JP7647439B2 - Sludge treatment method - Google Patents

Description

The present invention relates to a method for treating sludge that has settled and accumulated in a specified wastewater storage tank in a wastewater treatment facility at a power generation facility such as a thermal power plant.

One example of a wastewater treatment facility equipped with a thickening tank and a dehydrator is shown in Patent Document 1. In this wastewater treatment facility, the slurry generated by treating flue gas desulfurization wastewater is sent to a thickening tank where it is precipitated and thickened, then sent to the dehydrator where it is dehydrated to reduce the moisture concentration to a specified level and turned into a cake, which is then transported by truck to the outside as industrial waste.

On the other hand, wastewater treatment facilities at power generation facilities such as thermal power plants may have two parallel wastewater storage tanks (for example, one is called wastewater storage tank A and the other is called wastewater storage tank B) to which water, etc. produced by rinsing the air preheater (heat exchanger) is sent to prevent the heat exchanger called an air preheater (AH), which exchanges heat in the boiler, from becoming clogged with ash, etc., or to eliminate a state in which the heat exchanger is clogged with ash, etc.

In these two parallel wastewater storage tanks, as the air preheater (heat exchanger) is repeatedly washed with water, large particles of sludge produced by the washing of the air preheater (heat exchanger) settle and accumulate over time.

JP 2020-127911 A

However, until now, there has been no established method for treating the large-particle sludge that settles and accumulates in these wastewater storage tanks. For this reason, it has been necessary to alternately carry out regular inspections of the two parallel wastewater storage tanks at regular intervals, for example every two years. When carrying out regular inspections of one of the wastewater storage tanks, the method adopted has been to transfer the sludge that has settled and accumulated from one wastewater storage tank to the other.

However, simply transferring the sludge that has settled and accumulated from one wastewater storage tank to the other is not a final solution to the problem of large-particle sludge that has settled and accumulated in the wastewater storage tank. For this reason, it is necessary to remove the sludge from the wastewater storage tank and treat it before the wastewater storage tank becomes unable to function due to the settlement and accumulation of sludge, which is likely to result in high sludge treatment costs. In addition, the total amount of large-particle sludge that has settled and accumulated in both wastewater storage tanks will gradually increase over time, resulting in the inconvenience of it taking longer to transfer sludge from one wastewater storage tank to the other.

The present invention was made to solve these problems, and its main objective is to provide a sludge treatment method that focuses on the fact that since sludge with large particles is heavy and settles naturally, there is no need for a process to make such sludge settleable.

In order to achieve the above object, the sludge treatment method of the present invention is a method for treating sludge used in a wastewater treatment facility, comprising a wastewater storage tank to which water generated by washing a specified appliance is sent, a wastewater treatment system for treating the water sent to the wastewater storage tank, and a first sludge treatment system for treating sludge contained in the water that has passed through the wastewater treatment system from the wastewater storage tank, the wastewater treatment system having a settling tank for settling the sludge contained in the water sent from the wastewater storage tank as a component of the wastewater treatment system, and the first sludge treatment system having a dehydrator for dehydrating the sludge to a predetermined moisture concentration to form a cake as a component of the first sludge treatment system, characterized in that a second sludge treatment system is formed having a step of removing from the wastewater storage tank sludge having larger particles than the sludge contained in the water that passes through the wastewater treatment system from the wastewater storage tank, and a step of sending the sludge to the dehydrator in a state in which a coagulant has been injected into the sludge, without passing through the wastewater storage tank to the settling tank of the wastewater treatment system. The wastewater treatment facility is, for example, a wastewater treatment facility in a power generation facility such as a thermal power plant. The specific equipment is, for example, a heat exchanger called an air preheater that performs heat exchange in a boiler. The wastewater storage tank is, for example, two wastewater storage tanks arranged in parallel, one of which is called wastewater storage tank A and the other is called wastewater storage tank B.

