BOILER OPERATION METHOD AND BOILER

Abstract

A boiler according to the present invention is equipped with: a water supply system (11) in which boiler water flows; ammonia addition equipment (12) that adds an ammonia solution to the boiler water; a pH measurement device (14) that measures the pH of the boiler water; and a control device (15). When the boiler water is heated the control device (15) controls the ammonia addition equipment (12) such that the pH of the boiler water is within a preservation pH range, and controls the ammonia addition equipment (12) such that the pH of the boiler water is within the preservation pH range before the flow of the boiler water in the water supply system (11) is stopped. At this time, a given pH within the preservation pH range is greater than a given pH within the operating pH range. With such a boiler, corrosion of the water supply system (11) can more easily be prevented than when the water supply system (11) is charged with preservation boiler water containing hydrazine.

Description

TECHNICAL FIELD

The present invention relates to a boiler operation method and a boiler, and more particularly relates to a boiler operation method and a boiler used when preserving a water supply system through which boiler water is circulated.

BACKGROUND ART

Boiler and steam turbine power plant, gas turbine and (heat recovery steam generator) steam turbine combined cycle power plant, and the like have water supply systems through which boiler water is circulated for generating steam (water vapor), but integrated coal gasification combined cycle (IGCC) power plants have many water supply systems for generating steam. An integrated coal gasification combined cycle power plant includes a gasifier, a gas cooler, a gas turbine section, a heat recovery steam generator, a steam turbine section, and a generator. The gasifier generates combustible raw syngas from the gasification of pulverized coal. The gas cooler cools the raw syngas. The gas turbine section generates high temperature high pressure combustion gas by combustion of the cooled raw syngas, thereby generating rotational power. The heat recovery steam generator recovers thermal energy from the exhaust gas from the gas turbine section, to generate high pressure steam. The steam turbine section generates rotational power using the steam. The generator converts the rotational power generated by the gas turbine section and the steam turbine section into electrical power.

The gas cooler and the heat recovery steam generator include water supply systems through which boiler water is circulated. The gas cooler cools the raw syngas generated by the gasifier and the heat recovery steam generator cools the exhaust gas discharged from the gas turbine section by circulating boiler water through the water supply systems. In addition, the gas cooler and the heat recovery steam generator heat the boiler water and generate steam supplied to the steam turbine section, by circulating the boiler water through the water supply systems.

Meanwhile, during periodic inspection when the operation of the integrated coal gasification combined cycle power plant is stopped and the equipment preservation time is long, the boiler water is discharged when it is necessary to change the piping or the like of the water supply system. However, when the boiler water is preserved without discharging it in order to rapidly restart the power plant, it is desirable to prevent corrosion of the metallic components such as the inside of the piping of the water supply systems and the like.

CITATION LIST

Patent Literature

Patent Document 1: Japanese Unexamined Patent Application Publication No. 2004-323954A

Patent Document 2: Japanese Unexamined Patent Application Publication No. 2003-39084A

Patent Document 3: Japanese Unexamined Patent Application Publication No. H44-83592A

SUMMARY OF INVENTION

Technical Problem

The occurrence of corrosion in the inside of piping and the like can be reduced by filling the water supply system with preserved water that contains hydrazine during the preservation period when operation of the power plant is stopped and the boiler water is not discharged while the equipment is being preserved to enable rapid restarting. However, it is known that hydrazine has an adverse effect on health, so it is necessary to take care when handling it (see Patent Documents 1, 2, and 3). It is desirable that corrosion of the metal members of the water supply system be reduced more easily and over a longer period of time.

It is an object of the present invention to provide a boiler operation method and a boiler in which corrosion of the water supply system through which the boiler water flows is easily reduced.

Solution to Problem

The boiler operation method according to a first aspect of the present invention is executed using a water supply system of a boiler. The boiler includes the water supply system through which the boiler water to be heated flows, and ammonia addition equipment configured to add ammonia to the boiler water to adjust the pH of the boiler water. The boiler operation method according to the present invention includes: measuring a pH of the boiler water; passing the boiler water through the water supply system when the pH is within an operational pH range so that the boiler water is heated upon operating the boiler; controlling the ammonia addition equipment so that ammonia is added to the boiler water until the pH is within a preservation pH range upon stopping the boiler; and stopping the flow of the boiler water in the water supply system when the pH is within the preservation pH range. At this time, a discretionary pH within the preservation pH range is equal to or greater than a discretionary pH within the operational pH range.

