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Mixing distance in a pipe

Mixing distance in a pipe

Mixing distance in a pipe

(OP)
In a water treatment plant, I need to start injecting caustic for pH adjustment. It will be in a 30" pipe with velocities in the 1.2-2.4 fps range. How far after the injection point will the mixing be complete enough so that a pH probe will give me a good indication?

RE: Mixing distance in a pipe

Are there some baffles in the pipe to insure turbulence?

RE: Mixing distance in a pipe

(OP)
There are no baffles or bends. Just straight pipe in an existing concrete vault.

RE: Mixing distance in a pipe

You need about 4 turns or changes of direction to be sure that the solution is mixed. At the low of velocity that you describe, it is going to take a long distance, maybe 100 feet or so.

Have you considered using a mixer?

Not sure why you would be injecting caustic for pH control. Use of caustic (NaOH) is going to be very expensive for that capacity. Have you considered use of lime?

RE: Mixing distance in a pipe

Bimr's idea is OK as long as no unwanted calcium salt precipitates out of solution under the process conditions.

RE: Mixing distance in a pipe

You guys have bauxite industry nearby? They will love to sell you caustic since it's their by-product, but don't use lime, please...

30" pipe? that's a large TP.

Cheers
munich

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