A study of diabatic distillation in a column with a low pressure drop

Abstract

This paper examines diabatic columns with a new type of tray. The design provides effective liquid reflux flow in each column tray and a low pressure drop. The contact devices comprise a stack of multi-diameter plates with raised edges. The vertical tubes of the dephlegmator integrated into the column centre pass across all plates, and are used for heat removal. Vapors of the ascending mixture partially condense onto the plate surfaces and the dephlegmator, resulting in vapor enrichment. The liquid flow down the column forms a thin layer on the surfaces of the middle and bottom plates. When the condensate drops onto the smaller-diameter top tray, it partially evaporates, is then mixed with the liquid flow on the underlying plates, and partially evaporates again. An algorithm calculation of distillation parameters for a diabatic column, with a known reflux flow rate, vapor velocity and heat transfer coefficient, is proposed and approbated. The column separation efficiency is assessed depending on the temperature and cooling-water flow rate in the dephlegmator pipe. Several approaches for enhancing the heat transfer intensity in the column dephlegmator pipe were analysed. Several heat removal methods, including liquid film flow cooling of the inner dephlegmator pipe surface, were examined. Experimental tests were carried out using an ethanol-water binary mixture and a raw spirit complex mixture. Comparison of the characteristics of the new diabatic unit and a packed column with a spiral prismatic packing showed that the plate column with the same separation efficiency has a lower pressure drop and metal consumption. The results encourage further research on this new diabatic column design.