According to this boiler operation method, by filling the water supply system with boiler water having a pH within the preservation pH range, it is possible to reduce corrosion of the water supply system for a longer period of time during preservation of the equipment when the operation of the power plant has stopped compared with filling the water supply system with boiler water having a pH within the operational pH range. In addition, ammonia can normally be handled more easily compared with hydrazine. Therefore, this boiler operation method can more easily prevent corrosion of the water supply system compared with filling the water supply system with preservation boiler water that contains hydrazine.

The boiler operation method according to the first aspect further includes passing the boiler water through the water supply system when the pH is within the operational pH range so that the boiler water is heated, upon restarting operation of the boiler after the flow of the boiler water in the water supply system has been stopped.

According to this boiler operation method, the pH of the preservation boiler water is within the operational pH range, so it is possible to restart the boiler more easily and in a shorter period of time by using the preservation boiler water as it is as operation boiler water.

The boiler operation method according to the first aspect further includes referring to a table of a plurality of preservation periods mapped to a plurality of preservation pH ranges, and introducing the preservation pH range corresponding to the period of time that a power plant is stopped and boiler water is not flowing through the water supply system, from among the plurality of preservation pH ranges. At this time, a lower limit of a first preservation pH range corresponding to a first period from among the plurality of preservation pH ranges is greater than a lower limit of a second preservation pH range corresponding to a second period that is longer than the first period from among the plurality of preservation pH ranges.

According to this boiler operation method, it is possible to add an appropriate quantity of ammonia to the boiler water, and more appropriately reduce corrosion of the water supply system during preservation of the equipment.

The boiler according to a second aspect of the present invention includes: a water supply system through which boiler water to be heated flows; ammonia addition equipment configured to add ammonia to the boiler water; a pH measurement device configured to measure the pH of the boiler water; and a control device configured to control the ammonia addition equipment. Upon operating the boiler, the control device includes a control circuit for normal operation configured to control the ammonia addition equipment so that the pH is within an operational pH range when the boiler water is flowing through the water supply system so that the boiler water is heated, and a control circuit for preservation period configured to control the ammonia addition equipment so that, upon stopping the boiler, the pH is within the preservation pH range before stopping the flow of the boiler water through the water supply system. At this time, a discretionary pH within the preservation pH range is equal to or greater than a discretionary pH within the operational pH range.

With this boiler, it is possible to further reduce corrosion of the water supply system by filling the water supply system with boiler water having a pH within the preservation pH range compared with filling the water supply system with boiler water having a pH within the operational pH range. In addition, ammonia can normally be handled more easily compared with hydrazine. Therefore, with this boiler, corrosion of the water supply system during equipment preservation can be more easily suppressed compared with filling the water supply system with preservation boiler water that contains hydrazine.

A gas cooler according to a third aspect of the present invention includes a flow path through which raw syngas generated by gasification of a carbonaceous solid fuel with an oxidant, and a flow path (boiler water circulation system) through which supply water flows. At this time, the water supply system heats the boiler water using the heat of the raw syngas.

This gas cooler can more easily suppress corrosion of the water supply system during equipment preservation when a power plant is stopped.

A heat recovery steam generator according to a fourth aspect of the present invention includes a flow path through which exhaust gas discharged from a gas turbine flows, and a flow path (boiler water circulation system) through which supply water flows. The water supply system heats the boiler water using the heat of the exhaust gas.

This heat recovery steam generator can more easily prevent corrosion of the water supply system during equipment preservation when the power plant is stopped.

An integrated coal gasification combined cycle power plant according to a fifth aspect of the present invention includes: the heat recovery steam generator according to the present invention; a gasifier configured to generate raw syngas by gasification of a carbonaceous solid fuel; a gas turbine configured to discharge exhaust gas by generating power using the raw syngas; and a steam turbine configured to generate power using steam. At this time, the steam is generated by the water supply system by heating the boiler water using the heat of the raw syngas and using the heat of the exhaust gas.

This integrated coal gasification combined cycle power plant can more easily suppress corrosion of the water supply system during equipment preservation when the power plant is stopped.

