Drain recovery device

Abstract

To provide a drain recovery device which can inhibit occurrence of cavitation to perform water supply control from a drain tank continuously even if a water level in the drain tank gets to a full water level.SOLUTION: A drain recovery device includes: a drain tank 3 which recovers and stores drainage from a steam using device 8 which uses steam generated by a boiler body without releasing the drainage to atmospheric air; a drainage supply unit for supplying the drainage stored in the drain tank 3 to the boiler body; a water level detection unit 5 which detects a water level in the drain tank 3; a temperature detection unit 34 which detects a temperature in the drain tank 3; and a state control unit which controls a state of the device in a first state in which the drainage is stored in the drain tank 3 or a second state in which the drainage is blown. The state control unit controls the state of the device into the second state on the condition that the water level detected by the water level detection unit 5 reaches a predetermined water level and the temperature detected by the temperature detection unit 34 reaches a predetermined temperature when the state of the device is controlled in the first state.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a drain recovery device. [Background technology]

[0002] Conventionally, a closed-type boiler system has been proposed in which steam generated by a boiler is supplied to a load device, and drain generated by condensation of the steam used as a heat source in the load device is collected in a high-temperature, high-pressure state in a pressure-resistant sealed drain tank (also called a closed tank), and the drain is then supplied to the boiler again (see, for example, Patent Document 1). Also, when the water temperature in the sealed drain tank becomes higher than a predetermined value, control is performed to replenish water in order to lower the temperature in the tank. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2006-105442 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in conventional control, when the water temperature in the drain tank becomes high and the tank is already full or nearly full, it is not possible to supply the water required to lower the water temperature to an appropriate temperature. Meanwhile, the water temperature in the drain tank continues to rise due to the continuous collection of drain and pressure being applied. As a result, cavitation occurs in the feed water pump, reducing the amount of water supplied, and there is a risk that water cannot be supplied appropriately to the boiler body.

[0005] The present invention has been devised in consideration of the above-mentioned situation, and its purpose is to provide a drain recovery device that can suppress the occurrence of cavitation and continuously control the water supply from the drain tank, even when the water level in the drain tank is full. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, the drain recovery device of the present invention comprises a drain tank that recovers and stores drain from steam-using equipment that uses steam generated by a boiler body without releasing it to the atmosphere, a drain supply unit for supplying the drain stored in the drain tank to the boiler body, a water level detection unit that detects the water level in the drain tank, a temperature detection unit that detects the temperature in the drain tank, and a state control unit that controls the drain tank to either a first state in which drain is stored in the drain tank or a second state in which drain is blown out, and the state control unit controls the drain tank to the second state on the condition that, when controlled to the first state, the water level detected by the water level detection unit reaches a predetermined water level and the temperature detected by the temperature detection unit reaches a predetermined temperature.

[0007] According to the above configuration, the drain in the drain tank is blown out under the condition that the water level in the drain tank reaches a predetermined water level and the temperature in the drain tank reaches a predetermined temperature. Therefore, even if the water level in the drain tank rises and water cannot be replenished, the water level in the drain tank can be lowered to make it possible to replenish water. This lowers the temperature in the drain tank, suppresses the occurrence of cavitation, and allows continuous water supply control from the drain tank.

[0008] Preferably, the boiler includes a water supply unit capable of supplying water to the boiler body, and in response to being controlled to the second state, a process of supplying water to the boiler body by the water supply unit is performed.

[0009] According to the above configuration, water can be supplied to the boiler body in response to the drain being blown out, so that it is possible to prevent the boiler from having to stop operating.

[0010] Preferably, the state control unit controls the water level to the first state on the condition that the water level detected by the water level detection unit when controlling the water level to the second state is lower than a predetermined specific water level that is lower than the specified water level.

[0011] According to the above configuration, if the water level in the drain tank falls below a specific water level due to the drain being blown out, the drain can be stored again, thereby preventing the drain from being blown out more than necessary, which would result in a decrease in combustion efficiency.

[0012] Preferably, the specific process is performed on the condition that the number of times that the first state is controlled to the second state within a predetermined period of time reaches a predetermined number of times.

[0013] According to the above configuration, it is possible to carry out a specific process when, for example, there is a risk of the water quality in the drain tank decreasing due to excessive drainage being blown out.

[0014] Preferably, the specific process includes a process for issuing an alarm.

