JPH0210328B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drum water level control device for cooperatively controlling the water level of each drum in a boiler equipped with two or more drums.

FIG. 1 shows the configuration of a water supply and steam piping system for a boiler having two air-water drums connected in series, and a conventional drum water level control device. The boiler 1 has a low-pressure air-water drum (hereinafter referred to as low-pressure drum) 2 and a high-pressure air-water drum (hereinafter referred to as
(high pressure drum) 3.

First, the water supply system and evaporation system will be explained. Low-pressure feed water F _l is supplied from a condenser (not shown) and guided to a low-pressure energy saver 6 via a low-pressure drum water level control valve 4 and a low-pressure feed water flow rate detector 5 . Next, the feed water _Fl is heated by the low pressure economizer 6 and sent to the low pressure drum 2. The low-pressure drum 2 separates low-pressure steam S _l generated by the low-pressure vaporizer 7 from water to water. Then low pressure steam S _l
passes through the low-pressure steam flow rate detector 8 to a turbine (not shown), where it does work.

On the other hand, the high-pressure drum 3 receives high-pressure water supply F _h from the low-pressure drum 2 through a high-pressure drum water level control valve 9, a high-pressure water supply flow rate detector 10, and a high-pressure energy saver 11. The obtained high-pressure feed water F _h is turned into steam by the high-pressure vaporizer 12, and is separated into steam and water by the high-pressure drum 3. The separated high-pressure steam S _h is sent to a turbine (not shown) through a high-pressure superheater 13 and a high-pressure steam flow rate detector 14 to perform work.

Next, a conventional drum water level control device will be explained. Conventionally, the water level control of each drum 2, 3 was performed independently for each drum 2, 3. That is, as shown in FIG. 1, a low pressure side water level control device 16 that controls the water level of the low pressure drum 2 and a high pressure side water level control device 18 that controls the water level of the high pressure drum 3 are provided. The low-pressure side water level control device 16 uses the low-pressure drum water level set value M _l as a reference, and detects the low-pressure drum water level detected by the low-pressure drum water level detector 15, the low-pressure feed water flow rate detected by the low-pressure feed water flow rate detector 5, and the low-pressure steam flow rate detector. 8
Using the detected low-pressure steam flow rate value as a detection input signal, the opening control of the low-pressure drum water level control valve 4 is performed by making advance correction for water level fluctuations so that the water level of the low-pressure drum 2 becomes equal to the set value _Ml . By doing this, the drum water level is kept constant.
Similarly, the high-pressure side water level control device 18 uses the high-pressure drum water level set value M _h as a reference, and detects the high-pressure drum water level detected by the high-pressure drum water level detector 17, the high-pressure steam flow rate detected by the high-pressure water supply flow rate detector 10, and the high-pressure steam Using the high-pressure steam flow rate detected by the flow rate detector 14 as a detection input signal, the low-pressure drum water level control valve 4 is adjusted by making advance correction for water level fluctuations so that the water level of the high-pressure drum 3 becomes equal to its set value M _h . The drum water level is kept constant by controlling the opening.

The problem that arises from controlling the water level individually for each boiler, as in the conventional water level control device described above, is that if the water level of one or both of the two drums fluctuates abnormally, it is difficult to avoid the abnormal situation. This is difficult and requires a lot of time to return to normal conditions.

In other words, the water level of each drum 2 and 3 is the set value.
If M _l and M _h are close to each other, no control problem will occur. However, for example, suppose that the water level of the high-pressure drum 3 is around the set value M _h , but the water level of the low-pressure drum 2 becomes abnormally high. At this time, the opening degree of the low-pressure drum water level control valve 4 is throttled by the low-pressure side water level control device 16, and the inflow water supply amount F _l to the low-pressure drum 2 is suppressed, but no change occurs in the outflow steam flow rate.
On the other hand, the opening degree of the high-pressure drum water level control valve 9 remains unchanged. This is because the high pressure side water level control device 18 independently controls the water level regardless of the low pressure side. The above embodiment is the same even if the relationship between the low pressure drum 2 and the high pressure drum 3 is reversed. In this way, conventional water level control devices control the low-pressure side and the high-pressure side independently, so even if an abnormality occurs in the water level of one drum, it takes time to return to normal, making it difficult to avoid abnormal conditions. It was difficult.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a drum water level control device that can quickly restore a normal state when an abnormality occurs in the drum water level in one or both of a plurality of drums.

