Wastewater treatment methods

Abstract

To provide a wastewater treatment method with a reduced drainage volume for defluorination by not going through a retarding basin into which wastewater with high fluorine concentration flows, as a wastewater treatment line of water used in a hydraulic test of a fuel oil tank.SOLUTION: As a wastewater treatment method, provided is a line used in a power generation facility assembled with a fuel oil tank 2, a retarding basin 4, a C storage tank 36, a defluorination apparatus 37 for performing defluorination of wastewater sent from the C storage tank 36, an intermediate drain tank 8 where wastewater not needing defluorination is stored, wastewater storage tanks 10, 11 where defluorinated wastewater is sent to and stored in, and a heavy metal treatment apparatus 9 for heavy metal treatment of wastewater sent from the wastewater storage tanks 10, 11. In the line, wastewater used in a hydraulic test of the fuel oil tank 2 is sent to the wastewater storage tanks 10, 11 via an intermediate drain tank 8 but not via the retarding basin 4 and the C storage tank 36, and further sent to the heavy metal treatment apparatus 9 to perform heavy metal treatment in the heavy metal treatment apparatus 9, followed by discharging to a sea area.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for treating water used in a hydraulic test of a fuel oil tank as wastewater, and particularly relates to an improved wastewater treatment line before discharging such wastewater into sea areas or other water areas.

Background Art

[0002] Fuel oil tanks, which are one of the facilities of certain thermal power plants, are required to undergo a hydraulic test (pressure resistance test) after inspection in accordance with predetermined laws and regulations such as the Fire Service Act to confirm whether there is any problem with the use of the fuel oil tank. The water used in this hydraulic test is subjected to wastewater treatment and then discharged into sea areas and other water areas (ponds, lakes, rivers, etc.). However, since fuel oil tanks normally contain oil, as shown by the broken lines in Figures 1 and 2 of the present application, pipes constituting a drainage line for draining water from the tank are temporarily installed. For example, after oil derived from residual oil in the tank contained in the water used for the hydraulic test is separated in a temporary oil separation tank (not shown), the water may be sent to a retarding basin with a large water storage capacity through the temporary pipes. Note that since the temporary oil separation tank is omitted in the broken lines in Figures 1 and 2 of the present application, for convenience, the figure shows the temporary pipes extending from the tank instead of from the temporary oil separation tank.

[0003] The wastewater sent to the retarding basin includes wastewater with high fluorine concentration such as coal ash transportation water and wastewater from desulfurization units (desulfurization wastewater). Under recent environmental regulations, wastewater with high fluorine concentration cannot be discharged into water areas such as sea areas unless it is subjected to defluorination treatment by a defluorination treatment device before heavy metal treatment by a heavy metal treatment device. For this reason, as disclosed in Patent Document 1, a wastewater treatment line is provided, through which wastewater is sent from the retarding basin to a heavy metal treatment device via a defluorination treatment device.

[0004] In contrast, the water used in the hydrostatic testing of fuel oil tanks is industrial water taken from nearby rivers, for example, and the fluorine concentration in the water after the hydrostatic testing is not high. However, when it is sent to the retention basin, it is mixed with wastewater with high fluorine concentrations, such as coal ash transport water and desulfurization wastewater, which necessitates that the water used in the hydrostatic testing of fuel oil tanks also be defluorinated using a defluorination treatment device. Moreover, the amount of water sent to the retention basin for the hydrostatic testing of fuel oil tanks is large, for example, 15,000 kiloliters, which may cause the water level in the retention basin to rise, potentially leading to problems such as water overflowing from the retention basin and flowing back into the adjacent drainage area.

[0005] On the other hand, as shown in Patent Document 2, hydrostatic pressure tests are sometimes performed on condensers, which are one of the facilities of a certain thermal power plant. Patent Document 2 describes a treatment process in which wastewater generated during hydrostatic pressure tests of condensers, which was previously discharged into the sea, is recovered, impurities are removed, and then it is sent to a pure water system. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2016-70640 [Patent Document 1] Japanese Patent Publication No. 2004-290749 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, Patent Document 2 is intended for the reuse of wastewater generated in condenser hydrostatic tests, and it does not show that the wastewater generated in the condenser hydrostatic tests was mixed with wastewater with a high fluorine concentration. Therefore, it does not provide any idea to solve the problem that the water used in fuel oil tank hydrostatic tests was mixed with wastewater with a high fluorine concentration, and thus the water used in the fuel oil tank hydrostatic tests also needed to be defluorinated using a defluorination treatment device.

