JP2680454B2 - Method and apparatus for controlling chemical injection of waste heat recovery heat exchanger - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of use) The present invention relates to a chemical injection control method and apparatus for an exhaust heat recovery heat exchanger, which is composed of a plurality of steam generators having different pressures.

(Prior Art) A combined cycle power plant (combined cycle plant) for generating power by integrally combining a gas turbine with a steam turbine used in general thermal power generation is being put into practical use. According to this combined cycle power generation, high temperature gas discharged from a gas turbine is guided to an exhaust heat recovery heat exchanger to generate steam, and the steam turbine is driven by the generated steam, so compared to conventional steam turbine power generation. The efficiency can be increased by several points, and the energy utilization efficiency can be greatly improved.

In this combined cycle plant, an exhaust heat recovery heat exchanger configured by combining a plurality of boilers with different operating pressures is usually provided to generate low-pressure steam and high-pressure steam in order to further improve thermal efficiency. .

FIG. 3 is a system diagram showing the configuration of a conventional combined cycle plant. The exhaust heat recovery heat exchanger includes a preheater 2, a low pressure evaporator 4 of a low pressure steam drum 3, a high pressure economizer 5, a high pressure evaporator 7 of a high pressure steam drum 6 in a flue 1 through which combustion exhaust gas of a gas turbine passes. The superheater 8 is arranged in series.

Condensed water condensed in the condenser 9 is supplied to the preheater 2 as boiler feed water by the condensate pump 10. The feed water is here preheated and supplied to the low-pressure steam drum 3. The supplied feed water is heated in the low-pressure evaporator 4 to become low-pressure steam, and this low-pressure steam is supplied to the low-pressure side of the steam turbine 12 through the steam pipe 11.

On the other hand, the feed water supplied from the low-pressure steam drum 3 to the high-pressure steam drum 6 by the high-pressure water supply pump 13 through the high-pressure economizer 5 becomes high-pressure steam in the high-pressure evaporator 11. The generated high-pressure steam is superheated in the superheater 8 and then passes through the steam pipe 14 to be supplied to the high-pressure side of the steam turbine 12.

By the way, in this type of exhaust heat recovery heat exchanger, management of boiler feed water is extremely important in order to prevent corrosion and scale formation. Especially, in the exhaust heat recovery heat exchanger operated at high temperature and high pressure in order to increase efficiency, the required level for the water quality of boiler feed water is higher. A chemical injection control device is equipped to perform water treatment of the boiler feed water and maintain the water quality appropriately.

The chemical injection control device generally adds low phosphate such as sodium phosphate to the feed water to adjust the PH (hydrogen ion concentration index) of the feed water.
By maintaining the temperature at about 9.5 to 11, corrosion of the boiler components at high temperature is prevented.

However, in the case of an exhaust heat recovery heat exchanger consisting of multiple steam generators such as a low-pressure steam drum and a high-pressure steam drum, a chemical injection control method in which sodium phosphate is intermittently injected into each steam generator drum. Is inappropriate. That is, as is clear from the structure of the exhaust heat recovery heat exchanger shown in FIG. 3, the condensate from the condenser 9 is continuously supplied to the low-pressure steam drum 3 as the boiler feed water by the condensate pump 10, and the low pressure is further reduced. Water is continuously supplied from the steam drum 3 to the high-pressure steam drum 6 by the high-pressure water supply pump 13. Therefore, in the low-pressure steam drum 3, the intermittently injected sodium phosphate is gradually diluted by the supplied water. Therefore, it is difficult to maintain the PH value (hydrogen ion concentration index) of the feed water at a predetermined value or more unless the continuous injection method is adopted for the low-pressure steam drum 3 rather than the intermittent injection method.

