I want to promote Scale Buildup in pipes and pumps

[benchtester]

(Please excuse a newbies cross-posting. I first put this in Process Development, but I think this is a better forum.)

This probably sounds strange but I want to cause scale. I want to build a test bed to compare different pumps and their relative ability to tolerate scale that might occur in drinking water systems. While I would like to accelerate the rate of buildup; it would also be fairly important to have the areas of precipitation to be similar to real world systems. For example, would there be less scale in high flow areas and more in stagnate areas? I wouldn't want to precipitate free particles in the fluid stream (unless this too happens in real life).

I am a mechanical engineer with a fairly limited background in chemistry. So feel free to "talk-down" to me in the answer. What would the best salts to use? Should I start a little acidic and then adjust the PH higher over the test period?

 

[ekolog16]

Read up on scaling and fouling and then do the opposite.

http://www.jaeger.com/1996foul.htm

http://www.watertreatmentguide.com/membrane_fouling_solutions.htm

Calcium sulfate (CaSO4) or calcium carbonate (CaCO3) may be good salts to start (>1000 ppm). As for adjusting pH for these particular salts, say if you go from pH 4 to 9, scaling and fouling should increase with higher pH.

 

[bimr]

Scale is typically caused by water hardness and elevated pH.

Two types of hardness are generally recognized: carbonate (sometimes referred to as temporary hardness) and non-carbonate hardness. Carbonate hardness, depending upon the nature of the water is composed of calcium or magnesium carbonates and bicarbonates. It is this form of hardness (calcium carbonate) that contributes most to scale formation. Non-carbonate hardness is normally a small component of the total hardness and is characterized by much higher solubility. As a result it’s role in scale formation is generally negligibile.

Water hardness is classified according to a somewhat subjective criteria that varies from reference to reference. Table 1 provides a common interpretation. Scaling problems typically occur above levels of 100 ppm hardness.

http://geoheat.oit.edu/bulletin/bull21-1/art3.pdf

If you elevate the water pH above 10 to 11 pH units, your water will be scale forming (if the water hardness is above 35 mg/l of calcium carbonate hardness). From that point, the higher the hardness, the more scale that you will encounter.

 

[QualityTime]

Hi, I just had a discussion about this in the WASTE DISPOSAL AND TREATMENT forum but in this case the questioner wanted to prevent calcium carbonate precipitation. I gave the questioner some information and the questioner is actually doing jar tests right now

As people have said here, you will have to elevate the pH of the water. I would suggest that for the pipe velocities you will typically encounter you will not able to prevent the scale from forming on the pipe wall.

 

[bimr]

http://faculty.washington.edu/markbenj/CEE483/Opflow_2000-06 corrosion control.pdf

Forgot to mention, if you elevate the temperature, the scaling will increase.

 

[QualityTime]

You will be precipitating free particles in the fluid stream because if you are oversaturated (aka the water is unstable) calcium carbonate will be going in an out of sokution

 

[bimr]

Maybe you can post a link that documents what you are referring to.

The CO32– reacts with Ca2+ or Mg2+ ions, to form insoluble calcium and magnesium carbonates which precipitate out. The key word there is INSOLUBLE.

Once material precipitates out of solution, the bulk of the material will not go back into solution unless you change the solution properties such as the addition of an acid.

Here is a picture of pipe scale. If what you are proposing is true, the material will not form the scale shown in the picture.

http://www.rswaterservice.com/images/pipe_scale.gif

 

[ekolog16]

I'm interested in how this experiment might work for pumps. Would the inlet and outlet pipes of the pump foul before the pump itself (since higher velocity and shear stress reduce fouling)?

In fouling applications in P&T systems I've seen, the pump efficiency is affected by the increased head from fouled pipes like the one in the picture you've shown. I suppose you could use anti-fouling pipes or cathodic protection to isolate the pump first.

 

[bimr]

The fouling of the pumps will be somewhat unpredictable because the fouling will vary with the metallurgy of the pump (which you have not stated). You also will experience some fouling/corrosion of the bearings and seals (this will vary with the type of pump). The type of solids that precipitate will effect the pump (some solids will be more abrasive than others), Finally, there will be the effects of higher velocity and shear stress which is also unpredictable.

However, if you are interested in the most common type of scale in potable water systems, then you should focus on the scale associated with water hardness.