CN111573971A - A system and method for reusing urban reclaimed water by using a full-membrane method - Google Patents

Abstract

The invention discloses a system for reusing urban regenerated water by using an all-membrane method. A raw water tank is connected to a PCF fiber filter through a raw water lifting pump, and the PCF fiber filter is connected to an ultrafiltration device; the ultrafiltration device is connected to an ultrafiltration water tank, and the ultrafiltration The water tank is cyclically connected to the ultrafiltration device through the ultrafiltration backwash pump; the ultrafiltration device is connected to the reverse osmosis security filter through the reverse osmosis lifting pump, the reverse osmosis security filter is connected to the reverse osmosis device, the reverse osmosis device is connected to the reverse osmosis production tank, and the reverse osmosis production tank is connected. The water tank is connected to the reverse osmosis device through the reverse osmosis flushing pump; the reverse osmosis production water tank is connected to the electric desalination device through the electric desalination EDI feed pump, and the electric desalination device is connected to the desalted water tank. The invention has the advantages of no pollution to the environment; simple system, small footprint, small installation, operation and maintenance workload; stable system operation, strong continuous water production capacity, no need for separate regeneration; and high water recovery rate.

Description

A system and method for reusing urban reclaimed water by using a full-membrane method

technical field

The invention relates to the technical field of wastewater treatment, in particular to a system and a method for reusing urban reclaimed water by using an all-membrane method.

Background technique

The quality of urban reclaimed water is between urban sewage and tap water. It is non-drinking water that can be used within a certain range after urban sewage has been purified and treated to meet national standards. It can be used in industrial production, people's life, urban landscape and many other aspects. In order to solve the problem of water shortage, the development and utilization of urban reclaimed water has significant advantages compared with other water sources.

The amount of urban reclaimed water is huge and stable, and is not limited by climatic conditions and other natural conditions, so it can be used as a reliable and reusable second water source, and is a very valuable water resource. Compared with the development and utilization of other water resources, the utilization of urban reclaimed water has the following economic advantages:

(1) Cheaper than long-distance water diversion

Urban reclaimed water is the secondary treatment of urban sewage, which is then reused as reclaimed water resources to suitable locations after advanced treatment. Infrastructure investment costs are more economical than long-distance water diversion. Practice has proved that the popularization and application of sewage treatment technology is imperative, and urban reclaimed water as the second urban water source is also an inevitable development trend.

(2) Economical than seawater desalination

The impurities contained in urban sewage are less than 0.1% and can be removed by advanced treatment methods, while seawater contains 3.5% dissolved salts and a large amount of organic matter, and its impurity content is more than 35 times that of the effluent of secondary sewage treatment. Pretreatment and expensive treatment technologies such as reverse osmosis or flash evaporation, so regardless of capital investment cost or unit operating cost, seawater desalination is higher than urban reclaimed water reuse.

(3) Significant social benefits can be achieved

In today's increasingly scarce water resources, the treated urban reclaimed water is reused for industrial production and residential water use, reducing pollutant emissions and thus reducing the impact on the water environment around the city. This change is conducive to protecting the environment. It can enhance the self-purification of water body without adversely affecting the hydrological environment of the whole region, and its application prospect is broad.

Water is an extremely precious natural resource. Thermal power plants are large consumers of water, but they must not become large consumers of water. The society needs to build thermal power plants into water-saving enterprises. Faced with the severe water shortage situation and the seriously deteriorating water environment, the use of the full-membrane method to reuse urban reclaimed water as a new process for boiler supply water in thermal power plants is in line with the national environmental protection policy requirements and in line with the country's promotion of industrial development. Require. It has good environmental benefits, economic benefits and social benefits.

Therefore, the reuse of urban reclaimed water provides a very economical new water source for people and reduces the social demand for fresh water resources. important strategy. Promoting advanced sewage treatment and popularizing the utilization of reclaimed water is an important measure for the coordinated development of human and nature, creating a good water environment, and promoting the development process of a circular city.

SUMMARY OF THE INVENTION

In order to solve the above problems, the present invention discloses a system and method for reusing urban reclaimed water by using a full-membrane method.

