JP7363695B2 - Boiler chemical cleaning method - Google Patents

Description

The present invention relates to a method for chemically cleaning a boiler, and particularly to a method for chemically cleaning a brackish water separator and a furnace side thereof.

Figure 3 shows an example of a thermal power boiler. Furthermore, a water supply system diagram of the boiler is shown in FIG. 2.

This boiler includes a furnace 9, a downstream exhaust gas flow path (rear flue), and an upstream exhaust gas flow path that connects the upper part of the furnace 9 and the downstream exhaust gas flow path.

High-temperature combustion gas generated from a plurality of burners 80 provided at the lower part of the furnace 9 rises inside the furnace 9 . The combustion gas passes through the upstream exhaust gas flow path and the downstream exhaust gas flow path, and is discharged from the flow path outlet 93 to the outside of the boiler as exhaust gas. Inside the furnace 9, a water-cooled wall lower circumferential wall tube 10, an upper water-cooled wall tube 12, and a nose wall tube 105 are provided. The water-cooled wall lower circumferential wall tube 10 extends upward from the lower part of the furnace 9 in a spiral manner within the furnace 9 . The upper water-cooled wall tubes 12 each include a plurality of tubes, each of which extends vertically within the furnace 9 toward the top of the furnace 9. The nose tube 105 also consists of a plurality of tubes.

The rear flue is defined by a rear heat transfer wall 33 made up of a plurality of tubes. The rear flue is divided into two gas flow paths by a dividing wall 120 extending along the flow of exhaust gas. The dividing wall 120 also consists of a plurality of tubes.

A reheater 71 is disposed in one of the divided gas passages of the rear flue, and a primary superheater 40 and a economizer 2 are disposed in the other divided gas passage. Further, an evaporator is provided in the divided gas flow path as necessary.

The rear flue is defined by a ceiling wall 30 made up of a plurality of pipes, side walls, and the like. A secondary superheater 50 and a tertiary superheater 60 are arranged in the upstream exhaust gas flow path. Additionally, a quaternary superheater may also be installed.

Next, the water supply system for this boiler will be explained. Water to the boiler is first supplied to the energy saver 2 from a water supply pipe 1 having a high-pressure feedwater heater 1h (FIG. 2) and a water supply valve 1a. In the economizer 2, water supplied from the economizer inlet header 100 absorbs heat from the exhaust gas flow while passing through the economizer 2, and then flows from the economizer outlet header 101 to the water-cooled wall downcomer. 3. The water that has passed through the water-cooled wall downcomer pipe 3 is distributed to the water-cooled wall lower header 103, and rises through the water-cooled wall lower circumferential wall pipe 10 that spirally surrounds the furnace 9 while absorbing the heat inside the furnace 9. Water is heated to near saturation temperature.

The high-temperature water that has risen through the water-cooled wall lower circumferential wall tube 10 flows into the intermediate fluid mixing header 11 of the furnace 9, where its temperature is made uniform. While rising through the tube 12 or the nose wall tube 105, the fluid absorbs heat in the furnace 9 and becomes a mixed fluid of high temperature water in the liquid phase and steam in the gas phase. This mixed fluid flows into the upper fluid mixing header 13 of the furnace 9 from the water-cooled wall upper header 12a or the nose wall header 105B, and the fluid temperature is equalized. The steam flows into the steam separator 20 and is separated into steam and water. The separated water is circulated from the drain tank 21 to the water supply pipe 1 again via a circulation pipe 22 having a boiler circulation pump 24 and valves 23 and 25. Further, the steam separated by the steam separator 20 is supplied to the ceiling wall inlet header 107 via the communication pipe 44.

The steam supplied to the ceiling wall inlet header 107 passes through the ceiling wall pipes forming the ceiling wall 30 provided from the upper part of the furnace 9 to the upper part of the exhaust gas flow on the downstream side, to the ceiling wall outlet header 108. During this period, it is heated by heat absorption and becomes saturated steam.

