Boiler water treatment device and treatment method

Abstract

To provide a boiler water treatment device and treatment method capable of preventing carbon dioxide in the atmosphere from being mixed into water in a tank.SOLUTION: A boiler water treatment device comprises a water supply tank 7 that receives pure water from a pure water tank 2 and condensate from a condensate tank 4, and a nitrogen gas is supplied from a nitrogen gas source 8 to the pure water tank 2, the condensate tank 4, and the water supply tank 7. Water from the water supply tank 7 is supplied to a boiler, and is also passed through either an OH type anion exchange resin tower 17 or 18 by switching using valves 15a, 16a. Treated water from the OH type anion exchange resin tower 17 or 18 is returned to the water supply tank 7.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a boiler water treatment apparatus and a treatment method for treating boiler feed water supplied to a steam boiler.

Background Art

[0002] In boiler facilities, pure water is produced from industrial water or the like by pretreatment (such as coagulation solid-liquid separation and desalination treatment), the produced pure water is stored in a feed water tank, and is supplied as boiler feed water from the feed water tank to the boiler. In the boiler, steam is generated by heating this boiler feed water.

[0003] In addition, the condensate generated by condensing the steam from the boiler is returned to the feed water tank through a condensate return line and reused as boiler feed water.

[0004] Conventionally, in order to suppress scale and corrosion of steam turbines, entrainment of silica, chloride ions, sulfate ions, etc. into steam has been strictly suppressed. In order to confirm the suppression status of this scale and corrosion, the silica concentration of steam and the acid electric conductivity (CC: Cation Conductivity, the electric conductivity of water after passing through a cation resin) are defined as the quality of steam (for example, JIS B8223: 2021) and are managed at each power plant.

[0005] Ions such as silica ions, chloride ions, and sulfate ions are removed by treatment with an ion exchange resin, but colloidal silica and organic substances are not sufficiently removed by the ion exchange resin because of their low ionicity.

[0006] Therefore, conventionally, when pretreating the raw water for producing pure water, coagulation sedimentation is performed to remove colloidal silica and organic substances. However, when heavy rain or the like occurs, the quality of the raw water itself fluctuates greatly, the concentration of colloidal silica in the boiler feed water increases, and the silica concentration in the boiler water may exceed the water quality management standard value. As a countermeasure, the amount of boiler blowdown may be increased, but the heat loss increases.

[0007] In addition, the eutrophication in the raw water source may increase the organic matter concentration in the raw water, or the turbidity concentration in the raw water may increase due to heavy rain. Organic matter and turbidity components cannot be sufficiently removed by the ion exchange device. Since organic matter undergoes thermal decomposition in the boiler to generate organic acids such as formic acid and acetic acid, the acid electric conductivity of the feed water and the main steam may increase due to this, and it is often the case that the management standards cannot be achieved.

[0008] In industrial boilers and the like, when process condensate is stored in a tank with open atmosphere and then recovered to the condenser or the feed water tank, or when makeup water is received in a feed water tank with open atmosphere, carbon dioxide in the atmosphere dissolves into the condensate. Since this carbon dioxide cannot be sufficiently removed by the deaerator, the acid electric conductivity of the feed water and the steam may not be maintained within the management value.

[0009] Conventionally, treating condensate with a mixed-bed ion exchange resin has been carried out, but it is targeted at seawater leakage in the condenser fine tubes and the like, and does not assume carbon dioxide mixing in the open atmosphere part of the feed water system or the recovery of process condensate.

[0010] Colloidal silica and organic matter may be removed by treating the ion-exchanged water replenished to the feed water tank with an RO membrane or an ultrafiltration membrane. However, this method cannot remove organic matter and the like from process condensate.

[0011] Patent Document 1 describes a boiler water treatment device and a treatment method capable of stably supplying high-quality boiler feed water to the boiler at the initial stage of the boiler equipment operation start or when restarting the operation after the operation stop.

[0012] The boiler water treatment method and apparatus of Patent Document 1 produce pure water by treating raw water with a pretreatment apparatus, and in the boiler water treatment method and apparatus for supplying the pure water from the pretreatment apparatus to a boiler via a pure water supply line, a part of the pure water is taken out from a take-out section and subjected to impurity removal treatment by an impurity removal means, and this treated water is returned to the take-out section or the pure water supply line upstream thereof. It is a boiler water treatment method for switching, by a switching means, whether to take out at least a part of the pure water from the pure water supply line to the impurity removal line or supply the entire amount to the boiler.