[0015] According to the above configuration, an alarm is issued if the drain is blown out too much, making it possible for the boiler manager or other such person to recognize that the drain is being blown out too much, for example, and that there is a risk of the water quality in the drain tank declining, and to take appropriate action. [Brief description of the drawings]

[0016] [Figure 1] 1 is a diagram for explaining a schematic configuration of a drain recovery device according to an embodiment of the present invention; [Diagram 2] 13 is a flowchart for explaining an example of a closed tank water supply continuation process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] <Overview of the configuration> Hereinafter, an embodiment of the present invention will be described with reference to the drawings. First, a schematic configuration of a drain recovery device according to this embodiment will be described with reference to Fig. 1. The drain recovery device 1 is a system used in a boiler, and as shown in Fig. 1, includes a boiler body 2, a closed type drain tank (closed tank) 3, a make-up water tank (open tank) 4, and a control unit 10 that performs various controls such as the operation of the boiler. The drain recovery device 1 also includes a plurality of lines that connect these devices and through which steam or water flows, a plurality of valves that open and close these multiple lines, and a plurality of pumps arranged on predetermined lines.

[0018] The boiler body 2 includes a burner and a combustion chamber, and heats the water tubes by burning fuel to heat the feed water supplied inside, generating steam, and supplies the generated steam to a load device (steam-using device) 8 through a steam supply line L1. The load device 8 uses the steam generated in the boiler body 2 as a heat source, and exchanges heat with an object to be heated.

[0019] The drain return line L3 supplies the drain discharged from the load equipment 8 to a drain tank 3 (closed tank) via a steam trap (not shown), and is equipped with a drain return valve V3 consisting of a normally closed motor valve.

[0020] The drain tank 3 is composed of a pressure vessel having pressure resistance. This drain tank 3 collects and stores drainage generated by condensation of steam generated by the boiler body 2 when the steam is used by the load equipment 8 (steam-using equipment) while maintaining high temperature and pressure without releasing the drainage to the atmosphere. The stored drainage is supplied to the boiler body 2 through a drain supply line L6 having a drain pump P6.

[0021] A water level detection unit 5 that detects the water level in the drain tank 3 is connected to the drain tank 3. The gas phase and liquid phase of the water level detection unit 5 and the drain tank 3 are connected to each other by a communication pipe. The communication pipe on the gas phase side is provided with a pressure sensor (pressure detection unit) 33 that detects the pressure in the drain tank 3. In addition, the drain tank 3 is provided with a temperature sensor (temperature detection unit) 34 at a position where the temperature of the liquid phase of the drain tank 3 can be detected. The pressure sensor 33 may be provided in the drain tank 3 or in the liquid phase (or gas phase) of the water level detection unit 5.

[0022] The water level detection unit 5 has an electrode rod 51. The water level detection unit 5 in this embodiment includes at least a first water level detection unit 51H and a second water level detection unit 51D, which are two electrode rods 51 with different lengths. The first water level detection unit 51H and the second water level detection unit 51D are arranged with their respective tips (lower ends) spaced apart from each other in the vertical direction. The first water level detection unit 51H detects a first water level HH. The second water level detection unit 51D detects a second water level DF that is lower than the first water level HH. The first water level HH is a water level that is determined in advance as a water level at which it is considered that there is no free capacity to add water required for cooling when the temperature inside the drain tank 3 reaches or exceeds the saturation temperature. For example, the first water level HH may be a water level lower than the full water level (such as a water level at which the tank becomes full immediately even if new water is added without sufficient cooling), or a water level that is considered to be full water. The second water level DF is a water level that allows the amount of water required to be poured into the drain tank 3 to cool the inside of the drain tank 3 to an appropriate temperature (predetermined temperature) when, for example, the temperature inside the drain tank 3 is high. Note that, although an example has been described in which an electrode rod 51 (electrode type water level detector) is used as the water level detector (water level detection unit 5) that automatically detects the water level, the present invention is not limited to this, and may be, for example, a float type water level detection device.

[0023] When the first water level HH is detected, it can be considered that the water level in the drain tank 3 is high (e.g., full), and there is no free capacity to add water to the drain tank 3 from outside. On the other hand, when the second water level DF is detected, it can be considered that the water level in the drain tank 3 is at a level at which the inside of the drain tank 3 can be cooled to an appropriate temperature by adding water to the drain tank 3 from outside, even if the temperature inside the drain tank 3 is high.

