Selection of vacuum unit flow rate
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Hello everyone. The design for the top of a vacuum distillation tower includes a total condenser, followed by a vacuum unit. How should the flow rate of this vacuum unit be determined? Should we take into account the amount of leakage – what is the typical value? Or should we consider the efficiency of the total condenser (since complete condensation is not possible in practice)? What is the typical percentage of non-condensable gas, based on experience? Or should we consider the internal volume of the unit? Which of these factors is the most important in achieving the desired pressure within a few hours of operation? Thank you
The term \"overall condenser efficiency\" is not correct; the so-called non-condensable gas should refer to the vapor pressure at the cooling temperature of the material, and this is what matters most. In a high vacuum, leakage is the main issue. There is no specific calculation formula; the selection of a vacuum system generally involves scaling up from existing equipment or relying on experience.
The amount of air that leaks into the vacuum equipment = k×V²/³, where when the pressure is greater than 90 torr, k=4.8； When the pressure is between 3 and 20 torr, k=1.9 ； When the pressure is less than 1 torr, k=0.6 ； V is the volume of the vacuum equipment, in m3 ； Amount of air leaking into vacuum equipment, kg/h
Could those of you who have experience with such calculations share it? I’m facing the same problem now; it actually relates to the calculation of the pumping rate of the vacuum system. I hope experts can offer some guidance! Thank you! Also, I’m not sure where the formula mentioned above comes from – is it V squared divided by 2 then multiplied by 3, or is it V to the power of 2/3? Please give me some advice!
Reply to 4# lei0571: Volume 1 of the 4th edition of the Chemical Process Design Manual, page 969, also explains it in detail. Take another good look at this post: http://bbs.hcbbs.com/viewthread.php?from=notice&tid=764429