In order to achieve the above purpose, the present invention provides the following technical solutions:

A system for reusing urban reclaimed water by a full-membrane method, including a raw water tank, a PCF fiber filter, an ultrafiltration device, an ultrafiltration water tank, a reverse osmosis security filter, a reverse osmosis device, a reverse osmosis production water tank, and an electric desalination device. , Demineralized water tank; the raw water tank is connected to the PCF fiber filter through the raw water lift pump, and the PCF fiber filter is connected to the ultrafiltration device; the ultrafiltration device is connected to the ultrafiltration water tank, and the ultrafiltration water tank is connected to the ultrafiltration device through the ultrafiltration backwash pump cycle; The ultrafiltration device is connected to the reverse osmosis security filter through the reverse osmosis lifting pump, the reverse osmosis security filter is connected to the reverse osmosis device, the reverse osmosis device is connected to the reverse osmosis production water tank, and the reverse osmosis production water tank is connected to the reverse osmosis device through the reverse osmosis flushing pump; The permeate production tank is connected to the electric desalination device through the electric desalination EDI feed pump, and the electric desalination device is connected to the desalted water tank.

Further, the reverse osmosis device is provided with two stages; the reverse osmosis device includes a first-level reverse osmosis device and a second-level reverse osmosis device; the ultrafiltration device is connected to the first-level reverse osmosis security filter through the first-level reverse osmosis lifting pump, and the first-level reverse osmosis security filter is used. The filter is connected to the primary reverse osmosis device, the primary reverse osmosis device is connected to the primary reverse osmosis water production tank, and the primary reverse osmosis production water tank is connected to the primary reverse osmosis device through the primary reverse osmosis flushing pump; The secondary reverse osmosis lift pump is connected to the secondary reverse osmosis security filter, and the secondary reverse osmosis security filter is connected to the secondary reverse osmosis device; the secondary reverse osmosis device is connected to the secondary reverse osmosis production water tank, and the secondary reverse osmosis production water tank passes through EDI The feed water pump is connected to the electric desalination device.

Further, the secondary reverse osmosis production water tank and the electric desalination device are connected to the ultrafiltration water tank.

Further, the demineralized water tank is connected to the boiler water supply pipe network through the demineralized water pump.

Further, a self-cleaning filter is also provided between the PCF fiber filter and the ultrafiltration device.

Further, a carbon remover is arranged between the primary reverse osmosis device and the primary reverse osmosis production water tank (fresh water tank).

Further, the electric desalination device includes a fresh water chamber and a concentrated water chamber; a concentrated water chamber is arranged on the outer side of the fresh water chamber, a positive membrane is arranged between the fresh water chamber and the concentrated water chamber, an anion membrane is arranged on the outer wall of the concentrated water chamber, and the fresh water chamber is provided with a negative membrane. With anion exchange resin and cation exchange resin.

A method for reusing urban reclaimed water by a full-membrane method, comprising the following steps:

Step 1, the urban reclaimed water heated by the heat exchanger is transported to the raw water pool by the lift pump; after the biochemical treatment, the reclaimed water enters the fiber filter;

Step 2, then filter pretreatment through PCF fiber filter,

Step 3, further filter through the ultrafiltration device system,

In step 4, the ultrafiltration water product enters the primary reverse osmosis device and the secondary reverse osmosis device for pre-desalting successively,

Step 5, further desalination treatment through electric desalination device;

Step 6, making qualified reuse water.

Further, according to the principle of water source classification and quality use, the concentrated water of the secondary reverse osmosis device and the concentrated water of the electric desalination device are returned to the ultrafiltration water production tank, which is used as the influent of the primary reverse osmosis device to fully recover the usable water source. Reverse osmosis concentrated water, electric desalination concentrated water, etc. are classified and recycled.

Further, in step 1, a bactericide is added during the heating process to sterilize the urban regenerated water.

Further, chemical cleaning is performed on the ultrafiltration device, the primary reverse osmosis device, the secondary reverse osmosis device, and the electric desalination device.

The present invention adopts the above-mentioned all-membrane method to reuse the urban reclaimed water as the make-up water for the boiler of the thermal power plant. Compared with the traditional ion exchange method, the present invention has the following advantages:

(1) No acid and alkali waste liquid discharge, no pollution to the environment. (2) The system is simple, occupies less floor space, and requires less installation, operation and maintenance. (3) The system runs stably, with strong continuous water production capacity, and does not require separate regeneration. (4) The recovery rate of water is high. When the hardness of the influent water is less than 0.02 mmol/L, the recovery rate can reach 90% to 95%.

