Flash steam utilization system

Abstract

The utility model relates to the technical field of chemical equipment, and provides a flash steam utilization system which comprises a reaction kettle, a preheating unit, a flash unit and a steam generator. Wherein the preheating unit is connected to the upstream of the reaction kettle, and ore pulp can enter the reaction kettle after being preheated by the preheating unit; the flash evaporation unit is connected to the downstream of the reaction kettle and is used for carrying out flash evaporation on ore pulp after reaction, and generated steam can be introduced into the preheating unit through a steam pipe; the steam generator is installed on the steam pipe and can generate electric energy through steam, and the steam can enter the preheating unit after passing through the steam generator. And relatively high heat of steam is used as a heat source of the preheating unit to preheat ore pulp. And electric energy is generated through the steam generator by utilizing higher pressure of the steam. In this way, recycling of reaction waste heat is achieved, and energy loss is reduced.

Description

Technical Field

[0001] This utility model relates to the field of chemical equipment technology, and in particular to a flash steam utilization system. Background Technology

[0002] Flash evaporation refers to the process where high-pressure slurry from a high-pressure reactor enters a lower-pressure container, where the sudden pressure drop transforms the slurry into saturated steam and saturated slurry. Since the boiling point of a substance is directly proportional to its pressure, depressurization lowers the boiling point of the high-pressure, high-temperature slurry, allowing it to enter the flash evaporation process. The function of a flash evaporator is to provide a space for rapid vaporization and gas-liquid separation of fluids.

[0003] In the hydrometallurgical process for laterite nickel ore, the ore slurry, sulfuric acid, and steam are typically injected into a high-pressure reactor for leaching of high-valence metals from the laterite nickel ore under high pressure. After the reaction, the ore slurry and sulfuric acid are introduced into a flash tank for depressurization. The steam generated during depressurization is at a high temperature; direct discharge of this steam would result in energy waste.

[0004] Therefore, there is an urgent need for a flash steam utilization system to solve the above-mentioned technical problems. Utility Model Content

[0005] The purpose of this invention is to propose a flash steam utilization system that can fully utilize the energy of steam for preheating slurry and generating electricity.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] Flash steam utilization system includes:

[0008] Reactor;

[0009] A preheating unit is connected upstream of the reactor. The slurry is preheated in the preheating unit and then enters the reactor.

[0010] A flash evaporation unit is connected downstream of the reactor and is used to flash evaporate the slurry after the reaction. The generated steam can be introduced into the preheating unit through a steam pipe.

[0011] A steam generator, installed on the steam pipe, is capable of generating electrical energy from the steam. The steam passes through the steam generator and then enters the preheating unit.

[0012] As a preferred technical solution of the above-mentioned flash steam utilization system, it also includes a gas-liquid separator. The flash unit can be connected to the steam generator through the gas-liquid separator, and the gas-liquid separator can separate sulfuric acid droplets in the steam.

[0013] As a preferred technical solution of the above-mentioned flash steam utilization system, the flash unit includes a first flash tank and a second flash tank, and the above-mentioned reactor, the above-mentioned first flash tank and the above-mentioned second flash tank are connected in series along the transfer direction of the slurry.

[0014] As a preferred technical solution of the above-mentioned flash steam utilization system, the steam generator is installed between the first flash tank and the preheating unit.

[0015] As a preferred technical solution of the above-mentioned flash steam utilization system, the preheating unit includes a first preheating tower and a second preheating tower. Along the transfer direction of the slurry, the second preheating tower, the first preheating tower and the reactor are connected in sequence. The second preheating tower is connected to the second flash tank and the first preheating tower is connected to the first flash tank.

[0016] As a preferred technical solution of the above-mentioned flash steam utilization system, the gas-liquid separator includes a shell and a liquid-separating baffle. The shell has a separation chamber inside and also forms an air inlet, an air outlet, and a liquid outlet that communicate with the separation chamber. The liquid-separating baffle is disposed on the airflow path between the air inlet and the air outlet, and the liquid outlet is located below the liquid-separating baffle. The air inlet is connected to the steam outlet of the flash unit, and the air outlet is connected to the steam generator.

