JPH0634104A - Water quality controller - Google Patents

Abstract

(57) [Summary] [Object] The present invention is a water quality adjusting device capable of preventing water from diffusing and dissolving high-concentration oxygen in a deaerator that occurs when a plant load changes and enabling stable water quality adjustment. To provide. [Structure] The present invention relates to a water quality adjusting device for a condensate / water supply system in a power plant or the like, and a pressure detector for detecting the internal pressure of a deaerator into which oxygen-injected condensate flows, and to the deaerator. A temperature detector that detects the temperature of the condensate that flows in, a switching calculator that compares the pressure drop rate due to a plant load drop or a temperature set value for the load, and an output signal of the switching calculator to output the deaerator into the deaerator. Since it is composed of an automatic adjustment valve that discharges the high concentration of accumulated oxygen, if the deaerator internal pressure exceeds a prescribed pressure drop rate due to a load decrease, the deaerator vent valve When the automatic control valve is opened to release high-concentration oxygen to the atmosphere, and when the condensate temperature corresponding to the load plus the bias temperature is exceeded, the automatic control valve of the deaerator vent valve is opened to supply water. Keep the oxygen concentration inside properly.

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 a condensate / water supply system in a power plant or the like.

[0002]

2. Description of the Related Art At a thermal power plant in Japan, the water quality of condensate / supply water / boiler water and steam is adjusted to minimize corrosion in the system, and the boiler water pipe / steam pipe and water pump intake We have tried to prevent the scale from sticking to the strainer. When the boiler type is a once-through type, volatile substance treatment (hereinafter referred to as the AVT method) is performed by injecting volatile chemicals of ammonia (NH ₃ ) and hydrazine (N ₂ H ₄ ) into the condensate / water supply system, pH value from 9 to 9.5
And deoxidation is controlled.

However, in the above AVT method, in order to obtain a higher anticorrosion effect, a high ammonia concentration (pH>
9.4), which is required in the ammonia concentrating section in the plant (eg, condenser air cooling section, etc.)
Since damage due to ammonia (ammonia attack) occurs, anticorrosion measures cannot be taken with high-concentration ammonia.

As a result, iron is leached from the carbon steel in the plant into the condensate / water supply system by hydrazine, which is a reducing agent, and adheres to the boiler water pipe / steam pipe and the feed water pump suction strainer, etc. Will increase. For this reason, the attached iron oxide must be removed at an appropriate time, which is a great obstacle to the plant operation plan. Also,
Without this removal, there was a risk of overload operation of the water supply pump and cracks in the boiler tube.

In order to improve the above-mentioned drawbacks of the conventional AVT method, ammonia (NH ₃ ) and oxygen (O) are added to the condensate / feed water system.
₂ ) Injecting complex neutral water treatment (hereinafter referred to as CWT method) is being carried out stepwise. According to this CWT method, by changing the conventional strong alkali to weak alkali in the condensate / water supply system and by injecting oxygen, the adhesion of iron oxide to the boiler water pipe / steam pipe and the feed water pump suction strainer is greatly reduced. can do.

Such a conventional water quality adjusting device will be described with reference to the system diagram of FIG. In the figure, the turbine exhaust steam and the heater drain (both not shown) collected in the condenser 1 are heat-exchanged with circulating water using seawater as cooling water to be condensed, and then are condensed by the condensate pump 2. Water is sent to the water desalination device 3. In this condensate demineralizer 3 (hereinafter referred to as “condemi”), after removing suspended solids such as iron oxides and dissolved solids such as chlorine ions in the condensate, the low pressure feed water heater 5 is heated by the condensate booster pump 4. Is heated by the water and sent to the deaerator 6. The condensate sent to the deaerator 6 is sent to a water supply pump 7 together with a high-pressure heater drain (not shown), is heated by a high-pressure feed water heater 8, passes through a economizer 9, and is sent to the boiler 10.

On the other hand, water quality adjustment (oxygen injection) is installed in each of the condensate system and the water supply system. Condensate system is the oxygen O ₂ is injected from the outlet side of the Kondemi 3, the water supply system is implanting oxygen O ₂ from the outlet side of the deaerator 6.

