JP2023072143A - Boiler water supply piping system capable of preventing water hammer and boiler water supply method using the same - Google Patents

Abstract

To provide an inexpensive, simple water hammer-preventable boiler feedwater piping system capable of preventing the occurrence of water hammer.SOLUTION: A boiler feedwater piping system is provided in which a deaerated water storage tank 14 receiving boiler feedwater deaerated by a deaerator 13, a boiler feedwater pump 15 increasing the pressure of the boiler feedwater extracted from a bottom portion of the deaerated water storage tank 14, and a boiler drum 4 supplied with the pressure-increased boiler feedwater are connected in this order, and which comprises a feedwater control valve 17 which adjusts a flow rate of the boiler feedwater increased in pressure by the boiler feedwater pump 15. The boiler feedwater piping system comprises: a mechanical relief valve 16 which is disposed in delivery-side piping of the boiler feedwater pump 15 upstream from the feedwater control valve and extracts and returns a part of the boiler feedwater to the deaerated water storage tank 14 through return piping 18 when excessive pressure is applied to the boiler feedwater flowing on an upstream side of the feedwater control valve 17; a part of the boiler feedwater to the deaerated water storage tank 14 through return piping 18, in delivery-side piping of the boiler feedwater pump 15 upstream from the feedwater control valve; and second return piping 30 which comprises a water hammer preventing valve 31 always extracting and returning a part of the boiler feedwater to the deaerated water storage tank 14.SELECTED DRAWING: Figure 2

Description

TECHNICAL FIELD The present invention relates to a boiler water supply piping system and a boiler water supply method capable of preventing the occurrence of water hammer.

Dry firing occurs in boiler equipment, which is a device that creates steam or hot water with a desired pressure by heating boiler feed water circulating in the system with high-temperature combustion gas obtained by burning fuel such as coal. Since this leads to equipment damage, boiler water supply is controlled to ensure a stable supply. Specifically, a water supply control valve is provided in the water supply piping system that supplies boiler water to the boiler drum provided in the above system, thereby controlling the liquid level in the boiler drum within an appropriate range. is being carried out.

Since the operating conditions of the boiler equipment do not normally fluctuate greatly, the boiler feed water can be stably supplied to the boiler drum by the above control. Conditions may fluctuate greatly, and as a result, the degree of opening of the water supply control valve may fluctuate greatly, resulting in occurrence of water hammer in the water supply piping system.

Water hammer is a phenomenon in which an incompressible fluid such as water flowing through a piping system is suddenly stopped by closing a shut-off valve, etc., and as a result, its kinetic energy changes to pressure energy and propagates through the piping system. is. If the occurrence of such a water hammer is left unattended, it will lead to damage to the equipment and piping system. It has been proposed to stop the pressurizing means such as a pump provided at the water supply source of the system, thereby removing the pressure in the water supply piping system, and then activating the shutoff device. Alternatively, when the pressurizing means of the water supply source cannot be stopped, a method of suppressing sudden pressure fluctuations by gradually restricting the flow rate by the flow rate limiting means such as the water supply control valve is generally known.

Further, for example, as shown in Non-Patent Document 1, a pipe having a relief valve is branched from a connection pipe between a control valve that causes water hammer and a device equipped with a pump on the upstream side, and this branch pipe is connected to the return pipe of the device to construct a bypass circuit in the circulation pipe system. As a result, when excessive pressure is generated in the circulation piping system, the pressure can be released to the bypass circuit side via the relief valve, so that the pressure in the circulation piping system can be automatically adjusted. Therefore, it is possible to minimize damage to pipes and pumps due to water hammer.

JP 2019-105303 A

Abist Co., Ltd., "Method to prevent water hammer in piping", [Searched on October 1, 2021], Internet (URL: https://www.apiste.co.jp/column/detail/id=4605 #h3_5)

Although the occurrence of water hammer can be suppressed to some extent by taking the various measures described above, even if a bypass circuit having a mechanical relief valve is provided in the boiler water supply piping system, for example, at the time of startup of the boiler equipment, Water hammer still occurred in some cases under highly fluctuating operating conditions. SUMMARY OF THE INVENTION It is an object of the present invention to provide an inexpensive and simple boiler water supply piping system capable of suppressing the occurrence of water hammer.

