JP2016191527A - Chemical cleaning method for main steam pipe or reheat steam pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a chemical cleaning method capable of efficiently and sufficiently cleaning a main steam pipe or reheat steam pipe by preventing sedimentation of sludge, without using a large-sized pump or a pipeline having a large aperture and without enlarging the aperture of a cleaning seat.SOLUTION: In lateral pipe parts 6B, 6F, 6G of a reheat steam pipe 6, cleaning seats 21-24 are provided at the upper surface portions in the vicinities of vertical pipe parts 6A, 6D, 6E. On the upper surface of a bypass pipe 6H, a cleaning seat 25 is also provided. At the lower surface portions of the terminals of the lateral pipe parts 6F, 6G, cleaning seats 26, 27 are provided. A pump 45 causes cleaning liquid to circulate, cleaning liquid is pushed from cleaning liquid pushing nozzles 60 provided in the cleaning seats 21-25, and thereby segmentation of sludge is prevented.SELECTED DRAWING: Figure 1

Description

  The present invention has a main steam pipe such as a thermal power generation boiler or a reheat steam pipe (a boiler having one or two reheaters includes a first stage reheat steam pipe or a two stage reheat steam pipe). The present invention relates to a method of chemically cleaning a grown scale using a chemical cleaning liquid, and more particularly to a method of chemically cleaning while preventing sludge from accumulating in these steam pipes during cleaning.

  An example of the steam system of a thermal power generation boiler is shown in FIG. In FIG. 6, steam generated by burning fuel in the furnace 2 by the burner 1 is supplied to the high-pressure turbine 7 through the brackish water separator 3, boiler steam communication pipe 4, superheater 5, and reheat steam pipe 6. The The steam that has worked in the high-pressure turbine 7 is sent to the reheater 9 through the low-temperature reheat steam pipe 8 and heated, and then passed through the high-temperature reheat steam pipe 10 to the intermediate-pressure turbine 11 and the low-pressure turbine 12. Supplied to do work. The steam that has worked in the low-pressure turbine 12 is condensed in the condenser 13 and then returned to the furnace 2 again through the deaeration pipe 14 and the boiler feed water pump 15.

  FIG. 7 is a schematic perspective view showing the routing structure of the reheat steam pipe 6. The reheat steam pipe 6 includes a first horizontal part 6a that is substantially horizontal from the superheater outlet pipe 17 side, a vertical pipe part 6b that is routed in a substantially vertical direction, and a second horizontal part 6c that is substantially horizontal. Yes. The downstream end of the reheat steam pipe 6 is connected to a turbine inlet main steam stop valve 18.

  In the steam system of such a thermal power generation boiler, a steam oxidation scale grows with the operation for many years on the inner surface of the reheat steam pipe 6 or the reheat steam pipe 10, and a part of the steam oxidation scale peels off at a certain thickness. It will fly and cause troubles such as turbine damage. Therefore, these scales are dissolved and removed by chemical cleaning.

  Conventionally, as a chemical cleaning method performed for such a purpose, a superheater pipe or a reheater pipe (hereinafter referred to as “non-cleaning zone”) that communicates with a main steam pipe or a reheated steam pipe and is not subject to chemical cleaning. In order to prevent chemical cleaning liquid from flowing into the pipe and damaging its soundness, cut both ends of the superheater pipe or reheater pipe, connect a temporary pipe, and pass the chemical cleaning liquid only to the target steam pipe. A method has been proposed (Japanese Patent Laid-Open No. 64-23096, Japanese Utility Model Laid-Open No. 4-3286).

  However, in such a conventional chemical cleaning method, the main steam pipe and the reheat steam pipe having a large diameter and a large pipe thickness are cut prior to the chemical cleaning, and after the cleaning, the work for restoring this is performed. This cutting and restoration requires a great deal of labor, cost, and construction period.

