JP2007064501A - Steaming method for boiler plant, boiler plant, and steaming device for boiler plant - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steaming method for a boiler plant preventing stress corrosion cracking in a turbine, and capable of preventing malfunction due to scale separation in a superheater or the like by sufficiently mixing an oxygen scavenger in steam from a boiler, and efficiently and effectively reducing a dissolved oxygen amount. <P>SOLUTION: In the steaming method for the boiler plant 1, boiler water turned into reducing water or active hydrogen water is poured into an outlet fluid of the boiler supplied with water wherein oxygen is injected into condensed water to reduce dissolved oxygen in steam. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a steam treatment method for a boiler plant, a boiler plant, and a steam treatment apparatus for a boiler plant.

In recent years, as a water supply process in a boiler plant, an oxygen injection process that generates hematite scale as a protective film by injecting oxygen into condensate from a condenser and / or water supplied from a deaerator outlet has been applied. This oxygen implantation process includes NWT (Neutral Water Treatment) for injecting only oxygen and CWT (Combined Water Treatment) for injecting oxygen and ammonia.
However, in these oxygen injection processes, oxygen is contained in the steam from the boiler, so the stress corrosion cracking of the turbine caused by this dissolved oxygen and the special purpose stainless steel (SUS) scale from the boiler superheater or reheater. Excessive peeling may occur.
In order to solve this problem, as disclosed in Patent Document 1, oxygen scavenger is supplied to the fluid from the boiler outlet, dissolved oxygen supplied to the turbine and the steam system of the boiler is reduced as much as possible, and stress corrosion of the turbine Those that suppress cracking and excessive peeling of the SUS scale from boiler superheaters and reheaters have been proposed.

Japanese Examined Patent Publication No. 7-43093 (column 4, lines 4 to 32, and FIG. 1)

  However, hydrazine listed as an oxygen scavenger in Patent Document 1 is generally a harmful substance having carcinogenicity and the like, and is not preferable for measures against environmental pollution.

  In view of the above-mentioned problems, the present invention prevents stress corrosion cracking in a turbine without directly injecting an oxygen scavenger such as hydrazine into steam from a boiler, and prevents scale corrosion in a superheater and a reheater. It aims at providing the steam processing method of a boiler plant which can prevent a malfunction, a boiler plant, and the steam processing apparatus of a boiler plant.

In order to solve the above problems, the present invention employs the following means.
That is, the steam treatment method of the boiler plant according to the present invention is the method of injecting oxygen water into the condensate and supplying boiler water that has been reduced or activated hydrogenated into the outlet fluid of the boiler, and dissolved oxygen in the steam. In a steam treatment method for a boiler plant that reduces boiler water, the boiler water that has been reduced or activated hydrogenated is used as a boiler steam system (for example, upstream of a superheater or superheater, or upstream or reheater of a reheater). It is characterized by being injected into.

According to the steam treatment method for a boiler plant of the present invention, steam with a sufficiently reduced amount of dissolved oxygen is supplied to the steam system of the boiler, so stress due to oxygen in the steam system such as a superheater, a reheater, and a turbine. Corrosion cracking can be prevented and dissolved oxygen can prevent hematization from progressing and the scale from being easily peeled off.
In addition, since the amount of scale peeling is reduced by suppressing hematite formation, it is possible to prevent the peeled scale from accumulating in a thin tube such as a superheater or reheater and further accumulating and closing the tube. It can be prevented that the thin tube is overheated and eventually leads to a blast accident. Further, it is possible to prevent the peeled scale from damaging the turbine.
Furthermore, according to the steam treatment method of the boiler plant of the present invention, the dissolved oxygen in the steam is reduced by injecting the boiler water in the boiler plant system into reduced water or active hydrogen water and injecting it into the outlet fluid of the boiler. Therefore, it is not necessary to introduce a toxic substance such as hydrazine as an oxygen scavenger from the outside of the boiler plant, and environmental pollution countermeasures for such oxygen scavenger become unnecessary.