In order to achieve the above object, the boiler feed water piping system according to the present invention comprises a degassed water storage tank for receiving boiler feed water degassed by a deaerator, and a boiler for pressurizing the boiler feed water extracted from the bottom of the degassed water storage tank. A boiler feedwater piping system, in which a feedwater pump and a boiler drum to which the pressurized boiler feedwater is supplied are connected in this order, and a feedwater control valve is provided for adjusting the flow rate of the boiler feedwater pressurized by the boiler feedwater pump. In the discharge side piping of the boiler feed water pump, the upstream side of the feed water control valve is provided with a part of the boiler feed water flowing through the upstream side, which is extracted through a return pipe when an excessive pressure is applied to the boiler feed water. A mechanical relief valve returning to the degassed water storage tank and a second return pipe equipped with a water hammer prevention valve that always extracts part of the boiler feed water at the time of startup and returns it to the degassed water storage tank are provided. It is characterized by

A boiler feed water method according to the present invention includes a degassed water storage tank for receiving boiler feed water degassed by a deaerator, a boiler feed water pump for increasing the pressure of the boiler feed water extracted from the bottom of the degassed water storage tank, and the boosting A boiler feed water method in a boiler feed water piping system comprising: When excessive pressure is applied to the boiler feedwater flowing upstream of the feedwater control valve in the discharge side pipe of the boiler feedwater pump, a mechanical relief valve is operated to extract part of the boiler feedwater and return it. A part of the boiler feed water is always supplied to the degassed water storage tank through a second return pipe provided on the discharge side pipe so that the mechanical relief valve does not operate at the time of start-up. It is characterized by returning the part.

ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to suppress generation|occurrence|production of the water hammer of a boiler feedwater piping system cheaply and simply.

1 is a schematic flow diagram of coal-fired boiler equipment to which the boiler water supply piping system of the present invention is preferably applied; FIG. 1 is a flow diagram of an embodiment of a boiler feedwater piping system of the present invention; FIG. FIG. 3 is a schematic longitudinal sectional view of a mechanical relief valve used in the boiler water supply piping system of FIG. 2; 1 is a block flow diagram of one specific example of a water supply method for a boiler water supply piping system of the present invention; FIG.

First, coal-fired boiler equipment to which the boiler feedwater piping system capable of preventing water hammer according to the present invention is suitably applied will be described with reference to FIG. The boiler shown in FIG. 1 is a circulating fluidized bed boiler, and this system can increase the superficial velocity in the furnace as compared with the fluidized bed boiler, so that the combustion efficiency can be improved. Specifically, the furnace 1 has a vertical cylindrical shape with a taper structure at the bottom, and the fuel coal fed through the coal supply facility 2 to the bottom of the furnace 1 is used for removing sulfur oxides. Combustion is performed while being fluidized by air introduced from below the furnace 1 together with limestone powder fed as a desulfurizing agent through the limestone supply equipment 3 and fluidized sand previously charged into the furnace 1 . The resulting radiant heat transfer of the combustion gas warms the boiler feed water flowing in the water tube group provided along the inner wall surface of the furnace 1, and steam is generated from the boiler drum 4 communicating with the water tube group.

Combustion gas exiting the furnace 1 is introduced into a cyclone 5, where solids such as fluidized sand and unburned coal that fly out of the furnace 1 with the combustion gas are collected and sent to the furnace 1 through a circulation path. returned. After that, the combustion gas is introduced into a heat recovery section 6, where heat is recovered by convective heat transfer by a superheater (superheater) 6a, an economizer (economizer) 6b, and a preheater 6c. The combustion gas heat-recovered by the heat recovery unit 6 is introduced into the electric dust collector 7 as combustion exhaust gas to be dust-removed, and then released to the atmosphere through the chimney 8 .