  Japanese Patent Application Laid-Open No. 2004-278861 (Patent Document 3) prevents the inflow of chemical cleaning liquid into a non-cleaning area without cutting a large-diameter and thick main steam pipe or reheat steam pipe, and the soundness of the equipment. As a chemical cleaning method for the main steam pipe or the reheat steam pipe that can be cleaned at low cost and efficiently while ensuring the above, in the main steam pipe or the reheat steam pipe communicating with the superheater pipe or the reheat pipe In the method of chemically cleaning the main steam pipe or the reheat steam pipe, a cleaning seat is installed above the vertical pipe located on the most upstream side in the steam flow direction of the main steam pipe or the reheat steam pipe. A step of attaching a surface gauge and a step of supplying a chemical cleaning liquid from the cleaning seat into the main steam pipe or the reheat steam pipe, the chemical level of the chemical cleaning liquid in the main steam pipe or the reheat steam pipe by the level gauge Monitor the liquid level and connect to the superheater tube or reheater tube. How to prevent the inflow of academic cleaning liquid is described.

  In the method disclosed in Patent Document 3, the processing applied to the main steam pipe or the reheat steam pipe to be cleaned only needs to install a cleaning seat having a small diameter. By monitoring the liquid level of the level gauge attached to this cleaning seat, it is easy to prevent the chemical cleaning liquid from flowing into the superheater pipe or reheater pipe in the non-cleaning area, and the non-cleaning area during chemical cleaning. The soundness of the piping can be maintained. For this reason, it is not necessary to cut the pipe before chemical cleaning and to recover after chemical cleaning, and it is possible to greatly reduce the labor, time and cost of steam pipe cleaning.

  A chemical cleaning method using a cleaning seat is also described in JP2013-170762A (Patent Document 4).

JP-A 64-23096 Japanese Utility Model Publication No. 4-3286 JP 2004-278861 A JP2013-170762A

  In the chemical cleaning method for the main steam pipe or the reheat steam pipe in Patent Documents 3 and 4, the vertical pipe section (hereinafter sometimes referred to as a vertical pipe section) in the substantially vertical direction of the main steam pipe or the reheat steam pipe. In some cases, sludge accumulates in a substantially horizontal horizontal portion (hereinafter also referred to as a horizontal tube portion) connected to the lower end portion of the first through an elbow portion. That is, when the cleaning liquid flowing down the vertical pipe part flows into the horizontal pipe part from the elbow part, the sludge flowing along with the cleaning liquid tends to be deposited near the elbow part of the horizontal pipe part. In the portion where the sludge is accumulated, the scale is not sufficiently cleaned and removed because the inner surface of the main steam pipe or the reheat steam pipe is not sufficiently in contact with the cleaning liquid. The sludge that has not been removed may peel off when the boiler operation is resumed and fly to the turbine system, damaging the turbine equipment. In addition, the accumulated sludge remains in the circulation without being washed away, and this residual sludge may fly to the turbine system when the operation is resumed.

  Since this sludge has a large diameter and a large specific gravity, once it has accumulated, it is difficult to flow even if the cleaning liquid flow rate is increased. is there. For this purpose, it is necessary to use a large pump, increase the diameter of the cleaning liquid pipe, or increase the diameter of the cleaning seat in the case of Patent Documents 3 and 4. Further, the cleaning time is long.

  The present invention does not require the use of a large pump or a large-diameter pipe, and does not increase the diameter of the washing seat, preventing sludge accumulation and washing the main steam pipe or reheat steam pipe efficiently and sufficiently. It is an object of the present invention to provide a chemical cleaning method that can be performed.

