Troubleshooting a 2 stage liquid ring vacuum pump
Troubleshooting a 2 stage liquid ring vacuum pump
(OP)
Hi everyone,
My situation is that I have 3 vessels that are all connected to one 2 stage liquid ring vacuum pump (Kinney, further info below) and this pump is used to pull methylene chloride (MeCl) from the batch. We are having performance issues such that the vacuum set points are not achieved and that it takes a much longer (2x more time) time to pull the MeCl from the batch even when we are lets say within 1 to 2 in. Hg on the set point. I am going to test the vacuum pump in idealized situations were I blind all other lines on the inlet header and try to pull down to the lowest set point on a vessel. I expect to have to hold a low pressure state for a moderate period of time to look for leaks if I cannot attain a set point. Do I need to provide something in the vapor space of the vessel for the pump to move to protect the pump or is the seal fluid supposed to* provide the needed cooling as well as make the pockets that the vapor gets carried in when inside the pump housing?
I am assuming I should provide something for the pump to actually move, but if it is not necessary then I can proceed with my test if ops folks are unable to charge some water to one of the affected vessels tomorrow; we are cleaning the water system tomorrow so I have a window to run a couple tests while the batches sit but I'd need ops to fill water before they shut that system down.
Thanks for your time,
J
Info gathered:
Lowest pressure set point on a vessel is 12" Hg
P&ID specs motor at 20 HP at 1000 rpm
Batch temp maintained at 26oC
Seal fluid is methanol at 10oC, I think it is constantly circulated from the separator part of the vac system to a HX for temp and then back into the pump
Pump curve and other info
Manufacturer's Manual
*I still have to confirm there have been no deviations on the seal fluid volume or temp.
My situation is that I have 3 vessels that are all connected to one 2 stage liquid ring vacuum pump (Kinney, further info below) and this pump is used to pull methylene chloride (MeCl) from the batch. We are having performance issues such that the vacuum set points are not achieved and that it takes a much longer (2x more time) time to pull the MeCl from the batch even when we are lets say within 1 to 2 in. Hg on the set point. I am going to test the vacuum pump in idealized situations were I blind all other lines on the inlet header and try to pull down to the lowest set point on a vessel. I expect to have to hold a low pressure state for a moderate period of time to look for leaks if I cannot attain a set point. Do I need to provide something in the vapor space of the vessel for the pump to move to protect the pump or is the seal fluid supposed to* provide the needed cooling as well as make the pockets that the vapor gets carried in when inside the pump housing?
I am assuming I should provide something for the pump to actually move, but if it is not necessary then I can proceed with my test if ops folks are unable to charge some water to one of the affected vessels tomorrow; we are cleaning the water system tomorrow so I have a window to run a couple tests while the batches sit but I'd need ops to fill water before they shut that system down.
Thanks for your time,
J
Info gathered:
Lowest pressure set point on a vessel is 12" Hg
P&ID specs motor at 20 HP at 1000 rpm
Batch temp maintained at 26oC
Seal fluid is methanol at 10oC, I think it is constantly circulated from the separator part of the vac system to a HX for temp and then back into the pump
Pump curve and other info
Manufacturer's Manual
*I still have to confirm there have been no deviations on the seal fluid volume or temp.
RE: Troubleshooting a 2 stage liquid ring vacuum pump
RE: Troubleshooting a 2 stage liquid ring vacuum pump
RE: Troubleshooting a 2 stage liquid ring vacuum pump
That is issue #1 with liquid ring pumps, you can't pump below the boiling point of the seal liquid.
If they are cool enough and give good vacuum blanked off, then hunt for leaks.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube
RE: Troubleshooting a 2 stage liquid ring vacuum pump
Methylene chloride sat vp at 10degC = 4psi = 8.25inHg - so methylene chloride would be still be in liquid phase at 12inHg - this may be the reason why the suction pressure is hovering around 13-14inHg.
The vac pump final suction pressure is now a function of the operating temp in these vessels, and not following the setpoint.
RE: Troubleshooting a 2 stage liquid ring vacuum pump
I believe I have leaks which is why I want to run these tests, my concern is coming from an equipment operation standpoint. I went ahead and asked for water to be charged to the average volumes each tank would hold in preparation for today's tests just to be safe. However, I would still like to know if it is acceptable to run this type of vacuum pump without having any vapor to remove from the vessel. I initially said I thought vapor traffic was needed (equating this vacuum pump to a centrifugal pump), but now I realize that compared to the seal fluid, any vapor that this pump is removing would do almost nothing for heat transfer so it would be okay to run the pump without a continuous stream of vapor. Please do correct me if I am mistaken.
Thanks,
J
RE: Troubleshooting a 2 stage liquid ring vacuum pump
Dont think there is any risk of zero vapor feed to this pump, since even water has a non negligible vapor pressure at 26degC, and more so for MeOH. Agreed, most of the heat developed in the pump would be absorbed by the seal fluid. Yes, can see the rational for these leak tests now, if you find the vac pump is struggling to get down to 12inHg even after all the methylene chloride is drawn out - or maybe there are some liquid phase non azeotropic contaminants in this methylene chloride with a sat vapor pressure lower that 12inHg ?
RE: Troubleshooting a 2 stage liquid ring vacuum pump
RE: Troubleshooting a 2 stage liquid ring vacuum pump