KR100273500B1 - Method and apparatus for removing silica from borated water using reverse osmosis system - Google Patents

Abstract

PURPOSE: A method and an apparatus for removing silica in boric acid are provided to reduce the amount of radioactive waste water and boric acid by recovering boric acid solution and separating silica through condensation by using reverse osmotic pressure for selective penetration of boric acid and silica. CONSTITUTION: The first reverse osmotic membrane group(100) has 15 osmotic membranes, and makes a boric acid solution from boric acid solution tank(500) to be returned to the boric acid solution tank(500) through penetration. The second reverse osmotic membrane group(200) has 4 osmotic membranes, and performs one more penetration of the boric acid solution. The residual of boric acid solution from the penetration is discarded. The third reverse osmotic membrane group(300) has 4 osmotic membranes with high removing rate of silica to filter silica, and sends the boric acid solution removed with silica to the boric acid solution tank(500) and discards the residual of silica and boric acid solution.

Description

Silica Removal Method and Apparatus for Boric Acid Water Using Reverse Osmosis Membrane

The present invention more efficiently removes silica that is present as an impurity in boric acid water in the primary system water side, such as spent fuel storage tank (SFP) and nuclear fuel replacement boric acid storage tank (RWST). And a device thereof.

In general, in a pressurized water reactor type nuclear power plant, boric acid is used as a neutron absorber for controlling the output of a reactor, and boric acid used is temporarily stored in a boric acid recovery tank, and concentrated (7000 ppm) using an evaporator. Recovered to the storage tank, the recovered boric acid is reused. Therefore, impurities (silica) introduced during replenishment water supply and nuclear fuel replacement work may be concentrated. To prevent this, the replenishment water is supplied and the water quality is purified by ion exchange resin.

However, silicas with lower ionic selectivity than boric acid are not removed from boron acid-saturated ion exchange resins, and these silica layers combine with cationic impurities at high temperature and high pressure operating conditions to impede heat transfer to the fuel cladding. Formation of can lead to nuclear fuel damage by local heating. Therefore, there is a need for an efficient silica removal technique.

In conventional nuclear power plants, silica concentration increases in the borated water of the primary system water (reactor coolant) as the number of years of operation increases, and in order to remove the silica, new boric acid water is supplied by the feed & breeding method. A method of diluting boric acid water containing was used.

However, this conventional silica removal method has a disadvantage in that a large amount of radioactive wastewater is generated and boric acid replenishment is required.

On the other hand, in the US (Summer) nuclear power plant was used to remove the silica in two stages using a hollow fiber membrane, the same membrane used was a 10-inch (inch) film and two 4 inch (inch) film. However, when the reverse osmosis membrane capacity of the first stage and the second stage is determined in this way, the optimum operating conditions, that is, the recovery rate, the operating pressure, and the supply flow rate are determined at the first stage 10 inch membrane, In the second stage, it is difficult to adjust the recovery rate and pressure as desired. In addition, since the minute change of the recovery rate and the pressure greatly affects the silica removal rate and the boron recovery rate, there is a disadvantage that accurate adjustment of the silica removal rate is not performed.

In addition, since the amount of exclusion water to be disposed of under optimum operating conditions and the silica concentration of the exclusion water to be discarded are determined, to reduce this, the exclusion water must be reprocessed. Tanks of more than 140 tons are needed for 24 hours of operation, and the maximum workload is difficult to exceed 6 tons per hour. Therefore, it is difficult to efficiently cope with the operating conditions and only uniform processing is possible, and there is a problem in that the processing cost is increased.

Therefore, in the present invention, boric acid is recovered using a reverse osmosis membrane through which boric acid and silica are selectively permeated to recover the above disadvantages, and silica is concentrated and separated to reduce the amount of radioactive waste and the amount of boric acid used in the removal of silica in boric acid. And an apparatus thereof.

The silica removal device provided in the present invention is connected in parallel with a plurality of reverse osmosis membranes having good silica removal rate and first and second stage reverse osmosis membranes connected in parallel with a plurality of reverse osmosis membranes having good permeation characteristics (95-98%) of boric acid water in parallel. It consists of one third stage reverse osmosis membrane, and each stage connects up to 15 reverse osmosis membranes in parallel, and each reverse osmosis membrane is provided with an opening / closing valve to selectively open and close each one to control the number of reverse osmosis membranes of each stage. The borated water, which is supplied with silica from the borated water tank, is selectively passed through the first stage, the second stage, and the third stage, and the borated water that is permeated is sent to a recycled boric acid tank for recycling, and the filtered silica is permeated. The remaining boric acid water is characterized in that it is configured to be discharged for disposal.

