JPH0236841B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for a variable pressure once-through boiler,
In particular, the condition of the fluid flowing into the steam/water separator may be wet or
This invention relates to improving the control characteristics of a boiler in an operating region where dryness changes.

A steam system diagram of an example of a variable pressure once-through boiler is shown in FIG.

In FIG. 1, water sent out from a feed water pump 1 is heated by a feed water heater 2, and is supplied to an energy saver 4 via a recirculation water confluence section 3. The water further heated by the economizer 4 flows into the furnace water wall 5, is heated by the furnace water wall 5, becomes steam, and is sent to the steam-water separator 6. The steam-water separator 6 separates water contained in steam, and the separated water (drain) is extracted by the recirculation pump 11 and flows into the recirculation water confluence section 3 from the water supply pump 1. It is combined with the collected water and supplied to the economizer 4. On the other hand, steam sent out from the steam separator 6 is superheated by a primary superheater 7, and is supplied to a steam turbine 10 via a superheater attemperator 8 and a secondary superheater 9. Further, water is injected into the superheater desuperheater 8 from the feed water heater 2 through the superheater water injection line 12.

As an example of a control device for a variable pressure once-through boiler configured in this manner, a control device shown in a system diagram shown in FIG. 2 is known.

In FIG. 2, the load request signal D corresponding to the load amount of the boiler is transmitted to the function generating elements 13A, 13B, 13.
These are respectively input to C. Function generation element 13A~
Reference numeral 13C outputs a steam pressure setting signal P _S , a steam temperature setting signal T _S , and a water supply amount advance value signal _WF correlated with the load request signal D, respectively. The output of the function generation element 13A is input to a subtraction element 14A, and this subtraction element 14A outputs a deviation signal between the steam pressure detection signal P _A input from the steam pressure detection terminal 15 and the setting signal P _S. This deviation signal is sent to the signal switching element 17 as a water supply vapor pressure correction signal Wcp and a fuel vapor pressure correction signal Fcp corresponding to the steam pressure, respectively, via the proportional-integral elements 16A and 16B.
A and 17B are input. A zero signal is input from the zero signal element 18 to this signal switching element 17A, and one of the input signals is outputted to the addition element 19A according to a command. This addition element 1
9A adds the water supply amount advance value signal W _F and the signal output from the signal switching element 17A, and outputs the result to the function generation element 13D and the signal selection element 20 as the water supply amount target value signal W _T. This signal selection element 20 outputs a water supply amount target value signal having a higher value of either the minimum water supply amount setting signal W _Tnio inputted from the minimum water supply amount setting element 21 or the signal W _T.

On the other hand, the subtraction element 14B outputs a deviation signal between the steam temperature detection signal _TA inputted from the steam temperature detection end 22 and the setting signal _TS , and this deviation signal is passed through the proportional-integral element 16C. It is input to the signal switching element 17B as a fuel steam temperature correction signal _FcT that corrects the amount of heat supply according to the steam temperature. This signal switching element 17B inputs either of the correction signals Fcp and _FcT to the addition element 19 according to a command.
This is what is output to B. This addition element 19B
is a fuel supply amount advance value signal corresponding to the water supply amount target value signal W _T outputted from the function generating element 13D.
The fuel supply amount target value signal F _T is output by adding F _F and the correction signal output from the signal switching element 17B.

The control operation of the conventional example configured in this way will be described next.

First, a description will be given of the steam pressure and temperature control operations when the boiler is in a once-through operation, that is, when the steam sent from the furnace water wall 5 is in a dry region. Since the steam pressure during once-through operation is determined depending on the water supply amount supplied to the energy saver 4, the water supply amount advance value signal W _F corresponding to the load request signal D is used as the water supply amount corresponding to the steam pressure. The steam pressure is maintained at a predetermined value by controlling the water supply amount using the water supply amount target value signal W _T corrected by the water vapor pressure correction signal Wcp. Note that, in order to protect the furnace and the like, the minimum amount of water supply is selected and outputted by the signal selection element 20 so as to be equal to or higher than the minimum water supply amount setting signal W _Tnio . In addition, steam temperature control during once-through operation is performed using a fuel supply amount advance value signal determined by the water-fuel ratio.
F _F is the fuel steam temperature correction signal Fc _T according to the steam temperature.
The steam temperature is maintained at a predetermined value by controlling the fuel supply amount using the fuel supply amount target value signal F _T corrected by .