  The chemical cleaning method of the main steam pipe or reheat steam pipe of the present invention is a method of chemically cleaning the inside of the main steam pipe or reheat steam pipe communicating with the superheater pipe or reheat steam pipe using a chemical cleaning liquid, A cleaning liquid inflow seat is provided upstream of the main steam pipe or the reheat steam pipe, a cleaning liquid outflow seat is provided in the downstream part, and the cleaning liquid is supplied into the main steam pipe or the reheat steam pipe through these seats. In the chemical cleaning method for a main steam pipe or a reheat steam pipe having a chemical cleaning step for circulating and cleaning the main steam pipe or the reheat steam pipe, the main steam pipe or the reheat steam pipe has a vertical pipe portion and a horizontal pipe connected to the lower end of the vertical pipe portion. A cleaning seat is provided on at least the upper surface portion of the horizontal tube portion in the vicinity of the vertical tube portion, and a cleaning liquid pushing nozzle is installed on the cleaning seat, and the main steam pipe or the reheat steam pipe is provided. When the cleaning liquid is circulated, the cleaning liquid flows out from the cleaning liquid pushing nozzle into the horizontal tube. It is characterized in preventing the deposition of sludge by.

  In one aspect of the present invention, the amount of washing liquid pushed from the washing liquid pushing nozzle is changed.

  In one aspect of the present invention, after the washing by the circulation of the washing liquid is completed, a washing process is performed in which washing water is supplied into the main steam pipe or the reheat steam pipe and washed, and the amount of water in the washing process is continuously increased. Or make it fluctuate intermittently.

  In one aspect of the present invention, after the water washing step, the washing seat is opened, a water ejection nozzle is inserted into the main steam pipe or the reheat steam pipe, and water is ejected from the water ejection nozzle to push away the sludge.

  In one aspect of the present invention, a cleaning seat is also provided on the upper surface portion of the bypass pipe communicating with the main steam pipes, a cleaning liquid pushing nozzle is provided in the cleaning seat, and the cleaning liquid is circulated in the main steam pipe or the reheat steam pipe. The cleaning liquid is allowed to flow out from the cleaning liquid pushing nozzle into the bypass pipe to prevent the accumulation of sludge. After the water washing step, the cleaning seat of the bypass pipe is opened and the water ejection nozzle is inserted into the bypass pipe. Then, water is ejected from the water ejection nozzle to sweep away the sludge.

  In one aspect of the present invention, the water ejection nozzle is provided at the tip of the hose, water can be ejected from both the hose side and the opposite side, and the ejection direction can be switched.

In the present invention, as the chemical cleaning liquid, a chemical cleaning liquid having excellent cleaning properties for contaminants in the pipe to be cleaned can be used. For example, when the main steam pipe is a target, the cleaning target is an iron oxide. Therefore, citric acid, glycolic acid, formic acid, or a mixture thereof, a chelating agent such as ethylenediaminetetraacetic acid, ammonium citrate, or the like is generally used. The chemical cleaning solution may be prepared in advance adjusted to a predetermined concentration, but it is general to prepare a chemical solution with a high concentration and dilute it with water to a predetermined concentration at the time of use. .

  In the chemical cleaning method for a main steam pipe or a reheat steam pipe according to the present invention, the main steam pipe or the reheat steam pipe is inserted into the main steam pipe or the reheat steam pipe via the chemical cleaning liquid inflow seat and the outflow seat provided at the upper and lower portions. In the method of chemically cleaning the main steam pipe or the reheat steam pipe by circulating the cleaning liquid in the reheat steam pipe, a cleaning seat is provided on the upper surface portion in the vicinity of the vertical pipe section of the horizontal pipe section, and the cleaning liquid installed in this cleaning seat Since the cleaning liquid is pushed into the horizontal tube portion from the pushing nozzle, the sludge is washed away in the vicinity of the washing seat, and sludge accumulation in the vicinity is prevented. Therefore, the lower surface of the horizontal tube near the cleaning seat is sufficiently chemically cleaned without flowing the cleaning liquid at a large flow rate. At this time, it is not necessary to use a large pump or a large-diameter pipe or to increase the diameter of the cleaning seat.

  By varying the amount of cleaning liquid pushed from the cleaning liquid pushing nozzle, sludge accumulation is effectively prevented.

