Method for preparing desalted water from reuse water in coal chemical industry

Abstract

The invention provides a method for preparing desalted water from coal chemical industry reuse water. The method specifically comprises the four steps of pretreatment, primary reverse osmosis and secondary reverse osmosis treatment, electrodeionization treatment and mixed bed treatment. According to the invention, an electric deionization and mixed bed series connection mode is adopted for operation, compared with mixed bed desalination, the electric deionization technology is more convenient for operation and maintenance, does not need acid-base regeneration and does not generate harmful waste liquid discharge, and the electric deionization is used for desalination before bed mixing, so that the water inlet conductivity of the mixed bed can be reduced to be not higher than 0.5 [mu] s / cm; the method is simple and convenient to operate and maintain, high in inflow fluctuation resistance, stable in effluent quality and low in operation cost, acid and alkali consumption and harmful waste liquid discharge are greatly reduced, and the requirements of coal chemical boiler water and process water are met.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment technology, and specifically relates to a method for preparing desalted water using recycled water from coal chemical industry. Background Art

[0002] The coal chemical industry has the typical characteristics of "high energy consumption and high pollution". In recent years, with the further improvement of the country's environmental protection requirements and the fact that the coal chemical industry is often distributed in water-scarce areas, coal chemical enterprises are required to achieve zero wastewater discharge. Therefore, coal chemical enterprises need to reuse production wastewater in production processes. According to the production water balance requirements, the raw water of desalted water needs to be mixed with a certain proportion of production reuse water, resulting in problems of varying degrees in the existing technical solutions.

[0003] The patent application with publication number CN106007059A discloses a process for producing demineralized water by reverse osmosis, which includes the following steps: (1) pretreatment of raw water: filtering impurities and adding non-oxidizing bactericide for sterilization; (2) scale prevention of raw water: filtering the sterilized raw water again, and passing the filtered raw water into a copper-based catalyst anti-scaling device for scale prevention; (3) desalting the scale-prevented raw water through a reverse osmosis device. Desalination is carried out using reverse osmosis technology. The reverse osmosis method has high requirements for the quality of the influent water, and the reverse osmosis membrane is easily contaminated.

[0004] The patent authorization document with publication number CN102616962B discloses a method for deep graded treatment of industrial wastewater, including the following steps: (1) preliminary hardness reduction, precipitation, and neutralization; (2) filtration; (3) moderate desalination by electrosorption; (4) deep desalination by reverse osmosis. Desalination is achieved by electrosorption and reverse osmosis. The electrosorption method has wide requirements for influent water, has a certain anti-pollution ability, and has no secondary pollution. It is a partial desalination process, and the produced water is currently only suitable for circulating cooling water replenishment.

[0005] The patent application with publication number CN109020002A discloses a coal chemical desalted water treatment process, provides a new coal chemical desalted water treatment process based on electrodeionization technology (EDI) and its special device, integrates the secondary RO unit, the total carbon removal filtration unit and the EDI unit into a desalted water special device for coal chemical desalted water treatment, which is simple to operate, does not consume acid and alkali during operation, has no hazardous waste liquid discharge, and has stable effluent quality, meeting the requirements of coal chemical boiler water and process water. However, due to the large fluctuations in the quality of the raw water and the inability to completely remove small molecular organic matter after the total carbon removal filtration unit, the quality of the EDI produced water has seriously deteriorated, causing a large increase in the hydrogen conductivity of the boiler desalted water, which does not meet the user's use requirements.

[0006] In addition, if the desalted water process route is designed as "pretreatment + ultrafiltration system + primary reverse osmosis + decarbonizer + secondary reverse osmosis + mixed bed", the batch size of the mixed bed will decay sharply, requiring frequent acid and alkali regeneration, which increases huge operating costs and even causes the desalted water preparation process to be unable to continuously and stably provide qualified water production. The desalted water preparation process of the prior art cannot solve the new problem of using coal chemical recycled water as a water source, and a new method for preparing desalted water from coal chemical recycled water is urgently needed. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a method for preparing desalted water from coal chemical industry recycled water, so as to solve the problems that the desalted water preparation process in the prior art cannot continuously and stably provide qualified water, the desalination cost is high, and the service life of the purification equipment is short.

[0008] The present invention includes: a method for preparing desalted water from coal chemical industry recycled water, comprising the following steps: (1) Pre-treating the recycled water from coal chemical industry to obtain pre-treated raw water; (2) subjecting the pretreated raw water to primary reverse osmosis treatment and then to secondary reverse osmosis treatment to obtain concentrated water after secondary reverse osmosis treatment and fresh water after secondary reverse osmosis treatment; (3) subjecting the fresh water after the secondary reverse osmosis treatment to electrodeionization treatment to obtain fresh water after electrodeionization treatment, concentrated water after electrodeionization treatment, and polar water after electrodeionization treatment; (4) The fresh water after the electrodeionization treatment in step (3) is further subjected to mixed bed treatment to obtain desalted water.

