JP7183639B2 - Boiler chemical cleaning method - Google Patents

Description

The present invention relates to a method for chemically cleaning a boiler, and more particularly to a method for evenly chemically cleaning parallel wall tubes.

FIG. 3 shows a schematic configuration of a steam system of a thermal power boiler. Steam generated by burning fuel in a furnace 152 with a burner 151 is supplied to a high-pressure turbine 157 through a steam drum 153, a saturated steam pipe 154, a superheater 155, a main steam pipe 156, and a main steam stop valve 156a. . The steam that has worked in the high-pressure turbine 157 is sent through the low-temperature reheat steam pipe 158 to the reheater 159 to be heated, and then through the high-temperature reheat steam pipe 160 to the intermediate-pressure turbine 161 and the low-pressure turbine 162. Supplied to do the job. Also, the steam that has worked in the low-pressure turbine 162 is condensed in the condenser 163 and then returned to the furnace 152 through the degassing pipe 164 , the boiler feed pump 165 and the economizer 166 .

A drain pipe 156 b having a drain valve is connected to the main steam pipe 156 .

A nose wall tube 105 is provided on the exit side of the upper portion of the furnace wall tube. As shown in FIGS. 4 and 5, the nose wall pipe 105 is curved to have a nose shape (dogleg shape) when viewed from the side, and protrudes inward of the furnace. The nose wall pipe 105 is for preventing the combustion gas from short-circuiting to the furnace exit (Patent Document 1).

In the steam system of such a thermal power boiler, there is known a method of chemically cleaning the evaporator tubes, the steam drum, the downcomer tubes, the manifold, and the like by circulating a cleaning chemical solution (Patent Documents 2 and 3).

In commercial and general industrial boilers, when chemical cleaning is used to remove scales such as iron oxide that adheres to the inner surface of water cooling wall evaporator tubes, the chemical cleaning liquid flow balance is not balanced for each evaporator tube due to the structure of the boiler. In the evaporator tube where the flow rate has become uniform and the flow velocity has decreased, problems such as a failure to maintain a predetermined temperature due to heat radiation may occur, and there is a concern that scale cannot be removed and remains.

Especially in a large supercritical pressure boiler, the configuration and structure of the boiler evaporator tubes are complicated. There is a structure that separates the flow.

During chemical cleaning, circulation cleaning is performed at a smaller flow rate than during boiler operation due to restrictions on cleaning equipment. Although the flow rate sent to the boiler is controlled, the balance of the flow rate flowing to each evaporator tube after the split flow can be grasped. However, due to the structure of the boiler, there is a concern that a large amount of chemical cleaning liquid will flow through the middle side wall pipe and the upper water wall pipe, which have less pressure loss than the nose wall pipe.

Since the nose wall pipe has a bent structure, the passage of the cleaning liquid is likely to be hindered, causing a decrease in the flow velocity in some pipes, releasing heat, and the predetermined temperature cannot be maintained, possibly causing scale to remain.

In addition, as shown in FIG. 4, due to the decrease in the flow velocity, particles (sludge) of undissolved scale are deposited in the nose wall pipe without being discharged, blocking the contact between the scale surface and the cleaning liquid, preventing the dissolution of the scale from progressing. It is also possible to remain. In addition, the air that was mixed in before the cleaning liquid was passed, the carbon dioxide gas generated by the decomposition of the cleaning liquid, and the hydrogen gas generated by the contact between the cleaning liquid and the boiler tube remained in the horizontal part of the nose wall pipe, preventing the passage of the cleaning liquid. There are also concerns about obstruction.

WO2004/023037 Japanese Patent Application Laid-Open No. 2006-322672 JP 2015-230150 A

In the conventional chemical cleaning of supercritical pressure boilers, the chemical cleaning liquid splits into the nose wall tube and the middle side wall tube, and the flow rate of each evaporator tube could not be grasped and the liquid flow was not confirmed.

