JP2022048804A - Chemical cleaning method for boiler - Google Patents

Abstract

To prevent inflow of a chemical cleaning liquid to a non-cleaning target apparatus with higher accuracy during chemical cleaning of a boiler.SOLUTION: A chemical cleaning method for a boiler for chemically cleaning a furnace water wall tube of the thermal power generation boiler including an economizer, the furnace water wall tube and a superheater includes: a seal water injection step of injecting seal water to a heat transfer pipe in a non-cleaning part including the superheater to maintain a predetermined water level; and a cleaning step of circulating a chemical cleaning solution to a cleaning target apparatus including the economizer and the furnace water wall tube. During execution of the cleaning step, while the predetermined water level is maintained, the seal water is caused to continuously flow in the heat transfer pipe in the non-cleaning part.SELECTED DRAWING: Figure 4

Description

The present invention relates to a method for chemically cleaning a boiler.

In thermal power generation boilers, chemical cleaning is regularly performed to remove scale adhering to or accumulated in the heat transfer pipes and pipes of the water supply system of the thermal power generation boiler. For chemical cleaning of thermal power generation boilers, a circulation path is installed between the equipment to be cleaned from the economizer to the steam water separator, and an acidic chemical cleaning chemical solution (hereinafter referred to as chemical cleaning solution) is circulated in the circulation path. Thereby, the scale in the pipe of the equipment to be cleaned is removed.

In recent years, a lotion having a great effect of removing scale has been used as a lotion. However, the chemical lotion having a large scale removing effect has high scale solubility but high foaming property. When foaming occurs in the equipment of a thermal power boiler, so-called "bubble block" is generated, and the foam becomes a resistor, and not only does the lotion stop flowing, but also the steam system that should not flow the lotion. For example, carryover is likely to occur in which the chemical lotion flows into non-cleaning equipment such as a superheater. If this foam stays in the device, the device may be damaged by acid.

When cleaning the equipment to be cleaned, in order to prevent the vapor of the chemical washing liquid from flowing into the superheater side, only the superheater (primary superheater) in the uppermost stream is filled with water, and then the cleaning target is used. A method for chemically cleaning an apparatus is known (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2015-230150

The technique disclosed in Patent Document 1 attempts to prevent carryover by filling the primary superheater with water (sealing water) to the same level as the cleaning liquid of the brackish water separator.

However, according to the technique described in Patent Document 1, when the steam water separator is filled with bubbles, the chemical lotion is extruded, and accordingly, the seal water in the primary superheater is also extruded, so that the chemical lotion and the chemical lotion are extruded. The sealing water mixed with the foam from the above reaches the non-cleaning target equipment such as the secondary superheater and the tertiary superheater. As a result, the heat transfer tube of the superheater may come into contact with the chemical washing liquid and corrode.

The present invention has been made in view of the above circumstances, and an object of the present invention is to prevent the inflow of chemical washing liquid into a non-cleaning target device with higher accuracy during chemical cleaning of a boiler.

The present invention is a method for chemically cleaning a boiler that chemically cleans the furnace water wall pipe of a thermal power generation boiler including a coal saver, a furnace water wall pipe, and a superheater, and is a transmission in a non-cleaning portion including the superheater. It is provided with a seal water injection step of injecting seal water into a hot tube so as to maintain a predetermined water level, and a cleaning step of circulating a chemical cleaning agent solution to a device to be cleaned including the coal saver and the furnace water wall tube. During the cleaning step, the sealing water is continuously flowed to the heat transfer tube in the non-cleaning portion while maintaining the predetermined water level.

According to the present invention, it is possible to prevent the inflow of the chemical washing liquid into the non-cleaning target device with higher accuracy during the chemical cleaning of the boiler. Issues, configurations and effects other than those described above will be clarified by the description of the following embodiments.

It is a system diagram of the water supply system and the steam system of the power plant which uses the thermal power generation boiler of 1st Embodiment. It is a schematic diagram of the thermal power generation boiler of 1st Embodiment. It is a boiler heat transfer surface block diagram of the thermal power generation boiler of 1st Embodiment. It is explanatory drawing for demonstrating the piping at the time of chemical cleaning of the thermal power generation boiler of 1st Embodiment. It is explanatory drawing for demonstrating the water level measurement at the time of the chemical cleaning of the thermal power generation boiler of 1st Embodiment. It is a flowchart of the chemical cleaning method of 1st Embodiment. It is explanatory drawing for demonstrating the flow of water supply and chemical washing liquid at the time of chemical washing of 1st Embodiment. It is a flowchart of the wastewater property monitoring process of 1st Embodiment. It is explanatory drawing for demonstrating the piping at the time of chemical cleaning of the thermal power generation boiler of the modification of 1st Embodiment. It is explanatory drawing for demonstrating the piping at the time of chemical cleaning of the thermal power generation boiler of the modification of 1st Embodiment. It is explanatory drawing for demonstrating the flow of water at the time of cooling before the chemical cleaning of the thermal power generation boiler of the modification of 1st Embodiment. (A) is for explaining the piping for conventional chemical cleaning of a constant pressure once-through thermal power generation boiler without a brackish water separator, and (b) is for explaining the flow of sludge near the upper pipe after the cage. It is explanatory drawing. It is explanatory drawing for demonstrating another piping example at the time of the conventional chemical cleaning of the constant pressure once flow type thermal power generation boiler which does not have a brackish water separator. (A) is an explanatory diagram for explaining the piping at the time of chemical cleaning of the thermal power generation boiler of the second embodiment, and (b) is an explanatory diagram for explaining the flow of sludge near the upper pipe after the cage.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that the present invention is not limited to this embodiment, and when there are a plurality of embodiments, the present invention also includes a combination of the respective embodiments.

