【Q&A Question 223】2017.08.11
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【Q&A Question 223】August 11, 2017: What factors influence plate efficiency? The reference answer can be seen after responding; scoring is possible by identifying the key points. (Unless otherwise specified, all questions and answers are based on hydrogenation units.) In actual production, due to limited contact time, the entrainment of liquid (mist), as well as issues related to manufacturing and installation, the vapor-liquid phase cannot reach an equilibrium state; as a result, the actual number of plates is greater than the theoretical number. The ratio of the theoretical number of plates to the actual number is known as the plate efficiency. It is mainly influenced by the following factors ； (1) Physical properties of the gas and liquid phases, such as diffusion coefficient, relative volatility, and viscosity. (2) Operating parameters, such as the flow rates of the vapor and liquid phases, reflux ratio, pressure, temperature, etc. (3) The structure of the tower should facilitate good two-phase contact, such as through a large cross-section and induced turbulence. The daily activity shuts down after 7 days, with answers displayed automatically. (2017-8-16) Scoring criteria: A wrong answer earns 2 Wealth points; an *incomplete* answer yields 3–8 points. A correct answer with a detailed explanation grants 10 Wealth points, while a correct answer with insufficient supplementary *answers* earns 15–20 Wealth points. Please score according to these criteria. Note: If there are editing records after answering, only those who participated will be credited points. For continuous malicious spamming, 2 points will be deducted each time, with no upper limit. Pure numbers, pure emojis, or random letters that have nothing to do with the answer are all considered malicious spamming; points will start to be deducted after three warnings. 2017 Q&A Summary Thread (updates have begun) http://bbs.hcbbs.com/thread-1657793-1-1.html 2017 Daily Question Summary Thread (updates have begun) http://bbs.hcbbs.com/thread-1657794-1-1.html 2016 Q&A Summary Thread (updates completed) http://bbs.hcbbs.com/thread-1597792-1-1.html Petrochemical Zone – “Creative Ideas for Energy Saving” campaign (the second phase is in full swing) http://bbs.hcbbs.com/thread-1666758-1-1.html (Source: Haichuan Chemical Industry Forum)
①The rate of mass exchange between the gas and liquid phases; ② The degree of mixing between the vapor and liquid phases on the tray; ③ The amount of liquid droplets carried by the vapor to the upper trays
1. The rate of mass exchange between the gas and liquid phases; 2. The degree of mixing between the vapor and liquid phases on the tray; 3. The amount of liquid droplets carried by the vapor to the upper trays.
In actual production, due to limited contact time, the entrainment of liquid (mist), as well as issues related to manufacturing and installation, the vapor-liquid phase cannot reach an equilibrium state; as a result, the actual number of plates is greater than the theoretical number. The ratio of the theoretical number of plates to the actual number is known as the plate efficiency. It is mainly influenced by the following factors ； (1) Physical properties of the gas and liquid phases, such as diffusion coefficient, relative volatility, and viscosity. (2) Operating parameters, such as the flow rates of the vapor and liquid phases, reflux ratio, pressure, temperature, etc. (3) The structure of the tower should facilitate good two-phase contact, such as a large cross-section and induced turbulence.
①The rate of mass exchange between the gas and liquid phases; ② The degree of mixing between the vapor and liquid phases on the tray; ③ The amount of liquid droplets carried by the vapor to the upper trays.
(1) Physical properties of the gas and liquid phases, such as diffusion coefficient, relative volatility, and viscosity. (2) Operating parameters, such as the flow rates of the vapor and liquid phases, reflux ratio, pressure, temperature, etc. (3) The structure of the tower should facilitate good two-phase contact, such as a large cross-section to induce turbulence
Structure of the distillation tower: It mainly includes the height of the outlet weir, the flow length of the liquid across the trays, the tray spacing, the size and structure of the liquid dropping zone, as well as the structure, arrangement, and open area percentage of valves, screen pores, or bubble caps. Operating variables: mainly include gas velocity, reflux ratio, temperature, and pressure.
(1) Select an appropriate tray spacing to control the amount of mist entrainment. The tray spacing is related to both the tower diameter and the foam layer height. (2) Reduce the liquid level gradient on the tray to maintain uniform liquid flow. (3) A reasonable empty tower velocity to prevent flooding. (4) Prevent the stolen liquid from staying for too short a time in the downcomer, which could lead to entrainment of the liquid phase on the plates and subsequent gas-phase backmixing. (5) Eliminate the tray dead zone. (6) Prevent liquid bypass.
During the actual operation of a distillation column, factors such as gas-liquid mass transfer resistance, mixing, and foam entrainment cause the composition of the gas and liquid phases to deviate from their equilibrium states; therefore, plate efficiency should be taken into account when determining the actual number of theoretical plates. System properties, fluid dynamics, operating conditions, and tray structure parameters all affect tray efficiency, and tray efficiency cannot be predicted accurately.
This post was last edited by hesonchang214 on 2017-8-11 08:51. In actual production, due to limited contact time, the entrainment of liquid (mist), as well as issues related to manufacturing and installation, the vapor-liquid phase cannot reach an equilibrium state; as a result, the actual number of plates in the column is greater than the theoretical number. The ratio of the theoretical number of plates to the actual number is known as the plate efficiency. It is mainly influenced by the following factors ； (1) Physical properties of the gas and liquid phases, such as diffusion coefficient, relative volatility, and viscosity. (2) Operating parameters, such as the flow rates of the vapor and liquid phases, reflux ratio, pressure, temperature, etc. (3) The structure of the tower should facilitate good two-phase contact, such as a large cross-section to induce turbulence