JPH024352B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to a deaeration technology for removing non-condensable gases such as oxygen dissolved in the water supply in a thermal power plant, and in particular, The present invention relates to a feed water deaeration method and a feed water deaeration device suitable for reducing dissolved oxygen in a short period of time.

[Background of the invention]

Traditionally, thermal power plants have been equipped with deaerators to heat and deaerate feed water supplied to the boiler using turbine extraction air or boiler steam to prevent corrosion of the entire plant and improve thermal efficiency. . For the latest known technology regarding degassing methods and degassing devices, please refer to the US publication ``Theoretical aspects of physical degassing''.
pkysical de−aeration) published by Stoke.

Conventional technology related to deaeration methods and deaeration devices is described in the third section.
The figure will be described next.

The deaeration device is equipped with a deaeration chamber 1 and a water storage tank 12, and the deaeration chamber 1 heats and deaerates the feed water.
Water tank 12 stores degassed feed water.

The supplied water is led to the deaeration chamber 1 through the water supply pipe 6, and is sprayed by the spray valve 8 at the upper part of the deaeration chamber 1 to be atomized. Feed water, which has been atomized and has a rapidly increased surface area, exchanges heat with the steam through direct contact while flowing through the steam atmosphere at high speed, rising to the saturation temperature of the deaerator operating pressure. Diffusion deaeration (first stage deaeration) is performed by heat exchange,
This first stage deaeration removes a considerable amount of non-condensable gas.

Furthermore, water is supplied to the deaeration tray 5 by the distribution tray 4.
It is distributed above and flows down in a meandering manner, and is mixed with the heated steam rising in the tray to perform the second stage of deaeration. The supplied water that has passed through the tray and completed deaeration is transferred to deaeration chamber 1.
Once collected in the lower part, the water flows down the water supply connecting pipe 10 and is stored in the water storage tank 12.

On the other hand, the heated steam flows into the degassing chamber 1 from the steam inlet 9, circulates around the tray chamber and heats the feed water, and then flows into the tray chamber from the steam inflow path at the bottom of the tray chamber.
Rise between trays. The rising steam strips non-condensable gases from the falling feed water. The steam that has risen between the trays passes through the side of the distribution box 3 and enters the spray chamber 2, where it exchanges heat with the sprayed atomized feed water, becomes condensate, and flows down together with the feed water. The non-condensable gas that has not become condensed water is discharged from a vent pipe 7 provided at the seat of the spray valve 8.

When a plant equipped with a boiler equipment is operated regularly, sufficient turbine extraction air or boiler steam can be supplied to the deaerator, so the feed water can be degassed and the dissolved oxygen concentration can be kept below the specified value. There are no particular difficulties in maintaining the temperature.

However, during clean-up operation at plant start-up, a large amount of undegassed make-up water is introduced into the system via the condenser.

The operation of the deaerator and the piping system around it in this case will be explained with reference to FIG.

During clean-up, the heating steam is still before the boiler ignition, so turbine extraction or boiler steam cannot be extracted, and auxiliary steam from other cans or the in-house boiler is introduced into the deaerator through the heating steam pipe 18. 19 is a stop valve.

In addition, regarding the operation of the vent system of the deaerator, the stop valve 15 of the vent pipe 14 is open to enable effective heat exchange between the feed water and the auxiliary steam, but the stop valve 17 of the startup vent pipe 16 is closed. there was.

However, during clean-up operation at the time of plant start-up, there are many cases in which auxiliary steam cannot be sufficiently supplied to the deaerator due to various circumstances (for example, operational problems with the power plant as a whole).

In this case, sufficient heat exchange between the auxiliary steam and the feed water may not take place, or there may be a shortage of auxiliary steam in the deaeration chamber 1, and it will take a long time to reduce the dissolved oxygen concentration of the feed water to the specified value. .

In addition, recently, DSS (Daily Start & Stop) and WSS, which have frequently started and stopped plants as part of intermediate load operation,
(Weekly Start & Stop) plants require a small amount of auxiliary steam to reduce dissolved oxygen in the deaerator at the time of plant start-up, and in a short period of time due to the power plant's need to complete cleanup in a short period of time. be.

As described above, there are the following problems with the conventional technology for deaeration of feed water, and an immediate solution is desired.

(1) Deaeration/cleanup takes a long time. →Large start-up time/Large start-up loss (2) A large amount of auxiliary steam was required, increasing the capacity of the in-house boiler and increasing equipment costs.

[Purpose of the invention]

The present invention has been made in response to the above-mentioned needs, and includes (i) shortening of deaeration and cleanup time at startup, and (ii) saving of auxiliary steam amount and reduction of equipment costs for in-house boilers. We provide a deaeration method and a deaeration device that can improve the reliability of plants by improving the quality of water supply.
The purpose is to contribute to improving durability.