On the other hand, in the high-pressure steam drum 6, the feed water containing the sodium phosphate injected in the low-pressure steam generator is supplied as it is, so that it is not necessary to carry out the chemical injection treatment. It is concentrated and there is a high possibility that it will exceed the standard value of water quality. Therefore, in order to keep the water quality of the high-pressure evaporation system within the standard value, the high-pressure steam drum 6 is intermittently operated.
It is inevitable to carry out a blow operation for discharging the can water of the above to the outside of the system. Further, in order to prevent the above phenomenon, it is necessary to adopt different water treatment methods for the low-pressure evaporator and the high-pressure evaporator.

As one means for solving the above problems, a can water return pipe having a pressure reducing valve interposed between the high-pressure steam drum and the low-pressure steam drum is installed, and sodium phosphate concentrated in the high-pressure steam drum is used for the low-pressure steam drum. Japanese Patent Application Laid-Open No. 60-122802 discloses a means for making the water quality of both systems uniform.

However, when the above method is used, the high-temperature high-pressure can water is partially recirculated to the low-temperature low-pressure side, which leads to a decrease in the thermal efficiency of the plant and also causes erosion and corrosion of components such as pressure reducing valves and orifices. Frequently occurs, and there is a problem that the durability of the equipment is reduced.

As means for solving the above problems, for example, Japanese Patent Laid-Open No.
A drug injection control method disclosed in Japanese Patent Publication No. 91407 has been proposed. As shown in FIG. 3, the device used for this chemical injection control has a volatile alkali treatment agent such as ammonia as a chemical injection liquid in a pipe system for supplying condensate to the low-pressure steam drum 3 during normal operation. Ammonia pump to inject 15
And an ammonia tank 16 and a sodium phosphate injection valve 17 for supplying sodium phosphate to the high-pressure steam drum 6, a sodium phosphate pump 18, and a sodium phosphate tank 20. Then, while increasing the PH value of the can water on the low pressure side with ammonia, the PH value of the can water on the high pressure side is increased with sodium phosphate to prevent corrosion of equipment in each system.

(Problems to be Solved by the Invention) However, a chemical injection control device for controlling a PH value of can water by injecting a volatile alkali treating agent into a low-pressure steam drum as described above is used as an exhaust heat recovery heat exchange for a combined cycle plant. When equipped on a vessel, the following problems occurred.

By the way, the combined cycle plant has a large load adjustment function because the start-up of the operation is quick and easy, and in general, it is operated by the DSS (Daily Start and Stop) operation method that starts and stops every day in response to daily changes in the power demand. To be done.

PH of canned water in the low-pressure steam drum during this DSS operation,
Fig. 4 shows changes over time in operating variables such as the feed water flow rate, temperature, pressure and water level.

As is clear from FIG. 4, when the load on the gas turbine is reduced, the pressure in the low-pressure steam drum gradually decreases, and when the gas turbine stops, the pressure temporarily rises due to heat transfer from the high-pressure side. Due to the heat dissipation inside, the drum pressure drops. When the drum pressure decreases in this way, the gas-liquid distribution ratio of ammonia added by the chemical injection process increases from the relationship shown in FIG. At this time, since the ammonia that had been dissolved in the can water of the low-pressure steam drum and had increased its PH value is diffused from the can water into the vapor phase, the PH value of the can water decreases. This tendency becomes more remarkable as the drum pressure decreases as time passes after the gas turbine is stopped. Therefore, when the combined cycle plant is restarted the next day, the pH value of the can water often falls below the specified lower limit.

When the combined cycle plant is started in this state, the PH value of the can water is started below the predetermined lower limit value. To solve this inconvenience, ammonia may be injected at the time of starting. However, at the time of start-up, the can water in the low-pressure steam drum is swollen, and the drum water level is extremely high. At this point, it is impossible to supply water to the low-pressure steam drum. Therefore, it is impossible to inject ammonia into the low pressure steam drum into the water supply pipe on the outlet side of the condenser. If the drain valve is opened / closed at the time of startup, the ammonia that has moved from the can water to the steam side will flow out of the system.
As a result, the amount of ammonia in the low pressure steam drum system decreases,
Further, the decrease in pressure synergistically causes the PH value of the can water to be much lower than the predetermined lower limit value.

