EP3550208A1

EP3550208A1 - Steam temperature control device and control unit including same

Info

Publication number: EP3550208A1
Application number: EP17877376.8A
Authority: EP
Inventors: Takashi SHIMONASHI; Ko ARIMURA
Original assignee: Kobelco Eco Solutions Co Ltd
Current assignee: Shinko Pantec Co Ltd
Priority date: 2016-11-29
Filing date: 2017-09-04
Publication date: 2019-10-09
Anticipated expiration: 2037-09-04
Also published as: EP3550208B1; EP3550208A4; JP6630705B2; JP2018091600A

Abstract

A steam temperature control device (3) for controlling a main steam temperature which is a temperature of main steam generated from a superheater (14) of a boiler including a desuperheater (13) which decreases a temperature of steam using an amount of spray water based on a water amount control value and the superheater (14) for heating steam discharged from the desuperheater (13) by an exhaust gas. The steam temperature control device (3) includes a water amount control value calculation part (311) which calculates a water amount control value based on a main steam temperature such that the main steam temperature becomes a target temperature, and transmits the water amount control value to a spray water supply valve (24). The water amount control value calculation part (311) is configured to transmit, as a lower limit value of the water amount control value, a water amount control minimum value to the spray water supply valve (24). The water amount control minimum value is calculated based on a moving average of a supply water amount to the desuperheater (13) during a fixed period or a moving average of the water amount control value during a fixed period.

Description

Technical Field

The present invention relates to a steam temperature control device for controlling a temperature of main steam generated from a boiler in a facility which treats waste or the like.

Background Art

Conventionally, there has been known a system where main steam is generated by recovering heat generated in an incinerator or the like in a waste treatment facility by a boiler. Main steam generated in this system is supplied to a place of use and hence, it is desirable that a temperature of main steam be as stable as possible. Usually, in such a system, the boiler includes a desuperheater which decreases a temperature of steam discharged from a boiler drum with spray water and a superheater which heats steam discharged from the desuperheater by an exhaust gas discharged from the incinerator. An amount of spray water supplied to the desuperheater is regulated by regulating a degree of opening of a spray water supply valve.
For example, Patent Literature 1 discloses a steam temperature control device which makes a temperature of main steam generated from a boiler stable. The steam temperature control device has a water amount control value calculation part. The water amount control value calculation part calculates a water amount control value for determining a degree of opening of a spray water supply valve based on the main steam temperature, and transmits a degree-of-opening control value to the spray water supply valve so as to set a temperature of main steam discharged from a superheater (main steam temperature) to a target temperature. Accordingly, the main steam temperature substantially changes at a temperature in the vicinity of a target temperature. However, in an incinerator of a waste treatment facility or the like, there may be a case where calorie generated by burning changes depending on a property or the like of a waste. In this case, there is a possibility that the main steam temperature also changes. In the steam temperature control device described in Patent Literature 1, to suppress a rapid increase of the main steam temperature, a lower limit value of the water amount control value is set to be valuable. Specifically, the water amount control value calculation part calculates a water amount control minimum value which is increased or decreased along with the increase or decrease of a temperature of an exhaust gas as the lower limit value of the water amount control value, and transmits this water amount control minimum value to the spray water supply valve. That is, the water amount control minimum value is also increased or decreased along with the increase or decrease of the exhaust gas temperature and hence, compared to a case where a minimum value of a water amount control value is fixed to a specific value, a rapid increase of a main steam temperature can be suppressed. Accordingly, it is possible to prevent the main steam temperature from being deviated from a target temperature.
In the steam temperature control device described in Patent Literature 1, in a case where a soot blower operation (an operation for removing an ash component or the like adhered to a heat transfer tube of a superheater) in the boiler or the like is performed, there is a concern that a change width of the main steam temperature is increased. Specifically, when a soot blower operation is performed in the boiler, a heat exchange amount between steam and an exhaust gas in the superheater (a quantity of heat which steam passing through the heat transfer tube receives from the exhaust gas) is increased. As a result, a temperature of the main steam discharged from the superheater is increased and, at the same time, a temperature of an exhaust gas discharged from the boiler is lowered. On the other hand, in the steam temperature control device described in Patent Literature 1, when a temperature of an exhaust gas is lowered, a water amount control minimum value, that is, a supply water amount to the desuperheater is lowered and hence, there is a tendency that a temperature of main steam increases. In this manner, in the control using the steam temperature control device described in Patent Literature 1, there is a concern that a temperature of main steam is increased after a soot blower operation of the boiler is performed, for example.

