JP2013181679A - Power generation system, and steam temperature control method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve accuracy of main steam temperature control in a once-through boiler using fuel such as coal containing carbon.SOLUTION: A power generation system 1 includes a furnace 2 to burn coal fuel, a steam turbine 3 to generate power using steam produced in the furnace 2, steam piping L to supply the steam from the furnace 2 to the steam turbine 3, a secondary superheater 4b and tertiary superheater 4c both installed in the steam piping L, a secondary desuperheater 5b installed between the tertiary superheater 4c and the secondary superheater 4b in the steam piping L, and a steam temperature control device 10 to control a water-fuel ratio which is a ratio of an amount of heat generation in the furnace 2 and an amount of feed water. The steam temperature control device 10 includes a first calculation section to determine a first water-fuel ratio instruction that conforms a degree of superheat at a furnace outlet to a set value of a degree of superheat, and a set value correction section to correct the set value of a degree of superheat based on the difference between an inlet temperature and an outlet temperature of the secondary desuperheater 5b.

Description

  The present invention relates to a power generation system having a transformer once-through boiler and a steam temperature control method thereof.

  In thermal power plants and the like, many power generation systems including a variable-flow once-through boiler and a steam turbine (steam turbine) as main components are employed (for example, Patent Documents 1 to 3). This power generation system generates power with a steam turbine using steam generated by a transformer once-through boiler.

For example, Patent Document 1 discloses that steam generated in a furnace as a steam generation source passes through a primary superheater, a primary superheat reducer, a secondary superheater, a secondary superheat reducer, and a tertiary superheater. A power generation system is disclosed that is temperature adjusted and sent to a steam turbine.
In the power generation system disclosed in Patent Document 1, the water-fuel ratio control based on the outlet temperature of the primary superheater is performed during the once-through operation, and the primary superheat desuperheater based on the outlet temperature of the secondary superheater is performed. Spray valve control and spray valve control of the secondary superheat desuperheater based on the steam temperature at the boiler outlet (steam turbine inlet) (hereinafter, this temperature is referred to as “main steam temperature”) are performed. Further, during the start-up bypass operation, the water / fuel ratio control is performed based on the main steam temperature, and the spray valve of the primary superheat desuperheater is fully opened, and the secondary superheat reduction is reduced when the main steam temperature deviation is large. The spray valve of the warmer is opened to suppress main steam temperature fluctuations when fuel is excessive.

Japanese Patent Laid-Open No. 1-127806 JP-A-2-169902 Japanese Patent Laid-Open No. 7-310902

  Conventionally, as disclosed in Patent Document 1, water-fuel ratio control in a furnace has been performed based on the main steam temperature. However, this control has a drawback of poor response. Therefore, in recent years, a new control method for controlling the degree of superheat at the furnace outlet has been proposed for the purpose of improving responsiveness.

  However, this control method is effective in a power generation system that uses gas or heavy oil as the fuel for the furnace, but when using a fuel containing carbon such as coal whose properties (calorific value, etc.) are not stable, It is difficult to obtain the main steam temperature. That is, when using a fuel containing carbon such as coal, due to changes in the combustion state in the furnace due to fluctuations in the calorific value, changes in the heat absorption rate due to slag adhering to the water cooling wall or superheater, etc. The degree of superheat at the furnace outlet and superheater will fluctuate. Therefore, for example, even if the superheat degree at the furnace outlet can be controlled, there is a possibility that the desired main steam temperature cannot be obtained due to the change in the heat absorption characteristics of the superheater following the subsequent stage.

  In particular, since the newly proposed control method controls the degree of superheat at the furnace outlet, the main steam temperature at the boiler outlet can maintain the rated temperature, but the superheat at the downstream side of the furnace outlet. Depending on the amount of heat absorbed by the cooler, the required amount of spray from the superheat reducer cannot be injected, and the steam temperature control deviation at the time of load increase and decrease may increase.

  The present invention has been made in view of such circumstances, and in a once-through boiler using a fuel containing carbon such as coal, a power generation system capable of improving the accuracy of steam temperature control and the steam temperature control thereof It aims to provide a method.

In order to solve the above problems, the present invention employs the following means.
The present invention relates to a furnace for burning a fuel containing carbon such as coal, a steam turbine for generating electricity by rotating a turbine using steam generated in the furnace, and the steam from the furnace to the steam turbine. Steam pipe to be supplied; N-order (N is an integer greater than or equal to 3) superheater provided in series with the steam pipe; N-order superheater among the N-order superheaters provided to the steam pipe. And an N-1 primary superheat reducer provided between the N-1 primary superheater, and a control means for controlling a water / fuel ratio that is a ratio of a calorific value of fuel and a water supply amount in the furnace, The control means includes: a first calculation means for determining a first water-fuel ratio command that makes a superheat degree at the furnace outlet coincide with a superheat degree set value; and an inlet temperature and an outlet temperature of the N-1 primary superheat reducer. A setting for correcting the superheat setting value based on the deviation. Providing a power generation system comprising a value correcting means.

