深低温精馏过程强化机理研究

Air separation units (ASUs) tend to develop in the directions of large-scale, energy-saving and intelligence to satisfy the increasing demands of the petrochemical, metallurgical, and electronic industries. The mechanisms of cryogenic distillation, which is the core process in ASUs, involving the coupling process of two-phase flow, boiling and condensation heat transfer and mass transfer in complex geometry, are still not well understood. It leads to large design margin and low efficiency, which have become the bottleneck for the developments of industrial gases and relative industries. This study aims to significantly improve the efficiency of cryogenic distillation in ASUs, striving to make breakthrough of physical mechanisms and method innovation. Combining the method of computational fluid mechanics and visualization experiment at cryogenic temperatures, research on the coupling cryogenic two-phase heat and mass transfer, interface evolution and available energy transfer is carried out to reveal the mechanism of irreversible losses in the process of cryogenic distillation. A novel method is proposed to enhance the distillation by using magnetic force, centrifugal force and other additional forces, which supplies feasible ways to improve the efficiency of cryogenic distillation. Based on the above fundamental research, a more accurate hybrid model of the cryogenic distillation reflecting the physical phenomena will be developed and verified by the home-made cryogenic distillation test devices. This study is expected to provide a solid theoretical foundation for the development of the cryogenic distillation design for large-scale ASUs, from the stage of empirical and semi-empirical to theoretical perspective.

石化、冶金、电子等重要行业对工业气体的迫切需求，不断推动低温空分成套装备向大型化、节能化和智能化方向发展。低温精馏作为低温空分的核心过程，涉及复杂几何内低温两相逆流、冷凝沸腾传热、传质等耦合过程。长期以来人们对低温精馏机理认识不足，由此导致的设计余量大、能耗高等突出问题已成为工业气体及相关产业进一步发展的瓶颈。本项目以显著提高低温精馏效率为目标，力图从物理机制和方法创新两方面寻求突破。利用计算流体力学与低温可视化实验方法，着重研究低温两相混合物传热、传质与流动耦合的界面演化与有效能传递规律，全面揭示低温精馏过程中的不可逆损失机理；提出基于磁力、离心力等附加力场综合利用的精馏强化新方法，掌握提高低温精馏效率的有效途径；构建反映物理实际、更加准确的混合级低温精馏预测模型，并搭建低温精馏测试装置验证理论成果。本项目可望为低温精馏装置设计从经验化、半经验化向科学化发展奠定坚实的理论基础。

煤化工、化工、钢铁、航空航天等领域对以氧、氮为代表的工业气体需求日益增长，促进了低温空分系统向大型化、低能耗化和智能化方向发展。精馏是低温空气分离的核心过程，涉及多组份两相混合流体的流动、传热、传质的相互耦合，影响因素众多，作用机理复杂。.本项目以显著提高低温精馏效率为目标，从物理机理和方法创新两方面突破，着力解决如何描述低温精馏塔内复杂流动气液界面演化规律、如何揭示低温冷凝传热机理并提高传热效率、如何发展附加力场作用下的复合传质强化方法三个关键科学问题。针对问题一，我们提出了液氮-氮气两相流流型转变的理论预测模型、演变规律及数学描述并制作了流型图，实现了两相逆流液泛发生条件及影响机理的准确预测。提出将非接触式电容层析成像技术(ECT)应用于低温两相流测量，国内外首次获得了低温流体介电条件下ECT成像；阐明了低温流体在填料表面的流动形态并获取了低温精馏填料的改进方案。针对问题二，验证了Kutateladze关联式在低温冷凝波动层流区传热特性预测的有效性，基于Knudsen层导热理论提出了传质新模型，阐明了波动液膜和微结构表面强化氮蒸气冷凝传热机理，为低温换热表面传热强化提供了理论基础；针对问题三，提出磁场强化低温精馏新方法，揭示了磁场作用下气液界面的破碎现象与传质强化机理。建立了非平衡级低温精馏稳态模型，基于粒子群算法实现混整空间多目标稳态优化，该模型已在17000Nm3/h低温空分规整填料上塔获得工程应用。.本项目发表论文60余篇，其中SCI48篇，被引250余次；大会报告4次；授权发明专利11项。邱利民当选国际低温工程委员会副主席，王凯和包士然分获国际制冷学会青年奖卡诺奖和卡皮查奖，包士然获美国低温工程大会“最佳学生论文奖”、国际低温工程委员会“Klipping奖”，朱少龙入选博新计划等。本项目研究成果将为低温精馏装置设计从经验化、半经验化向科学化发展奠定坚实的理论基础。