[0024] The make-up water supply line L7 has a make-up water pump P7 and a make-up water check valve Vc7 that prevents backflow in the direction of the make-up water pump P7, and supplies make-up water stored in an open-to-atmospheric make-up water tank (open tank) 4 to the drain tank 3. Supplying make-up water from the make-up water tank 4 to the drain tank 3 can lower the temperature of the drain in the drain tank 3. The make-up water tank 4 is equipped with a new water replenishment line L9, and a water level detector (not shown) adjusts the flow rate of the new water replenishment line L9 so that the water level in the make-up water tank 4 becomes a set water level. The new water replenishment line L9 has a new water pump P9 and a new water check valve Vc9 that prevents backflow in the direction of the new water pump P9.

[0025] The drain supply line L6 is provided with a drain pump P6 and a drain check valve Vc6 that prevents backflow toward the drain pump P6. In this embodiment, high-temperature drain in the drain tank 3 can be supplied to the boiler body 2 through the drain supply line L6. The drain supply line L6, the drain pump P6, and the drain check valve Vc6 are collectively referred to as a drain supply section.

[0026] The drain relief line L4 connects the upstream side of the drain return valve V3 of the drain return line L3 to the makeup water tank 4, and is provided with a drain relief valve V4 formed of a normally open motor valve.

[0027] The pressurized steam line L2 connects the steam supply line L1, which is the steam outlet side of the boiler body 2, to the drain tank 3, and is provided with a pressurizing valve V2 consisting of a motor valve. A pressure reducing valve (not shown) may be provided on the primary side of the pressurizing valve V2 as necessary. Depending on the pressure in the drain tank 3 detected by the pressure sensor 33, the control unit 10 controls the opening and closing of the pressurizing valve V2 so that the pressure in the drain tank 3 is kept constant.

[0028] The pressure relief line L5 connects the gas phase of the drain tank 3 to the makeup water tank 4, and is provided with a pressure relief valve V5 that opens when the pressure reaches a set pressure or higher. By controlling the pressure relief valve V5 to an open state, the pressure in the drain tank 3 can be reduced when the pressure in the drain tank 3 becomes too high.

[0029] Furthermore, a spare water supply line L8 is provided between the make-up water tank 4 and the boiler body 2 to supply make-up water from the make-up water tank 4 to the boiler body 2 when the drain pump P6 stops and drain cannot be supplied to the boiler body 2. This spare water supply line L8 is provided with an auxiliary pump P8 attached to the boiler body 2 and a spare water supply check valve Vc8 that prevents backflow in the direction of the auxiliary pump P8. The make-up water tank 4, the spare water supply line L8, the auxiliary pump P8, and the spare water supply check valve Vc8 are collectively referred to as a water supply section.

[0030] Further, a drain tank blow line L30 is connected to the bottom of the drain tank 3 in this embodiment, and the drain stored in the drain tank 3 can be discharged to the outside of the drain tank 3 by controlling the drain tank blow valve V30 to an open state. This makes it possible to lower the water level in the drain tank 3. The state control between a first state in which the drain is stored in the drain tank 3 and a second state in which the drain is blown is performed by the control unit 10 and the drain tank blow valve V30 (these are also referred to as a state control unit).

[0031] The control unit 10 is realized by a computer including an internal memory, a timer, and an arithmetic processing unit, and controls the operation of various devices related to the closed tank water supply control in this embodiment. The control unit 10 performs opening and closing control of various valves (pressurizing valve V2, drain return valve V3, drain relief valve V4, pressure relief valve V5, and drain tank blow valve V30) and on / off switching control of various pumps (drain pump P6, makeup water pump P7, auxiliary pump P8, and new water pump P9) based on the detection results detected by the pressure sensor 33, temperature sensor 34, water level detection unit 5 (electrode rod 51), etc. The auxiliary pump P8 may be controlled by a control unit on the boiler main body 2 side.

[0032] Here, when the water temperature in the closed tank approaches the saturation temperature, the NPSH becomes insufficient, and there is a risk of cavitation occurring in the feedwater pump that supplies water to the boiler body. If cavitation occurs in the feedwater pump, the amount of water supplied decreases, and appropriate water supply control to the boiler body cannot be performed. For this reason, in the closed tank water supply control that has been used to supply water to boilers, when the temperature in the closed tank becomes high enough to exceed a predetermined temperature, make-up water control is performed to replenish water from an open tank in order to lower the temperature in the closed tank.