However, when the gas turbine is started, the pressure and temperature of the low-pressure steam drum rise regardless of the PH value of the can water, so the PH value of the can water is low, and the can water temperature rises to 140 to 200 ° C, causing corrosion. Is likely to appear at the time of startup.
As a result, erosion in the components of the exhaust heat recovery heat exchanger,
Corrosion is likely to occur, which in turn shortens the life of the entire plant.

The present invention has been made to solve the above problems, and is capable of preventing the occurrence of erosion and corrosion due to a decrease in PH in the low-pressure steam drum at gas turbine startup, an exhaust heat recovery heat exchanger. An object of the present invention is to provide a method and a device for controlling chemicals.

[Configuration of the invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a chemical injection control method for an exhaust heat recovery heat exchanger including a plurality of steam generators having different steam pressures such as a low pressure steam drum and a high pressure steam drum. At the time of starting the exhaust heat recovery heat exchanger, when the rotational speed of the gas turbine is equal to or higher than a predetermined value and the PH value of the can water of the low pressure steam drum is less than the predetermined lower limit value, phosphoric acid is stored in the low pressure steam drum. This is a method characterized in that by directly injecting soda, the PH value of the can water in the low-pressure steam drum immediately after starting is maintained at a predetermined lower limit value or more.

Further, the chemical injection control device of the exhaust heat recovery heat exchanger according to the present invention guides the high temperature gas discharged from the gas turbine to the exhaust heat recovery heat exchanger to generate steam, and the generated steam drives the steam turbine to generate electricity. In the chemical injection control device for the exhaust heat recovery heat exchanger for combined cycle power generation, the sodium phosphate injection device for injecting sodium phosphate through the injection valve into the low pressure steam drum of the exhaust heat recovery heat exchanger, and the gas turbine A tachometer that measures the number of revolutions, a PH meter that measures the PH value of the can water in the low-pressure steam drum, and a gas turbine rotation signal and PH from the above number of revolutions
An injection valve drive control device for opening the injection valve in response to a PH low signal from the meter is provided.

(Operation) According to the chemical injection control method and device for the exhaust heat recovery heat exchanger according to the above configuration, when the gas turbine and the exhaust heat recovery heat exchanger are activated, a rotation signal is output from the tachometer, while the activation is started. At that time, the PH value in the low-pressure steam drum is measured by the PH adjuster, and when the measured value is lower than the specified lower limit value and the PH low signal is output, the injection valve drive control device operates and opens the injection valve. Then, sodium phosphate is injected from the sodium phosphate injection device into the low-pressure steam drum. And when the PH value of the can water in the low-pressure injection steam drum rises, the PH low signal disappears,
The injection valve closes.

Therefore, according to the present invention, the pH of the can water of the low-pressure steam drum at the time of starting the gas turbine and the exhaust heat recovery heat exchanger
The decrease in the value can be effectively prevented, and deterioration and damage due to erosion and corrosion of the components of the exhaust heat recovery heat exchanger can be prevented. In particular, since the DSS operation in which the start and stop are repeated frequently is performed, it is effective for the exhaust heat recovery heat exchanger of the plant where a corrosive environment is easily formed, and the life of the entire plant can be significantly extended.

(Embodiment) Next, one embodiment of the present invention will be described with reference to the accompanying drawings, using an example installed in a combined cycle plant. FIG. 1 is a system diagram showing an embodiment of an apparatus for carrying out a chemical injection control method for an exhaust heat recovery heat exchanger according to the present invention. The same elements as those of the conventional example shown in FIG. 3 are designated by the same reference numerals, and duplicate description will be omitted.

