JP5750605B2 - Multi-pipe once-through boiler feed water control device - Google Patents

Description

  The present invention relates to a water supply control device for a multi-tube once-through boiler. More specifically, the present invention relates to a water supply control device for a multi-pipe once-through boiler that can stabilize the water level of a brackish water separator while suppressing fluctuations in the rotation speed of a water supply pump.

  Conventionally, a multitubular once-through boiler B configured as shown in FIG. 13 has been used to obtain steam. In this multi-pipe once-through boiler B, the water level of the brackish water separator is controlled by turning on and off the feed water pump from the viewpoint of simplification of configuration and cost reduction.

  However, as is well known, the required number of multi-tube once-through boilers B are operated in parallel to ensure a desired amount of steam. Therefore, when the load fluctuation is large, each of the multi-pipe once-through boilers B that are operated in parallel is frequently started and stopped. This also leads to frequent turning on and off of the water supply pump. However, since frequent ON / OFF is not preferable for the water supply pump, as shown in FIG. 14, the water supply pump is frequently controlled by so-called PID control based on the water level control value, the water level measurement value, and the deviation. Attempts have been made to avoid on / off.

  However, since the multi-pipe once-through boiler B is configured as described above, the water level of the boiler varies sensitively even when the amount of combustion changes.

  For this reason, even if PID control as shown in FIG. 14 is performed, it is similar to the state where the water supply pump is turned on / off, and both the water level of the brackish water separator and the stable operation of the water supply pump are compatible. I can't let you.

  The present invention has been made in view of the above-described problems of the prior art, and stabilizes the water level of a brackish water separator of a multi-pipe once-through boiler, while suppressing fluctuations in the feed water control amount. The object is to provide a control device.

A water supply control device for a multi-tube type once-through boiler according to the present invention comprises a water supply amount control value calculating means, a water supply amount command value calculating means, and a command value correcting means for correcting a water supply amount command value by steam pressure , The amount control value calculation means calculates a water supply amount input value based on a deviation between the water level control value and the water level measurement value, and the water supply amount command value calculation means performs the water supply amount by a proportional operation and an integration operation. Based on the deviation between the input value and the measured water supply value, the water supply command value is calculated, and the command value correcting means for correcting the water supply command value by the steam pressure sets the lower limit value of the water supply flow rate at the normal pressure. On the straight line connecting the point to be 50% and the zero point, the upper limit value of the water supply flow rate is 90% of the 100% water supply amount when the steam pressure is zero, and the water supply amount after the normal pressure is 100%. The steam pressure will be corrected as specified in Characterized by comprising been.

  Moreover, it is preferable that the water supply control device for a multi-tube type once-through boiler according to the present invention includes a measurement water level correcting means for correcting the water level measurement value.

  Furthermore, in the water supply control device for a multi-pipe once-through boiler according to the present invention, it is preferable that the water supply command value calculation means includes a differential operation, and the differential of the water supply measurement value is performed by the differential operation.

  Furthermore, in the water supply control device for a multi-pipe once-through boiler according to the present invention, it is preferable that the water supply amount moving average calculating means for calculating the moving average of the water supply amount measurement values is provided.

Furthermore, in the water supply control device for a multi-pipe once-through boiler according to the present invention, it is preferable to include a low-pass filter that filters the measured value of the water supply amount.

  Furthermore, in the water supply control device for a multi-pipe once-through boiler according to the present invention, it is preferable to include a low-pass filter for filtering the water level measurement value.

  Furthermore, in the water supply control device for a multi-pipe once-through boiler according to the present invention, it is preferable that a limiter for defining an upper limit of the water supply amount command value is provided.

  Further, the water supply control device for a multi-tube once-through boiler according to the present invention preferably includes a change rate limiter that defines a change rate of the water supply amount command value.

  Since this invention is comprised as mentioned above, the outstanding effect that the fluctuation | variation of water supply control amount is suppressed is obtained, keeping the water level of a brackish water separator constant.

