Device for producing desalted water by using reverse osmosis concentrated water

Abstract

The utility model discloses a device for producing desalted water by using reverse osmosis concentrated water, which comprises a pipeline reactor, a hollow fiber nanofiltration device, a degassing system and a two-section reverse osmosis device which are sequentially connected through pipelines, and further comprises a hydrochloric acid storage tank, a liquid outlet pipeline is arranged on the hydrochloric acid storage tank, and a liquid outlet pipeline is arranged on the liquid outlet pipeline. And the liquid outlet pipeline is connected to the pipeline reactor through a liquid outlet pump. The method comprises the following steps: firstly removing carbonate ions and bicarbonate ions in reverse osmosis concentrated water by adjusting the pH value, then removing most of calcium ions, magnesium ions and sulfate ions by virtue of a hollow fiber nanofiltration device, finally removing most of free carbon dioxide by virtue of a degassing system, and feeding into a second-stage reverse osmosis device to produce desalted water; according to the device, the scaling risk and the operation energy consumption of the two-stage reverse osmosis device can be greatly reduced, the recovery rate can be increased to 84%, the total recovery rate of desalted water is increased to 96%, and the production cost of the desalted water can be further reduced.

Description

Technical Field

[0001] The utility model belongs to the technical field of reverse osmosis, and in particular relates to a device for producing desalted water by utilizing reverse osmosis concentrated water. Background Art

[0002] Thermal power plants are typically equipped with reverse osmosis units to provide desalinated water for boilers. The design desalinated water recovery rate for these units is typically 75%, with approximately 25% of the brine discharged. To improve freshwater utilization, some thermal power plants incorporate a two-stage reverse osmosis unit, which reprocesses the 25% brine through reverse osmosis treatment and recovers a portion of the desalinated water. The designed recovery rate for this two-stage reverse osmosis unit is 50%, resulting in a total desalinated water recovery rate of 75% + 25% * 50% = 87.5%. However, the 12.5% ​​brine discharged remains relatively large. If the second-stage reverse osmosis recovery rate is further increased, calcium carbonate in the water will crystallize beyond the critical point, causing scaling of the reverse osmosis membrane.

[0003] The paper "Experimental Study on Reuse and Treatment of Reverse Osmosis Brine from Thermal Power Plants" published in "Industrial Water Treatment" (Volume 38, Issue 4, April 2018) discloses a treatment process for reverse osmosis brine from thermal power plants: the reverse osmosis brine from thermal power plants is filtered through ultrafiltration, strengthened with scale inhibitors, and then enters a two-stage reverse osmosis device. By strengthening the scale inhibitors, the precipitation of crystals and scaling on the membrane surface are suppressed. The recovery rate of the second-stage reverse osmosis can reach 60%, that is: the recovery rate of reverse osmosis desalted water is 75%, the recovery rate of 25% of the reverse osmosis brine after the second-stage reverse osmosis treatment is 60%, and the total recovery rate of desalted water is 75% + 25% * 60% = 90%. In this experimental scheme, ultrafiltration, as a reverse osmosis pretreatment process, effectively intercepts large suspended solids, but does not intercept inorganic salt ions. All scaling components remain in the secondary reverse osmosis feedwater, resulting in high ion concentrations and osmotic pressures. This increases the reverse osmosis operating pressure, increasing energy consumption and preventing further improvement in overall recovery. Furthermore, the scale inhibitor itself can foul and clog the reverse osmosis membrane, hindering industrial continuous production. Using enhanced scale inhibitors to increase secondary reverse osmosis recovery is not the optimal option for industrial production.

[0004] The discharge pressure of reverse osmosis concentrate from a thermal power plant is 0.7~0.8MPa. If this part of the reverse osmosis concentrate is recovered and used in a second-stage reverse osmosis device, and the inorganic salt scaling components in the reverse osmosis concentrate from the thermal power plant are first removed to reduce its ion content before entering the second-stage reverse osmosis device, then the operating pressure and scaling tendency of the second-stage reverse osmosis device will be reduced accordingly due to the reduction in osmotic pressure. The recovery rate of the second-stage reverse osmosis can be improved without adding scale inhibitors and at lower energy consumption, thereby achieving low-cost production of desalted water. Summary of the Invention

[0005] The utility model aims to provide a device for producing desalted water by utilizing reverse osmosis concentrated water, which can improve the recovery rate of the second stage reverse osmosis and realize the low-cost production of desalted water.