That is, the chemical injection control device of the exhaust heat recovery heat exchanger according to the present embodiment, the high temperature gas discharged from the gas turbine 20 is guided to the exhaust heat recovery heat exchanger to generate steam, and the steam turbine 12 is generated by the generated steam. In the chemical injection control device of the exhaust heat recovery heat exchanger for combined cycle power generation that drives and generates power, sodium phosphate injection for injecting sodium phosphate through the injection valve 21 into the low-pressure steam drum 3 of the exhaust heat recovery heat exchanger Device 22 and gas turbine 20
, A PH meter 24 for measuring the PH value of the can water of the low-pressure steam drum 3, a gas turbine rotation signal from the RPM meter 23, and a PH low signal from the PH meter 24. And an injection valve drive control device 25 for opening the injection valve 21.

Further, the compressor 26 is connected to one end of the rotating shaft of the gas turbine 20, and the generator 27 and the steam turbine 12 are connected in series to the other end.

Further, the injection valve drive control device 25 uses the PH from the PH meter 24.
The function generator 28 that outputs 1 when the measurement signal is lower than the predetermined lower limit value and outputs 0 when the measurement signal exceeds the lower limit value, and outputs 1 when the rotation speed signal from the tachometer 23 is equal to or higher than the predetermined value. A function generator 29 that outputs and outputs 0 when it is less than a predetermined value,
AND circuit 30 that receives the outputs from the function generators 28 and 29,
An automatic / manual switch 31 arranged on the secondary side of the AND circuit 30 for switching to automatic / manual operation, and when the automatic / manual switch 31 is automatic, the injection valve 21 is opened by an output signal of 1 from the AND circuit. And a drive mechanism 32 for operating.

The lower limit of PH set here depends on the operating pressure and temperature of the boiler, but it is 9.5 for the low-pressure steam drum of the exhaust heat recovery heat exchanger of a normal combined cycle plant.
It is good to set it to about.

When the gas turbine 20 and the exhaust heat recovery heat exchanger are started, the increase in the number of revolutions of the gas turbine 20 is measured by the tachometer 23. When the number of revolutions exceeds a predetermined value, the output signal of 1 from the function generator 29. (Gas turbine rotation signal) is AN
Input to the D circuit 30. On the other hand, the PH value of the water in the low-pressure steam drum 3 at the time of startup is measured by the PH meter 24.
Function generator 2 when the value is less than the specified lower limit (PH = 9.5)
The output signal from 8 to 1 (PH low signal) is input to the AND circuit 30. That is, when the gas turbine rotation signal and the PH low signal are simultaneously input to the AND circuit 30, the AND valve 30 outputs the injection valve opening operation signal. Then, the drive mechanism 32 is operated by the injection valve opening operation signal, the injection valve 21 is opened, and sodium phosphate is injected into the low-pressure steam drum 3. Then, when the PH value of the can water rises to 9.5 or more by the injected sodium phosphate, the output signal from the function generator 28 becomes zero and the output signal from the AND circuit 30 also becomes zero, so the injection valve 2
1 is closed.

The above is the case where the automatic / manual switch 31 is controlled to the automatic position, but by manually switching the switch to the manual position, the injection valve 21 is opened / closed and sodium phosphate is appropriately injected into the low-pressure steam drum 3. You can also

The sodium phosphate injected into the low-pressure steam drum 3 sequentially moves to the high-pressure steam drum side and is concentrated. However, the PH value required for the low-pressure steam drum 3 is about 9.5, which is low compared to 10-11 on the high-pressure side. Also, the sodium phosphate concentration is about 3 ppm on the low pressure side, which is very small compared to 10 to 100 ppm on the high pressure side. Therefore, the abnormal increase in PH value due to the concentration of sodium phosphate on the high pressure side is unlikely to occur.

FIG. 2 shows an example of measurement of changes over time in the operating variables of the low-pressure steam drum when the apparatus of this example is arranged in a combined cycle plant and the gas turbine is repeatedly started and stopped.

