In-line dosing in pipe position 2

[CARF]

Dear all,

For an in-line pipe dosing system we are considering dosing NaOH at the INLET of the main (mono)pump. Through this we want to avoid problems with high fluid pressures we expect when dosing at the pump outlet. Furthermore the pump may function as a MIXING device.

What you think?
Good or bad idea?
Anyone of you has done this before?

Thanks for typing a few words on this!

Best regards CARF,

 

[cub3bead]

It depends on whether the pump stator can take the heat generated by diluting the caustic. It can be significant.

Make sure you design in the block & bleed system for the caustic supply.

My preference is to design a mixing tee arrangement on the downstream side of the pump. The dosing pumps commonly used for this type of application can usually deliver the pressure needed.

 

[roker]

hi,

you can use a small side stream from the pump discharge as the motive fluid to an eductor (ejector with liquid motive stream) that will "pump" the caustic and back to the main discharge line.

regards

 

[CARF]

Thanks for the suggestions.

What you think; will it the pump help mixing ???

CARF

http://www.carf-engineering.com

 

[quark]

Worst case scenario will be separation of two fluids due to centrifugal action. All applications I saw and have been using are with dosing in discharge lines.

 

[sshep]

Injecting into a centrifugal pump suction works good for mixing and is in my experience a good injection point for antifoams, etc. A Mono pump however is a progressive cavity pump and as such will not have nearly as good of mixing effect. Mono pumps are in fact often touted for use in two liquid phase systems where you don't want to emmulsify the phases.

While it doesn't seem like there could be much harm in injecting into the suction, I wouldn't count on a Mono pump as a mixer if the application is critical.

 

[CARF]

Dear all,

Many thanks, you are helping me in getting the best solution.

I guess the only way with a centrifugal pump to separate fluids is when they have different density?

However we have a monopump ...

Yes, I can imagine for monopumps the mixing will not be that much. On the other hand it may not damage and we could apply a (static) in-line mixing device after the pump.

Any more idea's?
Thanks!

 

[bimr]

I agree with sshep. I would add that is also not a good idea to add fluid after the mono pump. The reason being is that the flow is pulsing with a mono pump.

However, if you use pumps such as the Braun & Luebbe where the pump drive trains are geared together, it would work.

Tee static mixer is probably not going to work either. The static mixer would have to be sized for the maximum flow rate, not the average flow. The maximum flow will occur during the pulse. So you are looking at a situation where it is not possible to size the static mixer correctly. I don't think it a good idea to use a static mixer on a pd pump.

 

[CARF]

Hi all,

It's an: eccentric screw pump; positive-displacement self-priming pumps with a single rotating axis. Steel rotor and rubber stator are the main elements for pumping. Their strong point is to move the product delicately and constantly.

http://www.csf.it/home.asp?mn=2

I agree with sshep that this pump will not mix that much so we will still need an addtional device to get a good homogeneuous mix.

Thanks for the Braun & Luebbe idea !

Any more experience from the field?
CARF

 

[ivanhoe374]

I have recently come accross the same problem where i was only using a tiny dosing pump (ALLDOS 0.4L/hr). This DP can only pump at 1-2 bar from memory and the line pressure needed to be at least 2.5bar(feed to an RO which had a low pressure switch on it).

In this case we have done exactly what you said and have dosed before the feed pump (with antiscalent for scale control and metabisulphite for chlorine removal).

But yes as mentioned the mono pump wont act as a mixer, in many cases we just install an inline static mixer to do this job. These often even have a 1/4" fitting for your dosing point to screw straight into which makes life easier as well.

 

[CARF]

ThanX Ivanhoe,

What's a RO ?

C.

 

[quark]

RO - Reverse Osmosis

Ivanhoe,

I would rather consider it as discharge side of the pump that feeds water to MGF and softner

 

[ivanhoe374]

Quark,

Youve lost me there...MGF, softner?