As a result, by forming a second sludge treatment system, it is possible to remove and treat sludge that is generated by washing certain equipment and has larger particles than the sludge contained in the water sent from the wastewater storage tank to the wastewater treatment system. Moreover, since the sludge with larger particles that has accumulated in the wastewater storage tank to be inspected can be discharged at the timing of the inspection of the wastewater storage tank, it is possible to reduce the cost required for the sludge discharge work. Furthermore, since the dehydrator, which is equipment of the first sludge treatment system, can be used in the process of the second sludge treatment system, no new equipment is required.

In the sludge treatment method of the present invention, the wastewater treatment facility further includes a thickening tank to which sludge before being dewatered by the dehydrator is sent as equipment constituting the first sludge treatment system, and includes, as the second sludge treatment system, a process for removing sludge having larger particles than the sludge contained in the water passing through the wastewater treatment system from the wastewater storage tank and sending it directly to the thickening tank, and a process for injecting the coagulant into the sludge while it is being sent from the thickening tank to the dehydrator.

This makes it possible to settle in the thickening tank sludge that is larger in particles than the sludge contained in the water removed from the wastewater storage tank and sent from the wastewater storage tank to the wastewater treatment system, and the sludge can be smoothly transferred from the thickening tank to the dehydrator using a pump installed in the thickening tank and piping connecting the thickening tank and the dehydrator. Moreover, since the thickening tank and its peripheral equipment, which are the equipment of the first sludge treatment system, can be used in the process of the second sludge treatment system, no new equipment is required.

As described above, according to the sludge treatment method of the present invention, it is possible to remove and treat sludge that is generated by washing certain equipment and has larger particles than the sludge contained in the water that passes from the wastewater tank through the wastewater treatment system by forming a second sludge treatment system. Furthermore, when the wastewater tank is inspected, the sludge with larger particles that has accumulated in the wastewater tank being inspected can be discharged. This reduces the cost of treating the sludge that has settled and accumulated in the wastewater tank.

In particular, the sludge treatment method of the invention according to claim 2 makes it possible to settle in a thickening tank sludge that is larger in particle size than the sludge contained in the water sent from the wastewater storage tank to the wastewater treatment system, and the sludge can be smoothly transferred from the thickening tank to the dehydrator using a pump provided in the thickening tank and piping connecting the thickening tank and the dehydrator.

As an example of a wastewater treatment facility to which the present invention is applied, this is a schematic diagram showing a part of a wastewater treatment system, a first sludge treatment system, and a second sludge treatment system, and showing an embodiment in which sludge with large particles is sent from wastewater storage tanks A and B to a concentration tank without passing through the wastewater system. 1A and 1B are schematic diagrams showing an example of the transport of large-particle sludge in the second sludge treatment system, in which (a) shows the process of removing large-particle sludge from a wastewater storage tank, and (b) shows the process of sending the removed large-particle sludge directly to a thickening tank. As another example of a wastewater treatment facility to which the present invention can be applied, this is a schematic diagram showing a part of a wastewater treatment system, a first sludge treatment system, and a second sludge treatment system, and also showing an embodiment in which sludge with large particles is sent from the A and B wastewater storage tanks to a dehydrator without passing through the wastewater system.

The following describes an embodiment of the present invention with reference to the drawings.

In FIG. 1, an example of a wastewater treatment facility 1 is shown, which may be found in a power generation facility such as a thermal power plant. In FIG. 1, only a portion of the equipment related to the present invention is shown, rather than all of the equipment in the wastewater treatment facility 1.