Next, the control method for water quality adjustment will be described with reference to FIG.
An explanation will be given with reference to a system diagram of oxygen injection into the water supply system. The condensate system inputs the oxygen concentration 13 at the inlet of the economizer 9, the condensate flow rate 21 at the inlet of the deaerator 6 and the oxygen injection amount 22 at the inlet of the condemi 3 to the oxygen injection calculator 23, and the output of this calculator 23 The opening of the injection valve 24 is controlled to keep the oxygen concentration in the condensate system. On the other hand, in the water supply system, similarly, the oxygen concentration 13 at the inlet of the economizer 9, the feed water flow rate 25 at the inlet of the economizer 9 and the oxygen injection amount 26 at the outlet of the deaerator 6 are used to operate the injection valve 28 via the oxygen injection calculator 27. The opening is controlled to keep the oxygen concentration in the water supply system. In addition, a deaerator vent valve (not shown) to prevent oxygen release in the system during plant operation by the CWT method
Is fully closed.

The behavior of the condensate flowing in the deaerator and the oxygen injected and dissolved at the condemi outlet when the CWT method is operated in the above system configuration will be described with reference to FIGS. 8 and 9.

In FIG. 8, the condensate containing oxygen under high load contacts the heated steam while dropping the distribution tray and the degassing tray in the deaerator and releases oxygen to be stored in the water storage tank. The oxygen released here stays in the upper part of the deaerator as a non-condensed gas and is in a high concentration state. This is affected by the upward flow of steam inside the deaerator and the pressure inside the vessel.

By the way, it is generally known that the solubility of oxygen is greatly affected by temperature, and the solubility increases as the temperature decreases. Therefore, when the pressure inside the deaerator decreases with the subsequent load drop, the high-concentration oxygen retained in the upper part of the deaerator spreads to the deaeration tray part, and the condensate temperature also decreases. As it dissolves in the feed water until the deaerator is in a heat balance equilibrium state (until the condensate reaches the saturation temperature of its load), it should show a peak value of oxygen concentration as shown in Fig. 9. become.

[0012]

In the CWT method, as described above, when the load is lowered, the high-concentration oxygen retained in the upper part of the deaerator diffuses, expands in volume and inflows back and forth when the internal pressure drops. It melts into the water supply as the water temperature decreases and shows a high peak value. This increases the oxygen concentration in the stagnant part of the water supply system and causes corrosion in that part. Therefore, when the oxygen concentration shows a high peak value, the deaerator vent valve must be manually opened each time to release oxygen to the atmosphere, which is very complicated in plant operation where daily load changes are severe. There is a problem that becomes.

The present invention has been made to solve the above problems, and its purpose is to prevent diffusion and dissolution of high-concentration oxygen in feed water in a deaerator, which occurs when the load on a plant changes, and stabilize the operation. An object is to provide a water quality adjusting device capable of adjusting water quality.

[0014]

In order to achieve the above object, the present invention provides a water quality adjusting device for a condensate / water supply system in a power plant or the like, in which a condensate infused with oxygen flows into a deaerator. A pressure detector for detecting the pressure, a temperature detector for detecting the temperature of the condensate flowing into the deaerator, an opening / closing calculator for comparing the pressure drop rate due to the plant load drop or a temperature set value for the load, and It is characterized by comprising an automatic adjustment valve for discharging the high concentration of oxygen accumulated in the deaerator according to the output signal of the opening / closing calculator.

[0015]

[Function] The pressure inside the deaerator decreases as the load decreases, and the rate of pressure decrease due to the volume expansion of oxygen retained in the deaerator is detected. Open the automatic control valve of the ventilator vent valve to release the high-concentration oxygen retained in the upper part of the deaerator to the atmosphere, reduce the dissolution into the water supply system, and maintain the oxygen concentration in the water supply properly. . If the condensate temperature equivalent to the load plus the bias temperature is exceeded, the deaerator vent valve automatic control valve is opened to maintain an appropriate oxygen concentration in the feed water.

[0016]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a system diagram of a water quality adjusting device for a condensate / water supply system in a power plant according to an embodiment of the present invention. The same parts as those in FIG. 6 already described are designated by the same reference numerals and the description thereof will be omitted.

In FIG. 1, the detection signal of the condensate temperature detector 12 for detecting the temperature of the condensate flowing into the deaerator 6 and the detection signal of the pressure detector 13 for detecting the pressure of the deaerator 6 are changed. Input to the switching calculator 17 via the rate calculator 14. In the opening / closing calculator 17, a signal for opening / closing the control valve 11 for discharging the oxygen filled in the deaerator 6 by the signals α, β from the set value calculator 15 for calculating the signals of the set values α, β by the load signal 16. Is output.

