JP4442764B2 - Drum boiler and exhaust heat recovery boiler equipped with drum boiler - Google Patents

Description

  In the present invention, when an oxygen treatment method (OT) is adopted for a drum-type boiler, the pre-boiler and the economizer are prevented by preventing the occurrence of pitting corrosion in the drum-around evaporator due to over-injection of oxygen and insufficient oxygen injection amount. The present invention relates to a drum boiler equipped with a drum boiler oxygen injection apparatus suitable for preventing corrosion of the boiler and an exhaust heat recovery boiler equipped with the drum boiler.

  As a boiler water treatment method, oxygen is appropriately injected into the water supply instead of the volatile substance treatment method (AVT) which keeps the water supply alkaline by reducing the oxygen concentration in the water supply as much as possible and forms a magnetite film to prevent corrosion. Thus, an oxygen treatment method (OT) for preventing corrosion by forming a hematite film has been adopted, and good results have been obtained.

  In order to employ the oxygen treatment method, the purity of water is very important. When the oxygen treatment method is employed in a state where the purity of the water is poor, pitting corrosion occurs in the tube or the pipe. Therefore, water quality is monitored by the cation path conductivity as an indicator of boiler water purity, and the oxygen treatment method (OT) is adopted as the boiler water treatment method only when the cation path conductivity is below the specified value. it can.

  In drum boilers, concentration by evaporation occurs in the evaporator system centering on the drum, and the impurity concentration is high, so if a certain amount of oxygen enters the water in this state, pitting corrosion may occur. There is sex.

In the conventional technology, when the oxygen treatment method is adopted for the once-through boiler, the dissolved oxygen concentration of the boiler water at the inlet of the economizer is 50 to 150 μg O / L (“O” is an element, “μg O / L” is equivalent to ppb) In contrast, when the oxygen treatment method is adopted for the drum type boiler, the dissolved oxygen concentration in the boiler water becomes 30 to 50 μg O / L at the economizer entrance. Thus, there has been no method for controlling the oxygen injection amount by directly sampling the dissolved oxygen concentration at the drum inlet only by limiting the oxygen injection amount.
In the case of a drum boiler as compared with a once-through boiler, the oxygen concentration at the entrance of the economizer is lowered in order to prevent pitting corrosion from occurring in the evaporator around the drum.

On the other hand, it is known that pitting corrosion does not occur if the oxygen concentration is 40 to 50 μg O / L or less even if impurities such as chloride are contained.
Further, the dissolved oxygen concentration in the boiler water for effective use of the oxygen treatment method needs to be at least 20 μg O / L, and preferably within a range not exceeding 40-50 μg O / L which is the upper limit of the dissolved oxygen concentration at the drum inlet. It is necessary to increase its concentration.
JP-A-53-74603 JP-A-9-170702 JP-T-2001-514368

  In order to make the oxygen treatment method work effectively for the pre-boiler system and the economizer in the drum type boiler, the dissolved oxygen concentration in the boiler water of the pre-boiler system and the economizer is kept as high as possible and surely 40 at the inlet of the drum. It is important to make it ˜50 μg O / L. However, the oxygen consumption varies depending on the state of the protective coating formed on the preboiler system and the wall of the economizer, so there is a problem that it is very difficult to control the oxygen injection amount.

  An object of the present invention is to provide a drum boiler or a drum boiler that keeps the dissolved oxygen concentration of the pre-boiler system and the economizer as high as possible within an allowable range so as to prevent corrosion and prevent pitting corrosion in the evaporator around the drum. To provide a waste heat recovery boiler.

  The object of the present invention is achieved by directly sampling the water supply to the drum and injecting oxygen into the pre-boiler system so that the dissolved oxygen concentration of the sampling water is the maximum dissolved oxygen concentration allowed in the drum water. Is done.

In the first aspect of the present invention, water is sequentially supplied to the drum via a pre-boiler system and a economizer by a water supply pipe, and a brackish water mixed fluid obtained by an evaporator installed at the lower part of the drum is supplied to the drum by a riser pipe. The oxygen injection means for injecting oxygen into the water supply pipe to the pre-boiler system in the drum boiler having a structure for supplying the water after the brackish water separation to the evaporator again via the drum precipitation pipe and the evaporator water supply pipe And a means for measuring the dissolved oxygen concentration in the communication pipe connecting the economizer and the drum, and depending on the dissolved oxygen concentration measured by the dissolved oxygen concentration measuring means, the supply pipe to the pre-boiler system It is a drum boiler provided with control means for adjusting the amount of oxygen injection from the oxygen injection means.

