Method for feeding chemical to steam system

Abstract

The present invention is a method for feeding a chemical to a steam system that controls the injection of a water treatment chemical to the steam system, the method being for feeding a chemical to the steam system that comprises: a pressure sensor, a temperature sensor, or a steam trap as a steam circulation detection means provided to the steam system; and a chemical feed pump for injecting the water treatment chemical to the steam system, said steam system controlling the injection of the water treatment chemical by means of the chemical feed pump in accordance with the steam circulation detection status of the steam circulation detection means.

Description

Chemical injection method for steam system

[0001] The present invention relates to a chemical injection method for injecting chemicals into a steam system.

[0002] 2. Description of the Related Art Chemicals are injected into steam systems to maintain the efficiency or maintain the air supply piping and equipment that uses steam generated from boilers (steam generators).

[0003] Generally, chemical injection into steam systems has two purposes: to prevent corrosion in the steam condensate system of steam generating equipment, and to improve the heating efficiency of heat exchangers.

[0004] To prevent corrosion in the steam condensate system of steam generating equipment, anticorrosive components such as volatile neutralizing amines or film-forming amines, such as morpholine, may be added alone to the boiler feedwater, condensate system, or makeup water system, or a boiler chemical may be added that contains an anticorrosive component such as a volatile neutralizing amine or film-forming amine together with the anticorrosive agent for the boiler body.

[0005] In this case, some of the corrosion inhibitor remains in the boiler water, which requires the addition of an excessive amount of chemical, which is uneconomical.Furthermore, even in systems where the presence of the chemical in the steam is undesirable (for example, steam humidification systems or processes that directly heat steam), the chemical may be entrained in the steam.

[0006] Therefore, these corrosion inhibitors are sometimes added directly to the steam system (Patent Document 1).

[0007] In many cases, expensive steam flow meters are not installed on the steam lines, and a fixed amount of corrosion inhibitor is injected without an interlock on the chemical injection device. In such cases, the corrosion inhibitor continues to be injected even when the target equipment is shut down and steam is no longer flowing, and when the steam is re-fed, a high concentration of the agent is dispersed in the system, which can cause odor problems and other problems.

[0008] Furthermore, even when boiler steam is branched and used, corrosion inhibitors continue to be injected even when the equipment in question is shut down and steam is not flowing, and when the steam is re-circulated, high concentrations of the agent are dispersed throughout the system, which can cause odor problems and other problems.

[0009] In order to improve the heating efficiency of a steam heat exchanger, chemicals such as polyamines are sometimes used (Patent Document 2).

[0010] In this case, too, there is no steam flow meter, and even when the target equipment is shut down, the chemical injection device cannot be interlocked, which can result in excessive amounts of chemical being added, leading to odor problems and clogging of strainers due to the generation of sticky substances.

[0011] JP 2004-69182 A JP 2019-56524 A

[0012] The present invention has been made in consideration of the above-described conventional situation, and an object of the present invention is to provide a chemical injection method that can appropriately inject a chemical into a steam system while suppressing costs.

[0013] The gist of the present invention is as follows.

[0014] [1] A chemical injection method for a steam system for controlling the injection of a water treatment chemical into the steam system, the method comprising: a pressure sensor, a temperature sensor, or a steam trap as steam flow detection means provided in the steam system; a chemical injection pump for injecting the water treatment chemical into the steam system; and control of the injection of the water treatment chemical by the chemical injection pump in accordance with the steam flow detection status of the steam flow detection means.

[0015] [2] The method for injecting chemicals into a steam system according to [1], characterized in that the steam flow detection means is a sensor consisting of the pressure sensor or the temperature sensor, and operates the chemical injection pump when the detection value of the sensor is equal to or greater than a threshold value, and stops the chemical injection pump when the detection value of the sensor is less than the threshold value.

[0016] [3] The method for dosing chemicals into a steam system according to [1], characterized in that the steam flow detection means includes the steam trap and a steam flow detection sensor for the steam trap, and operates the chemical dosing pump when the steam flow detection sensor detects steam flow, and stops the chemical dosing pump when the steam flow detection sensor does not detect steam flow.