[0009] Furthermore, the concentrated water after the secondary reverse osmosis treatment in step (2) is returned to the primary reverse osmosis for circulation treatment.

[0010] Furthermore, the concentrated water after the electrodeionization treatment in step (3) is returned to the primary reverse osmosis for circulation treatment.

[0011] Furthermore, the polar water after the electrodeionization treatment in step (3) is vented and then returned to the primary reverse osmosis for circulation treatment.

[0012] Furthermore, in step (2), the conductivity of the fresh water after the secondary reverse osmosis treatment does not exceed 10 μs / cm.

[0013] Furthermore, in step (3), the inlet water conditions for the electrodeionization treatment include: the carbon dioxide content of the inlet water is less than 20 mg / L, the conductivity is 1-10 μs / cm, the pH value is 6-8, the inlet water temperature is 25-35°C, and the inlet water pressure is 0.15-0.5 MPa.

[0014] Furthermore, in step (4), the conductivity of the desalted water after the mixed bed treatment is less than 0.1 μs / cm, the silicon dioxide content is less than 20 μg / L, and the hardness is 0.

[0015] Furthermore, the first-stage reverse osmosis uses a polysulfone nanofiltration membrane.

[0016] Furthermore, the secondary reverse osmosis adopts an aromatic polyamide composite membrane.

[0017] Furthermore, the pretreatment step includes adjusting pH value, dephenolization, ammonia nitrogen treatment and fluorine removal.

[0018] Electrodeionization (EDI), referred to as EDI, is an advanced technology that integrates electrodialysis and ion exchange technologies. The system can achieve directional migration of ions under the action of a direct current electric field through the selective permeation of anions and cations through anion and cation exchange membranes by electromagnetic fields and the exchange of ions by ion exchange resins, thereby completing the deep desalination of water. The system can complete the continuous and automatic regeneration of the resin without stopping the machine to use acid-base regeneration resins, thereby continuously producing high-quality pure water.

[0019] Mixed bed, also known as ion exchange column, refers to a columnar pressure vessel used for ion exchange reaction. It is an exchange device for column ion exchange. It is often used in laboratories and industries. According to the regeneration method, it can be divided into three types: in vivo regeneration mixed bed, in vitro regeneration mixed bed, and anion resin external regeneration mixed bed. In terms of the scope of use, it can be divided into laboratory ion exchange column and industrial ion exchange column.

[0020] Beneficial effects of the present invention: (1) The present invention uses EDI and mixed bed in series operation. Compared with mixed bed desalination, EDI technology is easier to operate and maintain, does not require acid-base regeneration, and does not produce hazardous waste liquid discharge. Using EDI for desalination before the mixed bed can reduce the conductivity of the mixed bed inlet water to no more than 0.5μs / cm. Compared with the process without mixed bed, the average regeneration batch of the water treatment process of the present invention is increased by 12.6 times, which improves the overall economic benefits of the zero-discharge / recycled water system. In the treatment of general wastewater, EDI or mixed bed treatment is used alone. Using one of them can meet the relevant wastewater treatment requirements. Considering the cost, they are generally not used together; (2) The preparation method of the present invention is easy to operate and maintain, reduces acid and alkali consumption and hazardous waste liquid discharge, has strong resistance to water inlet fluctuations, has stable effluent quality, low operating costs, and a system consumables replacement cycle of about 3 years. The system investment and consumables costs can be recovered in one year, meeting the water requirements for coal chemical boilers and process water; (3) The present invention utilizes a mixed bed to perform deep adsorption and impurity removal treatment on EDI produced water, effectively adsorbing weak electrolytes and small molecular organic matter that cannot be removed in time by electrodeionization technology, and obtaining deionized water with a produced water conductivity of less than 0.1 μs / cm, SiO2 less than 20 μg / L and a hardness close to 0, thereby effectively ensuring the water requirements of users. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The present invention is a schematic flow chart of a method for preparing desalted water for coal chemical recycling.

[0022] Figure 2 It is a schematic diagram of the amount of water adsorbed by the EDI series mixed bed and non-series mixed bed in the embodiments and comparative examples of the present invention from 1 to 4 months.

