JP2004278861A - Chemical flushing method for main steam pipe or reheating steam pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a chemical flushing method for a main steam pipe or a reheating steam pipe using a chemical flushing solution capable of performing flushing efficiently at low cost while the soundness of the apparatus is well secured by preventing the chemical flushing solution from flowing into the non-flush region without cutting the main steam pipe or the reheating steam pipe having a large bore and a large wall thickness. <P>SOLUTION: A seat 2 for flushing is formed in a vertical pipe 1b positioned in the uppermost stream about the steam flowing direction of the main steam pipe 1 having communication with an superheater tube, and a liquid level gauge 3 is installed leading from inside an outer cylindrical pipe 4 to inside the main steam pipe 1 upon penetrating the upper part of the outer cylindrical pipe 4 installed on the seat 2. The chemical flushing solution supplied from the seat 2 into the main steam pipe 1 is extracted out of a bonnet 12 and circulated via a provisionally provided circulation path 5, and chemical flushing is conducted. At this time of chemical flushing, the chemical flushing solution is prevented from flowing into the superheater tube by monitoring the liquid level of the solution on the liquid level gauge 3. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for chemically cleaning scale grown on the inner surface of a main steam pipe or a reheat steam pipe of a thermal power boiler or the like using a chemical cleaning liquid, and particularly to a superheater pipe or a reheat pipe communicating with these steam pipes. The present invention relates to a method for performing chemical cleaning while maintaining the integrity of a vessel.
[0002]
[Prior art]
FIG. 2 shows an example of a steam system of a thermal power boiler. In FIG. 2, steam generated by burning fuel in a furnace 22 by a burner 21 is supplied to a high-pressure turbine 27 through a steam separator 23, a boiler steam connection pipe 24, a superheater 25, and a main steam pipe 26. . Then, the steam that has worked in the high-pressure turbine 27 is sent to the reheater 29 through the low-temperature reheat steam pipe 28 and is heated, and passes through the high-temperature reheat steam pipe 30 to the medium-pressure turbine 31 and the low-pressure turbine 32. Supplied to do work. The steam that has worked in the low-pressure turbine 32 is condensed in the condenser 33, and then returned to the furnace 22 through the deaeration pipe 34 and the boiler feed pump 35.
[0003]
In the steam system of such a thermal power boiler, steam oxidation scale grows on the inner surface of the main steam pipe or the reheat steam pipe due to long-term operation, and when a certain thickness is reached, a part of the scale is separated and scattered. It may cause trouble such as turbine damage. Therefore, these scales are dissolved and removed by chemical cleaning.
[0004]
Conventionally, as a chemical cleaning method performed for such a purpose, a superheater pipe or a reheater pipe which communicates with a main steam pipe or a reheat steam pipe and is not subjected to chemical cleaning (hereinafter, referred to as “non-cleaning area”). Cut both ends of the superheater tube or reheater tube and connect a temporary pipe to pass the chemical cleaning liquid only to the target steam pipe in order to prevent the chemical cleaning liquid from flowing into and damaging its integrity. A method has been proposed (Japanese Patent Application Laid-Open No. Sho 64-23096, Japanese Utility Model Application Laid-Open No. Hei 4-3286). That is, as shown in FIGS. 3A and 3B, first, a portion 42A of the main steam pipe 42 communicating with the outlet portion (superheater outlet header) 41 of the superheater tube is cut off in the vicinity of the connecting portion. Then, the temporary pipe mounting adapter 43 is mounted. Then, the main steam stop valve 44 at the turbine inlet is opened, and a closing lid for preventing inflow to the turbine side is mounted inside. The temporary pipe mounting adapter 45 is attached to the main steam stop valve 44. The adapters 43 and 45 are connected by a temporary pipe 47 having a circulation pump 46 to form a circulation path, and the circulation pump 46 circulates a chemical cleaning solution to clean the inside of the main steam pipe 42.
[0005]
[Patent Document 1]
JP-A 64-23096 [Patent Document 2]
Japanese Utility Model Application Laid-Open No. Hei 4-3286 [0006]
[Problems to be solved by the invention]
However, in such a conventional chemical cleaning method, the main steam pipe and the reheat steam pipe having a large diameter and a large wall thickness are cut off before the chemical cleaning, and after the cleaning, the work for restoring the same is performed. This cutting and restoring requires a great deal of labor, cost and construction time.
[0007]
The present invention solves the above-mentioned conventional problems and prevents the flow of a chemical cleaning solution into a non-cleaning area without cutting a large-diameter thick-wall main steam pipe or a reheat steam pipe, thereby improving the soundness of equipment. An object of the present invention is to provide a method for chemically cleaning a main steam pipe or a reheat steam pipe, which can perform cleaning at a low cost and efficiently while securing the same.
