Abstract

A mathematical model based on the volume averaging method and a corresponding numerical strategy were developed to investigate the drying behavior of lignite. Simultaneous and continuous measurements of weight and temperature profiles were carried out for a lignite particle by employing a self-designed tunnel dryer to verify the predictive model. It was shown that the simulated results were in good agreement with the measured values. Based on the model, the evolution and distribution of moisture, temperature, and water vapor pressure (WVP) in a lignite particle were studied. It is shown that the hysteresis effect of the evaporative surface caused a significant moisture gradient in particle, and from the surface to the center of the particle, WVP grew with a decreasing rate. A higher drying temperature could accelerate the evolution of moisture in the particle and promote the development of “increasing local moisture”. The acceleration of the drying rate caused by increased temperature is less related to the moisture gradient but is greatly affected by the WVP. Furthermore, the humidity and temperature of the external environment of the lignite was also further studied based on above model. Thus, the model can be used for the optimization of the drying process parameters and can offer guidance for the development of new drying technologies.

摘要

开发了基于体积平均法的数学模型和相应的数值策略来研究褐煤的干燥行为。通过使用自行设计的隧道式干燥机来验证预测模型，对褐煤颗粒进行了重量和温度分布的同时和连续测量。结果表明，模拟结果与实测值吻合良好。基于该模型，研究了褐煤颗粒中水分、温度和水蒸气压（WVP）的演变和分布。结果表明，蒸发面的滞后效应导致颗粒内出现显着的水分梯度，从颗粒表面到颗粒中心，WVP 的增长速度逐渐减小。较高的干燥温度会加速颗粒中水分的演化，促进“局部水分增加”的发展。温度升高引起的干燥速率加速与水分梯度的关系不大，但受 WVP 的影响很大。此外，还基于上述模型进一步研究了褐煤外部环境的湿度和温度。因此，该模型可用于干燥工艺参数的优化，可为新型干燥技术的开发提供指导。在上述模型的基础上还进一步研究了褐煤外部环境的湿度和温度。因此，该模型可用于干燥工艺参数的优化，可为新型干燥技术的开发提供指导。在上述模型的基础上还进一步研究了褐煤外部环境的湿度和温度。因此，该模型可用于干燥工艺参数的优化，可为新型干燥技术的开发提供指导。