JP2012002384A - Drain recovery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a closed-type drain recovery system capable of preventing boiling of preheating water in an economizer.SOLUTION: The temperature of a drain in a drain tank 8 is detected by a temperature sensor 29. When reaching a set temperature, the make-up water of low temperature from a make-up water tank 15 is directly supplied to the drain serving as a liquid-phase part of the drain tank 8 through a liquid-phase water supply piping 17 in such a manner that the temperature of hot drain in the drain tank 8 is quickly lowered. The temperature of drain that is supplied to an economizer 2 from the drain tank 8 is rapidly lowered, to prevent boiling in the economizer 2.

Description

  The present invention relates to a drain recovery system that recovers drain discharged from a load device that uses steam from a boiler as a heat source and recirculates the drain to the boiler. More specifically, the drain discharged from the load device is a sealed drain. The present invention relates to a closed drain recovery system that recovers to a tank and returns to a boiler equipped with an economizer.

  Conventionally, in order to save boiler fuel costs and water, a drain recovery system has been proposed in which drain discharged from a load device is returned to a tank and reused. In this drain recovery system, the drain discharged from the load equipment is recovered in an open tank opened to the atmosphere, and the drain discharged from the load equipment is discharged to the atmosphere. There is known a closed system in which a high-temperature and high-pressure drain of 100 ° C. or higher collected in a closed tank that does not open to the boiler is supplied to the boiler (see, for example, Patent Document 1). .

  Further, in the boiler, an economizer is provided in an exhaust gas passage through which exhaust gas discharged from the boiler passes, and boiler water is preheated in the economizer to improve boiler efficiency.

JP 2006-105442 A

  In the case of a system with a high heat recovery rate in which the drain recovered in the closed type closed tank as described above is preheated by an economizer and supplied to the boiler, the economizer There is a problem in that the temperature of the drain (preheated water) preheated at the temperature becomes too high and the inside of the economizer boils and steam is generated, causing vibrations and pressure fluctuations, leading to a reduction in the life of boilers and economizers.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a closed-type drain recovery system capable of preventing boiling of preheated water in an economizer. .

  In order to achieve the above object, the drain recovery system of the present invention is configured as follows.

  (1) The drain recovery system of the present invention recovers drain discharged from load equipment using steam generated in a boiler into a sealed drain tank and supplies the drain recovered in the drain tank to the boiler A closed-type drain recovery system, wherein the drain supplied to the boiler is preheated by exhaust gas from the boiler, an economizer, water supply means for supplying makeup water to the drain tank, and the economizer Detection means for detecting the temperature of the drain, and control means for controlling the supply of the makeup water by the water supply means based on the detection output of the detection means.

  According to the closed-type drain recovery system of the present invention, the temperature of the drain supplied to the economizer from the sealed drain tank is detected, and the supply of makeup water to the drain tank is controlled based on the detected temperature. When the temperature of the drain supplied to the economizer is high and there is a risk of boiling in the economizer, low temperature makeup water can be supplied into the drain tank to lower the temperature of the high temperature drain, It is possible to prevent boiling in the economizer by lowering the temperature of the drain supplied from the drain tank to the economizer.

  (2) In a preferred embodiment of the drain recovery system of the present invention, the water supply means includes a liquid phase water supply path connected to a lower portion of the drain tank and supplying the makeup water to the liquid phase portion in the drain tank. The detection means includes a temperature sensor that detects the temperature of the drain in the drain tank, and the control means controls the supply of the makeup water to the liquid phase part based on the detection output of the temperature sensor. .

  The temperature sensor preferably detects whether or not the temperature of the drain in the drain tank has reached a set temperature, and this set temperature is preferably a temperature equal to or lower than the temperature at which the preheated water boils in the economizer.

  According to this embodiment, the temperature of the drain in the drain tank is detected by the temperature sensor, and based on this, the supply of makeup water to the liquid phase part in the drain tank is controlled, so that the drain tank supplied to the economizer When the temperature of the drain reaches a temperature that may cause boiling in the economizer, low-temperature makeup water is directly supplied to the hot drain, which is the liquid phase in the drain tank. Therefore, the temperature of the drain supplied from the drain tank to the economizer can be quickly lowered to prevent boiling in the economizer.