<< First Embodiment >>
The first embodiment of the present invention will be described.

[Overall configuration of power plant]
The power generation plant in which the thermal power generation boiler (hereinafter referred to as "boiler") according to the present embodiment has an exhaust gas system in which combustion gas (exhaust gas) discharged from the boiler flows, a steam system in which steam generated by the boiler flows, and a steam system in which steam generated by the boiler flows. It is equipped with a water supply system through which the water restored by the condenser flows.

The exhaust gas system is a system for guiding the high-temperature combustion gas generated from a plurality of burners provided in the lower part of the furnace of the boiler to the chimney. The combustion gas is discharged to the outside of the boiler as low-temperature exhaust gas from the exhaust gas flow path outlet through the exhaust gas flow path provided in the boiler.

The steam system is a system through which steam generated by the boiler flows, and the water supply system is a system for supplying the water restored by the condenser to the boiler. Hereinafter, the water supply system and the steam system of the power plant 101 will be described with reference to the drawings. The boiler 100 used in this embodiment is a "transformer once-through boiler".

FIG. 1 is a diagram showing an example of a water supply system and a steam system of the power plant 101. As shown in this figure, the power generation plant 101 of the present embodiment rotates a turbine using a boiler 100 that burns fuel and generates steam (superheated steam) by the heat of the combustion, and the steam generated by the boiler 100. A steam turbine 160 (high-pressure turbine 161, medium-pressure turbine 162, low-pressure turbine 163) that drives a generator to generate power, and a water supply line (mainly) that returns the exhaust steam from the steam turbine to water and supplies it to the boiler 100. A water supply pipe 216) is provided.

The boiler 100 includes an economizer (ECO) 129, a furnace water wall pipe 222, a brackish water separator 130, a superheater 140, and a reheater 150. The superheater 140 and the reheater 150 may be provided in a plurality of stages from the downstream to the upstream. In the present embodiment, the superheater 140 has a three-stage configuration of a primary superheater 141, a secondary superheater 142, and a tertiary superheater 143 (see FIG. 2).

The steam turbine 160 includes a high-pressure turbine (HPT) 161, a medium-pressure turbine (IPT) 162, and a low-pressure turbine (LPT) 163, each of which performs a predetermined task for rotationally driving the generator 102.

On the main feed water pipe 216, there are a condenser 170, a condenser pump 181, a low pressure feed water heater (low pressure heater) 182, a deaerator 183, a water supply pump 184, and a high pressure feed water heater (high pressure heater). 185 and are provided.

In the power plant 101 having the above configuration, the economizer 129 preheats the supplied water by heat exchange with the combustion gas. The water preheated by the economizer 129 becomes a water-steam two-phase fluid by passing through the furnace wall pipe formed on the wall in the furnace water wall pipe 222. The water-steam two-phase fluid generated in the furnace water wall pipe 222 is sent to the brackish water separator 130 via the first connecting pipe 225 and separated into saturated steam and saturated water. Here, the saturated steam is guided to the superheater 140, and the saturated water is guided to the condenser 170 through the saturated water pipe 217.

The saturated steam separated by the steam water separator 130 is superheated by the superheater 140 by heat exchange with the combustion gas, and the generated superheated steam is introduced into the high-pressure turbine 161 via the main steam pipe 212. The main steam pipe 212 is provided with a main steam check valve 262 (see FIG. 3).

The steam that has performed the predetermined work in the high-pressure turbine 161 is guided to the reheater 150 via the low-temperature reheat steam pipe 213. The reheater 150 reheats the steam that has performed the predetermined work in the high pressure turbine 161. The steam superheated by the reheater 150 is supplied to the medium pressure turbine 162 and the low pressure turbine 163 via the high temperature reheat steam pipe 214, where they work and drive the generator 102.

The steam that has finished its work in the low pressure turbine 163 is introduced into the condenser 170 by the turbine exhaust pipe 215. The condensate condensed in the condenser 170 passes through the low pressure heater 182 by the condensate pump 181 together with the saturated water sent from the brackish water separator 130, and then sent to the deaerator 183 to remove the gas component in the condensate. Will be done. The condensate that has passed through the deaerator 183 is further boosted by the water supply pump 184, then fed to the high-pressure heater 185 to be heated, and finally returned to the boiler 100.

[Overall composition of boiler]
Next, the boiler 100 will be described. FIG. 2 is a schematic diagram of the overall configuration of the boiler 100 of the present embodiment. Here, only the configuration related to the present embodiment will be described. As shown in this figure, the boiler 100 has a furnace 120 for burning fuel and a rear heat transfer arranged on the rear side of the furnace 120 via a sub-side wall portion 121 with respect to the flow path of the combustion gas generated in the furnace 120. A portion (cage portion) 123 and a ceiling portion 122 of the furnace 120 and the rear heat transfer portion 123 are provided.