Next, a description will be given of the steam pressure and temperature control operations when the boiler is in recirculation operation, that is, when the steam sent from the furnace water wall 5 is in a wet region operation mode. The steam pressure during recirculation operation is determined not only by the amount of water supplied, but also by the amount of steam, which is the product of the amount of water supplied and the dryness of the steam sent from the furnace water wall 5. If the amount of water supplied is increased in response to a decrease in steam pressure, the dryness will be reduced by more than the rate of increase in the amount of water supplied if the amount of heat absorbed by the furnace water wall 5 is the same. Therefore, during recirculation operation, the signal switching element 17A is activated to switch the feed water amount vapor pressure correction signal Wcp to a zero signal, and the water feed amount advance value signal is changed without correcting the feed water amount according to the steam pressure.
It is controlled by W _F or the minimum water supply amount setting signal W _Tnio , and the steam pressure is maintained at a predetermined value by correcting and controlling the fuel supply amount. That is, during recirculation operation, the signal switching element 17B is operated to switch the fuel vapor temperature correction signal _FcT to the fuel vapor pressure correction signal Fcp, and the fuel supply amount advance value signal is changed according to the water supply amount.
The fuel supply amount is controlled by the fuel supply amount target value signal F _T obtained by correcting F _F to maintain the steam pressure at a predetermined value.

However, according to the above control method, a reverse response phenomenon of steam pressure may occur during once-through operation immediately after switching from recirculation operation to once-through operation or immediately before switching from once-through operation to recirculation operation. In other words, once the control reaches a stable state, the furnace heats according to the amount of fuel supplied in correlation with the amount of water supplied.
Since the amount of water supplied and the amount of heat absorbed by the furnace are balanced, the steam pressure and temperature are controlled to a predetermined level, but when the control is in a transient state, for example, when the steam pressure decreases, the amount of water supplied is increased to increase the steam pressure. If such an operation is performed, the amount of heat absorbed by the furnace cannot quickly follow the increase in the amount of water supplied, and the enthalpy of the steam sent out from the furnace water wall 5 decreases and the steam enters the wet region, which is the opposite of steam pressure. This method has the disadvantage that a response phenomenon may occur, which makes the steam pressure unstable.

An object of the present invention is to provide a control device for a variable pressure once-through boiler that prevents the occurrence of a reverse response phenomenon in steam pressure control that occurs when switching between once-through operation and recirculation operation in a variable-pressure once-through boiler, and enables stable steam pressure control. Our goal is to provide the following.

The present invention focuses on the phenomenon that the fluid temperature in the steam-water separator (hereinafter abbreviated as "steam-water separator temperature") changes depending on the transient imbalance between the boiler water supply amount and the furnace heat absorption amount. It was created by
By detecting the temperature of the steam water separator and correcting and controlling the water supply amount and fuel supply amount according to the deviation between this temperature and a predetermined temperature setting value, the occurrence of a reverse response phenomenon in steam pressure control is prevented. The aim is to achieve stable steam pressure control.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below based on illustrated embodiments.

FIG. 3 shows a control block system diagram of an embodiment to which the present invention is applied. It should be noted that components in FIG. 3 with the same reference numerals as those in the conventional example shown in FIG.

In FIG. 3, the steam-water separator temperature H _A output from the steam-water separator temperature detection end 23 is the subtraction element 14.
A steam/water separator temperature setting signal H _S outputted from the function generation element 13E in accordance with the required load amount D is input to the subtraction element 14C. The output of this subtraction element 14C is input to proportional elements 24A and 24B via a proportional-integral element 16D. The output of this proportional element 24A is input as a water supply amount reverse response correction signal W _cH to a subtraction element 14D connected between the proportional integral element 16A and the signal switching element 17A. In addition, the output of the proportional element 24B is the fuel reverse response correction signal F _cH ,
It is input to an addition element 19C connected between the proportional-integral element 16C and the signal switching element 17B.

Since it is configured in this way, when the steam/water separation temperature H _A is higher than the set signal H _S , the water supply amount inverse response correction signal W _cH and the fuel are proportionally and integrally processed according to the deviation. The reverse response correction signal F _cH increases the water supply amount and reduces the fuel supply amount, respectively.
In addition, when the steam-water separator temperature H _A is lower than the set signal H _S , the above-mentioned correction signals W _cH and F _cH are processed proportionally and integrally according to the deviation to reduce the water supply amount and fuel supply, respectively. By increasing the amount, the steam pressure is maintained at a predetermined value without causing an adverse response phenomenon to steam pressure fluctuations.

Therefore, according to this embodiment, it is possible to prevent the reverse response phenomenon that occurs in the once-through operation mode close to the recirculation operation mode, and it is possible to perform stable steam pressure control. .

FIG. 4 shows a control block system diagram of another embodiment of the present invention. Components in FIG. 4 denoted by the same reference numerals as those in the conventional example shown in FIG. 1 or the embodiment shown in FIG.

The difference between the embodiment shown in FIG. 4 and the embodiment shown in FIG. 3 is that the steam pressure and temperature are controlled by a common control method without changing the correction signal depending on the operating mode of the boiler. There is a particular thing.