[Summary of the invention]

The basic principle of the method of the present invention created to achieve the above object will be briefly described below.

The main point of the present invention is to focus on the fact that the lower the pressure and the higher the temperature, the lower the oxygen solubility in the feed water, and to effectively heat the feed water sent to the deaerator with auxiliary steam and desorb it. The goal is to create a vacuum inside the deaerator using the air vent system and effectively reduce dissolved oxygen in the water supply.

In order to achieve the above-mentioned goal based on the above-mentioned principle, the method for deaeration of feed water according to the present invention provides a water storage tank below the deaeration chamber, and communicates the deaeration chamber and the water storage tank with a water supply connection pipe. However, the lower end of the water supply connecting pipe shall reach below the water surface in the water storage tank, and between the deaeration chamber and the condenser, (a)
A vent pipe equipped with an orifice and a vent pipe stop valve,
and (b) using a feed water deaerator which is equipped with a starting vent pipe equipped with a starting vent pipe stop valve and connected in parallel, and a heating steam pipe that supplies heated steam to the deaeration chamber. The method for heating feed water for a boiler is characterized in that when starting the boiler, the starting vent pipe stop valve is opened and a portion of the heated steam is introduced into a water storage tank.

In addition, the device of the present invention, which was created so that the above-mentioned method can be easily carried out and fully exhibit its effects, has a water storage tank provided below the deaeration chamber, and a water supply tank that connects the deaeration chamber and the water storage tank. communicate through a connecting pipe,
The lower end of the above water supply connecting pipe shall reach below the water surface in the water storage tank, and between the above degassing chamber and the condenser, (a) a vent pipe equipped with an orifice and a vent pipe stop valve; and (b) a feed water deaeration device in which a starting vent pipe provided with a starting vent pipe stop valve is connected in parallel and a heating steam pipe for supplying heated steam to the deaeration chamber, A steam injection nozzle is provided below the water surface of the deaerator water storage tank, and a pipe line is provided for supplying a portion of the heated steam to the steam injection nozzle.

[Embodiments of the invention]

FIG. 1 shows the steps taken to carry out the deaeration method of the present invention.
An embodiment will be shown in which the feed water deaerator of the present invention is applied and improved to the above-mentioned known feed water deaerator (FIG. 4).

The difference from the known device (FIG. 4) is as follows. A water supply communication pipe 10 connecting a deaeration chamber 1 and a water storage tank 12 is divided above the water surface in the water storage tank 12. In addition, a starting heating steam pipe 20 is branched from the heating steam pipe 18 to the degassing chamber 1, and is connected to the lower part of the water storage tank 12 (below the distribution pipe 13) via the stop valve 21.
A spray nozzle 22 that blows water upward is installed near the bottom of the water storage tank 12.

When implementing the degassing method of the present invention using the apparatus of this embodiment (Fig. 1), when introducing heating steam for startup, the stop valve 15 installed in the vent pipe 14, which is the deaerator vent system, and the It is operated by opening the stop valve 17 installed in the startup vent pipe 16.

Next, the operation and deaeration effect will be explained.

When starting up the plant and introducing heated steam into the deaerator, the stop valve 15 of the vent pipe 14 and the stop valve 17 of the starting vent pipe 16 are kept fully open. The effect of fully opening the stop valve 17 is as follows.

Since the vent pipe 14 is provided with an orifice 14a, the degree of vacuum in the degassing chamber 1 will not reach the vacuum degree of the condenser just by fully opening the stop valve 15, but the starting vent also has a large diameter pipe. By fully opening the stop valve 17 of the pipe 16, the degree of vacuum in the deaeration chamber 1 is made approximately equal to the degree of vacuum in the condenser, making it possible to achieve a vacuum deaeration effect of dissolved oxygen in the feed water and to reduce the amount of heating steam. (This principle will be explained later.)

Heating steam pipe 20 for starting heating steam in the above state
The liquid is introduced from the spray nozzle 22 to the upper distribution pipe 13 side. The blown steam becomes bubbles and reaches the water surface while directly exchanging heat with the water supplied in the water storage tank 12 and increasing the temperature. The pressure on the water surface is a vacuum, and the specific volume of the steam bubbles is significantly increased, and while flying upward at high speed, they ascend the pressure equalization pipe 11 and the water supply pipe 10 and are introduced into the degassing chamber 1. . Here, connect the water supply pipe 10 to the water storage tank 1
The effect of dividing the water storage tank 12 into two parts is that the steam flowing upward on the water surface of the water storage tank 12 can be uniformly introduced into the deaeration chamber 1, and the pressure difference between the deaeration chamber 1 and the water storage tank 12 causes the steam inside the water storage tank 12 to be uniformly introduced. This makes it possible to prevent the water supply from flowing back through the water supply connection pipe 10 to the deaeration chamber 1 side (the above-mentioned backflow prevention is effective even during normal operation, and also during FCB or when the load is reduced). Similar effects can be obtained in

The steam uniformly introduced into the deaeration chamber 1 exchanges heat with the atomized feed water flowing down while ascending the deaeration tray 5 and the distribution tray 4, thereby precipitating non-condensable gases in the feed water. It degasses, becomes condensate, and flows down with the water supply. The non-condensable gas that has not become condensed water is discharged to the condenser through the vent pipe 14 and the startup vent pipe 16.