According to the second aspect of the present invention, water is sequentially supplied to the drum via the pre-boiler system and the economizer by the water supply pipe, and the brackish water mixed fluid obtained by the evaporator installed at the lower part of the drum is supplied to the drum by the riser pipe. The oxygen injection means for injecting oxygen into the water supply pipe to the pre-boiler system in the drum boiler having a structure for supplying the water after the brackish water separation to the evaporator again via the drum precipitation pipe and the evaporator water supply pipe And a means for measuring the dissolved oxygen concentration in the connecting pipe connecting the economizer and the drum, and an electric conductivity measuring means for measuring the cation path electric conductivity in the drum. An arithmetic unit for calculating an allowable oxygen concentration from the electrical conductivity measured by the means and the dissolved oxygen concentration measured by the means for measuring the dissolved oxygen concentration, and the acid so as to be within the allowable oxygen concentration calculated by the arithmetic unit. Control means for adjusting the oxygen injection amount to Pureboira lineage from the injection means is a drum boiler provided.

  The invention according to claim 3 is that water is supplied to the drum sequentially through the preboiler system and the economizer by the water supply pipe, and the brackish water mixed fluid obtained from the evaporator installed at the lower part of the drum is supplied to the drum through the riser pipe. The oxygen injection means for injecting oxygen into the water supply pipe to the pre-boiler system in the drum boiler having a structure for supplying the water after the brackish water separation to the evaporator again via the drum precipitation pipe and the evaporator water supply pipe And a dissolved oxygen concentration measuring means for measuring the dissolved oxygen concentration in the drum downcomer, and according to the dissolved oxygen concentration measured by the dissolved oxygen concentration measuring means, from the oxygen injection means to the water supply pipe to the pre-boiler It is a drum boiler provided with a control means for adjusting the amount of oxygen injection.

  In the invention according to claim 4, water is sequentially supplied to the drum via the pre-boiler system and the economizer by the water supply pipe, and the brackish water mixed fluid obtained by the evaporator installed in the lower part of the drum is supplied to the drum by the riser pipe. The oxygen injection means for injecting oxygen into the water supply pipe to the pre-boiler system in the drum boiler having a structure for supplying the water after the brackish water separation to the evaporator again via the drum precipitation pipe and the evaporator water supply pipe And a dissolved oxygen concentration measuring means for measuring the dissolved oxygen concentration in the drum downcomer, and an electrical conductivity measuring means for measuring the cation path electrical conductivity in the drum downcomer. An arithmetic unit is provided for calculating the allowable oxygen concentration from the measured electrical conductivity and the dissolved oxygen concentration measured by the dissolved oxygen concentration measuring means, so that it is within the allowable oxygen concentration calculated by the arithmetic unit. Serial is a drum boiler provided with control means for adjusting the oxygen injection amount to Pureboira line from the oxygen injection means.

  The invention according to claim 5 includes a high-pressure and / or medium-pressure system heat exchanger and a low-pressure system heat exchanger, wherein the high-pressure and / or medium-pressure system heat exchanger is configured by a once-through boiler, and The system heat exchanger is a double-pressure or triple-pressure type exhaust heat recovery boiler constituted by a drum boiler, and the drum boiler of the low-pressure system heat exchanger is the drum boiler according to any one of claims 1 to 4. It is an exhaust heat recovery boiler.

  The invention according to claim 6 includes heat exchangers of a high pressure system, a medium pressure system, and a low pressure system, the heat exchanger of the high pressure system is configured by a once-through boiler, and the heat exchanger of the low pressure system and the medium pressure system Is a double-pressure or triple-pressure exhaust heat recovery boiler composed of a drum boiler, wherein the drum boiler of the heat exchanger of the low pressure system and the intermediate pressure system is the drum boiler according to any one of claims 1 to 4. It is a heat recovery boiler.

