JP2672729B2 - Water quality adjustment device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water quality adjusting device for adjusting the water quality of condensate and feed water of a power plant or the like.

[0002]

2. Description of the Related Art Generally, in a system such as a power plant,
It is necessary to reduce corrosion in the system as much as possible and prevent scale from adhering to the boiler water pipe, steam pipe, and feed water pump suction strainer. For this, condensate, water supply,
Adjusts and treats the quality of boiler water and steam. In this case, if the boiler type is a once-through type, volatile substance treatment (hereinafter referred to as "AVT method") is performed in the condensate and water supply systems. In this treatment, volatile chemicals such as ammonia (NH ₃ ) and hydrazine (N ₂ H ₄ ) are injected to obtain a PH value of 9.
It is controlled so as to be 0 to 9.5 and deoxidized.

However, in this AVT method, in order to obtain a higher anticorrosion effect, a high ammonia concentration, for example, P
An H value of 9.4 or more is required. Therefore, according to the AVT method, a so-called ammonia attack due to damage due to concentrated ammonia occurs in an ammonia concentrating section in a plant, for example, an air cooling section of a condenser.

Therefore, the AVT method using high-concentration ammonia cannot contribute to anticorrosion measures. As a result, iron is eluted from the carbon steel in the plant into the condensate / water supply system by hydrazine, which is a reducing agent, and adheres to boiler water pipes, steam pipes, suction strainers of water supply pumps, etc., and the thickness increases over time. This must be removed at an appropriate time, which is a major obstacle to the plant operation plan. If this is not removed, there is a risk of overload operation of the water supply pump and cracks in the boiler tube.

By the way, in order to improve the above-mentioned drawbacks of the conventional AVT method, in recent years, ammonia N has been added to the condensate and water supply systems.
Complex neutral water treatment by injecting H ₃ oxygen O ₂ (hereinafter “CWT
Law ”) is being implemented in stages.

According to this CWT method, the inside of the system is changed from a conventional strong alkali to a weak alkali, and oxygen is injected to attach and bring in iron oxide to the boiler water pipe, steam pipe and feed water pump suction strainer. Can be greatly reduced.

FIG. 6 shows a general system diagram of the processing by the above CWT method.

The turbine exhaust and the heater drain (both not shown) collected in the condenser 1 are heat-exchanged with circulating water having seawater as cooling water to be condensed. This condensate is sent to the deaerator 5 through the low-pressure feed water heater 4 by the condensate pump 2 and the condensate booster pump 3.

A condensate demineralizer 6 (hereinafter referred to as "condemi") is installed as a water treatment device on the outlet side of the condensate pump 2 to suspend iron oxide and the like in the condensate. Recycle the system by removing solids and dissolved solids such as chloride ions.

The condensate sent to the deaerator 5 is sent to a water supply pump 7 together with a high-pressure heater drain (not shown), and further passes through a high-pressure feed water heater 8 and a economizer 9 to a boiler 1
Water is sent to 0. In addition, 5a shows a deaeration chamber and 5b shows a deaerator tank, respectively.

On the other hand, the water quality adjusting device by oxygen injection is installed in each of the condensate system and the water supply system. In the condensate system, oxygen is injected into a point a in the figure on the outlet side of the condensate demineralizer 6, and the injection amount of oxygen is controlled. In the water supply system, oxygen is injected into the outlet b of the deaerator 5 at a point b in the figure, and the injection amount of oxygen is controlled.

Specifically, in the condensate system, as shown in FIG. 7, first, the function calculator 13 of the oxygen injection calculator 12 is used to restore the signal from the flow rate signal from the condensate flow rate detector 11 at the inlet of the deaerator 5. Calculate the water-based oxygen injection target value. Further, as a correction calculation, the oxygen concentration signal from the oxygen concentration detector 14 at the inlet of the economizer 9 is subjected to the addition / subtraction calculation by the addition / subtraction calculator 15, and the value is finally set as the target value of the oxygen injection amount.

The target value of the injection amount is compared with the signal of the oxygen injection amount detector 16 on the condensate side which detects the amount of oxygen injected from the outlet side of the condensate desalination device 6 by the comparison calculator 17, The deviation value between the two is obtained by. And this deviation value is P
The I calculator 18 calculates proportional and integral operations, and based on this calculation signal, the injection valve 19 is controlled to open and close to control the oxygen injection amount of the condensate system.

In the water supply system, as shown in FIG. 7, the target oxygen calculator 21 calculates the target value of oxygen injection in the water supply system from the flow rate signal from the water supply flow rate detector 20 at the inlet of the economizer 9, and further, as a correction calculation, Oxygen concentration detector 1 at the inlet of the economizer 9
The oxygen concentration signal according to No. 4 is added / subtracted by the addition / subtraction calculator 22 and this value is set as the target value of the injection amount.