  (3) In the embodiment of the above (2), the water supply means is connected to an upper portion of the drain tank and supplies the makeup water to the gas phase portion in the drain tank; An injection unit that is provided at a water supply port of the water supply channel and injects the makeup water into the gas phase unit, and the control unit controls the supply of the makeup water to the gas phase unit by the injection unit. You may do it.

  According to this embodiment, since the makeup water is injected into the gas phase portion in the drain tank, the flash vapor discharged by flash evaporation in the drain tank can be condensed again and recovered as drain. The recovery rate is improved.

  (4) In the embodiment of the above (3), the detection means includes a pressure sensor for detecting the pressure in the drain tank, and the control means is based on the detection output of the pressure sensor, and You may make it control supply of the said makeup water to the said gaseous-phase part.

  The pressure sensor preferably detects whether or not the pressure in the drain tank has become equal to or lower than a set pressure, and this set pressure is a pushing pressure that does not cause cavitation in the feed water pump that supplies the drain in the drain tank to the economizer. The pressure is preferably equal to or higher than the so-called NPSH (Net Positive Suction Head).

  When the makeup water is injected into the gas phase part in the drain tank, the pressure in the drain tank decreases, and there is a risk that cavitation may occur in the water supply pump that supplies the drain in the drain tank to the economizer. When the pressure in the drain tank detected by the pressure sensor is high and cavitation does not occur in the water supply pump, it becomes possible to inject makeup water into the gas phase in the drain tank and collect flash vapor as drain The cavitation of the water supply pump can be prevented.

  (5) In the embodiment of the above (4), a water supply pump for supplying the drain collected in the drain tank to the economizer is provided, and the control means controls the water pump based on a detection output of the pressure sensor. You may make it control.

  According to this embodiment, when the drain is not sufficiently collected in the drain tank, the pressure in the drain tank detected by the pressure sensor is low, and cavitation may occur in the feed water pump, the feed water pump may be stopped. As a result, cavitation of the water supply pump can be prevented.

  (6) In a preferred embodiment of the drain recovery system of the present invention, the detection means includes a water level sensor for detecting a water level in the drain tank, and the control means is based on a detection output of the water level sensor. The supply of the makeup water to at least one of the liquid phase part and the gas phase part in the drain tank is controlled.

  According to this embodiment, since the makeup water is supplied to the liquid phase part and the gas phase part in the drain tank according to the water level in the drain tank detected by the water level sensor, the water level in the drain tank is kept within the required range. Can be maintained.

  (7) In another preferred embodiment of the drain recovery system of the present invention, the drain tank is connected to a steam header installed between the boiler and the load device via a pressure regulating valve.

  According to this embodiment, since the drain tank is connected to the high-pressure steam header via the pressure regulating valve, the pressure in the drain tank is maintained at a constant pressure that does not cause cavitation in the water supply pump that supplies the drain to the economizer. Therefore, it is possible to prevent cavitation of the water supply pump.

  According to the closed-type drain recovery system of the present invention, the temperature of the drain supplied from the sealed drain tank to the economizer is detected, and the supply of makeup water to the drain tank is controlled based on the detected temperature. Therefore, when the temperature of the drain supplied to the economizer is high and there is a risk of boiling in the economizer, low temperature makeup water can be supplied into the drain tank to reduce the temperature of the high temperature drain. The temperature of the drain supplied from the drain tank to the economizer can be lowered to prevent boiling in the economizer.

FIG. 1 is a diagram showing a configuration of a drain recovery system according to an embodiment of the present invention. FIG. 2 is a time chart for explaining the operation of the drain recovery system of FIG. FIG. 3 is a diagram showing a configuration of a drain recovery system according to another embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 is a diagram illustrating an example of a configuration of a drain recovery system according to an embodiment of the present invention.

  The boiler 1 of this embodiment includes an economizer 2 that preheats water supplied to the boiler 1 with exhaust gas. The steam generated in the boiler 1 by further heating the preheated water supplied from the economizer 2 is stored in the steam header 4 via the main steam pipe 3 and then used for steam via the steam pipe 5. It is supplied to a load device 6 such as an exchanger.

  Since the load device 6 uses the heat of the steam, the steam is deprived of heat and condensed to be drained and discharged from the load device 6. The drain discharged from the load device 6 is collected through a steam trap 7 into a drain tank 8 that is a sealed pressurized tank. Connected to the upper portion of the drain tank 8 is a pressurizing pipe 9 for introducing steam from the steam header 4 to pressurize the drain tank 8, and the pressurizing pipe 9 is used as a pressurizing control valve. A motor valve 10 is installed.