[0017] As a preferred technical solution of the above-mentioned flash steam utilization system, the bottom surface of the outer shell is a slope, and the liquid outlet is located at the lowest point of the slope.

[0018] As a preferred technical solution of the above-mentioned flash steam utilization system, the liquid separation baffle has multiple bending structures to divide multiple bending channels in the separation chamber. When water vapor passes through the channels, sulfuric acid droplets will hit the liquid separation baffle and drip down.

[0019] As a preferred technical solution of the above-mentioned flash steam utilization system, the gas-liquid separator further includes a liquid storage tank, the upper end of which is connected to the liquid outlet, and the lower end of which has a closable drain port.

[0020] As a preferred technical solution of the above-mentioned flash steam utilization system, it also includes a sulfuric acid collection tank, the above-mentioned drain port is connected to the above-mentioned sulfuric acid collection tank through a sulfuric acid pipe, and a valve is installed on the above-mentioned sulfuric acid pipe.

[0021] The beneficial effects of this utility model are:

[0022] This invention provides a flash steam utilization system, comprising: a reactor, a preheating unit, a flash evaporation unit, and a steam generator. The preheating unit is connected upstream of the reactor, and the slurry, after being preheated in the preheating unit, can enter the reactor. The flash evaporation unit is connected downstream of the reactor and is used to flash-evaporate the reacted slurry; the generated steam can be introduced into the preheating unit through a steam pipe. The steam generator is installed on the steam pipe and can generate electricity from the steam; the steam can pass through the steam generator and then enter the preheating unit.

[0023] In operation, the slurry is first injected into the preheating unit, where it absorbs heat to initially raise its temperature before being injected into the reactor for reaction. This shortens the heating time and reaction time within the reactor, improving reaction efficiency. The resulting high-pressure slurry is injected from the reactor into the flash evaporation unit for depressurization, generating steam with relatively high heat and pressure. This steam is then introduced into the preheating unit as a heat source to preheat the slurry. A steam generator is installed between the flash evaporation unit and the preheating unit to generate electricity from the steam. This process recovers and reuses waste heat from the reaction, reducing energy consumption. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the description of the embodiments of this utility model will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on the content of the embodiments of this utility model and these drawings without creative effort.

[0025] Figure 1 A schematic diagram of the structure of the flash steam utilization system provided in this embodiment of the utility model;

[0026] Figure 2 for Figure 1 Cross-sectional view of a gas-liquid separator.

[0027] In the picture:

[0028] 1. Reactor;

[0029] 2. Preheating unit; 211. First preheating tower A; 212. First preheating tower B; 22. Second preheating tower;

[0030] 3. Flash evaporation unit; 311. First flash evaporator A; 312. First flash evaporator B; 32. Second flash evaporator;

[0031] 4. Steam generator; 41. Steam generator A; 42. Steam generator B;

[0032] 5. Gas-liquid separator; 501. Outer shell; 502. Liquid separating baffle; 503. Air inlet; 504. Air outlet; 505. Liquid outlet; 506. Liquid storage tank; 507. Liquid drain; 511. First gas-liquid separator A; 512. First gas-liquid separator B; 52. Second gas-liquid separator;

[0033] 6. Collection tank. Detailed Implementation

[0034] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, not the entire structure.

[0035] In the description of this utility model, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0036] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0037] In the description of this embodiment, the terms "upper," "lower," "right," etc., refer to the orientation or positional relationship shown in the accompanying drawings. They are used only for ease of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model. In addition, the terms "first" and "second" are only used for distinction in description and have no special meaning.

[0038] It should be noted that the flash steam utilization system of this application is used, but not limited to, in the smelting of laterite nickel ore, and can also be applied to other smelting production processes that require sulfuric acid and flash tanks. In this application, only the application of the flash steam utilization system to the smelting of laterite nickel ore is used as an example for illustration. The principle of the flash steam utilization system applied to the smelting of other ores is essentially the same as that applied to the smelting of laterite nickel ore, and will not be elaborated here.

