JPH06220661A - Water quality regulator - Google Patents

Abstract

PURPOSE:To enable stable water quality regulation with the water quality regulator by determining an injected oxygen quantity in accordance with the suction flow rate and recirculation flow rate of a water feed pump. CONSTITUTION:An oxygen density signal is inputted from a detector 13 to an addition/ subtraction computing element in an oxygen injection computing element 15 and is corrected and computed to the signal from a target oxygen computing element at the time the operation pattern of the water feed pump 7 is changed. This target oxygen computing element calculates the target value of the injected oxygen quantity on the bases of the flow rate of the feed water to be substantially fed to a boiler from the signal of a flow rate detector 16 which detects the suction flow rate of the water feed pump 7 and the signal of a flow rate detector 12 which detects the recirculation flow rate of the water feed pump 7. The signal of the corrected target oxygen quantity in the addition/subtraction computing element is inputted to a relational computing element which computes the deviation in the actual inflow rate from the target oxygen quantity by the target oxygen quantity and the input signal from an injected oxygen detector 14. The result of the computation is subjected to [proportional + integral] computation in a PI computing element, by which an oxygen injection valve 17 is controlled.

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 in a power plant or the like.

[0002]

2. Description of the Related Art In domestic thermal power plants, the water quality of condensate / supply water / boiler water / steam is adjusted / treated to minimize corrosion in the system, and boiler water pipe /
We have been trying to prevent scale from adhering to the steam pipe and suction pump of the water feed pump.

When the boiler type is a once-through type, ammonia (NH ₃ ) and hydrazine (N
A volatile substance treatment (hereinafter referred to as the AVT method) of injecting a volatile chemical of ₂ H ₄ ) is performed, and the PH value is controlled to be 9.0 to 9.5 and deoxidized.

However, in the AVT method, in order to obtain a higher anticorrosion effect, a high ammonia concentration (PH> 9.4
) Is required, which causes damage (ammonia tack) due to concentrated ammonia in the ammonia concentrating section in the plant (for example, the air cooling section of the condenser). Therefore, it is not possible to take anticorrosion measures with high-concentration ammonia.

As a result, iron is leached from the carbon steel in the plant to the condensate / water supply system by the reducing agent hydrazine and adheres to the boiler water pipe / steam pipe or the feed water pump suction strainer to increase the thickness over time. . Therefore, this must be removed at an appropriate time, which is a great obstacle to the plant operation plan. If this removal is not done,
There is a risk of overload operation of the feed pump and cracks in the boiler tube.

In order to improve these drawbacks of the conventional AVT method, in recent years, a complex neutral water treatment (hereinafter referred to as the CWT method) in which ammonia (NH ₃ ) and oxygen (O ₂ ) are injected into the condensate / water supply system. Is being implemented in stages.

In the CWT method, the inside of the system is changed from a conventional strong alkali to a weak alkali, and oxygen is injected,
It is possible to greatly reduce the adhesion and carry-on of iron oxide to the boiler water pipe / steam pipe and the feed water pump suction strainer.

A general system configuration is shown in FIG. Condenser 1
The turbine exhaust and the heater drain (both not shown) collected in (1) are heat-exchanged with the circulating water using seawater as cooling water to be condensed. This condensate is passed through the low-pressure feed water heater 5 by the condensate pump 2 and the condensate booster pump 4, and the deaerator 6
Sent to.

On the outlet side of the condensate pump 2, a condensate demineralizer 3 (hereinafter referred to as "condemi") is installed as a water treatment device, and suspended solids such as iron oxide and chlorine ions in the condensate are installed. Dissolved solids such as are removed to regenerate the system.

Condensate sent to the deaerator 6 is sent to a water supply pump 7 together with a high-pressure heater drain (not shown), passes through a high-pressure feed water heater 8 and a economizer 9, and is sent to a boiler 10. .

On the other hand, water quality adjustment (oxygen injection)
It is installed in each water supply system. In the condensate system, oxygen is injected from the outlet side of the condemi 3 and the water supply system is injected from the outlet side of the deaerator 6.

