干燥机理，促进联合干燥技术的工业化应用提供了重要参考。