7 replies to this topic

[Ali4269278331]

dear Sir

what's main porpuse of Siphon pipe to the sewer and vent tube on the water seal drum(API521)?

we are fill drum as 50% of level with fresh water and after 3days open the valve drain and the dirty fluid goes to the closed drain.

 

thanks

Ali

 

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[Pilesar]

The 'siphon pipe' loop elevation is above the gas inlet. The distance between these two elevations sets the maximum water height above the gas inlet and determines the water seal maximum backpressure. The tube at the top is connected to the seal drum so that the pressures are equalized and there will be no siphon when the valves are open. The liquid will drain by gravity until the loop height and the liquid height in the drum are equal. With the loop open and the pressure equalization line open, there should be no way to put too much liquid into the drum according to the design intent.

Edited by Pilesar, 05 April 2024 - 08:34 PM.

[breizh]

Hi,

The design is for a continuous operation and the syphon is there to keep constant the level of liquid in the drum.

https://heatmfs.com/...atalog-2023.pdf

Breizh 

[shvet1]

This is not a siphon, this is a liquid seal. This would become a siphon if one closes the valve on siphon break.

 

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[Ali4269278331]

The 'siphon pipe' loop elevation is above the gas inlet. The distance between these two elevations sets the maximum water height above the gas inlet and determines the water seal maximum backpressure. The tube at the top is connected to the seal drum so that the pressures are equalized and there will be no siphon when the valves are open. The liquid will drain by gravity until the loop height and the liquid height in the drum are equal. With the loop open and the pressure equalization line open, there should be no way to put too much liquid into the drum according to the design intent.

thanks for your answer. do you think it is better one of valves is locked open and other is closed(as bypass)?

[Pilesar]

The control system you have now is to batch load water for three days operation while relying on the level gauge to manually set the water level. For that procedure, there is no use of the water drain line or the pressure equalization line and they will remain closed. If you are changing the operating procedure, then first determine how you want to operate! The drum appears to have been designed to allow the choice for water to continually flow through the loop with the equalization line open to the vessel. This would be an advantage if there were a continual source of liquid. Does the water level increase over the three days or does the level drop? If it increases, then keeping the loop open will drain just the right amount to maintain level. If the water level drops over the three days, then the loop will not be of much benefit because nothing will flow through the loop without additional water makeup to the drum. If you want to put the loop into service, the equalization line must be open at the same time. You will still need to blow down the water from the lower drain valve periodically to get rid of crud. If you put the loop in continual service, consider the destination of any vapor leaving the drum through the equalization line. There may be safety or environmental consequences for vapor flow through that line. Do you lock open or closed any valves in this system now? I would think operator training and procedures would be sufficient safeguard but you will need to consider what is appropriate according to your plant control philosophy. 

[Ali4269278331]

The control system you have now is to batch load water for three days operation while relying on the level gauge to manually set the water level. For that procedure, there is no use of the water drain line or the pressure equalization line and they will remain closed. If you are changing the operating procedure, then first determine how you want to operate! The drum appears to have been designed to allow the choice for water to continually flow through the loop with the equalization line open to the vessel. This would be an advantage if there were a continual source of liquid. Does the water level increase over the three days or does the level drop? If it increases, then keeping the loop open will drain just the right amount to maintain level. If the water level drops over the three days, then the loop will not be of much benefit because nothing will flow through the loop without additional water makeup to the drum. If you want to put the loop into service, the equalization line must be open at the same time. You will still need to blow down the water from the lower drain valve periodically to get rid of crud. If you put the loop in continual service, consider the destination of any vapor leaving the drum through the equalization line. There may be safety or environmental consequences for vapor flow through that line. Do you lock open or closed any valves in this system now? I would think operator training and procedures would be sufficient safeguard but you will need to consider what is appropriate according to your plant control philosophy. 

thanks dear Pilesar for your sharing, for your information, we have a sour gas that release from 3rd stage separator and then goes in the water seal drum. we are inject the chemical as gas corrosion in the gas outlet line. so, we use of fresh water with 3bar of pressure that change and drain the dirty water in drum every 2-3 days. when i want to drain the water seal drum, i should be open the fresh water and lower valve in the siphon loop. and after close the valve. this procedure is correct or not?

[Pilesar]

Is the procedure you describe the current practice? If you are seeking a change, first understand why the historical operation choices were made. Sometimes first impressions may be that the current practice or design is obviously wrong when the true situation exists for good reason which is only discovered after looking deeper. Do not write a procedure without understanding how the process works, what can go wrong, and what to do if when it does go wrong. Get input from experienced operators on site. Learn the consequences of valves sticking or other events that interrupt the action. Assume mechanical equipment will fail. Assume operators will get distracted. Sour gas kills. Do not determine how to operate this equipment based on what some unknown person writes in this forum.