  The economizer 2 for preheating the feed water to the boiler 1 and the bottom of the drain tank 8 are connected by a feed water pipe 11, and a feed water pump 12, motor valve 13 and 1 Check valve 14 is installed. This motor valve 13 is ON / OFF controlled according to the water supply request of the boiler 1. A return pipe 36 is connected to the downstream side of the feed water pump 12 to return the feed water from the feed water pump 12 to the feed water pipe 11 when the motor valve 13 is OFF (closed). A backup pipe 33 that supplies makeup water directly from the makeup water tank 15 to the economizer 2 is connected to the downstream side of the first check valve 14 for backup in the event of a failure.

  A drain tank 8 and a makeup water tank 15 for supplying makeup water to the drain tank 8 are connected by a makeup water pipe 16. The makeup water pipe 16 serves as a liquid-phase water supply channel on the drain tank 8 side. It is branched into a liquid phase water supply pipe 17 and a gas phase water supply pipe 18 as a gas phase water supply path.

  A water supply pump 19 and a second check valve 20 are installed in the makeup water pipe 16 from the upstream side. The liquid-phase water supply pipe 17 is provided with a liquid-phase water supply motor valve 21 as a control valve for water supply. The liquid-phase water supply pipe 17 is connected to the lower part of the drain tank 8 and is connected to the liquid in the drain tank 8. Supply low-temperature makeup water directly to the drain that is the phase. Thus, the temperature of the high-temperature drain in the drain tank 8 can be quickly lowered by supplying the low-temperature makeup water directly from the liquid-phase water supply pipe 17 to the drain which is the liquid phase portion in the drain tank 8. .

  The gas-phase water supply pipe 18 is provided with a gas-phase water supply motor valve 22 as a water supply control valve. The gas-phase water supply pipe 18 is introduced into the upper portion of the drain tank 8 and is connected to a plurality of water supply ports. Are provided with a plurality of nozzles 23 serving as a plurality of injection units for injecting makeup water into the gas phase portion in the drain tank 8. When the replenishment water is injected from the nozzle 23 into the gas phase portion in the drain tank 8, the flash vapor recovered in the drain tank 8 and flash-evaporated can be condensed again and recovered as drain. Can be improved.

  In this embodiment, the makeup water pipe 16, the liquid phase water supply pipe 17, the gas phase water supply pipe 18, the water supply pump 19, the motor valves 21 and 22, and the nozzle 23 supply the makeup water from the makeup water tank 15 to the drain tank 8. An example of the water supply means to supply water is constituted.

  A discharge pipe 24 for discharging the flash vapor flashed in the drain tank 8 is connected to the upper part of the drain tank 8. The discharge pipe 24 is connected to the upper part of the makeup water tank 15 via a primary pressure adjustment valve 25. The recovery pipe 26 is connected. An overflow pipe 27 of the drain tank 8 is connected to the recovery pipe 26, and an overflow motor valve 28 is installed in the overflow pipe 27. Therefore, flush steam and overflowed drain from the drain tank 8 are recovered in the makeup water tank 15 via the recovery pipe 26. Since this makeup water tank 15 stores low-temperature makeup water, it can be an open tank whose upper side is opened, and a lower portion of this makeup water tank 15 is used to replenish makeup water. A supplementary pipe 35 is connected.

  In the drain tank 8, as an example of detection means, a temperature sensor 29 that detects the temperature of the drain in the drain tank 8, a water level sensor 30 that detects the water level in the drain tank 8, and a pressure that detects the pressure in the drain tank 8. Each sensor 31 is provided.

  The temperature sensor 29 detects whether or not the temperature of the drain in the drain tank 8 is equal to or higher than a set temperature. This set temperature is an upper limit temperature at which the preheated water in the economizer 2 does not boil or an upper limit temperature Set temperature below. The temperature sensor 29 only needs to be able to detect the temperature of the drain supplied to the economizer 2. Therefore, instead of detecting the temperature of the drain in the drain tank 8, the drain in the water supply pipe 11 from the drain tank 8 to the economizer 2 is used. The temperature may be detected.

