Citric Acid as Scale Inhibitor

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Citric Acid as Scale Inhibitor

I have a problem with scale formation in my heat exchanger (plate and frame). The scale seems to be calcium carbonate, sulphate and silica.

Which scale inhibitors can I use to prevent scale formation in the heat exchanger?

Could I use the citric acid? 

If needed, I can provide further details.

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22 Answers

  1.   Hello Tamer, I guess you want to decrease the LSI of your water to reduce CaCO3 formation tendency. You can use sulfuric acid for pH adjustment i.e. LSI reducing. You will still need aniscalant. Consult your chemicals supplier for the proper choice of aniscalant. You also can pilot the process for evaluation. Regards, Taha

    1 Comment

  2. Thanks All for your support and interest,

    Prem Baboo 

    here is attached chemical analysis for the feed water to plate and frame heat exchanger, knowing that the operating temperature ranging from 80 up to 100 degree .

    Citric Acid Dosing proposal to prevent scaling depending on [decreasing pH which by the same time decrease the alkalinity and by the way decrease the scale tendency.] is this assumption true or not

    ??

    2 Comments

    1. Citric acid for such a purpose is also much more expensive than other acids you could use.

      1 Comment reply

    2. This analysis is not what we asked for. It shows only that anions of strong acids (not including nitrates) concentration is extremely high, making the water highly corrossive, especially for stainless steel.

      We need additionally p-alkalinity, m-alkalinity, Ca++, Mg++ and cooling liquid temperaure (what water is cooling).

      In which degrees you mention the temperature (80-100)?

      > Of course, citric acid will lower the m-alkalinity and pH, resulting in lower scaling, but you already have highly corrossive water and if you add more acid it will be even more corrossive. I suppose you have much corrosion under scale formations.

      2 Comment replies

      1. about alkalinity, there is alkalinity only in HERO Reject stream but the Softener reject has no Alkalinity so, not measured 

        pH mentioned in the attached analysis, 

        this streams will be heated through heat exchanger not cooled, temperature will be exchanged with distilled water.

  3. Thank you Editor for invitation,

    The formation of calcium sulphate and calcium carbonate scale poses major problems in heat exchangers and water cooling systems, thereby affecting the performance of these types of equipment. In order to inhibit these scale formations, new types of biodegradable water soluble single polymer and dual poly (aspartic acid-citric acid) polymers are used.Silica Scale Removal is a powder based additive for descaling solutions for silica or silicates scales removal from heat exchangers,. The citric acid  is inhibited with corrosion inhibitors but special care must be taken towards handling and storage.

    Citric acid  is an environment-friendly monomer since it derived from natural resources. Citrate has used as  scale inhibitor  for calcium carbonate (CaCO3). In order to  inhibit  these  scale  formations, new types of biodegradable water soluble single polymer and dual poly (aspartic acid- citric acid )  

    Citric acid is an efficient descaling agent that helps to remove scale, rust and grime deposits from various metal parts and still is safe for humans and in food grade applications. Citric Acid is also used as a cleaning agent or as a Descalant for cleaning of Heatexcahngers etc.

    In Plate type Heat exchanger the circulation of citric acid with pump collecting tank and piping system, time to time (interval) iron analysis to be done for corrosion)

    Care must be taken

    Citric Acid is a weak organic acid, but is still corrosive to metal parts when used for cleaning or descaling purpose. Hence it should be used along with Citric Acid Inhibitor. The inhibitor functions as a corrosion preventive agent that does not allow the acid to corrode the metallurgy while descaling of the heat exchanger or metal. 

    AVOID LOW pH for corrosion control

    The polymerization has confirmed to perform well and there are suspended carboxylic groups on the polymer molecules. Inhibition performance of new obtained poly (citric acid) for CaSO4 scale has evaluated by static scale inhibition method. When the dosage of polymer scale inhibitor is 2.5 mg/L in initial simulated scaling aqueous solution in which the ion concentrations of Ca2 + and SO42 − are both 2040 mg/L, the scale inhibition rate exceeds to 90%. When the dosage of polymer scale inhibitor is 25 mg/L, the scale inhibition rate is up to 98.8%.

    Regards,

    Prem Baboo

    1 Comment

  4. Dear Tamer,

    Citric acid can be used for cleaning the scaling after its formation. Other acids canbe used for cleaning (sulphamic, formic, hydrochloric) and the choice is based on the material of the tubes. All these cleaners are effective for carbonates and magnesium hydroxide with negigible efficiency for calcium sulphate.