A feature of the present invention is that the deviation value between each drum water level setting value and each drum water level detection value is determined, and based on the deviation value, a control signal is sent to the drum water level control valve of the water level control device individually installed in each drum. The key point is that the water level of each drum can be controlled in a coordinated manner by adding corrections to the system.

Hereinafter, the present invention will be described in detail based on illustrated embodiments. FIG. 2 shows the configuration of the drum water level control device according to the present invention and its relationship with the water supply and steam piping systems. Note that in FIG. 2, the same parts as in FIG. 1 are given the same reference numerals and used in the following explanation.

The drum water level control device according to the invention includes, in addition to the individual water level control devices 16, 18 mentioned above, a first
It includes a comparison calculator 19, a second comparison calculator 20, and a cooperative correction control device.

The first comparator 19 compares the low pressure drum water level detection value L _l from the low pressure drum water level detector 15 with the low pressure drum water level set value M _l , calculates the deviation value D l between both values, and calculates the deviation value D _l between the two values, and the cooperative correction control device Output to 21.

The second comparator 20 compares the low-pressure drum water level detection value L _h from the high-pressure drum water level detector 17 with the high-pressure drum water level set value M _h , calculates a deviation value D h between both values, and calculates the deviation value D _h between the two values. Output to 21.

The cooperative correction control device 21 adjusts each deviation value D _l , D _h ,
and control signals from each water level control device 16, 18
The status of each drum ₂ , 3 is determined based on the V l1 and V _h1 , and the control signals V _l1 and V _h1 are corrected based on the results, and the corrected control signals V _l2 and V _h2 are used to adjust the low pressure drum water level, respectively. The water is sent to the valve 4 and the high-pressure drum water level control valve 9 to adjust the valve opening degree. This cooperative correction control device 21 will be explained in more detail using FIG. 3.

In Fig. 3, each deviation value D _l and D _h is calculated by the adder 2.
2 and the determiner 23 in parallel. Adder 22 calculates the water level setting value for each drum 2, 3.
M _l and the deviation value D _l and M _h and D _h are added. If the absolute values of the added values A _l and A _h exceed certain limit values T _l and T _h (A _l ≧ T _l , A _h ≧ T _h ), that is, the water levels of both drums 2 and 3 are abnormally high. or is low, the alarm 24 outputs an alarm. This state requires abnormal operation of the plant, such as opening the drain valves (not shown) of each drum 2, 3. On the other hand, the absolute value of the addition values A _l and A _h is the limit value T _l ,
If it is less than T _h (A _l < T _l , A _h < T _h ), the additional value
A _l and A _h are sent to the next cooperative arithmetic unit 25 .

The determiner 23 determines the polarity of each deviation value D _l , D _{h ,} that is, whether it is positive or negative, and determines whether each drum water level (L _l , L _h ) is higher than, lower than, or equal to the water level set value M _l , M _h . Make a judgment. This determination result is sent to the next cooperative control calculator 25 as determination signals J _l and J _h .

The cooperative control calculator 25 receives the addition values A _l , A _h and the judgment signals J _l , J _h and predicts the direction of increase or decrease in the water level that will change due to control from the current water level of each drum 2, 3, and makes the prediction. Based on the results, correction signals C _l and _Ch are outputted so that the water level of the drum with an abnormal water level returns to the normal state as soon as possible.

Here, the calculation processing in the cooperative control calculation unit 25 will be explained using FIG. 4. The table shown in Figure 4 shows the water level values L _l and L _h of each drum 2 and 3 and the set values.
This shows the relationship between M _l and M _h , and this relationship can be roughly divided into nine types, a to i. states a and i
, both drums 2 and 3 are in an abnormal state, and the alarm 24 outputs an alarm. state e
, the water levels of both drums 2 and 3 are close to the set value, and good control is being performed. In this state e, the values of the correction signals C _l and _Ch output from the cooperative control calculation circuit 25 are zero, and therefore the control signals from each water level control device 16 and 18
V _l and V _h are applied to each drum water level control valve 16, 18 without any correction.

State c is a state in which the low pressure drum water level L _l is lower than the set value M _l and the high pressure drum water level L _h is higher than the set value M _h . In this state, each control signal V _l1 and V _h1 is not corrected and is output as is as V _l2 and V _h2 . As a result, the low-pressure drum water level control valve 4 is controlled in the open direction, and the high-pressure drum water level control valve 9 is controlled in the closed direction, and the abnormal state of the drum water level is resolved.