According to the present invention, the first stage alone, the first stage and the second stage, the first stage and the third stage, the first stage, the second stage and the third stage, and the third stage alone can selectively adjust the flow path as necessary. By permeating boric acid water to recycle and discarding silica that has not been permeated, it is possible to minimize the amount of radioactive waste and significantly reduce the amount of boric acid by obtaining the optimal operating conditions according to the change of the situation of each nuclear power plant.

1 is a block diagram of a silica removal apparatus according to an embodiment of the present invention.

2 is an operation flowchart of a silica removal apparatus according to the present invention.

Hereinafter, the present invention will be described in detail with reference to the drawings.

1 is a plan view of a silica removal apparatus according to an embodiment of the present invention, Figure 2 is an operation flowchart of the silica removal apparatus according to the present invention.

Referring to Figure 1, the silica removal apparatus of the present invention by connecting 15 reverse osmosis membranes having excellent permeation characteristics of boron in parallel, permeate boric acid containing silica from the boric acid tank 500, to recycle the permeated boric acid water In order to connect the reverse osmosis membrane 100 of the first stage to the boric acid tank and four reverse osmosis membranes having excellent boric water permeation characteristics in parallel, the boric acid water that has not permeated through the reverse osmosis membrane 100 of the first stage is permeated again. Boric acid water is sent to the boric acid tank for recycling, and the second stage reverse osmosis membrane 200 discharged to dispose of the borated water that has not been permeated and four reverse osmosis membranes having high removal rate of silica are connected in parallel to the reverse osmosis membrane of the first stage ( Permeate boric acid water that has not been permeated in 100) to filter out the silica, and the borated water from which silica is removed is sent to a boric acid tank for recycling, and permeated. Unsuccessful silica and boric acid water is composed of a reverse osmosis membrane 300 of the third stage to be discharged. Here, the reverse osmosis membrane is a filter using a reverse osmosis membrane, and is referred to as a reverse osmosis membrane for convenience in the description herein.

Here, between the boric water tank 500 and the reverse osmosis membrane 100 of the first stage is a pressure pump 400 for controlling the pressure difference between each other, the reverse osmosis membrane 100 and the second stage of the first stage The reverse osmosis membrane 200 used KH-8-ROS1, a modified Cellulose Triacetate membrane of KEPCO, which has excellent boric water permeation characteristics, and the reverse osmosis membrane 300 of the third stage has a higher silica concentration. A BW 30-8040 membrane from Filmtec was used for obtaining.

In addition, the two types of reverse osmosis membranes can be selectively opened and closed, including individual valves, so that driving factors such as wastewater generation rate and recovery rate can be set as desired by the driver.

The silica removal apparatus of the present invention configured as described above controls each of the valves of the reverse osmosis membranes, and when the concentration of silica in boric acid water is low as about 1 ppm, the boric acid water is permeated through the reverse osmosis membrane 100 of the first stage, and then permeated. The boric acid water is recycled and the non-permeable boric acid water is immediately disposed of.

When the concentration of silica in boric acid water is 1-5 ppm and the boron recovery rate is to be increased, the boric acid water is permeated through the reverse osmosis membrane 100 of the first stage, and the borated water that is permeated is recycled. The boric acid water permeated through the reverse osmosis membrane 200 of the second stage is recycled together with the boric acid water that has permeated through the reverse osmosis membrane 100 of the first stage, and the boric acid water that has not permeated is discarded.

In addition, when the silica concentration in boric acid water is 1-5 ppm, and the silica removal rate is to be increased, the boric acid water is permeated through the reverse osmosis membrane 100 of the first stage, and the perforated boric acid water is recycled. By permeating the reverse osmosis membrane 300 of the third stage again, the silica is removed to control the valves of the reverse osmosis membranes so that the perforated boric acid water is recycled and the permeate boric acid water is discarded.

In addition, in the case of increasing the silica removal rate to 98% or more during the final wastewater treatment, the boric acid water is permeated through the reverse osmosis membrane 300 of the third stage to discard all non-permeable boric acid water, and to recycle only the perforated boric acid water. Adjust the valve of the reverse osmosis membranes.

As described above, while passing through the first, second and third stage reverse osmosis membranes 100, 200, and 300 according to a desired process, the silica concentration in the boric acid water is lowered, and the permeate water in which the silica concentration is lower than the reference value of the power plant is Recovered and reused, silica-excluded exclusion water is discharged to minimize boric acid replenishment and radioactive waste generation.

In more detail, the silica removal device has a treatment capacity of about 18 tons per hour at a water temperature of 25 ° C. and a silica concentration of about 1 ppm, and operates about 75% of silica when operating at 90% or more of boron recovery. It is possible to exclude. In addition, in the case of highly concentrated operation using a three-stage membrane in order to minimize the amount of waste water, a toner having a capacity of 20 tons for recycling the concentrated effluent is provided. It is possible to concentrate silica 10 times or 60 ppm or more before treatment. And no fouling of the film is caused.

