Lime slurry info to prevent scaling

[Pulpboy]

I have to rework a lime addition system to our reactor clarifier. I'm wondering if there are any articles regarding the best makeup of lime to prevent scaling in piping.

1) % of hydrated lime in slurry
2) Flow rates in pipes to minimize scaling
3) Temperature ranges.

Any help would be appreciated but some sort of technical resource would be helpful so I can show where I got the information for justification of the project.

 

[stanier]

You will always get scaling whatever you8 do. I have used flexible PVC hose laid in cable ladder. The operators shake them occassionally. I have seen open troughs used made out of pVC pipe cut in half. At least they dont clog. Any spilaage dropped in the clarifier any way.

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[cub3bead]

Can you obtain 40% hydrated lime slurry easily? If you can it is by far the easiest way to go. If it is not available, then I have always set up my feed systems to use a 5-10% slurry.

You will want to use 5D pipe bends instead of elbows. If you must use an elbow, install a cross and plug two of the legs. That way when it plugs you can clear it easily. Keep your flowing velocities over 3 fps (5 fps is better).

I like to install a recirculation loop from the slurry tank to the point of application and back to the slurry tank. If the lime feed rate is X lbs/hr then I size the supply pump to deliver 3X. The return line will take the 2X flow back to the tank. Make sure you step the pipe size down on the return line. I normally use an actuated plug or ball valve to pulse the lime feed into the reactor/clarifier. Immediately downstream of the plug valve is a manual pinch valve that you use to adjust the lime slurry feed rate. You will want the plug valve to be open for about 30 sec out of every 2 minute period. Pace the operation of the valve off of the inlet flow meter.

Non-metallic hose and pipe are good for this application but require a tray for pipe support.

Another option is to use peristaltic pumps with VF motors. But you have to watch your lime velocity to make sure you don't settle out the solids.