Advantageous Effect of Invention

The boiler operation method and the boiler according to the present invention can easily reduce corrosion of the water supply system during equipment preservation by filling the water supply system with boiler water having a pH higher than the pH of the boiler water circulated during operation.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view illustrating the configuration of an integrated coal gasification combined cycle power plant.

FIG. 2 is a schematic view illustrating the configuration of a boiler water circulating system.

FIG. 3 is a block diagram illustrating a control device.

FIG. 4 is a flow illustrating a boiler preservation method of a comparative example.

FIG. 5 is a graph showing the relationship between pH and corrosion.

DESCRIPTION OF EMBODIMENTS

A description of the embodiments of the boiler according to the present invention will be described below with reference to the drawings. A water supply system portion of the boiler is used in an integrated coal gasification combined cycle power plant 10, as illustrated in FIG. 1. The integrated coal gasification combined cycle power plant 10 includes a gasifier 1, a gas cooler 2, a gas turbine 3, a heat recovery steam generator 5, a steam turbine 6, a generator 7, and a condenser 8. The gasifier 1 generates combustible high temperature raw syngas from pulverized coal obtained by pulverizing coal as carbonaceous solid fuel supplied from outside the power plant, and air (or oxygen) as an oxidant. The gas cooler 2 generates cooled raw syngas from the high temperature raw syngas generated by the gasifier 1. The gas cooler 2 generates high temperature high pressure steam from the boiler water generated by the condenser 8, by heat exchange when cooling the high temperature raw syngas.

The gas turbine 3 generates rotational power using the cooled raw syngas generated by the gas cooler 2, and discharges high temperature exhaust gas. The heat recovery steam generator 5 generates high temperature high pressure steam from the boiler water generated by the condenser 8, by heat exchange when cooling the high temperature exhaust gas discharged from the gas turbine 3. The steam turbine 6 generates rotational power using the steam generated by the gas cooler 2 and the steam generated by the heat recovery steam generator 5, and discharges exhaust steam. The generator 7 generates electrical power using the rotational power generated by the gas turbine 3 and the rotational power generated by the steam turbine 6. The condenser 8 generates water from the exhaust steam discharged from the steam turbine 6 to produce boiler water.

FIG. 2 illustrates a water supply (circulation) system portion of the gas cooler 2. The gas cooler 2 includes a water supply (circulation) system 11, ammonia addition equipment 12, a pH measurement device 14, and a control device 15, and includes a raw syngas flow path a. The raw syngas generated by the gasifier 1 flows through the raw syngas flow path a. The water supply system 11 includes a steam drum 16, a plurality of downcast pipes 17, a header 18, and a plurality of heat transfer pipes 19. The steam drum 16 is formed into a vessel formed from steel based material (hereinafter, referred to as “steel”). The steam drum 16 is connected to the condenser 8 via a pipe line 30 so that boiler water generated in the condenser 8 is supplied to the inside of the steam drum 16. The steam drum 16 is connected to the steam turbine 6 via a pipe line 31 so that steam generated in the inside of the steam drum 16 is supplied to the steam turbine 6. The steam drum 16 is also connected to the plurality of downcast pipes 17 so that the boiler water accumulated in the inside of the steam drum 16 is supplied to the plurality of downcast pipes 17.

Each of the plurality of downcast pipes 17 is formed from steel and is formed as a flow path through which boiler water supplied from the steam drum 16 flows. Each of the plurality of downcast pipes 17 is connected to the header 18 so that the boiler water is supplied to the header 18. The header 18 is formed from steel and is formed as a header into which the boiler water supplied from the plurality of downcast pipes 17 merge. The header 18 is connected to the plurality of heat transfer pipes 19 so that the boiler water is supplied to the plurality of heat transfer pipes 19.

The plurality of heat transfer pipes 19 is formed from steel and is formed as the flow path through which the boiler water supplied from the header 18 flows. The plurality of heat transfer pipes 19 is disposed within the flow path a of the raw syngas, so that the pipes are heated by the heat of the raw syngas generated by the gasifier 1. The plurality of heat transfer pipes 19 is connected to the steam drum 16 so that the boiler water supplied from the header 18 is supplied to the steam drum 16.

The ammonia addition equipment 12 is electrically connected to the control device 15 so as to enable transfer of information and accumulates ammonia solution. The ammonia addition equipment 12 is controlled by the control device 15 to supply ammonia solution to the pipe line 30 so that ammonia solution is added to the boiler water supplied to the steam drum 16 from the condenser 8.

