JPH04297704A - Controlling method for concentration of deoxidizer of boiler water - Google Patents

Abstract

PURPOSE:To provide a method, in which the concentration of a deoxidizer in boiler water is controlled within a proper value without the reconstruction of an existing facility. CONSTITUTION:In a boiler, in which water supply from a feed water tank supplied with make-up water and return water from the boiler and the injection of a deoxidizer are conducted, it is determined that there is excellent correlation in the relationship (Fig. 8) of feed-water temperature and the dissolved-oxygen concentration of boiler water from the relationship of the feed-water temperature and dissolved-oxygen concentration in supply water and the relationship of dissolved-oxygen concentration in supply water and the dissolved-oxygen concentration (a calculated value) of boiler water. The preset quantity of the deoxidizer injected is obtained on the basis of the feed-water temperature and a feed-water flow rate to the boiler, the deoxideizer concentration of boiler water, in which the deoxidizer is injected to the boiler in the quantity of injection, is controlled.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to boiler canned water, and more particularly to a method for adjusting the concentration of an oxygen scavenger added to boiler canned water.

0002

2. Description of the Related Art Steam generated in an in-house boiler of a power plant is sometimes used for air conditioning inside a nuclear power building, treating waste liquid, and washing and drying work clothes inside a nuclear power building. Therefore, the station boiler steam circulates in a closed loop. When there is a load change, pure water is replenished into this closed loop. As described above, high quality water is required for the in-house boilers of power plants, but if there is corrosion in the boiler can due to dissolved oxygen in the water, the closed loop will be broken. Therefore, in order to prevent corrosion inside the can of the station boiler, an oxygen scavenger such as hydrazine is continuously injected, and the can water is deoxidized by the reaction shown in the following reaction formula (A).

[0003] N2H4 + O2 → N2
+ 2H2O (A)

000
4] The target value (0.05
~1.0 ppm), and it is necessary to set the oxygen scavenger concentration in canned water within this target value.

[0005]

However, as shown in FIG. 18, the oxygen scavenger concentration in the boiler can water tended to deviate from the target value at the beginning of boiler operation and during fluctuations in the feed water flow rate. Furthermore, despite changing the injection volume of the oxygen scavenger injection pump, the target value was often not met. The following factors are thought to be responsible for these factors.

Lower limit deviation: When pure water is replenished into the water supply tank, a high concentration (approximately 8 ppm) of dissolved oxygen is brought into the can water, and the amount of hydrazine consumed in the can water becomes large, or If the flow rate increases and more oxygen is brought in.

[0007] Upper limit value deviation: When a large amount of water returns to the water supply tank and almost no pure water is replenished, or when the water supply flow rate decreases.

[0008] Regarding these problems, inspectors from the Ministry of International Trade and Industry pointed out that improvements should be made, but since it is not possible to directly measure dissolved oxygen in canned water, this has been a matter of concern for many years.

Originally, in order to control the concentration of oxygen scavenger in canned water, it would be sufficient to continuously measure the dissolved oxygen concentration or oxygen scavenger concentration in canned water and automatically control the operation of the chemical dosing pump. However, in the current operation of in-house boilers, it is impossible to continuously measure dissolved oxygen concentration or oxygen scavenger concentration because the crud concentration in canned water is high.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for controlling the oxygen scavenger concentration in boiler can water to within an appropriate value without modifying existing equipment.

[0011]

[Means for Solving the Problems] The above objects of the present invention are achieved by the following configuration. In other words, in a boiler where makeup water and return water from the boiler are supplied from a water supply tank and oxygen scavenger is injected into the boiler can water, the deoxidation rate is set in advance based on the water supply temperature and water supply flow rate to the boiler. This is a method for controlling the concentration of an oxygen scavenger in boiler can water, in which an amount of oxygen to be injected is determined and the amount of oxygen scavenger is injected into the can water.

0012

[Operation] The inventor thought that the flow rate of water supplied to the boiler can water, the amount of make-up water to the water supply tank, etc. affected the concentration change of the oxygen absorber, but just in case We checked the injection (hereinafter sometimes referred to as chemical injection) system, oxygen scavenger sampling method, and analysis method, and found that:
There was no change in the oxygen scavenger concentration in the chemical injection tank over time (see Figure 2), and the chemical injection pump stroke was stable. Regarding the sampling of oxygen scavengers, no difference in analytical values was observed depending on the blowing time at the time of sampling (Figure 3). Therefore,
Next, when we investigated the relationship between the temperature of the feed water supplied to the boiler can water and the dissolved oxygen concentration in the feed water, we found that the temperature change in the feed water depends on the amount of pure water supplied (not shown). It was also found that there is a good correlation between the temperature of the feed water and the dissolved oxygen concentration in the feed water (see Figure 4).