  A boiler plant according to the present invention is a boiler plant including a boiler that is supplied with water by injecting oxygen into condensate and / or feed water, and is a boiler steam system (for example, upstream of a superheater or a superheater or reheat). An injection line for injecting boiler water that has been reduced or activated hydrogenated is connected to the upstream or reheater).

In the boiler plant of the present invention, steam in which the amount of dissolved oxygen is sufficiently reduced is supplied to the steam system of the boiler, so stress corrosion cracking due to oxygen is unlikely to occur in steam systems such as superheaters, reheaters and turbines. In addition, since hematization proceeds with dissolved oxygen, the scale is difficult to peel off.
Further, since the amount of peeling of the scale is reduced by suppressing hematite formation, the peeled scale is prevented from accumulating in a thin tube such as a superheater or a reheater and further accumulating and blocking the tube.
Furthermore, the boiler plant of the present invention reduces the dissolved oxygen in the steam by reducing the boiler water in the boiler plant system into reduced water or active hydrogen water and injecting it into the outlet fluid of the boiler. Therefore, it is not necessary to introduce a toxic substance such as hydrazine as an oxygen scavenger, and it is not necessary to take measures against environmental pollution against such oxygen scavenger.

  Further, the boiler plant according to the present invention is provided with a measuring instrument for measuring the amount of dissolved oxygen on the downstream side of the superheater, and the reduced hydration or active hydrogen hydration is performed by the dissolved oxygen amount measured by the measuring instrument. It is good also as adjusting the supply amount of boiler water.

In this way, on the downstream side of the superheater, the amount of dissolved oxygen is measured by a measuring instrument to adjust the supply amount of boiler water that has been reduced or activated hydrogenated, so that it is reduced or activated hydrogenated. Only the required amount of boiler water can be supplied. For this reason, for example, there is insufficient supply of boiler water that has been reduced or activated hydrogenated, resulting in insufficient suppression of hematite scale, or excessive supply of boiler water that has been reduced or activated hydrogenated. It is possible to prevent the boiler water that has been excessively reduced or activated hydrogenated from being adversely affected.
The amount of dissolved oxygen is measured with a dissolved oxygen meter or an oxidation reduction potential (ORP) meter, and the target is a state where the water quality condition is an AVT condition in which magnetite is stably present as iron oxide ( It is preferable to inject boiler water reduced or activated hydrogenated so that the dissolved oxygen is 7 ppb or less or the ORP is −0.3 V to −0.4 V or less at 25 ° C., for example.
Further, as the installation location of the measuring device, the outlet of the superheater or the outlets of the superheater and the reheater, which are greatly affected by the hematite scale, are suitable. In some cases, the measuring device may measure the condensate before oxygen injection or the amount of dissolved oxygen in the drain of the high-pressure feed water heater and the low-pressure feed water heater.

  A steam treatment apparatus for a boiler plant according to the present invention converts boiler water into reduced water or activated hydrogen water, and injects oxygen into the condensed water and / or feed water from the reduced or activated hydrogen water. It is injected into the outlet fluid of the boiler supplied with water to reduce dissolved oxygen in the steam.

By using the steam treatment apparatus of the present invention in a boiler plant, steam with a sufficiently reduced amount of dissolved oxygen can be supplied to the outlet fluid of the boiler. Therefore, it is possible to prevent stress corrosion cracking due to oxygen in steam systems such as a superheater, a reheater, and a turbine of a boiler plant, and it is possible to suppress the scale from being easily peeled off due to hematization due to dissolved oxygen.
Further, since the amount of peeling of the scale is reduced by suppressing hematite formation, it is possible to prevent the peeled scale from accumulating in a thin tube such as a superheater or a reheater and further accumulating and blocking the tube. Further, it is possible to prevent the peeled scale from damaging the turbine.
Furthermore, the steam treatment apparatus for a boiler plant of the present invention reduces the dissolved oxygen in the steam by reducing the boiler water in the boiler plant system into reduced water or active hydrogen water and injecting it into the outlet fluid of the boiler. It is not necessary to introduce a toxic substance such as hydrazine as an oxygen scavenger from the outside of the plant, and environmental pollution countermeasures for such oxygen scavenger become unnecessary.

