JP3005083B2 - Recirculation flow control method in once-through boiler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a recirculation flow rate in a once-through boiler requiring a quick load follow-up property, such as a vertical pipe transformer Benson boiler having a recirculation line, and particularly to a brackish water separator. The present invention relates to a recirculation flow rate control method suitable for reducing fluctuations in the water storage tank level.

[0002]

2. Description of the Related Art A conventional once-through boiler is shown in FIG.
Shown in In the circulating operation region before the boiler 8 enters the once-through operation region, for example, when the load is rising, the brackish water mixed fluid discharged from the boiler 8 is separated by the steam separator 1, and the drain is stored in the water storage tank 2 of the steam separator 1. Is recirculated by the recirculation pump 5. Water storage tank 2 of brackish water separator 1
When the tank level is very high, the drain collected in the tank 4 flows to the condenser 4 by the level control valve 3 of the water storage tank 2 of the steam separator 1, but in an ordinary case, the drain is recirculated to an appropriate level. Is maintained. At this time, in the conventional boiler apparatus, as shown in FIG. 7, recirculation is performed from the water tank level signal 14 of the steam separator.
In this method, the flow rate is set, and the recirculation flow rate is controlled based on the recirculation flow rate signal 10 . However, in the prior art, when the water storage tank level of the brackish water separator fluctuates, there is a problem that the recirculation flow rate fluctuates and the temperature of the inlet of the economizer fluctuates, so that it takes a long time to stabilize the recirculation system. In particular,
In once-through boilers such as Benson boilers using vertical tubes,
The storage tank level of the brackish water separator was sensitive to the main steam pressure, so the storage tank level was liable to fluctuate, and no consideration was given to the fluctuations in the recirculation flow rate that would make the recirculation system unstable. In addition, as a prior art regarding the control method of the recirculation flow rate in the Benson boiler,
For example, JP-B-63-55601, JP-B1-35
242 publication.

[0003]

In the above-mentioned prior art, consideration is given to fluctuations in the water storage tank level of the steam separator in the circulating operation region of a once-through boiler requiring a fast load follow-up property such as a vertical tube transformer Benson boiler. The recirculation flow rate fluctuated with the fluctuations in the water storage tank level, which also fluctuated the inlet temperature of the economizer and the main steam pressure. There was a problem of instability. In particular, in a Benson boiler using a vertical pipe, the storage tank level of the steam separator is easily affected by the main steam pressure, so the storage tank level fluctuates significantly, and the recirculation system of the boiler is unstable due to fluctuations in the recirculation flow rate. There was a problem.

An object of the present invention is to reduce the fluctuation of the water storage tank level of the steam separator in the once-through boiler such as the above-mentioned conventional Benson boiler, suppress the fluctuation of the recirculation flow rate, and shorten the recirculation system of the boiler in a short time. An object of the present invention is to provide a recirculation flow control method for a once-through boiler that can be stabilized and has excellent load following ability.

[0005]

In order to achieve the object of the present invention, the recirculation flow rate at which the water tank level of the steam separator is stabilized in accordance with the boiler input is set, and the recirculation flow rate is set based on the water tank level of the steam separator. Than the recirculation flow setting control
The priority is given to the control by the recirculation flow rate set according to the boiler input. The present invention provides a brackish water separator,
In a recirculation flow control method for a once-through boiler including at least a pump that recirculates a water tank of a brackish water separator and a drain separated by the brackish water separator through the water storage tank, a recirculation set according to a boiler input The flow rate set value is compared with the recirculation flow rate set value set from the water storage tank level of the steam separator, and the smaller set value is selected, and the recirculation flow rate is controlled based on the set value. . Then, specifically, the smaller the recirculation flow set value compared with the recirculation flow set value set according to the boiler input and the recirculation flow set value set from the water storage tank level of the steam separator. A method for controlling a recirculation flow rate in a once-through boiler provided with a means for determining a deviation of the recirculation flow rate as a reference and controlling the recirculation flow rate through proportional and integral operations.

[0006]

According to the boiler input (demand signal), there is always an optimal recirculation flow rate at which the water tank level of the steam separator is stabilized. For the boiler input, the above-mentioned optimum recirculation flow rate is given as a set value, and the set value is compared with a set value from the water storage tank level of the steam separator to select a smaller set value. At this time, the set value of the recirculation flow rate from the storage tank level of the steam separator is set larger than the set value from the boiler input when the level is stable , so that the recirculation flow rate is set to the boiler input when the level is stable. Settings from
A value, that is, a stable operation region is set. By doing so, the fluctuation of the water storage tank level of the brackish water separator is reduced, and the time required for the water storage tank level to stabilize is shortened without the response operation of the control system diverging. If the water tank level of the brackish water separator drops sharply, the recirculation flow rate from the water tank level of the brackish water separator is prioritized and the recirculation flow rate is reduced. The trip of the circulation pump can be prevented beforehand.

