Boiler water treatment device and treatment method

Abstract

This boiler water treatment device is provided with a water supply tank (7) that receives pure water from a pure water tank (2) and condensed water from a condensed water tank (4), wherein nitrogen gas is supplied from a nitrogen gas source (8) to the pure water tank (2), the condensed water tank (4), and the water supply tank (7). Supply water from the water supply tank (7) is supplied to a boiler and is also switched by valves (15a, 16a) and passed through an OH-type anion exchange resin tower (17) or (18). Treated water from the OH-type anion exchange resin tower (17) or (18) is returned to the water supply tank (7).

Description

Boiler water treatment device and treatment method

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

[0002] In boiler facilities, pure water is produced from industrial water and other sources through pretreatment (such as coagulation and solid-liquid separation and desalination), and the pure water is stored in a water supply tank and supplied to the boiler from the water supply tank as boiler feedwater. In the boiler, this boiler feedwater is heated to generate steam.

[0003] Condensate produced by condensing steam from the boiler is returned to the feedwater tank via a condensate return line and reused as boiler feedwater.

[0004] Conventionally, to prevent scale and corrosion in steam turbines, the entrainment of silica, chloride ions, sulfate ions, etc. into steam has been strictly controlled. To confirm the state of prevention of scale and corrosion, the silica concentration of steam and the acid conductivity (CC: Cation Conductivity; the electrical 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 can be removed by treatment with ion exchange resins, but colloidal silica and organic substances cannot be sufficiently removed by ion exchange resins because of their low ionicity.

[0006] For this reason, in the past, raw water for pure water production was pretreated by coagulation and sedimentation to remove colloidal silica and organic matter, but when heavy rain occurs, the quality of the raw water itself fluctuates greatly, the colloidal silica concentration in the boiler feed water increases, and there is a risk that the silica concentration in the boiler water will exceed the water quality control standard. As a countermeasure, the amount of boiler blowdown water can be increased, but this increases heat loss.

[0007] Furthermore, eutrophication in the raw water source can increase the organic matter concentration in the raw water, and heavy rainfall can increase the turbidity concentration in the raw water. Organic matter and turbidity components cannot be sufficiently removed by ion exchange devices. Organic matter thermally decomposes in the boiler to produce organic acids such as formic acid and acetic acid, which increases the acid conductivity of the feedwater and main steam, often resulting in failure to meet the management standards.

[0008] In industrial boilers, when process condensate is stored in a tank open to the atmosphere and then recovered in a condenser or feedwater tank, or when makeup water is received in a feedwater tank open to the atmosphere, carbon dioxide from the atmosphere dissolves in the condensate. This carbon dioxide cannot be sufficiently removed by a deaerator, and it may not be possible to maintain the acid conductivity of the feedwater or steam within the control value.

[0009] Conventionally, condensate has been treated with mixed-bed ion exchange resins, but this is intended to address issues such as seawater leaks in condenser tubes, and does not take into account the possibility of carbon dioxide contamination in the atmospherically open parts of the feedwater system or the recovery of process condensate.

[0010] Although colloidal silica and organic matter can be removed by treating the ion-exchanged water supplied to the water supply tank with an RO membrane or an ultrafiltration membrane, this method cannot remove organic matter from the process condensate.

[0011] Patent Document 1 describes a boiler water treatment device and treatment method that can stably supply high-quality boiler feedwater to a boiler when the boiler facility is first started to operate or when operation is restarted after being shut down.

[0012] The boiler water treatment device and method of Patent Document 1 treats raw water in a pretreatment device to produce pure water, and supplies the pure water from the pretreatment device to a boiler via a pure water supply line.The boiler water treatment method involves extracting a portion of the pure water from the pure water supply line through an extraction section and subjecting it to impurity removal treatment using an impurity removal means, and returning this treated water to the extraction section or to the pure water supply line upstream thereof, and a switching means switches between extracting at least a portion of the pure water from the pure water supply line to the impurity removal line or supplying the entire amount to the boiler.

[0013] The technology disclosed in Patent Document 1 is primarily intended to prevent carbon dioxide from being mixed in when the boiler is started up, and is not intended to prevent impurities from being mixed in while the boiler is in operation.