Compared with the traditional ion exchange method, the initial investment of the full-membrane method is slightly higher, but the operating cost is significantly reduced due to the elimination of acid-base consumption, regeneration water, wastewater treatment and sewage discharge, and the one-time investment can be compensated for about one year. difference. In addition, the EDI installation has a smaller footprint. About 1/3 of the mixed bed of the same system water yield. It can be seen from the comprehensive comparison that the whole membrane technology is of outstanding quality compared with the mixed bed technology.

Description of drawings

Figure 1: Process flow diagram;

Figure 2. The operating principle of the fiber filter;

Figure 3. The operation principle of Electrodemineralization (EDI);

Figure 4. Ultrafiltration (UF) operation record;

Figure 5. First-stage reverse osmosis (RO) operation record;

Figure 6. Secondary reverse osmosis (RO) operation record;

Figure 7, the process flow diagram of the present invention.

Among them: 1. Raw water tank; 2. Raw water lifting pump; 3. PCF fiber filter; 4. Self-cleaning filter; 5. Ultrafiltration (UF); 6. Ultrafiltration water tank; 7. Ultrafiltration backwash pump; 8. First-level reverse osmosis lift pump; 9. First-level reverse osmosis security filter; 10. First-level reverse osmosis (RO); 11. First-level reverse osmosis production tank; 12. First-level reverse osmosis flushing pump; 13. Second-level Reverse osmosis lift pump; 14, secondary reverse osmosis security filter; 15, secondary reverse osmosis (RO); 16, secondary reverse osmosis production tank; 17, EDI feed pump; 18, electric desalination (EDI); 19 , Demineralized water tank; 20. Demineralized water pump.

Detailed ways

The present invention will be further clarified below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

As shown in Figure 7, a full-membrane method is used to reuse urban reclaimed water, including raw water pool, PCF fiber filter, ultrafiltration (UF), ultrafiltration water tank, reverse osmosis security filter, reverse osmosis (RO) , reverse osmosis production water tank, electric desalination (EDI), demineralized water tank; raw water tank is connected to PCF fiber filter through raw water lift pump, PCF fiber filter is connected to ultrafiltration (UF); ultrafiltration (UF) is connected to ultrafiltration water tank , the ultrafiltration water tank is connected to the ultrafiltration (UF) through the ultrafiltration backwash pump; the ultrafiltration (UF) is connected to the reverse osmosis security filter through the reverse osmosis lifting pump, and the reverse osmosis security filter is connected to the reverse osmosis (RO), and the reverse osmosis ( RO) is connected to the reverse osmosis production water tank, and the reverse osmosis production water tank is connected to the reverse osmosis (RO) through the reverse osmosis flushing pump; Connect the demineralized water tank.

Two-stage reverse osmosis (RO) is set up; reverse osmosis (RO) includes one-stage reverse osmosis (RO) and two-stage reverse osmosis (RO); ultrafiltration (UF) is connected to one-stage reverse osmosis security filtration through a first-stage reverse osmosis lift pump The first stage reverse osmosis security filter is connected to the first stage reverse osmosis (RO), the first stage reverse osmosis (RO) is connected to the first stage reverse osmosis production water tank, and the first stage reverse osmosis production water tank is connected to the first stage through the first stage reverse osmosis flushing pump. Reverse osmosis (RO); the primary reverse osmosis production tank is connected to the secondary reverse osmosis security filter through the secondary reverse osmosis lifting pump, and the secondary reverse osmosis security filter is connected to the secondary reverse osmosis (RO); the secondary reverse osmosis (RO) ) is connected to the secondary reverse osmosis production water tank, and the secondary reverse osmosis production water tank is connected to the electric desalination (EDI) through the EDI feed pump.

The secondary reverse osmosis production water tank and electric desalination (EDI) are connected to the ultrafiltration water tank.

The demineralized water tank is connected to the boiler water supply pipe network through the demineralized water pump.

There is also a self-cleaning filter between the PCF fiber filter and the ultrafiltration (UF).

A carbon remover is arranged between the primary reverse osmosis (RO) and the primary reverse osmosis production water tank (fresh water tank).

Electrodemineralization (EDI) includes fresh water chamber and concentrated water chamber; the outer side of the fresh water chamber is provided with a concentrated water chamber, a positive membrane is arranged between the fresh water chamber and the concentrated water chamber, the outer wall of the concentrated water chamber is provided with an anionic membrane, and the fresh water chamber is provided with a negative membrane. There are anion exchange resins and cation exchange resins.

