HCl vs SO4H2 for demin water plant regeneration

[22854]

1)I would like to know advantages and disadvantages of using HCl or SO4H2 for the regeneration in a demineralization water plant.

2) How can I make an economical evaluation from the point of view of chemicals consumption ?

3) Is it possible to use our actual SO4H2, Carbon Steel tank to store the HCl?, Which should be the best suited material for the HCl.

4) The mixed bed vessel have distributors made of SS AISI 316L are they good for HCl or we have to change the material.

Actually we are processing an average of 180 m3/hr of water in the cation-anion exchangers and our consumption of Sulfuric acid 98% is 560 lts per regeneration.

In the mixed beds we are processint an average of 300 m3/hr of water and we are consuming 360 lts. of sulfuric acid 98 % per regeneration.

Thanks in advance for any help

 

[mohtogh]

Hello,
Ans. 1.
(a) It is related to price of H2SO4 and HCl in your country.
(b) For regeneration of 1 Kg resin ,HCl consume more than H2SO4, because HCl has one H ,and for H2SO4 2H . And also concentrated H2SO4 is 98% but concentrated HCl is only 36% .
(c) When your feed water has high concentration of SO4 anion , You should use of HCl not H2SO4, Because of risk of CaSO4 persipitation,during regeneration.
(d) We can store 98%H2SO4 in mild steel tanks but for HCl ,we need plastic tank or coated steel tanks (e.g. rubber coated).
Ans. 3. Above
Ans. 4. SS316L is also good for HCl.

 

[Dofsteel]

I would suggest that you use sulfuric acid as a regenerant instead of hydrochloric acid. There are several reason why you should do this:
1) Sulfuric acid is usually cheaper, but this will depend on where your plant is.
2) You need less sulfuric acid to regenerate your resin because there are two hydrogen ions per molecule, as opposed to one per molecule of HCl.
3) You can store 98% H2SO4. This means that you will have to refill your tank less often, decreasing shipping costs, risks of acid spills. Also, 98% H2SO4 can be stored in steel tanks, while 35% HCl is extremely corrosive (which leads to higher maintenance costs)
4) Even if you have a significant portion of calcium ions in your feedwater to your demineralization plant, you can perform a stepwise regeneration of your cation, reducing the possibility of precipitating CaSO4.
5) Since you are currently using H2SO4, a change to HCl could cause you problems in terms of corrosion of your vessels or piping.

Hope I was helpful...

 

[22854]

Thanks to those who have answered my questions, but I have another one.

Actually we are regenerating the cation in two steps. First with Sulfuric Acid 1,5% and the other one with sulfuric acid at 3% concentration (This is to avoid CaSO4 precipitation). And, we are regenerating de mixed beds with SO4H2 at 5% concentration.

Taking this into account or generally speaking, which are the HCl concentrations normally used for both cases ?

Thanks

 

[DeltaCascade]

Hi.
H2SO4 only uses 1 H+ ... HSO4- is a weak acid that tends not to dissociate further...although HCl is used slighly more efficiently than H2SO4 (see ion exchange resin design data from supplier). HCl vapour can be a problem.
CaSO4 precipitation during regeneration is a common problem, commonly overcome by proper design and operation (1%, 2% and 4% acid regen steps, proper flowrates, etc).

For additional info contact ion exchange resin suppliers .. in particular, ion exchange handbooks or, really, ion exchange resin product guides which give design info for different regenerants (HCl or H2SO4) .. there are many pros and cons but the exchange resin data will give you basis on which to make economic and operability analyses.
As others have said, if HCl cost is low enough, it's use may be justified.

Good luck