Furthermore, about 500 evaporator tubes are arranged in a line in one nose wall pipe, and the chemical cleaning liquid is supplied from both ends of the nose wall pipe inlet header. In the central part, it is not possible to grasp whether or not the flow rate is uniform in the evaporator tube, and there is a possibility that the flow rate becomes non-uniform as shown in FIG.

The present invention increases the flow rate in the nose wall pipe by connecting temporary cleaning pipes to the inlet and outlet nozzles of the nose wall pipe where the flow speed may decrease, in addition to the flow rate of washing sent to the entire boiler. It is an object of the present invention to provide a chemical cleaning method for a boiler that can perform chemical cleaning while preventing temperature drop due to heat radiation, inhibition of liquid flow due to gas accumulation, and inhibition of contact with cleaning liquid due to exfoliated particles of undissolved scale.

The boiler chemical cleaning method of the present invention has an economizer into which feed water is introduced through a feed pipe, and a wall pipe into which water from the economizer is introduced, and a part of the wall pipe is a nose wall pipe. Alternatively, the furnace is a wall pipe that is curved so that the side view shape is nose-shaped and protrudes into the furnace, a steam separator connected to the wall pipe, and the steam from the steam separator is superheated. A method for chemically cleaning a boiler having a superheater, a drain tank for receiving water from a steam separator, and a pump and piping for circulating water in the drain tank to the water supply pipe, the method comprising the steam separator, In a boiler chemical cleaning method in which a temporary pipe for circulating cleaning water is installed in the drain tank, the economizer and the wall pipe, and a circulation pump is installed in the temporary pipe to circulate the cleaning water, the temporary pipe on the downstream side of the circulation pump. to the nose wall pipe inlet header, and a second additional temporary pipe to connect the temporary pipe upstream of the circulation pump to the nose wall pipe outlet header. A part of the washing water is circulated to the nose wall pipe through the first and second additional temporary pipes.

In one aspect of the present invention, the downstream side of the first additional temporary pipe is branched into two or more pipes, and communicates with at least two points, namely, the longitudinal center portion and both end sides of the nose wall pipe inlet wall pipe. do. Further, the upstream portion of the second additional temporary pipe is branched into two or more, and communicates with at least two locations, namely, the center portion and both end sides of the nose wall pipe outlet wall pipe in the longitudinal direction.

In the boiler chemical cleaning method of the present invention, in addition to the cleaning flow rate sent to the entire boiler, additional temporary cleaning pipes are connected to the nose wall pipe inlet and outlet nozzles where the flow velocity may decrease to clean the nose wall. By increasing the flow velocity in the pipe, it is possible to perform chemical cleaning while preventing temperature drop due to heat dissipation, inhibition of liquid flow due to gas accumulation, and inhibition of contact with the cleaning liquid due to exfoliated particles of undissolved scale.

According to the present invention, the non-uniformity of liquid flow during chemical cleaning is predicted in advance, and an additional temporary pipe is connected to the nozzle of the nose wall pipe at the relevant portion to allow liquid to flow. Since sludge deposition is avoided and scale is prevented from being left behind, long-term safe operation of the boiler plant becomes possible.

BRIEF DESCRIPTION OF THE DRAWINGS It is a system diagram explaining the chemical cleaning method of the boiler which concerns on embodiment. BRIEF DESCRIPTION OF THE DRAWINGS It is typical sectional drawing of a boiler explaining the chemical cleaning method of the boiler which concerns on embodiment. 1 is a schematic system diagram of a boiler apparatus; FIG. Fig. 10 is a side view of the nose wall tube; Fig. 3 is a schematic perspective view of a nose wall tube; FIG. 4 is an explanatory diagram of the water flow rate distribution of the nose wall pipe; It is a flow velocity distribution analysis diagram of a nose wall pipe.

FIG. 2 shows a configuration diagram of a boiler to which the cleaning method according to the embodiment of the invention is applied. FIG. 1 shows a flow system diagram of water and steam in this boiler.

