Similarities and differences between top reflux and intermediate reflux in vacuum distillation
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Please discuss the similarities and differences between top reflux and intermediate reflux in vacuum distillation. 1. What do they have in common, and what are their differences? 2. Under what circumstances is mid-stream reflux required? Why does atmospheric and vacuum distillation require intermediate reflux while other columns do not? 3. What are the respective effects of mid-section reflux and top reflux on the product? Thank you to all the sea friends.
Reply to 1# yuhou*yue: Fractionation towers generally have mid-stage reflux, with the aim of recovering heat as much as possible； Some towers are equipped with several mid-stage recirculations in order to recover heat at high temperatures as much as possible ； Only when the heat is not worth recovering or when the benefits of recovery are lower than the operating costs is a top condenser return stream installed ； Assume that the number of tray layers in a column with mid-section reflux is greater than that in a column with only top-reflux ；
Thank you to the friend upstairs for participating. So, what effects would there be if no mid-stage reflux is used in the atmospheric pressure tower, that is, if no heat extraction is carried out (other than the loss of energy efficiency)? Thank you
Reply to 3# yuhou*yue: 1. In a constant-pressure tower, no intermediate section is provided; only a top reflux section is used. The heat required for maintaining thermal equilibrium in the tower is taken from the tower top, with the top reflux being responsible for removing this heat to ensure thermal equilibrium throughout the tower； 2. Fewer fractionation tower plates, resulting in lower investment costs ； 3. The final boiling point of the side-stream products is greatly influenced by the tower top temperature; several distillation outlets need to be installed to increase the flexibility in the side-stream distillation process ； 4. The vapor-liquid phase load at the top of the tower is high. My personal understanding may not be accurate; please understand
Personal opinion: 1. Only when there is reflux at the tower top can the heat balance of the entire tower be adjusted based on the amount of reflux and its temperature. To improve the separation accuracy of the side-stream oils, it is necessary to increase the number of tray levels and add more side-stream extraction points in order to meet the requirements for processing different types of oils. 2. The gas-liquid load on the entire tower is high; for a fractionation tower with the same processing capacity, a larger tower diameter and more trays are required. Pros and cons: High investment, high energy consumption, high separation precision.