Citation List

Patent Literature

Patent Literature 1: JP 2016-145652 A

Summary of Invention

It is an object of the present invention to provide a steam temperature control device capable of reducing a change width of a temperature of main steam generated from a boiler, and a control unit which includes the steam temperature control device.
To overcome the above-mentioned drawbacks, inventors of the present invention have focused on a relationship between a main steam temperature and a supply water amount supplied to a desuperheater. Specifically, the inventors have found that the supply water amount, that is, a water amount control value of a spray water supply valve is regulated by a feedback control based on the main steam temperature and hence, tendency of the increase or decrease of a supply water amount and tendency of the increase or decrease of the main steam temperature become equal to each other. Based on such finding, the inventors have arrived at an idea that, by adopting a supply water amount (water amount control value) in place of a temperature of an exhaust gas as an index for acquiring a water amount control minimum value, a change width of the main steam temperature after a soot blower operation of a boiler is performed or the like can be reduced.
The present invention has been made in view of the above-mentioned viewpoints. Specifically, a steam temperature control device according to an aspect of the present invention is a steam temperature control device for controlling a main steam temperature which is a temperature of main steam generated from a superheater of a boiler including a desuperheater which decreases a temperature of steam using an amount of spray water based on a water amount control value for controlling a degree of opening of a spray water supply valve and the superheater for heating steam discharged from the desuperheater by an exhaust gas discharged from a furnace. The steam temperature control device includes a water amount control value calculation part which calculates the water amount control value based on the main steam temperature such that the main steam temperature becomes a target temperature, and transmits the water amount control value to the spray water supply valve. The water amount control value calculation part is configured to transmit, as a lower limit value of the water amount control value, a water amount control minimum value to the spray water supply valve. The water amount control minimum value is calculated based on a moving average of a supply water amount to the desuperheater during a fixed period or a moving average of the water amount control value during a fixed period.
A control unit according to another aspect of the present invention is a control unit which includes the steam temperature control device and a target temperature control device which controls a target temperature of the main steam temperature and transmits the target temperature to the steam temperature control device. The target temperature control device has a target temperature changing part which, upon receiving a quantity of heat lowering signal which is a signal indicative of lowering of a quantity of heat of an exhaust gas supplied to the superheater, changes a target temperature transmitted to the steam temperature control device to a low target temperature lower than a target temperature before the target temperature control device receives the quantity of heat lowering signal.

Brief Description of Drawings

FIG. 1 is a view showing a schematic configuration of a steam temperature control device according to an embodiment of the present invention.
FIG. 2 is a graph showing a relationship between a moving average during a fixed period of a supply water amount to a desuperheater and a supply water amount coefficient.
FIG. 3 is a graph showing a relationship between a main steam temperature and a main steam temperature coefficient.
FIG. 4 is a view showing a relationship between a deviation between a target temperature and a main steam temperature and a control gain.
FIG. 5 is a view showing an example of the configuration and the content of a main steam temperature log table.
FIG. 6 is a flowchart of water supply valve control value calculating processing.
FIG. 7 is a flowchart of target temperature control processing.

Description of Embodiments

A control unit including a steam temperature control device 3 and a target temperature control device 4 according to an embodiment of the present invention is described with reference to drawings.