This target value is calculated by comparing the signal of the oxygen injection amount detector 23 on the water supply side for detecting the amount of oxygen injected from the outlet side of the deaerator 5 with the comparison calculator 24 to obtain the deviation value.
This deviation value is calculated by the PI calculator 25 for proportional and integral operations, and the oxygen injection valve 26 is opened / closed based on this operation signal to control the oxygen injection amount of the water supply system. FIG.
Addition / subtraction calculator 15, addition / subtraction calculator 22, comparison calculator 1 shown in FIG.
7. In each of the comparison calculator 24, the addition / subtraction code is omitted in the drawing.

Here, the operation of the deaerator 5 will be described with reference to FIG.

The degassing chamber 5a heats and degass the condensed water (supply water). Further, the deaerator tank 5b stores condensate water (water supply). The heated steam is introduced from the deaeration chamber side portion 5c, flows to the lower portion, and rises inside the deaeration tray 5d. Condensed water (supply water) is guided to the degassing chamber 5a by the water supply pipe 5e, and is sprayed by the spray valve 5f above the degassing chamber 5a to be atomized.

Condensed water (feed water) which has been atomized and whose surface area has rapidly increased undergoes heat exchange by direct contact in steam, and its temperature rises to a saturation temperature corresponding to the operating pressure of the deaerator 5. Due to this rapid heat exchange, diffusion deaeration is performed, and most deaeration during condensate (water supply) is achieved.

Further, the condensate water (supply water) is distributed on the degassing tray 5d by the distribution tray 5g, and is agitated with the heated steam rising in the tray by meandering to degas the second stage. The non-condensed gas released by the condensed water (water supply) in the spray chamber 5h is continuously vented from the vent pipe 5j above the degassing chamber 5a.

Reference numeral 5k denotes a high-pressure feed water heater, 5i denotes feed water injected from the spray valve 5f, and
The solid arrow lines in the figure show the flow of steam, and the broken arrow lines show the direction of water flow.

[0021]

However, the above-mentioned water quality control device by the CWT method has the following problems.

According to the above-mentioned water quality adjustment by the CWT method, when the plant load rises, the released oxygen is accumulated and accumulated in the upper part of the deaerator 5, and the solubility in the feed water decreases as the temperature of the inflowing condensate rises. There is a problem of doing.

That is, the condensate containing oxygen comes into contact with the heated steam and releases oxygen while falling in the distribution tray 5g and the deaeration tray 5d in the deaeration chamber 5a, and the condensate is a deaerator. Tank 5
It is accumulated in b and released. In this way, oxygen accumulates / accumulates in the degassing chamber, and part of it dissolves into the condensate water (feed water) again in the degassing tray portion 5d. As shown in the example of FIG. 9, the oxygen concentration D is at time t0. From time t1 to t1, equilibrium is maintained when the plant load P is constant.

After that, from time t1 when the plant load P rises, the released oxygen is released from the deaeration chamber 5a as the pressure inside the vessel rises.
Is pushed up to the upper part of and is accumulated in the upper part of the deaeration chamber 5a. As a result, recondensation (water supply) is performed in the deaeration tray section 5d
Will not be melted in.

At this time, the solubility of oxygen is greatly influenced by the temperature, so that the solubility decreases greatly as the temperature rises, and the oxygen concentration D also stabilizes at time t2 when the plant load P becomes constant. This is because the oxygen released when the plant load rises is accumulated in the upper part of the deaerator 5 and the inflow condensate temperature also gradually rises, so that the deaerator 5 is in a new equilibrium state in terms of heat balance (dewatering of the water storage section). This is because the oxygen concentration in the condensate (supply water) becomes a low value until the condensate flowing into the carton tank 5b reaches the saturation temperature of the load).

As described above, the oxygen concentration in the condensate water (supply water) greatly decreases when the load on the plant increases, and when it is long, the oxygen concentration is 1
Continue for ~ 2 hours. This means that compared to the conventional AVT method, the CWT method lowers the PH value of the water supply system, so that the anticorrosion effect of the condensate / water supply system decreases, and the elution of iron increases. As a result, the effect of the CWT method is reduced.

Therefore, an object of the present invention is to provide a water quality adjusting device for properly adjusting the oxygen concentration of the condensate and the water supply system.

[0028]

According to the present invention, there is provided a control arithmetic unit based on an oxygen concentration target value for setting condensate water and feed water to a predetermined oxygen concentration, and the oxygen concentration target value and the amount of oxygen to be injected. In the water quality control device for complex neutral water treatment, which performs arithmetic processing and controls the oxygen concentration of the condensate and feed water to a specified value by opening and closing the oxygen injection valve based on the output value of this arithmetic processing, in a state corresponding to the plant load or plant load. A change rate calculator that calculates the plant load or the change rate of the state quantity corresponding to the plant load based on the change in the quantity state, and the calculation processing output of the control calculator according to the change rate calculated by this change rate calculator An adder / subtractor that increases or decreases the value is provided.