It is a block diagram of the feed water control apparatus of the multi-tube type once-through boiler which concerns on Embodiment 1 of this invention. It is a principal part block diagram of the feed water control apparatus of the multipipe type once-through boiler which concerns on Embodiment 2 of this invention. It is a graph which prescribes | regulates the relationship between the steam pressure and water supply amount used for the embodiment. It is a principal part block diagram of the water supply control apparatus of the multitubular once-through boiler which concerns on Embodiment 3 of this invention. It is a principal part block diagram of the water supply control apparatus of the multitubular once-through boiler which concerns on Embodiment 4 of this invention. It is a principal part block diagram of the water supply control apparatus of the multitubular once-through boiler which concerns on Embodiment 5 of this invention. It is a principal part block diagram of the water supply control apparatus of the multitubular once-through boiler which concerns on Embodiment 6 of this invention. It is a principal part block diagram of the water supply control apparatus of the multitubular once-through boiler which concerns on Embodiment 7 of this invention. It is a principal part block diagram of an example of the modification of this invention. It is a principal part block diagram of the other example of the modification of this invention. It is a schematic diagram which shows the water level fluctuation | variation of the brackish water separator in an Example, and the time change of a feed water flow rate. It is a schematic diagram which shows the water level fluctuation | variation of the brackish water separator in a comparative example, and the time change of a feed water flow rate. It is the schematic of a multi-tube type once-through boiler. It is a PID control block diagram of water supply control in the conventional multi-tube type once-through boiler.

  Hereinafter, although the present invention is explained based on an embodiment, referring to an accompanying drawing, the present invention is not limited only to this embodiment.

Embodiment 1
FIG. 1 shows a water supply control device (hereinafter simply referred to as a control device) C1 of a multitubular once-through boiler (hereinafter also simply referred to as a boiler) according to Embodiment 1 of the present invention.

  As shown in FIG. 1, the control device C <b> 1 includes a water supply amount control value calculation unit 1 and a water supply amount command value calculation unit 2 as main components.

  The water supply amount control value calculating means 1 calculates a required water supply amount, that is, a water supply amount input value, from the deviation between the control water level and the measured water level. The water supply amount command value calculation means 2 calculates a water supply amount command value, that is, a water supply control amount, from the deviation between the water supply amount input value calculated by the water supply amount control value calculation means 1 and the water supply amount measurement value. More specifically, the water supply amount command value calculation means 2 calculates the water supply amount command value by PI control, that is, control that combines proportional operation and integration operation.

  Here, the input of the feed water amount command value calculation means 2 is the feed water amount, as described above, when the water level fluctuation in the brackish water separator is large, when the water level of the brackish water separator is input, This is because the stability of the control is lacking, and there is a possibility that the stable operation of the water supply pump cannot be secured as in the PID control in the prior art.

  Each means having the functions is realized by storing a program corresponding to the microcomputer. Alternatively, it may be realized by a so-called PID adjuster.

  Thus, according to the first embodiment, the feed water flow rate input value is calculated by calculation from the deviation between the control water level and the measured water level, and the deviation between it and the feed water flow rate measurement value is used as the input to the feed water amount command value calculation means 2. Therefore, compared with the case where the water level deviation is input, the fluctuation of the water supply control amount can be reduced while the water level fluctuation due to the combustion load is alleviated and the water level of the brackish water separator is made substantially constant.

Embodiment 2
The principal part of the control apparatus C2 which concerns on Embodiment 2 of this invention is shown with a block diagram in FIG.

  The second embodiment is a modification of the first embodiment, and includes command value correcting means 3 for correcting the output of the water supply command value calculating means 2 with the steam pressure of the multi-tube once-through boiler. The

  Here, the output of the water supply amount command value calculating means 2 is corrected by the steam pressure, even if the rotation speed of the water supply pump is the same, if the boiler pressure is different, the water supply amount actually supplied to the boiler is different. Because. In particular, in a multi-tube once-through boiler, since the number control is scheduled as described above, it is not uncommon to supply water from a state where the steam pressure is zero.

  The correction by the steam pressure is performed as shown in FIG. 3, for example. In other words, the lower limit value of the feed water flow rate is defined on a straight line connecting the point where the normal pressure is 50% and the zero point, while the upper limit value of the feed water flow rate is the maximum water supply amount when the steam pressure is zero (100% water supply amount). For example, it is 90%, and it is defined to be the maximum water supply amount (100% water supply amount) after the normal pressure.

  Since the remaining configuration of the second embodiment is the same as that of the first embodiment, detailed description thereof is omitted.

  Thus, in Embodiment 2, since the water supply amount command value output by the water supply amount command value calculating means 2 is corrected by the steam pressure of the multi-tube once-through boiler, the water supply according to the steam pressure is performed. You can get none. Therefore, the fluctuation of the water supply control amount can be reduced as compared with the first embodiment.

  In addition, since the other effect | action and effect of Embodiment 2 are the same as that of Embodiment 1, the detailed description is abbreviate | omitted.

Embodiment 3
The principal part of Embodiment 3 of this invention is shown with a block diagram in FIG.

  The third embodiment is obtained by modifying the first embodiment, and includes measurement water level correcting means 4 for correcting the measurement water level.