  After the main steam pipe or the reheat steam pipe is washed with water after washing by circulation of the washing liquid, the washing seat is opened, the water jet nozzle is inserted into the main steam pipe or the reheat steam pipe, and water is jetted from the nozzle. As a result, the sludge can be washed away sufficiently.

  In the present invention, a bypass pipe is provided by providing a cleaning seat on an upper surface portion of a portion where sludge is likely to accumulate, such as a bypass pipe communicating with main steam pipes, and pushing a cleaning liquid or inserting a water ejection nozzle. Etc. can be sufficiently washed.

  In the present invention, the sludge in the main steam pipe or the reheat steam pipe can be sufficiently swept away by changing the amount of water jetted from the water jet nozzle.

  The chemical cleaning method of the present invention is extremely useful for chemical cleaning of large-diameter and thick-walled pipes such as main steam pipes or reheat steam pipes of thermal power plants, and ensures the soundness of equipment in non-cleaning areas. Thus, the main steam pipe or the reheat steam pipe can be chemically cleaned at a low cost in a significantly shorter construction period than the construction method of cutting and restoring both ends of the pipe.

It is a systematic diagram which shows the chemical cleaning method of the reheat steam pipe which concerns on embodiment. It is an enlarged vertical sectional view of a part of the horizontal tube portion. (A) is a perspective view of the front-end | tip part of a washing | cleaning liquid pushing nozzle, (b) is the longitudinal cross-sectional view. (A) is a perspective view of the front-end | tip part of a washing | cleaning liquid pushing nozzle, (b) is the side view, (c) is CC arrow directional view of (b). It is a longitudinal cross-sectional view in alignment with the longitudinal direction of a part of horizontal pipe part. It is a systematic diagram of a boiler steam system. It is a perspective view near a reheat steam pipe.

  Embodiments of a chemical cleaning method for a main steam pipe or a reheat steam pipe according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a system diagram showing an embodiment of a chemical cleaning method for a main steam pipe according to the present invention. In this embodiment, as in FIG. 7, the upstream end of the reheat steam pipe 6 to be chemically cleaned communicates with the outlet of the reheater pipe in the non-cleaning zone, and the downstream end is a stop valve. It is configured to be partitioned by. The downstream side of the stop valve is connected to a turbine (not shown).

  The reheat steam pipe 6 includes, from the top, a substantially horizontal horizontal part 6a, a vertical pipe part 6A connected to the end of the horizontal part 6a, and a horizontal pipe part 6B connected to the lower end of the vertical pipe part 6A via an elbow part. The vertical tube 6C connected to the end of the horizontal tube 6B, the two vertical tubes 6D and 6E branched from the vertical tube 6C, and the horizontal tubes connected to the lower ends of the vertical tubes 6D and 6E via elbows 6F, 6G. Further, a substantially horizontal bypass pipe 6H is provided that communicates the middle portions of the horizontal pipe portions 6F and 6G.

  In the horizontal tube portion 6B, cleaning seats 21 and 22 are provided on the upper surface portion in the vicinity of the vertical tube portion 6A and the upper surface portion on the end side, respectively. As shown in FIG. 2, the cleaning seats 21 and 22 are formed by opening a small-diameter opening 20 on the upper surface of the horizontal tube portion 6 </ b> B and welding a short cylindrical member having a flange portion to the periphery of the opening 20. It is a thing. The following cleaning seats 23 to 25 are also provided in the same manner.

  Cleaning seats 23 and 24 are provided on the upper surface portions of the horizontal tube portions 6F and 6G in the vicinity of the vertical tube portions 6D and 6E, and a cleaning seat 25 is provided on the upper surface portion in the middle of the bypass tube 6H.