At the same time, an operation method of the above-mentioned system for reusing urban reclaimed water by a full-membrane method is also disclosed, comprising the following steps:

Step 1, the urban reclaimed water heated by the heat exchanger is transported to the raw water pool by the lift pump; after the biochemical treatment, the reclaimed water enters the fiber filter;

Step 2, then filter pretreatment through PCF fiber filter,

Step 3, further filter through ultrafiltration (UF) system,

In step 4, the ultrafiltration water is successively entered into the primary reverse osmosis (RO) and the secondary reverse osmosis (RO) for pre-salting,

Step 5, further desalination treatment through Electrodemineralization (EDI);

Step 6, making qualified reuse water.

According to the principle of water source classification and quality, secondary reverse osmosis (RO) concentrated water and electric desalination (EDI) concentrated water are returned to the ultrafiltration production water tank as the influent of primary reverse osmosis (RO), which can be fully recovered and used. Reverse osmosis concentrated water, electric desalination concentrated water, etc. are classified and recycled.

In step 1, a bactericide is added during the heating process to sterilize the urban regenerated water.

Chemical cleaning for Ultrafiltration (UF), Primary Reverse Osmosis (RO), Secondary Reverse Osmosis (RO), Electrodemineralization (EDI).

The specific implementation carried out by the above-mentioned embodiment is as follows:

1. Introduction to the whole film process

Integrated Membrane Technology (IMT) water treatment process, which organically combines different membrane processes, takes conventional water source or municipal sewage discharged after conventional treatment such as biochemical and filtration as the influent, and adopts "superior" The combined process of filtration (UF) → reverse osmosis (RO) → electric desalination (EDI)” can achieve the purpose of efficient removal of pollutants and deep desalination, and meet the water quality requirements of various uses.

The process flow of the all-membrane method is: heated urban reclaimed water → raw water tank → raw water lift pump → PCF fiber filter → ultrafiltration (UF) → ultrafiltration water tank → ultrafiltration water pump → primary reverse osmosis (RO) → removal Carbonizer → fresh water tank → fresh water pump → secondary reverse osmosis (RO) → EDI feed water tank → EDI feed water pump → electric desalination (EDI) → desalted water tank → desalted water pump → thermal power plant boiler make-up water system.

The whole membrane method is used to reuse urban reclaimed water as a new process for making up water for boilers in thermal power plants. The following technologies are proposed:

(1) Integrated Membrane Technology (IMT) water treatment process, which organically combines different membrane processes, using conventional water sources or municipal sewage that has been discharged up to the standard after conventional treatment such as biochemical and filtration as the influent, The combined process of "ultrafiltration (UF) → reverse osmosis (RO) → electric desalination (EDI)" is adopted to achieve the purpose of efficient removal of pollutants and deep desalination, and to meet the water quality requirements for various purposes.

(2) In the above process, the three membrane separation technologies of ultrafiltration (UF), reverse osmosis (RO) and electric desalination (EDI) are used as pretreatment, pre-desalination and fine desalination respectively, and the raw water is prepared to meet the requirements of various boilers. High-purity water required for makeup water. Ultrafiltration (UF) uses physical retention to remove impurities of a certain particle size in water. The water quality of ultrafiltration is better than that of traditional multi-media filtration. Even if the raw water is wastewater with poor water quality, the SDI of ultrafiltration water can also be used. Stable below 3, which greatly extends the life of the downstream reverse osmosis membrane. Reverse osmosis (RO) is driven by pressure to selectively remove more than 98% of inorganic ions, but the produced water cannot meet the water requirements of medium and high pressure boilers. Electrodeionization EDI (Electrodeionization) technology relies on the action of electric field to remove inorganic ions in water. It is an innovative ultrapure water preparation technology that has appeared in recent years. It organically combines traditional electrodialysis technology and ion exchange technology, which not only overcomes the shortcomings of electrodialysis that cannot be deeply desalinated, but also makes up for the shortcomings that ion exchange cannot work continuously and needs to consume acid and alkali for regeneration. The water quality of the product meets the requirements of boiler water for conductivity, hardness and silicon.

(3) The whole-membrane method is based on the principle of water source classification and quality, and the secondary reverse osmosis (RO) concentrated water and the electric desalination (EDI) concentrated water are returned to the ultrafiltration water production tank as the primary reverse osmosis (RO) It can fully recover the available water source, greatly improve the water recovery rate of the system, and save the system investment.