Next, an example of the relationship between the amount of dissolved oxygen in the water supply and the degree of vacuum and temperature, which is the basic principle of the present invention, will be explained with reference to FIG.

From this figure, it can be seen that the amount of dissolved oxygen in the water supply decreases as the degree of vacuum and temperature increase.

For example, in the conventional vacuum deaeration state shown in FIG. 4, the stop valve 15 of the deaerator vent pipe 14 is open and the stop valve 17 of the startup vent pipe 16 is closed, so that becomes higher than the condenser internal pressure due to orifice action. In this state, the amount of dissolved oxygen is approximately 10 ppm at a feed water temperature of 15°C and atmospheric pressure as shown in Figure 2.
From (point), when the deaerator internal pressure is 700mmHgVac,
At this stage, the amount of dissolved oxygen is
It is over 500ppm. Furthermore, by introducing heated steam to the deaerator, the temperature of the feed water was raised from 15℃ to 40℃ (ΔT=
(25℃), the amount of dissolved oxygen reaches the specified value of 50ppb or less at startup.

However, in the vacuum deaeration state shown in FIG. 1 according to the present invention, the deaerator internal pressure is bypassed by the orifice by opening the stop valve 7 of the startup vent pipe 16, unlike the prior art, and is therefore lowered. It becomes approximately equal to the internal pressure of the condenser, the specific volume increases, and the degassing efficiency also improves. In this state, the amount of dissolved oxygen becomes a point from the point in Figure 2 when the feed water temperature is 15°C and the deaerator internal pressure is 730 mmHgVac, and the amount of dissolved oxygen is reduced to about 220 ppb at this stage. From this stage point, the feed water is further heated by heated steam to reach a specified dissolved oxygen concentration of 50 ppb.
The temperature increase required to achieve this is approximately 11℃ from point to point, i.e. from the supply water temperature of 15℃ to 26℃.
That's enough.

Furthermore, in cold regions, when the seawater temperature is low and there is no turbine heat load, the deaerator internal pressure drops further to about 740 mmHgVac, so the vacuum rises to about 90 ppb (points), and the deaerator heated steam is introduced. The temperature rise required to achieve the specified dissolved oxygen content of 50 ppb is from point to point, i.e. when the feed water temperature is 15°C.
By increasing the temperature by approximately 18°C (ΔT≒3°C), the specified dissolved oxygen concentration can be maintained, and the amount of auxiliary steam can be further reduced.

Here, the required auxiliary steam amount G ₅ (T/H) is as follows.
It is determined by equation (1).

G _S = G _B (H ₂ - H ₃ ) / H ₁ - H ... (1) However, G = Water supply amount (Set as 500 T/H.) H ₁ = Auxiliary steam enthalpy (Set as 700 Kcal/H.) H ₂ = Deaerator outlet feed water enthalpy H ₃ = Deaerator inlet feed water enthalpy Next, regarding the boiler equipment in a 60 MW class power plant, the amount of auxiliary steam required to increase the temperature from point to point in Figure 2 above ( Conventional example)
is, G _S =500(40-15)/700-15≒18T/H Also, when pressurized degassing in the conventional example, assume that the pressure inside the deaerator is maintained at 1.5 ata and the water storage temperature is maintained at 111℃. , G _S =500 (111-15)/700-15≒70T/H Next, the amount of auxiliary steam required to raise the temperature from point to point in the embodiment of the present invention is G _S =500 (26-15 )/700-15≒8T/H Similarly, regarding the temperature rise from point to point in the embodiment of the present invention (cold region), G _S =500(18-15)/700-15≒2T/H or more. As shown, the amount of auxiliary steam required for degassing feed water was approximately 18 T/H for conventional vacuum degassing, and approximately 70 T/H for conventional pressurized degassing. In some cases, the amount of auxiliary steam can be significantly reduced to about 8T/H, and even to about 2T/H in plants in cold regions.

In this way, in this embodiment, (a) During the deaeration operation using the deaerator at startup, it is possible to increase the vacuum in the deaerator, which reduces the amount of auxiliary steam by 50% or more compared to the conventional required amount of auxiliary steam. This makes it possible to save energy and reduce the capacity of the boiler in the plant. Conventionally, approximately 18 T/H of auxiliary steam was required during vacuum degassing in a 600 MW class plant, but this can be reduced to 2 to 8 T/H with the present invention.