  The pre-boiler system generally refers to a system from a condenser (not shown) to a water heater. In the present embodiment described below, the system from the condenser to the water supply tank 1 is not shown, and thus refers to the system between the water supply tank 1 and the water supply heater 5.

(Function)
According to the inventions of claims 1 to 6 of the present invention, if the dissolved oxygen concentration of water supplied to the drum is high, there is a risk of pitting corrosion occurring in the evaporator around the drum, and there is much fear of this pitting corrosion. If the amount of oxygen injected into the pre-boiler system is kept low, there will be a problem that the pre-boiler system and the economizer cannot be adequately protected. Therefore, in order to establish an oxygen treatment method for the pre-boiler and the economizer by directly sampling the water supply to the drum and controlling the dissolved oxygen concentration so that the maximum dissolved oxygen amount allowed as drum water is obtained. Since the necessary dissolved oxygen is reliably maintained, the occurrence of pitting corrosion in the evaporator around the drum and the corrosion of the preboiler and the economizer due to lack of oxygen do not occur.

  In the inventions according to claims 2 and 4, the optimum is achieved by controlling the dissolved oxygen concentration at the drum inlet to the maximum allowable oxygen concentration taking into account the cation path electrical conductivity of the drum water at this time. Control of dissolved oxygen becomes possible.

According to the first aspect of the present invention, the dissolved oxygen concentration of the water in the connecting pipe connecting the economizer and the drum is measured, so that the dissolved oxygen concentration of the preboiler system and the economizer is pitted by the evaporator around the drum. Therefore, it is possible to adjust the dissolved oxygen concentration so that the pre-boiler system, the economizer and the drum-circulating evaporator can always exhibit the optimum anticorrosion effect.

According to the second aspect of the present invention, the dissolved oxygen concentration of the water in the connecting pipe connecting the economizer and the drum is measured, and the dissolved oxygen concentration at the drum inlet is taken into consideration of the cation path electrical conductivity of the drum water. by controlling such that the allowable maximum oxygen concentrations, that Do is possible to control the optimal dissolved oxygen.
According to the third aspect of the present invention, by directly measuring the oxygen concentration of the drum water, the dissolved oxygen concentration at the drum inlet is kept at the maximum allowable level so as not to cause pitting corrosion in the evaporator around the drum. Therefore, it is possible to adjust the dissolved oxygen concentration so that the pre-boiler system, the economizer, and the drum-around evaporator always exhibit the optimum anticorrosion effect.

  According to the fourth aspect of the invention, the dissolved oxygen concentration at the drum inlet is transferred to the evaporator around the drum by directly taking into account the cation path conductivity of the drum water and directly measuring the oxygen concentration of the drum water. It is possible to keep the maximum allowable level so as not to cause pitting corrosion, and it is possible to adjust the residual oxygen concentration so that the pre-boiler system, the economizer, and the drum-around evaporator always exhibit the optimum anti-corrosion effect. It becomes. .

  According to the invention of claim 5 and claim 6, the dissolved oxygen concentration of the feed water in the drums of the intermediate pressure and / or low pressure system is set to the specified value, and the heat exchanger ( The dissolved oxygen concentration of the economizer can be set high so that pitting corrosion does not occur in the heat exchanger (evaporator) around the drum of the low pressure system, and the preboiler system, economizer and drum evaporator are installed. It is possible to adjust the dissolved oxygen concentration to always exhibit the optimum anticorrosion effect.

  Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a configuration diagram of a pre-boiler system including a drum boiler oxygen injection device of the present embodiment, an entire system around a boiler economizer and a boiler drum evaporator.
The water discharged from the water supply tank 1 passes through the water supply tank downcomer 2 and is sent to the boiler water supply pump 4. The water boosted by the boiler feed pump 4 is sent to the feed water heater 5 through the feed water pipe 3, and the water exiting the feed water heater 5 is sent to the economizer 6. The water exiting the economizer 6 is supplied to the drum 8 through the economizer drum connecting pipe 7.

  The water that has entered the drum 8 is sent from the drum downpipe 9 to the evaporator water supply pipe 10 and supplied from the evaporator water supply pipe 10 to the evaporator 11. The water that has received heat in the evaporator 11 becomes an air-water mixed fluid and returns to the drum 8 through the riser 12. The gas-water mixed fluid is separated into water and steam in the drum 8, and the steam passes through the saturated steam pipe 13 and is supplied to a superheater (not shown) or the like.