  The pressure sensor 31 detects whether or not the pressure in the drain tank 8 is equal to or lower than a set pressure, and this set pressure is NPSH (Net Positive), which is a pushing pressure that does not cause cavitation in the water supply pump 12. Suction Head: Net suction head) or higher pressure. Since the pressure sensor 31 only needs to be able to detect the pressure in the drain tank 8, instead of being installed in the drain tank 8 itself, a place where the pressure equivalent to the pressure in the drain tank 8 can be detected, for example, the discharge pipe 24. May be installed on the primary side of the primary pressure regulating valve 25 in FIG.

  The water level sensor 30 includes a plurality of level switches, and detects, for example, each of the water levels LL, L, H, and HH from a low water level to a high water level, and gives a corresponding detection output.

  Based on the detection outputs of these sensors 29 to 31, as will be described later, the water supply pump 12, the water supply pump 19, the pressurization motor valve 10, the liquid phase water supply motor valve 21, the gas phase water supply motor valve 22, and the overflow A control unit 32 is provided as an example of a control unit that controls each unit such as the motor valve 28.

  When the water level in the drain tank 8 detected by the water level sensor 30 falls below the water level L, the control unit 32 turns on the water supply pump 19 to supply makeup water from the makeup water tank 15 to the drain tank 8. It continues until the water level in the tank 8 reaches the water level H.

  When the pressure in the drain tank 8 detected by the pressure sensor 31 exceeds the above set pressure, that is, when the pressure is such that NPSH does not become insufficient, this water supply is for gas-phase water supply in the gas-phase water supply pipe 18. The motor valve 22 is turned on to replenish the replenished water from the nozzle 23 to the gas phase portion in the drain tank 8 to supply water, and the flash vapor that has flashed and evaporated is condensed again and recovered as drain. In addition, when the pressure detected by the pressure sensor 31 is equal to or lower than the set pressure, if water is supplied to the gas phase portion, the pressure in the drain tank 8 decreases, and NPSH becomes insufficient, which may cause cavitation in the water supply pump 12. Therefore, instead of supplying water to the gas phase part in the drain tank 8, the liquid phase water supply motor valve 21 of the liquid phase water supply pipe 17 is turned on to supply water to the liquid phase part of the drain tank 8.

  In this embodiment, when the temperature of the drain in the drain tank 8 detected by the temperature sensor 29 is higher than the set temperature in order to prevent boiling of preheated water in the economizer 2, the control unit 32 The water supply pump 19 is turned on, and the liquid phase water supply motor valve 21 of the liquid phase water supply pipe 17 is turned on to supply low-temperature makeup water directly to the drain which is the liquid phase portion in the drain tank 8. As a result, the temperature of the hot drain in the drain tank 8, and thus the temperature of the hot drain supplied to the economizer 2, is quickly lowered to prevent boiling in the economizer 2. This water supply continues until the detected drain temperature reaches the differential set value.

  The water supply to the liquid phase part is performed regardless of the pressure detected by the pressure sensor 31. Further, when the pressure detected by the pressure sensor 31 is equal to or higher than the set pressure at which NPSH is not insufficient and the water level in the drain tank 8 detected by the water level sensor 30 is equal to or lower than the water level H, the gas-phase water supply pipe The gas phase water supply motor valve 18 is turned on to supply water to the gas phase portion in the drain tank 8 by spraying makeup water from the nozzle 23.

  In this embodiment, when the water level in the drain tank 8 falls below the water level L, the water supply pump 19 is turned on to supply makeup water from the makeup water tank 15 to the drain tank 8. When the water level is maintained until the water level reaches the water level H, and when the temperature of the drain in the drain tank 8 exceeds the set temperature, the water supply pump 19 is turned on and the liquid phase water supply pipe 17 is turned on. The water supply condition in which the motor valve 21 is turned on to supply makeup water to the liquid phase portion in the drain tank 8 and continue until the differential set value is reached is an OR condition.

  When the water level in the drain tank 8 detected by the water level sensor 30 is a low water level equal to or lower than the water level LL, the control unit 32 forcibly turns off (closes) the water supply pump 12 of the water supply pipe 11 so that the water level does not drop. ) To stop water supply to the economizer 2 of the boiler 1. In this case, when the water level in the drain tank 8 rises and becomes equal to or higher than the water level L due to the supply of makeup water from the makeup water tank 15, the water supply pump 12 is forcibly turned off.

  When the pressure in the drain tank 8 detected by the pressure sensor 31 is equal to or lower than the set pressure, that is, when there is a possibility that the NPSH will be insufficient, the control unit 32 supplies water to prevent cavitation from occurring in the water supply pump 12. The pump 12 is forcibly turned off.

