Summary of softened water treatment and softened water treatment equipment knowledge

Difference between softened water and other types of water

Raw water refers to untreated water. Broadly speaking, water entering a water treatment process is also called the raw water for that treatment. For example, water delivered from a source to a clarifier for treatment is called raw water.

Softened water refers to water in which the hardness (mainly calcium and magnesium ions) has been removed or reduced to a certain extent. During the softening process, only the hardness is reduced, while the total salt content remains unchanged.

Desalinated water refers to water in which salts (mainly strong electrolytes dissolved in water) have been removed or reduced to a certain extent. Its conductivity is generally 1.0～10.0µS/cm, resistivity (25℃) (0.1～1.0) ×106Ω·cm, and salt content is 1～5mg/L.

Pure water refers to water in which strong and weak electrolytes (such as SiO2, CO2, etc.) have been removed or reduced to a certain extent. Its conductivity is generally: 1.0～0.1µS/cm, resistivity (1.01.0～10.0) ×106Ω·cm. Salt content is <1mg/L.

Ultrapure water refers to water in which conductive media have been almost completely removed, and non-dissociated gases, colloids, and organic substances (including bacteria) have also been removed to a very low extent. Its conductivity is generally 0.1～0.055µS/cm, resistivity (25℃) ﹥10×106Ω·cm, and salt content ﹤0.1 mg/L. Ideal pure water (theoretically) has a conductivity of 0.05µS/cm and a resistivity (25℃) of 18.3×106Ω·cm.

Working principle

1. Ion exchange method

(1) Method: Specific cation exchange resin is used to replace calcium and magnesium ions in water with sodium ions. Due to the high solubility of sodium salts, the formation of scale due to temperature increase is avoided.

(2) Characteristics and effects: Stable and accurate effect, mature technology. Hardness can be reduced to 0.

(3) Application range: Catering, food, chemical, pharmaceutical industries, air conditioning, industrial circulating water, etc. Currently the most commonly used standard method.

2. Electromagnetic method

(1) Method: Applying a certain electric or magnetic field in water to change the characteristics of ions, thereby changing the speed of calcium carbonate (magnesium carbonate) deposition and the physical properties during deposition to prevent the formation of hard scale.

(2) Characteristics and effects: Low equipment investment, easy installation, low operating costs. The effect is not stable enough, there is no unified measurement standard, and because the main function is only to affect the physical properties of scale within a certain range, the use time and distance of the treated water are limited.

(4) Application range: Mostly used for the treatment of commercial (such as central air conditioning) circulating cooling water, and cannot be used for industrial production and boiler feed water treatment.

3. Membrane separation method

(1) Method: Nanofiltration (NF) and reverse osmosis (RO) membranes can both intercept calcium and magnesium ions in water, thus fundamentally reducing water hardness. Hardness can only be reduced to a certain range.

(2) Characteristics and effects: The effect is obvious and stable, and the treated water has a wide range of applications. It has high requirements for inlet pressure, and the equipment investment and operating costs are high.

(3) Application range: Generally less used for specialized softening treatment.

4. Lime method

(1) Method: Adding lime to the water.

(2) Characteristics and effects: Hardness can only be reduced to a certain range.

(3) Application range: Suitable for high-hardness water with large flow rates.

5. Chemical addition method

(1) Method: Adding a special scale inhibitor to the water can change the characteristics of calcium and magnesium ions combining with carbonate ions, so that scale cannot precipitate and deposit.

(2) Characteristics and effects: Low initial investment, wide adaptability. Operating costs are high when the water volume is large.

(3) Application range: Due to the addition of chemicals, the application of water is greatly limited, and generally cannot be used for drinking, food processing, industrial production, etc. It is also rarely used in the civil field.

Softened water equipment workflow and requirements

1. Softened water equipment workflow

Operation (sometimes called water production, the same below), backwashing, salting (regeneration), slow rinsing (displacement), and fast rinsing. The procedures of different softened water equipment are very similar, but due to differences in actual technology or control needs, there may be some additional processes. Any softened water equipment based on sodium ion exchange is developed on the basis of these five processes (among them, fully automatic softened water equipment will add a brine recharge process).

(1) Backwashing: After the equipment has been operating for a period of time, a lot of impurities from the raw water will be intercepted on the top of the resin. After these impurities are removed, the ion exchange resin can be fully exposed, and the regeneration effect can be guaranteed. The backwashing process is that water is washed in from the bottom of the resin and flows out from the top, so that the impurities intercepted at the top can be flushed away. This process generally takes about 5-15 minutes.

(2) Salting (regeneration): This is the process of injecting brine into the resin tank. Traditional equipment uses a salt pump to inject brine, while fully automatic equipment uses a special built-in injector to suck in brine (as long as the inlet water has a certain pressure). In the actual operation process, the brine flows through the resin at a slower speed, and the regeneration effect is better than simply soaking the resin in brine, so softened water equipment all uses the method of slow brine flow through the resin for regeneration. This process generally takes about 30 minutes, and the actual time is affected by the amount of salt used.

(3) Slow rinsing (displacement): After the resin is flushed with brine, the process of slowly rinsing the salt out of the resin with raw water at the same flow rate is called slow rinsing. Since a large number of calcium and magnesium ions on the functional groups are still exchanged with sodium ions during this rinsing process, based on practical experience, this process is the main regeneration process, so many people call this process displacement. This process generally takes the same time as salt absorption, about 30 minutes.

(4) Fast rinsing: In order to thoroughly rinse away the remaining salt, raw water is used to rinse the resin at a flow rate close to the actual working flow rate. The final effluent of this process should be qualified softened water. Generally, the fast rinsing process takes 5-15 minutes.

2. Technical indicators and operating requirements of water softening equipment:

Inlet water pressure: 0.18-0.6Mpa

Operating temperature: 1-55℃ Raw water hardness: <8mmol/L

Operation mode: Automatic/Manual Effluent hardness: ≤0.03mmol/L

Regenerant: NaCL Regeneration method: Co-current/Counter-current

Exchanger: 001*7 strong acid cation exchange resin

Control method: Time/Flow rate Power supply: 220V/50Hz

The role of water softening treatment

1. The use of water softening equipment saves a lot of wasted fuel

When boiler scale is present, for a boiler with a working pressure of 1.4 MPa, 1 mm of scale will result in 8% fuel waste.

2. Water softening equipment improves thermal efficiency and reduces output

When boiler scale is present on the evaporation surface, the heat on the fire side cannot be quickly transferred to the water side, which will reduce the boiler's output. If the boiler scaling is caused by improper water treatment, the boiler's evaporation capacity is reduced by one third, and the automatic production line cannot be started due to insufficient air supply.

3. The use of water softening equipment reduces boiler maintenance

Once boiler plates or pipes are scaled, they are very difficult to clean, especially leaks, cracks, breakage, deformation, and corrosion caused by scale. This not only damages the boiler but also consumes a lot of manpower and material resources for maintenance, shortening the operating time and increasing maintenance costs.

4. The application of water softening equipment reduces safety hazards

Boiler accidents caused by scale account for more than 20% of the total number of boiler accidents, not only causing equipment losses but also threatening personal safety. The construction and operating costs of water treatment account for one-fourth of the total savings.