JP2670059B2 - Drum level controller for waste heat recovery boiler - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a waste heat recovery boiler installed in a combined plant of, for example, a gas turbine and a steam turbine, and particularly, to reduce the amount of external blow at the time of startup. The present invention relates to a drum level control device for a waste heat recovery boiler suitable for. [Prior Art] FIG. 5 is a system diagram around a drum level in a conventional waste heat recovery boiler. In the figure, 1 is a steam drum,
2 is a superheater, 3 is a economizer, 4 is a drum level detector, 5
Is a level switch, 6 is a level controller on the water supply side, 7 is a water supply pump, 8 is a water reduction valve, 9 is a water supply adjustment valve, and 10 is water. In the initial stage of activation of the waste heat recovery boiler, the steam generated in the boiler is boosted without being used anywhere, and in this boosting process, the water supply pump 7 does not pass water to the boiler. On the other hand, immediately after the ignition of the gas turbine, the high-temperature exhaust gas from the gas turbine passes through the waste heat recovery boiler, so that the specific volume of the canned water 10 of the steam drum 1 rapidly increases, and the level of the canned water 10 rapidly increases accordingly. , Swelling phenomenon occurs. As a countermeasure against this swelling phenomenon, FIG. 3 and FIG.
The drum level control shown in the figure was performed. The drum level control device of the waste heat recovery boiler is, for example, as shown in FIG. 3, a drum level detector 4, a low drum level signal setting device 11 at startup, a high drum level signal setting device 12 at normal operation, and a switching device 13. , A change rate limiter 14, a comparator 15, a proportional integrator 16, and a manual / automatic station 17. In FIG. 3, the control signal of the canned water reduction valve 8 is connected to the low drum level signal setter 11 at the time of passing gas. Further, after starting the gas flow, the switching device 13 is connected to the low drum level signal setting device 11 side until a certain time, so that the low drum level setting signal 18 from the switching device 13 passes through the change rate limiter 14. It is given to the comparator 15 as the drum level setting signal 19, compared with the drum level detection signal 20 from the drum level detector 4, and if there is a deviation between the drum level setting signal 19 and the drum level detection signal 20, the comparator 15 Output signal 21 increases and decreases, passes through the proportional / integrator, and the calculated control signal 22 is guided to the manual / automatic station 17 and the can water reduction valve 8 to open and close the can water reduction valve 8 to set the drum level setting signal. The drum water level is maintained at 19. Further, swelling of the steam drum 1 starts after a lapse of a certain time after starting the gas passage, so that the drum level signal setting device is switched from the low drum level signal setting device 11 side to the high drum level signal setting device 12 side. Therefore, after a certain period of time has passed after starting the gas flow, the high drum level setting signal 23 from the high drum level signal setting device 23
Is supplied to the comparator 15 as a drum level setting signal 19 via the change rate limiter 14 and compared with the drum level detection signal 20 of the drum level detector 4 to control the can water reduction valve 8. Hereinafter, description will be made with reference to (a), (b), and (c) of FIG. In these figures, the horizontal axis represents time, and the vertical axis represents the drum level of the steam drum 1, the opening of the water reduction valve 8, the water level.