A primary superheater 141 and an economizer 129 are installed in the rear heat transfer unit 123. Further, a secondary superheater 142 and a tertiary superheater 143 are installed at positions where the combustion gas generated in the furnace 120 faces the rear heat transfer unit 123. The primary superheater 141 is a so-called horizontal heat exchanger provided with a horizontal heat transfer surface, and the secondary superheater 142 and the tertiary superheater 143 are provided with a suspended heat transfer surface, so-called. It is a hanging type heat exchanger. In the boiler 100 of the present embodiment, the tertiary superheater 143 is the final superheater provided in the final stage on the steam piping system of the boiler 100. Other heat exchangers such as the reheater 150 are installed in the required parts of the furnace 120 and the rear heat transfer unit 123.

Next, the details of the water supply system in the boiler 100 will be described. FIG. 3 is a boiler heat transfer surface configuration diagram of the boiler 100. Here, only the configuration related to the present embodiment will be described. For example, the reheater 150 and the like are omitted. As shown in this figure, the boiler water supplied to the boiler 100 is first supplied to the economizer 129 from the main water supply pipe 216 having the water supply valve 266. In the economizer 129, the supplied water absorbs heat from the combustion gas while passing through the economizer 129, and is supplied to the water-cooled wall descent pipe 221. The water that has passed through the water-cooled wall descending pipe 221 passes through the furnace water wall pipe 222 of the furnace 120 and rises while absorbing the heat in the furnace 120. Here, the boiler water is heated to near the saturation temperature.

The hot boiler water that has been heated by absorbing the heat in the furnace 120 while ascending the furnace water wall tube 222 is a mixed fluid of liquid phase high temperature water and vapor phase steam (water-steam two-phase fluid). Will be. This mixed fluid flows into the brackish water separator 130 provided above the boiler 100 via the first connecting pipe 225, and is separated into steam and water.

The separated water is circulated again from the brackish water separator water storage tank (drain tank) 131 to the main water supply pipe 216 via the saturated water pipe 217.

On the other hand, the steam separated by the steam separator 130 flows into the primary superheater 141 through the saturated steam pipe 211, and then superheats through the secondary superheater 142 and the tertiary superheater 143 provided on the upper part of the furnace 120 in order. After that, it is sent to the high pressure turbine 161 via the main steam pipe 212 and the main steam stop valve 262.

[Composition during chemical cleaning]
In the boiler 100 having such a configuration, the brackish water separator 130 is chemically cleaned from the economizer 129 of the water supply system. Hereinafter, the part (equipment) for which chemical cleaning is performed is referred to as a cleaning target device. Chemical cleaning is performed by stopping the operation of the boiler 100, closing the main steam check valve 262, installing a temporary pipe, and circulating the chemical cleaning liquid in the equipment to be cleaned. Hereinafter, the configuration of temporary piping and the like installed during chemical cleaning will be described.

FIG. 4 is a diagram for explaining a temporary pipe or the like installed in the boiler 100 of FIG. 3 for chemical cleaning. Temporary pipes, etc. are shown by broken lines. For the temporary piping, for example, a port for connecting the temporary piping at the time of chemical cleaning (for example, a flange connection portion closed by a blind flange) is provided in advance in the connection destination pipe, and the port is opened for connection. do.

First, a first temporary pipe 311 is provided from the saturated water pipe 217 to the main water supply pipe 216 so as to bypass the recirculation valve 267 and the water supply valve 266 of the circulation pipe. Further, a temporary circulation pump (cleaning pump) 312 is provided in the first temporary pipe 311. The washing pump 312 circulates the water or the chemical washing liquid supplied to the first temporary pipe 311. The chemical washing liquid is separated by the washing pump 312 into the first temporary pipe 311, the main water supply pipe 216, the coal saver 129, the water cooling wall descending pipe 221 and the furnace water wall pipe 222, the first connecting pipe 225, the steam water separator 130, and the steam water separation. The scale is removed by circulating in the water storage tank 131 and the saturated water pipe 217.

The first temporary pipe 311 may be provided with a heater 314 in the front stage of the cleaning pump 312 and a sludge removing device 315 in the rear stage. The heater 314 heats the circulating fluid. Further, the sludge removing device 315 is a device for recovering the scale contained in the chemical washing liquid and removed from the equipment to be cleaned.

Further, in the present embodiment, in order to supply the seal water (filled water) to the superheater 140, the main is downstream from the make-up water tank 333 to the tertiary superheater 143 and upstream from the main steam stop valve 262. The second temporary pipe 331 is connected to the steam pipe 212. The connection port of the second temporary pipe 331 of the main steam pipe 212 is referred to as a seal water supply port 339. Further, the second temporary pipe 331 is provided with a supply valve 334, and a superheater seal pump 332 for supplying seal water is provided between the make-up water tank 333 and the supply valve 334.

Further, as shown in FIG. 4, a temporary water level gauge 321 is provided in the saturated steam pipe 211 connected from the brackish water separator 130 to the primary superheater 141. The temporary water level gauge 321 is provided to monitor the balance between the supply and discharge of the seal water by monitoring the water level of the seal water supplied to the superheater 140. The temporary water level gauge 321 is composed of a water level gauge tube 322 and a valve 323.

Further, in the present embodiment, a temporary drain pipe 341 having a primary superheater inlet drain valve 342 is connected to the saturated steam pipe 211. The connection port of the temporary drainage pipe 341 of the saturated steam pipe 211 is referred to as a seal water drainage port 349. The seal water supplied from the make-up water tank 333 to the superheat line through the second temporary pipe 331 and from the seal water supply port 339 is discharged from the seal water drain port 349 via the temporary drain pipe 341. Further, when the chemical washing liquid is extruded from the brackish water separator 130, the chemical washing liquid is also discharged through the temporary drain pipe 341. Hereinafter, the area from the seal water supply port 339 into which the seal water is injected to the seal water drain port 349 through which the seal water is discharged through the superheater 140 is referred to as a non-cleaning unit as a system for injecting the seal water.