Oxygen is injected into the water flowing through the water supply tank downcomer 2 from the oxygen generator 14. Oxygen generated by the oxygen generator 14 is injected into the water supply tank downcomer 2 through the oxygen injection pipe 15.
Control of the amount of oxygen injected into the water in the water tank precipitation pipe 2 is performed by the oxygen control valve 16 installed in the oxygen injection pipe 15, and the control of the oxygen control valve 16 is performed by the following operation.

  The water extracted from the economizer drum connecting pipe 7 is sent to the dissolved oxygen meter 18 through the drum inlet sampling pipe 17. The signal of the dissolved oxygen meter 18 is sent to the calculator 23 by the control cable 19, and the control signal obtained by the calculator 23 is sent from the control cable 19 to the oxygen control valve 16, so that the dissolved oxygen concentration of the drum feed water becomes the specified value. Thus, the opening degree of the oxygen control valve 16 is set.

  By adopting the above drum boiler oxygen injection device, the dissolved oxygen concentration of the pre-boiler system and the economizer 6 can be set high within a range where no pitting corrosion occurs in the evaporator 11 around the drum 8, so that the optimum anticorrosion effect is always achieved. It is possible to adjust the dissolved oxygen concentration so as to exhibit the above.

FIG. 2 shows that the dissolved oxygen concentration of the pre-boiler system and the economizer can be set higher to the limit value as compared with the embodiment shown in FIG. 2 that are the same as those shown in FIG. 1 are given the same reference numerals, and descriptions thereof are omitted.
The embodiment shown in FIG. 2 is different from the embodiment shown in FIG. 1 in that the dissolved oxygen allowable value is calculated by the cation path electrical conductivity of water in the drum 8 and the dissolved oxygen injection amount is controlled by the calculated value. This is the point.

  In FIG. 2, the drum water of the drum 8 is extracted from the drum water sampling pipe 20 and supplied to the cation path conductivity meter 21. In the cation path conductivity meter 21, the cation path conductivity of the drum water is converted into an electric signal. The signal of the cation path conductivity obtained by the cation path conductivity meter 21 is sent to the allowable oxygen concentration calculator 23 via the signal cable 22.

Incidentally, there is a relationship shown in FIG. 3 between the allowable oxygen concentration of the drum water and the cation path electrical conductivity. This relationship is incorporated into the allowable oxygen concentration calculator 23.
In consideration of the cation path electrical conductivity of the drum water, the dissolved oxygen concentration calculated by the allowable oxygen concentration calculator 23 is matched with the dissolved oxygen concentration at the drum inlet so that the allowable oxygen concentration becomes the allowable oxygen concentration. By sending a signal to the limit through the signal cable 19 and adjusting the oxygen control valve 16, optimal control of dissolved oxygen becomes possible.

Next, specific control set values will be described.
Chlorine ions are typical impurities that accelerate corrosion, but the limit value of the chlorine ion concentration at which pitting corrosion does not occur was determined by experiment using dissolved oxygen concentration as a parameter. As experimental conditions, the temperature is 160 ° C., the pH is 8.5, the flow rate is 0.18 mm / s, and the material is carbon steel.

  The limit values of dissolved oxygen concentration and chloride ion concentration at which pitting corrosion does not occur are shown below.

Limit value that does not cause pitting corrosion
Chlorine ion concentration when the dissolved oxygen concentration is 40 μg O / L 120 μg Cl / L
Chlorine ion concentration when the dissolved oxygen concentration is 100 μg O / L 12 μg Cl / L
When the chlorine ion concentration of 120 μg Cl / L is converted to the cation path conductivity, it is 0.154 mS / m, and when the chlorine ion concentration of 12 μg Cl / L is converted to the cation path conductivity, it is 0.016 mS / m.

From the above experimental results, the specific function of FIG. 3 is expressed as follows.
Y = 107-435X
Here, Y is the dissolved oxygen concentration, and X is the cation path electrical conductivity.

  By incorporating the above function formula into the allowable oxygen concentration calculator 23, a signal necessary for control can be easily created.