[0006] In order to solve the above technical problems, the technical solution of the utility model is:

[0007] A device for producing desalted water using reverse osmosis concentrated water comprises a reverse osmosis concentrated water pipe, which is connected to a pipeline reactor via a pipeline. The device has the following structural features: the reverse osmosis concentrated water pipe is provided with a nanofiltration water supply pump, and the pipeline reactor is sequentially connected via pipelines to a hollow fiber nanofiltration device with a hollow fiber nanofiltration membrane, a degassing system with a hollow fiber degassing membrane, and a two-stage reverse osmosis device. The device for producing desalted water using reverse osmosis concentrated water also comprises a hydrochloric acid storage tank containing hydrochloric acid, the hydrochloric acid storage tank is provided with a liquid outlet pipeline, the liquid outlet pipeline is connected to a hydrochloric acid metering pump and is connected to the pipeline reactor.

[0008] The pore size of the hollow fiber nanofiltration membrane of the hollow fiber nanofiltration device is 1-2 nm, and the Ca 2+ Retention rate ≥59%, Mg 2+ Retention rate ≥70%, SO4 2- Retention rate ≥73%.

[0009] The hollow fiber degassing membrane of the degassing system has a pore size of 10-20 nm and a carbon dioxide removal rate of ≥90%.

[0010] A liquid supply pump is installed on the pipeline between the hollow fiber nanofiltration device and the degassing system.

[0011] The degassing system is connected to an air inlet pipe and an exhaust pipe provided with a vacuum pump.

[0012] A nanofiltration device concentrated water pipe is installed on the side of the hollow fiber nanofiltration device.

[0013] The reverse osmosis concentrated water from thermal power plants contains dissolved carbon dioxide, carbonate ions and bicarbonate ions. There is dissolution of carbon dioxide and ionization of carbonic acid. Carbon dioxide, carbonate and bicarbonate ions transform into each other and reach a dynamic equilibrium. When hydrochloric acid is added to adjust its pH to 4, carbonate and bicarbonate ions will all be converted into carbon dioxide. pH 4 also meets the tolerance pH range of hollow fiber nanofiltration membranes.

[0014] The surface of the hollow fiber nanofiltration membrane in the hollow fiber nanofiltration device carries a certain charge. According to the Donan effect, divalent ions such as calcium ions, magnesium ions and sulfate in the reverse osmosis concentrate can be removed, which can further reduce the scaling ion content of the reverse osmosis concentrate.

[0015] The hollow fiber degassing membrane in the degassing system is a membrane product that uses the principle of diffusion to remove gas from liquid. The micropores in the membrane wall can only pass through gas molecules. The free carbon dioxide dissolved in the nanofiltration water can be continuously extracted from the water through a vacuum pump. The reduction of free carbon dioxide can reduce the conductivity of the desalted water.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) in the prior art, the scale-forming divalent salt ions in the reverse osmosis concentrated water of the thermal power plant are not removed before entering the second-stage reverse osmosis device. The concentration of scale-forming divalent salt ions in the water entering the second-stage reverse osmosis device is high, and the recovery rate of the second-stage reverse osmosis device is at a risk of scaling when it reaches 60%, and this risk cannot be increased any further. The present invention adds hydrochloric acid to the reverse osmosis concentrated water of the thermal power plant and then performs nanofiltration treatment to remove most of the scale-forming divalent salt ions before reverse osmosis treatment. This method can greatly reduce the scale risk of the second-stage reverse osmosis device, increase the second-stage reverse osmosis recovery rate to 84%, and increase the total recovery rate to 96%. (2) In the prior art, the scaling divalent salt ions in the reverse osmosis concentrated water of the thermal power plant are not removed. When the recovery rate of the second-stage reverse osmosis device is 60%, a strong scale inhibitor needs to be added to prevent the reverse osmosis membrane from scaling and clogging. The addition of the strong scale inhibitor not only increases the desalination cost, but also causes pollution and clogging of the reverse osmosis membrane. In the present invention, the scaling divalent salt ions in the influent of the second-stage reverse osmosis device have been mostly removed, and the scaling tendency during the reverse osmosis process is also greatly reduced. Without adding the scale inhibitor, the second-stage reverse osmosis recovery rate can be increased to 84%, thereby reducing the desalination cost. (3) Compared with the existing technology, the technical solution of the utility model can increase the recovery rate of the two-stage reverse osmosis device from 60% to 84%, and save the purchase cost of strong scale inhibitors. Taking the Haihua Thermal Power Plant, which discharges 4,800 cubic meters of reverse osmosis concentrated water per day, as an example, after the implementation of this technical solution, 4,800*(84%-60%)=1,152 cubic meters of desalted water can be recovered per day. The price of desalted water is calculated at 10 yuan / cubic meter, and the price of desalted water produced per day is 1,152*10=11,520 yuan; the strong scale inhibitor is added to each cubic meter of reverse osmosis concentrated water. The input is calculated at 0.25 yuan, and the cost of strong scale inhibitors is saved at 4800*0.25 yuan=1200 yuan / day. The consumption of 31% hydrochloric acid is 0.172 cubic meters / day. Calculated at 500 yuan / cubic meter, the cost of 31% hydrochloric acid is 0.172*500=86 yuan / day, and the total economic benefit is 11520+1200-86=12634 yuan / day. In addition, compared with the existing technology, the technical solution of the utility model has low operating pressure of the two-stage reverse osmosis device, small pump motor power, and significantly reduced energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of system connection of the utility model;

