For molecular distillation processes: Selection of pumps with high vacuum inlet pressures
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I encountered the following operating conditions: Material: lubricating oil; Temperature: 300 degrees; Flow rate: 3 m3/h; Viscosity: 4 cp at 300 degrees. Inlet pressure: 10 Pa (absolute pressure); Outlet pressure: atmospheric pressure. This is for molecular distillation of lubricating oil. High requirements are placed on pumps: 1. A strong suction power to draw out the material; 2. Ensuring the pump’s sealing properties, so that no air leaks under high vacuum conditions. Those with experience, please share what kind of pump to use. You can contact me via QQ at 87615523 or by email at lxn_663@163.com to discuss this.
Reply to 1# lxn_663: We just conducted a DHA distillation experiment yesterday. We used a gear pump at the feed inlet, and its airtightness was indeed poor; later, we used vacuum to draw in the material.
I am aware of your situation. Since distillation processes generally take place under vacuum, high demands are placed on suction pumps – in particular, good sealing performance, high efficiency, and low inlet pressure loss are required. The last point is particularly special: a low inlet pressure loss is a key factor in choosing a suction pump, as the continuous optimization of the process requires that the vacuum level remain stable and at a low level at all times; as a result, the feed pressure of the pump is **significantly reduced. The pump system can minimize the required net positive suction head by optimizing the pump’s inlet flow geometry and rotational speed. If the inlet pressure loss is higher than the difference between the feed pressure and the vapor pressure, the medium will vaporize at the pump inlet, and cavitation will occur as a result of the pressure increase between the gears, which is undoubtedly fatal for the pump. On the other hand, gear pumps generally use a portion of the medium being transported to lubricate the bearings, which then flows back to the inlet end of the pump. This internal circulation effectively reduces the temperature of the pump body on one hand, but it also causes the medium used for lubrication to gradually heat up due to the heat absorbed from the pump body. It is worth noting that the pump body itself should not generate too much heat for the medium, as the returning medium will directly affect the temperature of the inlet medium. As the temperature rises, the vapor pressure of the medium also increases, which can likewise induce cavitation. The internal circulation design concept of gear pumps effectively controls the temperature rise of the medium within the pump, which is undoubtedly an important factor in ensuring product quality for distillation processes.
Moderator, has the pump been determined? What model of pump was used in the end?
The last edit to this post was made by lxn_663 on 2012-1-5 at 16:38; reply to 4#: In search of a suitable solution, the end user chose the Swiss Maag gear pump.
Reply to 5# lxn_663: I have a question – in conditions of high temperature and high vacuum, how should one choose a seal for the pump? What kind of seal can meet the requirements? Could you provide the relevant materials and pictures? Thank you for your advice!
Reply to 6# Rose Quartz, Mr. Li: All high-vacuum Magti models come with double sealing. It has also been done using a single envelope, with good results as well.
The efficiency of this software is 6%-8% higher than the actual efficiency; the motor power specified for the software is set at a level between 1.1 and 1.2.
Reply to 8# wildewan: What software are you talking about? ?
A Roots screw vacuum unit can be used.