[0014] Japanese Patent Application Laid-Open No. 2020-67209

[0015] Colloidal silica and organic matter entrained in makeup water, and organic acids in process drains are thermally decomposed in the boiler and converted into low-molecular-weight ionic silica and organic acids (formic acid, acetic acid, etc.). These are volatile and are contained in the condensate, which is collected in the feedwater tank.

[0016] Low-molecular-weight ionic silica and organic acids can be removed using a condensate demineralizer consisting of anion exchange resin and cation exchange resin. However, amines and ammonia, which are used to adjust the pH, are dissolved in the condensate, and treating the condensate with a condensate demineralizer consisting of anion exchange resin and cation exchange resin also removes the useful amines and ammonia.

[0017] Furthermore, when the condensate is treated in a condensate demineralizer comprising 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 condensate is large, the anion load becomes large.

[0018] Furthermore, if the condensate is treated only with anion exchange resin, only anions of salts such as NaCl are removed, which may make it impossible to detect impurities such as Na, Ca, and Mg from seawater or the like that have been mixed in using an acid conductivity measuring device.

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

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

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

[0022] [1] A boiler water treatment device having a pure water tank for receiving pure water and a condensate tank for receiving condensate, characterized in that it is provided with nitrogen gas supply means for supplying nitrogen gas to at least one of the tanks.

[0023] [2] A boiler water treatment device comprising a pure water tank for receiving pure water, a condensate tank for receiving condensate, and a water supply tank for receiving the pure water from the pure water tank and the condensate from the condensate tank, and 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.

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

[0025] [4] The boiler water treatment device according to [2], wherein the nitrogen gas supply means supplies nitrogen gas to the pure water tank, the condensate tank, and the feedwater tank, respectively.

[0026] [5] The boiler water treatment device according to [2], further comprising an OH-type anion exchange resin tower through which water from the water supply tank is passed, and the treated water that has passed through the OH-type anion exchange resin tower is returned to the water supply tank.

[0027] [6] A boiler water treatment device according to [1], which is provided with an OH-type anion exchange resin tower through which a portion of the combined water formed by combining the pure water from the pure water tank and the condensate from the condensate tank is passed, and the treated water that has passed through the OH-type anion exchange resin tower is combined with the remainder of the combined water and supplied to the boiler.

[0028] [7] The boiler water treatment device according to [5] or [6], comprising an acid conductivity meter for measuring the acid conductivity of the treated water from the OH-type anion exchange resin tower.

[0029] [8] The boiler water treatment device according to any one of [5] to [7], further comprising a sodium concentration meter for measuring the sodium 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 a plurality of the OH type anion exchange resin towers are installed in parallel, and when the acid electrical conductivity detected by the acid electrical conductivity meter reaches or exceeds a predetermined value, the OH type anion exchange resin tower to which the water is passed is switched.

[10] A boiler water treatment method using the boiler water treatment device of [7], wherein when the acid electrical conductivity detected by the acid electrical conductivity meter reaches or exceeds a predetermined value, the OH type anion exchange resin tower is replaced.

[0031] In the present invention, by creating a nitrogen atmosphere inside tanks such as a condensate tank, a pure water tank, and a water supply tank, carbon dioxide in the atmosphere is prevented from being mixed into the water in the tanks.

[0032] Incidentally, conventionally, there are no examples of nitrogen pressurization of tanks such as feedwater tanks in medium- to high-pressure boilers (especially boiler steam systems with steam turbines in the system). Nitrogen pressurization is sometimes performed in soft water feedwater boilers to prevent corrosion caused by oxygen contamination, but it is not generally performed to prevent, detect, or remove impurities from pure water feedwater.

[0033] In one aspect of the present invention, low-molecular-weight ionic silica and organic acids are removed from boiler feedwater by treating the condensate and feedwater with an OH-type anion exchange resin. Furthermore, since this OH-type anion exchange resin does not remove amines or ammonia from the water, the amines and ammonia used to adjust the pH of the condensate are supplied to the boiler water and reused.

[0034] In one aspect of the present invention, when Na ion-containing impurities such as seawater, industrial water, cooling water, etc. are mixed into condensate or feedwater, 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 the mixing of Na ion-containing impurities such as seawater, industrial water, cooling water, etc. can be detected from this measurement value.

