Brining techniques and regeneration cycle programming are two noteworthy modifications and features, which can be useful for studying water softener guidelines.  

Let’s review few guidelines for designing water softeners.

The following introduction provides helpful guidance on selecting the right water softener size, and configuration for various applications, including residential, commercial, and non-critical industrial ones.  

What are the Guidelines for designing Water Softeners?

STEP 1: Choose the control valve you wish to use based on the service flow specifications of the application. The primary goal is to choose a valve that gives a tolerable pressure drop from the softener's intake, to output at the service flow specifications of the application. For the valve alone, use a maximum service flow pressure drop guideline of 15 psi (1 bar).

STEP 2: Determine the volume of cation resin needed. The amount of cation resin is typically governed by four factors:

a. service flow rate;

b. water hardness;

c. amount of water to be treated; and

d. frequency of softener regeneration (i.e., valves with flow metres allow multiple regeneration per day).

It usually takes up to two hours to regenerate, and it can take up to three hours depending on temperature, to create a saturated salt solution in the brine tank, making three times the practical maximum number of regenerations per day.

There are two approaches to calculate the volume of cation resin, necessary for a specific flow rate:

1) By resin volume, which affects contact duration, and

2) By resin bed cross section area, which affects pressure drop in the resin bed or the tank

By contact time

For continuous flow, use 42 cubic metres per hour per cubic metre, or 5 gpm/ft³, and for peak flow, use 60 m³/h/m³ (or 7.5 gpm/ft³). The flow rate should be restricted to 3 gpm/ft³ in order to achieve low hardness leakage, as required in applications like boiler water treatment.

Use a constant flow rate of 10 gallons per minute per square foot (ft²), or 25 m³/h per square metre (m²), and a peak flow rate of 15 gpm/ft² for resin bed areas. Limit the area flow to 8 gpm/ft² to ensure low hardness leakage.

Salt dose vs. resin capacity

How much salt is used (dosage) to regenerate each litre or cubic foot of cation resin, determines the resin's capacity for hardness, or how much hardness may be eliminated by cation resin.

Standard mesh resin typically ranges between 6 lbs of salt per cubic foot (lbs salt/ft³ or lbs/ft³) of resin—roughly 100 g of salt per litre (g salt/L or g/L) of resin—and 15 lbs of salt/ft³ (approximately 240 g salt/L).

Low limit salt dosage—6 lbs salt/ft³ (about 100 g salt/L) resin affords hardness removal capacity of about 21,000 grains/ft³—48 grammes of hardness as calcium carbonate (CaCO₃) per litre [g(CaCO₃)/L] or 0.96 equivalents per litre (eq./L) of hardness.

A resin with a medium salt dose of 9 pounds salt/ft³ (or 150 g salt/L) can remove hardness from a space, at a rate of roughly 26,000 grains/ft³—or 60 g(CaCO₃)/L, or 1.19 eq/L.

Hardness removal capability is approximately 29,000 grains/ft³ (66 g(CaCO₃)/L or 1.33 eq/L) with a high salt dosage of 12 lbs/ft³ (or around 200 g salt/L) resin.

The absolute maximum salt concentration is 15 lbs/ft³ (or 250 g/L). An estimated 31,000 grains/ft³—71 g(CaCO₃)/L or 1.42 eq/L—of resin can remove hardness.

Observe how the capacity to remove hardness does not increase even when the salt dosage more than doubles. The salt efficiency decreases with increasing salt dosage.

Resin volume vs. treated water volume

Start by estimating the maximum total grains (or kilos) of hardness that must be eliminated each day, in order to calculate the volume of resin by volume of water treated and hardness.

Take into account much regeneration. It's crucial to realise that a system's size and expense can be decreased by doing multiple daily softener regenerations. A more cost-effective softening system can be constructed if the application is suitable for numerous regenerations per day, which can supply treated water for the customer during regeneration.

STEP 3: Determine the tank size. Typically, tanks are filled to between 1/2 and 2/3 of their overall volume. In smaller tanks, the cation resin should be at least 24" (0.6 m) deep, and in bigger tanks, 30" (0.75 m). The tank needs to be tall enough for the resin to extend into the vacuum area, at least halfway of its regular depth.