[0033] In addition, in the closed tank water supply control, even when water is not being supplied to the boiler, the pressure in the closed tank (drain tank) is controlled to be kept at a predetermined value. Therefore, even when water is not being supplied to the boiler (stopped), for example, when the boiler is in standby mode, the temperature in the closed tank gradually rises due to the pressurization control. Therefore, when the boiler is started from the standby mode, the temperature of the water in the closed tank approaches the saturation temperature, and there is a risk of cavitation occurring in the water supply pump.

[0034] However, if the water level in the closed tank is full or nearly full, it is not possible to add make-up water, or even if make-up water is added, it is not possible to lower the temperature to an appropriate level. On the other hand, the water level in the closed tank can only be lowered by supplying water to the boiler body, but supplying water will cause the above-mentioned cavitation.

[0035] Therefore, in the drain recovery device 1 of this embodiment, a drain tank blow line L30 for blowing out the water in the drain tank (closed tank) 3 is provided in the drain tank 3, and is controlled to blow out the drain under predetermined conditions. As a result, even if water cannot be supplied to the boiler body 2 and the water level in the drain tank 3 is high, water can be replenished into the drain tank 3 to lower the temperature.

[0036] Furthermore, if chemical treatment for managing the pH of water is not performed in the drain tank 3 but is performed when the water is supplied to the boiler body 2, and if the drain in the drain tank 3 is blown out too much and the proportion of new water becomes greater than the drain, the pH may become low and corrosion may occur in the drain tank 3. Furthermore, if the chemical treatment is performed on the assumption that drain is included, there is a risk that water with a low pH may be supplied to the boiler body 2 if the pH management is insufficient in the chemical treatment when the water is supplied to the boiler body 2.

[0037] Therefore, the control unit 10 in this embodiment stores the number of times that blow control has been performed from the drain tank 3 in the storage unit, and when blow control has been performed a predetermined number of times or more, sets a specific flag that enables control to perform a specific process. For example, the count of the number of blows is reset on a daily basis, and when blow control has been performed a predetermined number of times (for example, 5 times) in one day (within 24 hours), a specific process is performed. The specific process is, for example, an alarm to notify an administrator or the like of the fact, or a process to drive the auxiliary pump P8 to supply water from the make-up water tank (open tank) 4 to the boiler body 2 via the spare water supply line L8. By supplying water from the make-up water tank 4 to the boiler body 2, new water is supplied to the boiler body 2. When the auxiliary pump P8 is driven, the drain pump P6 is stopped. After water is supplied from the auxiliary pump P8 to the boiler body 2, when there is no longer a risk of cavitation occurring in the drain pump P6, for example, when the temperature in the drain tank 3 becomes equal to or lower than the temperature T2, the supply of water from the auxiliary pump P8 is stopped and the drain pump P6 is restarted. The predetermined number of blows, which is a condition for setting the specific flag, is not limited to five times, and may be, for example, three times. Depending on the drain tank to which the present invention can be applied, the number of blows at which there is a risk of the pH of the water in the drain tank 3 dropping too much may be appropriately set as the predetermined number, taking into consideration the amount of drain blow and chemicals (type or timing of chemical treatment).

[0038] <Closed tank water supply control> 2 is a flowchart showing an example of the continuous water supply process to the closed tank of the drain recovery device 1 in this embodiment. The control unit 10 executes the continuous water supply process to the closed tank continuously at regular time intervals (for example, every second).

[0039] In step S01, it is determined whether the water level of the drain tank 3 (closed tank) detected by the water level detection unit 5 is equal to or higher than the first water level HH and whether the temperature in the drain tank 3 (closed tank) detected by the temperature sensor 34 is equal to or higher than T1. The temperature T1 is a temperature at which cavitation does not occur in the feedwater pump (drain pump P6) provided on the secondary side (drain supply line L6 side) of the drain tank 3 when the NPSH of the feedwater pump and the piping pressure loss to the feedwater pump are excluded from the pressure applied to the drain tank 3, for example. If the temperature in the drain tank 3 exceeds the temperature T1, there is a possibility that cavitation may occur in the drain pump P6.

[0040] When it is not determined in step S01 that the water level in the drain tank 3 is equal to or higher than the first water level HH and the temperature is equal to or higher than the temperature T1, the closed tank water supply continuation process is terminated.