In the superheater 6a provided in the heat recovery section 6, saturated steam generated from the boiler drum 4 is heated to generate superheated steam for private power generation. The superheated steam generated by the superheater 6 a is introduced into the turbine generator 9 and used to rotate the turbine, then condensed in the condenser 10 and recovered in the boiler water supply tank 11 . Since air is dissolved in the collected boiler feed water, the dissolved gas is deaerated by the deaerator 13 and then sent to the deaerated water storage tank 14 described above. In the economizer 6 b of the heat recovery unit 6 , boiler feed water supplied from the degassed water storage tank 14 via the boiler feed water pump 15 is preheated. Further, in the preheater 6c of the heat recovery section 6, the air introduced from below the furnace 1 is preheated.

Next, an embodiment of the boiler water supply piping system of the present invention from the degassed water storage tank 14 located below the deaerator 13 to the boiler drum 4 of the above boiler equipment will be described in detail with reference to FIG. do. As described above, since oxygen and carbon dioxide in the air are dissolved in the boiler feed water recovered by condensing the steam discharged from the turbine generator 9 with the condenser (also referred to as a condenser) 10, Boiler drums and water tube groups corrode. Therefore, the boiler feedwater drawn from the bottom of the boiler feedwater tank 11 is introduced into the deaerator 13 after being pressurized by the deaerator feedwater pump 12 .

The deaerator 13 heats the boiler feed water with steam to make it saturated water, thereby removing the dissolved gas contained in the boiler feed water. The boiler feedwater deaerated by the deaerator 13 is temporarily received in the deaerated water storage tank 14 located below it, and then extracted from the bottom of the deaerated water storage tank 14 . After being pressurized by the boiler feed water pump 15, the feed water is introduced into the economizer 6b through a mechanical relief valve 16 and a feed water control valve 17, which will be described later. The economizer 6b is a device for preheating the boiler feed water using the residual heat of the combustion gas discharged from the furnace 1 as described above, and generally a corrugated tube heat exchanger is used. The boiler feedwater leaving the economizer 6b is supplied to the boiler drum 4.

The water supply control valve 17 is opened by a control means 20 such as a PLC (Program Logic Controller) or DCS (Distributed Control System) in order to prevent the boiler water supply to the boiler drum 4 from running dry due to insufficient boiler water supply. degree is controlled. In the control of this feed water control valve 17, in order to stabilize the liquid level of the boiler drum 4 more, as shown in FIG. The flow rate of boiler feed water supplied to the boiler drum 4 is controlled based on the three factors of the flow rate of high-pressure steam discharged from the boiler drum 4 and the flow rate of boiler feed water supplied to the boiler drum 4 measured by the boiler feed water flow meter 23. Three-factor control is preferably adopted. In this case, the set value of the boiler feed water flow rate controller is the sum of the flow rate of the high-pressure steam discharged from the boiler drum 4 and the controller output for controlling the liquid level in the boiler drum 4 at a constant level. Common.

As described above, the mechanical relief valve 16 is provided on the upstream side of the feedwater control valve 17, and operates when excessive pressure is applied to the upstream side, thereby opening the discharge side pipe of the boiler feedwater pump 15. A portion of the boiler feed water inside can be returned to the degassed water storage tank 14 via a return pipe 18 . This mechanical relief valve 16 has, for example, the structure shown in FIG. An inlet nozzle P and an outlet nozzle B are provided, respectively, and a liquid relief nozzle R is provided at the top to serve as an outlet for boiler feed water discharged in the direction of the black arrow during operation.