FIG.1 shows a configurational example of a boiler 1 in a waste treatment facility, a configurational example of the steam temperature control device 3 and a configurational example of the target temperature control device 4.
The boiler 1 generates steam by recovering heat of an exhaust gas discharged from an incinerator 5 in the waste treatment facility. A waste is supplied to the incinerator 5 from a refuse feeder 6. The refuse feeder 6 has a feeding part (not shown in the drawings) for feeding a waste to the incinerator 5 and a motor (not shown in the drawings) for driving the feeding part.
As shown in Fig 1, the boiler 1 has a boiler drum 11, a primary superheater 12 for heating steam discharged from the boiler drum 11 by the exhaust gas, a desuperheater 13 for decreasing a temperature of steam discharged from the primary superheater 12 by spray water and a secondary superheater 14 for heating steam discharged from the desuperheater 13 by the exhaust gas. Steam discharged from the secondary superheater 14, that is, main steam is fed to a place of use.
Each of the superheaters 12, 14 has a plurality of heat transfer tubes through which steam fed from the boiler drum 11 flows. That is, in each of the superheaters 12, 14, steam which flows through each of the heat transfer tubes is heated by an exhaust gas which is brought into contact with an outer peripheral surface of each of the heat transfer tubes. An ash component or the like contained in the exhaust gas adheres to each of the heat transfer tubes. Accordingly, in the boiler 1, a soot blower operation is periodically performed for removing such an ash component or the like. When the soot blower operation is performed in the boiler 1, an exchange quantity of heat between steam in each of the superheaters 12, 14 and an exhaust gas (a quantity of heat which steam flowing through the heat transfer tube receives from an exhaust gas) is increased. Accordingly, after the soot blower operation is performed, a temperature of steam discharged from each of the superheaters 12, 14 is increased and, at the same time, a temperature of an exhaust gas discharged from the boiler 1 is lowered.
An amount of spray water based on a degree of opening of a spray water supply valve 24 is supplied to the desuperheater 13. That is, a temperature of main steam generated in the boiler 1 is regulated by the degree of opening of the spray water supply valve 24 (hereinafter referred to as "water amount control value"). The spray water supply valve 24 is provided to a supply water flow passage 26 for supplying spray water from the outside to the desuperheater 13.
The steam temperature control device 3 is a device for controlling a temperature of main steam generated from the boiler 1 (hereinafter referred to as "main steam temperature"). Specifically, the steam temperature control device 3 controls a degree of opening of the spray water supply valve 24 so as to set a main steam temperature to a target temperature SV. The steam temperature control device 3 is a so-called computer, and collects data which various sensors detect or the like at a predetermined cycle. Based on data such as temperatures acquired from the respective sensors, the steam temperature control device 3 forms control data for controlling a degree of opening of the spray water supply valve 24 (water amount control value MV). The steam temperature control device 3 also transmits the water amount control value MV to the spray water supply valve 24. That is, the steam temperature control device 3 performs a feedback control using a so-called PID control (Proportional-Integral-Derivative Controller) so as to set a main steam temperature to a target temperature SV. The sensors include a main steam temperature detector 21 for detecting a temperature of main steam discharged from the secondary superheater 14, a main steam flow rate detector 22 for detecting a flow rate of main steam discharged from the secondary superheater 14, an outlet temperature detector 23 for detecting a temperature of steam which flows between the desuperheater 13 and the secondary superheater 14 (steam flowing out from the desuperheater 13) and a supply water flow rate detector 25 for detecting a water amount which flows through the supply water flow passage (an instantaneous value of spray water supplied to the desuperheater 13). The target temperature SV is input from the target temperature control device 4.
The steam temperature control device 3 includes a main steam temperature controller 31, an outlet temperature controller 32 and a supply water flow rate controller 33.
The main steam temperature controller 31 acquires data detected by the respective sensors at a predetermined cycle (for example one second), and calculates a water amount control value MV with which a temperature of steam discharged from the secondary superheater 14 becomes a target temperature SV based on the acquired data. The main steam temperature controller 31 is configured to detect timing at which data is acquired by interruption from a timer (not shown in the drawings) incorporated in the steam temperature control device 3.
The main steam temperature controller 31 stores data acquired from the sensors in a memory (not shown in the drawings) as a log when necessary. The memory may be an internal memory of the steam temperature control device 3 or may be an external memory connected through a network. In this embodiment, the main steam temperature controller 31 time-sequentially stores a main steam temperature acquired from the main steam temperature detector 21. Respective data stored in the memory can be looked up also from other functional parts.
FIG. 5 shows an example of the configuration and the content of a main steam temperature log table 210. In the main steam temperature log table 210, each time the main steam temperature controller 31 acquires data from the main steam temperature detector 21, 1 record is added. The main steam temperature log table 210 includes log number of times 211 and a main steam temperature 212.
The log number of times 211 indicates the order that main steam temperature (log data) is acquired, and the main steam temperature 212 indicates the content of data, that is, an acquired main steam temperature. For example, a record where the log number of times 211 is "n" (log data on main steam temperature acquired at the n-th time) in the main steam temperature log table 210 means a record added at the latest time. In this case, data indicated in the main steam temperature 212 is "500" and hence, a current main steam temperature is assumed as 500°C. The main steam temperature controller 31 acquires data from the sensor at a predetermined cycle (for example, one second). Accordingly, the record where the log number of times 211 is "n-1" is log data before a period of a predetermined cycle, that is, log data before one second. Data indicated in the main steam temperature 212 at this point of time is "505" and hence, it is understood that the main steam temperature before one second was 505°C. The detail of processing of the main steam temperature controller 31 is described in a column "Manner of operation".
The outlet temperature controller 32 corrects (regulates) a water amount control value MV which the main steam temperature controller 31 calculates using a steam temperature or the like at an outlet side of the desuperheater 13 which the outlet temperature detector 23 detects.
The supply water flow rate controller 33 transmits the water amount control value MV corrected by the outlet temperature controller 32 to the spray water supply valve 24. Accordingly, an amount of spray water corresponding to the water amount control value MV is supplied to the desuperheater 13.
