Sludge Cake Pumping to Sludge Silo 4

[qubitsized]

Hi everyone!

We have a 15 bar progressive cavity pump that is conveying lime-treated sludge to an 8-m high, 4-mΦ cylindrical concrete silo at the rate of 5 m[sup]3[/sup]/h. We decided to inject the sludge cake at the bottom of the silo instead of the top as shown below:

Diameter of conveying stainless pipe is 150mm, sludge cake density is 1070 kg/m[sup]3[/sup]. Conveying distance is ~5.0m.

Will this work?

 

[zelgar]

Does the PM have engineering experience? If not, I wouldn't take their advice that it'll work with much confidence and design it the way you think it should be (you're the engineer). Either way, I would talk to the PM and bring up the issues (e.g., increase load on equipment, drying out of material in silo, Last in = First out) of the bottom loading.

 

[qubitsized]

Yes, PM is also an engineer, double-degreed. He is actually pretty good in process stuff. I already brought this up and we had a long written correspondence. He said he does not agree with my interpretation. See attached rough sketch I sent 2 weeks ago. I also added that there might be pressure spikes in the piping since the Positive Displacement Pump is continuously pumping material, and we've got something blocking at the end. I said that it's like running the pump and gradually closing a valve downstream.

 

[MartinLe]

I'd be concerned if the bridge breaker is enough for mixing. Look at this video:

https://www.youtube.com/watch?v=dr30WEVsX5I

What you see is sewage sludge at 20% (later 45% with added lime and wood shavings) TS pumped with a piston concrete pump. Note the action in the twin auger feeder of the pump early in the video. Confirm with Seepex that the bridge breaker is up to the task.

You'll also see that the pressure rises up to 20 bar on the stroke of the pump, at rather low flowrates. Since ths sludge in the video is 20%TS and you have 15%, I think you are still save. Viscosity (and non-Newtonian behaviour) seems to rise sharply (> linear) with TS content.

I second checking out similar installations, preparing a flange for top feeding operation and seriously looking at an auger.

 

[zelgar]

Personally, what I would do is design it both ways. I'd present a list of pro's & con's for both designs. Unfortunately, a lot of the con's for the bottom loading design are hard to quantify (e.g., How much of an increase load is it for pump? How much of an increase load on the tank due to the bottom loading? Will the material dry out on the top? How difficult is it to replace/repair the feed line into the tank? How often could it fail?)) One big advantage of the top loading design is that most of the con's of the bottom loading design are nullified.

In the end, you need to satisfy your PM. One important thing if you do provide the two different designs is you put the responsibility of the final decision of the design of the tank with your PM. You minimize your risk if the bottom loading design fails because you have a paper trail indicating that you had a lot of concerns with that design.