  Further, in order to prevent cavitation of the water supply pump 12, the control unit 32 turns on the pressurizing motor valve 10 of the pressurizing pipe 9 and steams when the pressure detected by the pressure sensor 31 is equal to or lower than the set pressure. Steam is introduced into the drain tank 8 from the header 4 and pressurized.

  When the water level in the drain tank 8 detected by the water level sensor 30 becomes a high water level equal to or higher than the water level HH, the control unit 32 turns on the overflow motor valve 28 of the overflow pipe 27 to perform overflow. It continues until the water level in 8 becomes below the water level H.

  FIG. 2 is a time chart showing an example of the operation of each part of this embodiment.

  4A shows the water level in the drain tank 8 detected by the water level sensor 30, FIG. 4B shows the detection output of the temperature sensor 29, FIG. 4C shows the detection output of the pressure sensor 31, and FIG. FIG. 4D shows the state of the pressurizing motor valve 10 of the pressurizing pipe 9, FIG. 5E shows the state of the water supply pump 19, and FIG. 4F shows the gas phase water supply motor valve of the gas phase water supply pipe 18. 22 (g) shows the state of the liquid-phase water supply motor valve 21 of the liquid-phase water supply pipe 17, FIG. 11 (h) shows the state of the water supply pump 12, and FIG. The states of the overflow motor valve 28 are respectively shown.

  The detection output of the temperature sensor 29 in FIG. 5B is ON when the temperature is higher than the set temperature, and is OFF when the temperature is lower than the set temperature. The detection output of the pressure sensor 31 in FIG. When a differential value higher than the pressure is reached, it is turned OFF.

  In FIG. 2, a period T1 in which the water level in the drain tank 8 detected by the water level sensor 30 is a low water level below the water level LL, a period T2 in which the water level in the drain tank 8 is from the water level L to the water level H, The period T3 during which the water level is higher than the water level H, the period T4 during which the water level in the drain tank 8 is higher than the water level HH, the period T5 during which the water level in the drain tank 8 is from the water level H to the water level L, and the water level in the drain tank 8 is the water level. A period T6 below L and a period T7 where the water level in the drain tank 8 is a low water level below the water level LL are shown.

  Further, in each of the periods T1 to T7, the periods T1 (1) to T7 (in which the temperature of the drain in the drain tank 8 detected by the temperature sensor 29 shown in FIG. 1) and periods T1 (2) to T7 (2) that are equal to or higher than the set temperature (ON).

  Hereinafter, each period will be described sequentially.

(A) Period T1 In order to prevent the water level from being lowered in the low-level period T1 in which the water level in the drain tank 8 shown in FIG. 5 (a) is lower than the water level LL, as shown in FIG. 12 is forcibly turned off to stop water supply from the drain tank 8 to the economizer 2. Further, in order to raise the water level, the water supply pump 19 is turned on to supply makeup water from the makeup water tank 15 to the drain tank 8 as shown in FIG.

  Within this period T1, during the period T1 (1) in which the temperature of the drain in the drain tank 8 detected by the temperature sensor 29 shown in FIG. When the pressure in the drain tank 8 detected by the pressure sensor 31 shown in FIG. 4 exceeds the set pressure (OFF), the gas supply water motor valve 22 of the gas supply pipe 18 is shown in FIG. Is turned on, and makeup water is injected from the nozzle 23 into the gas phase portion in the drain tank 8 to supply water, and the flash vapor is condensed and recovered as drain.

  When the pressure in the drain tank 8 is equal to or lower than the set pressure (ON), water is not supplied to the gas phase part so that the pressure in the drain tank 8 does not decrease, as shown in FIG. The liquid phase water supply motor valve 21 of the liquid phase water supply pipe 17 is turned ON to supply makeup water to the liquid phase portion in the drain tank 8. At this time, the pressurizing motor valve 10 of the pressurizing pipe 9 is turned on to introduce steam from the steam header 4 to pressurize the drain tank 8 as shown in FIG.

  Further, in the period T1 (2) in which the drain temperature in the drain tank 8 detected by the temperature sensor 29 shown in FIG. As shown in (g), the liquid phase water supply motor valve 21 of the liquid phase water supply pipe 17 is turned ON, and the low temperature makeup water is directly supplied to the drain which is the liquid phase portion in the drain tank 8 to adjust the temperature of the drain. Decrease promptly.