The configuration of the main steam temperature controller 31 is described in detail. The main steam temperature controller 31 has a water amount control value calculation part 311, a control gain calculation part 312 and a water amount control minimum value calculation part 313.
The water amount control value calculation part 311 calculates a water amount control value MV based on a deviation between a main steam temperature detected by the main steam temperature detector 21 and a target temperature SV, and a main steam flow rate or the like detected by the main steam flow rate detector 22, to perform a so-called PID control.
The control gain calculation part 312 calculates a so-called control gain (a proportional gain) used when the water amount control value calculation part 311 calculates a water amount control value MV. In this embodiment, the control gain calculation part 312 obtains a control gain using a function shown in FIG. 4. In a graph shown in FIG. 4, a deviation between a target temperature SV and a main steam temperature detected by the main steam temperature detector 21 is taken on an axis of abscissas, and a control gain is taken on an axis of ordinates. For example, in FIG.4, the control gain is 5 when the deviation is 0 or less, and the control gain is 30 when the deviation is 5 or more. The control gain is increased from 5 to 30 in proportion to the deviation when the deviation falls between 0 and 5.
The water amount control minimum value calculation part 313 calculates a water amount control minimum value ML which is a lower limit value of a water amount control value MV, and transmits the water amount control minimum value ML to the water amount control value calculation part 311. The water amount control minimum value ML is used when the water amount control value calculation part 311 calculates a water amount control value MV. As will be described later in a column "Manner of operation", the water amount control value calculation part 311 transmits, when a main steam temperature exhibits a lowering tendency, a water amount control minimum value ML calculated by the water amount control minimum value calculation part 313 to the outlet temperature controller 32 as a water amount control value MV. When the main steam temperature takes the lowering tendency, even when the main steam temperature is higher than a target temperature SV, the water amount control minimum value ML is set as the water amount control value MV. When the main steam temperature takes the lowering tendency, the steam temperature control device 3 estimates that the main steam temperature continues lowering, and sets a supply water amount to the desuperheater 13 to the water amount control minimum value ML.
In this embodiment, the water amount control minimum value calculation part 313 calculates a water amount control minimum value ML based on a moving average of a supply water amount to the desuperheater 13 (a detected value of the supply water flow rate detector 25) during a fixed period. Specifically, the water amount control minimum value calculation part 313 calculates a value obtained by multiplying a supply water amount coefficient indicated in FIG.2 by a main steam temperature coefficient indicated in FIG.3 as a water amount control minimum value ML. The water amount control minimum value calculation part 313 may calculate a water amount control minimum value ML based on a moving average of a water amount control value MV during a fixed period.
In a graph shown in FIG. 2, a moving average of a supply water amount to the desuperheater 13 during a fixed period (20 minutes in this embodiment) is take on an axis of abscissas, and supply water amount coefficient is taken on an axis of ordinates. The supply water amount coefficient indicates a degree of opening of a spray water supply valve 24 corresponding to the moving average (the value on the axis of abscissas in FIG. 2). As shown in FIG. 2, the supply water amount coefficient is gradually increased along with the increase of the moving average.
In a graph shown in FIG. 3, a main steam temperature is taken on an axis of abscissas, and a main steam temperature coefficient is taken on an axis of ordinates. As shown in FIG. 3, the main steam temperature coefficient exhibits a lowest value (zero in this embodiment) when the main steam temperature is equal to or below a set temperature (450°C in this embodiment). On the other hand, when the main steam temperature is higher than the set temperature, the main steam temperature coefficient is increased to 1.0 along with the increase of the main steam temperature. In this embodiment, the main steam temperature coefficient is increased from the lowest value to 1.0 along with the increase of the main steam temperature from the set temperature toward a prescribed temperature (for example, 460°C). On the other hand, the main steam temperature coefficient exhibits 1.0 when the main steam temperature is equal to or above the prescribed temperature. The lowest value may be set to a numerical value smaller than 1.0 and larger than zero.
That is, the water amount control minimum value calculation part 313 transmits the lowest value to the water amount control value calculation part 311 as a water amount control minimum value ML when the main steam temperature is equal to or below the set temperature. On the other hand, within a range where the main steam temperature is higher than the set temperature, the water amount control minimum value calculation part 313 transmits a product of a supply water amount coefficient and a main steam temperature coefficient to the water amount control value calculation part 311 as a water amount control minimum value ML. More specifically, the water amount control minimum value calculation part 313 transmits a value which directly indicates a supply water amount coefficient to the water amount control value calculation part 311 as a water amount control minimum value ML within a range where a main steam temperature is equal to or above the prescribed temperature.
As described above, in this embodiment, a supply water amount to the desuperheater 13 is adopted as an index for calculating a water amount control minimum value ML. This supply water amount is regulated by a feedback control based on a main steam temperature and hence, tendency of increase or decrease of the supply water amount becomes equal to tendency of the increase or decrease of the main steam temperature. Accordingly, in this embodiment, a change width of a main steam temperature after a soot blower operation of the boiler 1 is performed or the like is lowered. Further, the water amount control minimum value calculation part 313 calculates a water amount control minimum value ML based on a moving average of the supply water amount during a fixed period and hence, the change width of the main steam temperature is lowered with more certainty.
The water amount control minimum value calculation part 313 transmits a lowest value to the water amount control value calculation part 311 as a water amount control minimum value ML when a main steam temperature is equal to or below a set temperature. Accordingly, when the main steam temperature is equal to or below the set temperature, a supply water amount to the desuperheater 13 (a degree of opening of the spray water supply valve 24) is maintained at a lowest value. As a result, excessive lowering of the main steam temperature can be suppressed.
As described previously, the steam temperature control device 3 of the embodiment may be formed of a computer such as a personal computer, for example. The above-mentioned water amount control value calculation part 311 and the like are functionally incorporated in the computer by executing a software which is stored in a memory part (not shown in the drawings) such as a hard disk and in which a water amount control value calculation method or the like is programed.