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

High-temperature combustion gas generated by a plurality of burners 80 provided in the lower portion of the furnace 9 rises inside the furnace 9 and is discharged from the rear flue outlet 93 as low-temperature exhaust gas to the outside of the boiler. The furnace 9 is provided with a furnace lower wall tube 10, an upper water-cooled wall tube 12, a nose wall tube 105, and the like. The furnace lower wall tube 10 extends upward from the lower part of the furnace 9 in a spiral manner. The upper water wall pipes 12 each consisting of a plurality of pipes extend vertically toward the upper part of the furnace 9 . The nose wall tube 105 consists of a plurality of tubes as shown in FIG.

The rear flue is defined by a rear heat transfer wall tube 33 or the like consisting of a plurality of tubes. The rear flue is divided into two gas flow paths by a dividing wall tube 120 extending along the exhaust gas flow. The split-wall tube 120 also consists of a plurality of tubes.

A reheater 71 is arranged in one of the gas channel divisions of the rear flue. A primary superheater 40 and an economizer 2 are arranged in the other split gas flow path. Also, an evaporator may be provided in the divided gas flow path as required.

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

Next, the water supply system of this boiler will be described. Water to the boiler is first supplied to an economizer 2 from a water supply pipe 1 having a water supply valve 1a. In the economizer 2, the 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 wall downcomer. 3. The water that has passed through the water-cooled wall downcomer 3 is distributed to the furnace wall tube inlet header 103 via the furnace wall tube inlet manifold 103a (FIG. 1), and flows through the furnace lower wall tube 10 spirally surrounding the furnace 9. rises while absorbing the heat of Water is heated to near saturation temperature.

The high-temperature water that has risen up the furnace lower wall pipe 10 flows into the furnace 9 intermediate header 11, where its temperature is homogenized, and then flows into the furnace upper wall pipe 12 provided in the upper part of the furnace 9. It flows through furnace wall tube outlet header 12a, furnace nose wall tube inlet manifold 105a and into furnace outlet wall tube 106 (FIG. 1) or nose wall tube 105 via respective inlet headers 105A, 106A. The high-temperature water absorbs heat in the furnace 9 while ascending the wall pipes 105 and 106, and becomes a mixed fluid of liquid-phase high-temperature water and gas-phase steam. This mixed fluid flows into the steam separator inlet manifold 13 through the outlet headers 105B and 106B of the wall pipes 105 and 106, and after the fluid temperature is equalized, it flows into the steam separator 20, Separates into steam and water. The separated water is recirculated from the drain tank 21 to the water supply pipe 1 via the boiler circulation pump 24 and the circulation pipe 22 having the valves 23 and 25 . Also, the steam separated by the steam separator 20 is supplied to the ceiling wall inlet header 107 (FIG. 2).

As shown in FIG. 2, the steam supplied to the ceiling wall inlet header 107 passes through a ceiling wall pipe that constitutes the ceiling wall 30 provided from the upper part of the furnace 9 to the upper part of the downstream exhaust gas flow path, and flows into the ceiling wall pipe. On the way to the wall outlet header 108, it is heated by heat absorption and becomes superheated steam.

The superheated steam gathered at the ceiling wall outlet header 108 is distributed to the rear heat transfer wall inlet header 110 through the rear heat transfer wall downcomer 31 and the rear heat transfer wall inlet connecting pipe 109, and further to the rear heat transfer wall 33. After being heated at , it collects in the rear heat transfer wall rear wall outlet header 34 via the rear heat transfer wall outlet header 111 and the rear heat transfer wall outlet connecting pipe 112 or from the rear heat transfer wall 33 .

The superheated steam collected at the rear wall outlet header 34 of the rear heat transfer wall flows through the primary superheater connecting pipe 35 into the primary superheater 40 installed in the rear flue, and then installed at the upper part of the furnace 9. After being superheated through the secondary superheater 50 and the tertiary superheater 60 in order, the steam is sent to the high pressure turbine via the main steam pipe 61 and the main steam stop valve 62 .