[0039] like Figure 1 As shown, this utility model provides a flash steam utilization system, including: a reaction vessel 1, a preheating unit 2, a flash evaporation unit 3, and a steam generator 4. The preheating unit 2 is connected upstream of the reaction vessel 1, and the slurry, after being preheated in the preheating unit 2, can enter the reaction vessel 1. The flash evaporation unit 3 is connected downstream of the reaction vessel 1 and is used to flash evaporate the reacted slurry; the generated steam can be introduced into the preheating unit 2 through a steam pipe. The steam generator 4 is installed on the steam pipe and can generate electricity using the steam; the steam can enter the preheating unit 2 after passing through the steam generator 4.

[0040] In operation, the slurry is first injected into preheating unit 2, where it absorbs heat to initially raise its temperature before being injected into reactor 1 for reaction. This shortens the heating time in reactor 1, reduces reaction time, and improves reaction efficiency. The resulting slurry, under high pressure, is injected from reactor 1 into flash evaporation unit 3 for depressurization. Steam, possessing relatively high heat and pressure, is generated during this process and introduced into preheating unit 2 as its heat source to preheat the slurry. A steam generator 4 is installed between flash evaporation unit 3 and preheating unit 2 to generate electricity from the steam. This process recovers and reuses waste heat from the reaction, reducing energy consumption.

[0041] It should be noted that within the preheating unit 2, the unreacted slurry and the steam from the flash unit 3 can exchange heat through a heat exchange mechanism, which can prevent the slurry from being contaminated or reacting prematurely. The unreacted slurry and the steam from the flash unit 3 can also directly contact each other for heat exchange.

[0042] It should be noted that the basic principle of flash evaporation technology is that when a high-pressure saturated liquid enters a relatively low-pressure container, the sudden drop in pressure causes some of the saturated liquid to vaporize into saturated vapor. This is existing technology, and the specific mechanism will not be elaborated upon here.

[0043] It should be noted that the steam generator 4 is existing technology. For example, the steam generator 4 includes a turbine, which is driven by high-pressure steam to rotate, thereby generating electricity. Its specific working principle and mechanism will not be described in detail here.

[0044] Furthermore, the preheating unit 2 is equipped with a backup heat source device. In the initial stage of operation, before any slurry enters the flash unit 3, the flash unit 3 cannot provide steam to the preheating unit 2. At this time, the backup heat source device is activated to provide heat energy to the preheating unit 2 to heat the slurry. When steam begins to be generated in the flash unit 3, the backup heat source device can be selectively shut down or reduce its output power according to the usage scenario.

[0045] Because the steam generated by the flash evaporation unit 3 includes water vapor and some sulfuric acid droplets, and these sulfuric acid droplets are acidic, they can corrode the internal pipes when they enter the preheating unit 2 and / or the steam generator 4 along with the water vapor. Therefore, in this embodiment, the flash steam utilization system also includes a gas-liquid separator 5. The flash evaporation unit 3 can be connected to the steam generator 4 through the gas-liquid separator 5, which can separate the sulfuric acid droplets from the steam. Thus, after passing through the gas-liquid separator 5, the water vapor and sulfuric acid in the steam can be separated. The water vapor can then sequentially enter the steam generator 4 and the preheating unit 2, while the sulfuric acid droplets are intercepted, preventing them from corroding the preheating unit 2 and the steam generator 4.

[0046] Optionally, the flash evaporation unit 3 includes a first flash tank and a second flash tank 32. Along the direction of slurry transfer, the reactor 1, the first flash tank, and the second flash tank 32 are connected in series. This arrangement, by setting multiple flash tanks in series, allows for a gradual reduction in slurry pressure, preventing excessive pressure on the flash tanks and protecting each tank. Specifically, the pressure of the reacted slurry is P0, the pressure in the first flash tank is P1, and the pressure in the second flash tank 32 is P2, satisfying P0 > P1 > P2. After the slurry is discharged from the reactor 1, it first enters the first flash tank for initial depressurization, then enters the second flash tank 32 for further depressurization. After meeting the discharge requirements, it is discharged from the second flash tank 32.