Next, supply water amount control processing (steam temperature control processing) which the steam temperature control device 3 performs is described with reference to FIG. 6. FIG. 6 is a flowchart of the supply water amount control processing.
When the main steam temperature controller 31 accepts interruption indicative of timing at which data is acquired from a timer (step S10: Yes), the main steam temperature controller 31 acquires sensor measured data from respective sensors. Specifically, the main steam temperature controller 31 acquires a main steam temperature from the main steam temperature detector 21, acquires a main steam flow rate (an instantaneous value) from the main steam flow rate detector 22, and acquires a supply water flow rate (an instantaneous value) from the supply water flow rate detector 25 (step S11). The main steam temperature controller 31 stores the acquired data in the memory. The main steam temperature controller 31 sets the acquired main steam temperature as the main steam temperature 212, and prepares 1 record where a value obtained by adding 1 to a value set as the log number of times 211 in the last record is set as the log number of times 211, and the record is added to the main steam temperature log table 210.
The main steam temperature controller 31 where data is stored in the memory requests the water amount control value calculation part 311 to calculate a water amount control value MV.
The water amount control value calculation part 311 which accepts the request firstly determines whether or not the main steam temperature detected by the main steam temperature detector 21 is lowered over a predetermined period (step S12). Assume that the predetermined period is set in advance depending on an empirical rule, a kind of a boiler or the like. The water amount control value calculation part 311 firstly reads a record corresponding to the predetermined period from the main steam temperature log table 210. For example, in the case where the predetermined period is two seconds and a predetermined cycle is one second, three records are read from the latest record. To be more in detail, three records where "n", "n-1" and "n-2" are set as the log number of times 211 are read. Then, the water amount control value calculation part 311 determines that the main steam temperature is lowered over a predetermined period (the main steam temperature exhibits lowering tendency) in the following case. That is, a main steam temperature set as the main steam temperature 212 in the latest record where "n" is set as the log number of times 211 is lower than a main steam temperature set as the main steam temperature 212 in the record where "n-1" is set as the log number of times 211, and a main steam temperature set as the main steam temperature 212 in the record where "n-1" is set as the log number of times 211 is lower than a main steam temperature set as the main steam temperature 212 in the record where "n-2" is set as the log number of times 211. On the other hand, the water amount control value calculation part 311 determines that the main steam temperature is not lowered over the predetermined period (the main steam temperature does not exhibit lowering tendency) in the following case. That is, a main steam temperature set as the main steam temperature 212 in the record where "n" is set as the log number of times 211 is higher than a main steam temperature set as the main steam temperature 212 in the record where "n-1" is set as the log number of times 211, or a main steam temperature set as the main steam temperature 212 in the record where "n-1" is set as the log number of times 211 is higher than a main steam temperature set as the main steam temperature 212 in the record where "n-2" is set as the log number of times 211.
In the case where the water amount control value calculation part 311 determines that the main steam temperature detected by the main steam temperature detector 21 is not lowered over the predetermined period (step S12: No), the water amount control value calculation part 311 requests the control gain calculation part 312 to calculate a control gain.
The control gain calculation part 312 which accepts the request reads a main steam temperature acquired by the main steam temperature detector 21 and a target temperature SV from the memory, and obtains a control gain using the function shown in FIG. 4. The control gain calculation part 312 transfers the control gain to the water amount control value calculation part 311 (step S13).
The water amount control value calculation part 311 which receives the control gain calculates a water amount control value MV based on data stored in the memory (step S14). For example, the water amount control value calculation part 311 obtains a main steam flow rate (instantaneous value) acquired by the main steam flow rate detector 22. Then, the water amount control value calculation part 311 obtains a corrected value by adding an external gain or an external bias to a differential between a value obtained this time and the value obtained previous time, and calculates a water amount control value MV of this time by adding the corrected value to a water amount control value MV of previous time.
On the other hand, in step S12, in the case where the water amount control value calculation part 311 determines that the main steam temperature detected by the main steam temperature detector 21 is lowered over the predetermined period (step S12: Yes), the water amount control value calculation part 311 requests the water amount control minimum value calculation part 313 to calculate a water amount control minimum value ML.
The water amount control minimum value calculation part 313 which accepts the request reads a moving average of a supply water flow rate acquired by the supply water flow rate detector 25 from the memory, and obtains a water amount control minimum value ML using the functions shown in FIG. 2 and FIG. 3. The water amount control minimum value calculation part 313 transfers the water amount control minimum value ML to the water amount control value calculation part 311 (step S15).
The water amount control value calculation part 311 which accepts the water amount control minimum value ML sets the water amount control minimum value ML as a water amount control value MV (step S16).
The water amount control value calculation part 311 which obtained the water amount control value MV transfers the water amount control value MV to the outlet temperature controller 32.
The outlet temperature controller 32 which accepts the water amount control value MV reads an outlet temperature of steam acquired by the outlet temperature detector 23 from the memory, and corrects the water amount control value MV based on the outlet temperature (step S17). For example, when the outlet temperature is higher than a predetermined set value, the outlet temperature controller 32 adds a corrected value obtained by multiplying a deviation between an outlet temperature and a set value by a coefficient to the water amount control value MV thus calculating a corrected water amount control value MV. The predetermined set value is, for example, a value obtained by subtracting a preset temperature from a target temperature SV.
The outlet temperature controller 32 which calculates the water amount control value MV transfers the water amount control value MV to the supply water flow rate controller 33.
The supply water flow rate controller 33 controls the spray water supply valve 24 based on the water amount control value MV transferred from the outlet temperature controller 32 (step S18). Accordingly, a supply water amount to the desuperheater 13 is regulated.
The steam temperature control device 3 repeats processing in step S10 to step S18 at a predetermined cycle.
