JP2880558B2 - Control method of once-through boiler and control device of once-through boiler - Google Patents

Description

The present invention relates to a control method and a control device for a once-through boiler having a recirculation system, and particularly to a control method for a boiler even in an abnormal situation where the use of a boiler recirculation system becomes impossible. The present invention relates to a once-through boiler control method and control apparatus having a recirculation system capable of starting and stopping.

[Conventional technology]

FIG. 5 shows a startup bypass system of a variable-pressure Benson boiler as an example of a once-through boiler having an evaporator, a superheater, and a boiler recirculation system.

The feed water supplied from the boiler feed pump is preheated by the economizer 2 to obtain a large amount of heat at the furnace water wall 3 and flows into the steam separator 4. In the steam-water separator 4, the steam is separated into saturated steam and saturated water according to the dryness (steam content) of the inflowing fluid, and the saturated steam is sent to the primary superheater 9, the secondary superheater 11, and the tertiary superheater 13. After being sequentially guided, heated, and turned into superheated steam, the steam flows into the steam turbine 14 where work is performed, and then the steam is condensed.
After being led to 16 and condensed, it is heated by a feed water heater and then sent to a boiler feed pump. On the other hand, the saturated water separated by the steam separator 4 is stored in the water storage tank 5, and the flow thereof is controlled by the boiler recirculation pump 6 and the boiler recirculation flow rate control valve 7, and rejoins the inlet of the economizer 2. To recover heat. The can water blow valve 8 is used for controlling the water level of the water storage tank 5 and blows the drain having a specified water level or higher. This blow water enters the condenser 16 and merges with the one coming from the turbine.

Regarding the operation control, Fig. 4 (a), (b), (c)
As shown in the characteristic diagram of FIG. 5, the steam flow rate (flow rate at point A in FIG. 5) flowing into the turbine 14 after the load operation at the start-up becomes a characteristic that increases in proportion to the load (( A) A
Line) is the flow rate of the point C of the fluid flow rate (FIG. 5 that passes through the furnace water wall 3) The following load a% that considers the furnace waterwall flow properties, so that substantially constant prescribed rate alpha ₁ Is controlled by a circulation operation of circulating water from the water storage tank 5 using a recirculation circuit. However, in general, the specified flow rate α
₁ is controlled by the total value of the flow rate of the furnace water wall 3 and the flow rate of the water injected into the heater spray system 15, and as a result, the flow rate of the furnace water wall 3 is reduced by the characteristic curve C shown in FIG.
The characteristics shown in FIG. Here, the fluid flowing into the steam-water separator 4 at the load a% becomes all saturated steam on balance, and the drain amount falling from the steam-water separator 4 to the water storage tank 5 becomes 0. At a load higher than this, the water storage tank 5 and the boiler recirculate. There is no saturated water (flow rate at point D in FIG. 5) recirculating in the recirculation path including the pump 6, and all the saturated steam that has exited the furnace water wall flows into the primary superheater 9 via the steam separator 4. That is, the flow-through operation is performed (the D line in (c) of FIG. 4).

Conventionally, a control circuit as shown in FIG. 3 has been used to perform such an operation.

That is, basically, the difference between the boiler input command signal 110 and the furnace feed water flow rate signal 112 is subtracted so that the flow rate passing through the furnace water wall 3 becomes a flow rate according to the boiler input request.
At 114, feed water master command signal through PI controller 115
It is 116, and the feed water pump discharge flow rate is adjusted.

However, as described above, in order to prevent the flow rate through the furnace water wall 3 from falling below a specified value at a low load, the signal generator 10 is used.
A signal corresponding to α ₁ % = x ₁ % + y% is generated by the adders 109, 106 and the adder 109, and the higher one of the signal and the boiler input command signal 110 is selected by the high selector 111.

The total value of the above-mentioned furnace passing water supply flow rate and the superheater spray flow rate is set to α by adding the superheater spray flow rate signal 101 to the furnace passing water supply flow rate signal 112 by the adder 113.
Although characteristic of controlling the _1% is obtained, since the superheater spray flow rate to prevent the furnace passing feed water flow becomes transitionally excessive drops unexpectedly, superheater spray flow rate signal 10
1 and y% equivalent to higher a fixed value signal (output of the signal generator 102) to select a high selector 105, an adder and a signal from the signal and x _1% is equivalent signal generator 106 It is configured to add by 109.

With such a configuration, by appropriately determining x ₁ and y under the condition of α ₁ % = x ₁ % + y%, the superheater spray flow becomes unexpectedly large, and if y% is exceeded, a high selection is made. In the heater 105, the superheater spray flow signal 101 side is selected.In that case, the superheater spray flow signal is eventually added to both the measurement signal side and the set value side of the furnace passing water supply flow rate. feedwater flow is controlled so as not turn down _1% x.