The wastewater treatment facility 1 has, for example, an A wastewater storage tank 3 and a B wastewater storage tank 4 to which water, etc. is sent from a wastewater pit 2. The wastewater pit 2 is used to receive cleaning water, etc., generated when washing a heat exchanger (not shown) called an air preheater, which exchanges heat in a boiler, and the cleaning water is sent from the wastewater pit 2 to either or both of the A wastewater storage tank 3 and the B wastewater storage tank 4. In other words, the cleaning water for the heat exchanger contains ash, rust, etc. that has accumulated in the heat exchanger due to clogging, etc., and as shown in Figure 2(a), it has settled and accumulated as sludge S of relatively large particles in the A wastewater storage tank 3 and the B wastewater storage tank 4.

In this embodiment, the A drainage tank 3 and the B drainage tank 4 are drainage tanks with an open top, as shown in part in FIG. 2(a), and the A drainage tank 3 and the B drainage tank 4 are arranged side by side, separated into two by a partition wall (not shown). In FIG. 1, valves 5, 6, and 7 are provided on the piping connecting the drainage pit 2 and the A drainage tank 3 and the B drainage tank 4, but the number and arrangement of the valves shown in FIG. 1 are not limited as long as water, etc. can be sent from the drainage pit 2 to either or both of the A drainage tank 3 and the B drainage tank 4. Although not shown, the A drainage tank 3 and the B drainage tank 4 are appropriately connected to a boiler water tank, a drainage tank pump, etc., so that water, etc. is sent to the A drainage tank 3 and the B drainage tank 4, and valves are provided on the piping route.

In this embodiment, the wastewater treatment facility 1 includes a pH adjustment tank 10, a flocculation tank 11, a sedimentation tank 12, an intermediate water tank 13, and a filter 14 as equipment constituting the wastewater treatment system L1 for treating the water sent to the A wastewater storage tank 3 and the B wastewater storage tank 4. The pH adjustment tank 10, the flocculation tank 11, the sedimentation tank 12, the intermediate water tank 13, and the filter 14 are part of the wastewater treatment system L1.

Water containing sludge with relatively small particles is sent from the A wastewater storage tank 3 and the B wastewater storage tank 4 by pumps 8 and 9 to the pH adjustment tank 10, where the pH of the water is adjusted by adding chemicals, and then flocs are formed in the coagulation tank 11 by adding chemicals. The water treated in the coagulation tank is then sent to the settling tank 12, where even the sludge with relatively small particles settles and accumulates at the bottom of the settling tank 12. The topside water separated from the sludge in the settling tank 12 is sent to the intermediate water tank 13, and then further sent to the filter 14 by pump 15, where foreign matter is removed, and then sent to the equipment (not shown) that constitutes the wastewater treatment system L1 by pump 16. In this embodiment, valve 17 is placed in the path between pump 8 and pH adjustment tank 10, valve 18 is placed in the path between pump 9 and pH adjustment tank 10, valve 19 is placed in the path on the filter 14 side of pump 16, and valve 20 is placed in the path on the opposite side of pump 16 from filter 14.

In this embodiment, the wastewater treatment facility 1 has a thickening tank 21, a flocculant solution tank 22, and a dehydrator 23 as equipment constituting the first sludge treatment system L2, which is a normal equipment for treating sludge separated from water in the sedimentation tank 12. The thickening tank 21 is for thickening the sludge sent by the pump 24 from the bottom of the sedimentation tank 12, and is a tank with an open top, as shown in FIG. 2(b). When the sludge passes through the piping connecting the pump 24 and the thickening tank 21, the flocculant sent by the pump 25 from the flocculant solution tank 22 is added and the sludge is sent to the thickening tank 21. The sludge is then sent from the bottom of the thickening tank 21 to the dehydrator 23 by the pump 26, where it is dehydrated to a predetermined moisture content to become a cake, and then sent to the cake hopper 29, 30 by the belt conveyors 27, 28, and transported outside the wastewater treatment facility 1 as industrial waste. There are two types of dehydrators 23: a centrifugal type and a belt type that squeezes the sludge between two belts to extract water. The belt type is more preferable because the centrifugal type may become clogged with large sludge particles.