The saturated steam collected in the ceiling wall outlet header 108 passes through the rear heat transfer wall downcomer pipe 31, the rear heat transfer wall inlet connecting pipe 109, is distributed to the rear heat transfer wall inlet header 110, and is further transferred to the cage wall (rear heat transfer wall inlet header 110). After being heated in the rear heat transfer wall (heat transfer wall) 33, the rear heat transfer wall outlet pipe is heated via the rear heat transfer wall outlet header 111 and the rear heat transfer wall outlet connecting pipe 112, or from the cage wall (rear heat transfer wall) 33 to the rear heat transfer wall rear wall outlet pipe. Gather at Yose 34.

The saturated steam collected at the rear wall outlet header 34 of the rear heat transfer wall flows into the primary superheater 40 installed in the rear flue via the primary superheater connecting pipe 35, and then flows into the primary superheater 40 installed in the rear flue. After being superheated through a secondary superheater 50 and a tertiary superheater (in this boiler, the final superheater) 60, it is sent to the high-pressure turbine via a main steam pipe 61 and a main stop valve 62.

The exhaust steam that has done work in the high-pressure steam turbine is led to a reheater 71 installed in the rear flue by a low-temperature reheat steam pipe (not shown), and is heated to a predetermined reheat steam temperature. , sent to an intermediate pressure turbine. A gas distribution damper 90 is provided at the outlet of the rear flue, and by adjusting the flow rate of gas passing therethrough, the total amount of heat absorbed by the reheater 71 can be adjusted, and the temperature of the reheated steam can be controlled to a predetermined value.

When chemically cleaning the steam water separator 20 and the furnace side of this boiler, after stopping the boiler operation, blow out all the canned water that was used during operation in the furnace evaporation pipe, which is the area of chemical cleaning. After cutting the inspection hole etc. of the existing pressure-resistant part, a temporary valve and temporary piping are connected thereto by welding 26W, and connected to other chemical cleaning piping and equipment. For example, as shown in FIG. 2, a temporary pipe 26 is provided to bypass the circulation pump 24 and valves 23 and 25 in the circulation pipe 22, and the temporary pipe 26 is equipped with a temporary circulation pump 27 and a temporary drainage having a valve 1b. A pure water supply pipe 26a having a pipe 1c and a valve 26b is provided. The temporary pipe 26 is connected to the water economizer 2 side of the water supply pipe 1 rather than the water supply valve 1a.

Before connecting (welding) temporary valves and temporary piping, blowing out all the canned water that was used during operation inside the boiler furnace evaporation pipe is a problem if the pressure-resistant part is cut off without completely blowing out the boiler canned water. This is because canned water leaks out and welding work cannot be done. Furthermore, even if there is a valve in the pressure-resistant part, there are many items to be inspected during periodic inspections, so the purpose is to blow out all the canned water in the boiler to prevent unexpected water spill accidents.

After installing the temporary valves, piping, etc. as described above, the chemical cleaning liquid can be supplied to the brackish water separator 20 from the chemical liquid tank (not shown) via the temporary cleaning chemical liquid supply pipe. As the chemical cleaning solution, an organic acid aqueous solution containing citric acid or glycolic acid as a main ingredient is used.

In addition, when chemically cleaning only the steam water separator and the furnace side of such a boiler, the liquid temperature during cleaning is as high as 80 to 98 degrees Celsius, and vapor containing cleaning chemical components flows to the superheater side. Since it is necessary to prevent water and droplets from entering, the superheater (non-cleaning section) and main steam pipe are filled with pure water (ion-exchanged water) containing hydrazine and ammonia, and then the brackish water separator and Clean the furnace side with chemical solution.

Specifically, a temporary supply pipe 64 for filling with water, which has a pump 64a (FIG. 2) and a valve 63, is connected to the drain pipe of the main steam pipe 61 on the upstream side of the main blocking valve 62. Next, the temporary pump 64a passes through the main steam pipe 61, the final superheater 60, the secondary superheater 50, and the primary superheater 40, and fills the water up to the brackish water separator 20, which is the boundary with the cleaning section. Hereinafter, this filled water may be referred to as "sealing water."

