Dealkalizer Performance Calculations

We recently had questions about a perceived problem with a dealkalizer. This customer believed the capacity of the dealkalizer was lower than originally specified and was unhappy with its performance. The customer was regenerating this new system more often than they regenerated the older system. We reviewed the system design and operation and found the problems.

Determining the Dealkalizer Capacity:
In order for us to know how long a dealkalizer system will produce dealkalized water between regenerations, we need a complete water analysis. There are a number of factors in determining the capacity of Dealkalizer Systems. The two most important things used to determine resin capacity are: Influent TDS and Alkalinity (as a percentage of the TDS). Once these are known, the resin capacity can be determined by using established resin manufacturers' charts, or by doing calculations based on total exchangeable anions and percentages of alkalinity and chlorides.

Based on using the charts and info from Purolite and Rohm & Haas

the capacity they should be getting is approximately 2,900 grains/cu ft x 15 cu ft = 43,500 grains removal. With 50 ppm (2.93 grains/gallon) alkalinity, this equates to 14,846 gallons between regenerations.

Minimum Flow Rate:
This capacity is further based on the flow rate of the system. Ideally, the unit should run @ 2 gpm/cu ft of resin or 30 gpm. Further, the minimum flow rate to insure proper kinetics and to prevent channeling is 2 gpm/sq ft of tank surface area. In their case, with a 30" diameter fiberglass tank, which has a surface area of 4.6 sq ft, the minimum flow rate should be 9.2 gpm.

We advised the customer that their average real time flow rate is 271 gph, which is 4.5 gpm. This is well below the recommended flow rate of 9.2 gpm. At this rate, the water is definitely channeling resulting in premature alkalinity breakthrough.

Premature alkalinity breakthrough would necessitate regenerating the system more often. If the dealkalizer was being run at the design rate of 9.2 gpm it would regenerate less often.

Resin Regeneration Frequency and Resin Life:
Before this customer understood the cause of the dealkalizer problem he was concerned the dealkalizer resin had lost its original capacity. Furthermore he was concerned that regenerating the dealkalizer more often would affect the life of the resin. The answer in both cases was no. The resin was in good shape and regenerating the system more often would not be detrimental to it.

Their very old dealkalizer did not appear to regenerate as often as the new system. There could have been any number of reasons it didn't.

• Was it actually producing dealkalized water in the 5 ppm range?
• Was the resin broken down to the point where it could operate at low flows and still work?
• Is the water analysis from 2008 the same as now?

We don't know the answers to the first two questions but it's very doubtful that the analysis is the same, as water in most areas can change dramatically from summer to winter and from drought to rainy times. We asked them to check the water in the winter when there is a lot of snow and/or ice. The salt on the roads increases the TDS of the water, not to mention the alkalinity and chlorides; all of which will have a significant affect on the performance of a dealkalizer.

Solutions and Recomendations:

Adding Caustic to Salt During Regeneration Increases Resin Capacity
They may be able to increase the capacity of the dealkalizer somewhat by increasing the amount of the salt and caustic. However, it may not be worth it given the low flow rate of operation.

We don't feel making changes to the dealkalizer will enable it to produce more treated water between regenerations. If the real time flow will continue at 4.5 gpm (or less), we suggested they installation of a recirculation pump on the softener/dealkalizer system. This will insure there is enough water going through the units and prevent channeling.

Dealkalizer Control Upgrade

The Problem:
A seafood processing plant called Res-Kem Corp to service their Brunermatic Dealkalizer. Their problem was of water running to drain during backwash and rinse stages. To repair the valve, Res-Kem service personnel would need to replace or rebuild the backwash outlet port and rinse outlet port.

The Analysis:
The Res-Kem service manager noted during the site visit that the control on the dealkalizer is no longer manufactured and the caustic pump was not functioning. With a dealkalizer, caustic can be fed during the regeneration cycle to enhance dealkalizer performance. The addition of caustic to the brine gives greater capacity to the Type II strong base anion ion exchange resin used in the dealkalization process. The following shows the increase in dealkalizer capacity with the addition of caustic to the brine regeneration step.


The Solutions:
Having seen this problem before, the Res-Kem service manager suggested the customer consider an upgrade to a current design that incorporates the Signet Flow Sensor and caustic pump. Res-Kem uses the Aquamatic 962 Controller and Stager. The Aquamatic 962 controller is a programmable electronic control with a relay that can be used to signal the chemical feed pump. The cost to repair the existing caustic pump exceeded the cost of a new one and the customer was happy to learn the pump manufacturer they use elsewhere in the boiler house could be used in conjunction with the new Aquamatic 962 controller.

The Benefits:
This simple upgrade to the existing dealkalizer benefits the customer by:

Allowing use of their standard pump manufacturer and enabling them to keep "standard" repair parts on hand

Allowing continued successful operation of the existing dealkalizer

Gets them back to the original design - automatic operation of the dealkalizer.

Save $91,000 Annually In Low Pressure Boiler Water Treatment Chemical And Fuel Costs Using a Dealkalizer

A white paper entitled "Save $91,000 Annually In Low Pressure Boiler Water Treatment Chemical And Fuel Costs Using a Dealkalizer" was written by Kevin Preising a Sales Engineer at Res-Kem Corp.

This white paper explains how dealkalization of boiler feedwater improves boiler steam/condensate systems reliability, fuel savings, and chemical savings. The Return on Investment, ROI, is substantially less than one year when a dealkalizer is added to an existing boiler feedwater plant with a conventional sodium cycle water softener - deaerator pretreatment.

Annual chemical savings are over $76,000 and "cycle-up" energy savings are over $15,000 savings using a dealkalizer with chloride form anion ion exchange resin. Reductions in condensate piping replacements can add further cost savings and will make the ROI even more attractive. In applications where neutralizing amine concentrations are limited by FDA regulations, the dealkalizer can be used in conjunction with reduced feed of neutralizing amines, achieving an optimized solution of reduced chemical feed with improved return condensate pH numbers.

The goal of this discussion is confined to the addition of a dealkalizer post water softener.
The results of adding a dealkalizer are:
- Minimized waterside scale formation
- Minimized boiler-carryover
- Minimized boiler blow down through increased boiler cycles
- Increased return condensate pH values - thereby reducing the need for neutralizing amine chemical feed to control corrosion in the condensate.