[0008]
[Means for Solving the Problems]
The method for chemically cleaning a main steam pipe or a reheat steam pipe according to the present invention is a method for chemically cleaning the inside of a main steam pipe or a reheat steam pipe communicating with a superheater pipe or a reheat pipe using a chemical cleaning liquid. Installing a washing seat on the upper part of the vertical pipe located at the most upstream side in the steam flow direction of the steam pipe or the reheat steam pipe, and attaching a liquid level gauge to the washing seat; Supplying a chemical cleaning liquid into a steam pipe or a reheat steam pipe, wherein the level of the chemical cleaning liquid in the main steam pipe or the reheat steam pipe is monitored by the liquid level gauge, and the superheater pipe or the reheater is monitored. It is characterized in that the chemical cleaning liquid is prevented from flowing into the pipe.
[0009]
In the method of the present invention, the processing to be applied to the main steam pipe or the reheat steam pipe to be cleaned only requires installing a small-diameter cleaning seat. By monitoring the liquid level of the liquid level gauge attached to the cleaning seat, it is possible to easily prevent the chemical cleaning liquid from flowing into the superheater pipe or reheater pipe in the non-cleaning area, and to prevent the non-cleaning area during chemical cleaning. The soundness of the piping can be maintained. Therefore, according to the present invention, it is not necessary to cut the pipe before the chemical cleaning and restore the pipe after the chemical cleaning, and it is possible to greatly reduce the labor, time, and cost of cleaning the steam pipe.
[0010]
This liquid level gauge penetrates the upper part of the outer cylinder pipe attached to the washing seat, and at least a part thereof is formed into a transparent tubular member from the inside of the outer pipe to the inside of the main steam pipe or the reheat steam pipe. May be configured.
[0011]
The liquid level inside the tubular member can be monitored from the transparent portion of the tubular member.
[0012]
In the present invention, the upper end of the liquid level gauge is connected to the instrumentation seat or the air vent attached to the gas phase section above the level of the chemical cleaning liquid in the main steam pipe or the reheat steam pipe, and May be an inert gas atmosphere.
[0013]
In this way, even if water vapor evaporates from the interface of the cleaning liquid and condenses on the gas phase and the inner surface of the pipe in the non-cleaning area, it is possible to avoid secondary problems such as material corrosion and the like. It is possible to further ensure the performance.
[0014]
In the method of the present invention, the chemical cleaning liquid supplied into the main steam pipe or the reheat steam pipe is withdrawn from a downstream portion of the main steam pipe or the reheat steam pipe in the steam flow direction, and is provided outside the main steam pipe or the reheat steam pipe. May be circulated through a flow path provided in the apparatus.
[0015]
According to such circulating cleaning, the flow rate and the stirring action due to the circulation of the liquid are added, so that the cleaning effect can be further improved. In a long piping system such as a main steam pipe or a reheat steam pipe, the entire inside of the system can be uniformly circulated and cleaned by extracting the cleaning liquid from one end and returning the cleaning liquid to the other end. it can.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a method for chemically cleaning a main steam pipe or a reheat steam pipe according to the present invention will be described with reference to the drawings.
[0017]
FIG. 1 is a system diagram showing an embodiment of a method for chemically cleaning a main steam pipe according to the present invention.
[0018]
In this embodiment, the upstream end of the main steam pipe 1 to be subjected to chemical cleaning communicates with a superheater tube group in a non-cleaning area, and the downstream end is partitioned by a stop valve 11. The downstream side of the stop valve 11 is connected to a turbine (not shown).
[0019]
The upstream end side 1a of the main steam pipe 1 is drawn substantially horizontally, and a pressure gauge installation seat 15 or an air vent seat is provided in this portion. During normal operation, a pressure gauge (not shown) is attached to the seat 15.
[0020]
The portion of the main steam pipe 1 that continues to the upstream end side 1a is a vertical pipe section 1b that is routed substantially vertically.
[0021]
A hole having a diameter of about 100 mm is formed in the vertical pipe portion 1b, and a dedicated washing seat 2 is provided. An outer pipe 4 is connected to the washing seat 2 by a flange. The liquid level gauge 3 is attached to the outer pipe 4.
[0022]
The liquid level gauge 3 is formed of a transparent pipe, and an intermediate portion thereof is disposed vertically. One end (lower end) of the liquid level gauge 3 penetrates the outer pipe 4 and is inserted into the main steam pipe 1 from the inside of the outer pipe 4. The other end of the liquid level gauge 3 is connected to the pressure gauge installation seat 15. The middle of the liquid level gauge 3 is a substantially vertical vertical portion, and an openable / closable valve 3a is provided below the vertical portion. A pressure gauge 3P is connected to the lower side of the valve 3a.