  According to the steam treatment method for a boiler plant, the boiler plant, and the steam treatment apparatus for a boiler plant according to the present invention, it is possible to prevent stress corrosion cracking due to oxygen in a steam system such as a superheater and to reduce generation of a hematite scale that easily peels. As a result, the hematite scale that has peeled off accumulates in thin tubes such as superheaters and reheaters, and further accumulates to block the tubes.Then these closed tubes are overheated, eventually leading to an eruption accident. Can be prevented. Further, according to the steam treatment method for a boiler plant, the boiler plant, and the steam treatment apparatus for the boiler plant according to the present invention, it is not necessary to introduce a harmful substance such as hydrazine as an oxygen scavenger from the outside of the boiler plant. Environmental pollution measures against oxygen scavengers are no longer necessary.

Embodiments according to the present invention will be described below with reference to the drawings.
Hereinafter, a boiler plant 1 for thermal power generation according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2.
FIG. 1 is a block diagram showing an overall schematic configuration of a boiler plant 1.
The boiler plant 1 is provided with a steam system 3 and a water supply system 5.

The steam system 3 includes a brackish water separator 9 that separates the saturated steam generated in the furnace water wall pipe 7 into steam and water, a superheater 11 that superheats the saturated steam to form superheated steam, and heat of the superheated steam. A high-pressure turbine 13 that converts energy into rotational power; a reheater 15 that reheats the exhaust of the high-pressure turbine 13; a medium-pressure turbine 17 that converts thermal energy of superheated steam from the reheater 15 into rotational power; A low-pressure turbine 19 that converts thermal energy of exhaust gas from the intermediate-pressure turbine 17 into rotational power is provided.
The brackish water separator 9, the superheater 11, the high pressure turbine 13, the reheater 15, the intermediate pressure turbine 17 and the low pressure turbine 19 are connected by a steam pipe 10.

The water supply system 5 includes a condenser 21 that cools and condenses exhaust gas from the low-pressure turbine 19, a condensate pump 23 that extracts the condensate from the condenser 21, and a condensate drain that removes ions in the condensate. A salt device 25, a ground steam condenser 27, a condensate booster pump 29 that boosts the condensate to a required pressure, a low-pressure feed water heater 31 that heats feed water by extraction from the low-pressure turbine 19, and an intermediate-pressure turbine A deaerator 33 that directly heats the feed water with steam extracted from 17 and physically separates and removes dissolved gas in the feed water, a feed water pump 35 that raises the pressure of the feed water and pushes it downstream, and a steam system 3 A high-pressure feed water heating device 37 that heats the feed water by extracting air and a economizer 39 that heats the feed water by combustion exhaust gas are provided.
These condenser 21, condensate pump 23, condensate demineralizer 25, ground steam condenser 27, condensate booster pump 29, low pressure feed water heater 31, deaerator 33, feed water pump 35, high pressure feed water heater 37 and the economizer 39 are connected by a water supply pipe 20.

The condenser 21 is configured to be supplied with water by a makeup water pump 43 from a makeup water tank 41.
The low-pressure feed water heater 31 is configured by connecting four heat exchangers in series. The steam extracted by the low-pressure turbine 19 is supplied to each heat exchanger, and the feed water sent through the feed water pipe 20 is heated by the amount of heat of the steam. The steam drain supplied to the low-pressure feed water heating device 31 is supplied to the feed water pipe 20 in the middle of the low-pressure feed water heating device 31 and constitutes part of the feed water.

The deaerator 33 heats the stored water by directly supplying the steam extracted from the compartment of the intermediate pressure turbine 17 to the stored water. In this way, the dissolved gas contained in the water is separated and removed by heating the water.
The high-pressure feed water heater 37 is configured by arranging two sets of three heat exchangers connected in series and arranged in parallel. In the heat exchangers connected in series, the steam extracted from the casing of the intermediate pressure turbine 17, the steam extracted from the reheater 15, and the steam extracted from the casing of the high pressure turbine 13, respectively, from the upstream side. Is supplied as a heat source. These steams heat the feed water sent through the feed water pipe 20, lose the amount of heat, and become drain. This drain is supplied to the deaerator 33 and constitutes a part of the water supply.