According to the present disclosure, after the reverse osmosis membrane 100 of the first stage is treated, the reverse osmosis membrane 200 of the second stage or the reverse osmosis membrane 300 of the third stage may be treated according to the driver's judgment. Only the reverse osmosis membrane 100 and the third stage reverse osmosis membrane 300 can be operated alone depending on the situation, which can be optimally obtained only by operating elastically according to the concentration of silica in the tree to be treated. Because time can also be shortened.

If the purity of the system water is too good or the water temperature rises, the permeate flow rate to be treated increases, which leads to a decrease in the pressure of the feed water, and when the valve on the first stage discharge water is closed to raise the pressure, the recovery rate of the first stage is increased. The permeation composition of boron and silica is changed. At this time, in severe cases, the change in silica transmittance may be 50% or more, and the second stage may have the same phenomenon. In the present invention, in order to solve such a phenomenon, the number of modules can be flexibly changed to obtain the optimum operating conditions, that is, the proper pressure, the proper flow rate, and the proper recovery rate, in any case. After treatment, it can move to another power station and operate.

2, the operation flow of the silica removal apparatus according to the present invention is as follows. First, when 15 tons of boric acid with boron 2000ppm and silica 1ppm is introduced from the boric acid tank 10, the boric acid water passes through 15 KH-8-ROS1 membranes 20, and the boron concentration is 1700 ppm, and the silica concentration is 11.3 tons of boric acid water, 0.2 ppm, is recovered to the recoverable boric acid tank 70, and 3.7 tons of boric acid water having a boron concentration of 2400 ppm and a silica concentration of 3 ppm are again sent to the four KH-8-ROS1 membranes 40. It is determined whether or not to be sent to the four BW 30-8040 film 50 (30). The boric acid water passing through the KH-8-ROS1 membrane 40 in the crystal 30 is recovered (60) to the recovery boric acid tank 70 after removing the silica, or in the crystal 30 BW 30- After passing through the BW 30-8040 membrane 50 with boric acid water sent to the 8040 membrane 50, the silica is concentrated and discharged 70.

In this case, the case of increasing the silica removal rate to 98% or more during the final wastewater treatment is not shown in the drawing, in which case it is sent directly from the boric acid tank 10 to the BW 30-8040 membrane 50 and passed therethrough. The boric acid water is recovered 60 to the boric acid tank again, and is discarded if it cannot pass.

This data is an example of preliminary tests before actual operation in a nuclear power plant. Using these data obtained by variables such as the number of membranes and the temperature at each stage, it can be easily used to find the optimal conditions in actual situations.

Next, an example is shown for the removal of silica present in boric acid water.

In the following example, in order to minimize wastewater generation when silica is present in boric acid water, 19.5 tons of waste liquid was separated from 175 tons of silica-containing boric acid water using 1st and 2nd stage membranes, and then again using 3rd stage membranes. The wastewater was recycled to reduce the final waste to 6.8 tonnes.

Table 1 Example showing removal of silica present in boric acid water

EXAMPLE Test Condition Driving example of summer nuclear power plant 1st stage → 2nd stage treatment of the present invention 3-stage treatment of the present invention Temperature (℃) 30 24 27 Total throughput (ton) 175 175 19.5 Supply pressure (kg / cm ² ) 35 17 20 Supply flow rate (ℓ / min) 94.6 297 48 Permeate Flow Rate (ℓ / min) 85.2 258 22 Excluded water flow rate (ℓ / min) 9.46 55 Recirculation Boric acid transmittance (%) 87-92 95-97 42 Silica Exclusion Rate (%) 65 to 75 66-78 97.6 Final waste (ton) 17.5 19.5 6.8 Driving time (hr) 30.8 9.8 6.8

Referring to Table 1, there is little difference in the exclusion rate of silica in the operation example of the summer nuclear power plant and the first-stage → two-stage treatment of the present invention, but the recovery rate of boric acid is about 6% higher in the case of the present invention. In addition, the treatment time is 53%, and the final waste volume is only 39% compared to that of the summer nuclear power plant.

Therefore, the present invention as described above can obtain the optimal operating conditions according to the change of the situation of each nuclear power plant to minimize the amount of radioactive waste generated and significantly reduce the amount of boric acid, thereby reducing the cost.