The control method will be described with reference to FIG. In the condensate system, the function calculator 25 calculates the target value of oxygen injection in the condensate system from the flow rate signal from the condensate flow rate detector 23 at the inlet of the deaerator 6, and further performs the correction calculation to make the oxygen concentration detector 13 at the inlet of the economizer 9
The oxygen concentration signal due to is calculated by the addition and subtraction calculator 26 as a target value of the injection amount, and the signal of the condensate side injection oxygen detector 24 that detects the amount of oxygen injected from the outlet side of the condemi 3 is compared with the calculator 27 Then, the PI calculator 28 calculates "proportional + integral" to control the injection valve 29 to control the oxygen injection amount of the condensate system.

The water supply system is a water supply flow rate detector 30 at the inlet of the economizer 9.
From the flow rate signal by the function calculator, the feed water system oxygen injection target value is calculated, and further correction calculation is performed, and the oxygen concentration signal from the oxygen concentration detector 13 at the inlet of the economizer 9 is adjusted by the addition and subtraction calculator 20, The amount of oxygen injected from the outlet side of the deaerator 6 is detected by setting the target value of the amount of injection. The deviation is calculated by the comparison calculator 21 with the signal from the feed water injection oxygen detector 14, and the PI calculator 22 calculates “proportional + integral” to control the injection valve 17. The outlet side of the injection valve is branched into the number of installed water supply pumps 7, and stop valves 31, 32, 33 for ON-OFF operation are installed respectively, and the amount of oxygen injection of the water supply system is controlled by opening and closing according to the number of operating water supply pumps. is doing. When the CWT method is used in such a system configuration, the oxygen concentration in the water supply system varies depending on the operation pattern of the water supply pump in the water supply system.

This is caused by the following factors. That is, the amount of injected oxygen is determined by the total amount of water supply at the inlet of the economizer 9, and the distribution is performed by the stop valves 31, 32, 33 at the outlet of the injection valve 17, so that the discharge flow rate unbalanced state of the water supply pump is adjusted. It cannot be taken into consideration (for example, switching from 2 turbine drives to 1 turbine, para-run operation of turbine drive and electric drive).
In addition, the operation of the stop valve 31, 32, 33 at the outlet of the injection valve 17 is ON-
Since it is OFF, the fluctuation is large.

[0015]

However, the following problems remain in the general method of the CWT method. When the operation pattern of the water supply pump is changed, the discharge amount of each water supply pump becomes unbalanced, but the oxygen injection amount is determined by the total water supply amount at the economizer inlet, and then the injection valve outlets are evenly distributed.

As a result, the oxygen concentration is low on the pump side with a large discharge amount, and the oxygen concentration is high on the pump side with a small discharge amount. Both of them merge at the outlet side and are made uniform, but the solubility of oxygen is greatly affected by the temperature, so that the pump 1
When starting from one to two units, the oxygen concentration fluctuates because the uniformity on the outlet side is not properly performed. Further, since the operation of the stop valve at the outlet of the injection valve is ON-OFF, the concentration fluctuation is further promoted.

[0017]

In the present invention, the oxygen injection control is installed in each pump, and the oxygen injection target value is based on the suction flow rate of each pump, and the recirculation flow rate of each pump is also taken into consideration. And decide.

[0018]

According to the structure of the present invention, when the operation pattern of the water supply pump is changed, the oxygen concentration changes due to the imbalance of the discharge amount, the oxygen injection control is installed in each water supply pump, and the oxygen injection amount is set. The fluctuation can be prevented because it is determined by the intake flow rate of each water supply pump. Further, since the oxygen injection amount is corrected in the pump recirculation operation, it is possible to prevent the fluctuation of the oxygen concentration even when the pump is started and stopped. As a result, oxygen injection control can be performed according to plant operation (water supply pump operation pattern).

[0019]

An embodiment of the present invention will be described below with reference to the accompanying drawings. The same reference numerals as those in FIG. 3 indicate the same or corresponding portions. In FIG. 1, the oxygen concentration of the water supply system is detected by the oxygen concentration detector 13, and the signal is input to the oxygen injection calculator 15.