  According to the present invention, the superheat degree set value at the furnace outlet based on the deviation between the inlet temperature and the outlet temperature of the N-1 primary superheat reducer provided between the Nth superheater and the N-1 primary superheater. Is corrected. Thereby, the superheat degree of a furnace exit is controllable to the superheat degree which considered the temperature difference of the input-output of a N-1 primary superheat reducer. As a result, a sufficient temperature difference in the N-1 primary overheat reducer can be secured, and a margin can be provided for the temperature reduction adjustment of the N-1 primary overheat reducer. Therefore, it becomes possible to adjust the inlet temperature of the N-th superheater to an appropriate temperature, and it is possible to eliminate the shortage of heat input, which has been a problem in the past, and to match the main steam temperature with the main steam temperature set value. Is possible.

  In the power generation system, the set value correction means calculates a correction value that matches a deviation between an inlet temperature and an outlet temperature of the N-1 primary superheat reducer with a target temperature difference, and uses the correction value. The superheat degree set value may be corrected.

  According to the above configuration, since the superheat degree setting value is corrected using the correction value that matches the deviation between the inlet temperature and the outlet temperature of the N-1 primary superheat reducer with the target temperature difference, the N-1 primary superheater is corrected. The difference between the inlet temperature and the outlet temperature of the reducer can be made closer to the target temperature difference.

  In the power generation system, the target temperature difference may be determined according to a required load of the steam turbine.

  According to the above configuration, since the target temperature difference is determined according to the required load of the steam turbine, the difference between the inlet temperature and the outlet temperature of the N-1 primary superheat reducer is changed to an appropriate temperature difference according to the required load. It becomes possible to approach.

  In the power generation system, the control means includes the first calculation means and the set value correction means, and the first control means for determining the first water-fuel ratio command and the main steam temperature coincide with the main steam temperature set value. Determined by the second control means for determining the second water-fuel ratio command, the gain determining means for determining the weighting coefficient of the first water-fuel ratio command and the second water-fuel ratio command, and the first control means. A first water-fuel ratio command, a second water-fuel ratio command determined by the second control means, and a water-fuel ratio determining means for determining a final water-fuel ratio command using the weighting coefficient determined by the gain determining means; It is good also as providing.

  According to such a configuration, the first control means determines the first water-fuel ratio command to make the superheat degree at the furnace outlet coincide with the superheat degree set value, and the second control means sets the main steam temperature to the main steam temperature. A second water-fuel ratio command that matches the temperature set value is determined. Then, the final water-fuel ratio command is determined by using the weighting coefficient determined by the gain determining means for the first water-fuel ratio command and the second water-fuel ratio command. Since two control means are provided in this way, an appropriate water-fuel ratio command suitable for the operating state can be obtained by appropriately changing the weighting of the first water-fuel ratio command and the second water-fuel ratio command according to the operating state. Is possible.

  In the power generation system, the weighting coefficient of the second water-fuel ratio command is set higher than the weighting coefficient of the first water-fuel ratio command in the high load zone, and the second water ratio is set in the low load zone. The weighting coefficient of the first water-fuel ratio command is set higher than the weighting coefficient of the fuel ratio command.

  Generally, the steam flowing into the superheater needs to be superheated steam. However, for example, as shown in FIG. 10, in the low load region where the boiler outlet main steam pressure is low, the furnace outlet may enter the saturation region, and it is important to maintain the degree of superheat. On the other hand, in the high load region where the boiler outlet main steam pressure is high, the steam moves away from the saturation region, so there is no fear of becoming wet steam, and superheated steam is naturally obtained. Therefore, in such a load band, the importance of superheat degree control becomes low. Therefore, the weighting coefficient of the second water-fuel ratio command determined based on the main steam temperature is set to a large value in the high load zone, and the weighting coefficient of the first water-fuel ratio command determined based on the degree of superheat in the low load zone. By setting the value to a large value, it becomes possible to perform water-fuel ratio control in accordance with the steam state.

  The power generation system includes a low-pressure steam turbine that is driven at a steam pressure lower than that of the steam turbine, reheat means that reheats the steam used in the steam turbine and supplies the steam to the low-pressure steam turbine, and is generated in the furnace And an inflow amount adjusting means for adjusting an inflow amount of the burned combustion gas to the reheating means, and the inflow amount adjusting means is rated for the distribution of passage of the combustion gas that flows into the reheating means when the load drops. It is good also as increasing from the time of driving | operation.

