压缩空气溶液干燥新方法及其关键基础问题研究

Compressed air dryers have been widely used and massively demanded in industrial processes such as pneumatic power and process gas source. The conventional freeze drying technology and solid desiccant adsorption method suffer from the problem of huge energy consumption and complex systems due to the low-temperature evaporation and the high-temperature regeneration respectively. In this project, a novel idea of compressed air drying method with high efficiency is proposed by combining liquid desiccant dehumidification with waste heat recovery from air compressors, which makes use of the waste heat during the compressing process to drive the liquid desiccant dehumidification cycle. In order to build theoretical models to describe the drying process by pressurized liquid desiccants, the characteristics of compressed air-aqueous solution interfaces and the forming mechanisms of mass transfer resistances are investigated by molecular dynamics. The mechanisms of liquid-film breakup and carrying are further studied in mesoscopic level under the conditions that liquid desiccants contact compressed air directly. Thus, the dominant factors of diameter distribution and substance composition for carried droplets can be determined. Theories and measures can also be developed to depress or even eliminate the generation of droplets. In addition, the methods of achieving better energy-saving effect and lower dew point temperature are explored based on the drying cycle using mixed liquid desiccants as well as its thermodynamic characteristics. This gives theoretical and technological guidance to developing heat and mass transfer models between compressed air and pressurized solution, enhancing efficient drying methods and solving droplet carrying problem.

压缩空气干燥设备在气动动力与工艺气源等工业生产过程有广泛的应用和大量的需求，常规的压缩空气冷冻干燥和固体吸附干燥分别因冷冻除湿及固体再生等过程存在能耗大、系统复杂等问题。本项目提出溶液除湿与空压机余热回收有机结合的高效节能压缩空气溶液干燥新思路，充分利用压缩空气过程产生的废热驱动溶液除湿干燥循环。在微观层面通过分子动力学的方法，研究压缩空气干燥过程中压缩空气-溶液界面热质迁移特性及传质阻力形成机制，建立压缩空气溶液干燥过程理论模型；从介观层面研究压缩空气-溶液直接接触液膜破碎和携带机理，揭示携带液滴粒径尺度与粒径分布的决定因素，探究液滴产生和携带的抑制方法与措施；从宏观系统层面，研究基于混合溶液的压缩空气溶液干燥循环形式及热力特性，探讨压缩空气溶液干燥系统高效节能及降低压力露点的方法，为发展压缩空气-溶液热质耦合传递模型、高效的压缩空气溶液干燥方法、抑制液滴携带等方面提供理论和技术支撑。

压缩空气干燥系统在气动动力与工艺气源等工业生产过程有广泛的应用和大量的需求，常规的冷冻式压缩空气干燥方法和固体吸附式压缩空气干燥方法分别因降温除湿、固体吸附剂再生等过程存在除湿能效低、系统复杂、能耗高等问题。本项目提出的溶液式压缩空气干燥新方法，将溶液除湿循环与空压机余热回收有机结合，形成了高效节能压缩空气干燥新思路，充分利用压缩空气过程产生的废热驱动溶液除湿循环，对压缩空气进行除湿干燥，无需传统的电驱动制冷系统或者电驱动吸附-脱附床。采用分子动力学方法研究了盐溶液与高压空气间的能质输运过程，揭示了其能量、质量输运过程的分子行为及其在多参数作用下的变化规律，阐明了盐溶液-高压空气之间耦合能质传递机理，提出了用自由能垒大小解释除湿/再生过程传质系数的相对大小，获得了压缩空气-溶液界面附近热质耦合传递阻力形成的机制及主导因素。提出了通过多元组分调控的新思路形成饱和蒸气压温度敏感型新溶液配置方法，实现压力露点的调节控制。建立了多元近饱和盐溶液蒸气压的热力学模型，较常规模型具有更高的预测精度，基于该模型指导了针对性低成本、高性能多元除湿溶液的优化与开发，实现成本降低近50%，驱动热源温度降低5oC以上，使得空压机废热等低品位热能得到充分高效利用。测试了盐溶液降膜流动过程中气体携带液滴的颗粒物质量浓度及影响因素，为填料结构及运行参数的优化提供参考。研制了溶液式压缩空气干燥系统实验台并获得了系统运行特性，建立了高压空气-除湿溶液耦合热质传递过程稳态与动态模型，指导了系统的运行参数优化设计，提升了系统能效水平。结果表明本项目提出的方法可以充分利用空压机余热，实现压缩空气的干燥，并能够将压力露点控制到-3oC以下，有效拓展了冷冻式压缩空气干燥的压力露点调节范围。研究结果为溶液式压缩空气干燥系统设计、压缩空气-溶液热质耦合传递模型建立、抑制液滴携带控制等方面提供理论和技术支撑。