Short Ion Exchange Resin Life-What's Happening?

Lately I've been hearing our sales people commenting that customers don't think their cation softening resin is lasting as long as it used to. This is a general comment, not something we're surveying. Here is some food for thought:

Has the manufacturing process changed?
Yes. One of the relatively recent changes to the process came with the non-solvent resins. The greatest motivating factor behind the non-solvent resin came from the EPA. Simply put, the resin manufacturers had to stop manufacturing the resin using solvents because they couldn't put the by-products down the drain. So the resin we used to clean up the water had a manufacturing process that potentially contaminated the water. Makes sense!

Are the non-solvent cation resins lasting as long as the solvent based resins?
According to a major manufacturer non-solvent ion exchange resins are manufactured to meet the same standards of the solvent type. That is, both the solvent and non-solvent resins are 8% crosslink and will react similarly under the same set of circumstances. For instance, both resins, in the presence of 2 ppm chlorine, will react and break down.

Should the solvent free ion exchange resins be used in industrial applications?
According to the data sheets for Sybron C-249 NS and Purolite C-100, the answer to this is yes.

So what are some of the reasons we are seeing shortened life/capacity?
Is there chlorine in the feed water?
In the presence of chlorine or any oxidant, cation ion exchange resins will breakdown prematurely. You say - yes, but the chlorine has always been there. I agree. However, as our water infrastructure has aged have the municipalities been forced in some instances to add more chlorine to compensate?

Are there higher levels of iron in the water?
As we know cation resin will remove ferrous iron but regenerating the iron off of the resin is challenging. Over time there is a loss of capacity as a result of the iron being embedded into the cation bead.

Is the cation resin seeing higher temperatures?
Gel cation resin can tolerate high temperatures but the combination of higher temperatures and an oxidant such as chlorine will dramatically lessen the life of the resin.

We've been supplying ion exchange resins for over 25 years now. We have customers who call every three years, most commonly replacement of anion resin in a demineralizer application and other customers we hear from every 5 or even 7 years - softener applications. I can't say as I've seen a trend that points to bad manufacturing practices by manufacturers.

In my opinion, the overwhelmingly majority of the problems result from oxidants such as chlorine and chloramine and my favorite - Operator Error - Oops ... we just backwashed all the resin out!

Industrial Water Softener Maintenance

Res-Kem Corp. and our sister company General Water Services offer preventative maintenance contracts for customers here in the Mid-Atlantic region. I thought it might be helpful to go over our Preventative Maintenance procedures for a commercial or industrial water softener for those of you who maintain your own water softening equipment.

For an industrial water softener we suggest our customers have bi-annual visits by our technicians. It's a very simple inspection that can prevent unscheduled downtime and the associated problems. How often our customer tests the water hardness is largely determined by how critical the application is and the availability of staff. We strongly suggest testing the water hardness on a daily basis if possible.

Res-Kem service technicians do a mechanical inspection that includes the following:
Inlet and Outlet Water Hardness - When we specify a commercial or industrial water softener we are given a water analysis, the average, high and low flow rates, hours of operation, and desired end-point. It's important to note changes against the design specification. If all things are equal, seeing hard water at the outlet points to a mechanical problem with the water softener (or no salt in the brine tank). If something else has changed - flow rate is lower or higher than specified or the inlet water hardness has increased - our technician will review the data with our engineering department and discuss the problem in greater depth with the customer.

Inlet and Outlet Pressures - Pressure testing is done when the water softener is running at the design specification. If there is a high differential the water softener might be running at too high a rate. If the water softener is running at a typical flow rate, (10 – 15 gpm/ft2) and there is a high differential pressure, the resin bed could be plugging up and preventing the water from flowing through the softener correctly. The differential pressure across a softener resin bed should generally run less than 15 psig. Of course there are many factors, which can result in higher differential pressures, i.e. depth of the resin bed, design of the internal distribution, age of resin, etc.

Inlet Chlorine (in absence of carbon filter or bi-sulfite feed) - Chlorine will break down cation ion exchange resin. Exposure to significant amounts of free chlorine, "hypochlorite" ions, or other strong oxidizing agents over long periods of time will eventually break down the crosslinking. Over time the cation resin turns to mush and will plug up the bed or eventually be flushed out so there remains much less resin than required.

Check salt level in brine tank, add if necessary

Make Note of Leaks - Our technicians are trained to look carefully for that small drip. We'll fix it if possible while we're there, otherwise we will make an appointment to come back to service the problem. You should have gaskets in on hand for both the manway and handhole openings.

Make Adjustments to the Control Valve - You should have received an operating manual with the water softener which includes information about the system settings.

If outlet water is out of hardness specification adjustments may be necessary.

Verify water softener timer is set to correct time and day.

Recalculate how often the water softener should be regenerating based on hardness and gallons and adjust control as necessary.

