JP7283302B2 - Boiler chemical cleaning method - Google Patents

Description

The present invention relates to a method of chemically cleaning a boiler, and more particularly to a method of chemically cleaning a steam separator and a furnace side thereof.

An example of a steam system of a thermal power boiler is shown in FIG. Boiler feedwater is supplied to the economizer 4 of the furnace 10 via the feedwater pump 1, the feedwater valve 2, and the feedwater pipe 3, and is heated. Heated feedwater is supplied to the tube walls of the furnace 10 via the pipe 5 and the header 6 . Steam generated by burning fuel by the burner 11 is supplied to the high pressure turbine 17 through the header 12, the steam separator 13, the saturated steam pipe 14, the superheater 15, the main steam pipe 16, and the main steam stop valve 16a. be done. The steam that has done work in the high pressure turbine 17 is sent through the cold reheat steam pipe 18 to the reheater 19 where it is heated, and through the hot reheat steam pipe 20 to the intermediate pressure turbine 21 and the low pressure turbine 22 in sequence. Supplied to do the job. Also, the steam that has worked in the low-pressure turbine 22 is condensed in the condenser 23 and then returned to the economizer 4 through the pump 24 and condensate piping 25 .

The water separated by the steam separator 13 is introduced into a drain tank 26 and returned to the economizer 4 via a pipe 29 having a valve 27 and a pump 28 .

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 Document 1).

In Patent Document 1, as a method of chemically cleaning the steam separator of the boiler and the furnace side thereof, a temporary pipe that bypasses the valve 27 and the pump 28 is provided, a temporary pump is provided in the temporary pipe, and the steam separator describes a method of delivering cleaning chemicals to the

JP 2015-230150 A

In chemical cleaning of a boiler, pure water is circulated in advance, and a preheating step is performed in which steam is blown into the pure water to raise the temperature, and then cleaning chemicals are injected into the pure water. This is because the cleaning chemicals are at room temperature, especially in winter, and the temperature is low. Therefore, pure water is preheated to about 50 to 60° C. for cleaning with inorganic acid, and to about 80 to 90° C. for cleaning with organic acid and chelate. In order to perform this preheating, as described above, steam is injected into the pure water, heated to a predetermined temperature, and the temperature is maintained.

Conventionally, the preheating step for preheating the pure water is performed, the chemical solution is injected, and then the temperature is adjusted, and then the cleaning step is performed, resulting in a long total cleaning time.

In addition, when the injection of the cleaning chemical is started after the pure water has risen to a predetermined temperature, the temperature of the circulating water drops. It is necessary to inject steam to raise the water temperature, and it is necessary to adjust the temperature by injecting steam again until the predetermined cleaning temperature is reached, which increases the cleaning time. It should be noted that the temperature drop of the cleaning liquid due to chemical injection may drop by 10° C. or more, depending on the amount of cleaning chemicals and the environment.

In addition, when steam is injected to maintain the temperature during cleaning, the cleaning liquid is diluted by the amount of water generated by condensation of the steam. . For example, if 0.5% of chemicals are added to the amount of cleaning liquid of 200 m ³ , 1,000 kg of chemicals must be added. In addition, since the amount of cleaning liquid increases by the volume of the condensed water of this steam, it is necessary to blow off the increased amount of water. Since this blow water contains the injected chemicals, the chemicals in the blow water are wasted without being used for cleaning. For this reason, the conventional cleaning method requires a high chemical cost.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a chemical boiler cleaning method capable of shortening the total cleaning time and reducing the cost of chemicals.

The boiler chemical cleaning method of the present invention comprises:
An economizer to which water is introduced by a water supply pipe, a furnace having wall pipes to which water is introduced from the economizer, a steam separator connected to the wall pipes, and receiving water from the steam separator. In a method for chemically cleaning a boiler having a drain tank and a pump and piping for circulating water in the drain tank to the water supply pipe,
providing a temporary line for communication between the drain tank and the economizer;
The temporary line is provided with a pump and a temporary line heat exchanger,
While circulating pure water to the steam separator and to the furnace side,
During this circulation, the pure water is heated by the temporary line heat exchanger, and the chemical is heated by the chemical solution heating heat exchanger using the heated pure water as a heat source,
A method of chemically cleaning a boiler, comprising heating pure water to a predetermined temperature or higher and then injecting the heated chemical solution into the pure water to carry out a chemical cleaning process;
is the gist.

In one aspect of the present invention, the cleaning liquid is heated by the temporary line heat exchanger during or after the injection of the chemical liquid in the chemical cleaning step.

In one aspect of the present invention, the temporary line heat exchanger is a heat exchanger in which steam is supplied to the heat source fluid side.