If the dissolved oxygen concentration in the feed water is constant and the feed water flow rate is also constant, if the oxygen scavenger is continuously injected in an amount greater than the amount required for the reaction shown by the reaction formula (A),
The oxygen scavenger concentration in canned water should increase linearly. However, as shown in Figure 5, after the start of chemical injection, the calculated value of the oxygen scavenger concentration in the can water (calculated from the amount of oxygen scavenger injected from the chemical injection tank) and the actual value (individually after eliminating the influence of cladding) There was a large difference in the results. As shown in FIG. 5, even if the oxygen absorber is injected into the can water at a constant flow rate per unit time, the actual measured value becomes far away from the calculated value as time passes, and the concentration of the oxygen absorber in the can water is It turns out that there is an equilibrium state.

The reason for the phenomenon shown in FIG. 5 is thought to be that the oxygen scavenger carried over with the water vapor. In order to find an appropriate carryover rate, actual measurements were repeated, but the measured values varied so much that it was not possible to obtain a constant value.

Next, after the chemical dosing pump was stopped, we measured the change over time in the concentration of the oxygen absorber in the can water while water supply continued. There was a difference between the measured concentration value and the calculated value (see Figure 6).
.

[0016] The concentration of the oxygen scavenger in the can water was calculated according to the following formula. Concentration of oxygen scavenger in can water = [{Amount of oxygen scavenger in can water before stopping the chemical dosing pump - Amount of oxygen scavenger consumed by dissolved oxygen in feed water}/Amount of can water]

[0017] Here, the dissolved oxygen in the water supply is 0.5 ppm.
It was calculated as When the amount of dissolved oxygen brought into the can water (=oxygen absorber consumption) is calculated based on the measured value of the concentration of the oxygen absorber in the can water, the actual value of the dissolved oxygen concentration in the feed water is 0.5 ppm. When it was 0.2pp in canned water
It was assumed that it would be about m. Previously, it was thought that the dissolved oxygen concentration in the feed water and the dissolved oxygen concentration brought into the canned water were the same, but since it was discovered that there was a gap between the two, the next step was to determine the dissolved oxygen concentration in the canned water. investigated.

[0018] Therefore, by varying the dissolved oxygen concentration in the feed water and supplying the feed water with each dissolved oxygen concentration to the in-house boiler, the concentration of dissolved oxygen brought into the canned water at that time is estimated, as shown in Figure 7. A good correlation was obtained. Naturally, the chemical injection pump is stopped at this time.

Furthermore, if we plot the relationship between the feed water temperature and the dissolved oxygen concentration brought into the canned water from the relationship shown in FIG. 7 and the relationship between the feed water temperature and the dissolved oxygen concentration in the feed water shown in FIG. , as shown in FIG. 8, a good correlation was obtained. Note that the relationships among the values shown in FIGS. 4, 7, and 8 are not actual measured values for each boiler, but conceptually represent typical examples thereof.

[0020] In this way, the amount of dissolved oxygen brought into the canned water can be predicted based on the amount of water supplied and the temperature of the supplied water, so naturally the amount of oxygen scavenger that needs to be replenished can also be determined.

Based on the above study results, a formula for calculating the oxygen scavenger concentration in canned water was created as follows. Note that hydrazine is used here as an oxygen scavenger, and hydrazine reacts with equimolar amounts of oxygen, and since 1 mole of both compounds consists of the same number of grams, the amount of oxygen scavenger that reacts with dissolved oxygen is equal to the amount of dissolved oxygen. It is assumed to be equal to the amount of oxygen.

First, the carryover rate of the oxygen scavenger is determined. The carryover amount is the following formula (1) x=k1・W・C

(1) x: Carryover amount (grams/hour) k1: Carryover rate W: Water supply flow rate (tons/hour) C: Oxygen absorber concentration in canned water (ppm = grams/ton)
As shown in , it is considered to be proportional to the oxygen absorber concentration in the can and the amount of water vapor generated per unit time (=water supply flow rate).

[0023] Therefore, the carryover rate k1 is calculated by the following formula (
2). k1=x/(W・C)

(2)

By the way, the amount of dissolved oxygen brought into the boiler can water is subtracted from the number of moles of the oxygen absorber injected into the boiler can water, and the result is the surplus amount of the oxygen absorber. Because, from reaction formula (A), 1 mol (32 g) of dissolved oxygen
On the other hand, if 1 mole (32 g) of hydrazine is consumed, the same amount of hydrazine as an oxygen scavenger is consumed as the amount of oxygen brought into the can water. Therefore, if the surplus amount of oxygen absorber in the can water per unit time and the carryover amount per unit time are equal, the amount of oxygen absorber in the can water should be a constant value.