[0017] [4] The method of feeding a chemical to a steam system according to any one of [1] to [3], characterized in that a check valve with a siphon stop is provided in the chemical feeding pipe that leads the water treatment chemical from the chemical feeding pump to the steam system.

[0018] [5] The method of dosing chemicals into a steam system according to any one of [1] to [4], wherein the location of the steam flow detection means in the steam system and the injection point of the water treatment chemical from the chemical dosing pump into the steam system are located on the secondary side of a steam flow control valve provided in the steam system.

[0019] [6] The method for injecting a chemical into a steam system according to any one of [1] to [5], wherein the water treatment chemical is sprayed by a spray nozzle at an injection point of the water treatment chemical from the chemical injection pump into the steam system and injected into the steam system.

[0020] Steam systems are normally pressurized or heated by steam while the boiler and heat exchanger equipment are in operation, so their pressure and temperature are high. However, when the boiler stops operating, the temperature of the steam system drops, the steam volume in the steam system decreases, and the steam condenses into water, causing a significant drop in the pressure of the steam system.

[0021] In the present invention, a steam flow detection means is provided in the steam system, and the feeding of water treatment chemicals is controlled in accordance with the steam flow condition detected by the steam flow detection means.

[0022] In one aspect of the present invention, a pressure sensor or a temperature sensor is installed in a steam system, and when the detected value of the pressure sensor or the temperature sensor is equal to or greater than a threshold value, the chemical injection pump is operated, and when the detected value of the sensor is less than the threshold value, the chemical injection pump is stopped.

[0023] In another aspect of the present invention, the steam flow detection means of the steam system includes a steam trap and a steam flow detection sensor for the steam trap, and operates a chemical injection pump when the steam flow detection sensor detects steam flow in the steam trap, and stops the chemical injection pump when the steam flow detection sensor does not detect steam flow.

[0024] According to the present invention, by stopping the addition of water treatment chemicals to the steam system when steam supply to the steam system is stopped, it is possible to prevent problems caused by the addition of excessive amounts of chemicals. Furthermore, since excessive addition of chemicals can be prevented when the equipment is stopped, this is advantageous both economically and from the viewpoint of feasibility.

[0025] Fig. 1 is a system diagram of a boiler system according to an embodiment. Fig. 2 is a system diagram of a boiler system according to an embodiment. Fig. 3 is a system diagram of a boiler system according to an embodiment. Fig. 4 is a system diagram of a boiler system according to an embodiment.

[0026] In the present invention, the steam system includes, but is not limited to, piping and headers for sending steam from a boiler or the like, as well as a heat exchanger to which steam is supplied.

[0027] One aspect of the method of chemical injection into a steam system of the present invention uses a pressure sensor and a temperature sensor provided in the steam system that supplies steam to a manufacturing process, a chemical injection pump for injecting water treatment chemicals into the steam system, and a chemical injection control device that controls the injection of water treatment chemicals in response to signals from the pressure sensor and the temperature sensor, and adjusts the amount of chemicals added by the chemical injection pump in response to the detected value of the pressure sensor or the temperature sensor.

[0028] In one aspect of the present invention, an ON / OFF control is performed in which the chemical injection pump is turned ON when the detected value of the pressure sensor or temperature sensor is equal to or greater than a preset threshold value, and the chemical injection pump is turned OFF when the detected value is lower than the threshold value.

[0029] In another aspect of the present invention, the steam flow detection means of the steam system includes the steam trap and a steam flow detection sensor for the steam trap, and operates the chemical injection pump when the steam flow detection sensor detects steam flow in the steam trap, and stops the chemical injection pump when the steam flow detection sensor does not detect steam flow.

[0030] As the steam trap, any type of steam trap can be used, such as a mechanical steam trap, a thermostatic steam trap, or a thermodynamic steam trap.

[0031] Examples of mechanical steam traps include bucket-type mechanical steam traps and lever-type float-type mechanical steam traps.

