5 replies to this topic

[Wyper]

Running into a issue of periodic liquid escaping out of the drains due to pressurization in a gravity drainage system. The system consists of a 60 m long 16" pipe at a 1% grade and about 40 drain ports inputting process solution vertically into the main pipe. Found several helpful information on this forum and hoping to focus down the cause. The pipe's are adequately sized using  fully flooded pipes, and open channel design and ideally they should act like an open channel. I suspect a significant amount of gas entertainment occurring since Froude's number is not <0.3 for the vertical drains causing a restriction in the pipe and liquid expulsion out of the drains. Another interesting point I found is that the 1% grade is not always followed along the line. Is there anything else I could be missing? Let me know if you need more details.

[thorium90]

Vertical entry into the header? Maybe having it going in at an angle of say 30Deg in the flow direction of the header might help.

It does seem odd that the gravity drain is sized for flooded pipes.

Possible hydraulic jump occurring inside the pipe? A hydraulic profile analysis would help.

Or, maybe it just plain old rubbish stuck in the pipe somewhere.

[breizh]

Hi ,

is the problem since the start up or recently ?  definitely gas will not help .

My thought .

Breizh

 

[Wyper]

Its been happening for awhile (years), not sure if its been since start up. thorium90 we did find cleaning the lines helped reduce but not entirely. An angled entry sounds interesting and helpful, and it may be easy to implement since the drains are flexible lines.

[bwirtz1224]

You say that "Another interesting point I found is that the 1% grade is not always followed along the line."  Any chance that the grade actually flows up enough that the pipe flows partially full under partial loads and fills up at full load enough to plug the line and pressures go up during full flow to overcome the uphill grade?

[Wyper]

You say that "Another interesting point I found is that the 1% grade is not always followed along the line."  Any chance that the grade actually flows up enough that the pipe flows partially full under partial loads and fills up at full load enough to plug the line and pressures go up during full flow to overcome the uphill grade?

There are several sections where the grade is less than 1%, and one 5 meter sections where the pipe goes up by 2-3 inches. One idea I had was that the uphill section creates a restriction and the down flowing fluid creates a pressurized air pocket between the full loaded pipe and partial loaded pipe. Currently in the process of resolving the pipe heights to return back to grade.