The pH measurement device 14 is electrically connected to the control device 15 so as to enable transfer of information. The pH measurement device 14 is controlled by the control device 15 to measure the pH of the boiler water accumulated in the steam drum 16 either at predetermined intervals or continuously.

The control device 15 is a computer that includes a CPU, a memory device, a memory drive, a communication device, and an interface, that are not illustrated on the drawings.

The interface outputs information generated by external equipment connected to the control device 15 to the CPU, and outputs information generated by the CPU to the external equipment. The external equipment includes the ammonia addition equipment 12 and the pH measurement device 14.

The computer programs installed in the control device 15 are formed from a plurality of computer programs to make the control device 15 realize a plurality of functions, as illustrated in FIG. 3. The plurality of functions includes a control circuit for normal operation 21 and a control circuit for preservation period 22.

During operation of the gasifier 1 and the gas cooler 2, the pH measurement device 14 measures the pH of the boiler water accumulated in the steam drum 16 at least once. The control circuit for normal operation 21 stores in advance an operational pH range in the memory device. The set value in the operational pH range is, for example, 9.7. The control circuit for normal operation 21 also controls the ammonia addition equipment 12 so that the pH of the boiler water accumulated in the steam drum 16 is within the operational pH range. In other words, the control circuit for normal operation 21 controls the ammonia addition equipment 12 so that when the pH of the boiler water is less than the set value in the operational pH range, ammonia solution is supplied to the pipe line 30. The control circuit for normal operation 21 controls the ammonia addition equipment 12 so that when the pH of the boiler water is equal to or greater than the set value in the operational pH range, the ammonia solution is not supplied to the pipe line 30.

The control circuit for preservation period 22 stores in advance a preservation pH range in the memory device. The lower limit of the preservation pH range is equal to or greater than the set value in the operational pH range, for example, 9.7. The control circuit for preservation period 22 also controls the ammonia addition equipment 12 so that the pH of the boiler water accumulated in the steam drum 16 is within the preservation pH range. In other words, the control circuit for preservation period 22 controls the ammonia addition equipment 12 so that when the pH of the boiler water accumulated in the steam drum 16 is lower than the lower limit of the preservation pH range, ammonia solution is supplied to the pipe line 30. The control circuit for preservation period 22 controls the ammonia addition equipment 12 so that when the pH of the boiler water accumulated in the steam drum 16 is greater than the lower limit of the preservation pH range, ammonia solution is not supplied to the pipe line 30.

The heat recovery steam generator 5 includes a water supply system that is not illustrated on the drawings. The water supply system is formed similar to the water supply system 11, in other words, it includes a steam drum, a plurality of downcast pipes, a header, and a plurality of heat transfer pipes. The steam drum is formed into a vessel formed from steel. The steam drum is connected to the pipe line 30, and connected to the pipe line 31. The steam drum is also connected to the plurality of downcast pipes so that the boiler water accumulated in the inside of the steam drum is supplied to the plurality of downcast pipes.

Each of the plurality of downcast pipes is formed from steel and is formed as a flow path through which boiler water supplied from the steam drum flows. Each of the plurality of downcast pipes is connected to the header so that the boiler water is supplied to the header. The header is formed from steel, and formed as a vessel in which boiler water supplied from the plurality of downcast pipes is accumulated. The header is connected to the plurality of heat transfer pipes so that the boiler water is supplied to the heat transfer pipes.

The plurality of heat transfer pipes is formed from steel and is and formed as a flow path through which the boiler water supplied from the header flows. The plurality of heat transfer pipes is disposed in the flow path through which the exhaust gas flows, so that it is heated by the heat of the exhaust gas discharged from the gas turbine 3. The plurality of heat transfer pipes is connected to the steam drum so that the boiler water supplied from the header is supplied to the steam drum.

The embodiment of the boiler operation method according to the present invention is implemented using the integrated coal gasification combined cycle power plant 10, and includes normal operation, preservation operation, and restart operation.

In normal operation, the gasifier 1 generates combustible high temperature raw syngas using air (or oxygen) supplied from external equipment, by pulverizing and burning coal as carbonaceous solid fuel supplied from external equipment. The gas cooler 2 generates cooled raw syngas by heat exchange using the boiler water generated by the condenser 8 so as to cool the high temperature raw syngas generated by the gasifier 1. At this time, the gas cooler 2 generates high temperature high pressure steam by heat exchange using the heat of the high temperature raw syngas generated by the gasifier 1 to heat the boiler water.

