ZLD Scaling Problem

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ZLD Scaling Problem

I have a scaling problem in my Zero Liquid Discharge (ZLD) Plant and this problem happened when two feeds met at the interstage tank.

We tried several antiscalants and problem still remains.

How can I achieve zero scaling? 

I can provide feed streams analysis and any required information if needed. 

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27 Answers

  1. Since the alkalinity in your water is at lower range, I recommend you to reduce the pH level between 5.8 to 6.2 , thereby eliminating 90% chances of scale formation. The remaining 10% can be controlled using  strong terpolymer with high thermal and pressure stability  produced by Dow, Biolabs etc.  Sometimes little surfactant may also helps.

  2. Hi Tamer,

    The descaler my company has developed and manufactured removes all types of scales. I have experience in its implementation in Australia to remove even tough silica scales.

    If you would like to trial the product, please email me at andrew@waterandoilsolutions.com.au and I am confident I can provide a solution for you.

  3. Exept of high alkalinity (carbonate scaling) there is too high sulfate concentration......

    you need an antiscaling agent for sulfate salts in very high dosage... without concerning the rest of impurities maybe included, because analysis is not complete.

  7. Matthew Brannock Thanks Very much for your interest ,
     you accurately what's happening in my process and our process is seeded slurry technology, but the issue that the mixing of feed streams occur in separate tank not containing seeds (interstage tank) . and scale mainly occur in this tank.
    Can you advice if adding acid on this mixed streams will help or not.

    Or

    preparing seeds in this tank and then restart feed streams again, and transfer to FFE while the re-circulation line of this tank opened to be sure that there will be minimum Seeds available there.

     

    1 Comment

    1. Hi Tamer,

      If the scale formed is in fact calcium carbonate, then destruction of alkalinity using acid would certainly be an option (we're currently working on a project where this is undertaken).  Understanding the implications of adding acid is also necessary though.  

      For example you also have to be careful that if you dose sulphuric acid it doesn't take you over the CaSO4 precipitation point too early in the process in locations where it would be inconvenient.  HCl may be an option but is much more expensive.  Modelling can help with this along with an ion balance composition from both streams.  

      Without knowing the process in detail, I can't say whether preparing the seed in that particular tank is going to create an issue for you.

      Cheers,

      Matt.

      matthew@​​saltwatersolutions​​​.​com.au  ​

      www.​saltwatersolutions​.​com.au  ​

      www.aqmb.net 

      1 Comment reply

  9. Tamer,

    Like Anro, I also initially thought that the scale in the feed could be calcium sulphate due to the high levels of each in the feed.  However, after looking more closely at the feed analysis and confirming via speciation/AqMB modelling (admittedly using a range of assumptions to complete the feed composition), calcium carbonate seems to form preferentially.  Although CaSO4 only needs to be above 0.15-0.20wt% at 100C to form, if alkalinity is also present, CaCO3 will form preferentially and consume a lot of the calcium before CaSO4 gets a chance to take hold.  A sample of the scale and XRD or FTIR analysis will confirm for sure.

    In the down stream process though, calcium sulphate will likely form due to the concentrating up of these two species... and this is what occurs in a seeded process.  Calcium sulphate is purposely precipitated in the thermal concentration unit (usually an FFE) to produce sites where other scale inducing species will preferentially form (instead of on heat exchange surfaces).  There is a set level (i.e. TSS) of calcium sulphate solids that you want to be at though; this is dependent on the concentration factor and there still may not be enough in Tamer's process to run in full seeding mode.  

    A seeded CaSO4 process won't help the scaling problem in the feed though.  On previous projects, where there is calcium and alkalinity in the feed, we have either dosed acid to prevent hardness formation or removed the hardness.  It becomes very much an economic question (CAPEX vs OPEX) which is very much scenario specific.

    For your scenario, you need to check that once you dose acid, that you don't inadvertently form CaSO4.  If you are below ~0.15% CaSO4 in the mixed stream, you should be okay.  Modelling will help confirm.

    Cheers,

    Matt.

    matthew@​saltwatersolutions​.​com.au 

    www.saltwatersolutions.com.au 

    www.aqmb.net 

  10. If you do find that the scale is calcium sulphate, you can either try to precipitate out calcium as CaCO3 in the pre-treatment as suggested by Anro, or alternatively precipitate out the sulphate using barium (e.g. barium carbonate) as BaSO4.  This is more expensive than adding lime to precipitate the calcium, but may be more suitable for your situation. This is also if the anti-scalents being offered still do not work.

  11. Tamer,

    You may want to look into Electronic Water Conditioning to prevent scale without chemicals.  See Hydropath.com for additional information and the distributor in your area.