[0047] Furthermore, flash evaporation unit 3 includes n 总 One flash evaporator, satisfying n 总 ≥2, where n1 flash tanks are the first flash tanks and the other n2 flash tanks are the second flash tanks. 32, satisfying n1 + n2 = n 总And n1≥1, n2≥1. Among them, n1 consecutive first flash tanks are connected in series, that is, the discharge port of the upstream first flash tank in two adjacent first flash tanks is connected to the inlet of the downstream first flash tank, and the inlet of the first first flash tank in the n1 first flash tanks is connected to the discharge port of reactor 1; n2 consecutive second flash tanks 32 are connected in series, that is, the discharge port of the upstream second flash tank 32 in two adjacent second flash tanks 32 is connected to the inlet of the downstream second flash tank 32, and the inlet of the first second flash tank 32 in the n2 second flash tanks 32 is connected to the discharge port of the last first flash tank, and the discharge port of the last second flash tank 32 is used to discharge the depressurized slurry.

[0048] It should be noted that, among the n1 first flash tanks, the pressure values ​​inside the first flash tanks decrease sequentially according to the order of slurry transfer; similarly, among the n2 second flash tanks 32, the pressure values ​​inside the second flash tanks 32 decrease sequentially according to the order of slurry transfer. Furthermore, the pressure inside the second flash tanks 32 is always lower than the pressure inside the first flash tanks.

[0049] Specifically, such as Figure 1 As shown, in this embodiment, n1 = 2, n2 = 1, and the two first flash tanks are denoted as first flash tank A311 and first flash tank B312, respectively. First flash tank A311 is located upstream of first flash tank B312. The inlet of first flash tank A311 is connected to the outlet of reactor 1, and the outlet of first flash tank A311 is connected to the inlet of first flash tank B312. The outlet of first flash tank B312 is connected to the inlet of second flash tank 32, and the outlet of second flash tank 32 is used to discharge the depressurized slurry.

[0050] Because the steam generated by the first flash tank is too hot to be used for preheating the slurry, in this embodiment, a steam generator 4 is positioned between the first flash tank and the preheating unit 2. The steam, after passing through the steam generator 4, cools to a suitable temperature before being introduced into the preheating unit 2 to preheat the slurry. This method fully utilizes the energy in the steam.

[0051] Optionally, the preheating unit 2 includes m 总 One preheating tower, m 总 It is a positive integer.

[0052] When m 总 When n = 1, preheating unit 2 has only one preheating tower. 总 Each flash tank can output steam to the same preheating tower, and multiple streams of steam mix in the steam pipe and / or in the preheating tower to preheat the slurry together.

[0053] Alternatively, based on the preheating temperature required for the operation, from n 总Several flash tanks whose output steam temperature is closest to the preheating temperature are selected to supply heat to the preheating tower.

[0054] Or, when m 总 When the value is greater than 1, the preheating unit 2 includes a first preheating tower and a second preheating tower 22. Along the direction of slurry transfer, the second preheating tower 22, the first preheating tower and the reactor 1 are connected in sequence. The second preheating tower 22 is connected to the second flash tank 32, and the first preheating tower is connected to the first flash tank.

[0055] The first preheating tower has m1 units, and the second preheating tower 22 has m2 units, satisfying 1 ≤ m1, 1 ≤ m2, and m1 + m2 = m 总 The system comprises m2 consecutive second preheating towers 22 connected in series. Specifically, in any two adjacent second preheating towers 22, the outlet of the upstream second preheating tower 22 is connected to the inlet of the downstream second preheating tower 22. The inlet of the first preheating tower 22 in the m2 series is used to collect unreacted slurry. Similarly, m1 consecutive first preheating towers are connected in series. Specifically, in any two adjacent first preheating towers, the outlet of the upstream first preheating tower is connected to the inlet of the downstream first preheating tower. The inlet of the first preheating tower in the m1 series is connected to the outlet of the last second preheating tower 22. The outlet of the last first preheating tower is connected to the inlet of the reactor 1.