Oxygen is injected into the feed water pipe 20 in order to form a hematite scale protective film at a position A located downstream of the ground steam condenser 27 and a position B between the deaerator 33 and the feed water pump 35. It is configured to be.
The water supply pipe 20 is provided with a spray line (water supply line) 49 branched at a position D located at the outlet of the economizer 39. The other end of the spray line 49 is connected to the steam pipe 10 at a position F located on the upstream side of the superheater 11. A spray (not shown) is provided at the other end of the spray line 49, and is configured to inject water that has passed through the economizer 39 into superheated steam in a sprayed state. By adjusting the amount of water supplied from the spray, the temperature of the superheated steam supplied to the superheater 11 is adjusted.

The water separated by the brackish water separator 9 is sent to the drain tank 45. In the drain tank 45, the remaining steam is supplied from the upper part to the steam pipe 10 side, and water is supplied from the lower part to the position C of the water supply pipe 20 by the circulation pump 47.
At the position E of the steam pipe 10 which is an inflow portion to the brackish water separator 9, a first reduced or activated hydrogen hydrated boiler in which boiler water that has been reduced or activated hydrogenated is injected into the steam line 10 A water injection line (hereinafter abbreviated as “first injection line”) 51 is connected.
Further, at the position H of the steam pipe 10 on the upstream side of the reheater 15, the second reduced or activated hydrogen water is injected into the steam pipe 10 by supplying boiler water that has been reduced or activated hydrogen water. A boiler water injection line (hereinafter abbreviated as “second injection line”) 53 is connected.

A first oxidation-reduction potentiometer 55 that measures the oxidation-reduction potential of the superheated steam at the position G is provided at a position G of the steam pipe 10 on the downstream side of the superheater 11.
Further, a second redox potential meter 57 for measuring the redox potential of the superheated steam at the position I is provided at the position I of the steam pipe 10 on the downstream side of the reheater 15.
In this embodiment, an oxidation-reduction potentiometer is used to measure the amount of dissolved oxygen in the superheated steam, but this may be a dissolved oxygen meter.

The first injection line 51 will be described with reference to FIG. In addition, although the example which inject | pours the boiler water reduced-reacted or activated hydrogenated with the brackish water separator 9 is given in FIG. 2, the injection | pouring point of the boiler water reduced-reacted or activated hydrogenated is the steam of a boiler. Any system can be used.
The brackish water separator 9 has a hollow substantially cylindrical shape. A steam pipe 10 connected to the superheater 11 is connected to the upper end portion. A pipe connected to the drain tank 45 is provided at the lower end. The steam pipe 10 from the furnace water wall pipe 7 is branched into two, and the inflow portion 12 is attached to the upper outer periphery of the brackish water separator 9 along the tangential direction of the circular cross section.

The first injection line 51 includes a tank 61 for storing boiler water reduced or activated hydrogenated, a pump 63 for supplying boiler water reduced or activated hydrogenated from the tank 61, and reduced hydrated Or the flow control valve 65 which adjusts the supply_amount | feed_rate of the boiler water turned into active hydrogen water is provided. The boiler water that has been reduced or activated hydrogenated and stored in the tank 61 is obtained by reducing or activating the boiler water derived from an arbitrary position of the boiler plant 1. The lead-out position of the boiler water can be, for example, a position L between the dehydrator 39 and the position where oxygen is injected. The derived boiler water is reduced to water by electrolysis by an electrolysis apparatus (not shown), or is activated hydrogenated by addition of hydrogen gas or the like by an addition apparatus (not shown) such as an hydrogen gas, thereby reducing the oxygen partial pressure. Reduced. The reduced oxygen partial pressure is, for example, 4.8 × 10 ⁻¹¹ atm or less.
The flow control valve 65 is configured to be driven by a control device (not shown) based on the measurement result of the first oxidation-reduction potentiometer 55.
The second injection line 53 has the same configuration as the first injection line 51, and the injection amount of boiler water that has been reduced or activated hydrogenated based on the measurement result of the second redox potential meter 57 is the same as that of the first injection line 51. It is configured to be adjusted.
Moreover, the position which inject | pours the boiler water reduced-reacted or activated hydrogenated is not limited to the example of this embodiment, if it is a steam system | strain of a boiler. For example, boiler water that has been reduced or activated hydrogenated to the steam line 10 side of the spray line 49 (position J in FIG. 1) or upstream of the superheater 11 in the steam line 10 (position K in FIG. 1). The injection line may be connected.