  In this way, when the load drops, the distribution distribution of the combustion gas flowing into the reheating means is increased as compared with the rated operation, so that the amount of heat absorbed by the reheating means when the load drops can be increased. A drop in steam temperature at the outlet of the heating means can be suppressed.

  The power generation system includes a low-pressure steam turbine that is driven at a steam pressure lower than that of the steam turbine, reheat means that reheats the steam used in the steam turbine and supplies the steam to the low-pressure steam turbine, and the steam pipe. A superheat reducer provided between the adjacent superheaters arranged; a spray pipe branched from a water supply line to the furnace and supplied to the superheat reducer; and the superheat reducer provided in the spray pipe. A spray valve for adjusting the amount of spray supplied to the heater, and the control means is based on an outlet temperature of the superheater provided immediately downstream of the superheat reducer on the steam flow downstream side. Opening determining means for determining the opening of the spray valve, and opening correcting means for increasing the opening of the spray valve determined by the opening determining means when the load drops. It is also possible to be.

  According to such a configuration, when the load drops, the amount of spray supplied to the superheat reducer is increased, so that the flow rate of fluid passing through the water supplied to the furnace decreases. When the flow rate of fluid through the furnace decreases, the water-fuel ratio increases and the degree of superheat at the furnace outlet can be increased. By increasing the degree of superheat in this way, heat absorption on the superheater side can be suppressed and more heat can be distributed to the reheating means. Thereby, the fall of the steam temperature in the exit of the reheating means at the time of load fall can be suppressed.

  In the power generation system, the superheat reducer may be provided between the primary superheater and the secondary superheater.

  It can be said that the superheat reducer provided between the primary superheater and the secondary superheater is the superheat reducer closest to the furnace outlet. The closer to the furnace, the more spray can be made, so the amount of water supplied to the furnace can be effectively reduced and the water / fuel ratio can be increased.

  The power generation system includes: a low-pressure steam turbine that is driven at a steam pressure lower than that of the steam turbine; and a reheat unit that reheats the steam used in the steam turbine and supplies the steam to the low-pressure steam turbine. 1 calculating means is provided with the correction means which correct | amends the superheat degree in the said furnace exit so that it may have predetermined time delay at the time of load fall, and makes the superheat degree in this furnace outlet after correction correspond to the said superheat degree setting value Such a first water-fuel ratio command may be determined.

  In this way, by giving a predetermined time delay to the superheat degree at the furnace outlet, it is possible to avoid a sudden drop in the superheat degree at the furnace outlet, and for a certain period of time after the required load decreases, It is possible to maintain a high degree of superheat. As a result, it is possible to prevent the reheating temperature from rapidly decreasing, and it is possible to gradually decrease the reheating temperature.

  The present invention relates to a furnace for burning a fuel containing carbon such as coal, a steam turbine for generating electricity by rotating a turbine using steam generated in the furnace, and the steam from the furnace to the steam turbine. A steam pipe to be supplied; an N-order (N is an integer of 3 or more) provided in series with the steam pipe; and an N-order superheater among the N-order superheaters provided in the steam pipe. Power generation comprising an N-1 primary superheat reducer provided between the refrigeration unit and the N-1 primary superheater, and control means for controlling the water / fuel ratio, which is the ratio of the calorific value of fuel and the amount of water supply in the furnace. A steam temperature control method applied to a system, wherein a first calculation process for determining a first water-fuel ratio command that makes a superheat degree at a furnace outlet coincide with a superheat degree set value, and the N-1st order superheat reduction Deviation between inlet temperature and outlet temperature Based providing steam temperature control method of a power generation system including a set value correcting step of correcting the superheat settings.

  ADVANTAGE OF THE INVENTION According to this invention, in the once-through boiler using the fuel containing carbon, such as coal, there exists an effect that the precision of steam temperature control can be improved.

It is the figure which showed roughly the structure of the electric power generation system which concerns on 1st Embodiment of this invention. It is the functional block diagram which expanded and showed the function regarding water-fuel ratio control among the various functions with which the steam temperature control apparatus shown in FIG. 1 is provided. It is the figure which showed an example of the control logic of a setting value correction | amendment part. It is the figure which showed an example of the control logic of a 1st calculating part and a 2nd calculating part. It is the figure which showed an example of the gain function used with a 1st gain determination part and a 2nd gain determination part. It is the figure which showed an example of the change of the steam temperature from a furnace exit temperature to the main steam temperature. It is the functional block diagram which expanded and showed the function regarding water-fuel ratio control among the various functions with which the steam temperature control apparatus which concerns on 2nd Embodiment of this invention is provided. It is the figure which showed an example of the control logic of the 2nd water fuel ratio command determination part. It is the figure which showed an example of the gain function used with a 3rd gain determination part and a 4th gain determination part. It is a figure for demonstrating the basis of the weighting coefficient determined by a gain determination part. It is the figure which showed schematically the structure of the electric power generation system which concerns on 3rd Embodiment of this invention. In 3rd Embodiment of this invention, it is the control block diagram which showed one structural example for implement | achieving the method for making the exit vapor | steam temperature of a reheater into a predetermined temperature range. In 3rd Embodiment of this invention, it is the control block diagram which showed one structural example for implement | achieving the method for making the exit vapor | steam temperature of a reheater into a predetermined temperature range.