This is taken into account in normal startup, but the story is different in startup when the boiler recirculation system cannot be used.

When fuel is supplied to the boiler furnace from the burner and burned, the boiler water flowing inside the furnace water wall at the time of full boiler load is used to prevent the heat transfer tubes on the furnace water wall that is most strongly heated from being excessively overheated. In order to secure the flow of boiler water regardless of the boiler load, the once-through boiler is provided with the above-mentioned recirculation circuit. During operation, recirculation circuits have been used. In this way, two recirculation pumps, which are the main equipment of the important recirculation circuit, were installed, including the spare unit. However, the installation of the spare unit was stopped. Instead, the recirculation pump failed or the recirculation flow rate was adjusted. When a valve fails, it is necessary to start and stop the boiler without using a recirculation circuit.

In other words, when the boiler recirculation system cannot be used, heat recovery using the boiler recirculation system cannot be performed.
The water supply temperature to the water is as low as 50 to 70 ° C with a low load, which is significantly lower than when heat recovery is performed (about 250 ° C depending on the operating conditions).

Problems in such a situation are as follows: (1) Degree of dryness of fluid to steam separator 4 (steam content)
Is hard to rise, and as a result, steam is hardly generated.

(2) As a solution to (1), it is conceivable to increase the fuel flow rate. However, as a result of an increase in the combustion gas temperature and flow rate, as a side effect in this case, the steam of the superheater or reheater provided in the downstream region of the boiler furnace has Temperature rises excessively, etc.

As a countermeasure against this, it is effective to operate the system with the flow rate of the supplied water passing through the furnace water wall 3 as small as possible in order to easily generate steam as much as possible.

However, as shown in FIG. 3, in the conventional control circuit, the set value of the feedwater flow rate passing through the furnace water wall 3 is predetermined to a value suitable for the normal start-up method, and is suitable when the boiler recirculation system is not used. As described above, it is impossible to cope with the above operation in which the flow rate of the supplied water is made as small as possible.

[Problems to be solved by the invention]

As described above, the prior art described above has a problem in that no consideration is given to the control circuit for performing low-range operation of the flow rate through the furnace water wall, which is suitable when the boiler recirculation system is not used.

SUMMARY OF THE INVENTION An object of the present invention is to correct the above problem, and to provide a control method and a control device for a once-through boiler which, when the boiler recirculation system is not used, senses the condition and automatically shifts to a furnace water wall passage flow reduction operation. To provide.

[Means for solving the problem]

The above purpose is for starting or stopping the boiler,
The boiler feed water is heated by the economizer and the furnace water wall, the heated furnace water wall outlet fluid is separated into steam and water by a steam separator, the steam is supplied to a superheater and heated, and the water is The boiler recirculation system cannot be used in a once-through boiler control method in which water is stored in the water storage tank and then recirculated to the furnace water wall through a recirculation system including a boiler recirculation pump and a boiler recirculation flow rate control valve. In the event of an abnormality, the furnace water wall portion heat transfer tube temperature is normal, and the furnace water wall portion passing water supply amount is reduced from that during normal operation, and recirculated to the furnace water wall portion through the steam separator. A method of controlling a once-through boiler, wherein circulating water is recirculated from the upstream side of the boiler recirculation pump to the furnace water wall through a condensing system, and a furnace for starting or stopping the boiler Water wall exit In a once-through boiler control device that recirculates water in the fluid to the furnace water wall through a boiler recirculation system including a boiler recirculation pump and a boiler recirculation flow control valve, the boiler is being started and stopped. A logic circuit that outputs a signal indicating that the furnace water wall passage water supply amount reduction condition is satisfied on condition that the boiler recirculation system is unusable and that there is no abnormality in the furnace water wall metal temperature; and Means for setting the set value of the amount of water supplied to the furnace water wall portion to a value lower than the normal value by an output signal.

[Action]

Performs a logic operation on the condition that the boiler recirculation system is not abnormal and the furnace water wall temperature is not abnormal, and if the condition is satisfied, automatically switches the furnace passage feedwater flow rate set value selection switch in the furnace passage feedwater flow control system from the normal side to the reduction side. Switch to furnace low flow rate operation. As a result, even when the boiler recirculation system, in which it is difficult to check the evaporation amount, is not used, it is possible to make the evaporation amount relatively easy to obtain as a boiler balance. It can be made stoppable. Alternatively, it can be started / stopped stably.

Further, the circulation / through flow switching load changing mechanism also changes the setting by the changeover switch when the condition of the logic operation is satisfied. Thereby, it is possible to accurately detect the transition of the control mode in which the control method is largely different between the circulation operation and the once-through operation of the boiler, and to realize a stable start-stop.