(4) Compared with the traditional ion exchange process, it can maintain the operation stability and reliability of the system under the condition of large water quality fluctuation, and the effluent water quality is stable; during the operation process, it does not need to consume chemicals such as acid and alkali, which can effectively avoid secondary pollution. In addition, it reduces the operating cost increased by adding chemicals to the system; the system has a high degree of automation, the workload of operation and maintenance is small, and the labor intensity of the operating personnel is reduced, which has a strong promotion and reference effect.

2. The main equipment of the new technology for the reuse of urban reclaimed water by the all-membrane method

serial number name Specifications and Technical Data unit quantity 1 raw water tank 400m³ seat 1 2 Raw water lift pump (frequency conversion) 150m³/h, 0.45MPa tower 3 3 PCF fiber filter 150m³/h tower 3 4 Self-cleaning filter 76m³/h tower 4 5 Ultrafiltration system 65m³/h, including the following: set 4 6 Ultrafiltration water tank 800m³ tower 1 7 Ultrafiltration backwash pump (frequency conversion) 350m³/h, 0.25MPa tower 2 8 One stage reverse osmosis lift pump 80m³/h, 0.30MPa tower 5 9 Security Overthinker 80m³/h tower 4 10 High pressure pump (frequency conversion) 80m³/h, 1.20MPa tower 4 11 Primary reverse osmosis unit 60m³/h set 4 12 Primary reverse osmosis production tank 400m³ tower 2 13 Primary reverse osmosis flushing water pump 80m³/h, 0.40MPa tower 2 14 Secondary reverse osmosis lift pump 43m³/h, 0.30MPa tower 2 15 Secondary security filter 43m³/h tower 2 16 Secondary high pressure pump 43m³/h, 1.20MPa tower 2 17 Secondary reverse osmosis unit 39m³/h set 2 18 Secondary reverse osmosis production tank 40m³ tower 1 19 EDI feed pump 40m³/h, 0.50MPa tower 3 20 EDI Security Filter 40m³/h tower 2 twenty one Electrodemineralization (EDI) 35m³/h set 2 twenty two Demineralized water tank 800m³ tower 2 twenty three Demineralized water pump 35m³/h, 0.80MPa frequency conversion tower 2 twenty four Dosing device set 1 25 Membrane cleaning device set 1

3. The effluent quality of the all-membrane process system

Ultrafiltration system effluent quality: SDI≤3, turbidity≤0.2NTU, TSS≤1mg/L

The average water recovery and filtration rate of ultrafiltration system: ≥90%

Desalination rate of primary reverse osmosis system: ≥98% (after one year of operation)

Desalination rate of primary reverse osmosis system: ≥97% (after three years of operation)

Water recovery rate of primary reverse osmosis system: ≥75% (after three years of operation)

Conductivity of water produced by secondary RO system: ≤5μS/cm (after one year of operation)

Conductivity of water produced by secondary RO system: ≤8μS/cm (after three years of operation)

Water recovery rate of secondary reverse osmosis system: ≥90% (after three years of operation)

Water quality after electric desalination treatment: silicon dioxide (SiO ₂ )≤20μg/L; conductivity (25℃)≤0.2μS/cm

4. Process flow

The main process flow of the boiler feed water treatment system of the present invention is shown in Figure 1:

Among them, according to the principle of water source classification and quality, the secondary reverse osmosis (RO) concentrated water and the electric desalination (EDI) concentrated water are returned to the ultrafiltration production water tank, as the influent of the primary reverse osmosis (RO), and fully recovered Reverse osmosis concentrated water, electric desalination concentrated water, etc. can be used for graded recycling, which greatly improves the system water recovery rate and saves system investment.

The urban reclaimed water heated by the heat exchanger is transported to the raw water tank by the lift pump, and then filtered and pretreated by the PCF fiber filter. (RO) and secondary reverse osmosis (RO) pre-desalination, and finally undergoes further desalination treatment by electric desalination (EDI) to make qualified reuse water.

5. Operation steps

The urban reclaimed water heated by the heat exchanger is transported to the raw water tank by the lift pump, and then filtered and pretreated by the PCF fiber filter. (RO) and secondary reverse osmosis (RO) pre-desalination, and finally undergoes further desalination treatment by electric desalination (EDI) to make qualified reuse water.

