Summary of knowledge of demineralized water treatment and demineralized water treatment equipment

Let's first understand what is softened water

In daily life, we often see that the inner wall of the kettle will generate scale after long use. What is the reason? It turns out that the water we take contains many inorganic salts, such as calcium and magnesium salts. These salts cannot be found by naked eyes in water at normal temperature. Once they are heated and boiled, many calcium and magnesium salts will precipitate in carbonate, and they will form scale when they cling to the wall of the pot. We usually use the index of "hardness" to express the content of calcium and magnesium ions in water. Hardness of 1 degree is equivalent to 10 mg of calcium oxide per liter of water. Water below 8 degrees is called soft water, water above 17 degrees is called hard water, and water between 8 and 17 degrees is called medium hard water. Rain, snow, rivers, rivers and lakes are soft water, while springs, deep wells and seawater are hard water.

Let's look at the difference between softened water and other water

Raw water refers to untreated water. In a broad sense, the water before entering the water treatment process is also called the raw water of the water treatment. For example, the water sent from the water source to the clarifier for treatment is called raw water.

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

Demineralized water refers to water in which salts (mainly strong electrolytes dissolved in water) are removed or reduced to a certain extent. The conductivity is generally 1.0 ~ 10.0 µ s/cm, and the resistivity (25 ℃) (0.1 ~ 1.0) × 106 Ω· cm, with salt content of 1 ~ 5mg/l.

Pure water refers to water with strong electrolyte and weak electrolyte (such as SiO2, CO2, etc.) removed or reduced to a certain extent. The conductivity is generally 1.0 ~ 0.1 µ s/cm, and the conductivity is (1.01.0 ~ 10.0) × 106 Ω· cm. The salt content is <1mg/l.

Ultra pure water refers to water in which the conductive medium in the water is almost completely removed, while the non dissociated gas, colloid and organic substances (including bacteria) are also removed to a very low degree. The conductivity is generally 0.1 ~ 0.055 µ s/cm, and the resistivity (25 ℃) > 10 × 106 Ω· cm, salt content ＜ 0.1 mg/l. The conductivity of ideal pure water (theoretically) is 0.05 µ s/cm, and the resistivity (25 ℃) is 18.3 × 106 Ω· cm.

What is demineralized water treatment?

The calcium and magnesium ions in raw water are replaced by strong acid cation resin, and the boiler water filtered by the softened water equipment becomes the softened purified water for boiler with very low hardness.

operational principle

Ion exchange method

Methods: calcium and magnesium ions in water were replaced by sodium ions with specific cation exchange resin. Due to the high solubility of sodium salt, the scale formation with the increase of temperature was avoided.

Features and effects: the effect is stable and accurate, and the process is mature. The hardness can be reduced to 0.

Scope of application: catering, food, chemical industry, medicine and other fields, air conditioning, industrial circulating water and other applications. The most commonly used standard method at present.

Electromagnetic method

Methods: adding a certain electric field or magnetic field to the water to change the characteristics of ions, so as to change the deposition rate of calcium carbonate (magnesium carbonate) and the physical characteristics during deposition to prevent the formation of hard scale.

Features and effects: small equipment investment, convenient installation and low operation cost. 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 treated water are limited.

Scope of application: it is mainly used for the treatment of circulating cooling water in commercial (such as central air conditioning, etc.), but not for industrial production and boiler make-up water treatment.

Membrane separation

Methods: both nanofiltration membrane (NF) and reverse osmosis membrane (RO) can intercept calcium and magnesium ions in water, thus fundamentally reducing the hardness of water.

The hardness can only be reduced to a certain range.

Characteristic effect: the effect is obvious and stable, and the treated water has a wide range of application. It has high requirements for inlet water pressure and high equipment investment and operation cost.

Scope of application: it is seldom used for special softening treatment.

Lime method

Method: add lime to the water.

Characteristic effect: the hardness can only be reduced to a certain range.

Scope of application: high hard water with large flow.

Dosing method

Methods: adding a special scale inhibitor to the water can change the characteristics of the combination of calcium and magnesium ions and carbonate ions, so that the scale can not be precipitated and deposited.

Characteristics and effects: less one-time investment and wide adaptability. When the water volume is soft and large, the operation cost is low.

Scope of application: due to the addition of chemicals, the application of water is greatly limited. Generally, it cannot be used in drinking, food processing, industrial production, etc. It is rarely used in the civil field.

Work flow and requirements of demineralized water equipment

1) Work flow of demineralized water equipment

Operation (sometimes called water production, the same below), backwashing, salt absorption (regeneration), slow flushing (replacement) and fast flushing. All processes of different softened water equipment are very similar, but there may be some additional processes due to different actual processes or control needs. Any softened water equipment based on sodium ion exchange is developed on the basis of these five processes (among them, the full-automatic softened water equipment will increase the brine reinjection process).

Backwashing: after working for a period of time, the equipment will intercept many pollutants brought by raw water on the upper part of the resin. After these pollutants 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 out from the top, so that the dirt intercepted from the top can be washed away. This process usually takes about 5-15 minutes.