Optional Annual Maintenance

Valve Maintenance - There are many different types of controls and valves used on a commercial industrial water softener. In general you will need the following parts on hand to perform this service:

Aquamatic Valve Nest Systems - Diaphragm & Seal Kits, Internal Parts Kits, Seat Tools and Shaft Tools.

Fleck Top Mounted Control Systems - Upper and Lower Seal & Spacer Kits, Top Piston Kit, Lower Piston Kit.

Autotrol Top Mounted Control Systems - Internal parts kits. Specific kits depend on valve type.

Ion Exchange Resin Test - Although softener resin will last significantly longer than deionizer resin, in the presence of chlorine or other oxidants it will break down. If your water is highly chlorinated or has other contaminants such as iron, you should test the resin within 18 to 24 months of start up and every year thereafter. Otherwise, test the resin after the third year and then every year thereafter. By doing so you will know when to budget softener resin replacement as it is often a major expense.

Type II Anion vs Type I Anion: Ion Exchange Resin Analysis Yields Regeneration Savings

Res-Kem is a supplier of ion exchange resins from several vendors including Purolite. Res-Kem is often asked to diagnose a potential ion exchange resin problem. Depending upon the resin type, cation, anion, or mixed bed, cost and length in service, it may make sense to sample the resin and test for parameters that can identify what has caused the resin not to perform and a potential remedy.

Problem:
One recent example of the value of an ion exchange resin analysis are the results of two anion samples sent to Res-Kem. The customer was noticing:

More frequent regenerations

Increased chemical usage

Longer rinse times This resulted in a much higher cost to produce water for use.

They needed a solution.

Ion Exchange Resin Analysis Reports:

Ion Exchange Resin Analysis Report for Train A
Ion Exchange Resin Analysis Report for Train B

Discussion of Resin Analysis (Written by Ted Begg of Purolite):

Train A & B strong base anion resin analysis concluded the samples are Type II Strong Base Anions, equivalent to Purolite A300. Both samples exhibited dramatic loss in strong base capacity and severe organic fouling. Typical Type II anions will have 90% strong base capacity when new, however, it is not uncommon to see severe reduction to the levels observed, ~ 60%, when the resin is continually subjected to temperatures well in excess of 95 degrees F. Strong base capacity is responsible for silica removal. As this capacity is lost, throughput to silica break gets lower and lower with cost of caustic for regeneration steadily increasing. Given caustic is approaching $1000/ dry ton, lost throughput due to resin degradation comes at a very high cost.

The organic fouling noted is severe and is likely contributing to lost throughput and increased rinse volume (fast rinse). The organics on the resin pick up sodium during caustic regeneration, which slowly elutes off during the fast rinse. Therefore the increased rinse volume.

The Demineralization System:

This plant was designed to mix returned hot condensate to the finished water make up storage tank. This water is used for boiler feedwater and as well as for regeneration. While the heated water is beneficial for boiler feedwater, it is not good for regeneration of the anion resins. This water can approach and possibly exceed 130 degrees F. The Type II strong base anion resin temperature limit is stated by manufacturers at 105 degrees F, however, it is more prudent to maintain the limit to a maximum of 95 degrees F. Given the plant operating conditions and the condition of the anion resin, we recommended that the anion be replaced with a more temperature stable product. A Type I porous anion resin with uniform particle size distribution is recommended as a replacement. The product, PFA400, is stable up to 140 degrees F and is more resistant to organic fouling than the incumbent resin. In this case longevity of the resin will improve. The throughput capacity of PFA400 will approach the incumbent resin as well. Thanks Ted for the detailed discussion above of the analyses.

Our Conclusions and Observations:

The conclusion is using a Type II anion in place of a Type I, where low silica water is required and the system can run above 95 degrees F, is a misapplication for the reasons stated above which are:

Less stable at higher temperatures

Strong base sites break down more easily breakdown to weak base sites

Lower capacity for silica

So how does this misapplication happen? The selection of the ion exchange resins for a demineralization system generally occurs many years before a system is started up. Depending upon the perceived complexity of the water treatment system which includes the demineralization system, an engineering company may be specifying the demineralization system components including the resins as well as a whole host of other pieces of equipment. Then these specifications will be bid on by a short or long list of OEM's each of whom wants to get the job. Most will bid to the specs, but others may suggest a cheaper alternative.

One common area to shave money from the whole job is to skimp on the demineralization system in particlar the anion system. When lowest installed cost is the driver, sometimes Res-Kem sees equipment companies selling deionization systems using a Type II anion resin. The reason they promote the use of a Type II anion is the anion portion of the system is smaller. Because the Type II anion resin has about a 10% higher initial capacity than a Type I, the equipment needs 10% less of the expensive anion resin and the size of the anion tank is smaller. The end result is several months after commissioning and transfer of the equipment from the OEM to the user, the problems begin. By then, the low budget OEM will be on to their next project and will often walk away from your problem.

Res-Kem believes the moral of the story is work work with a knowledgeable OEM with experienced personnel who will recommend the best equipment for your application and will stand behind their equipment when installed.