According to the present invention, since the chemical solution is heated in advance by the heat exchanger, it is possible to suppress the temperature drop of the cleaning solution when the chemical solution is injected.

In one aspect of the present invention, since the heat exchanger is used to raise the temperature and maintain the temperature during chemical injection and cleaning, the temperature is not raised by injecting steam. Therefore, dilution of the chemical is prevented. In addition, since the blowing for discharging the cleaning liquid by the volume of the steam condensed water is not performed, the outflow of the chemicals due to the blowing is prevented, and the cost of the chemicals is reduced.

It is a flow diagram explaining the method of the present invention. It is a flow diagram showing an example of a steam system of a thermal power boiler. It is a washing-process figure.

An embodiment will be described below with reference to FIG. FIG. 1 is a flow diagram of a furnace and a cleaning system when a cleaning system is provided in the steam system of the thermal power boiler shown in FIG.

In this embodiment, one end of temporary pipe 30 is connected to pipe 29 between drain tank 26 and valve 27 . The other end of the temporary pipe 30 includes a first heat exchanger 31 using steam as a heat source, a pipe 32, a pump 33, a pipe 34, a sludge catcher 35, a pipe 36, a filtration unit 37, a pipe 38, and a second heat exchanger using steam as a heat source. 2 It continues to the water supply pipe 3 via the heat exchanger 39 and the pipe 40 . A drain pipe 41 is branched from the pipe 40 and a valve 42 is provided in the pipe 41 .

A chemical liquid tank 50 containing a chemical liquid (cleaning chemical liquid) to be injected into this temporary line (the line from the pipe 30 to the pipe 40) is installed. The chemical in the chemical tank 50 is circulated through a pump 51, a pipe 52, a valve 53, a third heat exchanger 54 and a pipe 55, and can be heated by the heat exchanger 54 during this circulation. Further, a pipe 56 branched from the pipe 52 is connected to the pipe 32 via a valve 57 to enable chemical injection.

A pipe 60 branched from the pipe 34 is connected to a heat source fluid inlet of the third heat exchanger 54 via a valve 61 . A heat source fluid outlet of the third heat exchanger 54 is connected to the pipe 30 via a pipe 62 .

To chemically clean the furnace 10 side of the steam separator 13, after closing the main steam stop valve 16a, the temporary line from the pipe 30 to the pipe 40 is filled with pure water. (For example, the valve 27 is closed and the feed water pump 1 is operated to supply boiler feed water made of pure water through the feed pipe 3.) After that, the valve 2 is closed, the circulation pump 33 is operated, and the first And steam is supplied to the heat source fluid side (primary side) of the second heat exchangers 31 and 39 to heat the circulating pure water. The pure water circulating in the temporary line flows through the water supply pipe 3, the economizer 4, the header 6, the pipe wall of the furnace 10, the header 12, the steam separator 13, and the drain tank 26 in this order, and from the pipe 30 to the pipe 40. , and returns to the water supply pipe 3 to circulate.

By supplying steam to the primary sides of the first and third heat exchangers 31 and 39, the temperature of the circulating pure water gradually rises. When this temperature rises to approximately 50 to 95° C., the valves 53 and 61 are opened and the pump 51 is operated. As a result, the chemical in the chemical tank 50 circulates through the pump 51 , the pipe 52 , the third heat exchanger 54 and the pipe 55 and is heated by the third heat exchanger 54 . When the chemical liquid temperature rises to a predetermined temperature (for example, about 50° C.), the valves 53 and 61 are closed and the pump 51 is stopped. After that, the chemical in the chemical tank 50 is passed through the third heat exchanger 54 as necessary, and high-temperature water is passed through the pipe 34 to the primary side of the third heat exchanger 54 to increase the temperature of the chemical. Maintain within the above range.

After the temperature of the pure water flowing through the temporary line from the pipe 30 to the pipe 40 rises to 80 to 90° C., the valve 57 is opened, the pump 51 is operated, and the chemical solution is supplied to the circulating pure water. This chemical injection process is performed for a predetermined time, and the circulating water is used as the chemical cleaning liquid. After the chemical injection, the pump 51 is stopped and the valve 57 is closed, and the chemical cleaning liquid is supplied to the temporary line from the pipe 30 to the pipe 40, the economizer 4, the pipe wall of the furnace 10, the steam separator 13 and the drain tank 26. Chemical cleaning is performed by circulating and circulating the By performing this chemical cleaning process for a predetermined time, the steam separator 13, the drain tank 26, the water supply pipe 3, the economizer 4, the wall pipe of the furnace 10, the headers 6, 12, etc. are chemically cleaned.

When the temperature of the chemical cleaning liquid drops while this chemical cleaning is continued, steam is supplied to the primary side of at least one of the first and second heat exchangers 31 and 39 to heat the chemical cleaning liquid. Warm up.