In this manner, the steam temperature control device 3 changes a water amount control minimum value ML based on a moving average of a supply water flow rate which the supply water flow rate detector 25 detects at a predetermined cycle. Accordingly, even when a soot blower operation of the boiler 1 or the like is performed, a supply water amount to the desuperheater 13 is increased or decreased so as to follow the increase or decrease of a main steam temperature. That is, the steam temperature control device 3 can control a main steam temperature such that the deviation of the main steam temperature from a target temperature SV can be prevented as much as possible.
In this embodiment, whether or not the main steam temperature exhibits a lowering tendency for a predetermined period is determined by looking up the main steam temperature log table 210 which shows the history of a main steam temperature. However, such determination may be made using other method. For example, each time the water amount control value calculation part 311 acquires a main steam temperature from the main steam temperature detector 21, the water amount control value calculation part 311 compares this main steam temperature with a main steam temperature of previous time, and stores the number of times of the occurrence of the case that the temperature is lower than the main steam temperature of previous time in the memory. Specifically, in the case where a main steam temperature acquired this time is lower than a main steam temperature acquired previous time, 1 is added to the stored number of times of the occurrence of the case. On the other hand, in the case where the main steam temperature acquired this time is higher than the main steam temperature acquired previous time, the stored number of times of the occurrence of the case is cleared, that is, the stored number of times of the occurrence of the case is set to 0(zero). Then, when the stored number of times of the occurrence of the case where a main steam temperature acquired this time is lower than a main steam temperature acquired previous time becomes the predetermined number of times (for example, three times), the water amount control value calculation part 311 determines that the main steam temperature exhibits a lowering tendency for a predetermined period.
A case is considered where, in a state where a control by the steam temperature control device 3 is performed, a supply amount of a waste from the refuse feeder 6 to the incinerator 5 is largely lowered. In this case, a flow rate of an exhaust gas supplied to the respective superheaters 12, 14 from the incinerator 5 is lowered, that is, a main steam temperature is lowered. Accordingly, a supply water amount to the desuperheater 13 is also largely lowered. On the other hand, a certain amount of exhaust gas (quantity of heat) is continuously supplied to the respective superheaters 12, 14. As a result, pipes (pipes through which steam flows) 13a, 13b connected to the desuperheater 13 are heated by an exhaust gas and hence, a temperature of the pipes 13a, 13b is increased. Then, when a supply amount of waste to the incinerator 5 is recovered (when a flow rate of an exhaust gas supplied to the boiler 1 is recovered), a main steam temperature starts to be increased. With the increase of the main steam temperature, although a supply water amount to the desuperheater 13 is increased due to a control by the steam temperature control device 3, a part of cold heat of this water is used for cooling the pipes 13a, 13b during a period until a temperature of the pipes 13a, 13b is lowered to an appropriate temperature. Accordingly, there is a concern that a main steam temperature is increased to a temperature higher than a target temperature SV.
The control unit of this embodiment includes the target temperature control device 4 for overcoming such a drawback.
The target temperature control device 4 controls a target temperature SV of a main stream temperature, and transmits the target temperature SV to the main steam temperature controller 31 of the steam temperature control device 3. The target temperature control device 4 has a target temperature setting part 41 and a target temperature changing part 42.
The target temperature setting part 41 transmits the target temperature SV to the target temperature changing part 42. The target temperature SV (for example, 490°C) set by the target temperature setting part 41 is input from the outside of the target temperature control device 4, for example, by an operator.
Upon receiving a quantity of heat lowering signal which is a signal indicative of lowering of a quantity of heat of an exhaust gas supplied to the respective superheaters 12, 14, the target temperature changing part 42 changes the target temperature SV to be transmitted to the steam temperature control device 3 to a low target temperature lower than the target temperature SV (the target temperature SV received from the target temperature setting part 41) before the target temperature changing part 42 receives the quantity of heat lowering signal. That is, the target temperature changing part 42 transmits the low target temperature to the steam temperature control device 3 when the target temperature changing part 42 receives the quantity of heat lowering signal.
As such a quantity of heat lowering signal, the following signals may be named. That is, the signal may be a signal which indicates that a detection value of a rotational speed detector 27 which is mounted on the refuse feeder 6 and detects a rotational speed of a motor of the refuse feeder 6 becomes a predetermined value (for example, 15%) or less and a signal which indicates that a detection value of the main steam temperature detector 21 becomes a predetermined value (for example, 470°C) or less.
When the target temperature changing part 42 receives a quantity of heat recovery signal which is a signal indicative of recovery of a quantity of heat of an exhaust gas supplied to the respective superheaters 12, 14, the target temperature changing part 42 returns a target temperature to be transmitted to the steam temperature control device 3 to a target temperature SV before the target temperature changing part 42 receives the quantity of heat lowering signal. That is, when the target temperature changing part 42 receives a quantity of heat recovery signal, the target temperature changing part 42 transmits a target temperature SV received from the target temperature setting part 41 to the steam temperature control device 3.
As a quantity of heat recovery signal, the following signals are named. That is, such a signal may be a signal which indicates that a state where a detection value of the rotational speed detector 27 is equal to or above the predetermined value (for example, 15%) continues for 90 seconds or more and a signal which indicates that a state where a detection value of the main steam temperature detector 21 is equal to or above a predetermined value (for example, 470°C) continues for 5 minutes or more.
Next, target temperature control processing is described with reference to FIG. 7. This control processing is performed parallel to supply water amount control processing shown in FIG. 6.
In the target temperature control processing, firstly, the target temperature changing part 42 determines whether or not a quantity of heat lowering signal is received (step S20). As a result, when the quantity of heat lowering signal is not received, the target temperature changing part 42 returns to step S20 again. When the quantity of heat lowering signal is received, the target temperature changing part 42 lowers a target temperature SV to a low target temperature (step S21). At this stage of processing, the target temperature changing part 42 lowers the target temperature SV by 10°C at a rate of 2°C per 1 minute, for example. As a result, the steam temperature control device 3 increases a supply water amount to the desuperheater 13 such that a main steam temperature becomes the low target temperature and hence, the increase of a temperature of the pipes 13a, 13b connected to the desuperheater 13 is suppressed. Accordingly, even when a quantity of heat supplied to the boiler 1 is recovered so that the main steam temperature is increased thereafter, an excessive increase of the main steam temperature can be suppressed.