FIG. 5 describes the vertical positions of the brackish water separator 130, the superheater 140, the temporary water level gauge 321 and the primary superheater inlet drain valve 342 of the present embodiment. As shown in this figure, it is desirable that the temporary water level gauge 321 is provided vertically above the connecting pipe 212a connecting the primary superheater 141 and the secondary superheater 142 located above the ceiling portion 122. As shown in this figure, the seal water is supplied from the make-up water tank 333 so that the water level is monitored by the temporary water level meter 321 and the predetermined water level (water seal monitoring level) is always maintained. The water seal monitoring level is set above the connecting pipe 212a. As for the water level, for example, the position of the water surface in the water level gauge tube 322 is photographed by a camera, and the image is monitored by a monitor or the like in a separate room.

The chemical lotion is supplied from the chemical liquid tank through the temporary supply pipe 394 provided in the first temporary pipe 311.

Further, as the sealing water, for example, water containing hydrazine (N2H4) at a concentration of 100 ppm (100 mg / L) is used.

[Procedure for chemical cleaning]
Next, the flow of chemical cleaning of this embodiment will be described. FIG. 6 is a flow showing a procedure at the time of chemical cleaning of the present embodiment.

First, after the operation of the boiler 100 is stopped, for example, after the temperature of the primary superheater 141 is lowered to about 100 ° C. or less, the main steam check valve 262 is closed, and the water seal monitoring level is applied to the non-cleaning part (heat transfer tube). Inject sealing water up to (step S1101). Here, the supply valve 334 is opened, and the seal water is supplied from the make-up water tank 333 through the second temporary pipe 331 and the seal water supply port 339 of the main steam pipe 212, and the superheater 140 (primary superheater 141, 2) is supplied. Fill the secondary superheater 142 and the tertiary superheater 143) with sealing water. The water level is grasped by opening the valve 323 and monitoring the temporary water level meter 321.

After that, the drain valve 342 at the inlet of the primary superheater is opened, and the supply and discharge of the seal water (additional water) to the superheat line is started while maintaining the water level of the seal water (step S1102). As shown by the thick line in FIG. 7, the seal water containing the additional water is supplied from the make-up water tank 333 to the non-cleaning portion from the seal water supply port 339 via the second temporary pipe 331, and the tertiary superheater 143. It is discharged from the secondary superheater 142 and the primary superheater 141 via the saturated steam pipe 211, from the sealed water drain port 349 of the saturated steam pipe 211, and through the temporary drain pipe 341.

The seal water (tension water) to be added up here is supplied from the make-up water tank 333, for example, at a flow rate of 1 t / h. Then, the opening degree of the primary superheater inlet drain valve 342 is adjusted so that the water level in the water level gauge tube 322 of the temporary water level gauge 321 becomes constant.

After that, chemical cleaning of the device to be cleaned is started (step S1103). Here, the water supply valve 266 and the recirculation valve 267 are closed, the chemical washing liquid is added to the brackish water separator 130, and then the washing pump 312 is operated. Then, as shown by the broken line in FIG. 7, the chemical washing liquid in the brackish water separator 130 is the brackish water separator water storage tank 131, the first temporary pipe 311, the main water supply pipe 216, the coal saving device 129, and the furnace water of the furnace 120. It circulates to the brackish water separator 130 via the wall pipe 222 and the first connecting pipe 225, during which the brackish water separator 130, the brackish water separator water storage tank 131, the coal saving device 129, and the furnace water wall pipe 222 are chemically cleaned. ..

During this period, the drainage property monitoring process is performed by monitoring the water quality monitoring instrument 392 installed in the temporary drainage pipe 341.

After performing chemical cleaning for a predetermined time, the cleaning pump 312 is stopped and cleaning is performed with purged water (step S1104). Here, for example, first, the residual water in the system of the superheater 140 is supplied with purged water from the seal water supply port 339 by the superheater seal pump 332, and the system of the superheater 140 is purged (extruded and discharged by backflow). .. Next, purged water is flowed through the brackish water separator 130, the brackish water separator water storage tank 131, the furnace water wall pipe 222, the economizer 129, etc., and drained from the temporary drain pipe 341 to carry out the chemical washing remaining in the system. Push out the liquid.

After the extrusion of the chemical washing liquid remaining in the system is completed, the temporary pipe is removed, the start operation is performed, and the operation of the boiler 100 is restarted.

[Drainage property monitoring process]
Next, the flow of the wastewater property monitoring process in step S1103 will be described with reference to FIG. In the present embodiment, the conductivity and pH are monitored, and the amount of sealing water (tension amount) to be supplied is increased or decreased, or the concentration of the deoxidizing neutralizing agent is increased or decreased as necessary.

As described above, during chemical cleaning and until the end of cleaning, the seal water adjusted to a predetermined concentration by injecting a deoxidizing neutralizing agent into the make-up water from the make-up water tank 333 via a temporary supply pipe 393 is provided. It is supplied using a superheater seal pump 332. First, it is supplied at a predetermined flow rate (1 t / h) (initial amount) (step S1211). After that, the following processing is continued until the chemical cleaning elapses a predetermined cleaning time and the elution iron concentration in the chemical cleaning solution meets the end determination criteria (step S1212).