〔Example〕

In the embodiment of the present invention, the hardware configuration of the boiler main body is almost the same as that shown in FIG. 5 of the prior art, except for one point. After leaving, it enters the steam separator, the separated water enters the water storage tank, passes through the still water blow valve 8 to the condenser 16, from where it is circulated to the boiler's economizer 2 via the feedwater pump.

 The operation method is shown in (d), (e), and (f) of FIG.

As shown in FIG. 4 (F), the flow rate at point D, which is the outlet point of the boiler recirculation pump 6, is 0 because the boiler recirculation system is not used. As shown in FIG. 4 (d), the point A at the turbine inlet and the point B at the inlet of the primary superheater in FIG.
The flow rates indicated by A and B indicating the flow rates at the points are the same as those in the normal operation.

It should be noted that the flow rate of the feed water passing through the furnace water wall 3 is set at a value lower than that during normal operation (indicated by a dashed line) as shown by the characteristic line C in FIG. This is a characteristic (shown by a broken line) that is constant (α ₂ ) regardless of the increase or decrease of the spray flow rate. Here, the hatched portion 57 in the figure is the difference between the normal circulation operation and the low frequency setting in the present invention,
γ indicates that the switching load between the circulation operation and the once-through operation is shifted to a lower load side as compared with the normal operation by reducing the flow rate of the feedwater passing through the furnace.

In order to perform such an operation, the control circuit shown in FIGS. 1 and 2 is used in the present invention.

The difference between the prior art and the control circuit is that in FIG.
The addition of signal generators indicated by 3, 107 and 120, the addition of changeover switches indicated by reference numerals 104, 108 and 124, the addition of a subtractor 121, and the addition of a logic operation circuit shown in FIG. It was done.

In FIG. 1, a series of calculation methods using a superheater spray flow rate signal 101 and a furnace passing feed water flow rate signal 112 to obtain a feed water pump flow rate command 116 are similar to those described in the description of the control circuit according to the prior art. It is.

FIG. 2 shows an embodiment of a logic control circuit for satisfying the condition for reducing the flow rate of feed water through the furnace.

(B) Boiler recirculation system error (130) The system is unusable due to an abnormality (130), and (b) the boiler is starting and stopping (13)
1) (meaning that the boiler is starting, stopping, or about to start or stop in the future), and (c) the AND condition is satisfied when there is no abnormality in the water wall pipe metal temperature relationship. Let it. Therefore, the AND condition of (a) and (b) is taken by the AND circuit 134, and the signal is further taken by the AND circuit 137.

Regarding the condition (c), attention is paid to the presence or absence of an abnormality in the water wall metal temperature, and the flow rate reduction operation is not performed in an abnormal state.

Therefore, in the specific circuit for the condition (c), (e)
OR circuit 13 under the condition that none of the conditions of the water wall metal temperature is higher than the specified value (132) or (f) abnormal unbalance (133) occurs in the water wall metal temperature distribution
The signal is obtained by taking the result in step 5 and taking the negation in the NOT circuit 136.

The changeover switch 104 in FIG. 1 is switched by the furnace passage water supply flow rate reduction command when the furnace passage water supply flow rate reduction condition calculated by the logic operation circuit of FIG. 2 is satisfied.
Since the signal generator 103 which outputs the 0% signal is selected, the high selector 105 becomes meaningless and the superheater spray flow signal 101 is selected.
Is added to the set value side signal of the present feedback control system as long as the load is not high enough to select the boiler input command signal side 110 by the high selector 111, that is, during the boiler circulation operation.

On the other hand, the superheater spray flow rate signal 101 is also added to the process signal 112 side of the present feedback control system by the adder 113, and these set value signal and process signal are
Since the subtraction is performed by the subtractor 114, the component of the superheater spray flow rate signal 101 is deducted 0 as a result, and has no meaning on the control circuit.

Therefore, when the furnace feed water flow rate reduction condition is satisfied, the circuit means that the furnace feed water flow is simply controlled to a constant value X ₂ % regardless of the increase or decrease of the superheater spray flow rate signal 101 during the boiler circulation operation. As a result, the flow rate of the feed water passing through the furnace becomes constant on the static characteristics (the boiler input command signal is small in this case and is not selected by the high selector 111).

Further, the changeover switch 108 is switched by the furnace passing through the feed water flow rate reduction condition is _{satisfied, x 2% (<x 1} %) consisting furnace passing minimum water flow rate setting signal is selected, x _2% <x _1% because, at the time of startup During the boiler circulation operation (operation in which boiler water separated by the steam separator 4 enters the condenser 16 via the water storage tank 5 and the still water blow valve 8 and is circulated from the condenser 16 to the boiler.
Recirculation pump 6, differs from the boiler recirculation operation to circulate the boiler recirculation flow rate control valve 7), the normal start-stop time of the feed water flow rate set value (x _1%) lower than the setting value (x _2%) Be driven.

