Experimental Studies Of Externally Heat-Integrted Double Distillation Columns (EHIDDiC)

Distillation process is the main energy-consuming chemical industry unit. In order to improve the thermodynamic efficiency of the distillation, and reduce energy consumption, thermal coupling technology has been widely developed. Thermal coupling technology includes internally heat-integrated technology and externally heat-integrated technology. Due to the complex internal structure, the internally heat-integrated technology is difficult to be achieved in industrial production. The heat-integration of the externally heat-integrated technology is outside of the distillation column, therefor, the complexity of the heat-integration will be greatly reduced. Theoretical studies have shown that the externally heat-integrated technology can effectively use waste heat to improve the thermodynamic efficiency of the distillation system and cut the energy consumption with a large range. But there are no experimental data to support it. This article aims to verify the energy saving effect of the externally heat-integrated technology from the experimental point of view.The externally heat-integrated double distillation columns (EHIDDiC) include a high-pressure distillation column and a low-pressure distillation column. The rectifying section of the high-pressure distillation column (include the condenser) transfer heat to the stripping section of the low-pressure distillation column (include the reboiler). There is an external heat exchanger between each pair of heat-integrated stages. Compared with the internally heat-inteagrated distillation column, the EHIDDiC can avoid the limitation from the heat transfer area and simplify the structure of heat exchange.Due to the vast external heat exchangers, the externally heat-integrated structure is difficult to achieve in the actual process. So, on the basis of EHIDDiC, with the minimum total annual cost as an design goal, a simplified scheme (SEHIDDiC) has been derived, which only uses three external heat exchangers to approximate the external heat-integration.According to the SEHIDDiC, we carried out the design of expetimental equipment. This section includes choosing material of the external heat-integrated double distillation columns, calculating the column diameter, the handling capacity and other design patameters. In this section, the measurement and control facilities of the experimental apparatus are also designed.The experimental part of this paper introduces the content and results of the externally heat-integrated double distillation columns experiment. The content mainly includes the system start-up and the steady-state experiments. The steady-state expetiments include the vapour rising to the top, total reflux, the normal state with feed and products. Externally heat-integrated experiments include adjusting the number and combination of the heat exchangers.As the limitations of laboratory equipment, many experiments can not be achieved. In order to further analyze the performance of actual distillation using external heat-integration, a model of the experiment device should be established. Through the model, we can study and discuss the situations which can not be achieved in the laboratory equipment.The binary mixture of n- and i- propanol is selected as a separation object. Based on the analysis of the experimental results, the energy-saving effect of the externally heat-integrated double distillation columns in the acture saparation process has been preliminary verified. This study lays a foundation for the use of externally heat-integrated double distillation columns in the actual chemical production.