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

When chemically cleaning the wall pipes of the boiler, the economizer 2, etc., after stopping the operation of the boiler, as shown in FIGS. A temporary pipe 26 is provided so as to bypass the , and a temporary circulation pump 27 is provided in the temporary pipe 26 .

The upstream end of the temporary pipe 26 is connected to the upstream side of the circulation pump 24 of the circulation pipe 22 . The downstream end of the temporary pipe 26 is connected to the water supply pipe 1 downstream of the water supply valve 1a. The temporary pipe 26 is provided with an injection portion 201 for heating steam, an injection portion 202 for cleaning chemicals (an aqueous solution of chemicals), and a temporary circulation pump 27 in this order from the upstream side to the downstream side.

Further, a second additional temporary pipe 210 is provided to communicate the upstream side of the heating steam injection part 201 in the temporary pipe 26 with the nose wall pipe outlet header 105B. Furthermore, a first additional temporary pipe 210 is provided so that the downstream side of the temporary circulation pump 27 in the temporary pipe 26 communicates with the nose wall pipe inlet header 105A and the inflow pipe to it.

The upstream side of the additional temporary pipe 210 is branched into three and connected near the middle and near both ends in the longitudinal direction of the nose wall pipe outlet header 105B, but may be connected at more locations. The downstream side of the additional temporary pipe 211 is branched into three pipes, which are connected to near the middle of the nose wall pipe inlet header 105A in the longitudinal direction and to each of the inflow pipes at both ends of the header 105A. The additional temporary pipe 211 may also be connected to multiple locations in the longitudinal direction of the nose wall pipe inlet header 105A.

Also, a temporary supply pipe (not shown) for washing water (clear water such as pure water) is connected to an appropriate location of the temporary pipe 26 from the steam separator 20 . Further, as shown in FIG. 2, a temporary drainage pipe 1c having a valve 1b is connected to the water supply pipe 1 on the downstream side of the water supply valve 1a.

After stopping the operation of the boiler, the boiler is filled with water through a temporary supply pipe, the temporary circulation pump 27 is operated, and heating steam and cleaning chemicals are injected. The washing water is supplied to the temporary pipe 26, the water supply pipe 1, the economizer 2, the lower wall pipe 10 and the upper wall pipe 12 of the furnace 9, the furnace outlet wall pipe 106 or the nose wall pipe 105, the manifold 13, the steam separator 20 and The water is circulated to the drain tank 21, and the steam separator 20, the drain tank 21, the economizer 2, the wall pipes 10, 12, 105, 106 and each header are chemically washed during this time.

Furthermore, in this embodiment, part of the cleaning liquid from the temporary circulation pump 27 is supplied to the nose wall pipe lower header 105A from the center and both ends thereof via additional temporary pipes 211 as well. From the nose wall pipe upper header 105B, the cleaning liquid is returned to the temporary pipe 26 through the additional temporary pipe 210 also from both ends and the center. As a result, in the nose wall tube 105, the flow rate of the cleaning liquid is equalized between the central portion and both end sides of the nose wall tube 105 in the wall tube arrangement direction, and each wall tube is evenly cleaned. Also, in the wall pipe near the center in the arrangement direction, by increasing the flow velocity inside the pipe, it is possible to prevent temperature drop due to heat radiation, hindrance of liquid flow due to gas accumulation, and hindrance of contact with the cleaning liquid due to peeled particles of undissolved scale. .

After continuing this chemical cleaning for a predetermined time, the temporary circulation pump 27 is stopped and the cleaning water is discharged to the drain pipe 1c. Also, fresh water is supplied to wash the steam separator 20, the drain tank 21, the economizer 2, the wall pipes 10, 12, 105, 106 and the headers, and drain the water from the drain pipe 1c.

After the cleaning chemicals remaining in the system are pushed out, rust prevention and blowing are performed, the temporary piping is removed, normal water washing and starting operation are performed, and the operation of the boiler is restarted.