As is clear from FIG. 2, according to the method and apparatus of this embodiment, since sodium phosphate is injected at the same time as the gas turbine is started, the PH value of the can water immediately exceeds the predetermined lower limit value immediately after the start. To rise. Therefore, a corrosive environment will not be formed even if the temperature of the can water rapidly rises to a high temperature immediately after startup.

As described above, according to the present embodiment, when the gas turbine is started up, sodium phosphate having low volatility can be injected into the low-pressure steam drum 3 to reliably raise the PH value of the can water, and the exhaust heat at start-up There is no risk of forming a corrosive environment in the recovery heat exchanger, and erosion and corrosion of the constituent members can be effectively prevented.

〔The invention's effect〕

As described above, according to the present invention, it is possible to quickly and effectively prevent a decrease in the PH value of the can water of the low-pressure steam drum at the time of starting the gas turbine and the exhaust heat recovery heat exchanger, and to corrode the exhaust heat recovery heat exchanger. It is possible to prevent the environment from being formed in advance and to prevent deterioration and damage due to erosion and corrosion of the components of the exhaust heat recovery heat exchanger. In particular, it is effective for a waste heat recovery heat exchanger in a plant where a corrosive environment is likely to be formed in order to perform DSS operation in which start and stop are frequently repeated.
The life of the entire plant can be significantly extended.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention, FIG. 2 is a graph showing changes with time of operating variables when the chemical injection control device according to the present invention is used, and FIG. FIG. 4 is a system diagram showing a configuration example of a cycle plant, FIG. 4 is a graph showing changes with time of operating variables when a chemical injection control device of a conventional exhaust heat recovery heat exchanger is started, and FIG. 5 is a graph showing changes in the gas-liquid distribution rate of 1 ... Flue, 2 ... Preheater, 3 ... Low-pressure steam drum, 4
...... Low pressure evaporator, 5 ...... High pressure economizer, 6 ...... High pressure steam drum, 7 ...... High pressure evaporator, 8 ...... Superheater, 9 ...... Condenser, 10 ...... Condensation pump, 11 ... … Steam piping, 12 …… Steam turbine, 13 …… High-pressure water supply pump, 14 …… Steam piping, 15…
… Ammonia pump, 16 …… Ammonia tank, 17 ……
Sodium phosphate injection valve, 18 ... Sodium phosphate pump, 19 ...
… Sodium phosphate tank, 20… Gas turbine, 21… Injection valve, 22… Sodium phosphate injection device, 23… Tachometer,
24 …… PH meter, 25 …… Injection valve drive controller, 26 …… Compressor, 27 …… Generator, 28,29 …… Function generator, 30 …… AND circuit, 31 …… Automatic / manual selector , 32 …… Drive mechanism.

Claims (2)

(57) [Claims] 1. A chemical injection control method for an exhaust heat recovery heat exchanger comprising a plurality of steam generators having different steam pressures such as a low pressure steam drum and a high pressure steam drum. If the turbine speed is above a certain value,
In addition, if the pH value of the can water in the low-pressure steam drum is less than the specified lower limit, by directly injecting sodium phosphate into the low-pressure steam drum, the PH value of the can water in the low-pressure steam drum immediately after startup can be specified. A chemical injection control method for an exhaust heat recovery heat exchanger, which is characterized by holding at least a lower limit value. 2. A waste heat recovery heat exchanger for combined cycle power generation, in which high-temperature gas discharged from a gas turbine is guided to an exhaust heat recovery heat exchanger to generate steam, and the generated steam drives a steam turbine to generate electric power. In the chemical injection control device, a sodium phosphate injection device that injects sodium phosphate through the injection valve into the low pressure steam drum of the exhaust heat recovery heat exchanger, a tachometer that measures the number of revolutions of the gas turbine, and a low pressure steam A PH meter for measuring the PH value of the can water of the drum, and an injection valve drive control device for opening the injection valve by the gas turbine rotation signal from the tachometer and the PH low signal from the PH meter are provided. A chemical injection control device for the heat recovery heat exchanger.