FIG. 4 shows another embodiment in which the measurement point of the dissolved oxygen concentration in the feed water is a drum downcomer 9.
In this embodiment, the oxygen concentration of the injected water is not directly exceeded by directly measuring the oxygen concentration of the drum water. Drum water is sent to the dissolved oxygen meter 18 through the drum downcomer sampling pipe 24. By controlling the oxygen control valve 16 with the control cable 19 so that the oxygen concentration in the drum downcomer tube 9 does not exceed the specified value, the oxygen concentration in the drum water exceeds the specified value and pitting corrosion occurs in the evaporator 11 and the like around the drum. It can be prevented from occurring.

  FIG. 5 shows a pitting corrosion in the evaporator 11 and the like around the drum by adding a configuration for measuring the cation path conductivity of the drum downcomer 9 with the cation path conductivity meter 21 to the embodiment of FIG. Therefore, the oxygen concentration is increased to the limit to prevent the corrosion of the pre-boiler system and the economizer 6.

The anticorrosion method by the oxygen treatment method (OT) of the present invention is particularly effective when applied to a once-through HRSG (exhaust heat recovery boiler).
In order to increase plant efficiency, HRSG employed in a combined plant using gas turbine exhaust gas as a heat source often employs a double pressure or triple pressure system in which HRSG is divided into two or three types of steam pressure. For example, in the case of a drum type boiler, two or three drums are installed. In the case of a once-through type HRSG, a once-through type boiler is adopted for the low-pressure part, although a once-through type is adopted for the medium-pressure and high-pressure parts where it is effective from the start-up characteristics and the like. In some cases, drum-type boilers may be employed for the intermediate and low pressure portions.

An overall system diagram of a typical once-through HRSG is shown in FIG.
Condensate recovered from the condenser 25 passes through a condenser pipe 26 and is sent to a low-pressure economizer 28 by a condensate pump 27. A part of the water exiting the low pressure economizer 28 is sent to the low pressure drum 31 via the low pressure water supply pipe 29. The water that has entered the low-pressure drum 31 is sent from the low-pressure drum precipitation pipe 32 to the low-pressure evaporator water supply pipe 33 and supplied from the low-pressure evaporator water supply pipe 33 to the low-pressure evaporator 34. The water that has received heat in the low-pressure evaporator 34 becomes a gas-water mixed fluid, returns to the low-pressure drum 31 through the low-pressure steam riser 35. The water that has become the gas-water mixed fluid in the low-pressure evaporator 34 is separated into water and steam by the low-pressure drum 31, and the steam is superheated by the low-pressure superheater 36, and then passes through the low-pressure main steam pipe 37. Supplied to equipment used.

  Further, a part of the water exiting the low-pressure economizer 28 is sent to the medium-pressure / high-pressure feed pump 39 via the medium-pressure / high-pressure feed pump inlet pipe 38 branched from the low-pressure feed pipe 29. Water is supplied from the intermediate-pressure / high-pressure water supply pump 39 to the medium-pressure main water supply pipe 40 and the high-pressure main water supply pipe 46 in a pressurized state.

  First, the water that has entered the medium-pressure main water supply pipe 40 is sequentially sent to the medium-pressure economizer 42, the medium-pressure evaporator 43, and the medium-pressure superheater 44 through the medium-pressure feed valve 41. The medium pressure steam sufficiently superheated by the medium pressure superheater 44 is supplied from a medium pressure main steam pipe 45 to a medium pressure steam utilization device (not shown).

  Further, the water entering the high-pressure main water supply pipe 46 is sequentially sent to the high-pressure economizer 48, the high-pressure evaporator 49 and the high-pressure superheater 50 through the high-pressure water supply valve 47. The high-pressure steam sufficiently heated by the high-pressure superheater 50 is supplied from the high-pressure main steam pipe 51 to an unillustrated high-pressure steam utilization device or the like.