[0023] Figure 3 It is a schematic diagram of the amount of water adsorbed every day in March by the EDI series mixed bed and non-series mixed bed in the embodiments and comparative examples of the present invention. DETAILED DESCRIPTION

[0024] Example (EDI and mixed bed in series): The raw water of a coal chemical enterprise is affected by the quality of recycled water, among which the conductivity, alkalinity, silicon index and small molecular organic matter indexes such as carbon dioxide are all high. The specific steps include the following: (1) The raw water of the coal chemical enterprise is subjected to pretreatment steps such as pH adjustment, phenol removal, ammonia nitrogen treatment, and fluorine removal to obtain pretreated raw water; (2) The pre-treated raw water is treated by primary and secondary reverse osmosis and then enters the EDI unit. The secondary reverse osmosis removes most of the ions in the water, reduces the ion load, scaling pollution and oxidation indicators of the EDI inlet water, and the conductivity of the secondary reverse osmosis water does not exceed 10μs / cm, the content of CaCO3 is not higher than 0.01ppm, the content of Cl2 is not higher than 0.01ppm, the content of O3 is not higher than 0.01ppm, the content of heavy metals is not higher than 0.01ppm, the content of active silicon is not higher than 0.2ppm, and it does not contain oily substances. The concentrated water after the secondary reverse osmosis treatment is returned to the primary reverse osmosis circulation treatment.

[0025] (3) Then, under the conditions of carbon dioxide content less than 20 mg / L, conductivity of 5 μs / cm, pH value of 6, inlet water temperature of 25°C, and inlet water pressure of 0.15 MPa, it enters EDI treatment for deep desalination, and the conductivity of the produced water is ≤0.5 μs / cm.

[0026] (4) The water produced by the EDI unit directly enters the mixed bed unit, and after exchange adsorption by the mixed bed, desalted water with a conductivity of ≤0.1μs / cm, SiO2 less than 20μg / L and a hardness crystallization of 0 is obtained. The polar water of the EDI is exhausted and returned to the primary reverse osmosis cycle for treatment with the concentrated water. The waste liquid generated by the mixed bed regeneration is sent to the wastewater station for treatment along with the primary reverse osmosis and secondary reverse osmosis concentrated liquids.

[0027] Comparative example (EDI is not connected in series, and mixed bed is used alone): (1) The raw water of the coal chemical enterprise is subjected to pretreatment steps such as pH adjustment, phenol removal, ammonia nitrogen treatment, and fluorine removal to obtain pretreated raw water; (2) The pre-treated raw water is treated by primary reverse osmosis and secondary reverse osmosis and then enters the mixed bed unit. The secondary reverse osmosis removes most of the ions in the water. The conductivity of the secondary reverse osmosis water does not exceed 10μs / cm, the content of CaCO3 is not higher than 0.01ppm, the content of Cl2 is not higher than 0.01ppm, the content of O3 is not higher than 0.01ppm, the content of heavy metals is not higher than 0.01ppm, the content of active silicon is not higher than 0.2ppm, and it does not contain oily substances. The concentrated water after the secondary reverse osmosis treatment is returned to the primary reverse osmosis circulation treatment.

[0028] (3) After mixed bed exchange adsorption, demineralized water with conductivity ≤ 0.1 μs / cm, SiO2 less than 20 μg / L and hardness crystallization of 0 is obtained. The waste liquid generated by mixed bed regeneration is sent to the wastewater station for treatment along with the primary reverse osmosis and secondary reverse osmosis concentrates.

[0029] Related results analysis can be found in Figure 2-Figure 3 .

[0030] like Figure 2 As shown, the stage operation analysis: From January to April 2024, it will run for four consecutive months. The average regeneration batch of EDI series mixed bed in one month is 13909.4m 3 The average regeneration batch in February was 19393.5m 3 The average regeneration batch in March was 20256.4m 3 The average regeneration batch in April was 19982m 3 ; The average regeneration batch of EDI series mixed bed in four months is 18385.4m 3 The average regeneration batch of the mixed bed without EDI in series is 1437.5m3 per month 3 The average regeneration batch in February was 1340.9m 3 The average regeneration batch in March was 1462.2m 3 The average regeneration batch in April was 1598.6m 3 The average regeneration batch of the mixed bed without EDI in series for four months is 1459.8m 3; The average regeneration batch increased by 12.6 times.

[0031] like Figure 3 As shown in the figure, from March 1 to March 31, it operated continuously for 31 days. The cumulative water production of the series EDI and mixed bed is 457,000 m 3 The average regeneration batch is 19857.5m 3 ; The average regeneration batch of the EDI mixed bed without series connection is 1475.9m 3 , the average regeneration batch increased to 13.5 times.

[0032] In summary, the system adopts EDI and mixed bed series operation and has been running for 4 consecutive months. The overall operation trend is stable and the average regeneration batch of EDI series mixed bed is increased to 12.6 times.

[0033] Energy saving effect analysis: The process route of the present invention adopts EDI + mixed bed series operation to produce qualified demineralized water. The conductivity of EDI produced water is 0.3μs / cm and enters the mixed bed, which increases the water production of the mixed bed regeneration cycle by more than 12.6 times, and can significantly reduce the number of regenerations in the long term. Energy saving effect is achieved by reducing the energy consumption cost of water used in the regeneration process and the energy consumption cost of treating the regenerated acid and alkali waste liquid (clean wastewater). Since this project is a zero-emission project, reducing water consumption and drainage does not affect the overall water balance of the system, so the water extraction cost is not considered, as shown in Table 1.