[0008] To achieve the above objectives, the present invention provides a wastewater treatment method for treating water used in a hydrostatic test of a fuel oil tank as wastewater, comprising a fuel oil tank and a retention pond into which wastewater requiring defluorination treatment can flow, It is connected to the aforementioned retention pond by piping, and from the aforementioned retention pond Wastewater requiring fluorine removal treatment Sent This is used in a power generation facility comprising: a first storage tank for storage; a defluorination treatment device connected by piping to the first storage tank for defluorinating wastewater sent from the first storage tank; a wastewater tank for storing wastewater that does not require defluorination treatment; a second storage tank connected by piping to the defluorination treatment device for receiving and storing wastewater that has been defluorinated by the defluorination treatment device; and a heavy metal treatment device connected by piping to the second storage tank for treating wastewater sent from the second storage tank for heavy metals. A temporary line is constructed to drain the water used in the hydrostatic test of the fuel oil tank from the fuel oil tank. The hydrostatic test of the aforementioned fuel oil tank was performed water The wastewater is sent to the second storage tank via the drainage tank, without passing through the retention pond and the first storage tank, and further sent from the second storage tank to the heavy metal treatment device, where it is treated for heavy metals before being discharged into the water body. The piping connecting the first storage tank and the defluorination treatment device, the piping connecting the defluorination treatment device and the second storage tank, and the piping connecting the second storage tank and the heavy metal treatment device are, for example, existing piping. Wastewater requiring defluorination treatment is wastewater with a fluorine concentration above a predetermined level, so-called high-concentration wastewater. Wastewater not requiring defluorination treatment is wastewater with a fluorine concentration below a predetermined level, so-called low-concentration wastewater. [Means for solving the problem]

[0009] To achieve the above objectives, the wastewater treatment method of the present invention is a wastewater treatment method for treating water used in a hydrostatic pressure test of a fuel oil tank as wastewater, and is used in a power generation facility that includes a fuel oil tank, a retention pond into which wastewater requiring defluorination treatment can flow, a first storage tank for storing wastewater requiring defluorination treatment, a defluorination treatment device connected by piping to the first storage tank for defluorination treatment of wastewater sent from the first storage tank, a drainage tank for storing wastewater that does not require defluorination treatment, a second storage tank connected by piping to the defluorination treatment device for receiving and storing wastewater that has been defluorinated by the defluorination treatment device, and a heavy metal treatment device connected by piping to the second storage tank for heavy metal treatment of wastewater sent from the second storage tank, and is characterized in that the wastewater used in the hydrostatic pressure test of the fuel oil tank is sent to the second storage tank via the drainage tank without passing through the retention pond and the first storage tank, and further sent from the second storage tank to the heavy metal treatment device, and after heavy metal treatment by the heavy metal treatment device, is discharged into a body of water. The piping connecting the first storage tank and the defluorination treatment device, the piping connecting the defluorination treatment device and the second storage tank, and the piping connecting the second storage tank and the heavy metal treatment device are, for example, existing piping. Wastewater requiring defluorination treatment is wastewater with a fluorine concentration above a predetermined level, so-called high-concentration wastewater. Wastewater not requiring defluorination treatment is wastewater with a fluorine concentration below a predetermined level, so-called low-concentration wastewater.

[0010] As a result, the water used in the hydrostatic test of the fuel oil tank is sent to the second storage tank via a drainage tank that stores wastewater that does not require defluorination treatment, instead of passing through a retention pond into which wastewater requiring defluorination treatment can flow or a first storage tank where wastewater requiring defluorination treatment is stored. Therefore, it is not mixed with wastewater that requires defluorination treatment. Consequently, the wastewater requiring defluorination treatment will not contain the water used in the hydrostatic test of the fuel oil tank. Moreover, since the large amount of water used in the hydrostatic test of the fuel oil tank is not sent to the retention pond, it is prevented from overflowing from the retention pond and flowing back into the drainage area.