State g is a state in which the low pressure drum water level L _l is higher than the set value M _l and the high pressure drum water level L _h is lower than the set value M _h , which is the opposite of state C. In this state, no correction is applied to each control signal V _l1 and V _h1 , and they remain as they are.
Output as V _l1 and V _h2 . As a result, the low pressure drum water level control valve 4 is controlled in the opening direction, and the high pressure drum water level control valve 9 is controlled in the closing direction.

Next, state b is the low pressure drum water level L _l is the set value M _l
However, the high-pressure drum water level L _h is higher than the set value M _h . In this case, the opening degree of the low-pressure drum water level control valve 4 is maintained substantially unchanged, but the high-pressure drum water level control valve 9 is controlled in the closing direction. Through such control, the high pressure drum water level L _h
Since the inflow water supply amount F _h decreases, it will move toward the normal water level, but the low-pressure drum water level L _l is predicted to decrease because the outflow water supply amount decreases. Therefore,
It is necessary to correct the opening degree of the low-pressure drum water level adjustment valve 4 to the opening degree calculated based on the opening degree of the high-pressure drum water level adjustment valve 9. That is, in this case, the low-pressure drum water level control valve 4 is controlled in the closing direction, and the correction signal C _h is activated to prevent the low-pressure drum water level L _l from rising in advance.
is output from the cooperative arithmetic circuit 25 to the second signal corrector 27, and correction is performed on the control signal V _l1 ,
As a result, a correction control signal is sent to the high pressure drum water level control valve 9.
V _h2 is given.

State d is the opposite of state b, in which the low-pressure drum water level L _l is abnormally high and the high-pressure drum water level L _h is approximately at the set value M _h . In this case, the opening of the high-pressure drum water level control valve 9 is controlled in the opening direction to increase the amount of water supplied from the low-pressure drum, and the correction signal C _l is used to promptly eliminate the abnormally high period of the low-pressure drum water level L _l . is added to the control signal V _l1 , which controls the low pressure drum water level control valve 4.

Similarly, in state f, a correction signal C _l is used to quickly eliminate the abnormally low low pressure drum water level L _l .
In state h, the low pressure drum water level control valve ₄ is controlled by a correction signal C _{l that controls the low pressure drum water level control valve 4 in the opening direction so as to suppress the decrease in the low pressure drum water level L l} in advance.

<Modification> In the above explanation, two drums were explained, but the present invention can be applied to a larger number of drums if necessary, and is not limited to air/water drums but other drums. It is also applicable to a plurality of drums connected in series.

<Effects> As described above, according to the present invention, the water levels of a plurality of drums can be controlled in a coordinated manner, and even if an abnormality occurs in the water level of one or both drums, this can be promptly corrected, and in some cases, Advance cooperative control is possible.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of a water supply/steam piping system and a conventional drum water level control device for a boiler with two air-water drums connected in series, and Fig. 2 shows a drum water level control device according to the present invention in the piping system. FIG. 3 is a block diagram showing the configuration of a cooperative control computing unit, and FIG. 4 is a diagram showing the relationship between each drum water level and a set water level. 1...Boiler, 2...Low pressure drum, 3...High pressure drum, 16...Low pressure side water level control device, 18...
High pressure side water level control device, 19...first comparator,
20...Second comparator, 21...Cooperative correction control device, L _l ...Low pressure drum water level, L _h ...High pressure drum water level, M _l ...Low pressure drum water level setting value, M _h ...High pressure drum water level Set value, V _l1 ...Low pressure water level control signal,
V _h1 ...High pressure water level control signal, D _l ...Low pressure deviation value,
D _h ...High pressure deviation value.

Claims (1)

[Claims] 1. In a boiler equipped with a plurality of drums, the water level of each drum is independently determined based on the detected value of the feed water flow rate, the detected value of the steam discharge flow rate, the detected drum water level value, and the drum water level set value for each drum. a plurality of water level control devices individually installed to control the water level to an appropriate level; a comparison calculator that individually calculates the deviation value between the drum water level detection value and the drum water level setting value for each drum; and the water level control device. Based on the drum water level control signal outputted from the device and the deviation value signal, the water level of each drum is predicted to increase or decrease, and the drum water level control signal is corrected and output in order to quickly normalize the water level of the abnormal water level drum. A drum water level control device equipped with a cooperative control device.