  The measurement water level correction means 4 is provided because the pressure of the boiler fluctuates due to the above-described reason, and the specific volume fluctuates due to this pressure fluctuation, and an error occurs in the water level measured by the water level measuring instrument. Because.

  Since the remaining configuration of the third embodiment is the same as that of the first embodiment, detailed description thereof is omitted.

  Thus, in Embodiment 3, since the water level measured by the water level measuring device is corrected by the measured water level correcting means 4 and brought close to the actual water level, it is possible to alleviate the influence due to the pressure fluctuation of the boiler and The variation of the water supply control amount can be reduced as compared with the first embodiment while the water level is substantially constant.

  In addition, since the other effect | action and effect of Embodiment 3 are the same as that of Embodiment 1, the detailed description is abbreviate | omitted.

Embodiment 4
The principal part of Embodiment 4 of this invention is shown with a block diagram in FIG.

  The fourth embodiment is a modification of the first embodiment, in which a feed water amount measurement value is also input to the feed water amount command value calculation means 2 and a differential value of the feed water amount measurement value is combined, that is, a PID including a differential operation. The water supply amount command value is calculated and calculated by the control.

  Since the remaining configuration of the fourth embodiment is the same as that of the first embodiment, detailed description thereof is omitted.

  As described above, in the fourth embodiment, since the water supply amount command value is calculated by the PID control using the water supply amount measurement value, the control performance is improved as compared with the first embodiment. That is, the fluctuation of the water supply control amount can be further reduced.

  In addition, since the other effect | action and effect of Embodiment 4 are the same as that of Embodiment 1, the detailed description is abbreviate | omitted.

Embodiment 5
The principal part of Embodiment 5 of this invention is shown with a block diagram in FIG.

  The fifth embodiment is a modification of the third embodiment, and is provided with a water supply amount moving average calculation means 5 to calculate and calculate a moving average of a water supply amount measurement value for a predetermined time, and the calculated moving average. The value is added to the output from the water supply amount control value calculation means, and the deviation between the added value and the water supply amount measurement value is input to the water supply amount command value calculation means. The predetermined time is 15 seconds to 30 seconds. The reason for selecting the predetermined time in this way is that if the time is too short, the meaning of taking the moving average is lost, and conversely, if the time is too long, the control responsiveness deteriorates.

  The reason for adding the moving average value of the measured water supply amount is to compensate for disturbance of the water level due to combustion to ensure stable control.

  That is, in a multi-tube once-through boiler, the amount of combustion constantly changes from the point where the load fluctuation in each boiler is severe due to the parallel operation, so the amount of evaporation generated by the boiler is also constantly changing. If the amount of water supply is constant in such a state, the boiler will become a so-called empty can whenever the amount of evaporation exceeds the amount of water supply, and conversely, the boiler will become full only when the amount of water supply exceeds the amount of evaporation. This occurs.

  In order to avoid such a situation, the water level is generally controlled in the boiler. However, in the case of a multi-tube once-through boiler, the change in the combustion amount becomes a disturbance, and the fluctuation of the water level (brake separator side) There is a characteristic that becomes intense. For this reason, there is a possibility that stable control cannot be performed by the control based on the water supply amount command value calculated based on the water level. Therefore, the stability of control is achieved by adding the moving average value of the water supply amount measurement value to the water supply amount control value calculated by the water supply amount control value calculating means 1.

  Since the remaining configuration of the fifth embodiment is the same as that of the third embodiment, detailed description thereof is omitted.

  Thus, in the fifth embodiment, since the moving average value of the water supply measured value is added to the water supply control value calculated by the water supply control value calculating means 1, the water There is also an effect that cannot be obtained in the third embodiment, in which variation in the control amount can be suppressed to a small level.

  In addition, since the other effect | action and effect of Embodiment 5 are the same as that of Embodiment 3, the detailed description is abbreviate | omitted.

Embodiment 6
The principal part of Embodiment 6 of this invention is shown with a block diagram in FIG.

  The sixth embodiment is obtained by modifying the fourth embodiment, and the water supply amount measurement value is input to the water supply amount command value calculating means 2 after passing through the low-pass filter 6. That is, the measured water supply value subjected to the low-pass filter process is used as an input.

  Since the remaining configuration of the sixth embodiment is the same as that of the third embodiment, detailed description thereof is omitted.

  As described above, in the sixth embodiment, since the water supply amount measurement value subjected to the low-pass filter processing is input, noise included in the water supply amount measurement value is removed, so that the control is more stable than that in the fourth embodiment. Improves. That is, the fluctuation of the water supply control amount can be further suppressed.

