Sulphuric acid Storage and piping system 2

[Csqiz]

Hi everyone,

Currently I am designing for a Sulphuric acid dosing system for a water treatment plant. It involves bulk storage at 98% concentration sulphuric acid and dosing at +/- 3% concentration sulphuric acid. The process involve inline dilution.

1) Chemical Storage System
I read from the articles saying that HDPE could be used for 98% sulphuric acid but small amount, Carbon steel is recommended for bulk storage of more than 10,000 gallons.
May I know if a Mildsteel Tank with HDPE lining suitable to store 24.5 US gallon of 98% sulphuric acid, since HDPE is chemically resistant to the chemicals at this consentration. Is this practiced in the general industry?

2) Piping system
I am planning to use cPVC schedule 80 piping system for the concentrated sulphuric acid and uPVC schedule 80 for diluted sulphuric acid. At the T joint, the piping will be carbon steel with PTFE lining to withstand the heat generated from the dilution.
From what I read from the material chemical resistant chart, CPVC is suitable to be used for concentrated sulphuric acid. Let say it is not recomended, what will be the concern or reason behind this?
There is another problem when we are selecting the valves as well, the oring of cpvc valves, be it FKM, EPDM or FPM have no resistant to 98% conc. Sulphuric acid. What are the others recommended material for this application?

3) Dilution
From the dilution calculation, the final temperature of the diluted acid will be about 40 degreeC. Will there be any issue if the system is not installed with a cooling system? The system is adding acid into water, the dilution ration is about 25%. As we have larger flow of water, the temperature rise is smaller due to mCpDT?

I am sorry if I ask a stupid question, but I hope the above could be clarified. Thank you.

 

[Csqiz]

Anyone from Malaysia could provide professional design review service for the sulphuric acid system?

 

[shvet]

HDPE could be used for 98% sulphuric acid ... HDPE is chemically resistant to the chemicals at this consentration.
NACE RP0391-2001
2.6.1.2 Polyethylene (PE) and polypropylene (PP) are subject to environmental cracking. Likelihood of cracking increases with increasing acid concentration and temperature ...

Is this practiced in the general industry?
NACE SP0294-2006
2.6.6 High-temperature baked phenolic linings and epoxy novolac linings are commonly used in small carbon steel storage tanks if iron contamination is a concern for sulfuric acids in the 90 to 98% concentration range.
NACE RP0391-2001
2.6.1.1 The fluorinated plastics listed below are resistant to concentrated acid at the temperatures covered by this standard:
• polytetrafluoroethylene (PTFE);
• perfluoroalkoxy (PFA);
• ethylene chlorotrifluoroethylene (ECTFE);
• fluorinated ethylene propylene (FEP); and
• ethylene trifluoroethylene (ETFE).
...
2.6.1.3 Chlorosulfonated polyethylene has been successfully used for hoses handling up to 93% acid. However, see Paragraph 3.7.1 for more information.
2.6.1.4 High-temperature baked phenolic coatings are routinely used in storage tanks and rail tank cars containing 90 to 98% sulfuric acid in which iron contamination must be minimized and/or corrosion protection is required. At acid concentrations greater than 98%, some types of baked phenolic coatings slowly carbonize. Others perform well into a range suitable for oleum exposure. High-temperature baked phenolic coatings have provided many years of satisfactory service in concentrated sulfuric acid when properly applied, cured, monitored, and maintained.

I am planning to use cPVC schedule 80 piping system for the concentrated sulphuric acid and uPVC schedule 80 for diluted sulphuric acid.
Temperature?

At the T joint, the piping will be carbon steel with PTFE lining to withstand the heat generated from the dilution.
Temperature?

what will be the concern or reason behind this?
Degrading and rupture

From the dilution calculation, the final temperature of the diluted acid will be about 40 degreeC. ... the dilution ration is about 25%
Looks like a mistake

Will there be any issue if the system is not installed with a cooling system?
Overheating and rupture

As we have larger flow of water, the temperature rise is smaller due to mCpDT?
What is mCpDT? How is it related to dilution?

I am sorry if I ask a stupid question, but I hope the above could be clarified.
You should contact a proven engineering contractor to develop a system design. Although H2SO4 is one of the oldest substances in chemical industry it is still one of the most complicated in handling and processing and require proper background and experience.

Anyone from Malaysia could provide professional design review service for the sulphuric acid system?
Why Malaysia? Why engineering is related to a particular country?

PS
Have you an option to copy/adapt design of an existing unit having positive reports in operation?

https://files.engineering.com/getfi...e=Willoughby_Plastic_Piping_Handbook_2002.png

 

[Csqiz]

Temperature of cPVC piping system for 98% concentration will be 27-31 degree celsius (at normal temperature in Malaysia)
Temperature of diluted acid estimated around 40 degree celsius.

We are looking at the enthalphy of dilution for the Sulphuric acid at the molar concentration to get the Energy (Q) in unit Joule, and back calculate the final temperature using Q=mCp(Tfinal-T).

Because we are based in Malaysia and the water treatment Plant will be in Malaysia as well. Actually, any country will do, but it will be depending on the budget.

To be frankly said, this is the first portable water treatment plant we have in here (from my knowledge) with the large scale sulphuric acid storage and dosing system, not mentioning about the general industries and industrial waste water treatment plant, seldom there is sulphuric acid system at this high concentration and large scale.