[0011] More specifically, in the wastewater treatment method of the present invention, the power generation facility further comprises a third storage tank between the fuel oil tank and the second storage tank, in which wastewater that does not require defluorination treatment is stored, and the water used in the hydrostatic test of the fuel oil tank water A drain pipe that sends the water to the third storage tank is 、 Between the fuel oil tank and the third storage tank Temporarily constructed Furthermore, the drainage tank is connected by piping to the third storage tank and also by piping to the second storage tank, and is characterized in that the water used in the hydrostatic pressure test of the fuel oil tank is sent directly to the third storage tank via the drainage piping, then sent from the third storage tank to the drainage tank, and further sent to the second storage tank. The piping connecting the drainage tank and the third storage tank and the piping connecting the drainage tank and the second storage tank are, for example, existing piping. A desulfurization cooling tower pit is used as the third storage tank. The drainage piping is, for example, piping that is temporarily installed only during the test to drain the wastewater used in the hydrostatic pressure test of the fuel oil tank from the fuel oil tank.

[0012] The short distance between the fuel oil tank and the third storage tank allows for a shorter overall length of the temporary drainage piping. However, if the distance between the fuel oil tank and the drainage tank is short, the temporary drainage piping may be installed between the fuel oil tank and the drainage tank. [Effects of the Invention]

[0013] As described above, according to the wastewater treatment method of the present invention, the water used in the hydrostatic test of the fuel oil tank is sent to the second storage tank via a wastewater tank that stores wastewater that does not require defluorination treatment, without passing through a retention pond into which wastewater requiring defluorination treatment can flow or a first storage tank where wastewater requiring defluorination treatment is stored. Therefore, it is not mixed with wastewater that requires defluorination treatment. As a result, it is possible to ensure that the wastewater requiring defluorination treatment does not contain the water used in the hydrostatic test of the fuel oil tank. Consequently, the amount of water that undergoes defluorination treatment by the defluorination treatment device is reduced, and the cost required for defluorination treatment can be reduced. Moreover, it is possible to prevent the large amount of water used in the hydrostatic test of the fuel oil tank from being sent to the retention pond in the first place, thus preventing the water from overflowing from the retention pond due to the inflow of the large amount of water used in the hydrostatic test of the fuel oil tank.

[0014] In particular, according to the wastewater treatment method of the invention described in claim 2, since the distance between the fuel oil tank and the third storage tank is, for example, shorter than that between the fuel oil tank and the drainage tank, the total length of the temporary drainage piping can be made shorter than when temporary drainage piping is installed between the fuel oil tank and the drainage tank. This makes it possible to reduce the cost of installing the drainage piping and the area that needs to be secured as space for routing the drainage piping. [Brief explanation of the drawing]

[0015] [Figure 1] As an example of a power generation facility such as a thermal power plant to which the present invention is applied, a fuel oil tank, a defluorination treatment device, a heavy metal treatment device, an intermediate drainage tank, and a retention pond are shown, and a schematic diagram showing how the wastewater after the hydrostatic test is sent from the fuel oil tank to the intermediate drainage tank without passing through the retention pond is also shown. [Figure 2] This diagram provides a more detailed explanation than Figure 1, illustrating an example of a power generation facility such as a thermal power plant to which the present invention is applied, showing a fuel oil tank, various equipment constituting a wastewater treatment line mainly for defluorination, various equipment constituting a wastewater treatment line mainly for heavy metal treatment, an intermediate wastewater tank, and a retention pond, and also showing a configuration in which wastewater after a hydrostatic test is sent from the fuel oil tank to the intermediate wastewater tank without passing through the retention pond. DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0017] FIG. 1 and FIG. 2 show an example of equipment 1 included in a power generation facility such as a thermal power plant. The power generation facility equipment 1 shown in FIG. 1 and FIG. 2 does not illustrate the entire equipment used for heavy metal treatment, defluorination treatment, or desulfurization treatment, but only a part related to the present invention.

