Force main bypass into gravitatinal flow - how to discharge 3 bar (industrial sewage)

[TomaszKruk]

Hello,

the customer has a pumping station with a force main and second pipe acting as gravitational bypass. Gravitational line works 24/7 - it allows them to discharge a fraction of the sewage without it going to pumping station further down the line so they use it.

I'm to redesign the pumping station and design a new force main in place of the gravitational bypass. Up to this point everything is pretty much ok, but they want me to recreate the ability to use the gravitational line as the bypass. So I'm to pump industrial sewage for a few kilometers, discharge some of the fluid into the old gravitational line I replaced up to this point, and then continue with the force main up to the next pumping station.

It creates a couple of problems - the system in complicated enough to leave us with no data (we cannot even establish what's the pressure loss in current system since it has at least one other inflow and the pipes vary in material and installation age). We know that currently the pressure just before the second pumping station is around 3 bar.

Could you suggest sufficient means for flow control, and much more importantly I think, pressure control? When it comes to flow they are currently doing that by a gate valve (ofc - what else). A butterfly valve with an actuator with remote control would not be a problem for my project, so (since I need flow measurement anyway) I was thinking installing that and a flow meter would solve the issue of max flow. What about the pressure though? I'm buffled because it's the first time I'd have to design a force line discharge on-line, not at the end of it. And with pressure 3 bar no less. I cannot say if it's a lot but I'd think I should dissipate the energy somehow since it's also around 200 m3/h. The medium is water with solutions that sediment over time and attach to all surfaces. The more robust the construction the better (I was suggested a pressure reducing valve, but I'm not sure if I'm thrilled about the idea of using it with such medium).

Any suggestions or discussion would be much welcomed and appreciated.

 

[bimr]

It would be helpful if you would post a sketch with the elevations, flows, pipe lengths, and pipe sizes as well as a more informative description of the industrial wastewater.

 

[TomaszKruk]

hello,

thanks for the answer. I drew 2 diagrams that might be helpful. Hope they're clear enough. When it comes to elevation - it's pretty much an insignicifact slope down to the river. The change of elevation is small - no hills or depressions, just a gentle slope down to the river. All pipes are laid pretty much in parallel to the terrain.

"My" pumping station is P1.

My force main and the gravitational pipe will be DN600. Force mains join into DN900. It will create a peculiar situation where we change the flow for about 2 km for the existing pipe (which used to run 2200 m3/h and now will run 1400 m3/h) but we will not be able to replace the pipe - the entire line should be dismantled and built anew, but it creates a pile of problems that actively deter from investment. For whatever reasons - we are contracted to "solve" just P1 in best way possible.

The entire problem is that at this moment they use a manually operated gatevalve to divert some flow from P1 into a gravitational line. They are more than eager to do the same at the new location, but I don't think that's sound engineering practice and would like to at least anticipate better way to limit the pressure of the inflow into gravitational pipe. At least using a butterfly valve. Customer is supposedly always right, but it is brine and quite savage when spilling into open ground.

Problem is we are replacing just one line. All the rest will so far remain the same which makes the exact pressure in the system hard to predict.

The fluid is best described as brine of density 1 200 kg / m3.

 

[TomaszKruk]

Post just for the other diagram - cannot make multiple images work for this forums atm - sorry.