[0018] Figure: 1. Reverse osmosis concentrate pipe, 2. Nanofiltration inlet pump, 3. Pipeline reactor, 4. Nanofiltration unit inlet pipe, 5. Hollow fiber nanofiltration unit, 6. Nanofiltration unit concentrate pipe, 7. Degassing system inlet pump, 8. Degassing system, 9. Second-stage reverse osmosis unit, 10. Vacuum pump, 11. Degassing system water pipe, 12. Nanofiltration unit water pipe, 13. Hydrochloric acid metering pump, 14. Hydrochloric acid storage tank. DETAILED DESCRIPTION

[0019] In order to better illustrate the purpose, technical solutions and beneficial effects of the present invention, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0020] like Figure 1 As shown, a device for producing desalted water using reverse osmosis concentrated water includes a reverse osmosis concentrated water pipe 1, which is connected to a pipeline reactor 3 via a pipeline. The pipeline reactor 3 is sequentially connected to a hollow fiber nanofiltration device 5 with a hollow fiber nanofiltration membrane, a degassing system 8 with a hollow fiber degassing membrane, and a two-stage reverse osmosis device 9 via pipelines. The device for producing desalted water using reverse osmosis concentrated water also includes a hydrochloric acid storage tank 14 containing hydrochloric acid. The hydrochloric acid storage tank 14 is provided with a liquid outlet pipeline, which is connected to the pipeline reactor 3 via a hydrochloric acid metering pump 13. The membrane pore size of the hollow fiber nanofiltration membrane of the hollow fiber nanofiltration device 5 is 1-2 nm, and Ca 2+ Retention rate ≥59%, Mg 2+ Retention rate ≥70%, SO4 2- The retention rate is ≥73%. The membrane pore size of the hollow fiber degassing membrane of the degassing system 8 is 10~20nm, and the carbon dioxide removal rate is ≥90%. A liquid supply pump is installed on the pipeline between the hollow fiber nanofiltration device 2 and the degassing system 8, the pipeline between the hollow fiber nanofiltration device 5 and the degassing system 8 is the nanofiltration device water production pipe 12, and the liquid supply pump is the degassing system water inlet pump 7. The degassing system 8 is connected to an air inlet pipe and an emptying pipeline with a vacuum pump 10. The side of the hollow fiber nanofiltration device 5 is equipped with a nanofiltration device concentrated water pipe 6, the pipeline between the pipeline reactor 3 and the hollow fiber nanofiltration device 5 is the nanofiltration device water inlet pipe 4, and the pipeline between the degassing system 8 and the second-stage reverse osmosis device 9 is the degassing system water production pipe 11. Among the above-mentioned devices, the pipeline reactor 3 is a prior art, and its specific product structure is not described in detail here. The structure of the hollow fiber nanofiltration device 5 is also prior art. For example, the specific structure is introduced in the utility model patent with patent number 2023213054803. Of course, nanofiltration devices of other structural forms can also be used, which have a hollow fiber nanofiltration membrane with the above structure. Similarly, the degassing system 8 also adopts a degassing device of prior art; the two-stage reverse osmosis device 9 is a two-stage reverse osmosis equipment purchased on the market. It is a general product, and the specific structural model is prior art.