  Discharge cleaning seats 26 and 27 for flowing out the cleaning liquid are provided on the lower surfaces of the side pipe portions 6F and 6G on the end side. The seats 26 and 27 are used by cutting a main drain pipe. The structure of the cleaning seats 26 and 27 is the same as that of the cleaning seats 21 to 25 except that the opening 20 is provided on the lower surface of the horizontal tube portions 6F and 6G. The horizontal portion 6a is provided with a seat (not shown) for cleaning liquid inflow. The structure of the cleaning liquid inflow seat is the same as that of the cleaning seats 21-25.

  When the reheat steam pipe 6 is cleaned with the chemical cleaning liquid, the valves 31 to 37 are attached to the cleaning seats 21 to 27 as shown in FIGS. The valves 31 to 37 are fixed to the flange portions of the cleaning seats 21 to 27 by bolts. Similarly, a valve is provided in the seat for the cleaning liquid inflow of the horizontal portion 6a.

  As shown in FIG. 2, a cleaning liquid pushing nozzle 60 is connected to the valves 31 to 35 of the cleaning seats 21 to 25 of the horizontal pipe portions 6B, 6G and 6F and the bypass pipe 6H. The nozzle 60 passes through the opening 20 and is inserted into the horizontal tube portions 6B, 6G, and 6F. The lower end of the nozzle 60 extends to the vicinity of the central portion in the radial direction of the horizontal tube portions 6B, 6G, and 6F or slightly below it. The lower end surface of the nozzle 60 is sealed. A cleaning liquid outlet 61 is provided on the surface facing the downstream side of the lower end of the nozzle 60.

  Pipes 41 and 42 are connected to the valves 36 and 37 of the cleaning seats 26 and 27 on the end side of the reheat steam pipe 6. The cleaning liquid flowing out from the pipes 41 and 42 is returned to the pipe 74 through the pipe 43, the valve 44, the drain pump 45, and the pipe 46 and circulated. A part of the circulating cleaning liquid is supplied to the cleaning seat 25 via the piping 47, supplied to the cleaning seats 23 and 24 via the piping 49, and supplied to the cleaning seats 21 and 22 via the piping 51. The piping 41, 42, 43, 46, 48, 50, 52 and the reheat steam pipe 6 constitute a cleaning liquid circulation line. The cleaning liquid returned from the stop valves 72 and 73 is introduced into the circulation line through the pipe 74 through the pump 75, the pipe 76, the valve 55 and the pipe 56. A drain pipe 58 having a valve 57 branches from the pipe 43.

  When the reheat steam pipe 6 is cleaned with the chemical cleaning liquid, the valves 55 and 57 are closed, the other valves 31 to 37 and 44 are opened, and the pumps 45 and 75 are operated. Flows into the horizontal tube portion 6B through the vertical tube portion 6A, flows down the vertical tube portions 6C, 6D, and 6E, flows through the horizontal tube portions 6F and 6G, and flows out from the cleaning seats 26 and 27 to the pipes 41 and 42. Then, the pipes 43, 46, 48, 50, and 52 flow in the order and return to the horizontal portion 6a.

  In the middle of this, a part of the cleaning liquid is pushed into the horizontal pipe portions 6B, 6F, 6G and the bypass pipe 6H from the cleaning liquid pushing nozzle 60 of the washing seats 21-25 via the pipes 51, 49, 47. At this time, the cleaning liquid outflow rate from the nozzle 60 may be faster than the in-pipe flow rate of the reheat steam pipe 6. However, in order to suppress corrosion in the vicinity of the outlet of the outflow portion, it is preferable that the pressure is about 0.01 to 3 m / sec, particularly about 0.5 to 3 m / sec.

  In this way, since the cleaning liquid is pushed into the horizontal pipe portions 6B, 6F, 6G and the bypass pipe 6H from the cleaning liquid pushing nozzle 60, the sludge is washed away in the vicinity of the washing seats 21 to 25, and accumulation of sludge in the vicinity is prevented. The Therefore, the lower surface of the horizontal tube portions 6B, 6F and 6G and the bypass tube 6H near the cleaning seats 21 to 25 are sufficiently chemically cleaned without flowing the cleaning liquid at a large flow rate. For this reason, it is not necessary to use a large pump or a large-diameter pipe, or to increase the diameter of the cleaning seats 21 to 25.