 

[shvet]

Csqiz, looking at your questions and comments here and at cheresources it seems you are a water engineer and have no proper background in chemical industry.

Water you are used to is inert and it requires some conditions to become hazardous. And vice versa H2SO4 is - controlled conditions shall be provided to guarantee it is safe, and what is most important - the boundary limits are narrow. The proper design of H2SO4 installations is critical. Inadequate designs can and have lead to serious accidents in some of which I have been involved personally and much more - my colleagues have been. Have you ever seen how a human screams in pain when skin comes off his body? I have seen.

Is your case large or small - it does not matter. Design/engineering does not relate to capacity or volume or dimensions - time&efforts&knowledge should be invested are the same. Acid does not tolerate mistakes and a few drops are enough to make a person disabled. In theory a cup of acid is enough to kill.

The core idea is that design of acid (instead of water) is complex and the “why and how” is not obvious. I have been involved in operating and engineering of chemical facilities for many years and warn you from being self-confident. Proper background and experience are crucial and if you are feeling not having those I recommend leaving this issue to professionals.

It is well understood one's striving to implement materials and techniques that are well known and widely spread in water industry in a non-developed region. It is normal. What is abnormal is implementing those in a completely distinguished industry. Even that it is a small negligible part of a large water plant.

If text above is true for your case then I would recommend viewing on this issue as a water ocean having a small chemical island on it. Though 99,99999% of surface is occupied by water this island shall be treated completely different way and there is a high probability the amount of time&efforts&knowledge required by this 0.000001% is bigger that for the rest. If you know a lot how offshore works and a little how onshore does you should find a proper person/entity. And what is most important - find strong arguments to your bosses why you behave such way.

This situation is common and experience of others is:
- find a vendor that is specialized in treatment packaged unit that has references in supplying of chemicals dosing unit, believe me such device is not so expensive as may seem to a newcomer to chemical industry and has advantages
- find a relevant project designed by a reputable company and copy/adapt it, country/region does not matter as acid is acid everywhere
- find a relevant plant having positive operating reports of similar unit and do the same as the option above
- find a contractor/consultant that has proper background and references
Anonym forummembers are not the best choice for such issues. For info - as per my experience reputable water treatment reagents vendors offer packaged dosing units for leasing as an option of chemicals supply contract.

https://files.engineering.com/getfile.aspx?folder=7799e692-a7b3-4c2c-a7b6-4610c7f3c21a&file=1.pdf

The best option to start with is studying experience of operation of similar facilities as this plant is not unique. I recommend to start with inherently safer design for acid dosing units.

If you have questions please feel free to post here, I will try to help as much as I can. But doing this you should avoid random knowledge as one missing point is enough to lead and have led to a catastrophe.

Speaking of CS - in your particular case non-lined CS may be not the best choice from point of view of money. If there is a contact of metal and acid then hydrogen evolution leads to explosive atmospheres formation and Ex-proof design and certification of electrical and mechanical devices exposed. Depending on local codes and practice this is able to become the surprisingly expensive option I should say.

http://www.sulphuric-acid.com/Sulphuric-Acid-on-the-Web/Hydrogen-Safety.htm

 

[Andrew ONeill]

For storage tanks
plain carbon steel is often used for 98%..... but
-> the damage mechanism of concern is the air/liquid interface. The air has some water in it, resulting in a very thin dilute layer of acid on the top of the liquid. This results in severe material loss in the top shells of carbon steel tanks in acid service. typically, life end ups being 10 years give or take. This can be dealt with in numerous ways, each with Pro's and cons, which I wont discuss here. There is a NACE standard I highly recommend reading if you are going to design a tank for sulfuric acid. NACE SP0294. it deals with this dilution issue as well as many other problems related to sulfuric acid storage tanks. I'll be honest even if buying something "off the shelf" I would still recommend comparing it to this NACE standard as part of a due dilligence process.

For Piping
I've only ever dealt with carbon / stainless steels / PTFE lined pipes for sulfuric acid.

The damage mechanisms that are "hidden" are
1) Having dead legs, small pockets (valve bodies are classic for this). Air / water / something gets trapped in dead leg, and as a result dilution occurs, results in weak acid forming, which has a similar effect to the tank issue discussed above

2) Backflow from the mixing zone. It is very Easly for diluted product to travel back up the injection line, which is normally only designed for 98% acid, not for dilute acid. So pay particular attention to how to prevent backflow, and use valves that can do both the 98% duty and the dilute duty.

Thanks my brief summary of stuff to look out for.

Andrew O'Neill
Specialist Mechanical Engineer
Australia

 

[KevinNZ]

We often install systems for pH control in hot pressured water pipelines, 98% Acid sorted as above. Problems arise a the point of mixing. Here the materials are exotic. Titanium works.

 

[shvet]

I have positive experience in H2SO4 dilution with PVC, SS304 and glass-lined CS. Every material is able to fit depending on local conditions, even Ti. Process design is critical.

 

[EdStainless]

These small dilution/dosing systems are usually bought as a finished system.
Many water treatment specialists sell these.
And they have done the research on materials.
Yes you may pay more, but they known to work reliably.

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P.E. Metallurgy, consulting work welcomed