5.1PCF fiber filter:

The operation mode of the fiber filter is program-controlled automatic operation. During the filtration process, the fiber is pressed by a rotary machine to make the pores between the longitudinal directions of the fiber become smaller, and the suspended matter in the water is blocked and left outside the fiber. Clean treated water. When the suspended dirt (impurities) trapped in the filter increases, the amount of treated water decreases, the pressure difference reaches the set value, and the backwashing process is automatically entered; during backwashing, the press of the filter is loosened, so that the pores of the filter fibers are relaxed. In the state of the Roots blower, the air and the backwash water are combined to wash, and the dirt is discharged through the discharge pipe, and then automatically enters the filtration process. The working principle is shown in Figure 2 below.

5.2 Ultrafiltration (UF) system

The process of starting, running, flushing, shutting down and standby of the ultrafiltration system is automatically controlled by the ultrafiltration PLC. The raw water flows inside the hollow fiber, and the produced water is gradually permeated from the inner wall to the outer wall during the process of the raw water flowing through the membrane (called internal pressure type). During the ultrafiltration operation, the membrane filtration pressure difference (TMP) should be controlled to be less than 0.08MPa, and the maximum TMP should not exceed 0.10MPa, otherwise it will cause the formation of dirt on the surface of the membrane that cannot be backwashed. After the ultrafiltration runs for a period of time, the retained suspended solids, bacteria, macromolecular organic matter, colloids, etc. will accumulate on the inner surface of the fiber. At this time, the pressure difference between the water inlet side and the water production side of the membrane will gradually increase, and hydraulic cleaning is required.

5.3 Reverse osmosis (RO) system:

The operation and monitoring of the reverse osmosis desalination system are automatically controlled by instruments and PLCs. When the high-pressure pump is started during the operation of the system, in order to prevent the high-pressure water source from directly impacting the membrane element, causing the rupture of the membrane element, the electric slow-open door of the high-pressure pump outlet is gradually opened, so that the water pressure of the membrane system gradually increases steadily, and the dosing pump automatically starts ( When the reverse osmosis system is in normal operation, the feed water and concentrated water flow along the surface of the reverse osmosis membrane at a certain flow rate, and it is difficult for pollutants to deposit. down, but if the reverse osmosis system stops running, these pollutants will immediately deposit on the surface of the membrane, causing fouling of the membrane elements. Therefore, automatic flushing is set up before the shutdown of the reverse osmosis system, and the surface of the membrane element is flushed with clean water to prevent the deposition of these pollutants. The first-stage reverse osmosis flushing flow was 80 m ³ /h, the second-stage reverse osmosis flushing flow was 43 m ³ /h, and the flushing time was 10 min.

(1) Control the reverse osmosis inlet pressure to 1.0MPa during operation, and pay attention to the pressure difference between the inlet and outlet of the security filter is less than 0.2MPa, if it is greater than 0.2MPa, the filter element needs to be replaced.

(2) In order to ensure the safe operation of the high-pressure pump, low inlet pressure and high outlet pressure protection are set during the operation of the high-pressure pump. When the low-pressure signal or the high-pressure signal is triggered and held for 3s, the high-pressure pump automatically stops, and the set value is low pressure ≤ 0.1MPa , high pressure ≥1.8MPa.

(3) Although the reverse osmosis membrane can withstand short-term chlorine and hypochlorite attacks, continuous contact will destroy the separation ability of the membrane, and the membrane performance will decrease due to oxidative damage. The content of residual chlorine at the entrance of the reverse osmosis membrane is generally It is required to control less than 0.1mg/L. In order to prevent free chlorine from exceeding the standard, a reducing agent dosing pipeline is set at the inlet of the primary reverse osmosis, and an ORP table is installed to control and adjust the dosing amount. The reducing agent uses NaHSO ₃ , The mass fraction of the drug is 10%, and the dosing amount is controlled by the dosing device. When the ORP meter shows ≤150mV, stop the dosing pump; when 150mV＜ORP≤250mV, the dosing pump frequency is automatically controlled to 25Hz; when 250mV＜ORP＜300mV, the dosing pump frequency is automatically adjusted to 50Hz; when ORP>300mV , stop all reverse osmosis components in order to prevent serious damage to the membrane. In addition, when the system runs continuously for a long time, calcium and magnesium ions in the water will continue to precipitate and adhere to the surface of the reverse osmosis membrane, forming scaling and blocking the membrane pores. The scale inhibitor was added, the mass fraction of the scale inhibitor was 10%, and the dosage was 2-4 mg/L.