Therefore, as a result, the flow rate through the furnace becomes C in FIG.
The flow rate corresponding to the hatched portion is reduced as compared with the flow rate characteristic line according to the related art, which contributes to the increase in the amount of evaporation which is the object of the present invention.

Furthermore, since the flow rate of the feed water through the furnace has been reduced, the boiler water in the heat transfer tubes has become saturated steam at the outlet of the furnace water wall,
The water separated by the steam separator is circulated through the still water blow valve 8 to the condenser for the turbine. From the circulation operation to the once-through operation (all the water passing through the furnace water wall 3 becomes saturated steam and the steam-water separator 4 The operation mode switching load (wet / dry mode switching load) to the entire superheater 9 after the operation is lower than usual, but in order to cope with the shift of the switching load point, the flow rate of the feed water through the furnace is reduced. First due to satisfaction of condition
The changeover switch 124 in the figure is switched, and the signal of γ%> 0 is added to the generator output signal 118 by the adder 121, and this signal is monitored by the high / low monitors 122 and 123, so that the wet / dry state is obtained. The mode switching load is detected with a load lower than usual. In the high / low monitor, a switch is switched and monitored depending on whether a certain set value is large or small. Γ for generator output
Since the value added by% and the reference set value are compared, the switching is performed at a load where the actual generator output is γ% lower than that in the normal boiler recirculation operation.

During the furnace water wall passing water supply reduction operation, when the furnace water wall heat transfer tube temperature rises above a predetermined value, the furnace water wall passing water supply amount is restored to the value at the time of normal operation. Is preferred.

〔The invention's effect〕

According to the present invention, even in a situation where the boiler recirculation system of the once-through boiler cannot be used, this is detected, and the setting of the water supply flow rate to the boiler is automatically set to an appropriate value, and the stable start-up is performed. And operation such as stopping.
Therefore, the recirculation pump does not need to be provided with a spare machine as in the conventional case.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a once-through boiler control device according to the present invention,
FIG. 2 is a diagram of an embodiment of a logic control circuit of a once-through boiler control device according to the present invention, FIG. 3 is a system diagram of a control device of a once-through boiler according to the prior art, and FIG. FIG. 5 is a system diagram of a once-through boiler having a boiler recirculation system. 1 Start-up bypass system 2 ... Economizer 3 ... Furnace water wall 4 ... Steam separator 5 ... Water storage tank 6 ... Boiler recirculation pump 7 ... Boiler recirculation flow Control valve, 8 ...
... Canned water blow valve, 9 ... Primary superheater, 10 ... First stage superheater spray, 11 ... Secondary superheater, 12 ... Second stage superheater spray, 13 ... Tertiary superheater, 14 ... … Steam turbine, 16…
... condenser.

Claims (4)

(57) [Claims] When a boiler is started or stopped, boiler feed water is heated by a economizer and a furnace water wall, and the heated furnace water wall outlet fluid is separated into steam and water by a steam-water separator. The steam is supplied to the superheater to be heated, and the water is stored in the water storage tank and then recirculated to the furnace water wall through a recirculation system including a boiler recirculation pump and a boiler recirculation flow control valve. In the boiler control method, when the boiler recirculation system cannot be used, the amount of water passing through the furnace water wall is reduced from that during normal operation on condition that the temperature of the heat transfer tube of the furnace water wall is normal. A once-through boiler, characterized in that circulating water that is recirculated to the furnace water wall via a water separator is recirculated from the upstream side of the boiler recirculation pump to the furnace water wall via a condensing system. Control method. 2. The once-through flow according to claim 1, wherein when the temperature of the heat transfer pipe of the furnace water wall rises above a predetermined value, the amount of water supplied through the furnace water wall is restored to a value during normal operation. Boiler control method. 3. The water in the furnace water wall outlet fluid is recirculated to the furnace water wall through a boiler recirculation system including a boiler recirculation pump and a boiler recirculation flow rate control valve when the boiler is started or stopped. In the once-through boiler control device, the boiler is being started and stopped, the boiler recirculation system is unusable, and the furnace water wall metal temperature does not have any abnormality. A once-through boiler, comprising: a logic circuit that outputs a signal indicating that a water supply amount reduction condition is satisfied; and a unit that sets a set value of the water supply amount passing through a furnace water wall to a value lower than a normal time based on an output signal of the logic circuit. Control device. 4. The apparatus according to claim 3, further comprising means for changing a setting of an operation mode switching load from circulating operation to once-through operation on condition that a condition of a logic operation in said logic circuit is satisfied. Control device for once-through boiler.