  In this period T1 (2), when the pressure in the drain tank 8 detected by the pressure sensor 31 shown in FIG. 4C exceeds the set pressure (OFF), as shown in FIG. The gas-phase water supply motor valve 22 of the gas-phase water supply pipe 18 is turned on to supply water to the gas-phase portion in the drain tank 8 by spraying makeup water from the nozzle 23.

  Further, when the pressure in the drain tank 8 detected by the pressure sensor 31 is equal to or lower than the set pressure (ON), water is not supplied to the gas phase part so that the pressure in the drain tank 8 does not decrease. As shown in FIG. 4D, the pressurizing motor valve 10 of the pressurizing pipe 9 is turned on to introduce steam from the steam header 4 to pressurize the drain tank 8.

(B) Period T2 During the period T2 in which the water level in the drain tank 8 rises and the water level is the water level LH (from the water level L to the water level H), the water supply pump 12 is forcibly turned off. When the pressure in the drain tank 8 detected by the pressure sensor 31 shown in FIG. 4C exceeds the set pressure (OFF), cavitation of the feed water pump 12 does not occur. Therefore, as shown in FIG. When the water pump 12 is turned on to supply drain water from the drain tank 8 to the economizer 2 of the boiler 1, and when the pressure in the drain tank 8 is equal to or lower than the set pressure (ON), cavitation of the water pump 12 may occur. Since there is, the water supply pump 12 is turned OFF and the water supply to the economizer 2 is stopped.

  Within this period T2, during the period T2 (1) in which the drain temperature in the drain tank 8 detected by the temperature sensor 29 shown in FIG. When the pump 12 is turned on and drain water is supplied from the drain tank 8 to the economizer 2, the temperature of the drain in the drain tank 8 is lower than the set temperature, so that the preheated water does not boil in the economizer 2.

  Further, in the period T2 (2) in which the drain temperature in the drain tank 8 detected by the temperature sensor 29 shown in FIG. When the water supply pump 12 is turned on to supply water from the drain tank 8 to the economizer 2, the liquid phase water supply motor valve 21 of the liquid phase water supply pipe 17 is turned on as shown in FIG. Since the low temperature make-up water is directly supplied to the drain which is the liquid phase portion in the drain tank 8 and the temperature of the high temperature drain is quickly reduced, the temperature of the drain supplied to the economizer 2 is quickly reduced, and the economizer Boiling within 2 can be prevented.

  The operation of each other part is basically the same as that of the above-described period T1, and thus the description thereof is omitted.

(C) Period T3 In period T3 (1) in which the temperature in the drain tank 8 detected by the temperature sensor 29 shown in FIG. 4B is less than the set temperature (OFF), the water level in the drain tank 8 is When the water level rises and becomes the water level H, the water supply pump 19 is turned off as shown in FIG. 5E, and the gas-phase water supply pipe is turned off as shown in FIG. The gas-phase water supply motor valve 22 and the liquid-phase water supply motor valve 21 of the liquid-phase water supply pipe 17 are turned off to stop the supply of makeup water from the makeup water tank 15 to the drain tank 8.

  In this period T3 (1), when the pressure in the drain tank 8 detected by the pressure sensor 31 shown in FIG. 3C exceeds the set pressure (OFF), as shown in FIG. The pump 12 is turned on to supply water to the economizer 2 of the boiler 1. At this time, since the temperature of the drain in the drain tank 8 is less than the set temperature (OFF) as shown in FIG. 4B, the preheated water does not boil in the economizer 2.

  Further, when the pressure in the drain tank 8 is equal to or lower than the set pressure (ON), cavitation of the water supply pump 12 may occur, so the water supply pump 12 is turned off and water supply to the economizer 2 is not performed. As shown in d), the pressurizing motor valve 10 of the pressurizing pipe 9 is turned on to introduce steam from the steam header 4 to pressurize the drain tank 8.

