VMD-过热蒸汽干燥热敏性物料中的膜及过程研究

Reducing energy consumption and drying thermal-sensitive materials have been hot research focuses. Adopting vacuum membrane distillation (VMD) to produce low pressure superheated steam for thermal-sensitive materials drying is firstly suggested in this proposal. The latent heat of the exhaust steam is recovered via heat pump. The integrated dryer with VMD, dryer and heat pump will be optimized. The drying rate and quality will be improved and the energy consumption will be reduced. This proposal focuses on the preparation of heat transfer hollow fiber PVDF membrane with high hydrophobicity and mechanical strength in VMD. Three phase separation mechanisms including liquid-induced, thermally-induced and vapor-induced phase separations were firstly proposed in the dry-wet spinning process. The relationship of each unit in the integrated system will be studied by the combination of experimental and mathematical simulation, and the efficient matching of VMD, dryer and heat pump will be realized. The research results of this project will enrich and develop the basic theory of membrane distillation, drying and heat pump, provide technical support for drying, and have practical significance in energy consumption reduction.

降低能耗、处理热敏性物料一直是干燥研究的热点。本申请首次提出利用真空膜蒸馏产生低压过热蒸汽来干燥热敏性物料，并采用热泵回收干燥器排汽的潜热，形成真空膜蒸馏-干燥器-热泵集成干燥系统，提高干燥速率和质量，降低能耗。本课题重点研究用于真空膜蒸馏的导热疏水膜和集成系统的耦合机制。首次提出在干湿法纺丝过程中实现液致相分离、热致相分离和蒸汽诱导三种相分离机制，制备高通量、高疏水性、高机械强度的PVDF中空纤维膜。采用实验和理论相结合的方法研究集成系统中各单元的内在联系，实现真空膜蒸馏、干燥器、热泵的高效匹配，重点研究空气对膜和干燥器中传质和传热过程的影响。本课题的研究成果将丰富和发展膜蒸馏、干燥及热泵的基础理论，为干燥提供技术支撑，在节能降耗方面具有现实意义。

热敏性物料的干燥一直是研究热点。本项目成功搭建了全球首台真空膜蒸馏-干燥集成装置，并开展了辣椒种子的干燥实验。利用真空膜蒸馏产生低压过热蒸汽来干燥热敏性物料，提高干燥速率和质量，降低能耗。重点研究了用于真空膜蒸馏的疏水膜和膜组件以及集成系统的耦合机制。首先以磷酸三乙酯为溶剂、采用双层同步纺丝法制备具有双连续互穿网络结构的PVDF中空纤维疏水膜，实现高通量、高疏水性、高机械强度的三高性能。并开发出一步浸涂法改性制备PVDF全疏膜，进一步提高膜的抗润湿和抗结垢能力。提出了一种带中心穿孔管的新型真空膜蒸馏组件，使壳侧蒸汽压更均匀。真空膜蒸馏-干燥集成装置的干燥速率主要受过热蒸汽的有效焓值影响。相同压力下过热蒸汽的过热度越高干燥速率越快，并且相同过热度下过热蒸汽的绝对压力越高干燥速率也越快。集成装置的干燥能耗为111.2kg/ (kW·h)，比热风干燥节能44.4%，且种子发芽率略高于热风干燥。本课题的研究成果丰富和发展了膜蒸馏用疏水多孔膜耐结垢和抗润湿的机理，指出了提高工业化真空膜蒸馏组件的通量的途径，为膜蒸馏的应用开辟了新领域，在节能降耗方面具有现实意义。