The operation of the boiler plant 1 according to the present embodiment described above will be described.
Condensate from the condenser 21 is pressurized and supplied by a condensate booster pump 29 after cations and anions are removed by the condensate demineralizer 25. The condensate is heated by the extraction of the low-pressure turbine 19 in the low-pressure feed water heater 31 and supplied to the deaerator 33.
At this time, since an appropriate amount of oxygen is added at the position A, a hematite scale is formed on the downstream side of the position A, and the water supply pipe 20 can be protected from corrosion.

In the deaerator 33, the condensate is heated by extraction from the compartment of the intermediate pressure turbine 17 and the dissolved gas is removed. Therefore, an appropriate amount of oxygen is added to the water at position B, which is the outlet of the deaerator 33, so that an appropriate amount of oxygen is dissolved in the water supply.
Then, the water is supplied to the high-pressure feed water heater 37 by increasing the pressure by the feed water pump 35. The feed water is heated by the steam extracted in the steam system 3 by the high-pressure feed water heating device 37, then further heated by the economizer 39 and supplied to the furnace water wall pipe 7.
A hematite scale is formed on the downstream side of the position B by an appropriate amount of oxygen added at the position B, and the water supply pipe 20 can be protected from corrosion.

  Saturated steam generated in the furnace water wall pipe 7 is conveyed to the brackish water separator 9 through the steam pipe 10. In the brackish water separator 9, saturated steam flows from the inflow portion 12 of the steam pipe 10 toward the tangential direction of the circular cross section. This inflow creates a swirl flow within the brackish water separator 9. This swirling flow causes water and other high specific gravity to gather at the center and drop downward due to the weight, while steam having a low specific gravity collects on the outer peripheral surface and is sent to the superheater 11 through the steam pipe 10 connected to the upper end. It is done.

The steam from the brackish water separator 9 is superheated by the superheater 11 to become superheated steam. This superheated steam is supplied to the high-pressure turbine 13 and its thermal energy is converted into rotational power. The exhaust from the high pressure turbine 13 is reheated by the reheater 15 and supplied to the intermediate pressure turbine 17 and the low pressure turbine 19. In the intermediate pressure turbine 17 and the low pressure turbine 19, the heat energy of the superheated steam is converted into rotational power.
The rotational power converted in the high-pressure turbine 13, the intermediate-pressure turbine 17 and the low-pressure turbine 19 is used as rotational power for the generator and other auxiliary power.

At this time, since the boiler water reduced or activated hydrogenated is supplied from the first supply line 51 to the inlet 12 of the brackish water separator 9, the boiler water reduced or activated hydrogenated is steam. At the same time, it flows into the brackish water separator 9.
The amount of boiler water supplied into reduced water or activated hydrogen water is increased or decreased according to the deviation between the measured value of the first oxidation-reduction potentiometer 55 and the target value. The target value is, for example, −0.3 to −0.4 V or less at 25 ° C. This is a magnitude corresponding to 7 ppb or less as the amount of dissolved oxygen.

The required amount of boiler water that has flowed into the steam along with the steam is reduced or activated hydrogen water and moves at high speed while repeatedly colliding with the steam on the swirl flow generated inside the brackish water separator 9, so it mixes well with the steam. Is done.
In this way, boiler water that has been reduced or activated hydrogenated is well mixed with steam, and thus can sufficiently react with dissolved oxygen contained in the steam. For this reason, the dissolved oxygen in steam can be reduced efficiently and effectively.