  Further, in the period T3 (2) in which the temperature in the drain tank 8 detected by the temperature sensor 29 shown in FIG. ), The water pump 19 is turned ON, and the liquid phase water supply motor valve 21 of the liquid phase water supply pipe 17 is turned ON to turn on the liquid phase portion in the drain tank 8 as shown in FIG. A low temperature makeup water is directly supplied to a certain drain to quickly lower the temperature of the high temperature drain. In this period T3 (2), when the pressure in the drain tank 8 detected by the pressure sensor 31 shown in FIG. 3C exceeds the set pressure (ON), as shown in FIG. The pump 12 is turned on to supply water to the economizer 2 of the boiler 1. At this time, as described above, since the low-temperature makeup water is directly supplied to the drain which is the liquid phase portion in the drain tank 8 to quickly reduce the temperature of the high-temperature drain, the temperature of the drain supplied to the economizer 2 is reduced. It is possible to prevent the liquid from rapidly decreasing and boiling in the economizer 2.

  Further, when the pressure in the drain tank 8 is equal to or lower than the set pressure (ON), cavitation of the water supply pump 12 may occur, so that the water supply pump 12 is turned off and the economizer 2 is turned on as shown in FIG. Water is not supplied to Further, as shown in FIG. 4D, the pressurizing motor valve 10 of the pressurizing pipe 9 is turned ON to introduce steam from the steam header 4 to pressurize the drain tank 8.

(D) Period T4 In the period T4 when the water level in the drain tank 8 rises and the water level is higher than the water level HH, the overflow motor valve 28 of the overflow pipe 27 is shown in FIG. ON to overflow.

  Since the operation of each other part is basically the same as that in the above-described period T3, the description thereof is omitted.

(E) About period T5 In period T5 when the water level in the drain tank 8 falls and the water level is at the water level HL (from the water level H to the water level L), as shown in FIG. The overflow motor valve 28 is turned off.

  Further, in the period T5 (2) in which the temperature in the drain tank 8 detected by the temperature sensor 29 shown in FIG. 4B is equal to or higher than the set temperature (ON), the pressure sensor 31 shown in FIG. When the pressure in the drain tank 8 detected by the pressure exceeds the set pressure (OFF), the gas tank water supply motor valve 22 of the gas phase water supply pipe 18 is turned on as shown in FIG. Replenishment water is jetted from the nozzle 23 to the gas phase inside.

  The operations of the other units are basically the same as those in the above-described period T4, and thus the description thereof is omitted.

(F) Period T6 In the period T6 in which the water level in the drain tank 8 decreases and the water level is equal to or lower than the water level L, the water pump 19 is turned on as shown in FIG.

  In this period T6, in the period T6 (1) in which the temperature in the drain tank 8 detected by the temperature sensor 29 shown in FIG. When the pressure in the drain tank 8 detected by the pressure sensor 31 exceeds the set pressure (OFF), the gas-phase water supply motor valve 22 of the gas-phase water supply pipe 18 is turned ON as shown in FIG. Then, makeup water is injected from the nozzle 23 into the gas phase portion in the drain tank 8 to supply water, and the flash vapor is condensed and recovered as drain.

  Further, when the pressure in the drain tank 8 is equal to or lower than the set pressure (ON), the gas-phase water supply in the gas-phase water supply pipe 18 is shown in FIG. The motor valve 22 is turned off and water is not supplied to the gas phase section, and the liquid phase water supply motor valve 21 of the liquid phase water supply pipe 17 is turned on as shown in FIG. Supply makeup water to the liquid phase part.

  The operation of each other part is basically the same as that in the above-described period T5, and thus the description thereof is omitted.

(G) Period T7 In the period T7 in which the water level in the drain tank 8 is lowered and the water level is lower than the water level LL, the feed pump 12 is forcibly turned off as shown in FIG. The

  Since the operation of each other part is basically the same as that in the above-described period T6, the description thereof is omitted.

  Note that FIG. 2 shows an example of operation control of each part, and it is needless to say that various changes and the like may be made within the scope of the present invention described in the claims.

  As described above, when the temperature of the drain in the drain tank 8 detected by the temperature sensor 29 becomes higher than the set temperature, the water pump 19 is turned on and the liquid phase water supply motor valve 21 of the liquid phase water supply pipe 17 is turned on. Is turned on and low temperature makeup water is directly supplied to the drain which is the liquid phase part in the drain tank 8 to quickly lower the temperature of the high temperature drain, so that the temperature of the drain supplied to the economizer 2 is quickly reduced. In addition, boiling in the economizer 2 can be prevented. Thereby, it is possible to prevent the preheated water from boiling in the economizer 2 in a system with a high heat recovery rate in which closed-type drain recovery is applied to a boiler with an economizer.