The oxygen injection calculator 15 also receives a signal from the injection oxygen amount detector 14 which detects the amount of injected oxygen, and a signal water supply pump 7 from the water supply flow rate detector 16 which detects the suction flow rate of the water supply pump 7.
The signal of the recirculation flow rate detector 12 for detecting the recirculation flow rate of is input. The oxygen injection calculator 15 corrects and calculates oxygen concentration and recirculation flow rate based on the suction flow rate of the water supply pump 7, and calculates and outputs the opening degree of the injection valve 17. FIG. 2 shows the configuration of the oxygen injection calculator 15 that prevents fluctuations in oxygen concentration when the operation pattern of the water supply pump 7 is changed in the control device configured as described above. The oxygen concentration signal is input to the addition / subtraction calculator 20 in the oxygen injection calculator 15, where the signal from the target oxygen calculator 19 is subjected to correction calculation.

The target oxygen calculator 19 supplies water substantially to the boiler from the signal of the flow rate detector 16 which detects the suction flow rate of the water supply pump 7 and the signal of the flow rate detector 12 which detects the recirculation flow rate of the water supply pump 7. A target value of the amount of injected oxygen based on the flow rate is calculated. The signal of the corrected target oxygen amount in the adjusting calculator 20 is input to the comparing calculator 21.

In the comparison calculator 21, the target oxygen amount signal and the signal from the injected oxygen detector 14 are input, and the deviation of the actual inflow amount from the target oxygen amount is calculated. The result of this operation is P
"Proportion + integration" is calculated by the I calculator 22 to control the injection valve 17.

These control loops are installed for each of the installed water supply pumps 7. As a result, although a flow rate imbalance occurs between the water supply pumps depending on the operation pattern of the water supply pump 7, the injected oxygen amount becomes an injection amount commensurate with the boiler water supply amount of each water supply pump, and as a result, fluctuation can be prevented.

In the above description, the feedwater pump recirculation flow rate used to correct the boiler feedwater amount of the feedwater pump is measured by the flow rate detector. However, as another method, the feedwater pump recirculation flow rate control valve is actually opened. The flow rate can be obtained from the degree or opening signal, and the same effect can be obtained.

[0025]

As described above, according to the present invention, it is possible to prevent the fluctuation of the oxygen concentration at the inlet of the economizer at the inlet of the economizer, which is caused by the change of the operation pattern of the water supply pump in the CWT method, and the stable water quality adjustment becomes possible. .

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram of an arithmetic unit according to the present invention.

FIG. 3 is a system diagram showing a conventional example.

FIG. 4 is an explanatory diagram of oxygen injection into a conventional condensate water supply system.

[Explanation of symbols]

1 ... Condenser, 2 ... Condensate pump, 3 ... Condensate demineralizer, 4 ...
Condensate booster pump, 5 ... Low-pressure feed water heater, 6 ... Deaerator, 7
… Water supply pump, 8… High pressure water heater, 9… Economizer, 10…
Boiler, 11 ... Water supply pump recirculation flow valve, 12 ... Water supply pump recirculation flow detector, 13 ... Oxygen concentration detector, 14 ... Oxygen injection detector, 15 ... Oxygen injection calculator, 16 ... Water pump suction flow detection Device, 17 ... Oxygen injection valve, 18 ... Adjusting calculator, 19 ... Target oxygen calculator, 20 ... Adjusting calculator, 21 ... Comparison calculator, 22 ...
PI calculator, 23 ... Condensate flow rate detector, 24 ... Condensate side oxygen injection amount detector, 25 ... Target oxygen calculator, 26 ... Adjusting calculator, 27 ...
Comparative calculator, 28 ... PI calculator, 29 ... Condensate side oxygen injection valve,
30… Water supply flow rate detector, 31, 32, 33… Stop valve.

Claims (3)

[Claims] 1. In a water quality adjusting device for performing combined neutral water treatment in which ammonia and oxygen are injected as water quality adjustment of a condensate / water supply system in a power plant or the like, injecting oxygen on the basis of a feed water pump suction flow rate and a recirculation flow rate. A water quality adjusting device characterized in that the amount is obtained. 2. The water quality adjusting device according to claim 1, wherein the water supply adjusting device is installed for each of the installed water supply pumps. 3. The water quality adjusting device according to claim 1, wherein a lift of a control valve installed in a recirculation line is used instead of the recirculation amount.