[0013] This Patent Document 1 mainly prevents the mixing of carbon dioxide during boiler startup and does not prevent the mixing of impurities during boiler operation.

Prior Art Documents

Patent Documents

[0014]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0015] Colloidal silica, organic substances accompanied in makeup water, and organic acids in process drain are thermally decomposed in the boiler and changed into low molecular weight ionic silica and organic acids (such as formic acid and acetic acid). These are volatile and are contained in the condensate and recovered in the feed water tank.

[0016] Low molecular weight ionic silica and organic acids can be removed by a condensate desalination device composed of an anion exchange resin and a cation exchange resin. However, amines and ammonia for pH adjustment are dissolved in the condensate, and when the condensate is treated with a condensate desalination device composed of an anion exchange resin and a cation exchange resin, useful amines and ammonia are also removed.

[0017] In addition, when the reclaimed water is treated with a reclaimed water desalination device composed of an anion exchange resin and a cation exchange resin to remove low molecular weight ionic silica and organic acids, if the amount of carbon dioxide mixed in the reclaimed water is large, the anion load will increase.

[0018] In addition, when the reclaimed water is treated with only an anion exchange resin, only anions of salts such as NaCl are removed, so there is a risk that impurities such as Na, Ca, and Mg in seawater or the like mixed in cannot be detected by an acid electric conductivity measuring device.

[0019] An object of the present invention is to provide a boiler water treatment device and a treatment method that prevent carbon dioxide in the atmosphere from mixing into the water in the tank.

[0020] One aspect of the present invention is to provide a boiler water treatment device and a treatment method that can sufficiently remove low molecular weight ionic silica and organic acids, and can recover the reclaimed water without removing amines, ammonia, etc. in the reclaimed water.

Means for Solving the Problems

[0021] The gist of the present invention is as follows.

[0022] [1] In a boiler water treatment device having a pure water tank for receiving pure water and a reclaimed water tank for receiving reclaimed water, A boiler water treatment device characterized by comprising nitrogen gas supply means for supplying nitrogen gas to at least one of the tanks.

[0023] [2] A pure water tank for receiving pure water, a reclaimed water tank for receiving reclaimed water, and a water supply tank for receiving pure water from the pure water tank and reclaimed water from the reclaimed water tank, A boiler water treatment device characterized by comprising nitrogen gas supply means for supplying nitrogen gas to at least one of the pure water tank, the reclaimed water tank, and the water supply tank.

[0024] [3] The nitrogen gas supply means is a boiler water treatment device that supplies nitrogen gas to at least the condensate tank [1] or [2].

[0025] [4] The nitrogen gas supply means is a boiler water treatment device that supplies nitrogen gas to the pure water tank, the condensate tank, and the feed water tank respectively [2].

[0026] [5] An OH-type anion exchange resin tower through which water from the feed water tank passes is provided, and the treated water that has passed through the OH-type anion exchange resin tower is returned to the feed water tank [2] of the boiler water treatment device.

[0027] [6] An OH-type anion exchange resin tower through which a part of the combined water formed by the confluence of the pure water from the pure water tank and the condensate from the condensate tank passes is provided, and the treated water that has passed through the OH-type anion exchange resin tower and the remaining part of the combined water are combined and supplied to the boiler [1] of the boiler water treatment device.

[0028] [7] A boiler water treatment device [5] or [6] having an acid electric conductivity meter for measuring the acid electric conductivity of the treated water from the OH-type anion exchange resin tower.

[0029] [8] A boiler water treatment device [5] to [7] having a Na concentration meter for measuring the Na concentration of the treated water from the OH-type anion exchange resin tower.

[0030] [9] A boiler water treatment method using the boiler water treatment device of [7], wherein when the acid electric conductivity detected by the acid electric conductivity meter becomes a predetermined value or more, the OH-type anion exchange resin tower is replaced or the water flow is switched to the OH-type anion exchange resin towers installed in parallel.