[0018] FIG. 1 schematically shows new and old lines for treating, as wastewater, water that has been used in a hydraulic test of No. 3 fuel oil tank 2 among a plurality (e.g., five) of fuel oil tank groups included in equipment 1 of a power generation facility.

[0019] In this embodiment, the retarding basin 4 is sequentially connected via a pipe A to a flue gas desulfurization apparatus 5 that removes sulfur oxides contained in exhaust gas generated by a boiler, and to a drainage yard 3. Desulfurization wastewater generated by operation of the flue gas desulfurization apparatus 5 (wastewater from which fluorine has eluted and that requires defluorination treatment) flows in from the flue gas desulfurization apparatus 5 via the drainage yard 3, and is stored in the retarding basin 4. Accordingly, since the wastewater stored in the retarding basin 4 has a high fluorine concentration (e.g., 30 to 50 mg / l), when the wastewater is sent out from the retarding basin 4, the wastewater is first sent to a C storage tank 36 that serves as pre-equipment for a defluorination treatment apparatus 37, and then subjected to defluorination treatment in the defluorination treatment apparatus 37. That is, the retarding basin 4, the C storage tank 36, and the defluorination treatment apparatus 37 are sequentially connected via a pipe B, and wastewater requiring fluorine treatment is stored in the C storage tank 36. Details of the defluorination treatment line (system) including the defluorination treatment apparatus 37 will be described below with reference to FIG. 2. For example, existing pipes A and B can be used as they are. The range surrounded by a broken line in the lower part of FIG. 2 described below corresponds to the defluorination treatment apparatus 37.

[0020] In this embodiment, the flue gas desulfurization apparatus 5 is arranged relatively close to the No. 3 fuel oil tank 2. For example, although not shown in the figure, a desulfurization equipment yard is provided in an area surrounding the flue gas desulfurization apparatus 5. A desulfurization cooling tower pit 7, which also functions as a tank for the desulfurization equipment yard, is provided adjacent to the flue gas desulfurization apparatus 5. Furthermore, in this embodiment, an intermediate drainage tank 8 is provided at a position farther from the fuel oil tank 2 than the desulfurization cooling tower pit 7. That is, the desulfurization cooling tower pit 7 is located between the fuel oil tank 2 and the intermediate drainage tank 8.

[0021] The intermediate drainage tank 8 stores general drainage generated in power generation equipment (for example, drainage that is steam cooling water or boiler blow water and does not require defluorination treatment). The desulfurization cooling tower pit 7 normally stores rainwater that does not require defluorination treatment as drainage. Accordingly, the desulfurization cooling tower pit 7 and the intermediate drainage tank 8 are connected by pipe C, which enables drainage that does not require defluorination treatment to be sent from the desulfurization cooling tower pit 7 to the intermediate drainage tank 8. For example, an existing pipe C is used as it is.

[0022] The wastewater treated for defluorination in the defluorination treatment device 37 is sent to the heavy metal treatment device 9. However, wastewater storage tanks A 10 and B 11 are located before the heavy metal treatment device 9, and the defluorinated wastewater is stored in wastewater storage tanks A 10 and B 11. Wastewater storage tanks A 10 and B 11 also receive and store wastewater from the intermediate wastewater tank 8. Specifically, wastewater storage tanks A 10 and B 11 are connected to the defluorination treatment device 37 and the intermediate wastewater tank 8, respectively, by pipes D and E, and are also connected to the heavy metal treatment device 9 by piping line F. The wastewater sent from wastewater storage tanks A 10 and B 11 to the heavy metal treatment device 9 is treated for heavy metals in the heavy metal treatment device 9, and then sent to the discharge pit 25, which is connected to the heavy metal treatment device 9 by piping line G, and discharged into the sea from the discharge pit 25. Details of the heavy metal treatment lines (systems), including the heavy metal treatment device 9, and other wastewater treatment lines will be explained below using Figure 2. Piping C, D, E, F, and G can be used as they are, for example, existing ones. The area enclosed by the dashed line in the upper part of Figure 2 below corresponds to the heavy metal treatment device 9.