Next, the target temperature changing part 42 determines whether or not a quantity of heat recovery signal is received (step S22). As a result, when the quantity of heat recovery signal is not received, the target temperature changing part 42 returns to step S22 again. When the quantity of heat recovery signal is received, the target temperature changing part 42 increases a target temperature (step S22). Specifically, the target temperature changing part 42 returns the target temperature to be transmitted to the steam temperature control device 3 to the target temperature SV from the low target temperature. At this stage of processing, the target temperature changing part 42 increases the target temperature by 10°C at a rate of 1°C per 1 minute, for example. Accordingly, when a quantity of heat supplied to the boiler 1 is recovered, a state is restored where heat can be effectively recovered by the boiler 1.
It should be construed that the embodiment disclosed this time is illustrative and is not limitative in all aspects. The scope of the present invention is not defined by the description of the above-mentioned embodiment and is defined by Claims, and all modifications which are considered to be equivalent to Claims and are considered to fall within the scope of Claims are embraced by the scope of the present invention.
Hereinafter, the above-mentioned embodiment is recapitulated.
The steam temperature control device according to the embodiment is the steam temperature control device for controlling a main steam temperature which is a temperature of main steam generated from the superheater of the boiler including the desuperheater which decreases a temperature of steam using an amount of spray water based on a water amount control value for controlling a degree of opening of the spray water supply valve and the superheater for heating steam discharged from the desuperheater by an exhaust gas discharged from the furnace. The steam temperature control device includes the water amount control value calculation part which calculates the water amount control value based on the main steam temperature such that the main steam temperature becomes a target temperature, and transmits the water amount control value to the spray water supply valve. The water amount control value calculation part is configured to transmit, as a lower limit value of the water amount control value, a water amount control minimum value to the spray water supply valve. The water amount control minimum value is calculated based on a moving average of a supply water amount to the desuperheater during a fixed period or a moving average of the water amount control value during a fixed period.
In the steam temperature control device, as an index for calculating a water amount control minimum value (a lower limit value of a water amount control value), a supply water amount to the desuperheater or a water amount control value is adopted. Accordingly, a change width of a main steam temperature after a soot blower operation of the boiler or the like can be lowered. Further, the water amount control value calculation part of this device calculates a water amount control minimum value based on a moving average of a supply water amount to the desuperheater during a fixed period or a moving average of a water amount control value during a fixed period and hence, a change width of the main steam temperature can be decreased with certainty.
In this case, it is preferable that the water amount control value calculation part transmits a preset lowest value to the spray water supply valve as the water amount control minimum value when the main steam temperature is equal to or below a set temperature which is lower than the target temperature.
With such processing, when the main steam temperature is equal to or below the set temperature, a degree of opening of the spray water supply valve (supply water amount) is maintained at the lowest value. Accordingly, excessive lowering of the main steam temperature can be suppressed.
Specifically, it is preferable that the water amount control value calculation part transmits a value to be calculated by multiplying the moving average or a value based on the moving average by a main steam temperature coefficient to the spray water supply valve as the water amount control minimum value. The main steam temperature coefficient indicates the lowest value when the main steam temperature is equal to or below the set temperature, and is decided based on the main steam temperature when the main steam temperature is higher than the set value.
With such processing, when the main steam temperature is equal to or below the set temperature, a degree of opening of the spray water supply valve (supply water amount) is maintained at a lowest value, while when the main steam temperature is higher than the set temperature, an amount of spray water based on the main steam temperature is supplied to the desuperheater.
In the steam temperature control device, it is preferable that the water amount control value calculation part transmit the water amount control minimum value to the spray water supply valve as a lower limit value of the water amount control value, when the main steam temperature is continuously lowered for a predetermined period.
The control unit of the embodiment is the control unit which includes the steam temperature control device and the target temperature control device which controls a target temperature of the main steam temperature and transmits the target temperature to the steam temperature control device. The target temperature control device has the target temperature changing part which, upon receiving a quantity of heat lowering signal which is a signal indicative of lowering of a quantity of heat of an exhaust gas supplied to the superheater, changes a target temperature transmitted to the steam temperature control device to a low target temperature lower than a target temperature before the target temperature control device receives the quantity of heat lowering signal.
In the control unit, the target temperature changing part transmits, upon receiving a quantity of heat lowering signal, the low target temperature to the steam temperature control device as a target temperature and hence, the steam temperature control device increases a supply water amount to the desuperheater such that a main steam temperature becomes the low target temperature. Accordingly, an increase of a temperature of the pipes connected to the desuperheater is suppressed. Accordingly, even when a quantity of heat supplied to the boiler is recovered so that the main steam temperature is increased thereafter, an excessive increase of the main steam temperature can be suppressed.
In this case, it is preferable that the target temperature changing part returns a target temperature to be transmitted to the steam temperature control device to a target temperature before the target temperature changing part receives the quantity of heat lowering signal when the target temperature changing part receives a quantity of heat recovery signal which is a signal indicative of recovery of a quantity of heat of an exhaust gas supplied to the superheater.
With such processing, when a quantity of heat supplied to the boiler is recovered, a state is restored where heat can be effectively recovered by the boiler.