[0021] The working process is as follows: reverse osmosis concentrated water enters the pipeline reactor, is fully mixed with hydrochloric acid in the pipeline reactor, and enters the hollow fiber nanofiltration device after adjusting the pH to separate the calcium ions, magnesium ions and sulfate ions therein to obtain nanofiltration water and nanofiltration concentrated water. The nanofiltration concentrated water containing high concentrations of calcium ions, magnesium ions and sulfate ions is discharged, and the nanofiltration water enters the degassing system to remove free carbon dioxide in the water, and then enters the second-stage reverse osmosis device to produce desalted water. Example

[0022] Reference Figure 1 As shown, the utility model is a device for producing desalted water using reverse osmosis concentrated water. The reverse osmosis concentrated water from the thermal power plant is pressurized to 0.3 MPa by the nanofiltration inlet pump and then enters the pipeline reactor 3; the hydrochloric acid with a mass fraction of 31% in the hydrochloric acid storage tank 14 is pumped into the pipeline reactor 3 through the outlet pump at a preset flow rate of 120±5 ml / min. The reverse osmosis concentrated water and the hydrochloric acid are fully mixed in the pipeline reactor 3, and the pH value of the reverse osmosis concentrated water is adjusted to 4. The reverse osmosis concentrated water with carbonate and bicarbonate ions removed enters the hollow fiber nanofiltration device 2 to remove Ca 2+ Mg 2+ 、SO4 2- The divalent scaling components are intercepted and the above hardness is removed to obtain nanofiltration water and nanofiltration concentrated water, among which Ca 2+ The retention rate is 59%, Mg 2+ The interception rate is 70%, SO4 2- The rejection rate is 73%; the nanofiltration concentrated water containing high concentrations of calcium ions, magnesium ions and sulfate ions is discharged, and the volume ratio of nanofiltration product water to nanofiltration concentrated water is 9:1.

[0023] The nanofiltration produced water is pressurized to 0.1 MPa by a pump and then enters the degassing system 8. The free carbon dioxide dissolved in the nanofiltration produced water is removed. After being treated by the degassing system 8, the free carbon dioxide gas removal rate in the nanofiltration produced water is 90%. The nanofiltration produced water with free carbon dioxide removed is pressurized to 0.8 MPa by a pump and then enters the second-stage reverse osmosis device 9 to produce desalted water. The recovery rate of the second-stage reverse osmosis device 9 can be increased to 84%.

[0024] Table 1: Comparison of water quality and recovery rate of the two-stage reverse osmosis device of the present invention and the prior art

[0025] project <![CDATA[Ca 2+ (mg / L)]]> <![CDATA[Mg 2+ (mg / L)]]> <![CDATA[SO4 2- (mg / L)]]> <![CDATA[HCO3 - (mg / L)]]> <![CDATA[CO3 2- (mg / L)]]> Second stage reverse osmosis recovery rate% Total recovery% Existing technology 210 60 345 400 12.5 60 90 Example 1 86 18 92 0 0 84 96

[0026] Table 2: Comparison of water quality and operating pressure of the two-stage reverse osmosis device of the present invention and the prior art

[0027] project <![CDATA[Ca 2+ (mg / L)]]> <![CDATA[Mg 2+ (mg / L)]]> <![CDATA[Cl - (mg / L)]]> Turbidity (NTU) COD (mg / L) Conductivity (μs / cm) Operating pressure (MPa) Existing technology 7.38 3.49 28.69 0.2 5 72.8 1.0 Example 1 5.56 3.48 28.72 0.1 3 48.7 0.8