That is, as shown in FIG. 4, a control circuit for correcting the fuel supply amount based on the steam temperature is not provided. The steam/water separator temperature deviation signal Pc ₁ output from the proportional integral element 16D and the proportional integral element 1
An addition element 19D adds the steam pressure deviation signal PC ₁ output from 6A to the steam pressure deviation signal PC ₂ proportionally processed by a proportional element 24D, and from this addition element 19D, a fuel correction signal Fc is added.
is being output. A load request signal D is inputted to the function generating element 13F, and a fuel supply amount advance value signal F _D corresponding to the load request amount is outputted from the function generating element 13F. The addition element 19B adds the input fuel supply amount advance value signal F _D and the fuel correction signal Fc and outputs the fuel supply amount target value signal F _T. Further, a steam/water separator temperature deviation signal Hc ₂ obtained by proportionally processing the steam/water separator temperature deviation signal Hc ₁ outputted from the proportional integral element 16D by the proportional element 24C is input to the subtraction element 14D.

Since it is configured in this way, the fuel supply amount advance value signal is set so that the fuel supply amount increases as the steam pressure decreases or the steam water separator temperature decreases.
A fuel supply amount target value signal is obtained by adding the steam pressure deviation signal Pc ₂ and the steam water separator temperature deviation signal HC ₁ to F _D.
Outputting F _T. In addition, the steam pressure deviation signal is added to the water supply amount advance value signal W _F so that the water supply amount increases when the steam pressure decreases or the steam water separator temperature increases.
Pc ₁ and the steam/water separator temperature deviation signal Hc ₂ are added to output the water supply amount target value signal W _T.

The steam temperature control in this embodiment is mainly performed by controlling the temperature of the steam-water separator, and the steam temperature can be controlled by controlling the amount of water injected through the superheater water injection line 12 as necessary. Since the fuel supply amount can be controlled, the fuel supply amount is not particularly corrected based on the steam temperature, but even if the necessary circuit is added, the overall configuration can be made simpler than the previous embodiment. .

Therefore, according to this embodiment, in addition to the effects of the previous embodiments, there is an effect that the structure can be simplified.

As explained above, according to the present invention, when the internal fluid (steam) temperature at the outlet of the furnace water wall is higher than the set temperature, the water supply amount is increased and the fuel supply amount is reduced depending on the deviation. In addition, if it is lower than the set value, the water supply amount is reduced depending on the deviation, while the fuel supply amount is increased, so the steam pressure decreases and the water supply amount decreases during once-through operation before and after switching. For example, when the internal fluid temperature is low, the steam pressure tends to decrease because there is no margin in the furnace heat absorption amount, but the increased water supply amount is corrected and the fuel Since the steam pressure is increased, a drop in steam pressure can be prevented. Further, when the internal fluid temperature is high, there is a margin in the amount of heat absorbed by the furnace, so a correction opposite to the above effect is performed within the margin. As a result, it is possible to prevent the occurrence of a reverse response phenomenon in steam pressure control that occurs when switching between once-through operation and recirculation operation, and to achieve stable steam pressure control.

[Brief explanation of drawings]

Fig. 1 is a steam system diagram showing an example of a variable pressure once-through boiler, Fig. 2 is a control block system diagram of a conventional example, and Fig. 3 is a control block system diagram of an embodiment of the present invention.
FIG. 4 is a control block system diagram of another embodiment of the present invention. 6... Steam water separator, 13A-F... Function generation element, 14A-D... Subtraction element, 15... Steam pressure detection end, 16A-D... Proportional integral element, 17A-
B... Signal switching element, 19A-D... Addition element,
22...Steam temperature detection end, 23...Steam water separator temperature detection end.

Claims (1)

[Scope of Claims] 1. The water supply to the boiler is determined based on the water supply amount advance value and the fuel supply amount advance value, which are respectively determined according to the load requirement of the boiler in which the switching operation between the once-through operation and the recirculation operation is performed. During once-through operation, the steam pressure set value determined according to the load requirement and the detected steam pressure value are compared, and if the detected steam pressure value is high, the control is performed according to the deviation. When the amount of water supplied is low, the preceding value of the amount of water supplied is corrected to be reduced, and when it is low, the preceding value of the amount of water supplied is corrected to be increased according to the deviation.During recirculation operation, the amount of water supplied is made according to the deviation of the steam pressure. Correction of the preceding value is stopped, and when the steam pressure detected value is high, the fuel supply amount preceding value is corrected to be reduced according to the deviation, while when it is low, the fuel supply amount preceding value is reduced according to the deviation. A control device for a variable pressure once-through boiler comprising means for making a correction to increase a value, which detects an internal fluid temperature between the furnace water wall outlet and a primary superheater of the boiler, and compares the internal fluid detected temperature and the load. Comparison with an internal fluid temperature set value predetermined according to the requested amount, and when the detected internal fluid temperature is high, the correction increases the water supply amount advance value and reduces the fuel supply amount advance value according to the deviation. Control of a variable pressure once-through boiler, characterized in that, when the internal fluid temperature is low, correction means is provided for reducing the water supply amount advance value and increasing the fuel supply amount advance value according to the deviation. Device.