[0041] When it is determined in step S01 that the water level in the drain tank is equal to or higher than the first water level HH and equal to or higher than the temperature T1, in order to enable the drain water supply to continue, the drain return valve V3 is controlled to a closed state and the drain tank blow valve V30 is controlled to an open state in step S02. With the drain return valve V3 in the closed state, no new drain flows into the drain tank 3, and with the drain tank blow valve V30 in the open state, the drain is blown out and the water level in the drain tank 3 drops.

[0042] In step S03, it is determined whether the water level in the drain tank 3 has fallen to or below the second water level DF. That is, when the second water level DF is no longer detected by the water level detection unit 5, it is determined that the water level in the drain tank 3 has fallen to or below the second water level DF. Step S03 is repeatedly performed until it is determined that the water level has fallen to or below the second water level DF.

[0043] When it is determined in step S03 that the water level in the drain tank 3 is equal to or lower than the second water level DF, the drain tank blow valve V30 is closed in step S04. If the water level is equal to or lower than the second water level DF, it can be assumed that a sufficient amount of water can be supplied from the makeup water tank 4 to the drain tank 3 to lower the temperature in the drain tank 3, so that it is possible to prevent more drainage than necessary.

[0044] In step S05, the blow counter is incremented by 1, so that the counter stored in the storage unit of the control unit 10 is updated.

[0045] In step S06, it is determined whether the blow counter stored in the control unit 10 has reached a predetermined number or more. If it is determined in step S06 that the blow counter has not reached the predetermined number or more, in step S07, make-up water control from the make-up water tank 4 (open tank) to the drain tank 3 (closed tank) is started. By supplying water (e.g., new water) to the drain tank 3 through the make-up water control, the temperature inside the drain tank 3 drops.

[0046] On the other hand, when it is determined in step S06 that the blow counter is equal to or greater than the predetermined number of times, a specific flag is set in step S10. The specific flag is a flag that enables specific processing, such as issuing an alarm to the boiler manager or supplying new water from the makeup water tank 4 to the boiler body 2. When the specific flag is set in step S10, the process proceeds to step S07. Note that makeup water control in step S07 may be performed before setting the specific flag in step S10.

[0047] In step S08, it is determined whether the temperature in the drain tank 3 detected by the temperature sensor 34 has become equal to or lower than temperature T2. Temperature T2 is a temperature lower than temperature T1, and is, for example, a temperature with a certain margin before the temperature at which cavitation may occur in the drain pump P6. Step S08 is repeatedly executed until it is determined that the temperature is equal to or lower than temperature T2. That is, make-up water control is performed until the temperature in the drain tank 3 becomes equal to or lower than temperature T2. Note that if the tank becomes full before the temperature becomes equal to or lower than temperature T2, blow control may be performed again.

[0048] After it is determined in step S08 that the temperature is equal to or lower than the temperature T2, in step S09, the control of makeup water from the makeup water tank 4 to the drain tank 3 is stopped, and the process ends.

[0049] Although not shown in the figure, the control unit 10 performs normal drain water supply control processing continuously at regular intervals (for example, 1 second) in addition to the closed tank water supply continuation processing. The normal drain water supply control is a conventional closed tank water supply control, which is a water supply control in which the drain stored in the drain tank 3 is supplied to the boiler body 2 under certain conditions. The normal drain water supply control is performed in parallel with the closed tank water supply continuation processing in this embodiment. For example, when the water level of the boiler body 2 drops, the drain recovery signal is turned ON and the drain pump P6 is driven (turned ON). In addition, when the water temperature of the drain in the drain tank 3 becomes a high temperature at which cavitation may occur (for example, a temperature slightly lower than the saturation temperature for the pressure applied to the drain tank 3), new water is supplied from the makeup water tank 4 to the drain tank 3, and makeup water control is performed until the temperature reaches a temperature at which cavitation is not likely to occur. The closed tank water supply continuation process of this embodiment is continuously executed regardless of whether the boiler is in a standby state and drain is not being supplied with water, or whether the boiler is in an operating state and drain is being supplied with water. When performing the open water supply (supplying water from the spare water supply line L8), which is a specific process, the operation of the drain pump P6 is stopped (turned off). When the closed tank water supply continuation process is completed, the drain return valve V3 is returned to the open state and normal drain water supply control process is performed.