Claims (9)

The reverse osmosis membrane of the first stage sent to the boric acid tank for filtering the borated water containing silica supplied from the boric acid tank by connecting a predetermined number of reverse osmosis membranes with low silica permeability and high boric acid permeability in parallel. And the permeation characteristics of boric acid water is excellent and less than the number of reverse osmosis membrane of the first stage by connecting the reverse osmosis membrane in parallel to filter the boric acid water that has not permeated in the reverse osmosis membrane of the first stage to recycle the borated water to recycle The silica is obtained by filtering the boric acid water that has not permeated through the reverse osmosis membrane of the first stage by connecting the reverse osmosis membrane of the second stage to the boric acid tank and discharging boric water that is not permeated, and the reverse osmosis membrane of a predetermined number having high silica removal rate in parallel. And the silica permeated through the borated water can be A third stage reverse osmosis membrane which is sent to the water tank and discharges boric acid water containing silica which is not permeated, and a pressurized pump that pressurizes boric acid water containing silica stored in the boric acid tank to supply the reverse osmosis membrane of the first stage. Silica removal apparatus in boric acid water using the reverse osmosis membrane, characterized in that the configuration. According to claim 1, The reverse osmosis membranes of the first to third stages are provided with a respective opening and closing valve to selectively open and close each stage and each reverse osmosis membrane to set the operating factors such as the waste water generation amount, the recovery rate as desired by the driver Silica removal apparatus in boric acid water using a reverse osmosis membrane, characterized in that to enable. The reverse osmosis membrane of claim 2, wherein the reverse osmosis membrane of the third stage includes a flow path and an opening / closing valve supplied with boric acid water to be filtered directly from the boric acid tank so that only the third stage of the reverse osmosis membrane can be utilized. Silica removal apparatus in used boric acid water. The reverse osmosis membrane of claim 1, wherein the reverse osmosis membrane of the first stage is connected in parallel with 15 reverse osmosis membranes, and the reverse osmosis membrane of the second stage is connected with 4 reverse osmosis membranes in parallel, and the reverse osmosis membrane of the third stage has 4 reverse osmosis membranes connected in parallel. Silica removal apparatus in boric acid water using the reverse osmosis membrane, characterized in that configured. First and second stage reverse osmosis membranes in which a plurality of reverse osmosis membranes having high boric acid permeability are connected in parallel, and third stage reverse osmosis membranes in which a plurality of reverse osmosis membranes with high silica removal rate are connected in parallel, and according to operating conditions and concentration of silica Selecting a flow path for the reverse osmosis membranes of the first stage, the second stage, and the third stage, the first stage alone, the first stage and the second stage, the first stage and the third stage, or the third stage alone; Selectively opening and closing each reverse osmosis membrane in each stage in the flow path to adjust the number of reverse osmosis membranes in each stage; and operating a pressure pump to press borax water containing impurities such as silica into the selected flow path to boric acid water through the reverse osmosis membrane. The step of permeation, and the boric acid water that has passed through the reverse osmosis membrane of the selected flow path is recovered to a recycled boric acid water storage tank for recycling, and impurity boric acid water containing silica that has not been permeated. Method for removing silica in boric acid water using a reverse osmosis membrane, characterized in that comprising the step of discharging to discard. The method of claim 5, wherein when the concentration of silica in boric acid to be filtered is as low as 1 ppm, after passing the boric acid containing silica through the reverse osmosis membrane of the first stage, the perforated boric acid is recycled, and the non-permeable boric acid is immediately A method for removing silica in boric acid water using a reverse osmosis membrane, wherein the valves of the reverse osmosis membranes are adjusted to be discarded. The method of claim 5, wherein the silica concentration in the boric acid water is 1-5 ppm, in order to increase the recovery rate of boron, after passing the boric acid water through the reverse osmosis membrane of the first stage, the permeated boric acid water is recycled and not permeated. The boric acid water is permeated once again through the reverse osmosis membrane of the second stage, and the permeated boric acid is recycled together with the borated water that has permeated through the reverse osmosis membrane of the first stage, and the permeable boric acid water is controlled by adjusting the valves of the respective reverse osmosis membranes. Silica removal method in boric acid water using the reverse osmosis membrane which is used. 6. The method of claim 5, wherein the silica concentration in boric acid water is 1-5 ppm, and in order to increase the silica removal rate, the boric acid water is permeated through the reverse osmosis membrane of the first stage, and then the perforated boric acid water is recycled. The silica is removed from the boric acid water using the reverse osmosis membrane by adjusting the valves of the reverse osmosis membranes to remove the silica by permeating the third reverse osmosis membrane once again to recycle the perforated boric acid water and to discard the non-permeable boric acid water. Way. The method of claim 5, wherein in the case of increasing the silica removal rate to 98% or more during the final wastewater treatment, the boric acid water is permeated only to the reverse osmosis membrane of the third stage to discard all the borated water that is not permeated and to recycle only the perforated boric acid water. Silica removal method in boric acid water using a reverse osmosis membrane, characterized in that for controlling the valve of each reverse osmosis membrane.

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