Slurry has liquid moving much faster than solids? 1

[vanillabeans12]

I'm working with a slurry that has solids about 0.75 inches in diameter. The liquid isn't that viscous. This is a new slurry in a process where we handle other kinds of slurries no problem. We were draining the slurry from a batch tank to another tank as usual, and it was pumping fine, but when we look at the receiving end, it looks like all the liquid beat the solids, and the solids dragged behind.

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It didn't plug the pipes, but the first thing I thought of was slippage. The pump (positive displacement, not centrifugal) was operating at a rather fast flowrate, so that probably didn't help either. I was thinking of increasing the viscosity of the slurry, as well as increasing the agitation in the batch tank to give better distribution of the particles right before it pumps (some of the solids settle towards the bottom before pumping). Is this a good approach? What else am I missing?

 

[1503-44]

I would think your solid Density is well higher than the usual stuff. It doesn't sound like agitation is going to help without an increase in viscosity. You may wind up just agitating the liquid, which is what you appear to be doing now anyway. Also sounds like you have more than enough velocity, near 100% slip, and that isn't working out. I think you need to use a denser liquid to get the buoyant weight of the solids lower, which should also get your viscosity higher too. Both will help. The problem is your settling velocity is too fast. With both fluid density and viscosity reducing settling velocity you may be able to keep your solids in suspension and your forward velocity reasonable as well. Higher velocity is expensive, even when it works, and increases abrasion. You run out of road quickly on that route.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[LittleInch]

I'm with Mr 44 here. This doesn't sound like a slurry to me, more like dirty water with some stones in it.

Unless your pipe is pretty big I'm surprised you didn't get the stones jamming up at the first bend or low point.

The high velocity of the liquid is probably what helped you.

A much heavier and more viscous liquid is needed.

What type of pump? Progressive cavity or?

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

 

[vanillabeans12]

The "rocks" make up about 20% of the batch by weight, so wouldn't that be a slurry?

The pump is a rotary gear pump.

 

[1503-44]

I don't know officially, but in my book there has to be at least some suspension of the solid in the liquid to be a slurry. It seems like you have two-phase flow, and not really a whole lot of that. If you got 20% of water weight delivered as solids, it might be a slurry, but was it actually a slurry flow, or just rocks rolling along the pipe bottom? In a true slurry flow I would expect to see about the same mix Density at the top of the pipe as there is on the bottom, with about the same velocity at any upper radial distance as the same lower radial, if laminar. If turbulent, the density should be nearly the same throughout. If you don't get that, then you might have stratified flow. But this is more like stratified 2-phase flow, liquid above at one velocity and solid below at another. Am I right?

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[vanillabeans12]

The goal is indeed to get the solids suspended. But I have heard of slurries where the solids are completely stratified.

 

[LittleInch]

A gear pump for a fluid with that size particles doesn't sound right to me. Is this slurry basically water and these large stones?[pre][/pre]

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

 

[pierreick]

Hi,
Gear pump is definitely not the right technology because of the properties of the fluid.
Take a look at the document attached.
Pierre

 

[Artisi]

The carrying media for "rocks" needs to be a slurry.
Look on the internet for the Warman slurry pumping data - that will address your problem.
Check on the Weir engineering site as they now own the Warman product.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[pierreick]

Hi,
A handbook to support your work.
Pierre