[0050] As described above, in the drain recovery device 1 of this embodiment, the control unit 10 controls the drain tank blow valve V30 to a closed state to control the drain tank 3 to a first state in which the drain sent from the load device 8 is stored in the drain tank 3, and controls the drain tank blow valve V30 to an open state to control the drain tank 3 to a second state in which the drain in the drain tank 3 is blown out, on the condition that the water level in the drain tank 3 is detected by the water level detection unit 5 to reach a predetermined water level (for example, the first water level HH as a water level at which it is considered that there is no free capacity for storing water required for cooling) and the temperature in the drain tank 3 detected by the temperature sensor 34 reaches a predetermined temperature (for example, temperature T1 as a temperature slightly lower than the saturation temperature). As a result, even in a situation in which the water level in the drain tank 3 rises and water cannot be replenished into the drain tank 3, the water level in the drain tank 3 can be lowered to make it possible to replenish the water. As a result, the temperature in the drain tank 3 can be lowered, the occurrence of cavitation can be suppressed, and water supply control from the drain tank 3 can be continuously performed.

[0051] Furthermore, the drain recovery device 1 of this embodiment is provided with the make-up water tank 4 capable of supplying water to the boiler body 2, and water can be supplied to the boiler body in response to control to the second state in which the drain in the drain tank 3 is blown, thereby preventing the boiler from stopping operation. In addition, a specific flag is set in response to the drain being blown, so that, for example, a process of supplying water from the make-up water tank 4 to the boiler body 2 can be performed. This makes it possible to supply water to the boiler body 2 in cases where there is a risk of the water quality in the drain tank decreasing due to a situation in which the drain is blown too much.

[0052] Moreover, under the condition that the water level detected by the water level detection unit 5 during control to the second state in which the drain in the drain tank 3 is blown falls below a predetermined specific water level (e.g., second water level DF) that is lower than a specified water level (e.g., first water level HH), the drain tank blow valve V30 is closed to control to the first state in which the drain is stored in the drain tank 3. As a result, if the water level in the drain tank 3 falls below the specific water level, the drain can be stored again, thereby preventing the drain from being blown out more than necessary, which would result in a decrease in combustion efficiency.

[0053] Furthermore, in the drain recovery device 1 of this embodiment, a specific process such as issuing an alarm can be performed on the condition that the number of times that the drain is controlled from the first state in which the drain is stored in the drain tank 3 to the second state in which the drain in the drain tank 3 is blown reaches a predetermined number of times (for example, 5 times) within a predetermined period (for example, 24 hours). This makes it possible to make the boiler manager or the like recognize that the drain is being blown too much, and for example, there is a risk of a decrease in the water quality in the drain tank, and to take action.

[0054] The present invention is not limited to the above-described embodiment, and various modifications and applications are possible. Modifications of the above-described embodiment that can be applied to the present invention will be described below.

[0055] In the above embodiment, an example has been described in which the drain tank blow valve V30 is opened while the drain return valve V3 is closed in step S02. However, the present invention is not limited to this, and even when the drain tank blow valve V30 is opened, the drain return valve V3 may be maintained open, or the opening degree of the drain return valve V3 may be adjustable so that the amount of drain flowing into the drain tank 3 is reduced. In the present invention, even if drain has flowed into the drain tank 3, the drain can be blown out if the drain tank blow valve V30 is open, so that the water level in the drain tank 3 can be lowered.

[0056] In the above embodiment, the supply of new water from the makeup water tank 4 to the boiler body 2 (open water supply) has been described as a specific process that can be performed when blowing has been performed a predetermined number of times. However, the supply of new water from the makeup water tank 4 to the boiler body 2 may be performed when a specific condition is met regardless of whether blowing has been performed a predetermined number of times. For example, when the water level in the drain tank 3 in step S01 is equal to or higher than the first water level HH and the temperature T1, the supply of new water may be performed in parallel with the closed tank water supply continuation process (in response to the drain being blown). In that case, the operation of the drain pump P6 is stopped, and when the closed tank water supply continuation process is completed, the supply of new water from the makeup water tank 4 to the boiler body 2 (open water supply) is stopped and the operation of the drain pump P6 is resumed. Alternatively, the supply of new water to the boiler body 2 may be performed when the number of blows is less than a predetermined number (for example, the blow counter is 2). As a result, even if the water supply control from the drain tank 3 (closed tank) to the boiler main body 2 is temporarily stopped or the amount of water supply is reduced, water can still be supplied to the boiler main body 2, allowing the boiler to continue operating.