STEP 4: Determine the backwash flow rate in step 4 of the regeneration process, which involves cleaning the resin of dirt and debris.

a. Tank diameter: For the cross section area, consult the design chart provided by the manufacturer.

b. Water temperature: Viscosity of water is inversely related to water temperature. In colder water, the viscosity (thickness) increases, leading to increased expansion of the resin bed during backwash.

Water temperature vs. backwash flow rate

The need of proper water softener design may be the most ignored aspect, particularly in areas with warm water. The flow must be adequate to at least partially extend the bed. Use the following parameters, but consult your resin supplier's backwash needs vs. water viscosity chart for actual backwash flow requirements.

· Backwash flow of 4.2 gpm/ft² (10.3 m³/h/m²) at 10 °C (50 °F)

· At 15 °C (59 °F), the backwash flow is 5.0 gpm/ft² (12.3 m³/h/m)

· At 20 °C (68 °F), the backwash flow is 5.5 gpm/ft²

· Backwash flow of 16.4 m³/h/m², or 6.7 gpm/ft², at 25 °C (77 °F)

STEP 5: Determine the size of the brine injector because this is what draws the salt solution into a vacuum. Water is pumped via the injector venturi during regeneration, creating a vacuum that draws salt brine from the salt tank. The diameter of the tank has a major impact on the injector.

STEP 6: The regeneration cycle consists of a series of functions that correspond to control valve "positions." Calculate the regeneration function times. It is advised to perform regeneration functions in the following order, for the majority of clients who simply need to eliminate hardness:

· Down-flow Fast Rinse

· Salt Tank Refill

· Brine/Slow Rinse

· Return to Service

· Softener regeneration function

· Performing a backwash

Depending on the quantity of particle matter (sediment) in the water supply and water constraint, eight to fifteen minutes is advised. Use the higher range if there is iron present. A control orifice that limits the drain flow to the desired flow rate, controls the backwash flow.

It's crucial to realise that the down-flow brine function is simply one component of the whole "down-flow brine/slow rinse" operation.

Throughout the whole function, the control valve stays in the same location. This first stage involves sucking saturated salt brine solution out of the brine tank, and mixing it with the water stream coming from the venturi injector to a concentration, of about 10 to 13 percent, and regenerates it by flowing through the resin bed or chemically displaces the hardness removed. Saturated brine has a NaCl concentration of 2.7 lbs/gal (300 g/L).

Factors affecting brine function

The following factors affect brine function time:

1. The quantity of salt necessary to replenish the resin bed

2. How quickly the injector injects brine into the resin bed

3. The "down-flow brine/slow rinse" function is really extended by the "slow rinse" function, but without salt brine being emitted. This gentle rinsing is made possible by the on-going water flow through the injector. As a general rule, the down-flow brine and slow rinse cycle should last three times, as long as the brine cycle.

Rapid rinse function

To maintain a constant flow rate, the fast rinse passes through the backwash flow control. Depending on the volume of resin and the application, the rapid rinse time for the majority of applications should be 6 to 12 minutes. For example, the majority of home and commercial applications can use the lower range, whereas, industrial process applications that require longer rinse periods, should use reverse osmosis (RO) and deionization (DI) pretreatment and boiler feed.

Function of the salt tank refill

During this cycle, a controlled stream of water is pumped into the salt tank to create a brine solution, which is saturated and ready for the following regeneration. Based on the fact that 1 gallon of fresh water dissolves about 3 pounds of salt (1 L dissolves 360 g), the salt tank replenishment schedule should be determined.

Conclusion

The water softener design guidelines presented in this article are meant to serve as a foundation of knowledge, for general-purpose softening applications, including household use, as well as industrial non-critical processes, and low pressure boilers, and cooling towers, and RO - DI pretreatment.

Additional particular considerations are needed for more demanding applications like high-pressure boilers, medical autoclaves, and water sources with problematic pollutants like iron and manganese.

Water softener manufacturer and supplier

Netsol Water develops and produces water softeners that are highly successful, at lowering water hardness. By using a highly acidic cation exchanger to remove calcium and magnesium ions from the water, they aid in the production of soft water.

Our water softener plant is transportable and simple to relocate. Additionally, it requires less work for installation and upkeep. As one of the top manufacturers of water softening plants situated in India, we offer our products to customers at rates that are as low as possible.