Advantages of the Invention

[0031] In the present invention, by making the inside of tanks such as the condensate tank, the pure water tank, and the feed water tank into a nitrogen atmosphere, it is possible to prevent carbon dioxide in the atmosphere from mixing into the water in the tanks.

[0032] Conventionally, it is not common to pressurize the inside of a tank such as a feed water tank with nitrogen in a medium- or high-pressure boiler (especially a boiler steam system having a steam turbine in the system). Although nitrogen pressurization may be carried out for the purpose of preventing corrosion due to oxygen intrusion in a soft water feed boiler, it is generally not performed for the purpose of preventing, detecting, and removing impurities in pure water feed.

[0033] In one aspect of the present invention, by treating condensate or feed water with an OH-type anion exchange resin, low molecular weight ionic silica and organic acids in the boiler feed water are removed. Further, since this OH-type anion exchange resin does not remove amines and ammonia in water, amines and ammonia for pH adjustment in the condensate are supplied into the boiler water and reused.

[0034] In one aspect of the present invention, when Na ion-containing impurities such as seawater, industrial water, and cooling water are mixed into the condensate or feed water, Na ions and the like remain in the treated water treated with the OH-type anion exchange resin. Therefore, the Na concentration of the treated water from the OH-type anion exchange resin is measured with a Na concentration meter, and it is possible to detect the mixing of Na ion-containing impurities such as seawater, industrial water, and cooling water from this measured value.

[0035] In one aspect of the present invention, by detecting the acid electric conductivity of the treated water from the OH-type anion exchange resin, when the acid electric conductivity becomes equal to or higher than a predetermined value, it is possible to appropriately perform the exchange of the OH-type anion exchange resin tower or the switching of the water flow to the OH-type anion exchange resin towers installed in parallel.

Brief Description of the Drawings

[0036]

Figure 1

Embodiments for Carrying Out the Invention

[0037] Hereinafter, embodiments will be described with reference to FIG. 1.

[0038] In the boiler water treatment apparatus of this embodiment, pure water from a pure water production apparatus (not shown) is introduced into a pure water tank 2 through a pipe 1, and condensate such as turbine condensate or process condensate is introduced into a condensate tank 4 through a pipe 3. The pure water from the pure water tank 2 and the condensate from the condensate tank 4 are respectively introduced into a feed water tank 7 through pipes 5 and 6. Although not shown in the figure, valves are provided in the pipes 1, 3, 5, and 6 respectively.

[0039] Each of the tanks 2, 4, and 7 is a sealed tank provided with a relief valve (not shown) at the upper part, and nitrogen gas can be supplied from a nitrogen gas source 8 through a pipe 8a to the space above the water surface. By supplying nitrogen gas, the space above the water surface in each of the tanks 2, 4, and 7 is made into a nitrogen atmosphere where the pressure is equal to or higher than the atmospheric pressure and lower than the opening pressure of the relief valve.

[0040] The feed water in the feed water tank 7 is sent out to a pipe 11 by a pipe 9 and a feed water pump 10. The pipe 11 branches into pipes 12, 13, and 14, and valves 12a, 13a, and 14a are provided in the respective pipes 12, 13, and 14.

[0041] The pipe 12 is provided to supply feed water to the boiler. The pipe 13 is a drain pipe to the outside of the system.

[0042] The secondary side (downstream side) of the valve 14a of the pipe 14 branches into pipes 15 and 16, and the respective pipes 15 and 16 are connected to the tops of OH-type anion exchange resin towers 17 and 18. Valves 15a and 16a are provided in the pipes 15 and 16.

[0043] One ends of pipes 19 and 20 are connected to the treatment water outlets at the lower ends of the respective OH-type anion exchange resin towers 17 and 18. The other ends of the pipes 19 and 20 are connected to one end of a pipe 21.

[0044] The other end of this pipe 21 is connected to the feed water tank 7. A Na concentration meter 22 is provided in the pipe 21, and the valves 13a and 14a are opened and closed according to the detected Na concentration of this Na concentration meter 22.

[0045] In addition, an acid electric conductivity meter (CC meter) 23 is provided in the pipe 21, and the valves 15a and 16a are opened and closed according to the detected acid electric conductivity of the acid electric conductivity meter 23.

