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Diluting Of Sulphuric Acid In Water Treatment Plant Industries


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#1 YUMI

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Posted 15 January 2023 - 10:55 PM

Hi Everyone, 

 

I am currently designing on a Sulphuric Acid Dosing Plant for a water treatment plant. This is a new experience for my company and I have went through a lot of literatures. 

 

I have a lot of queries as I understand that to do this plant is not that easy due to a lot of safety circumstances in the storage and dosing system. 

 

The client is asking to use 98% of sulphuric acid as initial concentration and dilute to a concentration before dosing into the process line. In this case, the process line is the raw water from a river. The purpose is to reduce the pH to the optimum pH for the coagulant optimum performance. 

 

Firstly, in terms of the dosage required. I did my calculations and  the required amount of Sulphuric acid. The result to lower down the pH from pH 8 to 6 is about 0.49ppm of 10% Sulphuric Acid. This is contradict with the lab result report that it claimed to dose 98% H2SO4 at 20-30ppm. I understand that it could because certain organic matters in the raw water will react with the acid ions, but would it make a such different? I have no idea on what is wrong with my calculations. 

 

Secondly, to calculate the heat of enthalpy of dilution. From my understanding, It is batter to do a higher ratio dilution due to the higher amount of water creates a larger heat dissipating medium to absorb the heat of dilution due to the addition of acid to the water. I get the temperature rising from diluting 98% to 3% is about 30 degree C from my calculation. However, in reality, obviously, the temperature would go up to 180 degree C (boiling), and dilution shall be done by stages 98-60-30-20-10%, with heat removal system after each stages of dilution.

 

There is a lot of contradict when we look at literature and the reality in the industry in actual. I have no idea on it and hope anyone could answer my queries. 

 

Thank you very much in advanced. 

 

 

 

 

 

 

 

 

 



#2 breizh

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Posted 16 January 2023 - 12:02 AM

Hi Yumi,

Consider the doc attached to support your work. #7 in particular.

Note: To get the quantity of acid you need to neutralize the effluent, forget about calculation.

Take a sample of your water and perform a titration in the lab, you will get the right number of cm3 of Acid you need per g or kg of water. 100% accurate.

Yes, you are right about safety concern using sulfuric acid and water. More info in the doc attached. Always add Acid in water, not reverse.

Note: you may consider having a specific unit to prepare diluted acid solution.

 

Good luck.

Breizh



#3 YUMI

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Posted 17 January 2023 - 12:27 AM

Hi Breizh, 

 

Many thanks for the info. 

 

Have a great day ahead and Happy New Year!



#4 breizh

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Posted 17 January 2023 - 12:42 AM

Hi,

Welcome and happy new year!

Breizh



#5 modianurag

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Posted 14 September 2023 - 09:46 PM

Hi I am not able to see the attached files. 

Actually I am looking to treat ~98% Sulfuric acid (black in color) which has organics in it with H2O2. I am stuck at choosing a suitable MOC for Heat exchanger and the dosing point of H2O2 in Sulfuric acid circulation line. 

 

Any help in this regards would be appreciated.



#6 shvet1

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Posted 14 September 2023 - 11:14 PM

H2SO4 source and concentration after, temperature, peroxide concentration before and after, nature of organic contamination

 

Note that peroxide is explosive and should be handled/treated proper way. Several months from this time we had a near miss - explosion with subsequent fire, luck with slight injuries no deaths

 

Note that H2SO4 produces H2 (google - hydrogen grooving) while H2O2 produces O2 (google - peroxide decomposition). This means you are unable to avoid pure H2+O2 accumulation in vapor space (equipment) and gas pockets (piping). This mix is the most explosive in this universe and I do not understand how you are planning to deal with this.


Edited by shvet1, 14 September 2023 - 11:26 PM.


#7 breizh

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Posted 14 September 2023 - 11:49 PM

Hi modianurag,

A PFD /PID with data will be helpful to understand your plan. 

Too little information leads to guess.

Do you mean that you want to recover sulfuric acid?

Breizh



#8 modianurag

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Posted 18 September 2023 - 02:14 AM

We are trying to remove the black color of sulfuric acid.

 

Initial concentration of Sulfuric acid: 98%

Expected concentration of Sulfuric acid after Peroxide Treatment: ~88%

Expected temperature rise: 50 deg C to 130 deg C

Dosing of H2O2 to Sulfuric acid: 2% on weight % basis

 

 

 


Edited by modianurag, 18 September 2023 - 02:22 AM.


#9 breizh

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Posted 18 September 2023 - 02:27 AM

Hi,

I don't feel comfortable with your data. Safety first.

Your temperature increase is wrong. Did you perform tests in the lab?

http://www.sulphuric...acid_colour.htm

https://patents.goog...t/US5026535A/en

What is the quantity to be treated? 

