Dosing Pump and Concentration of Chemicals

[Nad87]

Hello,
I want to understand in general how to arrange percentage of dosing in the dosing pump? and what is the relation with the concentration of chemicals we need to add? and how we calculate the quantities?
Thanks in advance.

 

[EdStainless]

Algebra is how you do this.
Write the chemical balance equations and being plugging in values.
Typically you look at the chemicals and they have a maximum concentration that is either available or safe to handle.
At the same time you look at pump volumes and sort of choose minimum and maximum flows that you want to meter.
Then you can find a range of reasonable solutions.

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P.E. Metallurgy

 

[SJones]

1. Establish the basis for dosing, e.g., ppm on a total fluids basis; ppm on a water content basis
2. Establish the chemical concentration basis: total chemical volume, or specific agent basis
3. Ensure the dosing line has a flowmeter

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[Nad87]

Dear all,
thanks a lot for replying
I found one equation saying ppm = dosing pump flow*specific gravity*dilution*1000/feed flow.
I think for dilution the mean how many liters of chemical we should put and mix with water in the tank.
Really this is the first time I see this equation and am getting confused.
Now for exemple I have RO and I need to put anti scalant and HCL with two dosing pump.
I need to know how many litres from each chemical I should put in 2 tanks of 100 liters each and which percentage I should adjust my dosing pump on it?

 

[EdStainless]

This is going to take some basic chemistry.
Are you doing to a concentration of to a pH value?
I am guessing pH. Fortunately that is straight forward for this acid.
It is just a chemical balance, desired concentration in tank x tank volume = reagent concentration x injected volume
Watch the units, keep them consistent.
Most PLCs can be programed to do the basic math, so you can automate this process if needed.


= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy

 

[TiCl4]

To be honest, the equation needed to figure out how to achieve a given ppm of dosed material in a given flow-rate is simple and something you should be able to derive extemporaneously. If you cannot derive the formula yourself, I suggest you hire a contractor who can handle the whole dosing system for you. Companies that handle boiler treatment or cooling tower treatment systems can likely provide full-service installation for this.

If you are wanting to know what ppm level you need for dosing, that will be determined by your water quality. You should either ask the RO manufacturer for dosing recommendations or have a water analysis done to determine required dosing amounts for anti-scalants and HCl.

Note: I am surprised you are deliberately dosing the system with HCl. Our RO system has a carbon bed filter upstream to remove Cl ions - they would destroy our membranes.

 

[Iomcube]

carbon bed filter upstream to remove Cl ions

Are you sure Carbon bed remove Cl- ions?

 

[TiCl4]

Are you sure Carbon bed remove Cl- ions?

Bad terminology, thanks. We generally refer to the carbon bed as removing chlorine. To be more precise, it actually removals free chlorine in the water by reducing NaOCl to NaCl (or reducing chloramines). Some references are provided below.

I had forgotten that the chlorine in HCl doesn't really have any oxidizing potential and therefore wouldn't present an issue with membranes, hence my prior statement of surprise. HCl makes more sense than sulfuric acid if the incoming water is not softened and SO4 ions would increase scaling potential.

I can't seem to edit my previous post. Odd.

 

[Iomcube]

I had forgotten that the chlorine in HCl doesn't really have any oxidizing potential and therefore wouldn't present an issue with membranes,

I am afraid you have to review your sentence!
HCl in industry is prepared in furnaces that burn Cl2 in presence of H2 gas. Google SGL / Carbon Lorraine furnaces
This method can produce HCl batches that does have free Cl2 in it & are deleterious to resin beds / RO Membranes. We had employed a regular starch test to avoid it.

 

[TiCl4]

Thanks, I didn't know about the HCl production process. So injection of HCl is still a concern from a membrane perspective.

Well, I was correct that HCl itself has not oxidizing potential . It's just that pesky free chlorine that happens to be floating around with it.