Thus, since the dissolved oxygen amount of the vapor | steam sent to the superheater 11 or later can fully reduce, local corrosions, such as stress corrosion cracking by oxygen in the steam system 3 component apparatus after the superheater 11, can be prevented. This is particularly effective in the high-pressure turbine 13, the intermediate-pressure turbine 17 and the low-pressure turbine 19 that are subjected to excessive stress.
Moreover, since the amount of dissolved oxygen in the steam sent to the superheater 11 and thereafter is considerably small, the scale can be prevented from becoming hematite.
Since hematization of the scale is suppressed, the amount of scale peeling can be reduced. For this reason, it is possible to prevent the peeled scale from accumulating in a thin tube such as a superheater or a reheater and further accumulating and closing the tube. Thereby, for example, it is possible to prevent these blocked thin tubes from being overheated and eventually leading to a blowout accident. Further, it is possible to prevent the peeled scale from damaging the turbine.

  In addition, the amount of boiler water that has been reduced or activated hydrogenated supplied from the first injection line 51 is controlled so that the amount of dissolved oxygen measured at the position G that is the outlet of the superheater 11 becomes a target value. Therefore, the amount of dissolved oxygen in the superheater 11 can be quickly controlled. For this reason, protection of the superheater 11 can be sufficiently performed without delay.

Then, at the position H of the steam pipe 10, the second injection line 53 supplies boiler water that has been reduced or activated hydrogenated into the steam pipe 10, so that the superheated steam flowing into the reheater 15 The amount of dissolved oxygen is further reduced.
At this time, the amount of boiler water that has been reduced or activated hydrogen supplied from the second injection line 53 is increased or decreased in accordance with the deviation between the measured value of the second redox potential meter 57 and the target value. This target value may be the same as or smaller than the target value of the first injection line 51.
As described above, when the amount of dissolved oxygen in the superheated steam flowing into the reheater 15 is further reduced, scale hematization in the reheater 15 is suppressed. Can prevent malfunctions.

  Further, when the superheater tube or the reheater tube is new, scale hematite formation is more likely to occur than when the superheater tube or reheater tube is in operation, but the second injection line 53 is provided. Even in the case of replacement, the reheater 15 can be sufficiently protected.

  The supply amount of the boiler water that has been reduced or activated hydrogenated in the first injection line 51 and the second injection line 53 is the first oxidation-reduction potentiometer 55 and the second oxidation-reduction potentiometer provided on the adjacent downstream sides, respectively. Since it adjusts with the amount of dissolved oxygen measured by 57, only the required quantity of boiler water reduced-reacted or activated hydrogenated can be supplied. For this reason, for example, there is insufficient supply of boiler water that has been reduced or activated hydrogenated, resulting in insufficient suppression of scale hematization, or excess reduced or activated hydrogen water that has been supplied excessively. It is possible to prevent the boiler water from becoming harmful.

  In the present embodiment, the dissolved oxygen amount is measured at each outlet of the superheater 11 and the reheater 15, but is not limited to this. For example, condensate or high pressure before oxygen injection is used. You may measure the amount of dissolved oxygen of the drain of a feed water heater and a low-pressure feed water heater.

It is a block diagram showing the whole boiler plant composition concerning the embodiment of the present invention. It is a fragmentary sectional view showing the brackish water separator of the embodiment of the present invention.

Explanation of symbols

1 boiler plant 9 steam separator 10 steam pipe 11 superheater 15 reheater 39 economizer 49 spray line 51 first injection line 53 second injection line 55 first oxidation-reduction potentiometer 57 second oxidation-reduction potentiometer

Claims (3)

  A steam treatment method for a boiler plant that reduces dissolved oxygen in steam by injecting reduced or active hydrogenated boiler water into an outlet fluid of a boiler that is supplied by injecting oxygen into condensate and / or feed water. A boiler plant comprising a boiler that is supplied with water by injecting oxygen into condensate and / or feed water,
A boiler plant characterized in that an injection line for injecting boiler water reduced or activated hydrogenated is connected to a boiler steam system.   Boiler water is reduced or activated hydrogenated, and this reduced or activated hydrogenated boiler water is injected into the outlet fluid of the boiler that is supplied by injecting oxygen into condensate and / or feedwater. Steam treatment equipment for boiler plants that reduces dissolved oxygen in steam.

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