[0028] As shown in Table 1, conventional thermal power plant reverse osmosis concentrate does not remove scaling divalent salt ions before entering the secondary reverse osmosis unit. Consequently, the concentration of scaling divalent salt ions in the secondary reverse osmosis unit's influent is high. When the secondary reverse osmosis unit's recovery rate reaches 50%, calcium carbonate crystallizes. To suppress calcium carbonate crystal precipitation and scaling, conventional methods increase the recovery rate to 60% by adding strong antiscalants. However, at this point, the scaling risk increases, making further recovery impossible. The addition of strong antiscalants not only increases desalination costs but also contributes to reverse osmosis membrane contamination and clogging. The technical route selected by the utility model is to add hydrochloric acid to the reverse osmosis concentrated water and then perform nanofiltration treatment to first remove most of the scaling divalent salt ions, that is, add hydrochloric acid to adjust the pH to 4, so that carbonate and bicarbonate ions are converted into carbon dioxide, and then remove most of the calcium, magnesium and sulfate ions by nanofiltration. After removing most of the above-mentioned scaling divalent salt ions, the water enters the second-stage reverse osmosis device. At this time, the concentration of scaling divalent salt ions in the influent is reduced, and the scaling risk is reduced. Without adding scale inhibitors, compared with the recovery rate of 60% of the second-stage reverse osmosis and the total recovery rate of desalted water of 90% in the prior art, after the above-mentioned embodiment of the utility model, the recovery rate of the second-stage reverse osmosis device can be increased to 84%, and the total recovery rate of desalted water can be increased to 96%.

[0029] As shown in Table 2, the high ion concentration and osmotic pressure of the influent in the prior art two-stage reverse osmosis device also increase the reverse osmosis pressure. After the above-described embodiment of the present invention, the operating pressure of the two-stage reverse osmosis device was reduced from 1.0 MPa in the prior art to 0.8 MPa, significantly reducing energy consumption and further reducing desalination costs.

[0030] The above are preferred embodiments of the present invention. Those skilled in the art may make several changes and improvements without departing from the principles and spirit of the present invention. Therefore, the scope defined in the claims of the present invention is the scope of protection.

Claims

1. A device for producing desalted water using reverse osmosis concentrated water, comprising a reverse osmosis concentrated water pipe (1), the reverse osmosis concentrated water pipe (1) being connected to a pipeline reactor (3) via a pipeline, characterized in that The reverse osmosis concentrated water pipe (1) is provided with a nanofiltration water supply pump (2), and the pipeline reactor (3) is sequentially connected to a hollow fiber nanofiltration device (5) with a hollow fiber nanofiltration membrane, a degassing system (8) with a hollow fiber degassing membrane, and a two-stage reverse osmosis device (9) through pipelines. The device for producing desalted water using reverse osmosis concentrated water also includes a hydrochloric acid storage tank (14) containing hydrochloric acid. The hydrochloric acid storage tank (14) is provided with a liquid outlet pipeline, and the liquid outlet pipeline is connected to a hydrochloric acid metering pump (13) and is connected to the pipeline reactor (3).

2. The device for producing desalted water using reverse osmosis concentrated water according to claim 1, characterized in that: The pore size of the hollow fiber nanofiltration membrane of the hollow fiber nanofiltration device (5) is 1-2 nm, and Ca 2+ Retention rate ≥59%, Mg 2+ Retention rate ≥70%, SO4 2- Retention rate ≥73%.

3. The device for producing desalted water using reverse osmosis concentrated water according to claim 1, characterized in that: The hollow fiber degassing membrane of the degassing system (3) has a pore size of 10-20 nm and a carbon dioxide removal rate of ≥90%.

4. The device for producing desalted water using reverse osmosis concentrated water according to any one of claims 1 to 3, characterized in that: A liquid supply pump is installed on the pipeline between the hollow fiber nanofiltration device (2) and the degassing system (8).

5. The device for producing desalted water using reverse osmosis concentrated water according to any one of claims 1 to 3, characterized in that: The degassing system (8) is connected to an air inlet pipe and an exhaust pipe equipped with a vacuum pump (10).

6. The device for producing desalted water using reverse osmosis concentrated water according to any one of claims 1 to 3, characterized in that: A nanofiltration device concentrated water pipe (6) is installed on the side of the hollow fiber nanofiltration device (5).

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