[0056] It should be noted that, in the m1 first preheating towers, the temperature inside the first preheating towers increases sequentially according to the slurry transfer order; in the m2 second preheating towers 22, the temperature inside the second preheating towers 22 increases sequentially according to the slurry transfer order. Furthermore, the temperature of the second preheating towers 22 is lower than the temperature of the first preheating towers.

[0057] It should be noted that pumps are installed between adjacent preheating towers to pressurize the slurry and drive its flow.

[0058] like Figure 1 As shown, the first preheating tower is connected to the first flash tank in a one-to-one correspondence, and the second preheating tower 22 is connected to the second flash tank 32 in a one-to-one correspondence. There are two first preheating towers, designated as first preheating tower A211 and first preheating tower B212, respectively. Along the slurry transfer direction, first preheating tower A211 is located downstream of first preheating tower B212. That is, the slurry flows sequentially through second preheating tower 22, first preheating tower B212, and first preheating tower A211 before entering reactor 1. Correspondingly, steam from first flash tank A311 is introduced into first preheating tower A211, steam from first flash tank B312 is introduced into first preheating tower B212, and steam from second flash tank 32 is introduced into second preheating tower 22.

[0059] Furthermore, two steam generators 4 are provided, designated as steam generator A41 and steam generator B42 respectively; three gas-liquid separators 5 are provided, designated as first gas-liquid separator A511, first gas-liquid separator B512, and second gas-liquid separator 52 respectively. Along the steam transmission direction, the first flash tank A311, the first gas-liquid separator A511, and the steam generator A41 are sequentially connected to the first preheating tower A211; the first flash tank B312, the first gas-liquid separator B512, and the steam generator B42 are sequentially connected to the first preheating tower B212; and the second flash tank 32, the second gas-liquid separator 52, and the second preheating tower 22 are sequentially connected.

[0060] Furthermore, the output of steam generator A41 can be unidirectionally connected to the input of steam generator B42. That is, when the steam output from the first flash tank passes through steam generator A41 and its temperature is still higher than the preheating temperature required for operation, the steam can be fed into steam generator B42 to do work and release energy again. After the temperature is reduced, it is input to preheating unit 2 to preheat the slurry.

[0061] like Figure 2 As shown, optionally, the gas-liquid separator 5 includes a housing 501 and a liquid-separating baffle 502. The housing 501 has a separation chamber and also forms an air inlet 503, an air outlet 504, and a liquid outlet 505 that communicate with the separation chamber. The liquid-separating baffle 502 is disposed in the airflow path between the air inlet 503 and the air outlet 504, which can block the steam airflow so that sulfuric acid droplets collide with the liquid-separating baffle 502 and converge into large droplets that flow down. The liquid outlet 505 is located below the liquid-separating baffle 502 and is used to discharge the separated sulfuric acid. The air inlet 503 is connected to the steam outlet of the flash evaporation unit 3, and the air outlet 504 is connected to the steam generator 4.

[0062] Optionally, the bottom surface of the outer casing 501 is sloped, and the outlet 505 is located at the lowest point of the slope. This facilitates the collection of sulfuric acid at the outlet 505.

[0063] Optionally, the separating baffle 502 has multiple bends to create multiple bends in the separation chamber. When water vapor passes through the flow channels, sulfuric acid droplets will impact the separating baffle 502 and drip off. This multi-bend structure effectively separates sulfuric acid droplets from the water vapor, ensuring that the water vapor discharged from the outlet 504 does not contain sulfuric acid.