In this embodiment, valve 31 is arranged in the path on the sedimentation tank 12 side of the piping relative to pump 24, valve 32 is arranged in the path on the concentration tank 21 side of the piping relative to pump 24, valve 33 is arranged in the path on the coagulant dissolution tank 22 side of the piping relative to pump 25, valve 34 is arranged in the path on the opposite side of the coagulant dissolution tank 22 relative to pump 25, valve 35 is arranged in the path on the concentration tank 21 side of the piping relative to pump 26, and valve 36 is arranged in the path on the dehydrator 23 side of pump 26.

In the present invention, the wastewater treatment facility 1 has a second sludge treatment system L3 that treats sludge without passing through the wastewater treatment system L1. The second sludge treatment system L3 is designed to treat sludge S that has larger particles than the sludge contained in the water that passes through the wastewater treatment system L1 from the A wastewater storage tank 3 and the B wastewater storage tank 4.

More specifically, the second sludge treatment system L3 is a sludge treatment method that includes a process of removing the sludge S that has settled and accumulated in the A wastewater storage tank 3 and the B wastewater storage tank 4 from the A wastewater storage tank 3 and the B wastewater storage tank 4, and a process of sending the removed sludge S directly to the thickening tank 21 that constitutes the first sewage treatment system L2, without passing through the A wastewater storage tank 3 and the B wastewater storage tank 4 to the settling tank 12 of the wastewater treatment system L1. As with the first sludge treatment system L2, the sludge S sent to the thickening tank 21 also includes a process in which a flocculant sent by a pump 25 from the flocculant dissolving liquid tank 22 is added when passing through a pipe extending from the thickening tank 21 to the dehydrator 23, so that the sludge S is sent to the dehydrator 23 and turned into a cake, and can then be treated as industrial waste.

The particles of sludge S are larger and heavier than those of the sludge that passes through the wastewater treatment system L1, so it settles naturally. Therefore, no process is required to make the sludge settleable. Therefore, it is possible to carry out sludge treatment after the thickening tank 21 without passing the sludge S through the settling tank 12.

In the wastewater treatment facility 1 shown as an example in Figure 1, a vehicle 100 having a suction/discharge device 101 called a prober is used in the process of removing sludge S from the A wastewater storage tank 3 and the B wastewater storage tank 4, as shown in Figure 2(a), for example. When the tip 103 of a hose 102 extending from the suction/discharge device 101 reaches the sludge S in the A wastewater storage tank 3 and the B wastewater storage tank 4, the vehicle 100 operates the suction/discharge device 101 to take in the sludge S into the suction/discharge device 101. As a result, the sludge S is removed from the A wastewater storage tank 3 and the B wastewater storage tank 4. The vehicle 100 that has taken in the sludge S into the suction/discharge device 101 moves from the A wastewater storage tank 3 and the B wastewater storage tank 4 to the concentration tank 21 as shown by the thick dashed line in FIG. 1, and then, for example, as shown in FIG. 2(b), the tip 103 of the hose 102 extending from the suction/discharge device 101 is inserted into the concentration tank 21 to send the sludge S to the concentration tank 21 from above. As described above, the sludge S is large and heavy, so it settles directly to the bottom of the concentration tank 21. By using such a second wastewater treatment system L3, it is possible to use the concentration tank 21 and the dehydrator 23 of the first wastewater treatment facility, and further to use the existing route for injecting the coagulant from the coagulant dissolving liquid tank 22. Moreover, at the timing of inspection such as regular inspection of the A wastewater storage tank 3 and the B wastewater storage tank 4, it is possible to discharge the sludge with large particles that has accumulated in the wastewater storage tanks 3 and 4 to be inspected. Therefore, it is possible to reduce the cost associated with adopting the second wastewater treatment system L3.

Figure 3 shows an embodiment using a second drainage system L3 that is different from the second drainage system L3 shown in Figure 1. The second drainage system L3 shown in Figure 3 is suitable, for example, when the wastewater treatment facility 1 itself is newly constructed, and the sludge S is sent directly to the dehydrator 23 without passing through the thickening tank 21.