[0034] Table 1 Economic benefit calculation project (Not connected in series with EDI) Mixed bed Series connection of EDI and mixed bed Remark Recycled water ratio ≤50% ≤50% / Average batch size (m3) 1459.8 18385.4 Choose the worst working condition Cost of single hydrochloric acid regeneration / yuan 142.84 142.84 Tax included: 0.72 tons, unit price: 197.71 yuan Amount of liquid alkali cost per regeneration / yuan 907.32 907.32 Tax included: 1.44 tons, unit price: 620 yuan EDI and regeneration pump power consumption / yuan / 2500.6 Electricity consumption per ton of water: 0.28335; Electricity fee: 0.48 yuan / kW·h Savings on recycled water costs (yuan) 172 172 / Clean wastewater treatment costs (yuan) 216.52 216.52 / Total (Yuan) 1438.68 3939.28 / Cost per ton of water 0.99 0.21 / The economic benefit analysis adopts the latest market cost price to calculate, optimizes the energy consumption cost of water used in the regeneration process and the energy consumption cost of the treatment of the regenerated acid and alkali waste liquid (clean wastewater) to produce economic effects, and can recover the cost of EDI membrane block consumables within one year. At the same time, with long-term stable operation, there is the potential to further expand benefits. Therefore, the economic benefits of the present invention are considerable and have execution value.

[0035] A person skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of protection of the present application is limited to these examples. In line with the concept of the present application, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of different aspects of one or more embodiments of the present application as described above, which are not provided in detail for the sake of simplicity.

[0036] One or more embodiments of the present application are intended to cover all such substitutions, modifications and variations that fall within the broad scope of the present application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of one or more embodiments of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing desalted water from coal chemical industry recycled water, characterized in that: The steps include: (1) Pre-treating the recycled water from coal chemical industry to obtain pre-treated raw water; (2) subjecting the pretreated raw water to primary reverse osmosis treatment and then to secondary reverse osmosis treatment to obtain concentrated water after secondary reverse osmosis treatment and fresh water after secondary reverse osmosis treatment; (3) subjecting the fresh water after the secondary reverse osmosis treatment to electrodeionization treatment to obtain fresh water after electrodeionization treatment, concentrated water after electrodeionization treatment, and polar water after electrodeionization treatment; (4) The fresh water after the electrodeionization treatment in step (3) is further subjected to mixed bed treatment to obtain desalted water.

2. The method for preparing desalted water from coal chemical industry recycled water according to claim 1, characterized in that: The concentrated water after the secondary reverse osmosis treatment in step (2) is returned to the primary reverse osmosis for circulation treatment.

3. The method for preparing desalted water from coal chemical industry recycled water according to claim 1, characterized in that: The concentrated water after the electrodeionization treatment in step (3) is returned to the primary reverse osmosis for circulation treatment.

4. The method for preparing desalted water from coal chemical industry recycled water according to claim 1, characterized in that: The polar water after the electrodeionization treatment in step (3) is vented and then returned to the primary reverse osmosis for circulation treatment.

5. The method for preparing desalted water from coal chemical industry recycled water according to claim 1, characterized in that: In the step (2), the conductivity of the fresh water after the secondary reverse osmosis treatment does not exceed 10 μs / cm.

6. The method for preparing desalted water from coal chemical industry recycled water according to claim 1, characterized in that: In step (3), the inlet water conditions for the electrodeionization treatment include: the carbon dioxide content of the inlet water is less than 20 mg / L, the conductivity is 1-10 μs / cm, the pH value is 6-8, the inlet water temperature is 25-35°C, and the inlet water pressure is 0.15-0.5 MPa.

7. The method for preparing desalted water from coal chemical industry recycled water according to claim 1, characterized in that: In step (4), the conductivity of the desalted water after the mixed bed treatment is less than 0.1 μs / cm, the silicon dioxide content is less than 20 μg / L, and the hardness is 0.

8. The method for preparing desalted water from coal chemical industry recycled water according to claim 1, characterized in that: The first-stage reverse osmosis uses a polysulfone nanofiltration membrane.

9. The method for preparing desalted water from coal chemical industry recycled water according to claim 1, characterized in that: The secondary reverse osmosis adopts an aromatic polyamide composite membrane.

10. The method for preparing desalted water from coal chemical industry recycled water according to any one of claims 1 to 9, characterized in that: The pretreatment step includes adjusting pH value, dephenolization, ammonia nitrogen treatment and fluorine removal.

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