Lime soda Frustrations

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What are the primary frustrations that occur with operations that are using lime soda softening?

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5 Answers

  1. It requires the chemicals and generates the sludge that it is difficult to dispose off. Lime slurry preparation also generates the grit that is to be separated and dispose off. It need better control on the process to achieve the desired results.

  2. floc carry-over, floc carry-over, and low dose failure.

  3. I agree with Norris's comment on controlling the lime soda as well as his variations in raw flow comment. I have significantly more experience in "cold" lime softening as opposed to "hot" lime softening so I will keep my comments focused on the cold treatment.

    Some of the more common issues I have seen stem from poor quality control of the raw lime, especially if you are buying dried lime as opposed to a lime slurry solution. Sometimes they will over cook the lime and provide you with significantly more inert material than what you think you are getting, and sometimes there is just a large amount of inert material due to the source.

     

    Assuming your lime is up to your specifications, delivery of the lime solution can be challenging due to the viscoscity of lime slurry and precipitation/deposits that can form in the piping of the lime slurry. If your lime slurry is allowed to sit undisturbed in the piping for any significant period of time, your lines will plug and cause you significant issues.

     

    That is just some of the physical problems I have seen. As for chemical issues, varying water content can be an issue but one people often overlook in surface water treatment is the temperature change in the water being treated. Temperature greatly impacts the reaction of CaCO3 formation and in the winter times, we see significant challenges due to the lower reaction time.

    1 Comment

    1. I agree about the lime quality.  Sourcing the correct quality that keeps the plant running.  The danger is that a buyer sources a cheaper supply without understanding the quality issues.

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  5. You might want to specify whether this is cold or hot lime/soda softening.  Some issues are common to both operations - the challenge to control lime and soda slurry concentrations on a consistent basis, the control of carryover due to flow and/or chemistry (and temperature/pressure changes in the hot system) changes, variations in raw water quality and flow, post-precipitation of calcium salts in lines and/or filter bodies, and more!

    1 Comment

    1. Norris:  I could not agree more, and considering some advancements such as membrane capactitive deionization, softening and general lowering of TDS takes place, with minimal intervention, no bulk reagents, modest electrical requirements, and some PM such as cleaning with citric acid.  The only solute not removed is silica.  Cost of capital equipment for this for large cooling demand applications may be considerably higher than for a clarifier/lime handling equipment.