According to this cleaning method, in addition to the cleaning flow rate sent to the entire boiler, temporary cleaning pipes are connected to the inlet and outlet nozzles of the nose wall pipe where the flow velocity may decrease to increase the flow velocity in the nose wall pipe. As a result, chemical cleaning can be performed while preventing temperature drop due to heat dissipation, inhibition of liquid flow due to gas accumulation, and inhibition of contact with the cleaning liquid due to exfoliated particles of undissolved scale.

In the boilers of FIGS. 1 and 2, in addition to the circulation flow rate of the entire boiler (approximately the flow rate for two cycles of one volume of cleaning liquid per hour), for example, about 100 to 300 m ³ /hr within the margin of the circulation pump discharge rate. A flow rate of cleaning fluid is injected into the inlet header 211 of the nose wall tube.

By doing this, in addition to the circulating flow rate of the entire boiler, the flow rate injected from the nose wall pipe inlet joint is added to pass through the nose wall pipe 105, making it possible to perform chemical cleaning at a faster flow rate than before. rice field.

^For example, in the ^cleaning system of FIGS. By injecting closer, the flow velocity in the nose wall tube can be increased, as shown in FIG.

FIG. 7 shows an example of analysis results of the flow velocity distribution in the nose wall tube in the conventional example and the example of the present invention.

In the above embodiment, the entire boiler is cleaned, but the method of the present invention can selectively chemically clean only the nose wall pipe without cleaning the entire boiler.

Cleaners that dissolve and remove scale include inorganic acids such as hydrochloric acid, hydrofluoric acid, and sulfamic acid, and organic acids such as citric acid, glycolic acid, formic acid, oxalic acid, gluconic acid, maleic acid, malic acid, malonic acid, and acetic acid. Ethylenediaminetetraacetic acid and its salts are used as chelate detergents, and auxiliary agents such as ascorbic acid, erythorbic acid, hydrazine, and corrosion inhibitors are mixed with these as reducing agents. Which of the above chemicals is used does not limit the method of the present invention.

1 feed pipe 2 economizer 9 furnace 10 lower furnace wall pipe 12 upper furnace wall pipe 20 steam separator 21 drain tank 24 recirculation pump 26 temporary pipe 27 temporary recirculation pump 40, 50, 60 superheater 105 nose wall pipe 106 Furnace outlet wall pipe 210, 211 Additional temporary pipe

Claims (3)

an economizer into which water is introduced by a water supply pipe;
It has a wall pipe into which water from the economizer is introduced, and a part of the wall pipe is a nose wall pipe or is curved so as to have a nose shape when viewed from the side, and protrudes into the furnace. a furnace which is a wall tube with
a steam separator connected to the wall pipe;
a superheater for superheating the steam from the steam separator;
a drain tank for receiving water from the steam separator;
A method for chemically cleaning a boiler having a pump and piping for circulating water in the drain tank to the water supply pipe,
A boiler chemical cleaning method in which a temporary pipe for circulating cleaning water is provided in the steam separator, the drain tank, the economizer, and the wall pipe, and a circulation pump is provided in the temporary pipe to circulate the cleaning water,
a first additional temporary pipe that connects the temporary pipe on the downstream side of the circulation pump to the nose wall pipe inlet header;
A second additional temporary pipe is provided to connect the temporary pipe upstream of the circulation pump to the outlet header of the nose wall pipe, and part of the washing water from the circulation pump is channeled through the first and second additional temporary pipes. A method of chemically cleaning a boiler, characterized by circulating through said nose wall tube. In claim 1, the downstream side of the first additional temporary pipe is branched into two or more pipes and communicates with at least two locations, namely, the longitudinal center portion and both end sides of the nose wall pipe inlet wall pipe. A boiler chemical cleaning method characterized by: 3. In claim 1 or 2, the upstream portion of the second additional temporary pipe is branched into two or more pipes and communicates with at least two locations, namely, the center portion and both ends of the nose wall pipe outlet wall pipe in the longitudinal direction. A boiler chemical cleaning method characterized by:

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