  Further, when the pressure in the drain tank 8 detected by the pressure sensor 31 exceeds the set pressure, the gas-phase water supply motor valve 22 of the gas-phase water supply pipe 18 is turned on and a nozzle is formed in the gas-phase portion in the drain tank 8. Since the replenishing water is jetted from 23 and supplied, the flash vapor discharged by flash evaporation in the drain tank 8 can be condensed again and recovered as drain, thereby improving the drain recovery rate.

  Further, when the pressure in the drain tank 8 detected by the pressure sensor 31 becomes equal to or lower than the set pressure and the NPSH is insufficient, the feed water pump 12 is turned off, so that cavitation of the feed water pump 12 can be prevented. When the pressure in the drain tank 8 detected by the pressure sensor 31 is equal to or lower than the set pressure, the pressurizing motor valve 10 is turned on to introduce high-pressure steam from the steam header 4. Can be increased.

  Further, based on the water level in the drain tank 8 detected by the water level sensor 30, water is supplied from the makeup water tank 15 to the drain tank 8, and the overflow motor valve 28 and the like are controlled, so that the water level in the drain tank 8 is controlled. The desired range can be maintained.

(Embodiment 2)
In the above embodiment, the pressurizing motor valve 10 is installed in the pressurizing pipe 9 and the pressure in the drain tank 8 is adjusted by controlling the pressurizing motor valve 10 based on the detection output of the pressure sensor 31. As another embodiment of the present invention, for example, as shown in FIG. 3, a secondary pressure adjusting valve 34 is provided in the pressurizing pipe 9, and the pressure in the drain tank 8 is adjusted to a constant pressure that does not cause NPSH shortage. You may make it do. In this case, the control of the pressurization motor valve 10 based on the detection output of the pressure sensor 31 can be omitted.

  Other configurations are the same as those in the first embodiment.

 The present invention is useful as a closed type drain recovery system.

DESCRIPTION OF SYMBOLS 1 Boiler 2 Economizer 4 Steam header 6 Load equipment 8 Drain tank 10 Pressurization motor valve 12 Water supply pump 15 Replenishment water tank 17 Liquid phase water supply pipe 18 Gas phase water supply pipe 19 Water supply pump 21 Liquid phase water supply motor valve 22 For gas phase water supply Motor valve 23 Nozzle 28 Overflow motor valve 29 Temperature sensor 30 Water level sensor 31 Pressure sensor 32 Control unit 34 Secondary pressure adjustment valve

Claims (7)

A closed-type drain recovery system that recovers drain discharged from load equipment that uses steam generated in a boiler into a closed drain tank and supplies the drain recovered in the drain tank to the boiler,
An economizer for preheating the drain supplied to the boiler with exhaust gas from the boiler;
A water supply means for supplying makeup water into the drain tank;
Detection means for detecting the temperature of the drain supplied to the economizer;
Control means for controlling the supply of the makeup water by the water supply means based on the detection output of the detection means;
A drain recovery system comprising: The water supply means includes a liquid phase water supply path connected to a lower portion of the drain tank and supplying the makeup water to a liquid phase portion in the drain tank,
The detection means includes a temperature sensor for detecting the temperature of the drain in the drain tank,
The control means controls the supply of the makeup water to the liquid phase part based on the detection output of the temperature sensor.
The drain recovery system according to claim 1. The water supply means is connected to an upper part of the drain tank and is provided in a gas phase water supply path for supplying the makeup water to the gas phase portion in the drain tank, and a water supply port of the gas phase water supply path, and the makeup water is provided. And an injection part for injecting the gas to the gas phase part,
The control means controls the supply of the makeup water to the gas phase part by the injection part,
The drain recovery system according to claim 2. The detection means includes a pressure sensor that detects a pressure in the drain tank, and the control means supplies the makeup water to the gas phase part by the injection part based on a detection output of the pressure sensor. To control the
The drain recovery system according to claim 3. A water supply pump for supplying the drain collected in the drain tank to the economizer;
The control means controls the water supply pump based on a detection output of the pressure sensor.
The drain collection system according to claim 4. The detection means includes a water level sensor that detects a water level in the drain tank, and the control means is configured to detect the liquid phase part and the gas phase part in the drain tank based on a detection output of the water level sensor. Controlling the supply of the makeup water to at least one of them,
The drain recovery system according to any one of claims 3 to 5. The drain tank is connected to a steam header installed between the boiler and the load device via a pressure regulating valve.
The drain recovery system according to any one of claims 1 to 6.

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