In the second wastewater treatment system L3 in FIG. 3, the sludge S that has settled and accumulated in the A wastewater storage tank 3 and the B wastewater storage tank 4 is removed from the A wastewater storage tank 3 and the B wastewater storage tank 4 by a process of sucking it up from the A wastewater storage tank 3 and the B wastewater storage tank 4 using pumps 41 and 42. The pumps 41 and 42 may be, for example, submersible pumps installed in the wastewater storage tanks 3 and 4, or pump vehicles that can move on rails laid around the periphery of the wastewater storage tanks 3 and 4.

In this embodiment, the pumps 41 and 42 are connected to the dehydrator 23 by piping, so that the sludge S removed from the A wastewater storage tank 3 and the B wastewater storage tank 4 by the pumps 41 and 42 is sent to the dehydrator 23 through the piping. Then, between the pumps 41 and 42 and the dehydrator 23, the flocculant sent by the pump 43 from the flocculant dissolving liquid tank 22 is injected into the sludge S. As a result, in the wastewater treatment system L3 in FIG. 3, the sludge S is sent to the dehydrator 23 with the flocculant injected, so that the sludge S is appropriately caked in the dehydrator 23 and transported to the outside as industrial waste.

In this embodiment, a valve 44 is arranged in the path between the pump 41 of the piping and the dehydrator 23, a valve 45 is arranged in the path between the pump 42 of the piping and the dehydrator 23, a valve 46 is arranged in the path on the side of the flocculant dissolving liquid tank 22 relative to the pump 43 of the piping, and a valve 47 is arranged in the path on the opposite side of the flocculant dissolving liquid tank 22 relative to the pump 43 of the piping.

In addition, even in the wastewater treatment facility 1 shown in FIG. 1, pumps 41 and 42 (not shown) may be provided, and piping may be provided to transport the sludge S removed from the A wastewater storage tank 3 and the B wastewater storage tank 4 to the concentration tank 21, so that the sludge is sent into the concentration tank 21 from the opening of the piping.

1 Wastewater treatment facility 3 A wastewater storage tank 4 B wastewater storage tank 12 Settling tank 21 Thickening tank 23 Dehydrator L1 Wastewater treatment system L2 First sludge treatment system L3 Second sludge treatment system S Sludge

Claims (2)

a wastewater storage tank to which water generated by washing a predetermined appliance is sent, a wastewater treatment system that treats the water sent to the wastewater storage tank, and a first sludge treatment system that treats sludge contained in the water that has passed from the wastewater storage tank through the wastewater treatment system;
The wastewater treatment system includes a settling tank for settling sludge contained in the water sent from the wastewater storage tank as a component of the wastewater treatment system,
The first sludge treatment system is a sludge treatment method used in a wastewater treatment facility having a dehydrator that dehydrates the sludge to a predetermined moisture concentration to form a cake as equipment constituting the first sludge treatment system,
A sludge treatment method characterized by forming a second sludge treatment system, the method comprising the steps of: removing sludge from the wastewater storage tank, the sludge having larger particles than the sludge contained in the water passing through the wastewater treatment system from the wastewater storage tank; and sending the sludge to the dehydrator after injecting a coagulant into the sludge, without passing through the wastewater treatment system from the wastewater storage tank to the settling tank. The wastewater treatment facility further includes a thickening tank to which sludge before being dewatered by the dehydrator is sent as equipment constituting the first sludge treatment system,
The sludge treatment method according to claim 1, characterized in that the second sludge treatment system includes a step of removing sludge having larger particles than the sludge contained in the water passing through the wastewater treatment system from the wastewater storage tank and sending it directly to the thickening tank, and a step of injecting the coagulant into the sludge while the sludge is being sent from the thickening tank to the dewatering machine.