[0023]
A television camera 3C is installed so as to monitor the liquid level inside the vertical part of the liquid level gauge 3.
[0024]
A gas relief valve 14 is provided above the liquid level gauge 3 (in the vicinity of the seat 15 in this embodiment), and the gas inside can be vented through the gas relief valve 14.
[0025]
A temporary circulation channel 5 for circulating the chemical cleaning liquid through the main steam pipe 1 is provided. The upstream end of the circulation flow path 5 is connected to a bonnet 12 of a stop valve 11 via a valve 5a. The downstream end of the circulation channel 5 is connected to the outer pipe 4 via a valve 5j. The circulation flow path 5 includes the valve 5a, the pipe 5b, the valve 5c, the circulation tank 6, the pipe 5d, the valve 5e, the pipe 5f, the valve 5g, the heat exchanger 7, which are sequentially arranged from the upstream side to the downstream side. A pipe 5h, a circulation pump 8, a pipe 5i and the valve 5j are provided.
[0026]
The heat exchanger 7 is for heating the chemical cleaning liquid, and is connected to a heating steam supply pipe 7a, and the pipe 7a is provided with a valve 7b. A chemical solution tank 9 storing a chemical cleaning chemical is connected to a pipe 5h on the downstream side of the heat exchanger 7 via a chemical injection pump 9a, a pipe 9b, and a valve 9c.
[0027]
A water supply tank 10 for supplying water for adjusting the concentration of the chemical cleaning solution and water for washing is connected to the pipe 5f via a water supply pipe 10a and a water supply valve 10b. The pipe 5b is connected to a pipe 5k for discharging waste water after washing, and the pipe 5k is provided with a valve 5m.
[0028]
The pipe 5b and the pipe 5f are connected by a bypass pipe 5p having a valve 5q so that the liquid can pass through the circulation tank 6 by bypass.
[0029]
At the time of the chemical cleaning, the valves 5q and 5m are closed, the valves 10b, 5a, 5c, 5g and 5j are opened, and the circulation pump 8 is operated to supply pure water from the water supply tank 10 and the circulation tank 6 is opened. The pure water is circulated in the circulation flow path 5 and the pipe from the washing seat 2 to the bonnet 12 of the main steam pipe 1, and the valve 7 b is opened to inject high-temperature steam into the heat exchanger 7 to circulate in the circulation system. Preheat water. Further, while circulating water, the valve 9c is opened and the chemical injection pump 9a is operated so that the high-concentration chemical cleaning solution in the chemical solution tank 9 is supplied from the pipe 9b so as to have a predetermined chemical cleaning solution concentration. Inject into 5. In the final stage, the liquid level is adjusted to an appropriate level by the liquid level gauge 3 while adjusting the water supply amount. At this time, the level gauge 3 can be monitored remotely by installing a television camera 3C. After the liquid level of the liquid level gauge 3 reaches a predetermined position, the valve 10b is closed to stop water supply. After the concentration of the chemical cleaning solution in the system reaches a predetermined concentration, the chemical injection pump 9a is stopped, and the valve 9c is closed to stop the chemical injection.
[0030]
In this state, the chemical cleaning liquid in the circulation system is heated by the heat exchanger 7 and maintained at a predetermined temperature while being circulated in the system by the circulation pump 8 for a predetermined time to perform chemical cleaning. After the completion of the chemical cleaning, the valve 5m is opened and the valve 5c is closed, and the chemical cleaning liquid in the system is drained from the pipes 5b and 5k to the drainage tank, and thereafter, is washed with water. The water washing step can be performed by supplying pure water from the water supply tank 10 and filling and circulating pure water in the circulation system in the same manner as described above except that the chemical cleaning agent is not injected. Alternatively, the cleaning may be performed by extrusion cleaning in which a part of the pure water from the water supply tank 10 is discharged into the drainage tank while being pushed into the circulation flow path 5.
[0031]
Such a series of cleaning steps is performed by the same procedure as that of ordinary chemical cleaning. In the present invention, by monitoring the liquid level of the liquid level gauge 3 so as not to rise from the vertical piping section 1b to the superheater pipe side during the cleaning step, the chemical cleaning liquid to the superheater side is monitored. Prevent inflow. If the liquid level of the liquid level gauge 3 tends to rise above a predetermined level, the valve 5m may be opened and a part of the liquid in the circulation system may be discharged to the drainage tank. If the liquid level is lower than the predetermined position, the valve 10b may be opened to supply pure water from the water supply tank 10.