[0007]

Embodiments of the present invention will be described below in more detail with reference to the drawings. FIG. 6 is a system diagram showing a configuration of a conventional Benson boiler. In the figure, a brackish water mixed fluid discharged from a boiler 8 is separated into water and steam by a brackish water separator 1, and water (drain) is recirculated by a recirculation pump 5 through a water storage tank 2 of the brackish water separator 1. You. At this time, water equivalent to steam that has come out of the boiler 8 as steam is supplied by the water supply pump 7. FIG. 1 shows an embodiment of the present invention in a boiler 8 having such a system, and in a boiler 8 configured by a vertical tube as a water cooling wall. Differs from relative the prior art, by adding a function generator (2) 17 for setting whether we recirculation flow boiler input signal (demand signal) 18, or the water tank level signal 14
From function generator (1) 15 that sets recirculation flow rate from
Signal and the lower one of the signal from the function generator (2) 17
And add a low selector 16 to output to the subtractor 11
I just did it. A case where the method for controlling the recirculation flow rate in the present embodiment is applied to an actual machine will be described. For example,
The boiler input is 350MW from the operation data in the actual machine,
An example of the operation of a Benson boiler having an evaporation amount of 1050 t / h will be described. The recirculation flow rate for the boiler input near 85 MW where the boiler load is 25% is 191 t / h from FIG. 4 (FG2), and at this time, the water storage tank level of the steam separator becomes stable at around 10 m. From FIG. 3 (FG1), the recirculation flow rate set for the water tank level 10m of the brackish water separator is 353 t / h, so that the recirculation flow rate from FIG. Selected. FIG. 8 is a view similar to FIG.
Fig. 9 shows fluctuations in the water storage tank level of the steam separator when controlled only by the setting of the recirculation flow rate shown in (FG1). As shown in the figure, when the storage tank level of the brackish water separator fluctuates greatly, the recirculation flow rate also fluctuates, and the fluctuation of the circulation flow rate also causes a large change in the temperature of the inlet of the economizer and the main steam pressure changes. In the case of a Benson boiler using a vertical pipe, the recirculation system becomes extremely unstable because the level of the storage tank of the steam separator changes when the main steam pressure changes. FIG.
FIG. 9 shows the relationship between the fluctuation of the water storage tank level and the recirculation flow rate when the recirculation flow rate control method of the present invention is added with the setting of the recirculation flow rate for the boiler input signal shown in FIG. Is extremely stable. Then, when the water storage tank level of the steam separator becomes stable, the flow rate is switched to the conventional recirculation flow rate shown in FIG. 3 (FG1), and the stable operation of the boiler is continued. An adder can be used instead of the low selector 16 shown in FIG. 2 used in the above embodiment. in this way,
The set value of the recirculation flow rate corresponding to the boiler load (input)
Good control can be achieved because a correction is made by the deviation from the set value of the recirculation flow rate from the water tank level of the steam separator. However, in this case, for example, the set value of the recirculation flow rate on the storage tank level side A of the steam separator is multiplied by a coefficient of 0.4, and the boiler input signal side B is multiplied by a weight of 0.8 or the like. It is desirable to adjust the coefficient. In the above embodiment, when the recirculation flow rate control method of the present invention is used, the time required for the storage tank level of the steam separator to stabilize is reduced to about 60 to 70 minutes, whereas the conventional FIG. In the case of the control using only (FG1), it took more than 120 minutes for the water storage tank level to stabilize, and it was found that the circulating flow control method of the present invention was excellent.

[0008]

As described above in detail, according to the method for controlling the recirculation flow rate in the once-through boiler of the present invention, the recirculation of the water storage tank level of the steam separator is stabilized in response to the boiler input signal (demand signal). By adding the flow rate, fluctuations in the water storage tank level can be suppressed early, and the stabilization time of the water tank level recirculation system can be significantly reduced when the load on the boiler rises rapidly or when the load drops. For example, in the prior art, the time required for stabilization in the recirculation operation region of the boiler was 120 minutes or longer, but according to the method of the present invention, it can be reduced to about 70 minutes, Significant benefits can be obtained.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an example of a recirculation flow control system of the present invention.

FIG. 2 is a system diagram showing a recirculation flow rate control method exemplified in an embodiment of the present invention.

FIG. 3 is a graph showing a relationship between a water storage tank level of a brackish water separator and a set value of a recirculation flow rate.

FIG. 4 is a graph showing a relationship between a boiler input signal (demand signal) and a set value of a recirculation flow rate.

FIG. 5 is a graph showing the fluctuation of the water storage tank level of the brackish water separator exemplified in the embodiment of the present invention.

FIG. 6 is a system diagram showing a brackish water recirculation system to which the present invention can be applied in a conventional once-through boiler.

FIG. 7 is a system diagram showing a conventional recirculation flow control method.

FIG. 8 is a graph showing a change in a water storage tank level of a conventional brackish water separator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Steam separator 2 ... Water storage tank 3 ... Water storage tank level control valve 4 ... Condenser 5 ... Recirculation pump 6 ... Recirculation flow control valve 7 ... Water supply pump 8 ... Boiler 9 ... Superheater 10 ... Recirculation flow signal 11 ... Subtractor 12 Proportional integrator 13 Recirculation flow control valve 14 Reservoir tank level signal 15 Function generator (1) 16 Low selector 17 Function generator (2) 18 Boiler input signal 19 Reservoir tank Level 20: Recirculation flow

──────────────────────────────────────────────────続 き Continuation of the front page (56) References Japanese Utility Model Sho-58-175308 (JP, U) Japanese Utility Model Hei 1-136202 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) F22D 5/26 F22B 35/00

Claims (2)

(57) [Claims] 1. A method for controlling a recirculation flow rate in a once-through boiler including at least a steam separator, a water storage tank of the steam separator, and a pump for recirculating a drain separated by the steam separator through the water storage tank. The recirculation flow set value set according to the input is compared with the recirculation flow set value set from the water tank level of the steam separator, and the smaller set value is selected to control the recirculation flow. A method for controlling the recirculation flow rate in a once-through boiler. 2. A system according to claim 1, further comprising means for determining a deviation of the recirculation flow based on a smaller recirculation flow set value, and controlling the recirculation flow through a proportional and integral operation. Recirculation flow control method in once-through boiler.