  By varying the amount of cleaning liquid pushed from the cleaning liquid pushing nozzle 60, the accumulation of sludge is more effectively prevented. The fluctuation period at this time is preferably about 5 seconds to 20 minutes, particularly about 1 to 10 minutes. In this case, the maximum pushing flow rate is preferably about 1.5 to 10 times the average pushing flow rate.

  When the inside of the reheat steam pipe 6 is washed with water after washing by circulation of the washing liquid, the valve 44 is closed, the valve 57 is opened, water is supplied to the horizontal portion 6a, and the waste water is discharged from the pipe 58. Even during this water washing, it is preferable that water is ejected from the nozzle 60 to wash away the sludge. In this case, the ejection speed of water from the nozzle 60 may be 3 m / sec or more.

  After this water washing, the valves 31 to 35 are removed from the washing seats 21 to 25 and opened, and a hose 71 having a water jet nozzle 70 at the tip is inserted into the reheat steam pipe 6 as shown in FIG. By ejecting water from 70, sludge can be sufficiently swept away from each of the horizontal pipe portions 6B, 6F, 6G and the bypass pipe 6H.

  As the water ejection nozzle 70, water can be ejected not only from the distal end side opposite to the hose 71 but also from the proximal end side on the hose 71 side, and ejection from the distal end side and ejection from the proximal end side Those that can be switched between are preferable. According to such a nozzle 70, as shown in FIG. 5A, the nozzle 70 is inserted into the horizontal tube portion 6 </ b> B upstream of the cleaning seat 21, and water is ejected in the proximal direction from the cleaning seat 21. Also, the upstream sludge can be pushed downstream. Further, as shown in FIG. 5B, the nozzle 70 is inserted downstream of the cleaning seat 21 and water is ejected from the tip end side of the nozzle 70, so that the sludge downstream of the cleaning seat 21 is moved downstream. The sludge can be swept away and sludge can be swept away over a wide range in the vicinity of the cleaning seat 21. Similarly, sludge can be swept away over a wide range in the vicinity of the cleaning seats 22 to 25.

Since only the high-pressure water ejected from the nozzle 70 does not allow the sludge to move downward, it is preferable to flush the washing water from the washing seats 21 to 25 and push the sludge downward. At this time, it is preferable to change the flow rate of the washing water. The fluctuation period is preferably about 5 seconds to 20 minutes, particularly about 1 to 10 minutes. Sludge is efficiently discharged by setting the initial flow rate to 5 m ³ / h or more and changing the flow rate continuously or intermittently to give an impact to the sludge. The flow rate fluctuation range is not limited, but the maximum flow rate is preferably 1.5 to 10 times the average flow rate.

  Furthermore, since a flow stagnation portion does not occur by changing the flow rate of a curved portion such as an elbow, sludge can be discharged without remaining. At the time of this water washing, the piping may be full or not.

  After washing with water, each cleaning seat is cut and removed, and a steel plate is welded to the opening 20 and closed.

In addition, when this inventor left the sludge with a length of 1 to 4 mm and a density of ^{3 to 5} g / cm ³ in a horizontal pipe having a length of 2000 mm and a diameter of 240 mm or 600 mm, and flowing water, it was constant. Even when the flow rate was 30 m ³ / h, the sludge could not be discharged sufficiently.

On the other hand, when the flow rate was continuously changed at a fluctuation period of 10 seconds between 0 and 50 m ³ / h, it was recognized that sludge flows out in a short time.

When a similar test was performed on a horizontal pipe having an inner diameter of 240 mm and a length of about 15.5 m and having two elbows in the middle, the flow rate was continuously changed in the range of 0 to 50 m ³ / h. It was confirmed that all sludge was discharged.

  In the above description, the reheat steam pipe 6 is washed, but the main steam pipe can be washed in the same manner.

