Question of the Day: Condensate Value

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Question of the Day: Condensate Value
What is the true value of condensate in a boiler system?

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7 Answers

  3. The dew point is at  55 degrees , and for the boiler to condense the temperature of the water that returns to the boiler must be  55 degrees  or below. Many are set up with a flow and return temperature of  70 degrees.

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    1. Dew point varies with the weather, so I would use caution in applying such an assumption.

  4. Due to the high Make Up Cost including Pre Treatment, RO, CEDI or Mixed Bed DI and chemical dosing as well as due to the high typical acidity (typical pH 2-4, but have seen values of pH 1.4 - 1.9 on well designed high recycle rate condensate treatment plants)...

     

    so looking (internationally) at the following free resource will help:

    http://www.veoliawatertech.com/crownsolutions/ressources/documents/2/21886,Water-pp104-111.pdf

  5. Asking for the true value of the condensate tells us that the one asking the question has little to no understanding of a boiler system, or water treatment.

    These are only a few of the cost savings realized by haveing return condensate:

    The heat of the condensate water has already been paid for.  Return the condensate so you don't have to pay for it again in added fuel costs. 

    The returned condensate is distilled water: using condensate for makeup allows us to raise the cycles of concentration, and thus lower the percent of boiler blowdown.  Again, less fue cost. 

     

    More cycles of concentration, and less blowdown, means lower chemical costs for the boiler water treatment.

    Returned condensate lowers the impurityes in the makeup water because it is blended  with the feed water to give us the boiler makeup water.  The quality of the mekeup water is better with a lower M alkalinity resulting is less carbonates and bicarbonates: thus when heated there is less carbon dioxide generated in the boiler to mix with the condensate and make carbonic acid.  The result is less steam corrosion and the need for less steam line corrosion prevention by chemicals: again less cost. 

  6. I'm assuming that this question relates to a boiler system that was designed to recover >95% of the condensate from boiler steam. About the only boilers I can recall that do not recover steam condensate are steam driven farm equipment and steam railroad engines.

    Condensate that is not recovered is a heat loss from the system and may affect the costs for treating and discharging waste waters. Lost condensate must be replaced by treating and purifying the plants raw water supply, increasing the load and operating costs on the makeup water system. When considering the costs of minimizing condensate loss (plugging leaks, assuring that heater vents are working properly, etc), these should be balanced against the costs of providing fresh makeup.

  7. The Condensate lost is costly in terms of extra load on the deaerating feed-water tank system, and since it contains heat above ambient temperature, the heat BTU value is also lost.  Over time this can add up to thousands, or even hundreds of thousands of dollars depending on the size of the boiler, and the degree of loss (%), not to mention any damage to steam cycle equipment.

    The makeup system will become heavily taxed to keep up, depending on design parameters, especially if the system was designed with 95% condensate return or better in mind.

    This extra cost of make-up water to the boiler involves several factors: (1) the cost of water intake, (2) the energy of pumping this water including transfer pumps, R.O. pressure booster pumps, and any electrical power consumed by such devices as membrane capacitive deionization, EDR, CEDI, and or vapor compression stills, and (3) last but not least necessarily are chemical costs and expendable items such as cartridge filters, RO membranes, CEDI stacks, EDR stacks, new ion exchange resin, etc.