The gas turbine 3 generates high temperature high pressure exhaust gas by burning the cooled raw syngas generated by the gas cooler 2. The gas turbine 3 generates rotational power using the kinetic energy of the exhaust gas, and discharges the exhaust gas. The heat recovery steam generator 5 generates cooled exhaust gas by heat exchange using the boiler water generated by the condenser 8 to cool the high temperature exhaust gas discharged from the gas turbine 3. At this time, the heat recovery steam generator 5 generates high temperature high pressure steam by heat exchange using the heat of the high temperature exhaust gas discharged from the gas turbine 3 to heat the boiler water generated by the condenser 8.

The steam turbine 6 generates rotational power using the kinetic energy of the high temperature high pressure steam generated by the gas cooler 2 and the kinetic energy of the high temperature high pressure steam generated by the heat recovery steam generator 5, and discharges exhaust steam. The generator 7 generates power using the rotational power generated by the gas turbine 3 and the rotational power generated by the steam turbine 6. The condenser 8 carries out heat exchange to cool the exhaust steam discharged by the steam turbine 6 to generate water as boiler water, and supplies the boiler water to the gas cooler 2 and the heat recovery steam generator 5 via the pipe line 30.

At this time, the pH measurement device 14 measures the pH of the boiler water accumulated in the steam drum 16 of the gas cooler 2. The pH measurement device 14 transmits the measured pH to the control device 15. When the measured pH is equal to the set value in the operational pH range, or the measured pH is greater than the set value, the control device 15 controls the ammonia addition equipment 12 to stop the addition of ammonia solution to the boiler water supplied to the steam drum 16 from the condenser 8. When the measured pH is lower than the set value in the operational pH range that is set in advance, the control device 15 controls the ammonia addition equipment 12 to add ammonia solution to the boiler water supplied to the steam drum 16 from the condenser 8.

The gas cooler 2 circulates the boiler water supplied from the condenser 8 to the water supply system 11 via the pipe line 30 to generate steam from the boiler water. In other words, the plurality of downcast pipes 17 supplies the boiler water accumulated in the steam drum 16 to the header 18. In the header 18, the boiler water supplied from the plurality of downcast pipes 17 merge. The plurality of heat transfer pipes 19 carries out heat exchange so that the boiler water that has merged at the heating pipe header 18 is heated using the heat of the high temperature raw syngas generated by the gasifier 1, and the heated boiler water is supplied to the steam drum 16. The steam drum 16 accumulates the boiler water supplied from the condenser 8 via the pipe line 30 and the boiler water heated by the plurality of heat transfer pipes 19. In addition, in the steam drum 16, liquid-vapor separation of the accumulated heated boiler water is carried out and the liquid-vapor separated steam is supplied to the steam turbine 6.

The preservation operation is implemented immediately before stopping the integrated coal gasification combined cycle power plant 10 for periodic inspection, maintenance, and the like. Immediately before stopping the integrated coal gasification combined cycle power plant 10, the control device 15 first measures the pH of the boiler water accumulated in the steam drum 16 using the pH measurement device 14. When the measured pH is lower than the lower limit of the preservation pH range, the control device 15 controls the ammonia addition equipment 12 to supply ammonia solution to the pipe line 30. When the measured pH is equal to or greater than the lower limit of the preservation pH range, the control device 15 controls the ammonia addition equipment 12 to stop the supply of ammonia solution to the pipe line 30.

After it has been confirmed that the measured pH is equal to or greater than the lower limit of the preservation pH range, operation of the integrated coal gasification combined cycle power plant 10 is stopped. The water supply system 11 stops circulating the boiler water as a result of stopping the operation of the integrated coal gasification combined cycle power plant 10. In addition, after stopping circulation of the boiler water, oxygen is discharged from the spaces filled by gas within the water supply system 11 and the spaces are filled with pressurized nitrogen by injecting nitrogen under pressure.