  The cleaning liquid pushing nozzle 60 used in FIG. 3 is provided with a cleaning liquid outlet 61 on the downstream side of the flowing water in the pipe. However, like the cleaning liquid pushing nozzle 63 in FIG. 64 may be provided on the lower end surface. In the nozzle 63, the lower end surface of the nozzle is cut obliquely so as to be higher on the wake side. In addition, a slit-like cut portion 65 is provided on the surface facing the upstream side of the horizontal tube portion from the lower end to the upper side, so that the flow of the cleaning liquid in the horizontal tube portion is not hindered.

  The above embodiment is an example of the present invention, and the present invention may be other than the above.

6 Reheat steam pipe 6A, 6D, 6E Vertical pipe part 6B, 6F, 6G Horizontal pipe part 6H Bypass pipe 20 Opening 21-27 Cleaning seat 31-37 Valve 45 Drain pump 60, 63 Cleaning liquid pushing nozzle 70 Water ejection nozzle 71 Hose 72, 73 Stop valve 74, 76 Main circulation piping 75 Circulation pump

Claims (6)

A method of chemically cleaning a main steam pipe or a reheat steam pipe communicating with a superheater pipe or a reheater pipe using a chemical cleaning liquid,
A cleaning liquid inflow seat is provided upstream of the main steam pipe or the reheat steam pipe, a cleaning liquid outflow seat is provided in the downstream part, and the cleaning liquid is supplied into the main steam pipe or the reheat steam pipe through these seats. In the chemical cleaning method of the main steam pipe or the reheat steam pipe, which has a chemical cleaning step of circulating and cleaning
The main steam pipe or reheat steam pipe has a vertical pipe part and a horizontal pipe part connected to the lower end of the vertical pipe part,
A cleaning seat is provided on the upper surface portion in the vicinity of the vertical tube portion of at least the horizontal tube portion, and a cleaning liquid pushing nozzle is installed in the cleaning seat,
When the cleaning liquid is circulated in the main steam pipe or the reheat steam pipe, the cleaning liquid flows out from the cleaning liquid pushing nozzle into the horizontal pipe portion to prevent the accumulation of sludge. Chemical cleaning method for hot steam pipes.   2. The chemical cleaning method for a main steam pipe or a reheat steam pipe according to claim 1, wherein the amount of cleaning liquid pushed in from the washing liquid pushing nozzle is changed. The method according to claim 1 or 2, wherein after the cleaning by circulation of the cleaning liquid is completed, a water washing step is performed in which water is supplied to the main steam pipe or the reheat steam pipe and washed.
A chemical cleaning method for a main steam pipe or a reheat steam pipe, wherein the amount of water in the water washing step is changed continuously or intermittently.   4. The method according to claim 3, wherein after the water washing step, the washing seat is opened, a water ejection nozzle is inserted into the main steam pipe or the reheat steam pipe, and water is ejected from the water ejection nozzle to flush the sludge. Chemical cleaning method for main steam pipe or reheat steam pipe.   5. The cleaning seat is also provided in the upper surface portion of the bypass pipe communicating with the main steam pipes, and the cleaning liquid pushing nozzle is provided in the cleaning seat, and the cleaning liquid is circulated in the main steam pipe or the reheat steam pipe. Sometimes, the cleaning liquid flows out from the cleaning liquid pushing nozzle into the bypass pipe to prevent sludge accumulation, and after the water washing step, the cleaning seat of the bypass pipe is opened, and the water ejection nozzle is inserted into the bypass pipe. A chemical cleaning method for a main steam pipe or a reheat steam pipe, characterized in that water is jetted from the water jet nozzle and the sludge is washed away.   The water ejection nozzle according to claim 4 or 5, wherein the water ejection nozzle is provided at a tip of a hose, water can be ejected from both the hose side and the opposite side, and the ejection direction can be switched. Chemical cleaning method for main steam pipe or reheat steam pipe.

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