Too dangerous.

 

Breizh



#10 shvet1

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Posted 18 September 2023 - 04:16 AM

still missing - H2SO4 source, peroxide concentration before and after, nature of organic contamination

 

88% @ 130°C means glass or tantalum. Note that common grade glass lining (e.g. food grade) is not suitable - dedicated design and manufacturing procedure is required. Expensive option I should say. I am not sure you do understand how expensive and dangerous this is. As per my experience some grades of PTFE and graphite are suitable but this is not a widely accepted practice so I cant recommend these.

 

Note that some conditions of H2SO4 are able to be handled only with gold or some sorts of wood - see corrosion chart in file attached.

Note that even traces of Fe and some others ions in liquid lead to violent decomposition of peroxide.

 

The situation looks dangerous as unqualified persons are involved in process design. 

 

https://www.shi-pe.s...cture/basic008/

 

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Attached Files


Edited by shvet1, 18 September 2023 - 05:26 AM.


#11 sonu19921103

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Posted 18 September 2023 - 10:06 AM

Hi,
I understand you are trying to remove the colour from the spent concentrated H2SO4 by trating the same with dilute H2O2 solution.

The H2O2 oxides all organic to the CO2 and water thats how it works you will find patents from china on same.

But please note that you should evaluate the safety risk involves in this process. The mixture of H2O2 and H2So4 is know as piranha solution. Here is some text from the wiki as ready reference

"Piranha solution is dangerous to handle, being both strongly acidic and a strong oxidizer. Solution that is no longer being used should never be left unattended if hot. It should never be stored in a closed receptacle because of the risk of gas overpressure and explosive burst with spills (especially with fragile thin wall volumetric flask). Piranha solution should never be disposed of with organic solvents (e.g. in waste solvent carboys), as this will cause a violent reaction and a substantial explosion, and any aqueous waste container containing even a weak or depleted piranha solution should be labelled appropriately to prevent this".

Edited by sonu19921103, 18 September 2023 - 10:07 AM.


#12 YUMI

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Posted 22 September 2023 - 04:07 AM

Hi, 

 

I read some online material on the 98% sulphuric acid storage tanks I found the below informations: 

 

1) HDPE for full range of Sulhuric acid, but recommended for small storage volume which is less than 10,000 gallons

2) Carbon steel is excellent for storage volume larger than 10,000 galllons 

3) FRP are not recommended for high concentration sulphuric acid. 

 

My question is if Mild steel with HDPE lining recommended as 98% Sulphuric acid storage tank?



#13 breizh

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Posted 22 September 2023 - 04:38 AM

Hi Yumi,

Please don't jump in an existing post, please start a new topic related to storage of H2SO4 98%.

 

Breizh



#14 YUMI

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Posted 22 September 2023 - 05:25 AM

Hi Breizh, 

 

Sorry and noted on that. Will do. 



#15 shvet1

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Posted 25 September 2023 - 12:15 AM

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. Tanks that are being considered for lining should be small enough that the lining can be baked. Tank fabrication, surface finish, and design shall comply with NACE Standard RP0178.18 Proper application and curing must be ensured to achieve the long service life normally experienced in sulfuric acid service up to 98% concentration. At acid concentrations above 98%, high-baked phenolic linings have a short service life (see NACE Publication TPC #219 and NACE Standard RP018820). Alternative lining materials are available in addition to high-temperature baked phenolic and epoxy novalac linings. A coating supplier should be contacted for further information. NACE Standard SP059221 and NACE No. 11/SSPC(5) PA 822 contain information relevant to sulfuric acid tanks on the topics of surface preparation, coating selection, application, curing, inspection, and testing.

 

NACE RP0391-2001
2.6 Nonmetallic Materials
2.6.1 Organic
CAUTION: Solid plastic piping should be safeguarded.
ANSI(3)/ASME(4) B31.31 includes a section on safeguarding. A hazards review should be conducted if thermoplastic piping is to be used. Because of the mechanical weakness of thermoplastic material, lined piping should be considered. The chemical resistance of thermoplastic materials using plasticizers should always be verified with the manufacturer.
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).
2.6.1.2 Polyethylene (PE) and polypropylene (PP) are subject to environmental cracking. Likelihood of cracking increases with increasing acid concentration and temperature, and careful review of the long-term performance of these materials should be performed prior to application. 
Polyvinylchloride (PVC) and polyvinylidene chloride (PVDC) have been used successfully as piping materials for concentrated sulfuric acid, but should not be used for acid strengths greater than 96%. Temperature excursions in these materials must be minimized. Polyvinylidene fluoride (PVDF) is resistant to sulfuric acid up to 98% concentration.
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.
2.6.1.5 Polyester, vinyl ester, nylon, and epoxybased materials are attacked by concentrated sulfuric acid.





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