[0029]

With the above structure, the decrease in oxygen concentration in the feed water that occurs when the plant load rises is predicted in advance based on the plant load or the rate of change of the state quantity corresponding to the plant load, and oxygen injection is performed before the oxygen concentration falls below the predetermined oxygen concentration. Insufficient amount is injected by the valve to control the oxygen concentration properly. In this way, the preceding opening operation of the oxygen injection valve is performed based on the plant load or the rate of change of the state quantity corresponding to the plant load. The slow load change rate is a gentle opening operation and an opening operation according to the plant load or the state quantity corresponding to the plant load, and control can be performed without injecting oxygen more than necessary.

[0030]

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

FIG. 1 is a system diagram of a water quality adjusting device showing an embodiment of the present invention. 6 and 7 indicate the same or corresponding portions.

In this embodiment, the oxygen concentration detector 14 for the water supply system is used.
And the detection signal from the feed water flow rate detector 20, the detection signal from the condensate temperature detector 27 on the inlet side of the deaerator 5, and the detection signal from the oxygen injection amount detector 23, respectively. The oxygen injection valve 26 is controlled to open and close based on the operation signal of the oxygen injection operator 12.

The oxygen injection calculator 12 is, as shown in FIG.
Target oxygen calculator 21, adjustment calculator 22, comparison calculator 2
4, PI calculator 25, addition / subtraction calculator 28, change rate calculator 2
9.

The target oxygen calculator 21 is the feed water flow rate detector 2
A target signal of injected oxygen is calculated based on the detection signal of zero.

The addition / subtraction calculator 22 inputs the detection signal of the oxygen concentration detector 14 and the target signal of the target oxygen calculator 21, and corrects the oxygen concentration signal to the target signal of injected oxygen.

The comparison calculator 24 is an oxygen injection amount detector 23.
The injected oxygen signal and the target signal from the adjustment calculator 22 are compared and calculated, and the deviation thereof is calculated.

The PI calculator 25 receives the deviation signal from the comparison calculator 24 and performs proportional and integral calculations.

The addition / subtraction calculator 28 inputs the calculation output of the PI calculator 25 and the correction signal of the change rate calculator 29, which will be described later, and outputs an opening degree signal to the oxygen injection valve 26.

The change rate calculator 29 is used for the oxygen concentration detector 14
The change rate is calculated based on the oxygen concentration signal and the detection signal of the condensate temperature detector 27.

With the above structure, the oxygen concentration detector 14 for the water supply system
The oxygen concentration signal of is input to the adjustment calculator 22 in the oxygen injection calculator 12 and the change rate calculator 29.

The oxygen concentration signal and the target signal of the target oxygen calculator 21 are input to the addition / subtraction calculator 22. In this target oxygen calculator 21, for example, as shown in FIG. 3, the target value of the injected oxygen is predetermined corresponding to the feed water flow rate. With this, the water supply flow rate detector 20 for detecting the water supply flow rate
The injection amount of injected oxygen based on the feed water flow rate is calculated as a target value from the signal of.

In the adjustment calculator 22, the target oxygen calculator 21
The oxygen concentration signal is corrected to the target value of the injected oxygen from and the signal is output to the comparison calculator 24.

The comparison calculator 24 compares the injected oxygen amount from the oxygen injection amount detector 23 with the target value from the adjustment calculator 22 to obtain the deviation. This calculation result is PI
The calculator 25 calculates proportional and integral operations, and the calculation signal is input to the addition / subtraction calculator 28.

On the other hand, in addition to the above-mentioned oxygen concentration signal, the rate-of-change calculator 29 is provided with the condensate temperature detector 2 at the inlet of the deaerator 5.
The change rate calculator 29 calculates the respective change rates of the oxygen concentration and the condensate temperature generated with the change of the plant load, and outputs them to the adjusting calculator 28.

For example, the rate-of-change calculator 29 obtains a function calculation as shown in the following equation (1).

[0046]

## EQU1 ## Y = f (dT / dt, dO ₂ / dt) --- (1)

Here, Y: output (correction signal) T: condensate temperature O ₂ : oxygen concentration

The addition / subtraction calculator 28 adds / subtracts the correction signal of the change rate calculator 29 to / from the output signal of the PI calculator 25. Then, the oxygen injection valve 26 is output according to the output signal of the adjustment calculator 28.
Control the opening degree.