10 blow amounts are shown respectively. The curve A shows the actual change of the drum level, the drum level set value of the can water reduction valve 8 on the line B, the line C the set value of the water supply control valve, the curve D the opening of the can water reduction valve 8, E Indicates the amount of air blown out of the system when the can water reduction valve 8 is opened. Further, the point F on the horizontal axis indicates the start of gas passage, the point G indicates the point when a certain time elapses after starting gas passage, and the point H indicates the point of time when the steam turbine is installed. The drum level set value of the canned water reduction valve 8 is the line B shown in FIG. 4, but the rate of change limiter 14 is provided, and after switching to the high drum level signal setter 12, the canned water gradually increases. The operation of raising the drum level set value of the reduction valve 8 from the low drum level set value is performed. As shown in FIG. 4 (a), when the drum level (curve A) of the steam drum 1 starts swelling, the water reduction valve 8
Since the set value (curve B) is exceeded, the opening degree of the can water reduction valve 8 is opened as shown by the curve D, and the blow amount thereof is also increased as shown by the curve E. That is, the drum level of the steam drum 1 is controlled by controlling the opening and closing of the still water reduction valve 8 with respect to swelling. On the other hand, the drum water level setting value of the can water reduction valve 8 is as shown by the curve B, and the drum water level (curve A) is always below the drum level setting value after the steam turbine joining time H. 8 is closed. Canned water reduction valve 8
The can water discharged from the system is neutralized with a chemical solution and then drained to the outside of the system. [Problems to be Solved by the Invention] However, the conventional drum level control device is
Second blow when the amount of blowout outside the system is low, the level peak value of the swelling is sharply increased due to the high drum level setting value of the can water reduction valve 8, and the swelling phenomenon occurs multiple times instead of once. Since the safety of the plant against the excessive rise of the level peak value during the subsequent swelling was not taken into consideration, there was a drawback that the amount of blowout outside the system increased. Especially in the recent STAG plant combining a waste heat recovery boiler and a gas turbine, the daily start and stop (Daily Start St
op) It is necessary to operate DSS for short, and the requirement to minimize the amount of blow to the outside of the system for drum-level swelling at startup leads to reduction of makeup water cost and neutralizer cost, As a result, the maintenance cost of the plant is reduced, and there is an advantage in terms of power plant management. An object of the present invention is to reduce the amount of blowout to the outside of the system due to swelling of the drum level when the boiler is started, and to prevent carryover of the drum level. [Means for Solving the Problem] In order to achieve the above object, the present invention provides a differentiator for calculating a differential operation output signal from a drum level detection signal between a drum level detector and a comparator, and a differential operation. A function generator for calculating a correction signal from an output signal and an adder for calculating a correction signal and a drum level setting signal are provided. Embodiment An embodiment of the present invention will be described below with reference to the drawings. First
The figure is a control system diagram of the can water reduction valve 8 according to the embodiment of the present invention,
2 (a), (b), and (c) are characteristic curve diagrams showing time on the horizontal axis, drum level on the vertical axis, the opening of the can water reduction valve, and the outside blow amount. In FIG. 1, reference numerals 4 to 23 denote the same as the conventional ones. 24 is a differentiator, 25 is a differential operation output signal, 26 is a function generator, 27 is a correction signal, and 28 is an adder. The difference between the control system diagram of the present invention in FIG. 1 and the control system diagram of the prior art in FIG. 3 is that a differentiator 24, a function generator 26 and an adder 28 are provided. In FIG. 1, first, a drum level detector 4 detects a drum level detection signal 20, which is a comparator 15 and a differentiator.
Guided to 24. The output of the differentiator 24 is input to the function generator 26 as a differential operation output signal 25. The output of this function generator 26 is connected to the switch 13 'as a correction signal 27,
13 'always functions on the differentiator 24, function generator 26, and adder 28 side until swelling is completed. After swelling is completed, it switches to the level signal setter side. Further, a change rate limiter 14 for gradually changing the signal until the next drum level setting signal is changed at a constant change rate by signal switching, and an adder 28 for biasing are provided. The output signal 21 of the comparator 15 is a level deviation, which is processed by a proportional / integrator 16 and the can / water reducing valve 8 is controlled through a manual / automatic station 17. Here, the reference numerals in FIG. 2 will be described in advance. The solid line A in the figure is the actual drum level detected by the drum level detector, the alternate long and short dash line B is the level set value set by the level setters 11 and 12 or the correction signal 27 described later, and the dotted line C.