The water quality monitoring instrument 392 provided in the temporary drainage pipe 341 measures the electric conductivity and pH of the sealed water to be drained, and determines whether the electric conductivity tends to increase or decrease (step S1201). If the electric conductivity does not tend to increase or the pH does not tend to decrease (S1201; No), it is determined to be normal, the process returns to step S1212, and the process is continued as it is.

On the other hand, when the electric conductivity tends to increase or the pH tends to decrease (S1201; Yes), it is determined that the chemical washing liquid tends to flow in, and the supply flow rate of the sealing water to be added is increased by a predetermined amount (step). S1202). Here, the amount is gradually increased from 1 t / h to 20 t / h (maximum value).

During the increase, the conductivity and pH of the sealed water drainage are continuously measured until the maximum amount is reached (step S1203), and it is determined whether or not the tendency is statically indeterminate (step S1204). If the tendency of the conductivity to increase or the pH to decrease continues (S1204; Yes), the process returns to step S1202 to increase the supply flow rate. On the other hand, when the tendency of increasing the electric conductivity or the tendency of decreasing the pH is not observed (S1204; No), it is determined that the electric conductivity of the sealing water has settled, and the supply flow rate is gradually set to the initial value (S1204; No). Here, while returning to 1t / h) (step S1208), the process returns to step S1201 and the process is continued.

On the other hand, when the increasing tendency of the electric conductivity or the decreasing tendency of the pH does not improve even if the supply flow rate is increased to the maximum value (S1203; Yes), that is, it is determined whether the increasing tendency of the electric conductivity or the decreasing tendency of the pH continues. (Step S1214), if continuing (S1214; Yes), the concentration of the deoxidizing neutralizing agent is increased by a predetermined amount (step S1205). Here, for example, hydrazine (N2H4) is increased to 500 ppm (maximum concentration). If the tendency of increasing the conductivity or decreasing the pH does not continue even if the supply flow rate is increased to the maximum value (S1214; No), the process returns to step S1212 and the process is continued.

While the concentration is increasing, the conductivity and pH of the seal water are measured at predetermined time intervals until the maximum concentration is reached (step S1206), and it is determined whether or not the tendency is static (step S1207). If the tendency of increasing or decreasing pH continues (S1207; Yes), the process returns to step S1205 and the concentration is increased. On the other hand, if the electric conductivity does not tend to increase or the pH does not decrease (S1207; No), it is determined that the electric conductivity and pH of the sealed water drainage have settled, and the supply flow rate and concentration are gradually increased. The initial value (here, 100 ppm, 1 t / h) is returned to (step S1213), and the process returns to step S1214.

When the conductivity and pH do not improve even if the concentration of the deoxidizing neutralizer is increased to the maximum concentration (S1209; Yes), that is, when the acidity exceeds the pH threshold TH1 (for example, 5) (pH <5; S1209). Yes) makes a decision to move to the last resort and implements it (step S1210). On the other hand, when the acidity does not exceed the pH threshold TH1 (pH ≧ 5; S1209; No), it is determined that the acidity has improved, and the process returns to step S1212 as it is.

There is a correlation between the conductivity and the pH. For example, when the pH of the sealing water drops to 5 of the pH threshold TH1, the superheater 140 from the sealing water supply port 339 as a final means, for example, at 100 t / h. Continue chemical cleaning while protecting the superheater 140 by backwashing.

According to the present embodiment, in the chemical cleaning method of the boiler 100, a seal water injection step of injecting water into the non-cleaning portion of the boiler 100 so as to maintain a water seal monitoring level which is a predetermined water level, and a coal saving device 129. A cleaning step for circulating a chemical cleaning agent solution (chemical cleaning solution) to the equipment to be cleaned including the furnace water wall tube 222 is provided, and non-cleaning is performed while maintaining the water level at the water seal monitoring level during the cleaning step. Continue to flush the seal water to the part.

As described above, according to the present embodiment, the sealing water is continuously flowed to the superheated line during the chemical cleaning. Then, a temporary drain pipe 341 is provided in the saturated steam pipe 211 connecting the superheater 140 and the brackish water separator 130 in which the chemical washing liquid is distributed, and the sealing water flowing to the non-washing portion is discharged from there. Therefore, even if the chemical washing liquid flows into the saturated steam pipe 211 due to the foaming of the chemical washing liquid or being accompanied by the generated steam, it can be flushed to the temporary drainage pipe 341 by the pressure of the running water. Therefore, compared to static water filling to a partial device, the seal water is dynamically distributed to all routes of the non-cleaning part, so that the inflow of the chemical washing liquid to the non-cleaning target device is high in the boiler 100. It can be prevented with accuracy. Therefore, the superheater 140 of the boiler 100, which is a non-cleaning target device, can be protected from the chemical washing liquid, and the soundness of the structure of the entire boiler 100 can be maintained.

In addition, since the conductivity and pH are constantly monitored during chemical cleaning, it is possible to detect the inflow of chemical lotion or chemical lotion into non-cleaning equipment at an early stage, and it is possible to respond promptly. Furthermore, chemical cleaning can be realized only with simple temporary piping, and the work is simple because no special sealing member is required. Therefore, the work period can be shortened. In addition, the injection amount of a chemical solution such as an antifoaming agent is reduced or unnecessary, which is advantageous in terms of cost.

