CALCIUM CHLORINE DEALKILIZER ION EXCHANGE LED UV SOFTENING TECHNOLOGY ADVANCEMENT TOC UV

Abstract

(Editor’s note: This article is based on recent discussions in the LinkedIn Ultrapure Water and Industrial Water Treatment groups. This column seeks to accurately reflect comments from each contributor. On occasion, there may be the need to edit contributor comments for clarity or length. An important purpose of each group is to provide a forum for practical examination of issues facing endusers of high-purity and industrial water.)

Ultrapure Water Group Discussion

Compiled by Mike Henley, Editor, Ultrapure Water

Conventional UV versus LED UV

Mike: What are your thoughts on the following: 1. The value of ultraviolet (UV) in a UPW treatment system? 2. On the performance of conventional UV compared to the emerging light-emitting diode (LED) UV technologies?

Falk: “An interesting technology that has advantages (e.g., no ozone is produced). But this form of UV technology is not available for short wavelengths of 185 nanometer (nm).”

Ben: “Where are they (LED UV) available to buy? From the UPW point-of-use, as well as a central plant manufacturer, we could use it very well.

Does LED UV have the needed ray length of 185 nm against total organic carbon (TOC), or 254 nm against germs? If yes, with the same intensity as does conventional UV? Or, does it have higher intensity as other LEDs as normal light emits)?

With less energy, which UV form boiled UPW in recirculation? If the answers are ‘yes’, good. Does LED UV have a lifetime of more than 20,000 hours or more? Conventional UV-lamps contain mercury, which hurts people.”

Nissan: “LED UV is available from at least one vendor. The greatest aspects are: 1. the very low wattage; and 2. the instant UV intensity with no warm up or drift. Yes, there is not yet the 185-nm wavelength, but there are 254 nm and 300 nm wavelengths. The cost of operation is fantastic and the LEDs can last a lot longer than traditional mercury based UV. There is no disposal cost for mercury as in mercury-based lamps.”

Richard: “Good questions! I think the value of UV in UPW is twofold: TOC destruct and disinfection. Very few things accomplish this without the addition of chemicals, and UV is a great polishing step following a mechanical separation technology such as a membrane. I think the age of LED UV is coming. The output wavelength will be matched to required needs, but the major stumbling blocks are getting the price down to compete with standard UV units, the output up to reduce complexity, and integrators to provide standard units.”

Marc: “You also can use UV and other chemicals in an advanced oxidation process (AOP) to remove refractory contaminants like urea. You can use AOP, along with disinfection and TOC reduction to maximize the usage of UV in UPW. LED technology is promising; however, its use is still limited in scope due to wavelength, flowrate restrictions, and power supply reliability.”

Industrial Water Treatment Discussion

Compiled by James McDonald, PE, Chem-Aqua

James: When does it make sense to install a dealkalizer for low- to medium-pressure boiler makeup versus installing a reverse osmosis (RO) unit?

Ghazanfar: “A dealkalizer is similar to a water softener, as it uses ion exchange to remove unwanted ions from a water supply. Instead of removing calcium and magnesium ions, dealkalization removes carbonate ions, exchanging them for chloride ions. However, RO membrane rejects a maximum of salt ions from water. One must keep in view system sensitivity and the budget expert may then decide between softening, a dealkalizer, or RO.”

Greg: “I have seen exactly one time where a dealkalizer made more sense. The plant uses the boiler to destroy gases from the process. As such, they burn as much natural gas as is needed for destruction, and more often than not vent excess steam to the atmosphere. Thus, the gas savings from increased cycles are irrelevant.

Ghazanfar, are you speaking of a chloride cycle dealkalizer? A weakly acidic cation will remove an equivalent amount of hardness as alkalinity. Degasify and then polish with a sodium zeolite and you have pretty good water.”

Denis-François: “For instance, when silica is not the limiting factor. Or, when raw water silt density index (SDI) is too high for an RO or requires sophisticated pretreatment. Don't forget to soften the water after the dealkalizer.”

Cracked Softener Beads

James: What can cause water softener beads to crack?

Wouter: “Some causes can be: 1. Changes of pressure in the complete system causes “water hammer” on the beads, cracking them over time (for sure the old beads that are a bit weaker). I see the softener as a shock-absorber in the water-system. 2. In a (too) fast rinse, the beads also swell too quickly, which can cause cracking.”

François: “Point 1 of Wouter is correct (water hammer). I do not believe that Point 2 occurs in normal operations. The change in volume between regenerated sodium (Na) and exhausted (calcium [Ca] + magnesium [Mg]) resin is small. Only if the brine used for regeneration is by accident not diluted would the osmotic shock be sufficient to crack the resin beads. It is of course essential to purchase good quality resins. Although the manufacturing of softening resin is simple in principle, we have seen products with cracked beads when new, and products with insufficient osmotic stability.”

Keith: “Too high salt concentration can be a possible cause. The largest culprit we see, however, is excessive delta P across the softener, resulting in premature resin failure. Usually this occurs when discharging soft water to an atmospheric storage tank without flow limitation.”

Don: “High levels of chlorine cause softening of the beads so they are more subject to cracking.”

Vinod: “All the reasons cited earlier are good. Some other references on this topic can be found at: http://www.premierwatermn.com/hard-life-water-softener-resin/ and http://blog.klenzoid.com/blog/resin.”

Mohamed: “Dow (Chemical) has also explained the main reasons for resin cracking, including physical effect, excessive pressure, pressure drop, improper transfer, osmotic shock, and the oxidizing effect on the resin beads.”

Steve: “Don't forget thermal shock, which is often encountered with condensate polishers and hot water systems when regeneration steps don't include tempering rinses.”

Tracy: “From our experience, we see resin failure mostly related to chlorine exposure. We can usually double the life of resin by installing a carbon filter as pretreatment to the softener.”

What are your thoughts? Join the discussion on the LinkedIn Ultrapure Water and Industrial Water Treatment groups.

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