[0046] As the nitrogen gas source 8, any device that can supply nitrogen-rich gas with a lower concentration of oxygen and carbon dioxide than the atmosphere, such as a nitrogen cylinder or a nitrogen generator (PSA (Pressure Swing Adsorption)), may be used. It is preferable that the nitrogen gas source 8 has a high purity of nitrogen.

[0047] In the boiler water treatment apparatus configured as described above, during the operation, before the start of operation, and during the stop of the boiler, the water in the water supply tank 7 is passed through the OH-type anion exchange resin towers 17 or 18 via the pipe 9, the pump 10, and the pipes 11, 14 and the pipe 15 or 16, and the treated water of the OH-type anion exchange resin towers 17 or 18 is circulated to the water supply tank 7 via the pipe 19 or 20 and the pipe 21. As a result, anion components such as low molecular weight ionic silica and organic acids in the feed water are removed by the OH-type anion exchange resin towers 17 or 18.

[0048] During boiler operation, the valve 12a is opened. When the boiler stops, the valve 12a is closed.

[0049] During boiler operation, when the detected value of the Na concentration meter 22 is lower than a predetermined value, the valve 13a is closed, the valve 14a is opened, one of the valves 15a and 16a is opened and the other is closed, and water is passed through one of the OH-type anion exchange resin towers 17 or 18. In this case, first, water is passed through one of the OH-type anion exchange resin towers (for example, the OH-type anion exchange resin tower 17). Then, the acid electric conductivity of the treated water is monitored by the acid electric conductivity meter 23, and this state is maintained as long as the acid electric conductivity is below a predetermined value.

[0050] When the OH-type anion exchange resin column 17 breaks through and the acid conductivity detection value of the acid conductivity meter 23 exceeds a predetermined value, the opening and closing of the valves 15a and 16a are switched, and water is passed through the other OH-type anion exchange resin column 18. For the broken-through OH-type anion exchange resin column 17, regeneration is performed or it is exchanged with a regenerated OH-type anion exchange resin column.

[0051] During boiler operation, when the Na concentration detection value of the Na concentration meter 22 becomes equal to or higher than a preset reference value, the valve 14a is closed and the valve 13a is opened, and a predetermined amount of feed water is discharged from the feed water tank 7 to the outside of the system through the pipe 13. After supplying pure water to the feed water tank 7 to reduce the Na concentration in the feed water, the valve 13a is closed and the valve 14a is opened.

[0052] In this boiler water treatment apparatus, since the interiors of the tanks 2, 4, and 7 are in a positive pressure nitrogen atmosphere, carbon dioxide in the atmosphere does not dissolve in the water in the tanks.

[0053] Also, since the boiler feed water is treated by the OH-type anion exchange resin column 17 or 18, low molecular weight ionic silica and organic acids are removed from the feed water, and the quality of the feed water is good. Although pH adjusters such as amines and ammonia remain in the condensate, even if the feed water is treated by the OH-type anion exchange resin column 17 or 18, amines, ammonia, etc. in the feed water are not removed, so the additional addition amount of the pH adjuster is reduced and the chemical cost is reduced.

[0054] In this embodiment, since the Na concentration of the treated water of the OH-type anion exchange resin column is detected by the Na concentration meter 22, when Na ion-containing impurities such as seawater, industrial water, and cooling water are mixed into the feed water, this can be quickly detected.

[0055] In the above embodiment, all of the pure water tank 2, the condensate tank 4, and the water supply tank 7 are in a nitrogen atmosphere. However, a tank to which nitrogen gas is supplied may be selected according to the dissolution state of carbon dioxide. Further, when recovering condensate containing ammonia at a high concentration (200 to 400 mg / L or more), nitrogen may be supplied only to the condensate tank 4.

[0056] The supply of nitrogen gas is preferably carried out continuously so that air does not flow into the tank even when the water level in the tank drops. When the water level fluctuation in the tank is large, the amount of nitrogen gas supplied to the tank increases. Therefore, it is preferable to reduce the water level fluctuation in the tank, and it is more preferable to keep the water level constant.

[0057] However, in the present invention, the pressure in the tank may be measured, and nitrogen may be supplied when the pressure in the tank becomes lower than the atmospheric pressure.