In addition, when filling the superheater and the main steam pipe with water in this way, water is filled after the temperature of the main steam pipe material and the temperature of the main blocking valve are lowered to 200° C. or lower, particularly 100° C. or lower. The reason for this is that if water is filled when the pipe material temperature exceeds 200°C, the steam oxide scale will peel off due to the difference in thermal contraction rate between the pipe material and the steam oxide scale, and after the boiler is started up at a later date, the steam oxide scale will peel off. This is because there is a risk that the main blocking valve, which is at a high temperature, may be rapidly cooled down and have an adverse effect on the material.

After filling water to the superheater side of the steam, with the valves 1a, 23, 25 and temporary valves 1b, 26b closed, a cleaning chemical solution (organic acid solution) is added to the brackish water separator 20, The temporary circulation pump 27 is activated. Then, the cleaning liquid in the brackish water separator 20 is transferred to the drain tank 21, the temporary pipe 26, the water supply pipe 1, the economizer 2, the peripheral wall pipe 10 of the furnace 9, the upper water cooling pipe wall 12, the nose wall pipe 105, the pipe header 12a, or the 105B, the water is circulated to the brackish water separator 20 via the header 13, and the brackish water separator 20, drain tank 21, economizer 2, wall pipes 10, 12, 105, and each header are chemically cleaned.

After continuing this chemical cleaning for a predetermined time, cleaning water (pure water) is supplied to the main steam pipe 61 from the supply pipe 64 via the pump 64a, and the superheater pipes 60, 50, 40, wall pipes 33, and ceiling wall 30 , the steam system is flushed with water while forcing out the sealed water by backflowing to the steam separator 20. A part of the wash water that has flowed back into the brackish water separator 20 flows out from the brackish water separator 20 through the drain tank 21 to the drain pipe 1c. Further, the remainder of the wash water that has flowed back into the brackish water separator 20 flows out from the drain pipe 1c via the wall pipes 12 and 10 of the furnace 9, the nose wall pipe 105, the header 103, the downcomer pipe 3, and the economizer 2. .

After extrusion of the cleaning chemicals remaining in the system is completed, rust prevention and blowing are performed, the temporary piping is removed, and normal water flushing and startup operations are performed to resume boiler operation.

Japanese Patent Application Publication No. 2015-230150

As mentioned above, when chemically cleaning the brackish water separator and the furnace side, the superheater and main steam pipe are sealed with water. After the chemical cleaning is completed, this sealed water is pushed out from the superheater side to a brackish water separator and washed with water, thereby washing out the volatile components of the chemical cleaning liquid absorbed in the sealed water of the superheater.

However, if the sealed water absorbs a large amount of volatile components, or if a portion of the chemical cleaning solution flows into the sealed water, not only will it take time to wash out the water afterwards, but a large amount of water will also be required, and the entire chemical cleaning process will be interrupted. Process stretching occurs.

An object of the present invention is to provide a method for chemically cleaning a boiler that can prevent extension of the construction period when chemically cleaning the steam separator of the boiler and the furnace side thereof.

The chemical cleaning method for a boiler according to the present invention includes a fuel economizer into which water is introduced through a water supply pipe, a furnace having a wall pipe into which water from the economizer is introduced, and a brackish water separator to which the wall pipe is connected. Chemically cleaning a boiler having a ceiling wall for heating steam from a brackish water separator, a superheater for superheating steam from the ceiling wall, and circulation piping for circulating water from the brackish water separator to the water supply pipe. A method of chemically cleaning the brackish water separator and the furnace side by circulating a cleaning chemical solution after filling the non-cleaning part on the superheater side of the brackish water separator with water. , At least part of the time during the chemical cleaning, the sealed water is circulated or passed through, and the water quality of the water flowing out from the non-washed area is measured to prevent volatilization into the sealed water. It is characterized by detecting the inflow of components.

In one aspect of the invention, the water quality value is electrical conductivity or pH.