[0064] Optionally, the gas-liquid separator 5 also includes a storage tank 506, with an outlet 505 connected to the upper end of the storage tank 506 and a closable drain port 507 at the lower end. The separated sulfuric acid is collected in the storage tank 506 for temporary storage. When a certain amount is stored, the drain port 507 is opened to discharge it. Since the gas-liquid separator 5 is filled with high-pressure steam, the pressure of the high-pressure steam can automatically push the sulfuric acid out after the drain port 507 is opened.

[0065] Optionally, the flash steam utilization system also includes a sulfuric acid collection tank 6. A drain port 507 is connected to the sulfuric acid collection tank 6 via a sulfuric acid pipe, and a valve is installed on the sulfuric acid pipe to close the drain port 507. The sulfuric acid separated by the first gas-liquid separator 5 and the second gas-liquid separator 52 can be collected in the same sulfuric acid collection tank 6 for centralized collection, recovery, and reuse. It is easy to understand that the sulfuric acid collection tank 6 includes the necessary discharge structure to discharge the collected sulfuric acid.

[0066] Furthermore, the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the protection scope of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A flash steam utilization system, characterized in that, include: Reactor (1); A preheating unit (2) is connected upstream of the reactor (1). The slurry can enter the reactor (1) after being preheated by the preheating unit (2). Flash evaporation unit (3) is connected downstream of the reactor (1) and is used to flash evaporate the slurry after the reaction. The generated steam can be introduced into the preheating unit (2) through the steam pipe. A steam generator (4) is installed on the steam pipe and can generate electrical energy using the steam. The steam can enter the preheating unit (2) after passing through the steam generator (4).

2. The flash steam utilization system according to claim 1, characterized in that, It also includes a gas-liquid separator (5), the flash evaporation unit (3) can be connected to the steam generator (4) through the gas-liquid separator (5), and the gas-liquid separator (5) can separate sulfuric acid droplets in the steam.

3. The flash steam utilization system according to claim 1, characterized in that, The flash unit (3) includes a first flash tank and a second flash tank (32). Along the direction of slurry transfer, the reactor (1), the first flash tank and the second flash tank (32) are connected in series.

4. The flash steam utilization system according to claim 3, characterized in that, The steam generator (4) is located between the first flash tank and the preheating unit (2).

5. The flash steam utilization system according to claim 3, characterized in that, The preheating unit (2) includes a first preheating tower and a second preheating tower (22). Along the transfer direction of the slurry, the second preheating tower (22), the first preheating tower and the reactor (1) are connected in sequence. The second preheating tower (22) is connected to the second flash tank (32), and the first preheating tower is connected to the first flash tank.

6. The flash steam utilization system according to claim 2, characterized in that, The gas-liquid separator (5) includes a housing (501) and a liquid-separating baffle (502). The housing (501) has a separation chamber inside and also forms an air inlet (503), an air outlet (504), and a liquid outlet (505) that communicate with the separation chamber. The liquid-separating baffle (502) is disposed on the airflow path between the air inlet (503) and the air outlet (504). The liquid outlet (505) is located below the liquid-separating baffle (502). The air inlet (503) communicates with the steam outlet of the flash evaporation unit (3), and the air outlet (504) communicates with the steam generator (4).

7. The flash steam utilization system according to claim 6, characterized in that, The bottom surface of the outer shell (501) is a slope, and the liquid outlet (505) is located at the lowest point of the slope.

8. The flash steam utilization system according to claim 6, characterized in that, The liquid separation baffle (502) has multiple bends to divide multiple bends in the separation chamber. When water vapor passes through the flow channels, sulfuric acid droplets will hit the liquid separation baffle (502) and drip down.

9. The flash steam utilization system according to claim 6, characterized in that, The gas-liquid separator (5) also includes a storage tank (506), the upper end of which is connected to the outlet (505), and the lower end of which has a closable drain port (507).

10. The flash steam utilization system according to claim 9, characterized in that, It also includes a sulfuric acid collection tank (6), the drain port (507) is connected to the sulfuric acid collection tank (6) through a sulfuric acid pipe, and a valve is provided on the sulfuric acid pipe.

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