By the way, when the plant load increases rapidly,
The oxygen released from the tray of the degassing chamber 5a is pushed up and accumulated in the upper part of the degassing chamber 5a. Therefore, the temperature of the condensate flowing into the deaerator 5 is in the rising direction. This increase in temperature leads to a decrease in oxygen solubility in the water supply system, which promotes oxygen deficiency. As a result, the oxygen concentration at the inlet of the economizer 9 begins to gradually decrease.

With the above operation, when the plant load P is constant, for example, as in the example shown in FIG. 4, from the time t0 to the time t1, a deviation from the target set value is obtained from the oxygen concentration, and the deviation is proportional and integrated. A calculation is performed to control the oxygen injection valve 26. As a result, the oxygen concentration D is stable with respect to the plant load P.

Therefore, when the plant load P increases, the oxygen concentration and the condensate temperature are calculated by the change rate calculator 29 to calculate the oxygen concentration decrease rate and the condensate temperature increase rate, respectively. The correction value of the oxygen injection valve opening is calculated. The calculation result is feedforward added to the output of the PI calculator 25 by the addition / subtraction calculator 28.

For example, when the plant load P rises quickly at time t1, the oxygen injection valve 26 is opened rapidly to increase the oxygen injection amount. As a result, even if the plant load P changes suddenly as shown in FIG. 4, the change in oxygen concentration D is extremely small as compared with FIG. 9 of the conventional example. When the plant load P stabilizes at time t2,
The oxygen injection valve 26 is gently opened.

As described above, it is possible to control the drop in the oxygen concentration of the feed water at the inlet of the economizer 9 caused by the increase in the load of the plant within the target value to obtain an appropriate value.

Next, another embodiment of the present invention is shown in FIG.

In this embodiment, the oxygen concentration of the oxygen concentration detector 14 and the condensate temperature of the condensate temperature detector 27 are input to the change rate calculator 29, and the change rate calculator 29 lowers the oxygen concentration. The rate is calculated and the rate of rise is calculated for the condensate temperature. Then, the oxygen concentration correction set value corresponding to each change rate is calculated.

The calculation result is input to the comparison calculator 24 as a correction target set value of the PI calculator 25, and the deviation from the injected oxygen amount is obtained. This deviation is calculated by the PI calculator 25 for proportional and integral operations and used as the opening signal of the oxygen injection valve 26. The configuration described above can also be implemented in the same manner as the embodiment shown in FIG.

Incidentally, instead of the plant load or the condensate temperature as the state quantity corresponding to the plant load as the input of the change rate calculator, for example, the same effect can be obtained as the power generation output quantity. The same effect can be obtained by using the degasser outlet or the deaerator tank as the oxygen concentration detection point instead of the economizer inlet.

[0058]

As described above, according to the present invention, in the combined neutral water treatment of the condensate and the feed water system, the change in the plant load or the state quantity corresponding to the plant load can be grasped and, when the plant load changes, It is possible to control the water quality at an appropriate value by suppressing the oxygen concentration drop at the inlet of the economizer.

[Brief description of the drawings]

FIG. 1 is a system diagram of a water quality adjusting device showing an embodiment of the present invention.

FIG. 2 is a block diagram showing an oxygen injection calculator of the device.

FIG. 3 is an explanatory diagram showing an example of a target oxygen calculator of the same apparatus.

FIG. 4 is an explanatory diagram showing an example of the operation of the device.

FIG. 5 is a block diagram of an oxygen injection calculator showing another embodiment of the present invention.

FIG. 6 is a system diagram of a water quality adjusting device showing a conventional example.

FIG. 7 is a block configuration diagram showing an oxygen injection calculator of the apparatus.

FIG. 8 is an explanatory view showing an operation inside the deaerator by the device.

FIG. 9 is an explanatory diagram showing an example of the operation of the same device.

[Explanation of symbols]

 12 Oxygen injection calculator 14 Oxygen concentration detector 20 Water supply flow rate detector 21 Target oxygen calculator 22 Adjustable calculator 23 Oxygen injection amount detector 24 Comparison calculator 25 PI calculator 26 Oxygen injection valve 27 Condensate temperature detector 28 Adjust Calculator 29 Change rate calculator

Claims (1)

(57) [Claims] 1. An arithmetic processing by a control arithmetic unit on the basis of an oxygen concentration target value for making condensate water and feed water to have a predetermined oxygen concentration, and this oxygen concentration target value and the amount of oxygen to be injected, and the arithmetic processing output. In the water quality control device for complex neutral water treatment, which controls the oxygen concentration of the condensate and feed water to a predetermined value by opening and closing the oxygen injection valve according to the value of the plant load or the plant load based on the change in the state quantity corresponding to the plant load. Or a change rate calculator for calculating the change rate of the state quantity corresponding to the plant load, and an adder / subtractor for increasing or decreasing the calculation processing output value of the control calculator according to the change rate calculated by the change rate calculator A water quality control device characterized by