    The prevention of the scaling by carbonates can be carried out in two alternative ways:

    a)  by venting all CO2 out before heating. According to the carbon curves, the carbon Equilibrium is 100% to free CO2 for acid pH (below about 5,8). Acidification is typically achieved by injecting Sulphuric acid (rather inexpensive)

    b) by dosing antiscalant (typically a few ppm of polyphosphates or other brands such as Nalco 72990 or Belgard V)

    Scaling by Sulphates is much more critical and the best prevention is to keep the temperature and Ca++ concentration below the precipitation curves (curves available). Some efficiency is ensured by special antiscalant brands (like Genesys) which are effective anyhow only at low working temperature (let's say below 60°C). After the formation, the only effective cleaning technique is the mechanical brushing.

    In some cases, Ca++ was reduced by a pre-treatment of Nano-Filtration, thus preventing the formation of both sulphates and carbonates.

    Mg(OH)2 scales only for very high temperature or very high alkalinity (curves available) but may scale along with carbonates and form a composite incrustation

    2 Comments

  5. Tamer, Take a look at the WSA Engineered System web site at www.wsaes.com . They offer a system known as ABS. They have many installation in US and prevents scaling and fouling in the plate and frame heat exchangers, without using any chemical. They also offer systems for the shell and tube heat exchangers.

  10. Hello Tamer, you can use a Water-Activator. He helps to: 

    • Reduce of lime residue in pipelines.
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    • Sincerly Heidi

  11. Лучший способ предотвратить карбонатов в оборудование . Предлагает инновационный фильтр без сменных картриджей для удаления солей жесткости из воды снижает жесткость 7 раз. И началось оборудование для работы намного лучше.

  13. Dear Tamer, you are not specified MOC of heat exchanger and applicable Temp.

    you can use NaOH as scale softener before Descaling with 10% solution for 4-6 hrs as volume of system then use Sulfamic acid with 10% solution maintain pH 2-3 for cleaning till max. 4-6hr.

     

     

  14. You need to do complete analysis of the scale and based on that and water chemistry parameters the reasons of scaling are to be correlated. There are good antiscalants available such as phosphonates, polymers. Based on water chemistry, operating conditions correct antiscalant can be identified. Inhibited sulphamic acid can be used for cleaning the existing scale deposits

     

  15. Hi Tamer,

    Citric Acid serves better as a scale cleaner or Descaler not as a scale inhibitor. For Boiler Water Treatment Scale Inhibitor, you can use Sodium Hydroxide 5%, if the pH of the water needs to be adjusted with alkaline to avoid scaling. Sodium Hydroxide 5% and Sodium Molybdate 5% (in de-ionized water 90%) are good combination/formulation for Boiler Water Treatment Scale Inhibitor.

    Regards.

    Justin.

  16. As previously stated, citric acid is a weak acid and must be used only for removing iron and manganese. It's not going to avoid calcium sulphate or silica scaling.

    The problem is due to the inverse solubility of the calcium carbonate and sulphate, where the solubility decreases when the temperature increases.

    Citric acid could avoid the calcium carbonate scaling if you reach the right pH ( Negative Langelier Index) but has nothing to do against Calcium Sulphate or Silica.

    The solution is using the apropiate anti scalant from a recognized company like King Lee, Nalco, Genesys, etc, which have a battery of antiscalants for different scenarios.

    Send the water analysis to them and they will solve your problem.

  20. I agree with Troy Davis

    .. but for a verified answer we need the TH, alkalinity, Ca concentration, pH, TDS, temperature of water, skin temperature of exchanger (or higher temperature of cooling liquid) and construction material of piping and heat exchanger, in order to calculate the LSI and antiscaling treatment. 

    1 Comment

    1. That's right. Those are the informations that we need to simulate the system conditions and verify the scale potential of the system

  21. There are very good  scale inhibitor for calcium carbonate and/or sulfate (for example: Gengard line from GE Water) . The silica cause problem in the cold section of the system ( cooling tower, fill of tower), but silicate cause some problems in the hot section of the system ( heat exchange) . To silicate, we need to respect the solubility limit of magnesium silicate and magnesium/calcium silicate. There is system where is possible to simulate this situation in the cooling water system. 

  22. Tamer,

    Calcium carbonate and calcium sulfate scale is typically prevented by utilizing dispersant polymer technologies. These are typically acrylamide based polymers with differing functional groups. The type and amount of these dispersants required is dependent upon your calcium, alkalinity, and sulfur concentrations, pH, and temperature experienced within the system.

    In my experience, citric acid is utilized most effectively to chelate and clean iron scaling, however, it can be used for cleaning of calcium carbonate and sulfate scales.

    Unless something has been brought to market recently, I do not know of anything that will remove or prevent scaling of silica. This is typically done by limiting the silica concentration of your water and increasing the pH. Pretreatment of the water utilizing some form of lime softening will also help to reduce the amount of silica to a point.