[0057] In the above embodiment, an example has been described in which the make-up water control from the make-up water tank 4 to the drain tank 3 is started in step S07 after the drain tank blow valve V30 is controlled to the closed state in step S04. However, this is not limiting, and make-up water control may be performed even if the drain tank blow valve V30 remains in the open state. For example, when a water level higher than the second water level DF is detected in step S03, make-up water control may be started, blowing and cooling may be performed, and if the temperature in the drain tank 3 is detected to be equal to or lower than T2, the drain tank blow valve V30 may be closed and the make-up water control may be stopped.

[0058] In the above embodiment, the temperature T1 is set as the temperature at which cavitation does not occur in the feedwater pump (drain pump P6) provided on the secondary side (drain supply line L6 side) of the drain tank 3 when the NPSH of the feedwater pump (drain pump P6) and the piping pressure loss to the feedwater pump are excluded from the pressure applied to the drain tank 3. Therefore, even if it is determined in step S01 that the water level of the drain tank 3 (closed tank) is equal to or higher than the first water level HH and the temperature in the drain tank 3 (closed tank) detected by the temperature sensor 34 is equal to or higher than T1, the supply of drain to the boiler body 2 can be continued. However, this is not limited to the above, and when it is determined in step S01 that the water level of the drain tank 3 is equal to or higher than the first water level HH and the temperature in the drain tank 3 detected by the temperature sensor 34 is equal to or higher than T1, the drain pump P6 may be stopped well before cavitation occurs. Alternatively, a temperature corresponding to the saturation temperature may be set as the temperature T1, and the drain pump P6 may be stopped if it is determined in step S01 that the temperature is equal to or higher than the temperature T1. In the case where the drain pump P6 is stopped when it is determined in step S01 that the temperature is equal to or higher than the temperature T1, the drain pump P6 may be driven after it is determined in step S08 that the temperature is equal to or lower than the temperature T2. In addition, while the drain pump P6 is stopped, the auxiliary pump P8 may be driven to supply water from the makeup water tank 4 to the boiler body 2.

[0059] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0060] 1 Drain recovery device 2 Boiler body 3 Drain tank 4. Make-up water tank 5 Water level detector 51 Electrode rod 8 Loading equipment (steam-using equipment) 10 Control section 33 Pressure sensor (pressure detection part) 34 Temperature sensor (temperature detection part) L1 Steam supply line L2 Pressurized steam line L3 Drain return line L4 Drain relief line L5 Pressure relief line L6 Drain supply line L7 Make-up water supply line L8 Auxiliary water supply line L9 New water replenishment line L30 Drain tank blow line V2 Pressure Valve V3 Drain return valve V4 drain relief valve V5 Pressure Relief Valve V30 Drain tank blow valve Vc6 drain check valve Vc7 Makeup water check valve Vc8 Reserve water supply check valve Vc9 New water check valve P6 Drain Pump P7 Make-up water pump P8 Backing Pump P9 New Water Pump

Claims

1. A drain tank that collects and stores drainage from a steam-using device that uses the steam generated by the boiler body without releasing it to the atmosphere; A drain supply unit for supplying the drain stored in the drain tank to the boiler body; a water level detection unit that detects a water level in the drain tank; A temperature detection unit that detects a temperature inside the drain tank; a state control unit that controls the drain tank to either a first state in which drain is stored in the drain tank or a second state in which drain is blown out, The state control unit controls the drain recovery device to the second state under the condition that, when controlled to the first state, the water level detected by the water level detection unit reaches a predetermined water level and the temperature detected by the temperature detection unit reaches a predetermined temperature.

2. A water supply unit capable of supplying water to the boiler body, The drain recovery device according to claim 1 , wherein, in response to the control to the second state, a process of supplying water to the boiler body by the water supply unit is performed.

3. The drain recovery device of claim 1 or claim 2, wherein the state control unit controls the device to the first state on the condition that the water level detected by the water level detection unit when controlled to the second state is less than a predetermined specific water level that is lower than the specified water level.

4. 3. The drain recovery device according to claim 1, further comprising: a specific process being performed on condition that a number of times that the first state is changed to the second state within a predetermined period of time has reached a predetermined number of times.

5. The drain recovery device according to claim 4 , wherein the specific process includes a process for issuing an alarm.

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