[0035] In one aspect of the present invention, by detecting the acid electrical conductivity of treated water from an OH-type anion exchange resin, when the acid electrical conductivity reaches a predetermined value or more, it is possible to appropriately replace the OH-type anion exchange resin tower or switch the water flow to an OH-type anion exchange resin tower installed in parallel.

[0036] 1 is a configuration diagram of a boiler water treatment device according to an embodiment.

[0037] Hereinafter, an embodiment will be described with reference to FIG.

[0038] In the boiler water treatment system of this embodiment, pure water from a pure water production system (not shown) is introduced into pure water tank 2 through pipe 1, and condensate such as turbine condensate or process condensate is introduced into condensate tank 4 through pipe 3. The pure water from pure water tank 2 and the condensate from condensate tank 4 are introduced into feed water tank 7 through pipes 5 and 6, respectively. Although not shown, each of pipes 1, 3, 5, and 6 is provided with a valve. The valve of pipe 1 is opened and closed so that a required amount of pure water is stored in pure water tank 2, and by opening the valve of pipe 5, pure water is introduced from pure water tank 2 into feed water tank 7.

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

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

[0041] Pipe 12 is provided to supply water to the boiler, and pipe 13 is a pipe for draining water to the outside of the system.

[0042] The pipe 14 is branched into pipes 15 and 16 on the secondary side (downstream side) of the valve 14a, and each of the pipes 15 and 16 is connected to the top of an OH-type anion exchange resin tower 17 and 18. The pipes 15 and 16 are provided with valves 15a and 16a.

[0043] One end of each of pipes 19 and 20 is connected to the treated water outlet at the bottom of each of the OH-type anion exchange resin towers 17 and 18. The other end of each of the pipes 19 and 20 is connected to one end of a pipe 21.

[0044] The other end of the pipe 21 is connected to the water supply tank 7. A sodium concentration meter 22 is provided on the pipe 21, and the valves 13a and 14a are opened and closed in accordance with the sodium concentration detected by the sodium concentration meter 22.

[0045] An acid conductivity meter (CC meter) 23 is also provided on the pipe 21, and the valves 15a and 16a are opened and closed in accordance with the acid conductivity detected by the acid conductivity meter 23.

[0046] The nitrogen gas source 8 may be a nitrogen cylinder or a nitrogen generator (PSA (Pressure Swing Adsorption)) that can supply nitrogen-rich gas with lower concentrations of oxygen and carbon dioxide than the atmosphere. The nitrogen gas source 8 preferably has high nitrogen purity.

[0047] In the boiler water treatment device configured as described above, whether the boiler is operating, before starting operation, or is out of operation, except during blowing, valve 13a is closed, valve 14a is open, one of valves 15a and 16a is open and the other is closed, and pump 10 is operated. As a result, water in water supply tank 7 is passed from pipe 9, pump 10, and pipes 11 and 14 through pipe 15 or 16 to OH-type anion exchange resin tower 17 or 18, and treated water from OH-type anion exchange resin tower 17 or 18 is circulated through pipe 19 or 20 and pipe 21 to water supply tank 7. As a result, anion components such as low-molecular-weight ionic silica and organic acids in the feed water are removed in OH-type anion exchange resin tower 17 or 18.

[0048] When the boiler is operating, pump 10 is operated, valve 12a is open, and feedwater in feedwater tank 7 is sent to the boiler. Also, when the boiler is operating, the valves of pipes 3 and 6 are open, and condensate is introduced into feedwater tank 7 via condensate tank 4. When the boiler is stopped, valve 12a is closed. Also, when the boiler is stopped, the valves of pipes 3 and 6 are closed.

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

[0050] When the OH type anion exchange resin tower 17 breaks through and the acid electrical conductivity detected by the acid electrical conductivity meter 23 exceeds a predetermined value, the valves 15a and 16a are switched to open and closed states to pass water through the other OH type anion exchange resin tower 18. The OH type anion exchange resin tower 17 that has broken through is regenerated or replaced with a regenerated OH type anion exchange resin tower.