After the cleaning process is completed, the valve 42 is opened to discharge the chemical cleaning liquid, and pure water is supplied from the water supply pipe 3 to the economizer 4, the wall pipe, the header 12, the steam separator 13, and the drain tank 26. Squeeze out residual cleaning solution inside. After that, after performing rust prevention and blowing, the temporary pipes 30 to 40 are removed, normal water washing and starting operation are performed, and the operation of the boiler is resumed.

According to this cleaning method, as shown in FIG. 3B, the chemical solution in the chemical solution tank 50 is circulated and heated in the third heat exchanger 54 while the pure water preheating step is being performed. At or before the end of the process, the chemical solution can be injected into the circulating pure water, and the chemical cleaning can be started immediately after the end of this injection.

In addition, since the chemical solution is heated in advance by the third heat exchanger 54 in this way, it is possible to reduce the temperature drop of the cleaning solution that accompanies injection of the chemical solution.

In addition, since the heat exchangers 31, 39 and 54 are used to raise and maintain the temperature during chemical injection and during chemical cleaning, dilution of chemicals is prevented. This prevents the chemicals from being washed out due to the blowing, thereby reducing the cost of the chemicals.

For example, if the amount of cleaning liquid is 175 m ³ and the amount of chemical is 35 m ³ , and the cleaning chemical of 20° C. is injected into the preheated water of 90° C., the temperature of the cleaning liquid drops to 77° C. ).

On the other hand, when the temperature of the chemical solution is raised to 50° C. in advance, the temperature of the cleaning solution after injection of the chemical solution is 83° C. by the same calculation. Furthermore, by heating with the indirect heat exchangers 31 and 39 during chemical injection, it is possible to raise and maintain the temperature without diluting the cleaning liquid.

[Example 1]
Chemical cleaning of the boiler shown in FIG. 1 was performed according to the procedure of the method of the present invention shown in FIG. 3(b).

<Preheating process>
While circulating pure water in the cleaning system, steam was supplied to the first and second heat exchangers 31 and 39 to preheat the circulating pure water to 90°C.

In the preheating process, part of the circulating heated deionized water is passed through the third heat exchanger 54 to raise the temperature of the chemical in the chemical tank 50 to 50°C and lower the temperature of the chemical to 50°C. held to.

<Chemical solution injection>
50°C, 35m ³ chemical solution is injected into 90°C, 175m ³ preheated circulating water in about 2 cycles (450m ³ /h, 1 cycle about 23 minutes), and the first and third heat exchanges are performed in parallel. The temperature of the circulating water was maintained by the vessels 31 and 39 .

As a result, it was possible to keep the liquid temperature at 90° C. at the end of injection. Also, the total cleaning time was shortened by 2 hours compared to Comparative Example 1 described below.

In addition, by maintaining the temperature using the first and third heat exchangers 31 and 35 during washing, 0.5% (washing liquid amount 175 m ^{3 )} is added in anticipation of being diluted normally. 875 kg) of chemicals could be saved.

[Comparative Example 1]
Chemical cleaning was performed according to the procedure of the conventional method shown in FIG. 3(a). In this method, steam is injected into the circulating pure water in the preheating step, the chemical solution is injected after the preheating is finished, and the liquid temperature is set to 90° C. by the steam injection after the chemical solution injection is finished. In this method, the cleaning time was two hours longer than in the method of the present invention, and the amount of chemicals used was large.

3 feed pipe 4 economizer 10 furnace 13 steam separator 15 superheater 19 reheater 26 drain tank 31, 39, 54 heat exchanger

Claims (3)

An economizer to which water is introduced by a water supply pipe, a furnace having wall pipes to which water is introduced from the economizer, a steam separator connected to the wall pipes, and receiving water from the steam separator. In a method for chemically cleaning a boiler having a drain tank and a pump and piping for circulating water in the drain tank to the water supply pipe,
providing a temporary line for communication between the drain tank and the economizer;
The temporary line is provided with a pump and a temporary line heat exchanger,
While circulating pure water to the steam separator and to the furnace side,
During this circulation, the pure water is heated by the temporary line heat exchanger, and the chemical is heated by the chemical solution heating heat exchanger using the heated pure water as a heat source,
A chemical cleaning method for a boiler, comprising heating pure water to a predetermined temperature or higher and then injecting the heated chemical solution into the pure water to perform a chemical cleaning step. 2. The boiler chemical cleaning method according to claim 1, wherein the cleaning liquid is heated by the temporary line heat exchanger in the chemical cleaning step during or after injection of the chemical liquid. 3. A boiler chemical cleaning method according to claim 1, wherein said temporary line heat exchanger is a heat exchanger in which steam is supplied to the heat source fluid side.

Images