In one aspect of the present invention, pure water is passed through the non-cleaned portion during the chemical cleaning, and when the water quality value exceeds a predetermined range, it becomes within the predetermined range. Increase the flow rate of pure water.

In the chemical cleaning method for boilers of the present invention, seal water is flowed in the non-cleaned areas during chemical cleaning, and its conductivity, pH, etc. are measured to minimize the accumulation of volatile components of the chemical cleaning solution in the non-cleaned areas. Try to keep it there. This can prevent stretching during the chemical cleaning process.

FIG. 2 is a block diagram illustrating a method for chemically cleaning a boiler according to an embodiment. FIG. 2 is a block diagram illustrating a conventional boiler chemical cleaning method. It is a typical sectional view of a boiler.

Hereinafter, a method for chemically cleaning a boiler according to an embodiment will be described with reference to FIG. The configuration of the boiler in FIG. 1 is the same as in FIG. 2, and the same reference numerals indicate the same parts.

In the chemical cleaning method for a boiler according to this embodiment, when chemically cleaning the steam water separator 20 and the furnace side of the boiler, as in the case of FIG. 2, after stopping the operation of the boiler, All the canned water that was used during operation inside the furnace evaporation pipe will be blown out, and after cutting the inspection hole etc. of the existing pressure-resistant part, a temporary valve and temporary piping will be connected there with 26W welding, and other chemical Connect to cleaning piping and equipment. That is, a temporary pipe 26 is provided so as to bypass the circulation pump 24 and valves 23 and 25 in the circulation pipe 22, and the temporary circulation pump 27, a temporary drain pipe 1c having a valve 1b, and a valve 26b are installed in the temporary pipe 26. A pure water supply pipe 26a is provided. The temporary pipe 26 is connected to the water economizer 2 side of the water supply pipe 1 rather than the water supply valve 1a.

Further, a temporary supply pipe 64 for filling with water is connected to the drain pipe of the main steam pipe 61 upstream of the main blocking valve 62, which has a temporary pump 64a, a flow meter 64b, and valves 64c, 64d. Furthermore, a pipe 65 having a valve 65a is connected to the primary superheater 40, and a drainage tank 66 for receiving waste water from the pipe 65 is installed. A conductivity meter 65b, a pH meter 65c, and a flow meter 65d are installed in the pipe 65, and their detection signals are transmitted to a monitoring device 67.

In this way, after installing temporary valves, temporary piping, etc., the temporary pump 64a passes through the main steam pipe 61 → final superheater 60 → secondary superheater 50 → primary superheater 40, and at the boundary line with the cleaning section. Water is filled up to a certain brackish water separator 20. When the water level of the steam water separator 20 rises, it is confirmed that the superheater system is full of water.

After filling water to the superheater side as described above, a cleaning chemical solution (organic acid solution) is added to the brackish water separator 20 with valves 1a, 23, 25 and temporary valves 1b, 26b closed. After that, the temporary circulation pump 27 is activated. Then, the cleaning liquid in the brackish water separator 20 is transferred to the drain tank 21, the temporary pipe 26, the water supply pipe 1, the economizer 2, the peripheral wall pipe 10 of the furnace 9, the upper water cooling pipe wall 12, the nose wall pipe 105, the pipe header 12a, or the 105B, the water is circulated to the brackish water separator 20 via the header 13, and the brackish water separator 20, drain tank 21, economizer 2, wall pipes 10, 12, 105, and each header are chemically cleaned.

During chemical cleaning, the chemical components of the high-temperature chemical cleaning solution evaporate from the brackish water separator 20 and flow into the non-cleaning section via the connecting pipe 44.