[0032] Examples of thermostatic steam traps include bellows-type thermostatic steam traps and bimetal-type thermostatic steam traps.

[0033] Examples of thermodynamic steam traps include disc-type thermodynamic steam traps and air-insulated thermodynamic steam traps.

[0034] The steam flow detection sensor for detecting that steam is flowing through the steam trap may be a vibration sensor that detects vibrations that occur when the steam trap is opened or closed, a temperature sensor that detects the steam trap temperature that increases as steam flows through the steam trap, or an acoustic sensor that detects the sound generated from the steam trap due to steam flow through the steam trap.

[0035] In the present invention, in order to prevent excess chemicals from being sucked into the steam system even if the steam system becomes negative pressure when the equipment is stopped, it is preferable to provide a check valve with a siphon stopper in the chemical injection line from the chemical injection pump to the chemical injection point.

[0036] In one aspect of the present invention, the pressure sensor, temperature sensor, steam trap, and chemical injection point are installed on the secondary side (downstream in the steam flow direction) of a steam flow control valve provided in the steam system.

[0037] In addition, when water treatment chemicals are added to the entire steam flow rate from a boiler, rather than to a portion of the steam system, the boiler may be operated using a DSS (nightly start-stop operation) or WSS (weekend start-stop operation) method. In this DSS or WSS method, if the addition of water treatment chemicals to the steam system is stopped when the boiler is shut down, a pressure sensor, a temperature sensor, a steam trap, or a chemical injection point may be installed in addition to the secondary side of the steam flow control valve. For example, a pressure sensor, a temperature sensor, a steam trap, or a chemical injection point may be installed before or after the main steam valve immediately after the boiler body, in the steam header, or immediately before the heat exchanger.

[0038] The pressure sensor and the chemical injection point may be located close to each other or far apart. In addition, when multiple heat exchanger systems are installed and each system operates independently, it is desirable to install a pressure sensor and a chemical injection point separately.

[0039] The chemical is preferably in the form of a solution or dispersion and is delivered to the chemical injection point by a chemical injection pump.

[0040] In one aspect of the invention, water treatment chemicals are dispersed into the steam system by spraying them with spray nozzles at the injection points.

[0041] In the present invention, in order to prevent the check valve and chemical injection piping (hose) from being deteriorated by the heat of the steam system, it is desirable to install them at a sufficient distance from the steam system or to provide a loop section in the chemical injection piping.

[0042] Examples of water treatment chemicals to be added to the steam system include corrosion inhibitors as described in Patent Document 1 and heating efficiency improvers as described in Patent Document 2 and the like.

[0043] Specifically, this corrosion inhibitor may be any of a film-type corrosion inhibitor that forms a film on the pipe to prevent corrosion, a neutralization-type corrosion inhibitor that prevents corrosion by neutralizing acidic substances contained in water, and a composite corrosion inhibitor that combines a film-type corrosion inhibitor and a neutralization-type corrosion inhibitor.

[0044] Examples of the heating efficiency improver include long-chain fatty acid amines, such as polyamines represented by the following general formula (1).

[0045] R １-[NH-(CH ２ ) ｍ ] ｎ -NH ２ ...(1) (1) In the formula, R １ represents a saturated or unsaturated hydrocarbon group having 10 to 22 carbon atoms, m is an integer of 1 to 8, and n is an integer of 1 to 7. When n is 2 or more, a plurality of NH—(CH ２ ) ｍ may be the same or different.

[0046] Hereinafter, the embodiment will be described in more detail with reference to the drawings.

[0047] FIG. 1 is a diagram showing the configuration of a boiler system to which a chemical feeding method for a steam system according to an embodiment of the present invention is applied.

[0048] In FIG. 1, steam from a boiler 1 is sent through a pipe 2, passes through a flow control valve 3, and is sent to a heat exchanger 5 via a pipe 4.

[0049] The chemical liquid in the chemical tank 10 is supplied to the chemical injection nozzle (not shown) of the pipe 4 via the chemical injection pump 11, pipe 12, check valve with siphon stopper 13, and pipe 14, and is sprayed into the pipe 4 to perform chemical injection.