  In the HSGR configured as described above, oxygen is injected from the oxygen generator 14 into the water flowing through the condensate pipe 26. Oxygen generated in the oxygen generator 14 is injected into the condensate pipe 26 through the oxygen injection pipe 15. The oxygen injection amount is controlled by an oxygen control valve 16 installed in the oxygen injection pipe 15. The dissolved oxygen concentration of the water in the drum inlet sampling pipe 17 extracted from the low-pressure water supply pipe 29 is measured by the dissolved oxygen meter 18, and a necessary oxygen amount is calculated by the calculator 23 from this oxygen concentration signal, and this is controlled. In response to the cable 19, the oxygen control valve 16 is controlled. Thus, the dissolved oxygen concentration of the feed water in the low-pressure drum 31 is set to a specified value, and the dissolved oxygen concentration in the low-pressure economizer 28 is set within a range in which pitting corrosion is not generated in the low-pressure evaporator 34 around the low-pressure drum 31. Since it can be set high, it is possible to adjust the dissolved oxygen concentration so as to always exhibit the optimum anticorrosion effect.

  The oxygen treatment method (OT) is particularly effective in a once-through boiler, and in this embodiment, it is desired to adopt the oxygen treatment method, but there is a possibility that the corrosion of the drum boiler of the low-pressure system may be a problem, and the once-through and drum that could not be adopted. This is also effective for mixed boiler HRSG.

  According to the present invention, the dissolved oxygen concentration in the preboiler system and the economizer can be increased to the limit at which pitting corrosion does not occur in the evaporator around the drum, so that an optimum anticorrosion effect can be exhibited and at the same time a drum by oxygen over-injection The occurrence of pitting corrosion in the surrounding evaporator system can be prevented.

It is a whole system diagram at the time of using the oxygen injection apparatus for drum boilers by Example 1 of the present invention. It is a whole system diagram at the time of using the oxygen injection apparatus for drum boilers by Example 2 of this invention. It is explanatory drawing which showed the relationship between the thione path electrical conductivity of drum water, and allowable oxygen concentration. It is a whole system diagram at the time of using the oxygen injection apparatus for drum boilers by Example 3 of this invention. It is a whole system diagram at the time of using the oxygen injection apparatus for drum boilers by Example 4 of this invention. It is a whole system diagram at the time of using the oxygen injection apparatus for drum boilers in the system of the once-through type and drum type combined use HRSG by Example 5 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Water supply tank 2 Water supply tank precipitation pipe 3 Water supply pipe 4 Boiler water supply pump 5 Water supply heater 6 Carbon economizer 7 Carbon economizer drum connecting pipe 8 Drum 9 Drum precipitation pipe 10 Evaporator water supply pipe 11 Evaporator 12 Rise pipe 13 Saturated steam pipe DESCRIPTION OF SYMBOLS 14 Oxygen generator 15 Oxygen injection pipe 16 Oxygen control valve 17 Drum inlet water sampling pipe 18 Dissolved oxygen meter 19 Control cable 20 Drum water sampling pipe 21 Cation path electric conductivity meter 22 Signal cable 23 Allowable oxygen concentration calculator 24 Drum precipitation pipe Sampling pipe 25 Condenser 26 Condensate pipe 27 Condensate pump 28 Low-pressure economizer 29 Low-pressure feed water 30 Low-pressure drum feed water control valve 31 Low-pressure drum 32 Low-pressure drum precipitation pipe 33 Low-pressure evaporator water supply pipe 34 Low-pressure evaporator 35 Low-pressure evaporator Rising pipe 36 Low pressure superheater 37 Low pressure main steam pipe 38 Medium and high pressure supply Pump inlet piping 39 Medium pressure / high pressure water supply pump 40 Medium pressure main water supply pipe 41 Medium pressure water supply control valve 42 Medium pressure economizer 43 Medium pressure evaporator 44 Medium pressure superheater 45 Medium pressure main steam pipe 46 High pressure main water supply pipe 47 High-pressure water supply control valve 48 High-pressure economizer 49 High-pressure evaporator 50 High-pressure superheater 51 High-pressure main steam pipe

Claims (6)