[0023] As shown in Figure 2, in the wastewater treatment line (system) primarily for heavy metal treatment, wastewater is sent from wastewater storage tanks A 10 and B 11 (as shown in Figure 1) to the pH adjustment tank 12 and condensation tank 13 via pumps P1 and P2, respectively. After sludge settling in the sedimentation tank 14, the wastewater is sent to the intermediate tank 15. From the intermediate tank 15, the wastewater is sent to the filter 16 via pump P3. After being filtered in the filter 16, it passes through the backwash tank 17, pH adjustment tank 18, and retention tank 19 before being sent to the adsorption towers 20 and 21 via pump P4. Furthermore, the wastewater sent to the adsorption towers 20 and 21 passes through at least the neutralization tank 22, treatment tank 23, and monitoring tank 24 before being sent to the discharge pit 25 via pump P5. After water quality checks are performed in the discharge pit 25, the water is discharged into the sea.

[0024] As shown in Figure 2, the sludge that settles at the bottom in the sedimentation tank 14 is sent to the thickening tank 30 by pump P6 as part of the sludge treatment line (system). After being thickened, a coagulant is added from the coagulant dissolving tank 31 using pump P7, and the sludge is sent to the dewatering machine 32 by pump P8. In the dewatering machine 32, it is dewatered and discharged to the outside as a cake. The wastewater generated in the thickening tank 30 and the intermediate wastewater tank 15, etc., is sent to a wastewater pit (not shown) and then to wastewater storage tanks A 10 and B 11.

[0025] In the wastewater treatment line (system) primarily for defluorination treatment, desulfurized wastewater X is mixed with steady-state and transient wastewater in the chemical washing wastewater storage tank 35. This wastewater is then sent from the chemical washing wastewater storage tank 35 to the C wastewater tank 36, as shown in Figure 1, by pump P9, and further sent from the C wastewater tank 36 to the reaction tank 40 by pump P10. In this embodiment, the reaction tank 40 consists of four reaction tanks, from the first reaction tank 40a to the fourth reaction tank 40d. Although not shown, caustic soda is supplied to the first reaction tank 40a and the fourth reaction tank 40d by pump from the caustic soda storage tank, aluminum sulfate is supplied to the fourth reaction tank 40d by pump from the aluminum sulfate storage tank, and a coagulant is added to the second reaction tank 40b by pump from the coagulant dissolving tank. The wastewater is sequentially sent from the first reaction tank 40a to the fourth reaction tank 40d. The wastewater that has passed through these reaction tanks 40 is sent to a fluorine sedimentation tank 41, where the sludge generated in the flow up to this point is settled. Then it is sent to a fluorine intermediate layer tank 42, and then pumped by P11 to the aforementioned wastewater storage tanks A 10 and B 11. The sludge settled at the bottom of the fluorine sedimentation tank 41 is sent by pump P12 to a fluorine thickening tank 43 for concentration, and then sent from the fluorine thickening tank 43 to a dewatering machine 44 by pump P13 for dewatering, and discharged to the outside as a cake.

[0026] As with Figure 1, Figure 2 also shows the retention basin 4, the desulfurization cooling tower pit 7, and the intermediate drainage tank 8. The wastewater stored in the retention basin 4 also becomes wastewater requiring defluorination treatment when desulfurization wastewater X flows into it. As mentioned above, when it is discharged from the retention basin 4, it is sent to storage tank C 36 and undergoes defluorination treatment by passing through the defluorination treatment line. As mentioned above, the intermediate drainage tank 8 is connected by piping to the desulfurization cooling tower pit 7 and wastewater storage tanks A and B 10 and 11.

