Ion Exchange Feed Water Quality Consideration

Published on by in Technology

I am working in wastewater treatment in a petrochemical company, we want to reuse the effluent from Active sludge treatment by EDR (Pretreatments are lime softening, sand, active carbon and cartridge filter ). The end user of this effluent is boiler so  Ion exchange system (cation and Anion bed and mixed bed) are used for desalination water after EDR, I want to know the quality of EDR effluent suitable for Ion exchange resins.

 

Taxonomy

9 Answers

  1. There is an old joke about farmers being experts. "They are all people "out standing" in their fields". Much the same may be said for free advice.

    1st IX will not remove colloidal silica.

    2nd IX will not remove non-ionic surfactants or other non-ionic organic materials all of which you will have in a refinery wastewater.

    In some locations the spent regenerants are a problem. Then you have the issue of rinse water volume after regeneration a big issue in water short areas. Remember if you buy and use, in your regenerating operations, 90,000lbs of caustic and 45,000lbs of sulfuric those materials eventually end up in your wastewater adding to the TDS load.

    Both silica and non-ionic organic materials are problems in a boiler application. The level of the problems they cause increase with increasing boiler operating pressure.

     

    1 Comment

    1. If they are using this boiler for steam applied to prime movers (turbines, pumps, etc.), then yes, silica is a major issue as the pressure rating goes up.  I agree with other comments as well.  If the steam is used only for heat, then not so much, although I would suspect considerable fouling of heat exchange surfaces in the boiler from the contaminants you mentioned.

  2. less than 70 ppm TDS Ion Exchange it's more economic than RO. With strong Cation-Anion-Cation polisher process 2 parallel you don't need a Mixed Bed for > 10 MegOhm DI water.

  3. Your 1st step is to copy what others have been doing when doing this very thing. Those that have been successfully recovering effluent from an Active sludge plant all use lime softening. There are more than a handful of reasons why. After lime softening, it is best to use RO. You will want to use CO2 to reduce the pH after the lime softening. If you have the option, you will want to consider 2 stage lime softening since you are planning on using the water as boiler make-up. You will absolutely need to consider a biocide application for the feed to the RO unless you use 2 stage softening. The permeate from the RO needs to go to a mixed bed IX. The RO reject needs to go to an evaporator or evap ponds so that you do not build the salt concentration too high and kill your bugs in the bug plant. Use the painful mistakes of others. There is no reason not to copy success.

  4. After lime softening, only non-carbonate hardness will be in the water. In this case, it is advantageous to apply the process of RO desalination, which will have a very small discharge of wastewater. After RO, the water will have a slight salinity and this will significantly increase the filtercycle of ion exchange systems. If there are problems with high organic content, it is possible to combine the liming process with coagulation. It is necessary to use iron salts as a coagulant, not aluminum because of the high pH of the water.

  6. We have similar process for water reuse in cooling towers. EDR does not remove silica and TOC. For boiler feed water it would be better to consider RO.

  8. It depends on the cost of chemicals for regen vs the cost of electricity.   If your EDR product is greater than 100 ppm TDS, I think it is worth looking at an RO to reduce the conductivity further.  If your EDR product is below 100 ppm, an RO probably won’t be economical. 

    1 Comment

    1. Correct, the chemical costs determine the cutoff point between ion exchange (IX) and RO. We normally recommend RO above 500 ppm, but it also depends on scaling and fouling issues. IX is generally more robust with challenging waters.

       

  9. You need to provide further information for the best answer to your question.

    What boiler pressure?  Is the steam being utilized for turbine equipment, or just heat?

    Your ion exchange system may be able to handle nearly any output available from the EDR, but this depends on what your target final water quality actually is, and what throughput you expect to achieve from your cation and anion beds before breakthrough, and what you are using to determine breakthrough.  For example, you might base breakthrough on EC of anion bed output, or it might be silica.  You might base cation bed breakthrough on sodium level or pH increase, or even calcium, depending on the water reaching the cation bed, and what you want to do with it.

    The mixed bed will obviously last longer and perform at a higher output quality if the two-bed system is handling better than 95% of the ion load in a balanced way.