A detailed block diagram of the set value calculator 15 is shown in FIG. In the figure, the reset signal β is output from the heat balance graph 20 of the condensate temperature corresponding to the load flowing into the deaerator which is previously determined by the heat balance by the load signal 16. A bias value considering the condensate temperature delay by the load is input to the bias graph 21 by the load signal 16, and the bias signal and the β signal are added by the adder 22 to obtain the set temperature signal α for valve opening operation. Output.

A detailed block diagram of the opening / closing calculator 17 is shown in FIG. In the figure, when the temperature signal T of the condensate temperature detector 12 becomes equal to or higher than the set temperature value α ° C. in which the bias value is added, the control valve 11 is opened while having the self-holding circuit. After that, as the load stabilizes, the condensate temperature signal T becomes less than the set temperature value β ° C of the heat balance base until the control valve 1
The open state of 1 is continued, and the oxygen filled in the deaerator 6 is discharged before the oxygen dissolves into the water supply.

Further, in this embodiment, the function of discharging oxygen is also provided by pressure, and once the output signal P of the deaerator pressure change rate calculator 14 reaches a predetermined pressure change rate γ ₁ or more, The control valve 11 is opened in the same manner as the temperature signal of 1, and closed when the pressure change rate becomes γ ₂ or less.

By the opening / closing operation of the control valve 11 described above, oxygen that expands in volume as the load drops is detected by the pressure drop rate due to the load drop, and is discharged to the atmosphere, or as the temperature drops, the oxygen dissolves into the water supply. It becomes possible to discharge high-concentration oxygen before the increase.

FIG. 4 is a system diagram of another embodiment of the present invention. The configuration of this embodiment different from the embodiment of FIG. 1 omits the set value calculator 15 and omits the condensate temperature detector 12. The temperature signal is input to the switching calculator 17a via the temperature change rate calculator 18. Since other configurations are the same, the same reference numerals are given to the same portions and the description thereof will be omitted.

FIG. 5 is a block diagram of the opening / closing calculator 17a shown in FIG. In the figure, once the temperature signal T of the temperature change rate calculator 18 reaches a predetermined temperature change rate δ ₁ or more, the control valve 11 is opened and closed when the temperature change rate becomes δ ₂ or less.

The function of discharging oxygen is also provided by pressure, and once the pressure signal P of the deaerator pressure change rate calculator 14 reaches a predetermined pressure change rate γ ₁ or more, the same as the temperature signal. Then, the control valve 11 is opened and closed when the pressure change rate becomes γ ₂ or less.

By the opening / closing operation of the control valve 11 described above, oxygen that expands in volume as the load drops is detected by the rate of pressure decrease due to the load drop, and is discharged to the atmosphere, and as the temperature drops, oxygen dissolves into the water supply. It is possible to discharge high-concentration oxygen before the increase of E., and the effect is similar to that of the embodiment of FIG.

[0026]

As described above, according to the present invention,
High-concentration oxygen in the deaerator, which causes oxygen concentration increase at the inlet of the economizer when the load of the condensate / water supply system in the power generation plant changes due to the combined neutral water treatment. Stable water quality control is possible by preventing the diffusion and dissolution of water.

[Brief description of drawings]

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

FIG. 2 is a functional block diagram of the set value calculator of FIG.

FIG. 3 is a functional block diagram of the switching calculator of FIG.

FIG. 4 is a system diagram of another embodiment of the present invention.

5 is a functional block diagram of the opening / closing calculator shown in FIG. 4;

FIG. 6 is a system diagram of a conventional condensate / water supply system.

7 is a system diagram of oxygen injection into the condensate / water supply system of FIG.

8 is an internal configuration diagram of the deaerator shown in FIG.

9 is a diagram showing an oxygen behavior graph of FIG.

[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… Control valve, 12… Condensate temperature detector, 13
... pressure detector, 14 ... change rate calculator, 15 ... set value calculator, 16 ... load signal, 17, 17a ... open / close calculator, 18
... Temperature change rate calculator.

Claims (1)

[Claims] 1. In a water quality adjusting device for a condensate / water supply system in a power plant or the like, a pressure detector for detecting pressure in a deaerator into which condensate injected with oxygen flows, and a pressure detector for flowing into the deaerator. A temperature detector that detects the temperature of the condensate, a switching calculator that compares the pressure drop rate due to plant load drop or a temperature set value for the load, and an output signal from the switching calculator that accumulates in the deaerator. A water quality adjusting device comprising an automatic adjusting valve for discharging a high concentration of oxygen.