Question of the Day: RO vs DI

Published on by in Technology

Question of the Day: RO vs DI
What factors should go into determining whether reverse osmosis or deionized (i.e. ion exchange) water is used for boiler makeup?

Media

Taxonomy

16 Answers

  1. The boiler manufacturer will specify the water quality required. There are many different boilers and boiler applications.  RO usually is the last step after softening, filtering and polishing out any solids.  Ion Exchange water is necessary on almost all boilers.  RO is expensive and only justified if the manufacturer and application call for such high quality water.  Of equal importance is chemical pretreatment of the boiler water and consideration of the conductivity limits of the boiler.  Microfiltration and UUltra filtration are membrane technologies similar to RO but give results that might be sufficient for many high end boiler applications.  RO water and DI water is very corrosive and must be considered in the overall water management of boiler feedwater. Billg@prochemtech.com

  2. Hello,For RO and DI water TDS is different.Dionised required Ion exchange or Electro deionisation.DI water has 3 types Type-1,2,3 for reasearch and industrial process application it is needed.

    To determine factors

    Water quality inspection lab test.DI water TDS very low than RO.

    And Dionised water cannot keep open tank it required setup precise storage to eliminate bacteria will contaminate.

    We deal with Milliopore ultrapure systems in last project

  5. Good day!

    I think that these water treatment systems are not quite correct to compare as competitive, rather as increasing the efficiency of each other when used together. When only RO or deionization is used to produce make-up water for steam boilers, both systems have a number of significant drawbacks.

    If anyone is interested I publish my thoughts about the water chemical mode of low pressure steam boilers on my website- https://tiwater.info/en/

    The comparison of softening and RO systems for boilers that is taking into account the influence of carbon dioxide and carbonates in feed and boiler water–The assessment of the effect of carbon dioxide on the water-chemical modes of steam boilers 

    Examples from my practice of using RO for steam boilers- The features of the development and maintenance of water-chemical mode of low-pressure steam boilers using membrane technologies

    The use of the advantages of osmosis systems for complex water treatment for boilers, including degassing- Water degassing using reverse osmosis membranes 

  6. all depends on the water quality wanted in the boiler, thid depends on boiler pressure and steam use. You can always put a mixed bed after the RO to polish it

    Good luck and welcome

    jan@aquatreat.be

  7. With most boilers operating a PSI below 150 with good condensate return that increases the cycles of concentration and reduces the blowdown a water softener is all that is needed.

    See the comments b  James Stewart

  8. It depends on boiler pressure and source water quality.  Below 600 psi, single pass RO with a softener on the feed or polishing the RO permeate is usually sufficient unless you have a source with very high TDS and/or silica.  For those waters, two pass RO is likely sufficient.  High-Pressure boilers, >800 psi, will require DI water.  600-800 is a transition zone and dependent on the feed quality.  BUT, even when DI is required, feeding the DI with an RO almost always provides an economic benefit.  I would say if you are over 150-200 ppm TDS in your feed water, an RO is going to offer a sufficient payback.

  9. Start with the end goal.  Define the following: Steam Pressure?  Steam Quality?  Steam Purity?  Steam Quantity?  This will establish the Boiler Feedwater purity and thus the Boiler Feedwater Makeup purity.  Once known, compare from an economic and environmental perspective considering both capital and operating costs.  I have authored a paper that might help - since made into a Technical Information Paper by the Technical Association of Pulp and Paper Industry (TAPPI).  Go to TAPPI.org and search for "Design Engineers Decisions Tree: Boiler Feedwater Makeup in the Paper Industry."

  10. The answers so far reflect a difference in consideration basis: environmental, safety, capital cost, operating cost, and reliability.

    I would start with, what “purity” steam is required.  Then answer, what “quality” steam will the boilers make?  Finally, at how many cycles do I want to operate the boilers?

    Now I can specify the quality of boiler feedwater I require.  This combined with the condensate (amount and quality) returned will specify the quality of RO or DM requiired and a basis for proper design (there are many) and operating cost analysis.  

    I assure you that a poor choice will make you wish that someone else had been assigned to this project.  I could have made a career out of retrofitting and redesigning poor initial installations of both RO and DM units.

     

  11. RO output water quality is suitable for low pressure boilers on its own it may not be suitable for high pressure boilers. RO water needs to be polished by either MB ion exchange or CEDI system. In today's scenario Water recycling is being adopted at power plants. One common mode is CW blow - UF (or dolomite treatment to remove silica followed by UF) - RO - MB/EDI - Boiler feed water. Similar treatment could be there for sewage treated water.

  12. IF we are dealing with a lower pressure boiler system where steam quality with respect to silica is irrelevant, then ion exchange (sodium-cycle) to soften the water is sufficient, and far less expensive.  Slightly more expensive in terms of capital, membrane capacitive deionization can be tuned to the precise purity required, with the exception of no silica (or probably boron) removal.  Membrane capacitive deionization has the lowest specific energy input of any desalination technique, thus operating costs are expected to be low.

    Reverse osmosis is only needed when there are severe restrictions on the quality and quantity of boiler blow-down, or there is a definite need to remove most/all of the silica (boron, also).  Systems in this range of treatment then become expensive to invest in and to operate, but it is a necessary evil.  Usually at such a level, the RO may be multi-pass, may involve feed recycling, and can and perhaps be followed by downstream ion exchange, and/or Continuous electro-deionization equipment for final purity required.  Such equipment nearly rivals the output quality and quantity of that employed in semiconductor manufacturing.

  13. On a high-pressure boiler you will likely need fully deionized water as feed.  Depending on the daily volume of makeup water, an RO in front of the DI tanks may be justified.

    For a low-pressure boiler this decision is typically justified by weighing the capital expense and maintenance of the RO (with necessary pretreatment) against the recurring costs for DI tank exchanges.

    In regard to a previous comment, I'm not sure what would drive one to place an RO system after an ion exchange system, unless the ion exchange system in question is simply a sodium cycle softener.

  14. Part of the answer depends on what is more important to the facility- maximum water efficiency (favoring IX), or lower salt discharge (favoring RO).  This also applies to using one technology as a "polish" for the other- IX/RO versus RO/IX- to obtain very high quality feedwater.

    Answered on by

  15. First question is whether RO, by itself, will be able to meet the boiler feedwater quality needed.  If it can, then comes the financial question- maximize/minimize capital expenditures or life cycle cost?  RO, by itself, will almost always be less expensive than a capital installed IX system especially when considering on site regeneration system.  If the makeup water is of low TDS, IX system may be cheaper to operate than the RO (not sure where the breakeven point is but likely some where less than 200 mg/l TDS).

    Many operations do no want to deal with the bulk chemical issues that are inherent to IX operations and will often select RO only (or RO with off site IX regeneration) even though there may be a higher operating cost.

    The engineer inside of me says the correct answer is the lowest life cycle cost but, after doing this for 36+ years, that question is almost never asked/considered.  The direction has almost always been to provide the lowest total installed cost that will work which can easily lead towards higher operating costs and, potentially, higher life cycle costs.

  16. Conventionally it is ion exchanger, now moved towards RO followed by DM-MBor MB, (in seimens made plants in India it is DM-RO), now moving towards RO-EDI