Is the set value of the water supply regulating valve 9 (see FIG. 5), the solid line D is the opening of the still water reducing valve 8, and the solid line E is the blowout amount to the outside of the system. Further, point F is set by the high gas level starter, point G is set by the high drum level signal setter 12 and point H is set by the high drum level signal setter 12 after a certain period of time has passed since the start of gas passage. The drum level set value at the hot start, point J is the drum level set value at the cold start set by the low drum level signal setter 11, point K is the actual drum level at the time of swelling, and point L is The actual drum level at the point when the swelling is completed, the point M, is set by the high drum level signal setting unit 12 with the drum level set value during the normal load operation after the swelling is completed. T is the time when the can water reduction valve 8 is open. At the time of hot start, due to banking, the drum level set value of the steam drum is point I in FIG. 2 (a). The set value of the drum level at the cold start is point J in FIG. 2 (a). Since the DSS (Daily Start / Stop) operation is a hot start,
From the time of starting the boiler to the beginning of swelling, in FIG. 1, the switching device 13 is on the high drum level signal setting device 12 side, and the high drum level setting signal 23 is used as it is as the drum level setting signal 19 '. In FIG. 2, a high drum level set value indicated by a point I and a dashed line B drawn from the point I in parallel with the horizontal axis (up to a point directly above the point K) is selected. In the cold start, from the boiler start to the swelling start, the switch 13 is located on the low drum level signal setter 11 side in FIG. 1 and the low drum level setting signal 18 remains the drum level setting signal 19 as it is. 2 ', the low drum level set value indicated by the dashed line B (up to K point) drawn from the J point and the J point in parallel with the horizontal axis in FIG. 2 is selected. When swelling is started, the level change sharply increases from point K to point L in FIG. 2, and this is differentiated by the differentiator 24 to guide the differential operation output signal 25 to the function generator 26, and the function generator 26 Then, it becomes a correction signal 27 (minus signal) and is given as a bias signal to the adder 28 via the switch 13 '. That is, the start of swelling can be automatically detected by the input of the correction signal 27, whereby the outside blow can be started. Further, when the input of the correction signal 27 becomes zero, the completion of the swelling can be automatically detected, whereby the out-of-system blow can be stopped. In the hot start, the high drum level setting signal 23 set by the high drum level signal setting device 12 as described above was used as it was as the drum level setting signal 19 'before the start of the swelling. When the correction signal 27 (minus signal) is given to the adder 28 at the start, the drum level setting signal 19 'is changed from the point K in FIG.
Switches to the low drum level setting value indicated by. In cold start, the low drum level setting signal 18 set by the low drum level signal setting device 11 as described above was used as it was as the drum level setting signal 19 'before the start of swelling. Correction signal 27 (minus signal) is added by starter 28
The drum level setting signal 19 'is given to
In FIG. 2, the low drum level set value indicated by the alternate long and short dash line B drawn parallel to the horizontal axis from the point K is switched (in the case of the present embodiment, the line B drawn parallel to the horizontal axis from the point J). The line B drawn from the point K parallel to the horizontal axis is the same line, and there is virtually no switching of the set value). During this swelling, the can water reduction valve 8 opens and blows the can water out of the system because the drum level detection signal 20 is higher than the drum level setting signal 19 ', but as shown by the curve A in FIG. When the inclination of the level change disappears, the correction signal (bias) 27 becomes zero, and the drum level setting signal 19 ′, which is the basis of the control signal of the water reduction valve 8, is changed by the change rate limiter.
The drum level setting signal 19 is reached via 14, and the blow to the outside of the system is completed here. As a result, since the drum content integral can be used for the amount of blown can water, the amount of blown shaded in FIG. 2 (c) can be saved and swelling can be reliably detected. [Effects of the Invention] According to the present invention, at the time of swelling at the time of starting the boiler, the amount of still water blown out of the system can be reduced, so that the amount of the replenishing water and the neutralizing agent used at the time of drainage can be reduced. I can.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a control system diagram of a can water reduction valve according to an embodiment of the present invention, and FIGS. 2 (a), (b) and (c) are time on the horizontal axis and time on the vertical axis. FIG. 3 is a characteristic curve diagram showing the drum level, the opening of the can water reduction valve, and the amount of blowout to the outside of the system. FIG.
Figures (a), (b), and (c) are characteristic curves showing time on the horizontal axis, drum level on the vertical axis, the opening of the can water reduction valve, and the amount of blowout to the outside of the system. Figure 5 shows the drum level. 2 is a schematic configuration diagram of FIG. 1 ... Steam drum, 4 ... Drum level detector, 8 ...
Can water reduction valve, 11, 12 ...... Level setting device, 13, 13 '...... Switching device, 15 …… Comparator, 16 …… Proportional / integrator, 17 …… Manual / automatic station, 18, 23,19 , 19 '... Drum level setting signal, 20 ... Drum level detection signal, 24 ... Differentiator, 25 ... Differentiation operation output signal, 26 ... Function generator, 27 ...
... correction signal, 28 ... adder.

Claims (1)

(57) [Claims] A drum level detector that detects the drum level detection signal of the steam drum, a drum level setter that outputs the drum level setting signal, and a comparator that compares the drum level detection signal with the drum level setting signal are provided. And opening and closing the canned water reduction valve according to the deviation signal of the drum level setting signal, a differentiator for calculating a differential operation output signal from the drum level detection signal, and a differentiator between the drum level detector and the comparator. A function generator that calculates a modified signal from the calculated output signal,
A drum level control device for a waste heat recovery boiler, comprising an adder for calculating a correction signal and a drum level setting signal.