FIG. 5 is a graph showing the relationship between pH and corrosion. Test specimens were immersed in an ammonia solution with different pH within a sealed container under test conditions of oxygen saturation (25° C., 8 mg/L) and room temperature, and from the test results, it was determined whether or not there was corrosion by inspecting the surface, and the corrosion area was determined as a percentage of the total area. When steel is immersed in ammonia solution, the higher the pH of the ammonia solution, the more the corrosion speed is reduced, so it is possible to suppress corrosion in the steel over a longer period of time. Therefore, according to this preservation operation, it is possible to achieve a greater reduction in the corrosion of the water supply system 11 during preservation of the equipment when the integrated coal gasification combined cycle power plant 10 is stopped, by filling the water supply system 11 with boiler water having pH within the preservation pH range compared with filling the water supply system 11 with boiler water having pH within the operational pH range. As a result, according to this preservation operation, the water supply system 11 is able to be preserved in a manner that it does not corrode during preservation of the equipment when the integrated coal gasification combined cycle power plant 10 is stopped.

The restart operation is implemented after implementation of the preservation operation, after the integrated coal gasification combined cycle power plant 10 has been stopped for a predetermined period of time. In the restart operation, the operation of the integrated coal gasification combined cycle power plant 10 is restarted and normal operation is implemented without removing the boiler water from the water supply system 11 and without re-supplying boiler water that satisfies the water quality for normal operation, unlike the conventional method of initiating restart after filling the water supply system 11 with preserved water that contains hydrazine during the equipment preservation period.

According to this restart operation, it is possible to shorten the time required for restarting the integrated coal gasification combined cycle power plant 10 and restart in a shorter period of time than for a conventional restart operation, by not replacing the boiler water having a pH within the preservation pH range with boiler water having a pH within the operational pH range.

In a comparative example of the boiler operation method, as an embodiment of a conventional equipment preservation method, a similar boiler operation method as the embodiment described above is implemented using the integrated coal gasification combined cycle power plant 10, the preservation operation in the embodiment as described above is replaced with another preservation operation, and the restart operation in the embodiment as described above is replaced with another restart operation.

In the preservation operation, after the integrated coal gasification combined cycle power plant 10 has been stopped, the boiler water is removed from the water supply system 11I as illustrated in FIG. 4 (Step S1). After the boiler water has been removed, the water supply system 11 is filled with preserved water. The preserved water contains 50 mg/L of hydrazine. After filling with the preserved water, the air that contains oxygen is discharged from the spaces filled with gas within the water supply system 11, and the spaces are filled with pressurized nitrogen by injecting with nitrogen under pressure (Step S2).

According to this preservation operation, it is possible to suppress the corrosion of the steel from which the water supply system 11 is configured for a long period of time by filling the water supply system 11 with the preserved water that contains 50 mg/L of hydrazine while the integrated coal gasification combined cycle power plant 10 is stopped.

In the restart operation, before restarting the integrated coal gasification combined cycle power plant 10, the preserved water that contains hydrazine at a higher concentration than that of hydrazine suitable for normal operation is removed from the water supply system 11 (Step S3). After removal of the preserved water, the water supply system 11 is filled with boiler water (Step S4). The boiler water is formed from water that does not contain hydrazine. After filling the water supply system 11 with boiler water, operation of the integrated coal gasification combined cycle power plant 10 is restarted, and normal operation is implemented.

According to this restart operation of the conventional embodiment, it is possible to appropriately operate at normal operation the integrated coal gasification combined cycle power plant 10 by circulating boiler water that does not contain hydrazine in the water supply system 11.

Meanwhile, ammonia is normally easier to obtain compared with hydrazine, and can be handled more easily.

In addition, in the restart operation after equipment preservation in the embodiment as described above, the boiler water is not removed from the water supply system 11 before preservation of the water supply system 11. In other words, by restarting operation without removing the boiler water having pH within the preservation pH range as a result of injecting ammonia solution, it is possible to implement the restart operation in a shorter period of time and at lower cost due to the boiler water not being discarded, compared with the restart operation after equipment preservation of the comparative example. In the restart operation according to the embodiment as described above, by not removing the boiler water that filled the water supply system 11 during equipment preservation, it is possible to omit the step of filling the water supply system 11 with preserved water that contains hydrazine after removal of the boiler water from the water supply system 11 in order to start the equipment preservation after stopping the integrated coal gasification combined cycle power plant 10. In addition, it is possible to omit the step of filling the water supply system 11 with boiler water after removal of the preserved water that contains hydrazine, in order to implement the restart. It is possible to implement the restart operation in the embodiment as described above in a shorter period of time compared with the restart operation of the comparative example. Therefore, according to the boiler operation method of the embodiment as described above, it is possible to stop the integrated coal gasification combined cycle power plant 10 in a shorter period of time and to restart it in a shorter period of time compared with the boiler operation method according to the comparative example.