  In addition, since the other effect | action and effect of Embodiment 6 are the same as that of Embodiment 4, the detailed description is abbreviate | omitted.

Embodiment 7
The principal part of Embodiment 7 of this invention is shown with a block diagram in FIG.

  The seventh embodiment is obtained by modifying the third embodiment, and the water level measurement value is input to the measurement water level correcting means 4 after passing through the low-pass filter 7. That is, the water level measurement value that has been subjected to the low-pass filter process is used as an input.

  Since the remaining configuration of the seventh embodiment is the same as that of the third embodiment, detailed description thereof is omitted.

  As described above, in the seventh embodiment, since the water level measurement value subjected to the low-pass filter process is input, noise included in the water level measurement value is removed, so that the control stability is higher than that in the third embodiment. improves. That is, the fluctuation of the water supply control amount can be further suppressed.

  As mentioned above, although this invention has been demonstrated based on embodiment, this invention is not limited only to this embodiment, A various change is possible.

  For example, as shown in FIG. 9, a limiter 8 that defines the upper limit of the water supply amount command value output from the water supply amount command value calculating means 2 and a change rate limiter 9 that defines the change rate may be provided. Or the limiter 10 which prescribes | regulates the upper limit of the output from the water supply amount control value calculating means 1 may be provided.

  Further, as shown in FIG. 10, a limiter 11 that defines the upper limit of the input of the water supply moving average calculating means 5 may be provided.

  Hereinafter, the present invention will be described in more detail based on examples.

Example In a multi-tube once-through boiler having the specifications shown below, the water supply control of the fifth embodiment is applied to measure the fluctuations in the water level and the water supply amount of the brackish water separator with respect to the load fluctuations in 30 minutes, and the results are shown in FIG. Is shown in a schematic diagram.

Comparative Example In a multi-tube type once-through boiler having the same specifications as in the example, the PID control shown in FIG. 14 is applied to measure the fluctuations in the water level of the brackish water separator and the amount of water supply for 30 minutes, and the results are shown in the figure 12 is a schematic diagram.

  From FIG. 11 and FIG. 12, it can be seen that in the embodiment, the water level of the brackish water separator is kept substantially constant while suppressing fluctuations in the water supply amount.

Outline of boiler Pressure 1MPa
Evaporation 6T / H

  The present invention can be used for water supply control of a multi-tube once-through boiler.

DESCRIPTION OF SYMBOLS 1 Water supply amount control value calculation means 2 Water supply amount command value calculation means 3 Command value correction means 4 Measurement water level correction means 5 Water supply amount moving average value calculation means 6 Low pass filter 7 Low pass filter 8 Limiter 9 Change rate limiter 10 Limiter 11 Limiter B Many Pipe once-through boiler C Water supply control device

Claims (8)

A water supply control device for a multi-tube once-through boiler,
Water supply amount control value calculation means , water supply amount command value calculation means, and command value correction means for correcting the water supply amount command value by the steam pressure ,
The water supply amount control value calculating means calculates a water supply amount input value based on a deviation between the water level control value and the water level measurement value,
The water supply amount command value calculating means is configured to calculate a water supply amount command value based on a deviation between the water supply amount input value and the water supply amount measurement value by a proportional operation and an integration operation .
The command value correction means for correcting the feed water amount command value by the steam pressure defines the lower limit value of the feed water flow rate on a straight line connecting the point where the normal pressure is 50% and the zero point, while the upper limit value of the feed water flow rate is A multi-tube once-through boiler characterized in that the steam pressure is corrected so as to be defined as 90% of the 100% water supply amount when the steam pressure is zero, and 100% water supply amount after the normal pressure. Water supply control device. 2. The water supply control device for a multi-pipe once-through boiler according to claim 1, further comprising measurement water level correction means for correcting the water level measurement value. The feed water control device for a multi-pipe once-through boiler according to claim 1, wherein the feed water amount command value calculation means includes a differential operation, and the differential water operation is differentiated by the differential operation. The water supply control device for a multi-pipe once-through boiler according to claim 1, further comprising water supply moving average calculating means for calculating a moving average of measured values of water supply. The multi-pipe once-through boiler feed water control device according to claim 1, further comprising a low-pass filter for filtering the feed water measured value. 2. A multi-pipe once-through boiler feed water control device according to claim 1, further comprising a low-pass filter for filtering the water level measurement value. The water supply control device for a multi-pipe once-through boiler according to claim 1, further comprising a limiter for defining an upper limit of a water supply amount command value. 2. The feed control device for a multi-pipe once-through boiler according to claim 1, further comprising a change rate limiter for defining a change rate of the water supply amount command value.