[0032]
In this embodiment, an inert gas such as nitrogen or carbon dioxide gas is ventilated from the non-cleaning area side, and is released to the outside air from a gas relief valve 14 provided above the liquid level gauge 3 or an existing air vent tube. By setting the phase portion to an inert gas atmosphere, it is possible to prevent water vapor and mist volatilizing from the cleaning liquid from flowing into the non-cleaning area, thereby ensuring the soundness of the equipment and piping in the non-cleaning area. It will be more reliable. In addition, it is preferable that the ventilation of the inert gas is performed continuously, but it is not limited to this.
[0033]
In the present invention, as the chemical cleaning liquid, a liquid that is excellent in cleaning contaminants in the pipe to be cleaned can be used.For example, when the main steam pipe is used, the cleaning target is iron oxide. Since it is a so-called steam oxidation scale mainly composed of, for example, citric acid, glycolic acid, formic acid, or a mixture thereof, a chelating agent such as ethylenediaminetetraacetic acid, and ammonium citrate are generally used. The chemical cleaning solution may be prepared in advance at a predetermined concentration, but it is common to prepare a high-concentration chemical solution and dilute it to a predetermined concentration with water at the time of use. .
[0034]
INDUSTRIAL APPLICABILITY The chemical cleaning method of the present invention is extremely useful for chemical cleaning of large-diameter and thick-walled pipes such as a main steam pipe or a reheat steam pipe of a thermal power plant, while ensuring the soundness of equipment in a non-cleaning area. Thus, chemical cleaning of the main steam pipe or the reheat steam pipe can be performed at a low cost in a period significantly shorter than the conventional method of cutting and restoring both ends of the pipe.
[0035]
【The invention's effect】
As described in detail above, according to the method for chemically cleaning a main steam pipe or a reheat steam pipe of the present invention, a small-diameter cleaning seat is installed on a cleaning target without cutting a large-diameter, thick-walled steam pipe. By monitoring the liquid level of the liquid level gauge, the cleaning can be performed while easily preventing the chemical cleaning liquid from flowing into the non-cleaning area. Therefore, it is possible to significantly shorten the period of the chemical cleaning and reduce the cleaning cost.
[Brief description of the drawings]
FIG. 1 is a system diagram showing an example of an embodiment of a method for chemically cleaning a main steam pipe or a reheat steam pipe according to the present invention.
FIG. 2 is a system diagram of a steam system of a boiler.
FIG. 3 is a system diagram showing a conventional chemical cleaning method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Main steam pipe 2 Washing seat 3 Liquid level gauge 3C TV camera 4 Outer tube piping 5 Temporary circulation channel 6 Circulation tank 7 Heat exchanger 8 Circulation pump 9 Chemical tank 10 Water supply tank 9a Chemical liquid pump 11 Stop valve 12 Bonnet 14 Gas Relief valve 15 Pressure gauge installation seat

Claims (4)

In the method of chemically cleaning the inside of a main steam pipe or a reheat steam pipe communicating with a superheater pipe or a reheater pipe using a chemical cleaning liquid,
A step of installing a washing seat on the upper part of the vertical pipe located on the most upstream side of the main steam pipe or the reheat steam pipe in the steam flow direction, and attaching a liquid level gauge to the washing seat,
Supplying a chemical cleaning liquid from the cleaning seat into the main steam pipe or the reheated steam pipe,
The liquid level gauge monitors the level of the chemical cleaning liquid in the main steam pipe or the reheat steam pipe, and prevents the chemical cleaning liquid from flowing into the superheater pipe or the reheater pipe. Or a method for chemical cleaning of a reheat steam pipe. The liquid level gauge penetrates the upper part of the outer pipe attached to the washing seat, and extends from the inside of the outer pipe to the main steam pipe or the inside of the reheat steam pipe, at least a part of which is a transparent tube. The method for chemically cleaning a main steam pipe or a reheat steam pipe according to claim 1, comprising a member. The upper end of the liquid level gauge is connected to an instrumentation seat or an air release pipe attached to a gaseous phase section above the chemical cleaning liquid level in the main steam pipe or the reheated steam pipe, and the gas phase section is made inert. The method for chemically cleaning a main steam pipe or a reheat steam pipe according to claim 1 or 2, wherein the method is a gas atmosphere. The chemical cleaning liquid supplied into the main steam pipe or the reheat steam pipe was extracted from a downstream portion of the main steam pipe or the reheat steam pipe in the steam flow direction, and provided outside the main steam pipe or the reheat steam pipe. The method for chemically cleaning a main steam pipe or a reheat steam pipe according to any one of claims 1 to 3, further comprising a step of circulating through a flow path.

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