[0050] A pressure sensor 15 is provided in the pipe 4 , and its detection signal is input to a controller 16 , which controls the chemical injection pump 11 .

[0051] The controller 16 performs ON / OFF control by turning on the chemical injection pump 11 when the detection value of the pressure sensor 15 is equal to or greater than a preset threshold value, and turning off the chemical injection pump 11 when the detection value is lower than the threshold value.

[0052] It should be noted that one chemical injection pump may be controlled based on the detection signal of one pressure sensor, or multiple chemical injection pumps may be controlled based on the detection signal of one pressure sensor.

[0053] The same applies when a temperature sensor is used instead of the pressure sensor 11.

[0054] FIG. 2 is a configuration diagram of a boiler system to which a chemical dosing method according to another embodiment is applied.

[0055] 2, pressure sensor 15 is omitted. In this embodiment, a steam trap 18 is installed in steam piping 17 on the secondary side, i.e., downstream side, of heat exchanger 5, and a steam flow detection sensor 19 for steam trap 18 is provided in this steam trap 18, and a detection signal from this steam flow detection sensor 19 is input to controller 16. Controller 16 operates chemical injection pump 11 when steam flow detection sensor 19 detects steam flow in steam trap 18, and stops chemical injection pump 11 when steam flow detection sensor 19 does not detect steam flow.

[0056] As described above, the steam flow detection sensor 19 may be a vibration sensor that detects vibrations that occur when the steam trap 18 is opened or closed, a temperature sensor that detects the temperature of the steam trap 18 that rises as steam flows through the steam trap 18, or an acoustic sensor that detects sounds generated from the steam trap 18 due to the flow of steam through the steam trap 18.

[0057] The other configurations in FIG. 2 are the same as those in FIG. 1, and the same reference numerals denote the same parts.

[0058] Fig. 3 is a configuration diagram of a boiler system to which a chemical dosing method according to yet another embodiment is applied. In the boiler system of Fig. 3, the pressure sensor 15 and the controller 16 of the boiler system of Fig. 1 are omitted, and a pressure switch 22 is installed instead.

[0059] In FIG. 3, one end of a siphon tube 20 is connected to the piping 4 , and the other end of the siphon tube 20 is connected to a pressure switch 22 via a piping 21 .

[0060] A pipe 23 branches off from the pipe 21, and an air release valve 24 is provided at the tip of the pipe 23. Although not shown, the pipe 21 is provided with a pressure gauge.

[0061] The pipe 14 for introducing the chemical liquid from the chemical injection pump 11 is connected to this pipe 21 .

[0062] The siphon tube 20 is provided to reduce the heat transmitted from the piping 4 to the pressure switch 22 and the check valve 13, thereby protecting them.

[0063] The other configurations in FIG. 3 are the same as those in FIG. 1, and the same reference numerals denote the same parts.

[0064] In FIG. 3, when the pressure transmitted to the pressure switch 22 via the piping 21 is equal to or greater than a predetermined pressure, the pressure switch 22 activates the chemical injection pump 11, and when the pressure is lower than the predetermined pressure, the chemical injection pump 11 is stopped.

[0065] 3, the chemical supply pipe 14 is connected to the pipe 21, but as shown in FIG. 4, the pipe 14 may be configured to supply chemicals directly to the pipe 4 via a siphon pipe 25. The siphon pipe 25 is provided to reduce the transfer of heat from the pipe 4 to the check valve 13.

[0066] The other configurations and the control method of the chemical injection pump 11 in FIG. 4 are the same as those in FIG. 3, and the same reference numerals denote the same parts.

[0067] [Example 1] A boiler system having the configuration shown in Figure 1 was operated from Monday to Friday at a steady-state steam generation rate of 10 g / hr and a normal operating pressure of 0.78 MPa. The boiler operation was stopped on weekends (Saturday and Sunday).

[0068] The water treatment chemical in the chemical tank 10 was an 80 mass % aqueous solution of aminomethylpropanol. The chemical injection pump 11 was a diaphragm pump.

