Boiler Condensate Treatment

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What is the best method for Boiler Condensate Treatment?

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6 Answers

  1. In some cases condensate polishing (deep bed or powdered resin) or filtration is required or advisable.

    Oxygen scavengers such as hydrazine have been abandoned in the power generation industry due to concerns about flow accelerated corrosion except in the case where feedwater heaters have copper tubes.

    In the power generation industry ammonia is the most common chemical fed into condensate to elevate the pH.  Neutralizing amines are sometimes used but they produce carbon dioxide and organic acids as they decompose at the higher temperatures.  Filming amines are becoming more common but are supplemental to ammonia or a neutralizing amine.

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    1. These comments are definitely pertinent to Universal Pressure Boilers, and some others operating at high pressures.  I use MEKO as oxygen scavenger because it is less aggressive, and our boiler pressure falls in line with its use.  It only allows production of a coating of the nearly purple oxide of iron (hem-magnetite, not magnetite), and the "throw" of corrosion product (that can play havoc) is greatly diminished to almost nil.

  2. In general, since you did not mention the specifics of your steam generator, you need to control pH to a slightly elevated value, 8.7-9.3 depending on the situation, and limit or eliminate oxygen ingress.  Some will use oxygen scavenger(s), some will use removal and then back addition of up to 30 ppm oxygen, not air.

  3. The answer to such a general question can only be general - treatment, whether boiler water, feedwater, or condensate must all be prescribed/designed based upon the unit operations in the boiler system and the requirements of the users of the steam produced.  In fact, all water treatment operations should be dictated by the end goal.  

  4. It also depends on what industry you are working with.  If you are involved in the food industry then the next question becomes is there any live steam injection?  If the answer is yes , then there can be no treatment to the boiler steam.  If the condensate is not for the food industry, then treatment can be used.  DEHA removes oxygen in the boiler feed and is volatile and removes oxygen in the condensate or more importantly converts rust to stable magnetite under alkaline conditions and so needs neutralising amines as well.

    There are filming amines, which help protect the pipework. 

    If you are a high pressure boiler, then demineralisation is the answer.  In many boiler plants the first stage of pre-treatment is Base exchange softening.  This only removes calcium and magnesium and converts them to sodium.  Sodium bicarbonate breaks down to form sodium hydroxide in the boiler and carbon dioxide which flashes off with the steam and forms carbonic acid, which is the cause of grooving in the condensate.  The higher the level of bicarbonate in the water the higher the level of CO2 and therefor the higher the level of corrosion.

    The use of a de-alkalisition plant or more recently RO in conjunction with BX softening reduces the bicarbonate and reduces condensate corrosion.  

    There is another form of corrosion, which is caused by the boiler carry over.  This occurs due to either priming, or foaming.  I have seen severe damage to superheaters caused by the boiler foaming then baking hard generating crystalline cracking.  This same process can occur on heat exchangers.  As a result good control of boiler conditions is essential. 

    It may sound basic but the correct design of boiler plant is also essential.  A boiler rated at 6000 kg per hour will only provide 100kg per minute providing the feed water is @100 ºC.  Most boiler feeds are at a lower temperature and as such are no longer able to produce a full load.  Once the load is exceeded, then the boiler can prime causing water carryover, which in turn causes corrosion.  Dry steam does not cause corrosion, it is only when it is wet steam or when the steam condenses that corrosion can take place.  So the boiler plant needs to operate within its loading limit to maintain pure steam and control condensate corrosion.

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    1. I don't know about where you live, but here in the USA, the USDA has regulations for what treatment can be in a steam generator where there is steam contact with food.  For neutralizing amines: 10 ppm alone of either morpholine, cyclohexylamine, or diethylethanolamine (DEAE), or any of three in combination up to a total of 25 ppm.  Oxygen scavenger allowed is apparently only sodium erythorbate.  This is from my own experience at a cogeneration facility where the steam is supplied to a University, and steam is used in food preparation areas.

  5. Hello,The condensate of boiler is almost cases acidic.Around PH is 4 to 6.It will cause corrosion in condensate piping most likely effected is CI.We need to make this water is above neutral. PH slighly around 8-8.5.In big powerplant all condensate water goes to DEMIN PLANT.And goes to feed water of boiler.