<Modification 1>
In the above embodiment, the sealing water is supplied from the second temporary pipe 331 connected to the main steam pipe 212, but the follow-up after the start of cleaning is not limited to this. For example, as shown in FIG. 9, it may be supplied from the spray water system of each superheater 140. When supplying from the spray water system, the seal water is not injected from the main steam pipe 212.

Since the supply of the seal water from the spray water system is closer to the primary superheater 141 than the supply from the seal water supply port 339 of the main steam pipe 212, the time lag due to the injection of the seal water is small and the seal is more efficiently sealed. Water can be injected. Since the time to reach the primary superheater 141 is short, it is particularly effective when the concentration of the seal water is changed during the wastewater property monitoring process.

For example, during the wastewater property monitoring process, even if the seal water is supplied up to the maximum amount (20 t / h) in step S1203, no improvement is expected, and the seal water is supplied at the timing of increasing the concentration of the deoxidizing neutralizer. Change the mouth from the main steam pipe 212 to the spray water system. For example, even if the sealing water having a high concentration of hydrazine is supplied from the main steam pipe 212, it takes time to reach the primary superheater 141 due to the sealing water held in the secondary superheater 142 and the tertiary superheater 143. It takes. However, by supplying from the spray water system, the sealing water having a high concentration of hydrazine can be supplied to the primary superheater 141 in a short time.

<Modification 2>
Further, the seal water supplied from the make-up water tank 333 may be warmed. In this case, as shown in FIG. 10, a heater 335 is additionally attached to the second temporary pipe 331. The heater 335 is provided, for example, between the make-up water tank 333 and the superheater seal pump 332. The heater 335 uses, for example, the steam header 313, which is an auxiliary boiler, as a heat source, like the heater 314 of the first temporary pipe 311.

In the above embodiment, the sealing water supplied to the non-cleaning portion is at room temperature (for example, about 30 ° C.). In this modification, this is heated to 80 ° C. to 90 ° C. with a heater 335 and supplied as hot water.

With such a configuration, it is possible to prevent the sealing water at room temperature from flowing into the main steam check valve 262, and the main steam check valve 262 can be protected from the thermal shock caused by cold water. Generally, it takes about 4 days for the main steam check valve 262 to be cooled to such an extent that it is not damaged by thermal stress even if it comes into contact with the sealing water at room temperature. According to this modification, the temperature of the sealing water is high, so that this period can be shortened.

<Modification 3>
The method of avoiding thermal destruction of the main steam check valve 262 while shortening the construction period is not limited to the modified example 2. For example, after stopping the boiler 100, hot water heated by the heater 314 may be used as cooling water and passed through the entire boiler 100 to cool the boiler, and then the chemical cleaning operation may be started.

The distribution route of hot water in this case is shown in FIG. After the boiler 100 is stopped, the recirculation valve 267 and the water supply valve 266 are closed, and the temperature of the cold water in the system is raised to hot water. First, the cold water in the system is circulated through the furnace water wall pipe 222 by the heater 314 and the cleaning pump 312 to raise the temperature to hot water. The hot water after the temperature rise is passed from the brackish water separator 130 to the superheater 140 via the saturated steam pipe 211 to fill the main steam pipe 212 with water.

As a result, the main steam check valve 262 can be protected from the thermal shock caused by cold water, and the main steam pipe 212 can be filled with water at an early stage, so that the chemical cleaning procedure can be started at an early stage.

<< Second Embodiment >>
Next, the second embodiment of the present invention will be described. This embodiment is an example of a constant pressure once-through boiler 100a (hereinafter, simply referred to as "constant pressure once-through boiler 100a") without a brackish water separator 130. The same as those in the first embodiment are designated by the same reference numerals.

As shown in FIG. 12A, in the constant pressure once-through boiler 100a not provided with the brackish water separator 130, the furnace water wall pipe 222 has a cage outlet connecting pipe 232, a cage rear upper pipe 234, and a primary superheater inlet descending pipe 231. Is connected to the primary superheater 141. The boiler water that became hot in the furnace water wall pipe 222 reaches the upper pipe side 234 after the cage via the cage outlet connecting pipe 232, and partly reaches the superheater 140 via the primary superheater inlet descending pipe 231. Heads for the primary superheater bypass tube 233.

At the time of chemical cleaning, the water supply valve 266 is closed and the cleaning pump 312 is operated. Then, as shown by the thick line in FIG. 12 (a), the chemical washing liquid is supplied through the temporary supply pipe 394 (not shown) provided in the first temporary pipe 311. It joins the cage outlet connecting pipe 232 through the water supply pipe 216, the coal saver 129, and the furnace water wall pipe 222 of the furnace 120, and reaches the upper pipe side 234 after the cage. Then, it circulates by being returned to the first temporary pipe 311 branching from the primary superheater bypass pipe 233, and the economizer 129 and the furnace water wall pipe 222 are chemically cleaned.