[0027] In this wastewater treatment line, when a hydrostatic test is performed on fuel oil tank 3 2, a drainage pipe H is temporarily installed between fuel oil tank 3 2 and the desulfurization cooling tower pit 7, as shown by the dashed line in Figures 1 and 2, to drain the water used in the hydrostatic test from fuel oil tank 3 2. Since the water used in the hydrostatic test may contain oil from residual oil in fuel oil tank 3 2, the water is separated from the water by passing it through a temporary oil separator (not shown). Therefore, although the drainage pipe H is located between fuel oil tank 3 2 and the desulfurization cooling tower pit 7, it is not directly connected to fuel oil tank 3 2, but rather to the temporary oil separator, and is, strictly speaking, part of the line (system) after the temporary oil separator. However, since the temporary oil separator is omitted in Figures 1 and 2, for convenience, the drainage pipe H is shown extending from fuel oil tank 2 No. 3 rather than from the temporary oil separator. As a result, when treating the water used in the hydrostatic test of fuel oil tank 2 No. 3 as wastewater, it is sent from fuel oil tank 2 No. 3 to the intermediate wastewater tank 8 via the desulfurization cooling tower pit 7, and from the intermediate wastewater tank 8 to wastewater storage tanks 10 and 11 A and B, which are upstream facilities of the heavy metal treatment device 9. Therefore, the water used in the hydrostatic test of fuel oil tank 2 No. 3 is not sent to the retention pond 4 and storage tank 36 C, bypassing the defluorination treatment line, and thus defluorination treatment by the defluorination treatment device 37 is not performed.

[0028] Furthermore, if the water used in the hydrostatic test is treated as wastewater from fuel oil tanks other than Fuel Oil Tank No. 3 2, it is preferable, although not shown in the diagram, to similarly bypass the defluorination treatment line and prevent defluorination treatment by the defluorination treatment device 37 by sending it to the intermediate wastewater tank 8 instead of to the retention pond 4 and storage tank C 36. [Explanation of Symbols]

[0029] 1. Equipment of power generation facilities 2. Fuel oil tank (Fuel oil tank No. 3) 4. Flood control basin 5 Desulfurization smoke exhaust system 7. Third storage tank (desulfurization cooling tower pit) 8 Drainage tank (intermediate drainage tank) 9. Heavy metal treatment equipment 10. Second storage tank (A drainage storage tank) 11. Second storage tank (B drainage storage tank) 25 Discharge pit 36. First storage tank (Storage Tank C) 37. Defluorination treatment device Piping from A to G H Drainage pipe

Claims

1. A wastewater treatment method for treating water used in a hydrostatic test of a fuel oil tank as wastewater, This is used in a power generation facility comprising: a fuel oil tank; a retention pond into which wastewater requiring defluorination treatment can flow; a first storage tank connected by piping to the retention pond, into which wastewater requiring defluorination treatment is sent from the retention pond and stored; a defluorination treatment device connected by piping to the first storage tank, into which wastewater sent from the first storage tank is defluorinated; a drainage tank for storing wastewater that does not require defluorination treatment; a second storage tank connected by piping to the defluorination treatment device, into which wastewater that has been defluorinated by the defluorination treatment device is sent and stored; and a heavy metal treatment device connected by piping to the second storage tank, into which wastewater sent from the second storage tank is treated for heavy metals. A temporary line is constructed to drain the water used in the hydrostatic test of the fuel oil tank from the fuel oil tank. A method for treating wastewater, characterized in that the water used in the hydrostatic test of the fuel oil tank is sent to the second storage tank via the drainage tank, without passing through the retention pond and the first storage tank, and further sent from the second storage tank to the heavy metal treatment device, and after heavy metal treatment in the heavy metal treatment device, the water is discharged into a body of water.

2. The power generation facility further includes a third storage tank between the fuel oil tank and the second storage tank, in which wastewater that does not require defluorination treatment is stored. A drain pipe for sending the water used in the hydrostatic pressure test of the fuel oil tank to the third storage tank is temporarily installed between the fuel oil tank and the third storage tank, The drainage tank is connected by piping to the third storage tank and also by piping to the second storage tank. The wastewater treatment method according to claim 1, characterized in that the water used in the hydrostatic pressure test of the fuel oil tank is sent directly to the third storage tank via the drainage piping, then sent from the third storage tank to the drainage tank, and further sent to the second storage tank.

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