The operation executed by the control device 15 can be executed by a user. In other words, the pH of the boiler water accumulated in the steam drum 16 of the gas cooler 2 is measured by the user by controlling the pH measurement device 14. By operating the ammonia addition equipment 12, ammonia solution is added to the pipe line 30 and the addition of the ammonia solution is stopped. In this case also, it is possible to easily prevent corrosion in a similar way as the boiler operation method according to the embodiment as described above, and the integrated coal gasification combined cycle power plant 10 can be stopped in a shorter period of time and can be restarted in a shorter period of time. In other words, the gas cooler 2 and the heat recovery steam generator include a boiler, so the above effect can be exhibited. The boiler includes the water supply system through which the boiler water to be heated flows, ammonia addition equipment that adds ammonia to the boiler water, and the pH measurement device that measures the pH of the boiler water.

In another embodiment of the boiler according to the present invention, the control circuit for preservation period 22 of the embodiment as described above is replaced with another control circuit for preservation period. In the control circuit for preservation period, a plurality of preservation pH ranges corresponding to a plurality of preservation periods is stored in advance in the memory device. Each of the plurality of preservation pH ranges has a lower limit that is equal to or greater than the set value in the operational pH range. For example, according to the test results shown in FIG. 5, the lower limit of the preservation pH range corresponding to a period equal to or less than 24 hours may be 9.5. The lower limit of the preservation pH range corresponding to a period equal to or less than 72 hours may be 9.7. The lower limit of the preservation pH range corresponding to a period from 4 days to 7 days may be 9.8. The lower limit of the preservation pH range corresponding to a period from 7 days to 14 days may be 9.9. The lower limit of the preservation pH range corresponding to a period from 15 days to 30 days may be 10. The longer the preservation period, the higher the corresponding lower limit of the preservation pH range.

Also, for example, in a high temperature strong alkaline environment (pH 11 or higher), preferably, the upper limit of the preservation pH is less than pH 11, because of the possibility of alkaline corrosion even in steel that is normally strongly alkali resistant. However, this is not a limitation.

When a user inputs a preservation period into the control device 15, a control circuit for preservation operation calculates a preservation pH range corresponding to the preservation period from the plurality of preservation pH ranges. The control circuit for preservation operation controls the pH measurement device 14 to measure the pH of the boiler water accumulated in the steam drum 16. The control circuit for preservation period controls the ammonia addition equipment 12 so that the pH of the boiler water accumulated in the steam drum 16 is within the preservation pH range. Also, the ammonia addition equipment 12 may be operated by a manual operation, and is not limited to calculating the preservation pH range corresponding to the preservation period, and controlling the ammonia addition equipment 12.

The integrated coal gasification combined cycle power plant that includes such a control circuit for preservation period can more easily suppress the corrosion of the water supply system 11, can stop in a shorter period of time, and can restart in a shorter period of time, similar to the integrated coal gasification combined cycle power plant 10 according to the embodiment as described above.

FIG. 5 shows the relationship between pH of the preserved water and corrosion. This relationship shows the pH of the preserved water in which test specimens formed from the steel are immersed, and shows the corrosion area corresponding to the number of days elapsed after immersing the test specimens in the preserved water. The corrosion area shows the area of the region that is corroded after the elapsed time as a percentage of the area of the surface of the test specimen in contact with the preserved water. Also, this relationship shows the progression of corrosion with time. In addition, this relationship shows that the higher the pH of the preserved water, the longer the time at which corrosion of the test specimens starts is delayed. Therefore, this relationship shows that the greater the pH of the boiler water filling the water supply system 11 during preservation, the longer the period of time that corrosion can be prevented.

Therefore, with the integrated coal gasification combined cycle power plant that includes such a control circuit for preservation period, by increasing the lower limit of the preservation pH range the longer the preservation period when the integrated coal gasification combined cycle power plant is stopped, it is possible to reduce the addition quantity of ammonia used for preservation of the water supply system 11, and appropriately prevent corrosion of the water supply system 11.