[0069] When the pressure detected by the pressure sensor 15 was 0.5 MPa or higher, the chemical solution was injected at 200 mL / hr, and when the pressure was less than 0.5 MPa, the chemical injection pump 11 was stopped.

[0070] In this embodiment 1, when the boiler was stopped on Saturday and Sunday, the pressure in the steam system dropped and the chemical dosing pump 11 was stopped.

[0071] As a result, no chemicals were added during the weekend shutdown of the steam facility, and there was no odor in the steam or condensed water when the facility was restarted.

[0072] Example 2 In Example 2, operation was carried out in the same manner as in Example 1, except that the check valve with siphon stopper 13 was not installed.

[0073] In this Example 2, when the boiler was shut down on the weekend, the pressure in the steam system dropped and the chemical pump was stopped. However, because there was no check valve with a siphon stopper, as the pressure in the steam system dropped, some of the chemicals in the chemical tank were sucked in by negative pressure, and 1 liter of chemicals was added to the system. As a result, the steam and condensed water had a slight odor when the system was restarted.

[0074] Comparative Example 1 In Comparative Example 1, regardless of the pressure detected by the pressure sensor 15, the chemical injection pump 11 always injected chemicals at 200 mL / hr, even when the boiler was stopped. Therefore, chemicals continued to be injected even when the boiler was stopped on Saturdays and Sundays (weekends). In addition, because the boiler operation was also stopped during the weekend equipment shutdown, the pressure in the system dropped to negative pressure, and some of the chemicals in the chemical tank 10 were sucked into the system. Therefore, when the boiler equipment was restarted on Monday, the following week, the steam and condensed water were odorous. Furthermore, when the amount of chemical liquid in the chemical tank 10 was examined, it was found that 13 liters of chemicals had been added to the system over just two days, Saturday and Sunday, even though the boiler equipment was stopped.

[0075] Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications are possible within the scope of the invention.

[0076] This application is based on Japanese Patent Application No. 2023-032905, filed on March 3, 2023, the entire contents of which are incorporated by reference.

[0077] REFERENCE SIGNS LIST 1 Boiler 5 Heat exchanger 10 Chemical tank 11 Chemical dosing pump 13 Siphon stopper check valve 15 Pressure sensor 16 Controller 18 Steam trap 19 Steam flow detection sensor 20, 25 Siphon pipe 22 Pressure switch

Claims

1. A method for dosing a water treatment chemical into a steam system, comprising: a pressure sensor, a temperature sensor, or a steam trap as steam flow detection means provided in the steam system; a chemical dosing pump for injecting a water treatment chemical into the steam system; and controlling the injection of the water treatment chemical by the chemical dosing pump in accordance with the steam flow detection status of the steam flow detection means.

2. The method for injecting chemicals into a steam system as described in claim 1, characterized in that the steam flow detection means is a sensor consisting of the pressure sensor or the temperature sensor, and when the detection value of the sensor is equal to or greater than a threshold value, the chemical injection pump is operated, and when the detection value of the sensor is less than the threshold value, the chemical injection pump is stopped.

3. The method for dosing a chemical to a steam system as described in claim 1, characterized in that the steam flow detection means comprises the steam trap and a steam flow detection sensor for the steam trap, and operates the chemical dosing pump when the steam flow detection sensor detects steam flow, and stops the chemical dosing pump when the steam flow detection sensor does not detect steam flow.

4. The method of feeding a chemical to a steam system according to claim 1, further comprising providing a check valve with a siphon stopper in a chemical feeding pipe for conducting the water treatment chemical from the chemical feeding pump to the steam system.

5. A method of dosing chemicals into a steam system as described in claim 1, characterized in that the location of the steam flow detection means in the steam system and the injection point of the water treatment chemicals from the chemical dosing pump into the steam system are located on the secondary side of a steam flow control valve provided in the steam system.

6. A method for injecting a chemical into a steam system as described in any one of claims 1 to 5, characterized in that the water treatment chemical is sprayed with a spray nozzle and injected into the steam system at the point where the water treatment chemical is injected from the chemical injection pump into the steam system.