Here, FIG. 12B is a thin cross section of the rear upper pipe side 234 of the cage. As shown in this figure, in the constant pressure once-through boiler 100a, the primary superheater bypass pipe 233 is connected vertically upward to the cage rear upper pipe 234, and the primary superheater inlet descending pipe 231 is connected downward. .. Therefore, the scale that has moved during the chemical cleaning of the constant pressure once-through boiler 100a flows into the cage rear upper pipe side 234 from the cage outlet connecting pipe 232 or the like. At this time, due to the particle classification action due to the decrease in flow velocity inside the cage rear upper pipe 234, fine particles (fine particle sludge) such as powder scale are released from the primary superheater bypass pipe 233 at a high flow velocity, and the system of the constant pressure once-through boiler 100a. Transferred to the outside. On the other hand, coarse particles (coarse grain sludge) such as flake-shaped scales are transferred to the primary superheater 141 by the primary superheater inlet descending pipe 231 connected downward at a low flow velocity.

Generally, since the primary superheater 141 has a U-shaped structure (pocket structure) as a whole, sludge tends to accumulate structurally. That is, the flake-shaped coarse-grain sludge conveyed from the cage rear upper pipe side 234 by the primary superheater inlet descent pipe 231 settles and bends at low flow velocity or when the flow stops in the pipe on the outlet side of the U-shaped structure. Accumulate in the part.

Conventionally, in order to prevent this, as shown in FIG. 13, a temporary connection pipe 391 for connecting the second temporary pipe 331 and the primary superheater inlet lowering pipe 231 is provided, and the seal water is supplied to the primary superheater inlet lowering pipe 231. We are supplying. However, at this flow rate, it is not possible to prevent the mixing of large flaky sludge.

In the present embodiment, in order to prevent this, as shown in FIG. 14A, a third temporary pipe 351 that branches from the first temporary pipe 311 and reaches the primary superheater inlet descending pipe 231 is provided. The third temporary pipe 351 is connected between the sludge removing device 315 of the first temporary pipe 311 and the connection portion between the main water supply pipe 216. Further, the third temporary pipe 351 is provided with a valve 352 and a flow meter 353. note that. A valve 316 and a flow meter 317 are also provided between the branch portion of the first temporary pipe with the third temporary pipe 351 and the connection portion with the main water supply pipe 216.

At the time of chemical cleaning, the valve 352 and the valve 316 are opened, and the chemical washing liquid after removing the sludge by the sludge removing device 315 is sent to the primary superheater inlet lowering pipe 231 via the third temporary pipe 351. Since the amount of fluid supplied is larger than that of the conventional example, as shown in FIG. 14 (b), the flow rate from the primary superheater inlet descent pipe 231 increases at the cage rear upper pipe side 234, and the primary superheater inlet descends. It is possible to push back the mixing of large flake-like sludge into the tube 231. The flow rate of the chemical washing liquid supplied through the third temporary pipe 351 is monitored by the flow meter 353 and the flow meter 317.

Even in the conventional example, by supplying a large amount of sealing water, the flake-shaped sludge can be suspended without settling. However, in this case, the seal water supplied from the make-up water tank 333 mixes with the chemical washing liquid, the concentration of the chemical washing liquid decreases, and the ability to dissolve and remove the boiler scale greatly decreases. However, according to the present embodiment, since the chemical washing liquid is supplied as sealing water, it is possible to prevent a decrease in the chemical washing liquid concentration and maintain the dissolving and removing ability.

Also in this embodiment, as in the first embodiment, the second temporary pipe 331 is connected from the make-up water tank 333 to the main steam pipe 212 on the upstream side of the main steam check valve 262. The second temporary pipe 331 is provided with a supply valve 334, and a superheater seal pump 332 is provided between the make-up water tank 333 and the supply valve 334. Further, in the present embodiment, a temporary drainage pipe 341 having a primary superheater inlet drain valve 342 is connected to the primary superheater inlet descending pipe 231 connecting the superheater 140 and the furnace water wall pipe 222 to be cleaned. ..

During chemical cleaning, the seal water is continuously supplied from the make-up water tank 333 at a predetermined flow rate, and is discharged from the temporary drain pipe 341 to prevent the chemical cleaning liquid from entering the overheating line.

In this embodiment, instead of installing a water level gauge, whether or not the seal water is maintained at a predetermined water level is grasped by monitoring the flow rate of the flow meters 353, 395, and 396. The flow meter 353 is installed in the third temporary pipe 351. Further, the flow meter 395 is a seal water supply port flow meter installed in the second temporary pipe 331 to monitor the supply amount of seal water, and the flow meter 396 is temporarily installed to monitor the drainage amount of seal water. It is a sealed water discharge port flow meter installed in the drain pipe 341. Here, the flow rates of both flow meters 395 and 396 are monitored. For example, if the supply amount is less than the discharge amount, the acid solution is drawn from the primary superheater inlet lowering pipe 231. Dilute the mixed acid solution concentration. In the present embodiment, by matching the supply amount and the discharge amount of the seal water, the invasion of the acid liquid from the primary superheater inlet descending pipe 231 into the primary superheater 141 is prevented.

As described above, according to the present embodiment, even in the constant pressure once-through boiler 100a, the sealing water continues to flow to the superheated line during the chemical cleaning as in the first embodiment. Then, a temporary drainage pipe 341 is provided in the primary superheater inlet descending pipe 231 connecting the superheater 140 and the furnace water wall pipe 222 in which the chemical washing liquid is distributed, and the seal water flowing to the superheater line is discharged from there. Therefore, even if the chemical washing liquid flows into the primary superheater inlet lowering pipe 231 due to the foaming of the chemical washing liquid or being accompanied by the generated steam, it can be flushed to the temporary drainage pipe 341 by the pressure of the running water. ..