(b) According to the present invention, efficient steam supply operation is possible, so the clean-up time of the preboiler, which conventionally required about 10 days in the early stages, has been reduced to 3 to 4 days. This made it possible to reduce startup time and startup loss.

(c) Regarding items 1 and 2 above, since the amount of dissolved oxygen in the water supply could be efficiently reduced, the reliability of the plant could be ensured by improving the water quality.

This had a practical effect.

FIG. 5 shows a partial application of the degassing method according to the invention. This application example was carried out using the conventional deaerator shown in FIG. 4, and the stop valve 17 of the starting vent pipe 16 was opened during the starting operation. Thereby, the pressure inside the deaerator 1 is reduced and the specific volume of steam is increased, thereby improving steam efficiency and reducing the required amount of auxiliary steam.

FIG. 6 shows a different embodiment of the apparatus from FIG.

The principle is the same as the embodiment shown in FIG. 1, but
No opening is provided in the water supply connecting pipe 10'. By opening the stop valve 17 of the startup vent pipe 16 and introducing auxiliary steam into the lower part of the water storage tank 12, the temperature of the stored water can be effectively raised, and the deaeration effect can shorten the deaeration time and reduce the amount of auxiliary steam. can be achieved.

FIG. 7 shows a further different embodiment of the apparatus. This example differs from FIG. 1 in that in addition to the steam nozzle 22 below the water surface, a steam nozzle 22' above the water surface is also provided. This configuration has the effect of easily responding to fluctuations in the water level within the water storage tank 12.

〔Effect of the invention〕

As described above, according to the deaeration method of the present invention, (i) reduction of deaeration and cleanup time at start-up, and (ii) saving of auxiliary steam amount and reduction of facility boiler cost. This greatly contributes to improving the reliability and durability of the plant by improving the quality of the water supply.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of one embodiment of the present invention, Fig. 2 is a chart showing the relationship between the amount of dissolved oxygen and the degree of vacuum, and temperature, and Fig. 3 is a diagram showing the structure of the deaerator and the degassing action. FIG. 4 is an explanatory diagram of a conventional degassing state at startup, and FIG. 5 is an explanatory diagram of an application example of the present invention. FIGS. 6 and 7 are explanatory diagrams of embodiments different from those described above, respectively. 1... Deaeration chamber, 2... Spray room, 3... Distribution box, 4... Distribution tray, 5... Deaeration tray, 6...
... Water supply inlet pipe, 7 ... Vent pipe, 8 ... Spray valve, 9 ... Steam inlet, 10, 10' ... Water supply connection pipe, 11 ... Pressure equalization connection pipe, 12 ... Water storage tank, 13 ... Distribution pipe, 14...Vent pipe, 14a
...Orifice, 15...Vent pipe stop valve, 16...
...starting vent pipe, 17...starting vent pipe stop valve, 18...heating steam pipe, 19...stop valve, 20...
...Heating steam pipe for starting, 21, 21'...Stop valve, 2
2, 22'... Steam nozzle.

Claims (1)

[Claims] 1. A water storage tank is provided below the deaeration chamber, and
The deaeration chamber and the water storage tank are connected by a water supply communication pipe, the lower end of the water supply communication pipe reaching below the water surface in the water storage tank, and the connection between the deaeration chamber and the condenser. (a) A vent pipe equipped with an orifice and a vent pipe stop valve, and (b) a starting vent pipe equipped with a starting vent pipe stop valve are connected in parallel, and the degassing chamber is connected in parallel. In a method of heating feed water for a boiler using a feed water deaerator equipped with a heating steam pipe for supplying heating steam, when starting the boiler, the starting vent stop valve is opened, and the starting vent pipe stop valve is opened. A water supply degassing method characterized by introducing a portion of heated steam into a water storage tank. 2. A water storage tank is provided below the deaeration chamber, and the deaeration chamber and the water storage tank are connected through a water supply pipe,
The lower end of the above water supply connecting pipe shall reach below the water surface in the water storage tank, and between the above degassing chamber and the condenser, (a) a vent pipe equipped with an orifice and a vent pipe stop valve; , and (b) a feed water deaerator in which a starting vent pipe provided with a starting vent pipe stop valve is connected in parallel and a heating steam pipe for supplying heated steam to the deaeration chamber. A water supply deaerator, characterized in that a steam injection nozzle is provided below the water surface of the deaerator water storage tank, and a pipe line is provided for supplying a portion of the heated steam to the steam injection nozzle. 3. The water supply deaerator according to claim 2, wherein the water supply communication pipe is provided with an opening that communicates with a space above the water surface in the water storage tank.