Salt suction (regeneration): that is, the process of injecting salt water into the resin tank. The traditional equipment uses a salt pump to inject salt water, and the fully automatic equipment uses a special built-in ejector to suck salt water (as long as there is a certain pressure in the water). In the actual working process, the regeneration effect of salt water flowing through the resin at a slow speed is better than that of simply soaking the resin with salt water. Therefore, the softening water equipment adopts the method of salt water flowing through the resin at a slow speed. This process generally takes about 30 minutes. The actual time is affected by the amount of salt used.

Slow flushing (replacement): after salt water flows through the resin, the process of slowly flushing all the salt in the resin with raw water at the same flow rate is called slow flushing. Because a large number of calcium and magnesium ions on functional groups are still exchanged by sodium ions in this flushing process, according to practical experience, this process is the main process of regeneration, so many people call this process replacement. This process is generally the same as salt absorption, i.e. about 30 minutes.

Quick flushing: in order to thoroughly flush the residual salt, the resin shall be flushed with raw water at a flow rate close to the actual work. The final effluent of this process shall be soft water up to the standard. Generally, the fast flushing process takes 5-15 minutes.

2) Technical indicators and work requirements of demineralized water equipment:

Inlet water pressure: 0.18-0.6mpa

Working temperature: 1-55 ℃, hardness of source water: <8mmol/l

Operation mode: automatic / manual water outlet hardness: ≤ 0.03mmol/l

Regenerant: NaCl regeneration mode: downstream / countercurrent

Exchanger: 001*7 strong acid ion exchange resin

Control mode: time / flow working power supply: 220v/50hz

Function of soft water exchange treatment

1. the use of softened water equipment saves a lot of wasted fuel

When there is scale on the boiler, 1mm scale will be formed on the boiler with working pressure of 1.4mpa, and 8% fuel will be wasted.

2. softened water equipment improves thermal efficiency and reduces output

When there is scale on the evaporation surface of the boiler, the heat on the fire side cannot be transferred quickly to the feed water side, which will reduce the output of the boiler. If the boiler is scaled due to improper water treatment, the evaporation capacity of the boiler will be reduced by one third, and the automatic operation line cannot be started due to insufficient gas supply.

3. use of demineralized water equipment to reduce the maintenance amount of boiler

It is very difficult to remove the scale on the boiler plate or pipe, especially the boiler leakage, crack, damage, deformation, corrosion and other diseases caused by the scale. It not only damages the boiler, but also consumes a lot of manpower and material resources for maintenance, which not only shortens the operation time, but also increases the maintenance cost.

4. application of softened water equipment to reduce safety hazards

Boiler accidents caused by scale account for more than 20% of the total boiler accidents, which not only cause equipment losses, but also threaten personal safety. The capital construction and operation costs of water treatment account for one fourth of the savings.

Demineralized water treatment equipment

Water softening equipment, as the name suggests, is the equipment to reduce the hardness of water. It is mainly used to remove calcium and magnesium ions in the water. Popularly speaking, it is the equipment to reduce the hardness of water. Its main functions are to remove calcium and magnesium ions in the water, activate water quality, kill bacteria and algae, and prevent and remove scale. During the process of softening water, the total salt content in the water cannot be reduced by the softening water equipment. It is widely used in hot water boiler system, heat exchange system, industrial cooling system, central air conditioning system and other water equipment systems.

operational principle

Since the hardness of water is mainly formed and expressed by calcium and magnesium, cation exchange resin (water softener) is generally used to replace ca2+ and mg2+ (the main component forming scale) in the water. With the increase of ca2+ and mg2+ in the resin, the efficiency of removing ca2+ and mg2+ by the resin gradually decreases.

After the resin absorbs a certain amount of calcium and magnesium ions, it must be regenerated. The regeneration process is to wash the resin layer with salt water in the salt tank, replace the hardness ions on the resin, and discharge the regenerated waste liquid out of the tank, so that the resin can recover the softening and exchange function.

As the hardness of water is mainly formed by calcium and magnesium, the hardness of water is mainly formed by calcium and magnesium, and the principle of sodium ion exchange softening treatment is to exchange the hardness components ca2+ and mg2+ in the water with na+ in the resin through sodium cation exchange resin, so as to adsorb ca2+ and mg2+ in the water and soften the water.

Workflow

Operation (sometimes called water production, the same below), backwashing, salt absorption (regeneration), slow flushing (replacement) and fast flushing. All processes of different softened water equipment are very similar, but there may be some additional processes due to different actual processes or control needs. Any softened water equipment based on sodium ion exchange is developed on the basis of these five processes (among them, the full-automatic softened water equipment will increase the brine reinjection process).

Backwashing: after working for a period of time, the equipment will intercept many pollutants brought by raw water on the upper part of the resin. After these pollutants 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 out from the top, so that the dirt intercepted from the top can be washed away. This process usually takes about 5-15 minutes.

Salt suction (regeneration): that is, the process of injecting salt water into the resin tank. The traditional equipment uses a salt pump to inject salt water, and the fully automatic equipment uses a special built-in ejector to suck salt water (as long as there is a certain pressure in the water). In the actual working process, the regeneration effect of salt water flowing through the resin at a slow speed is better than that of simply soaking the resin with salt water. Therefore, the softening water equipment adopts the method of salt water flowing through the resin at a slow speed. This process generally takes about 30 minutes. The actual time is affected by the amount of salt used.