Note that the preservation pH range can be replaced with another preservation pH range whose lower limit is 9.5. The lower limit of the preservation pH range is equal to the set value in the operational pH range, or, is greater than the set value in the operational pH range.

REFERENCE SIGNS LIST

• 1 Gasifier
• 2 Gas cooler
• 3 Gas turbine
• 5 Heat recovery steam generator
• 6 Steam turbine
• 10 Integrated coal gasification combined cycle power plant
• 11 Water supply system
• 12 Ammonia addition equipment
• 14 pH measurement device
• 15 Control device
• 21 Control circuit for normal operation
• 22 Control circuit for preservation period

Claims

1. A boiler operation method implemented using a boiler that includes a water supply system through which boiler water flows, and ammonia addition equipment configured to add ammonia solution to the boiler water, the method comprising the steps of:

measuring a pH of the boiler water;

passing the boiler water through the water supply system when the pH is within an operational pH range so that the boiler water is heated, upon operating the boiler;

controlling the ammonia addition equipment so that ammonia solution is added to the boiler water until the pH is within a preservation pH range, upon stopping the boiler; and

stopping the flow of the boiler water in the water supply system when the pH is within the preservation pH range,

a discretionary pH within the preservation pH range being equal to or greater than a discretionary pH within the operational pH range.

2. The boiler operation method according to claim 1, further comprising passing the boiler water through the water supply system when the pH is within the operational pH range so that the boiler water is heated, upon restarting operation of the boiler after the flow of the boiler water in the water supply system has been stopped.

3. The boiler operation method according to claim 1, further comprising referring to a table of a plurality of preservation periods mapped to a plurality of preservation pH ranges, and introducing the preservation pH range corresponding to the period of time that a power plant is stopped and boiler water is not flowing through the water supply system, from among the plurality of the preservation pH ranges, wherein

a lower limit of a first preservation pH range corresponding to a first period from among the plurality of preservation pH ranges is greater than a lower limit of a second preservation pH range corresponding to a second period that is longer than the first period from among the plurality of preservation pH ranges.

4. The boiler operation method according to claim 3, wherein the lower limit of the first preservation pH range and the lower limit of the second preservation pH range have values within a range of 9.5 to 10.

5. A boiler, comprising:

a water supply system through which boiler water flows;

ammonia addition equipment configured to add ammonia solution to the boiler water;

a pH measurement device configured to measure a pH of the boiler water; and

a control device,

upon operating the boiler, the control device including

a control circuit for normal operation configured to control the ammonia addition equipment so that the pH is within a operational pH range when the boiler water is flowing through the water supply system so that the boiler water is heated, and

a control circuit for preservation period configured to control the ammonia addition equipment so that the pH is within the preservation pH range before stopping the flow of the boiler water through the water supply system upon stopping the boiler,

a discretionary pH within the preservation pH range being equal to or greater than a discretionary pH within the operational pH range.

6. A gas cooler, comprising:

the boiler described in claim 5; and

a flow path through which raw syngas generated by gasification of a carbonaceous solid fuel flows,

the water supply system heating the boiler water using heat of the raw syngas.

7. A heat recovery steam generator, comprising:

the boiler described in claim 5; and

a flow path through which exhaust gas discharged from a gas turbine flows,

the water supply system heating the boiler water using heat of the exhaust gas.

8. An integrated coal gasification combined cycle power plant, comprising:

the boiler according to claim 5;

a gasifier configured to generate raw syngas by gasification of a carbonaceous solid fuel;

a gas turbine configured to discharge exhaust gas by generating power using the raw syngas; and

a steam turbine configured to generate power using steam,

the steam being generated by the water supply system by heating the boiler water using heat of the raw syngas and using heat of the exhaust gas.

9. The boiler operation method according to claim 2, further comprising referring to a table of a plurality of preservation periods mapped to a plurality of preservation pH ranges, and introducing the preservation pH range corresponding to the period of time that a power plant is stopped and boiler water is not flowing through the water supply system, from among the plurality of the preservation pH ranges, wherein

a lower limit of a first preservation pH range corresponding to a first period from among the plurality of preservation pH ranges is greater than a lower limit of a second preservation pH range corresponding to a second period that is longer than the first period from among the plurality of preservation pH ranges.