[0051] During boiler operation, when the sodium concentration detected by sodium concentration meter 22 exceeds a preset reference value, valve 14a is closed and valve 13a is opened. Pump 10 remains in operation. As a result, a predetermined amount of feedwater is discharged from feedwater tank 7 to the outside of the system via pipe 13, and pure water is supplied to feedwater tank 7 to reduce the sodium concentration in the feedwater. After that, valve 13a is closed and valve 14a is opened.

[0052] In this boiler water treatment device, the tanks 2, 4, and 7 are filled with a positive nitrogen atmosphere, so that carbon dioxide in the atmosphere does not dissolve in the water in the tanks.

[0053] Furthermore, the boiler feedwater is treated in the OH-type anion exchange resin towers 17 or 18, so that low-molecular-weight ionic silica and organic acids are removed from the feedwater, resulting in good water quality. Although pH adjusters such as amines and ammonia remain in the condensate, treating the feedwater in the OH-type anion exchange resin towers 17 or 18 does not remove the amines and ammonia from the feedwater, so the amount of additional pH adjuster added is reduced, reducing chemical costs.

[0054] In this embodiment, the Na concentration of the treated water from the OH type anion exchange resin towers 17, 18 is detected by the Na concentration meter 22, so that when Na ion-containing impurities such as seawater, industrial water, cooling water, etc. are mixed into the feed water, this can be detected quickly.

[0055] In the above embodiment, the pure water tank 2, the condensate tank 4, and the water supply tank 7 are all filled with a nitrogen atmosphere, but a tank for supplying nitrogen gas may be selected depending on the dissolution state of carbon dioxide. Furthermore, 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] It is preferable to supply nitrogen gas continuously so that air does not flow into the tank even if the water level in the tank drops. If the water level in the tank fluctuates greatly, the amount of nitrogen gas supplied to the tank increases, so it is preferable to reduce the fluctuation in the water level in the tank, and it is even more preferable to keep the water level constant.

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

[0058] 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] If the temperature of the water 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 pipes 1, 3, 5, 6, and 21 may be connected to the top of tanks 2, 4, and 7, or may be connected to the bottom of tanks 2, 4, and 7 so that water from the pipes is introduced into the water in the tanks, or may be introduced from the top of the tank to the bottom of the tank below the water surface through a conduit. In this way, the inflow water is prevented from falling onto the surface of the tank and stirring up the water near the surface.

[0061] In the above embodiment, the OH type anion exchange resin towers 17 and 18 are installed in parallel, and the water flow to the OH type anion exchange resin towers 17 and 18 is switched by the valves 15a and 16a. However, it is also possible to install only one OH type anion exchange resin tower and replace it with a new OH type anion exchange resin tower when the resin breaks through.

[0062] In the present invention, when the temperature of the water passed through the OH type anion exchange resin tower is high (for example, 40°C or higher), it is preferable to lower the temperature using a heat exchanger before passing the water through the OH type anion exchange resin tower.

[0063] In the above embodiment, the water supply tank 7 is provided, but the water supply tank 7 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] As a result, the pure water from pipe 5 and the condensate from pipe 6 are joined in pipe 9. A part of this joined water is treated in OH type anion exchange resin tower 17 or 18, and the treated water is joined with the rest of the joined water in pipe 12 and supplied to the boiler.

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

[0066] Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the present invention. This application is based on Japanese Patent Application No. 2023-221336 filed on December 27, 2023, and is incorporated by reference in its entirety.

[0067] 2 Pure water tank 4 Condensate tank 7 Water supply tank 8 Nitrogen gas source 17, 18 OH type anion exchange resin tower 22 Na concentration meter 23 Acid electrical conductivity meter

Claims

1. A boiler water treatment apparatus having a pure water tank for receiving pure water and a condensate tank for receiving condensate, characterized in that it is provided with nitrogen gas supply means for supplying nitrogen gas to at least one of the tanks.

2. A boiler water treatment apparatus comprising 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, characterized in that it is provided with 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, further 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, further 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 remaining part of the combined water are combined and supplied to the boiler.

7. The boiler water treatment apparatus according to claim 5 or 6, further comprising 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, further comprising 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 a plurality of the OH-type anion exchange resin towers are installed in parallel, and 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 through which water flows is switched.

10. 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.

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