Slow flushing (replacement): after salt water flows through the resin, the process of slowly flushing all the salt in the resin with raw water at the same flow rate is called slow flushing. Because a large number of calcium and magnesium ions on functional groups are still exchanged by sodium ions in this flushing process, according to practical experience, this process is the main process of regeneration, so many people call this process replacement. This process is generally the same as salt absorption, i.e. about 30 minutes.

Quick flushing: in order to thoroughly flush the residual salt, the resin shall be flushed with raw water at a flow rate close to the actual work. The final effluent of this process shall be soft water up to the standard. Generally, the fast flushing process takes 5-15 minutes.

application

Choose different soft water treatment equipment for different applications

1. Application scope of demineralized water equipment:

① Heating

② Cooling water make-up

③ Process water

④ Steam boiler

⑤ Iron and steel smelting

⑥ Chemical pharmacy

2. System water consumption time required by the industry

System water consumption time: hourly water consumption, average value and peak value. The equipment can be selected according to the water supply time. If continuous water supply is not required, single valve and single tank equipment can be selected; If continuous water supply is required, double bed centralized control or double control double bed series softened water treatment device shall be selected.

3. Hardness of water source

If the water quality of the same type of water softener is hard, the water making cycle must be relatively reduced, and the water production is low, which leads to frequent regeneration of the softener, thus reducing the service life of the resin. In this case, it is necessary to select a larger model of water softener to increase the resin volume.

2、 Type selection of demineralized water equipment

① Controller: divided into automatic control and manual control. Brands can be imported or domestic.

② Resin tank: the tank material of the demineralized water device is divided into FRP, carbon steel and stainless steel.

③ Equipment control mode: one is automatic reduction when the preparation water volume reaches the set value, which is called flow type; It is applicable to all softened water treatment equipment of water supply system. The second method is to control regeneration metering by time, which is called time type; It is applicable to the water supply system with stable water volume, and the shortest reduction and regeneration cycle is 24 hours.

④ Equipment combination:

Single control single bed: stop water supply for 2 hours or continue to supply raw water (hard water bypass) during reduction.

Single control double bed: alternate water supply, one for use and one for standby.

Double control double bed: alternate water supply, one for use and one for standby.

Double control double bed: simultaneous water supply and alternate regeneration.

Multiple control beds: more than three softened water resin tanks are used in parallel, which is suitable for large-scale water supply systems.

It can be widely used to soften the make-up water of steam boilers, hot water boilers, exchangers, evaporative condensers, air conditioners, direct fired turbines and other systems. It can also be used for the treatment of domestic water in hotels, restaurants, office buildings, apartments, homes and other industries, as well as softened water treatment in food, beverage, wine making, laundry, printing and dyeing, chemical industry, medicine and other industries.

Technical indicators

1. water inlet pressure: 0.2~0.5mpa

2. raw water hardness: <12mmol/l (when raw water hardness >8 mmol/l, special design shall be made according to the water quality of different regions)

3. outlet water hardness: <0.03mmol/l (meet the requirements of national low pressure boiler water quality standard gb1576-2001);

4. salt content of raw water <1500mg/l, turbidity <5, iron ion <0.3mg/l

5. power supply: ~220v, 50Hz

6. salt consumption <100g/ g equivalent (related to raw water hardness);

7. water consumption <2%; Main technical specifications for automatic demineralized water desalination equipment with power consumption <50w

1. Technical code for construction and acceptance of electric power construction

2. Standard for acceptance and evaluation of thermal power construction quality

3. Jb/t74-94 technical conditions for pipeline flanges

4. Sand blasting shall comply with gb8923

5. Dl/t5054-1996 technical code for design of steam water piping in thermal power plants

6. Gb/t18300-2001 specification for automatic control sodium ion exchanger

7. GB 1576-2001 low pressure boiler water quality

8. GB 5462-199 industrial salt

9. Gb/t 13659-1992 001*7 strongly acidic styrene cation exchange resin

10. Jb/t 2932-1999 technical conditions for water treatment equipment

11. Gb/t 13384-1992 general specification for packaging of mechanical and electrical products

Equipment classification

Industrial water treatment equipment, drinking water treatment equipment, filling equipment and water treatment accessories.

Industrial water treatment equipment

Large reverse osmosis equipment in power plants, ultra pure water equipment in pharmaceutical and electronic industries, pure water equipment for flowers, melons and fruits irrigation, dosing equipment, boiler softened water equipment;

Drinking water treatment equipment

Purified water equipment for food and beverage industry, purified water and mineral water equipment for water plants, rural drinking water equipment, direct drinking water equipment for hotels, schools, government agencies and canteens;

Filling equipment

Large barrel and small bottle filling line, barrel brushing and capping machine;

Water treatment accessories

Filter material, filter element, booster pump, reverse osmosis membrane, membrane shell, precision filter, flowmeter, pressure gauge, ozone generator, ultraviolet sterilizer, scale inhibitor, etc.