A valve body V for opening and closing a flow path to the liquid relief nozzle R is provided in the main body so as to be able to reciprocate. It is biased in the direction of closing the flow path to the liquid relief nozzle R side. With such a configuration, the pressure of the spring S is normally higher than the pressure of the boiler feedwater flowing through the main body, so the flow path to the liquid relief nozzle R is closed. When the pressure of the boiler feed water flowing through the discharge side pipe 15 exceeds the pressing force of the spring S, the valve body V moves upward and part of the boiler feed water is discharged from the liquid relief nozzle R in the direction indicated by the black arrow. , is returned to the degassed water storage tank 14 via the return pipe 18 . This makes it possible to suppress the occurrence of water hammer caused by the water supply control valve 17 .

However, at the start-up of the boiler, such as when the boiler equipment is started up after regular maintenance, the adjustment of the opening of the feed water control valve 17 is generally performed on the boiler drum 4 without performing the above three-element control. It is operated manually while observing the liquid level. Therefore, the pressure of the boiler feedwater flowing through the discharge side pipe of the boiler feedwater pump 15 is likely to fluctuate greatly, and water hammer occurs due to the closing of the valve body V of the mechanical relief valve 16 that automatically operates accordingly. It happened.

Therefore, in the boiler feedwater piping system of the embodiment of the present invention, as shown in FIG. , a part of the boiler feedwater flowing through the discharge side pipe is extracted and returned to the deaerated water storage tank 14 so that the mechanical relief valve 16 does not operate when excessive pressure is applied to the upstream side; A second return line 30 with a blocking valve 31 is provided.

With this configuration, by keeping the water hammer prevention valve 31 in an open state, the mechanical relief valve 16 is operated when excessive pressure is applied to the boiler water supply flowing in the discharge side pipe of the boiler water supply pump 15. A part of the boiler feed water can be extracted and returned to the deaerated water storage tank 14 through the second return pipe 30 provided with the water hammer prevention valve 31. As a result, it is possible to prevent water hammer in the boiler water supply piping system that may occur when the valve body V of the mechanical relief valve 16 is closed. The position where the second return pipe 30 equipped with the water hammer prevention valve 31 is branched from the piping system between the boiler feed water pump 15 and the feed water control valve 17 is a mechanical relief as indicated by the thick solid line in FIG. It may be on the downstream side of the valve 16, or it may be on the upstream side of the mechanical relief valve 16 as indicated by the thick dotted line.

The inner diameter of the second return pipe 30 is set when excessive pressure is applied to the boiler feed water flowing through the discharge side pipe of the boiler feed water pump 15 when the feed water control valve 17 is closed or when it is suddenly closed. In addition, since it is only necessary to discharge a part of the boiler feed water, it may be sufficiently narrower than the inner diameter of the discharge side pipe, which is the main pipe. If the nominal size is 10 inches, the pipe size of the liquid relief nozzle R of the mechanical relief valve 16 and the second return pipe 30 connected thereto may be about 2.5 inches in JIS B designation.

The branch point at which the second return pipe 30 branches from the discharge side pipe of the boiler feed water pump 15 is not particularly limited as long as it is upstream of the feed water control valve 17, but the outlet nozzle B of the mechanical relief valve 16 It is preferable to branch from the immediate vicinity. The second return pipe 30 may be connected to the degassed water storage tank 14, but connecting it to the return pipe 18 connected to the liquid relief nozzle R of the mechanical relief valve 16 enables a simple and inexpensive structure. Moreover, it is possible to prevent excessive pressure loss in the second return pipe 30, which is preferable.

Next, a method for supplying water from the boiler to the boiler drum 4 using the boiler water supply piping system of the embodiment of the present invention will be described in detail with reference to the block flow diagram of FIG. In the startup of the boiler equipment, first, the deaerator feed pump 12 and the boiler feed pump 15 are started with the water hammer prevention valve 31 provided in the second return pipe 30 opened, and the boiler feed is supplied to the boiler feed pipe system. circulate. At that time, the operation of the water supply control valve 17 is not performed by the three-element control by the control means 20 shown in FIG. After that, the controller 20 switches to single-element control in which the opening of the water supply control valve 17 is adjusted based on the liquid level in the boiler drum 4 .

