热集成技术在微精馏系统设计中的应用研究

Micro-distillation systems, which can realize the quick mass transfer, have come into view in recent years. Compared to their macroscale counterparts, micro-distillation systems can be easily produced in low-cost materials, reduce the sample/reagent consumption and avoid the operation risk as well. However, there is a main obstacle in the development of micro-distillation: heat losses. With the decrease of device size, the surface-to-volume ratio increases, which leads to the significance of the heat losses. In this study, a new type of micro-distillation system, which is called heat integrated micro-distillation column (HIMDiC) is proposed based on the concept of heat integrated distillation column (HIDiC). The general structure used in HIMDiC is vacuum microfluidic distillation. By operating the liquid-vapour mixtures at the outlet of the inner microchannel, the liquid feed moves across a capillary. The liquid is drawn into the fine channels by the capillary force and its surface is curved according to the capillary diameter, whereby the vapour pressure and temperature are also raised with an auxiliary inert gas. These higher temperature/pressure mixtures move into the outer microchannel, therefore, heat transfer from the outer microchannel to the inner microchannel becomes possible. The contents of this study include: the optimal design of HIMDiC structure, the detailed analysis of heat balance and the control strategy of the system. The objective of this study is to give a comprehensive design procedure and operation sequence of HIMDiC. Moreover, CFD model and experimental results are used to demonstrate the effectiveness of the proposed structure and control strategies.

微精馏系统作为重要的化工过程强化单元，在提高传质效率，保障安全生产，降低试剂消耗等方面日益受到众多研究者的重视，是构建生产型微工厂的重要设备。但由于微通道比表面积大，使得减少整个生产过程中的热量损失成为难题。本项目以热集成微精馏系统作为研究对象，在真空精馏的基本结构中，利用热集成精馏的思想，将内层微通道内形成的汽液混合流体，经毛细管腔体后，结合辅助进气，压缩升压升温，再将流体返送回外层微通道内，通过金属管壁向内层传热。本项目主要研究：该系统的最优结构，热平衡分析和精确控制问题。最终形成热集成微精馏系统的设计流程和操作流程。本研究通过CFD仿真模拟和实验验证，为热集成微精馏系统的实施奠定理论基础和技术支持。

微精馏系统是重要的化工过程强化单元，但是小型化导致了高的表面温度和高的体表面积比，会造成比较大的热损失。热集成微精馏系统将微通道出口气相携带的热量作为热源二次加热微通道的加热方式，并通过多段串联和变管径压缩，逐级实现热集成。通过热量衡算和气相组分计算，确定了3段热集成的最优结构设计。在微精馏体系的建模过程过程中，首先假设了两种微通道类板式塔(方柱)和类填料塔(特斯拉阀)结构，围绕传质强化目标，计算了最大混合效率条件下的方柱个数和填料段个数，然后，建立了适合板式塔的MESH方程，将热集成模拟为精馏段和提馏段之间的内部热传递；同时，还建立了适合填料塔的非平衡传质模型。围绕MESH平衡模型，采用自抗扰控制器，实现了温度和组分之间的解耦控制。在微精馏实验系统中，建立了汽液两相流中气化率(气泡长度表征)和换热之间的关系，从实验手段上实现了换热强化的表征。实验和理论分析均表明：在微精馏分离体系中，决定传质效果的汽液接触面积具有可测量性，在热集成方式中，微通道的快速传热能力具有可控性。但是这种可控性不是通过控制系统实现的，而是通过多级结构设计实现的。