Claims

A steam temperature control device for controlling a main steam temperature which is a temperature of main steam generated from a superheater of a boiler including a desuperheater which decreases a temperature of steam using an amount of spray water based on a water amount control value for controlling a degree of opening of a spray water supply valve and the superheater for heating steam discharged from the desuperheater by an exhaust gas discharged from a furnace, wherein
the steam temperature control device comprises a water amount control value calculation part which calculates the water amount control value based on the main steam temperature such that the main steam temperature becomes a target temperature, and transmits the water amount control value to the spray water supply valve,
the water amount control value calculation part is configured to transmit, as a lower limit value of the water amount control value, a water amount control minimum value to the spray water supply valve,
the water amount control minimum value is calculated based on a moving average of a supply water amount to the desuperheater during a fixed period or a moving average of the water amount control value during a fixed period.
The steam temperature control device according to claim 1, wherein
the water amount control value calculation part transmits a preset lowest value to the spray water supply valve as the water amount control minimum value when the main steam temperature is equal to or below a set temperature which is lower than the target temperature.
The steam temperature control device according to claim 2, wherein
the water amount control value calculation part transmits a value to be calculated by multiplying the moving average or a value based on the moving average by a main steam temperature coefficient to the spray water supply valve as the water amount control minimum value,
the main steam temperature coefficient indicates the lowest value when the main steam temperature is equal to or below the set temperature, and is decided based on the main steam temperature when the main steam temperature is higher than the set value.
The steam temperature control device according to any one of claims 1 to 3, wherein
the water amount control value calculation part transmits the water amount control minimum value to the spray water supply valve as a lower limit value of the water amount control value, when the main steam temperature is continuously lowered for a predetermined period.
A control unit comprising:
the steam temperature control device according to any one of claims 1 to 4; and

a target temperature control device which controls a target temperature of the main steam temperature and transmits the target temperature to the steam temperature control device, wherein

the target temperature control device has a target temperature changing part which, upon receiving a quantity of heat lowering signal which is a signal indicative of lowering of a quantity of heat of an exhaust gas supplied to the superheater, changes a target temperature to be transmitted to the steam temperature control device to a low target temperature lower than a target temperature before the target temperature control device receives the quantity of heat lowering signal.
The control unit according to claim 5, wherein
the target temperature changing part returns a target temperature to be transmitted to the steam temperature control device to a target temperature before the target temperature changing part receives the quantity of heat lowering signal when the target temperature changing part receives a quantity of heat recovery signal which is a signal indicative of recovery of a quantity of heat of an exhaust gas supplied to the superheater.