Air Hammering Paste Backfill System

[NEMINING2]

Hi All,

I’m contacting you because i would like your input regarding a problematic we are facing in our paste backfill systeme at our underground mine.

We use a piston pump to get the paste from surface to underground. The horizontal distance can be relatively high (ratio H/V can be high for the stopes to be filled in the upper part of the mine), the pressure on the line could also be significant and produces line hammering (when high, we usually break the support of the steel conduits)

When we tried playing with properties of paste, such as adding superplastizer (lower viscosity of our paste), we experience significant drop of pressure on the line and the air hammering was reduced.

I’m looking for a way to eliminate the air hammering, and its difficult when you don’t know the source of the problem. We reviewed the hydraulic model and we believe its calibrated as the pressure gauges underground match with what the model is predicting. Please find attached a screen capture of the hydraulic model for a stope in the upper part of the mine

We think there is an air pocket, under pressure, that produces the hammering on the line.

Our idea/project, is to bleed the air pocket (that we think is trapped) by installing a valve on surface, on the conduit, that could be remotely opened :

1. Remotely open an actuated valve when the air trapped in the line is causing hydraulic hammer. In this case you would direct that high pressure air to a steel container which would act as a muffler and safely dissipate the air or paste released.
2. Remotely open and actuated valve to use a venturi to remove the trapped air from the pipe when the pressure is still low

Any input, ideas or comments are welcomed

Thanks,

Nemining

 

[MikeHalloran]

what sort of piston pump?
I'm thinking that, e.g. replacing a duplex pump with a triplex could reduce the amplitude of excitation traveling down the pipe, analagously to multiphase electricity.
Beyond that, maybe you have some control over the motion of the individual pistons, that could be adjusted to the same end.


Perhaps counterintuitively, in domestic water systems, water hammer is suppressed/ prevented/ controlled by >adding< an air pocket to the system.
... so maybe your system is actually too 'hard'.



Mike Halloran
Pembroke Pines, FL, USA

 

[LittleInch]

I'm not sure what you mean by "air hammering" or why you think that air is your problem.

From what I can figure out you're trying to pump a slurry or paste downhill using an unknown type of piston pump. Piston pumps are fairly notorious for introducing pulses and shock waves at a frequency which the pipework can respond to and vibrate. Normally air or some sort of cushioning effect makes life better, but a lot depends on the pipe configuration, the fluid density and speed of sound and the level of supports, clamps and guides in the pipework.

This sort of thing can be analysed and options developed which reduce or take out these pulses and sound waves which then react at various elbows and bends to create mechanical vibration and movement.

Have you ever done a vibration analysis? Are there any pulsation dampers, "hard filters" or similar items designed to reduce this pulsation effect?

Can your pressure transmitters pick up pulsation frequencies?

Have you thought about using a different type of positive displacement pump?

Can you vary the speed / flow of your pump to see if this only occurs at certain speeds?

Here's a simple starter

https://www.qualityhydraulics.com/files/2813/6726/9661/pulsation-cause-and-solutions.pdf

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[NEMINING2]

Thanks MikeHalloran and LittleInch for your answers,

By air hammering I mean pipe that displaces at a certain pulsation frequency. Repeatedly, this will break the support of the pipe in the drift and will potentially produce a Spill.

We have accelerometers installed in the pipe to monitor vibration. We thought at the time that a dampener would solve the issue, but after several trials with the dampener, we realized that it had no effect on the pipe hammering. We have values from the dampener in % terms as standard deviation. What does that represent ? How can we modify that to get an optimized pipe behavior ?

The other thing is when we reduced the flow of paste (Q in m3/s), we realized that the hammering is reduced significantly. Also, with adding superplastizer (paste less viscous), we were able to reduce it.

However, those are temporary solutions, and as tonnage increase, so our capacity to increase backfill underground. Therefore we can't afford to reduce Q or adding to much superplastizer ($$$)

Any input, ideas or comments could help me solve the issue.

Thanks,

 

[LittleInch]

I assume you mean some sort of fluid dampener and yes, in some cases they don't make a lot of difference.

The fact that the issue changes with flow and hence speed of your pumps and hence the frequency of the pulsation tells me you have a big issue with pulsation coming from your pumps. The orientation of the piping, number of bends, how the pipes are held down etc have as much if not more of an issue as the pump and any pulsation dampening devices. I suspect your plastisiser is somehow altering the physical aspects of the slurry and possibly also the speed of sound.

This needs proper analysis by vibration software to see where your issues lie and what the options are. Sometimes it is pipe layout, maybe a speed range you can't work at or other dampening or noise filtration issues.

Maybe a different pump or different type of pump would be better, but the devil is in the detail. Sometimes more supports works, sometimes flexible supports which stop the vibration from hitting the natural frequency of the pipe, maybe a bigger pipe - too many details and options to work out here.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MortenA]

You mention the positive effect of your additive. I was thinking that maybe your paste has a non-newtonian effect (e.g. could change properties to a solid at high velocity)? This could cause the pipe to temporarely block up (due to solid plug) that then dissolve itself in the accelerate/decelerate cycle of the piston pump? Maybe a pulsation dampener would help? If you should consider another pump type maybe a progressive cavity type?

Best regards, Morten

 

[NEMINING2]

Thank you MortenA,

Do you have documentation about changing properties of non newtonian fluid at high velocity. This is quite interesting theory. One would think that at low velocity, settlement of paste can occur and could cause blockage. But I guess at high velocities, segregation between particles could occur leaving heavy particles to settle.

Thanks for the theory

 

[hydtools]

If the fluid does behave as a non-newtonian fluid, reducing velocity reduces shear and the fluid becomes more liquid, easier flowing.
Larger piping would reduce flow velocity while maintaining required volume flow.

Ted

 

[LittleInch]

"Paste" implies a low liquid, semi solid material which doesn't separate into liquids and solid. Slurry is different.

Any non Newtownian fluid needs lab tests to determine whether there are strange effects at different shear rates or some trial and error yourself.

What is this paste?
Velocity at which you get this effect?
Pipe size?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MortenA]

I agree with littleinch