(4) An alkali addition system is set at the inlet of the secondary reverse osmosis. The alkali solution added is NaOH with a mass fraction of 20%. It is difficult to adjust the pH if the mass concentration is too high. The pH of the secondary reverse osmosis inlet is controlled to be about 8.3. There are two main purposes: First, since the permeability of the reverse osmosis membrane to _CO2 in water is almost 100%, and it can be seen from the relationship between the ionization degree of carbonic acid and the pH of the water, when the pH is about 8.3, almost Only HCO ₃ ^- is contained, so that HCO ₃ ^- is completely removed by the reverse osmosis system, which indirectly achieves the purpose of removing CO ₂ and improves the desalination rate of reverse osmosis. Second, when pH<8, the dissolved silicon exists in the form of silicic acid. If the concentration of silicic acid exceeds its solubility, silicon will be deposited; when the pH of water>8, the solubility of silicon increases. At this time, silicic acid The ionization is silicate radical SiO ₃ ^2- . In order to prevent the deposition of silicon on the membrane surface, it is necessary to ensure that the pH of the secondary reverse osmosis influent water is above 8.0. 5.4 Electrodemineralization (EDI) system:

EDI operation adopts automatic control, and the working process is shown in Figure 3.

As can be seen from Figure 3, the working process is generally divided into three steps: (1) the exchange of the ion exchange resin in the fresh water chamber to the electrolyte ions in the water to remove the ions in the water; (2) under the action of an external electric field, the electrolyte in the water moves along the resin particles. The formed conductive transfer path migrates to the membrane surface and enters the concentrated water chamber through the ion exchange membrane; (3) The polarization in the diffusion layer where the resin and membrane are in contact with water dissociates water into H ⁺ and OH ^- , except for some Participating in the load current, most of them regenerate the resin. Ion exchange, ion migration, and electrical regeneration occur together and promote each other, realizing the process of continuous ion removal.

(1) When the EDI is started, in order to prevent serious damage caused by water hammer, the EDI feed pump is designed as a variable frequency pump, and the time for the feed water pressure and flow to slowly rise to the operating pressure and flow is 1.5min.

(2) During startup and operation, each EDI membrane block is set with low flow protection for product water, concentrated water and extreme water. When any one of the three low flow signals is triggered and held for 3s, the EDI module will automatically power off, and a single EDI The protection value of the membrane block is the product water flow ≤ 2.3m ³ /h, the concentrated water flow ≤ 150L/h, and the extreme water flow ≤ 80L/h.

(3) The voltage of each module does not exceed 400V and the current does not exceed 5.2A during operation.

6. Run the data chart

As shown in Figure 4-Figure 6, the treatment effect of the Electrodemineralization (EDI) system:

After being put into operation, the two sets of electric desalination (EDI) water inflow were both 39m ³ /h, the average water production was 35m ³ /h, and the recovery rate of produced water was 90%. The average inlet pressure is 0.4MPa, and the average conductivity of the produced water is 0.15μS/cm, which meets the design requirements.

7. Conclusion

(1) The all-membrane process for boiler make-up water is the most advanced and environmentally friendly process at present. It can continuously prepare boiler make-up water without using acid and alkali for regeneration. Moreover, the all-membrane process saves a lot of floor space compared to the previous ultrafiltration, reverse osmosis, and ion exchange processes. This process only needs to use secondary reverse osmosis and electric desalination (EDI) racks, which can replace the anode in the previous process. bed, intermediate water tank, shaded bed, mixed bed, acid-base regeneration system and resin storage tank, etc., thereby reducing project investment and reducing project floor space.

(2) The technical key of the all-membrane process is to effectively control the pollution of the membrane. The control measures are reflected in three aspects: on the one hand, by adding chemicals to prevent pollution of the water quality; on the other hand, the pressure difference of the membrane (including ultrafiltration The TMP and reverse osmosis inter-stage pressure difference) and water production are monitored and alarmed by the upper computer, so as to grasp the degree of membrane pollution; the third aspect is to adopt an effective chemical cleaning method.

(3) The advanced treatment of urban reclaimed water by thermal power plants is an important method for recycling wastewater to the boiler feed water system. It can not only reduce environmental pollution, but also increase the available water resources and reduce corporate It has good economic, social and environmental benefits for the water-scarce cities.

The technical means disclosed in the solution of the present invention are not limited to the technical means disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features. It should be pointed out that for those skilled in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications are also regarded as the protection scope of the present invention.