Therefore, according to the present embodiment, it is possible to completely prevent the inflow of the chemical washing liquid into the non-cleaning target device in the constant pressure once-through boiler 100a by installing a simple temporary pipe. Therefore, the non-cleaning target device of the boiler 100 can be protected from the chemical washing liquid, and the soundness of the structure can be maintained.

Further, according to the present embodiment, in the constant pressure once-through boiler 100a, the chemical washing liquid is supplied to the primary superheater inlet lowering pipe 231 at the time of chemical washing. As a result, the flow rate of the primary superheater inlet lowering pipe 231 is increased, and the mixing of sludge into the primary superheater 141 can be reduced.

In this embodiment as well, modifications 1 to 3 of the first embodiment may be applied.

<Modification example 4>
Further, for example, a control unit (controller) may be provided, and the water supply control process and / or the drainage property monitoring process at the time of chemical cleaning of each of the above-described embodiments and modifications may be performed by the control unit. In this case, a sensor is provided in the temporary water level gauge 321 or the like, and the control unit controls the control signal for adjusting the opening degree of the primary superheater inlet drain valve 342 and the rotation of the superheater seal pump 332 in response to the signal from the sensor. Outputs control signals and the like.

100: Boiler, 100a: Constant pressure once-through boiler, 101: Power plant, 102: Generator, 120: Fire furnace, 121: Sub-side wall, 122: Ceiling, 123: Rear heat transfer part, 129: Coal saver, 130: Steam water separator, 131: steam water separator water storage tank, 140: superheater, 141: primary superheater, 142: secondary superheater, 143: tertiary superheater, 150: reheater, 160: steam turbine, 161: high pressure Turbine, 162: Medium pressure turbine, 163: Low pressure turbine, 170: Water recovery device, 181: Recovery pump, 182: Low pressure heater, 183: Boiler, 184: Water supply pump, 185: High pressure heater,
211: Saturated steam pipe, 212: Main steam pipe, 212a: Connecting pipe, 213: Low temperature reheated steam pipe, 214: High temperature reheated steam pipe, 215: Turbine exhaust pipe, 216: Main water supply pipe, 217: Saturated water pipe, 221: Water cooling wall descent pipe 222: Furnace water wall pipe 225: First connecting pipe, 231: Primary superheater inlet descent pipe 232: Cage outlet connecting pipe 233: Primary superheater bypass pipe 234: Cage rear upper part Pipe, 262: Main steam stop valve, 266: Water supply valve, 267: Recirculation valve,
311: First temporary pipe, 312: Cleaning pump, 313: Steam header, 314: Heater, 315: Sludge remover, 316: Valve, 317: Flow meter, 321: Temporary water level gauge, 322: Water level gauge tube, 323 : Valve, 331: Second temporary pipe, 332: Superheater seal pump, 333: Makeup water tank, 334: Supply valve, 335: Heater, 339: Seal water supply port, 341: Temporary drainage pipe, 342: Primary overheating Instrument inlet drain valve, 349: Sealed water drainage port, 351: Third temporary pipe, 352: Valve, 353: Flow meter, 391: Temporary connection pipe, 392: Water quality monitoring instrument, 393: Supply pipe, 394: Supply pipe, 395: Flow meter, 396: Flow meter

Claims (7)

A method for chemically cleaning a boiler that chemically cleans the furnace water wall pipe of a thermal power generation boiler equipped with an economizer, a furnace water wall pipe, and a superheater.
A seal water injection step of injecting seal water into a heat transfer tube in a non-cleaning portion including a superheater so as to maintain a predetermined water level, and a seal water injection step.
A cleaning step of circulating a chemical cleaning agent solution to the equipment to be cleaned including the economizer and the water wall pipe of the furnace is provided.
A method for chemically cleaning a boiler, in which the sealing water is continuously flowed through the heat transfer tube in the non-cleaning portion while maintaining the predetermined water level during the cleaning step. The method for chemically cleaning a boiler according to claim 1.
In the cleaning step, the sealing water is supplied from the sealing water supply port downstream of the superheater in the non-cleaning section, and drained from the sealing water drain port upstream of the superheater in the non-cleaning section. Boiler chemical cleaning method. The method for chemically cleaning a boiler according to claim 2.
The thermal power generation boiler includes a brackish water separator connected to the furnace water wall pipe via a connecting pipe and connected to the superheater via a saturated steam pipe.
The sealed water drain port is a method for chemically cleaning a boiler provided in the saturated steam pipe. The method for chemically cleaning a boiler according to claim 3.
The water level is a method for chemically cleaning a boiler, which is measured upstream of the sealed water drainage port of the saturated steam pipe. The method for chemically cleaning a boiler according to claim 2.
The sealed water drainage port is a method for chemically cleaning a boiler provided in a superheater inlet descending pipe that connects the superheater water wall pipe and the superheater. The method for chemically cleaning a boiler according to any one of claims 1 to 5.
In the seal water injection step, the seal water is supplied by heating the main steam stop valve of the thermal power generation boiler to a temperature that can be protected from thermal impact by using the heat of a heater that heats the chemical cleaning chemical solution. , Chemical cleaning method of boiler. The method for chemically cleaning a boiler according to any one of claims 1 to 5.
Prior to the sealing water injection step, a method for chemically cleaning a boiler in which cold water is heated by using a heater for heating the chemical cleaning chemical solution and the heat of the furnace water wall tube to fill the main steam tube with water. ..

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