Pumps for Slurry

© 2012 Dr. B. C. Paul

Note – These slide illustrate a solution approach using Sysel, a program developed by GIW and contain screen shots from the operation of the

program

Credit for the program is given to its developers.

Slysel Can Be Used for Plain Water or Water Containing Solids• Water containing solids is called a slurry• Solid particles usually increase the over-all

density (since most solids are more dense than water)• This increases the energy required to move the

flow

• Solid particles can make the water thicker and gooier (also called raising the viscosity)• This can also increase energy required.

Slurries Can Misbehave

• Usually the solids are not a part of the water and can separate out of the water

• Settling out can plug pipes rather nicely• Some slurries are fine enough and develop

enough charge on the particle surfaces to keep them stable almost indefinitely• This is not typical of something a mining engineer

would mix up to pump.

Lets Consider a Coal Prep Plant

• We will use a pump to feed a coal water slurry to a bank of cyclones.• We will go for 15% solids• We will assume our cyclones need about 15 psi

feed pressure• We will assume each of our cyclones need about

600 gpm and we have a bank of 6 such cyclones (ie 3600 gpm)

• Our coal is between -20 mesh and 100 mesh

My Layout

Slurry

Cyclone Feed Point

Pump

15 200

70

25

I Begin with My Normal Project Naming and Unit Selection

Use the firstTab.

I Start With My Suction Side

Note this timeI had aPositivePressure onThe intake side

Note also thatThis time myOutlet isRequired toProvide theNeeded feedPressure toThe cyclones.

Note I am on 2nd Tab

I Proceed to Enter My Pipe System

I Then Complete the Pipe System

My 3rd Panel Starts Out Normally

I specify my flowRate and tell theProgram toCompute myHeadRequirements.

We Need to Fill In Slurry Properties

We put the curser on the S.G. solids and the rightClick to get a list of typical specific gravities.

Obviously I’m going to pick coal

When I Type in 15% Solids By Weight the Program Fills in the

Other Mixture Properties

Now I Need to Deal With Particle Sizes

• My Slurry is 20 X 100 mesh• I assume my top size is controlled by

screening• I screen for the bottom size to but there will

always be some slimes that hold on to other particles

• The program wants dimensions in microns

Conversions

• 20 mesh = 0.85 mm• 100 mesh = 0.15 mm• We will assume our D50 (50% passing

size) is about 40 mesh = 0.425 mm• mm to microns 1mm= 1000 microns

• Top size is 850 microns• 100 mesh is 150 microns• D50 is 425 microns

Put in My Sizes

I had to uncheck the boxesBecause otherwise theProgram tries to estimateAll the other sizes from myD50 which makes eitherAn unrealistic top size orA D50 finer than 100 mesh.

(My D50 needs to be rightBecause it influences howEasy things settle out. MyLargest size needs to beRight because it controlsImpeller clearances needed)

Now I Need to Deal With the Miller Number (which is a measure of

abrasiveness and wear)

I use the right click for suggestions trick again and pick coal.

The Next Page Looks at Energy Requirements for Pumping Slurry

as Slurry Density ChangesIt’s really a sideCheck routineAnd not part ofThe mainProgram.

If you are doingLong rangeSolids transportIn a horizontalLine its helpful

In our case ourSlurry density isPretty well fixedBy our cyclones

Slysel Has Us Look at a Range of Flows in Our Pipes

(This is a critical punch-line section)

My target flow is 3600 GPM so I decided to try 3,000 to 4,900 in increments of100 GPM

The Top of the Report is an Echo of My Input

ObviouslyThis is a goodPlace to checkThat you areStudying whatYou believeYou are.

One defect IFind is it alwaysCall S.G. 2.65Even when a1.1 densitySlurry has 15%solids

We Are Told the Flow Rates to Minimize Friction and Avoid

Settling

Flow rates for minimal friction are all lower than our 3600 GPM – on the other handWe had not better try those flow rates or our solids will settle.

It recommends 2400 GPM to avoid settling – at 3600 GPM I should be OK.

Bottom of Table Shows Head Losses at Different Flow Rates

I’m notSeeingAnything thatMakes weWant toChange rightAway.

Configurator Allows Us to Specify Things About Pump Construction

I’m sticking withThe defaults hereFor now.

Now I Go to Pump Selections

They are in order of Efficiency – My top choice is 81% efficient and needs anImpeller speed of 930 RPM. 196 HP will be required.

I could scroll down looking for a lower RPM but my efficiency would be declining

To select this pump click on it and it highlights blue.

It Then Offers Me Some Additional Details

We will not be delving into the details of pump construction but you can see the bearingAssembly is what is changing. I will click on the first choice to move on.

A Bunch of Pump Details Appear

Slysel Does Not Draw Us the Pump Curve But It Does Give Us

the Points on It

This is the point where our pipe curve intersects the pump curve.

If We Plotted Things We Would See This

Flow Rate

Head

Pump Curve

Pipe Curve

Operating Point

A Critical Detail to Check

Net Positive SuctionHead (ie can the pumpSuck fluid into itself)

We need 10.6 ft

We Have 33.5

We are OK

For Motor Sizing

It is suggesting a 250 HP motor to meet our 196 HP Need(Motors come in standard sizes)

Under System Results it Shows Our Pipe System and Pump System at Different Flows

We could use these point toPlot the pump pipe curve IShowed a few slides back.

Under Sheave Duty It Shows

We could use a constant speed sheave with a 250 HP motor turning 1780 rpm andDriving the pump between 925 and 957 rpm.

Now Its Your Turn

• Feed a similar cyclone bank with a 15% phosphate rock slurry (will be apatite on the solids density selection).

• Draw Out the Pump Pipe Curve• Identify your motor size and speed and

your pump speed.• Turn in your Slysel File.