Therefore, when the oxygen absorber concentration in the can water becomes a constant value, the surplus amount of oxygen absorber per unit time =
The carryover rate can be determined as the carryover amount. Once the carryover rate is determined, the following formula (
3) dC/dt=(A-x)/G=(A-k1・W・C
)/G (3)x: Carryover amount (grams/hour) C: Oxygen absorber concentration in canned water (pp
m) k1: Carryover rate W: Water supply flow rate (tons/hour) A: Surplus amount of oxygen scavenger (grams/hour) G: Canned water amount (
t: elapsed time (hours) The oxygen scavenger concentration in the can water can be determined.

Solving this, the following equation (4) C={
C0-(A/k1・W)}EXP{(-k1・W/G)
・t} +A/k1・W

(4)

[0027] Here, A is expressed by the following equation (5). A = (amount of oxygen scavenger injected) - (amount of dissolved oxygen brought into canned water) (5)

[0028]The amount of oxygen scavenger injected is expressed by the formula (6): Amount of oxygen scavenger injected=k2cX×
10-3 (grams/hour) (6)
X: Chemical injection pump stroke (mm) k2: Conversion coefficient between chemical injection pump stroke and chemical injection amount (
1/hour・mm) c: The amount of dissolved oxygen brought into the canned water is determined from the oxygen scavenger concentration (ppm) in the chemical dosing tank, and is calculated from the relationship shown in Figure 8.

Equation (7) Amount of dissolved oxygen brought into canned water = (a-bT)
×W (7) T: Water supply temperature (°C) a: Constant (-) b: Constant (1/°C) are obtained.

Therefore, equation (5) can be expressed as the following equation (8). A=k2cX×10-3-(a-bT)W
(8) Here, the target oxygen scavenger concentration CT, which is the value after the oxygen scavenger concentration reaches equilibrium in the can water, is equal to the final term of equation (4), and (
Substituting equation (8) into equation (4), we get

The chemical injection pump stroke X is expressed by the following equation (9): X=W{k1CT
+(a-bT)}×103/k2c
It is obtained by (9). That is, once the target oxygen scavenger concentration is determined, the chemical injection pump stroke X can be determined from the water supply flow rate W and the water supply temperature T to the canned water.

[0032]

[Example] An example of the present invention will be explained. FIG. 1 shows a partial outline of the water quality test for the in-house boiler in this example. Water is supplied to the station boiler 1 from a water supply tank 2, and at the same time, a hydrazine aqueous solution is injected from a chemical injection tank 3. The water vapor used in the load 5 is collected as condensate in the water supply tank 2. A water supply pipe 6 from the water supply tank 2 to the in-house boiler 1 is provided with a thermal element 7 for measuring the temperature of the supply water. Further, a dissolved oxygen meter 9 in the water supply is connected to the branch pipe 6a of the water supply pipe 6. Before measuring the dissolved oxygen concentration, a cooler 10 is provided to keep the temperature of the water supply constant. Further, the sampling line 11 samples can water for measuring the hydrazine concentration in the can water.

In this example, two in-house boilers, No. A and No. B, were studied. For Units A and B, first find the relationship between the feed water temperature and dissolved oxygen concentration shown in Figures 9 and 10, respectively, and then find the correlation between the amount of water supplied and the dissolved oxygen concentration (calculated value) brought into the canned water. As a result, a good correlation was obtained as shown in FIGS. 11 and 12, respectively. Further, from the relationships shown in FIGS. 11 and 12 and the relationships shown in FIGS. 9 and 10, the relationship between the water supply temperature and the dissolved oxygen concentration brought into the can water is plotted, and the results are shown in FIGS. 13 and 14, respectively.

[0034] Furthermore, the carryover rate was determined as the excess amount of oxygen absorber per unit time = carryover amount when the oxygen absorber concentration in the can water became a constant value. A
As shown in Figures 15 and 16 for Unit No. 1 and Unit B, respectively, the carryover rates were approximately constant regardless of the water supply flow rate. For Unit A, k1 was conservatively set to 0.3 based on Figure 15. Similarly, k1 was set to 0.4 for the B machine based on FIG. 16.

Next, for Unit A, a formula for calculating the concentration of oxygen scavenger in canned water was created and actually verified. First, when the amount of oxygen scavenger to be injected is calculated based on the eigenvalues of k2=0.3 and c=4600 (ppm) in machine A, equation (6) becomes as follows.