[0058] The nitrogen gas may be supplied to the gas phase portion of the tank, or may be supplied into the water so that nitrogen gas bubbling is performed.

[0059] When the water temperature in the tank is high (for example, 80°C or higher), the amount of carbon dioxide dissolved in the water is small, so the supply of nitrogen gas may be stopped.

[0060] In the present invention, the downstream ends of the pipes 1, 3, the pipes 5, 6, and the pipe 21 may be connected to the upper portions of the tanks 2, 4, 7. However, they may be connected to the lower portions of the tanks 2, 4, 7 so that the water from the pipes is introduced into the water in the tanks, or the water may flow through the bottom of the tank below the water surface from the upper portion. In this way, it is possible to prevent the inflowing water from falling onto the water surface in the tank and stirring the vicinity of the water surface.

[0061] In the above embodiment, the OH-type anion exchange resin columns 17 and 18 are installed in parallel, and the water flow to the OH-type anion exchange resin columns 17 and 18 is switched by the valves 15a and 16a. However, only one OH-type anion exchange resin column may be installed, and it may be replaced with a new OH-type anion exchange resin column when breakthrough occurs.

[0062] In the present invention, when the water temperature of the water flowing through the OH-type anion exchange resin column is high (for example, 40 °C or higher), it is preferably cooled by a heat exchanger and then passed through the OH-type anion exchange resin column.

[0063] In the above embodiment, the water supply tank 7 is installed, but the water supply tank may be omitted. In this case, the pipes 5 and 6 are connected to the pipe 9, and the downstream end of the pipe 21 is connected to the pipe 12.

[0064] Thereby, the pure water from the pipe 5 and the condensate from the pipe 6 merge in the pipe 9. A part of this merged water is treated in the OH-type anion exchange resin column 17 or 18, and the treated water merges with the remainder of this merged water in the pipe 12 and is supplied to the boiler.

[0065] The above embodiment is an example of the present invention, and the present invention may be in other forms than the above.

Explanation of Signs

[0066] 2 Pure water tank 4 Condensate tank 7 Water supply tank 8 Nitrogen gas source 17,18 OH-type anion exchange resin columns 22 Na concentration meter 23 Acid electric conductivity meter

Claims

1. In a boiler water treatment apparatus having a pure water tank for receiving pure water and a condensate tank for receiving condensate, a boiler water treatment apparatus characterized by comprising nitrogen gas supply means for supplying nitrogen gas to at least one of the tanks.

2. A pure water tank for receiving pure water, a condensate tank for receiving condensate, and a water supply tank for receiving pure water from the pure water tank and condensate from the condensate tank, a boiler water treatment apparatus characterized by comprising nitrogen gas supply means for supplying nitrogen gas to at least one of the pure water tank, the condensate tank, and the water supply tank.

3. The boiler water treatment apparatus according to claim 1 or 2, wherein the nitrogen gas supply means supplies nitrogen gas to at least the condensate tank.

4. The boiler water treatment apparatus according to claim 2, wherein the nitrogen gas supply means supplies nitrogen gas to the pure water tank, the condensate tank, and the water supply tank, respectively.

5. The boiler water treatment apparatus according to claim 2, comprising an OH-type anion exchange resin tower through which water from the water supply tank flows, and the treated water passing through the OH-type anion exchange resin tower is returned to the water supply tank.

6. The boiler water treatment apparatus according to claim 1, comprising an OH-type anion exchange resin tower through which a part of the combined water obtained by combining pure water from the pure water tank and condensate from the condensate tank flows, and the treated water passing through the OH-type anion exchange resin tower and the remainder of the combined water are combined and supplied to the boiler.

7. The boiler water treatment apparatus according to claim 5 or 6, having an acid electric conductivity meter for measuring the acid electric conductivity of the treated water from the OH-type anion exchange resin tower.

8. The boiler water treatment apparatus according to claim 5 or 6, having a Na concentration meter for measuring the Na concentration of the treated water from the OH-type anion exchange resin tower.

9. A boiler water treatment method using the boiler water treatment apparatus according to claim 7, wherein when the acid electric conductivity detected by the acid electric conductivity meter becomes a predetermined value or more, the OH-type anion exchange resin tower is replaced or the water flow is switched to a parallelly installed OH-type anion exchange resin tower.

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