Claims (10)

1. A system for recycling urban reclaimed water by using a full membrane method is characterized in that: comprises a raw water tank, a PCF fiber filter, an ultrafiltration device, an ultrafiltration water tank, a reverse osmosis cartridge filter, a reverse osmosis device, a reverse osmosis water production tank, an electric desalting device and a desalting water tank; the raw water pool is connected with a PCF fiber filter through a raw water lifting pump, and the PCF fiber filter is connected with an ultrafiltration device; the ultrafiltration device is connected with an ultrafiltration water tank, and the ultrafiltration water tank is circularly connected with the ultrafiltration device through an ultrafiltration backwashing pump; the ultrafiltration device is connected with a reverse osmosis cartridge filter through a reverse osmosis lift pump, the reverse osmosis cartridge filter is connected with a reverse osmosis device, the reverse osmosis device is connected with a reverse osmosis water production tank, and the reverse osmosis water production tank is circularly connected with the reverse osmosis device through a reverse osmosis flushing pump; the reverse osmosis water production tank is connected with an electric desalting device through an electric desalting EDI water feed pump, and the electric desalting device is connected with a desalting water tank.

2. The system for recycling urban recycled water by using the whole membrane method according to claim 1, which is characterized in that: the reverse osmosis device is provided with two stages; the reverse osmosis device comprises a first-stage reverse osmosis device and a second-stage reverse osmosis device; the ultrafiltration device is connected with a primary reverse osmosis cartridge filter through a primary reverse osmosis lift pump, the primary reverse osmosis cartridge filter is connected with a primary reverse osmosis device, the primary reverse osmosis device is connected with a primary reverse osmosis water production tank, and the primary reverse osmosis water production tank is circularly connected with the primary reverse osmosis device through a primary reverse osmosis flushing pump; the first-stage reverse osmosis water production tank is connected with a second-stage reverse osmosis cartridge filter through a second-stage reverse osmosis lift pump, and the second-stage reverse osmosis cartridge filter is connected with a second-stage reverse osmosis device; the second-stage reverse osmosis device is connected with the second-stage reverse osmosis water production tank, and the second-stage reverse osmosis water production tank is connected with the electric desalting device through the EDI water feed pump.

3. The system for recycling urban recycled water by using the whole membrane method according to claim 2, which is characterized in that: the second-stage reverse osmosis water production tank and the electric desalting device are connected with the ultrafiltration water tank.

4. The system for recycling urban reclaimed water by using the whole membrane method according to claim 1 or 3, which is characterized in that: the demineralized water tank is connected with a boiler water supply pipe network through a demineralized water pump.

5. The system for recycling urban recycled water by using the whole membrane method according to claim 4, wherein: a self-cleaning filter is also arranged between the PCF fiber filter and the ultrafiltration device.

6. The system for recycling urban recycled water by using the whole membrane method according to claim 5, wherein: a carbon remover is arranged between the first-stage reverse osmosis device and the first-stage reverse osmosis water production tank (fresh water tank).

7. The system for recycling urban recycled water by using the whole membrane method according to claim 1, which is characterized in that: the electric desalting device comprises a fresh water chamber and a concentrated water chamber; the outer side of the fresh water chamber is provided with a concentrated water chamber, an anode membrane is arranged between the fresh water chamber and the concentrated water chamber, the outer wall of the concentrated water chamber is provided with a cathode membrane, and anion exchange resin and cation exchange resin are arranged in the fresh water chamber.

8. A method for recycling urban reclaimed water by using a full membrane method is characterized by comprising the following steps: the method comprises the following steps:

step 1, conveying the city regenerated water heated by the heat exchanger to a raw water pool through a lifting pump; after biochemical treatment, the regenerated water enters a fiber filter;

step 2, then filtering pretreatment is carried out through a PCF fiber filter,

step 3, further filtering the mixture by an ultrafiltration device system,

step 4, the ultrafiltration produced water enters a first-stage reverse osmosis device and a second-stage reverse osmosis device in sequence for pre-desalting,

step 5, further desalting treatment is carried out through an electric desalting device;

and 6, preparing qualified reuse water.

9. The method for recycling city reclaimed water by using the whole membrane method according to claim 8, which is characterized in that: in the step 1, bactericide is added in the heating process to sterilize the urban reclaimed water.

10. The method for recycling city reclaimed water by using the whole membrane method according to claim 8, which is characterized in that: and chemically cleaning the ultrafiltration device, the primary reverse osmosis device, the secondary reverse osmosis device and the electric desalting device.

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