Amount of oxygen scavenger injected=X×0.3 (1/h・mm)×4
600 (ppm) x 10-3
=1.38X (g/h)

Further, from FIG. 13, the amount of dissolved oxygen brought into the canned water is as follows. Amount of dissolved oxygen brought into canned water = (1.89-0.
017T)×W

Therefore, equation (8) becomes as follows, A=1.38X-(1.89-0.01
7T) W (g/h)

Equation (4), which is a calculation formula for the oxygen scavenger concentration in can water, is given as follows. C=[C0-{1.38X-(1.89-0.017T
)W}/0.3・W]×EXP(-k・W/4)t+{
1.38X-(1.89-0.017T)W}/0.3
・W Note that G = 4 tons here.

FIG. 17 shows a comparison between the calculated value and the measured value of the oxygen scavenger concentration when the pump stroke was changed using this formula. The two agreed well.

[0041] Furthermore, the target oxygen scavenger concentration CT (ppm) in the can water after the oxygen scavenger concentration reaches equilibrium is determined by the last term of the above equation. The chemical injection pump stroke X for Unit A is: X={CT-(0.17T-18.9)/3}×W
/4.6.

[0042] Also, when calculating machine B as described above, X={CT-(0.42T-42.3)/4}×W
/0.62.

[0043] In this way, the chemical injection pump stroke The amount of oxygen agent injected can be kept within an allowable range.

However, in the on-site settings, a certain amount of leeway is required to reduce the burden on the workers. Therefore, a table may be created that defines the lower and upper limits of the set values. Alternatively, a method may be adopted in which the chemical injection pump stroke X is calculated on computer software and the motor of the chemical injection pump is driven and controlled.

[0045]

According to the present invention, the oxygen scavenger concentration in boiler can water can be controlled within an allowable range using existing equipment and without installing any special new equipment.

[Brief explanation of drawings]

FIG. 1 is a partial schematic diagram of a water quality test of an in-house boiler used in an example of the present invention.

FIG. 2 is a diagram showing changes over time in the oxygen scavenger concentration in the chemical injection tank.

FIG. 3 is a diagram showing changes in oxygen scavenger sampling depending on blowing time.

FIG. 4 is a diagram conceptually illustrating the relationship between the water supply temperature of the station boiler and the dissolved oxygen concentration in the water supply.

FIG. 5 is a diagram showing changes over time in calculated values and actual measured values of the oxygen scavenger concentration supplied to canned water.

FIG. 6 is a diagram showing the change over time in the oxygen scavenger concentration in the can water after the chemical injection pump is stopped.

FIG. 7 is a diagram conceptually showing the relationship between the dissolved oxygen concentration in the water supply and the dissolved oxygen concentration brought into the canned water.

FIG. 8 is a diagram conceptually showing the relationship between the water supply temperature and the dissolved oxygen concentration brought into canned water.

FIG. 9 is a diagram showing the relationship between the feed water temperature of Unit A and the dissolved oxygen concentration in the feed water.

FIG. 10 is a diagram showing the relationship between the feed water temperature of Unit B and the dissolved oxygen concentration in the feed water.

FIG. 11 is a diagram showing the relationship between the dissolved oxygen concentration in the feed water of Unit A and the dissolved oxygen concentration brought into canned water.

FIG. 12 is a diagram showing the relationship between the dissolved oxygen concentration in the feed water of Unit B and the dissolved oxygen concentration brought into canned water.

FIG. 13 is a diagram showing the relationship between the water supply temperature of Unit A and the dissolved oxygen concentration brought into canned water.

FIG. 14 is a diagram showing the relationship between the feed water temperature of Unit B and the dissolved oxygen concentration in canned water.

FIG. 15 is a diagram showing the relationship between the water supply flow rate and the carryover rate of the oxygen scavenger for Unit A.

FIG. 16 is a diagram showing the relationship between the water supply flow rate and the oxygen scavenger carryover rate of the B machine.

FIG. 17 is a diagram showing changes in oxygen scavenger concentration over time due to changes in chemical injection pump stroke.

FIG. 18 is a diagram showing a conventional control state of oxygen scavenger concentration in can water.

[Explanation of symbols]

1　In-house boiler 2 Water tank 3. Chemical dosing tank 5 Load 7 Thermometer 9 Dissolved oxygen meter

Claims (1)

[Claims] [Claim 1] In a boiler in which water is supplied from a water supply tank to which make-up water and return water from the boiler are supplied and an oxygen absorber is injected into the boiler can water, the temperature and flow rate of the water supplied to the boiler are preset. A method for controlling the concentration of an oxygen scavenger in boiler can water, the method comprising: determining the amount of oxygen scavenger injected into the boiler can water, and injecting the amount of oxygen scavenger into the can water.