In order to prevent this chemical component from accumulating in the sealed water of the non-washed section, pure water is supplied at a constant flow rate to the sealed water of the non-washed section by a pump 64a, and is supplied to each superheater 60, 50, 40. Water is passed through once, and the conductivity and/or pH of the waste water is measured while discharging the waste water from the piping 65 into the waste water tank 66. If the measured value fluctuates by more than a predetermined value from the initial value at the start of chemical cleaning, the discharge amount of the pump 64a is increased to prevent the accumulation of volatile components of the chemical cleaning liquid downstream of the superheater 60, 50, 40. To prevent. When the measured value returns to within a predetermined range from the initial value at the start of chemical cleaning, the discharge amount of the pump 64a is returned to its original value.

If the numerical value fluctuation is slight, it can be dealt with by injecting a pH adjuster into the pure water supplied to the pump 64a.

After continuing this chemical cleaning for a predetermined time, cleaning water (pure water) is supplied to the main steam pipe 61 from the supply pipe 64 via the pump 64a, and the superheaters 60, 50, 40, wall pipes 33, ceiling wall 30, The water is made to flow back to the steam separator 20 to push out the sealed water and wash the steam system with water. A part of the wash water that has flowed back into the brackish water separator 20 flows out from the brackish water separator 20 through the drain tank 21 to the drain pipe 1c. Further, the remainder of the wash water that has flowed back into the brackish water separator 20 flows out from the drain pipe 1c via the wall pipes 12 and 10 of the furnace 9, the nose wall pipe 105, the header 103, the downcomer pipe 3, and the economizer 2. .

After extrusion of the cleaning chemicals remaining in the system is completed, rust prevention and blowing are performed, the temporary piping is removed, and normal water flushing and startup operations are performed to resume boiler operation.

In this way, by flowing the sealed water in the non-cleaned area during chemical cleaning and measuring its conductivity (or specific resistance) and pH, the volatile components of the chemical cleaning solution can be detected in the non-cleaned area. Accumulation can be kept to a minimum and it is possible to prevent extension of the chemical cleaning process.

Although the boiler chemical cleaning method of the present invention has been described above based on the embodiment shown in FIG. 1, the present invention is not limited to the embodiment. For example, in the embodiment described above, pure water is passed through the non-washed portion in a one-time manner, but the water in the drain tank 66 may be circulated. Furthermore, it goes without saying that the method of the present invention is applicable to various types of boilers. For example, the nose wall tube 105 may be omitted, and the water-cooled wall lower circumferential wall tube 10 may extend upward from the lower portion of the furnace 9 in a substantially vertical manner within the furnace 9 .

1 Water supply pipe 2 Energy saver 9 Furnace 20 Brackish water separator 21 Drain tank 22 Circulation piping 24 Recirculation pump 26 Temporary piping 26A, 26B Pressure resistant valve 26W Welding 27 Temporary recirculation pump 30 Ceiling wall 33 Cage wall 40, 50, 60 Overheating 61 Main steam pipe 62 Main blocking valve 64, 65 Temporary piping 67 Monitoring device

Claims (3)

A fuel economizer into which water is introduced through a water supply pipe, a furnace having a wall pipe into which water from the economizer is introduced, a brackish water separator connected to the wall pipes, and a steam water separator that heats the steam from the brackish water separator. A method for chemically cleaning a boiler having a ceiling wall, a superheater for superheating steam from the ceiling wall, and circulation piping for circulating water from a brackish water separator to the water supply pipe, the method comprising:
A method of chemically cleaning the brackish water separator and the furnace side by circulating a cleaning chemical solution after filling the non-cleaning part on the superheater side of the brackish water separator with water,
During at least a part of the chemical cleaning, the sealed water is circulated or passed through, and the quality of the water flowing out from the non-cleaned area is measured to remove volatile components from the sealed water. A method for chemically cleaning a boiler, characterized by detecting the inflow of water. 2. The method for chemically cleaning a boiler according to claim 1, wherein the water quality value is electrical conductivity or pH. While performing the chemical cleaning, pure water is passed through the non-cleaning area in a one-time manner, and when the water quality value exceeds a predetermined range, the amount of pure water to be passed is adjusted so that the water quality value falls within the predetermined range. 3. The method for chemically cleaning a boiler according to claim 1 or 2, further comprising increasing the amount of water.

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