    2 Comments

  12. Hi,

    Try and get a sample of the scale to determine the exact composition thereof.  Your feed composition is high in calcium and sulphates and therefore I would think that it is calcium sulphate scaling that occurs.  I worked on a falling film evaporator (FFE) where we had similar feed and issues which required regular shutdown for ultra high pressure cleaning.  Luckily there was more than one FFE and the cleaning could be staggered.  At that stage no one could provide us with a working cleaning in place program to prevent the scaling, only dosing programs to increase the runtime of the plant before mechanical cleaning was necessary.  The most common suggestion was to remove the calcium from the feed through pretreatment in order to prevent the scaling from happening.  We once introduced a softened feed to the FFE and could increase the cycles of concentration tremendously without any scaling taking place.

    Good luck with finding a workable solution.

  14. Dear Tamer,

    Scale buildup can also cause corrosion and the loss of heat transfer, so again, much of the contamination that can cause corrosion in the thermal parts of the ZLD process need to be addressed based on the individual system. The chemical balance, concentrations, level of heat, and pressure can all contribute to this complex calculation. What type of scaling ?

    General Problem of Scale

    1. High PH, Alkalinity
    2. High Temerature
    3. High TDS/TSS
    4. Corrosion.
    5. Sedimentation

    Solution

    1. To inject Acid or other chemical to down the PH.
    2. To inject anti scaling reagent easily available in market.
    3. To increase the fluid velocity to avoid sedimentation.

    1 Comment

  15. i need your feed quality information

    you send to this id: abdulgaffar557.ag@gmail.com

    i need you membrane details and plant details like permeate flow reject flow feed flow and TDS SILICA HARDNESS COD, and i need which membrane you are using in your plant model no and membrane make.

     

     

    REGARDS

    ABDUL GAFFAR - SENIOR CHEMIST

     

    1 Comment

  16. Hi Tamer,

    Thanks for the feed stream compositions.  It does make it easier to understand but it is still lacking some important information.  

    However, I did undertake a speciation simulation while making a few assumptions.  It appears that the high hardness in the softener waste stream and the alkalinity in your HERO reject stream may be leading to an amount of CaCO3 scale formation (potentially at difficult levels for anitscalant).  You may need to add some sulphuric acid to destroy the alkalinity in the HERO reject stream or even consider running the ZLD system (depending on how it is set up) in seeded mode.

    The above statement needs to be confirmed pending an ion balanced analysis.  I would also like to run it through our process simulation software AqMB which has the ability to take into account antiscalants performance within thermal processes.  It would also assist in investigating potential process related solutions (including running your ZLD system in seeded mode... the high calcium in one stream and high sulphate in the other may enable you to do this after some alkalinity destruction).  

    Please get in contact if you have any more detailed information about these streams.

    Cheers,

    Matt.

    matthew@saltwatersolutions.com.au

    www.saltwatersolutions.com.au

    www.aqmb.net

     

    1 Comment

    1. Thanks Matthew very much for your detailed reply,

      ,for your information scale mainly occur when two feeds mixed

      is it will be better to add acid on the mixed sterams!!

      Also,  i use hydrex Veolia but i inject before mixing

      1 Comment reply

      1. Hi Tamer,

        Assuming the scale is in fact CaCO3 (there is still a little uncertainty on this due to some missing analysis parameters), then you'd add it to the stream containing alkalinity (HERO Reject) before mixing.  You can either destroy all the alkalinity using acid (easily calculated - just use the M-alkalinity to work out how much is required) or destroy just enough to avoid scaling (process modelling would be required to do this).  

        Cheers,

        Matt.

  18. Hi Tami!

    Please provide more information about the process and the feed stream analysis. I agree with Nir it is useful to know if there is a rise on temperature or a pH variation at the mixing point. Thank you for shareing your case.

  20. Must share the process flow diagram and also analysis of the scales...which salts...Also the material of the inter-stage tank..Have you tried any electronic protection or any inert coating of inside of the tank..?

    1 Comment

  22. We are waiting for the feed streams analysis. 

    Anyway, as you can make trials, you can find the best available prduct this way.

    I can propose you an excellent antiscaling product which is produced under my recipe in Greece, but I could not know the final cost to you if I send it from Greece (shipping cost + customs cost). Anyway, I could send you a sample for trials for free, if you could pay the shipping cost.

    2 Comments

  27. Feed chemistry and equipment configuration are key aspects. Have you run any scale inhibition program using plant data? Please talk to your OEM. Of course we can discuss further if you share the data. Zero scaling in operating plant with its dynamics, you think it's possible?