Sulfuric acid application for cooling water treatment

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Hi everyone.

I have a question about Sulfuric acid application for cooling water treatment at Power plant. 

Owner wants to dose sulfuric acid for scale inhibition according to pH. But I am going to apply for each corrosion and scale inhibitor for cooling water treatment. 

I thought each sulfuric acid and scale inhibitor has same performance so i said to owner sulfuric acid dosing is absolutely not needed and water quality(pH) is 7.2 provided from site LAB.

However my opinion was rejected.

As replied by owner, is sulfuric acid dosing necessary?

If sulfuric acid dosing is not necessary, how to persuade and explain about that.

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10 Answers

  1. Study the relationship for scale precipitation as related to the P and M alkalinities.  You will find that lowering the pH to eliminate P ALKALINITY at pH of 8.2 changes dramatically the preciitation of calcium carbonate.  In the old times (40's and 50's) sulfuric acid was added to lower the pH to the 7.2 level with chromate and zinc as the corrosion inhibitors.  This was done on wooden towers.  With metal towers a pH of 7.2 would be a vert questionable practice.   Also keep in mind the precipition of gypsum caused by using SO4- .   

    You mentioned a power plant:  Ok, they are probably looking at overall costs.  Thus, sulfuric acid can yield higher cycles by knocking down the P alkalinity.  Look at the saturation indexes to see what is happening.  

    With sulfuric acid they probably need some corrosion inhibitors to protect the metals.  The probably need an azol for the copper/brass.  

    This could be a dangerous level running at 7.2, but it depends upon the other chemistry.  

    Have you done your homework, or are you just trying to sell chemicals.  The plant manaer may know more about water chemistry than you when we look at your statement:

    I thought ​each sulfuric ​acid and scale ​inhibitor has ​same performance....

     

    They are different, and do different things. 

    You need complete water analysis for both the tower, and the makeup water.  Ask the question: is the makup water the same year around, how does it differ with the season, does it have different water supplies.  How do changes in the makeup water affect the treatment?

     

     

     

  3. You have not provided us with the water make up analysis nor the proposed cycles of concentration.  Without these it is not possible to advise.

  4. Lowering the pH with an acid will convert a portion of the alkalinity (bicarbonate) to carbonic acid. Since there is less free bicarbonate, there will be less calcium carbonate scaling. If Calcium Carbonate is the only issue then you should be OK with just pH adjustment.

    But, in most cases there are other compounds (Calcium Sulfate, phosphate compounds, iron compounds, silica compounds) that are also sparingly soluble. Lowering the pH will have no, or very little benefit for these other compounds. If Calcium Sulfate is close to the solubility limit, then adding sulfuric acid will probably make the issue worse. Scale Inhibitors are available the will control all or most of the other compounds.

    You need to have a complete water analysis done to properly determine what you need to treat for. Be very careful of anyone who proposes a solution without seeing the complete water analysis.

  5. Simpke solution to cooling tower deposits.  Add one of our inline devices and ut will significantly reduce ir elimibate your issue whike helping balance your other chemical ussues.  Particularly if you are using a recirculating system.  We can remove most scale and prevent most scaling 

  6. pH control is to reduce bicarbonate alkalinity and the increase the solubility of calcium hardness. If pH is controlled automatically with a pH controller, at pH 7.2, usually acid feed is automatically stopped. Most control ranges are between 7.5 and 8.5. Lower than that is for phosphate control to increase the solubility of tri calcium phosphate.

    Hence, one has to know the saturation limits of the makeup minerals involved. Nowadays, calculation of limits is doen with software. The anti-scalant vendor can help calculate the pH set points.  

  7. I think there are other anti-scaling products. One reason to submit to your client is that  cooling water with Sulphuric acid as Ph rectification system will present two main handicaps:

    1.- Rectify Ph water is not an antiscalant system. Calcium will be in the pipes/cooling system.

    2.- Cooling water can have an evaporation degree. The acid addition should be done with cool water, and this evaporation rate will change the Acid rates and scaling issue will be there, a higher acid attack will be present due to Acid concentration is higher for evaporation and the anti-scaling goal will be not accomplished.  

     

  8. I agree with Benedict that's a bad idea in case of Calcium. BTW acidic pH is more corrosive in steel pipes then little

    alkaline

  9. Not a good idea. Calcium sulphate is very poorly soluble and will cause even worse scaling problems. Even the small amounts of scaling removed initially can clog your strainers. Better to use hydrochloric, nitric or citric acid because these will form highly soluble compounds that will remain in solution

  10. Hello Jo, there is not much information supplied on the quality of the water nor the usage data in the cooling towers.  However a couple of observations from my side:  calcium sulphate scale is very problematic to remove so it is always wise to limit the amount of sulphates added to a recirculating system where salts become more concentrated.  Secondly may I suggest you download the free software called STASOFT from the South African Water Research Commission's website which will allow you to assess the calcium carbonate precipitation potential under varying dosing regimes (it does not consider scale inhibitors, but does make allowance for acids and alkali additions.  Knowing the performance of the scale and corrosion inhibitors, you could link these with the CCPP outputs and make a recommendation.

    1 Comment

    1. I can help you with  a complete technical report  about  cooling water treatment but I need the  complete inorganic chemical analysis of the cooling tower feed water. Please send me this information : procesos@mentecsrl.com