Water is supplied to the drum sequentially through the pre-boiler system and the economizer through the water supply pipe, and the brackish water mixed fluid obtained from the evaporator installed at the bottom of the drum is supplied to the drum through the riser pipe, after the brackish water is separated In a drum boiler having a configuration in which water is supplied to the evaporator again via the drum precipitation pipe and the evaporator water supply pipe,
An oxygen injection means for injecting oxygen into the water supply pipe to the pre-boiler system is provided, and a means for measuring the dissolved oxygen concentration is provided in the connecting pipe connecting the economizer and the drum, and the dissolved oxygen concentration measuring means is measured. A drum boiler characterized by comprising a control means for adjusting the amount of oxygen injected from the oxygen injection means into the water supply pipe to the pre-boiler system according to the oxygen concentration. Water is supplied to the drum sequentially through the pre-boiler system and the economizer through the water supply pipe, and the brackish water mixed fluid obtained from the evaporator installed at the bottom of the drum is supplied to the drum through the riser pipe, after the brackish water is separated In a drum boiler having a configuration in which water is supplied to the evaporator again via the drum precipitation pipe and the evaporator water supply pipe,
Oxygen injection means for injecting oxygen into the water supply pipe to the pre-boiler system is provided, and a means for measuring the dissolved oxygen concentration is provided in the connecting pipe connecting the economizer and the drum, and the cation path conductivity in the drum is measured. An electrical conductivity measuring means, and an arithmetic unit for calculating an allowable oxygen concentration from the electrical conductivity measured by the electrical conductivity measuring means and the dissolved oxygen concentration measured by the dissolved oxygen concentration measuring means. A drum boiler comprising a control means for adjusting the amount of oxygen injected from the oxygen injection means into the pre-boiler system so as to be within the allowable oxygen concentration calculated in step (1). Water is supplied to the drum sequentially through the pre-boiler system and the economizer through the water supply pipe, and the brackish water mixed fluid obtained from the evaporator installed at the bottom of the drum is supplied to the drum through the riser pipe, after the brackish water is separated In a drum boiler having a configuration in which water is supplied to the evaporator again via the drum precipitation pipe and the evaporator water supply pipe,
An oxygen injection means for injecting oxygen into the water supply pipe to the pre-boiler system is provided, and a dissolved oxygen concentration measuring means for measuring the dissolved oxygen concentration in the drum downcomer is provided, and the dissolved oxygen concentration measured by the dissolved oxygen concentration measuring means is adjusted. Accordingly, a drum boiler comprising a control means for adjusting the amount of oxygen injected from the oxygen injection means to the water supply pipe to the pre-boiler. Water is supplied to the drum sequentially through the pre-boiler system and the economizer through the water supply pipe, and the brackish water mixed fluid obtained from the evaporator installed at the bottom of the drum is supplied to the drum through the riser pipe, after the brackish water is separated In a drum boiler having a configuration in which water is supplied to the evaporator again via the drum precipitation pipe and the evaporator water supply pipe,
An oxygen injection means for injecting oxygen into the water supply pipe to the pre-boiler system, a dissolved oxygen concentration measurement means for measuring the dissolved oxygen concentration in the drum downcomer, and an electric current for measuring the cation path electrical conductivity in the drum downcomer Conductivity measuring means is provided, and an arithmetic unit is provided for calculating the allowable oxygen concentration from the electrical conductivity measured by the electrical conductivity measuring means and the dissolved oxygen concentration measured by the dissolved oxygen concentration measuring means, and the arithmetic unit calculates A drum boiler comprising a control means for adjusting an oxygen injection amount from the oxygen injection means to the pre-boiler system so as to be within the allowable oxygen concentration. A high-pressure and / or medium-pressure system heat exchanger and a low-pressure system heat exchanger are provided, the high-pressure and / or medium-pressure system heat exchanger is constituted by a once-through boiler, and the low-pressure system heat exchanger is a drum boiler. A double-pressure or triple-pressure exhaust heat recovery boiler composed of
An exhaust heat recovery boiler, wherein the drum boiler of the low pressure system heat exchanger is the drum boiler according to any one of claims 1 to 4. A high-pressure system, a medium-pressure system, and a low-pressure system heat exchanger, the heat exchanger of the high-pressure system is configured with a once-through boiler, and the heat exchanger of the low-pressure system and the intermediate-pressure system is configured with a drum boiler Or a triple pressure exhaust heat recovery boiler,
The exhaust heat recovery boiler according to any one of claims 1 to 4, wherein the drum boiler of the heat exchanger of the low pressure system and the intermediate pressure system is the drum boiler according to any one of claims 1 to 4.

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