As a result, a small amount of boiler feed water can always be extracted from the discharge side piping system of the boiler feed water pump 15 and returned to the degassed water storage tank 14, so that opening and closing of the feed water control valve 17 causes excessive pressure in the discharge pipe. However, the operation of the mechanical relief valve 16 can be suppressed. That is, at the time of the start-up, the valve body V of the mechanical relief valve 16 can be maintained in a closed state, and as a result, the occurrence of the water hammer phenomenon caused by the operation of the mechanical relief valve 16 can be prevented. can be done.

Next, after activating the blower for blowing air into the furnace 1 and igniting the burner, the raw material coal and limestone powder as the desulfurizing agent are introduced, and the furnace 1 is started up. After a while, when the boiler drum 4 stably generates high-pressure steam, the high-pressure steam is introduced into the turbine generator 9 . The circulation of boiler water supply in the boiler water supply piping system is stabilized, the operation of the turbine generator 9 by high pressure steam is stabilized, and the flow rate of high pressure steam generated from the boiler drum 4 exceeds about 15% of the boiler capacity. Around this time, the control by the control means 20 is switched from the single-element control to the three-element control. Furthermore, the water hammer prevention valve 31 of the second return pipe 30 is switched from the open state to the closed state. As a result, even during normal operation, the boiler feedwater pressurized by the boiler feedwater pump 15 is not wastefully returned to the degassed water storage tank 14, and the occurrence of water hammer in the boiler feedwater piping system can be prevented.

REFERENCE SIGNS LIST 1 furnace 2 coal supply facility 3 limestone powder supply facility 4 boiler drum 5 cyclone 6 heat recovery unit 6a superheater (superheater)
6b economizer
6c preheater 7 electrostatic precipitator 8 chimney 9 turbine generator 10 condenser 11 boiler water supply tank 12 deaerator water supply pump 13 deaerator 14 deaerated water storage tank 15 boiler water supply pump 16 mechanical relief valve 17 water supply control valve 18 return pipe 20 Control Means 21 Liquid Level Gauge 22 Steam Flow Meter 23 Boiler Feed Water Flow Meter 30 Second Return Pipe 31 Water Hammer Prevention Valve B Outlet Nozzle P Inlet Nozzle R Liquid Relief Nozzle S Spring V Valve Body

Claims (2)

A deaerated water storage tank for receiving boiler feed water deaerated by a deaerator, a boiler feed water pump for pressurizing the boiler feed water extracted from the bottom of the deaerated water storage tank, and a boiler drum to which the pressurized boiler feed water is supplied. A boiler feedwater piping system connected in this order and provided with a feedwater control valve for adjusting the flow rate of boiler feedwater pressurized by the boiler feedwater pump, wherein the feedwater control valve in the discharge side pipe of the boiler feedwater pump On the upstream side of the is a mechanical relief valve that extracts part of the boiler feed water flowing on the upstream side when excessive pressure is applied and returns it to the degassed water storage tank through a return pipe, and a boiler at the time of startup and a second return pipe provided with a water hammer prevention valve for always extracting part of the feed water and returning it to the degassed water storage tank. A deaerated water storage tank for receiving boiler feed water deaerated by a deaerator, a boiler feed water pump for pressurizing the boiler feed water extracted from the bottom of the deaerated water storage tank, and a boiler drum to which the pressurized boiler feed water is supplied. A method of supplying water to a boiler in a boiler water supply piping system, which is connected in this order and is provided with a water supply control valve for adjusting the flow rate of boiler water supply pressurized by the boiler water supply pump, wherein: When excessive pressure is applied to the boiler feedwater flowing upstream of the feedwater control valve, a mechanical relief valve is operated to extract a portion of the boiler feedwater and return it to the degassed water storage tank through a return pipe. a boiler feed water method characterized by constantly returning part of the boiler feed water to the degassed water storage tank through a second return pipe provided on the discharge side pipe so that the mechanical relief valve does not operate at the time of start-up. .

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