[First Embodiment]
Hereinafter, a power generation system and a steam temperature control method thereof according to a first embodiment of the present invention will be described with reference to the drawings.
In FIG. 1, a power generation system 1 includes a furnace 2 that burns fuel containing carbon such as coal, a steam turbine 3 that generates power by rotating a turbine using steam generated by the furnace 2, and steam in the power generation system. And a steam temperature control device (control means) 10 for controlling the temperature.
Steam is supplied from the furnace 2 to the steam turbine 3 through a steam pipe L. The steam pipe L is provided with a primary superheater 4a, a secondary superheater 4b, and a tertiary superheater 4c provided in series. In the steam pipe L, a primary superheat reducer 5a is provided between the primary superheater 4a and the secondary superheater 4b, and a secondary superheat reduction is provided between the secondary superheater 4b and the tertiary superheater 4c. A vessel 5b is provided. Although the N-th order (N = 3) superheater is provided here, the number of stages of the superheater is not particularly limited as long as a third-order or higher superheater is provided. Further, at least between the superheater at the final stage (N-th superheater) and the superheater (N-1 primary superheater) provided in front of it, the N-1 primary superheat reducer (in this embodiment, A secondary overheat reducer 5b) is provided.

  In such a power generation system 1, in the furnace 2, fuel containing carbon such as coal is burned, and a feed water pump 18 described later is driven to circulate a fluid through a water cooling wall provided in the furnace 2. To generate steam. The steam generated in the furnace 2 is sent to the primary superheater 4a, the primary superheat reducer 5a, the secondary superheater 4b, the secondary superheat reducer 5b, and the tertiary superheater 4c in order, Heat removal is repeated and the steam temperature is adjusted. The temperature-adjusted steam is sent to the steam turbine 3 via the governor valve 7 and used to drive the steam turbine 3.

  The steam after driving the steam turbine 3 is guided to the condenser 8 and returned to water (liquid) by the condenser 8. The water generated in the condenser 8 is pumped by the condensate pump 9 in the order of the low-pressure feed water superheater 10 and the deaerator 11. The water deaerated by the deaerator 11 is pumped by the boiler feed pump 12 in the order of the high-pressure feed water superheater 13 and the economizer 14. Most of the water pumped to the economizer 14 is led to the furnace 2 by the feed water pump 18 and used again as steam, and a part of the water is primary spray pipe BS1 and secondary spray pipe BS2. Are supplied to the primary overheat reducer 5a and the secondary overheat reducer 5b, respectively.

  A primary spray valve 15a is provided in the primary spray pipe BS1, and the amount of spray in the primary superheat reducer 5a is adjusted by controlling the valve opening degree of the primary spray valve 15a. Similarly, the secondary spray pipe BS2 is provided with a secondary spray valve 15b, and the amount of spray in the secondary superheat reducer 5b is adjusted by controlling the valve opening degree.

  In the power generation system 1, the inlet temperature Ti and the outlet temperature To of the final stage superheat reducer, that is, the secondary superheat reducer 5 b are measured by the temperature sensors 16 a and 16 b, and the measured values are sent to the steam temperature control device 10. Is output. Further, the outlet steam temperature of the tertiary superheater 4 c, that is, the main steam temperature Tm is measured by the temperature sensor 16 c, and the measured value is output to the steam temperature control device 10. Further, the steam pressure Pw and the steam temperature Tw at the furnace outlet are respectively measured by the pressure sensor 16d and the temperature sensor 16e, and the measured values are output to the temperature control device 10.

  The steam temperature control device 10 uses the temperature and pressure notified from each temperature sensor and pressure sensor to control the water-fuel ratio in the furnace 2 and the valve opening control of the primary spray valve 15a and the secondary spray valve 15b. I do. Here, the water-fuel ratio is a ratio of the calorific value (kcal) of fuel and the amount of water supply (ton / h), and is defined by the following equation (1), for example.

  Water-fuel ratio = Fuel calorific value (kcal) / Water supply amount (ton / h) (1)

  The steam temperature control unit 10 is, for example, a computer, and includes a main storage device such as a CPU (Central Processing Unit) and a RAM (Random Access Memory) and an auxiliary storage device as main components. The auxiliary storage device is a computer-readable recording medium, such as a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, or a semiconductor memory. Various programs (for example, a water-fuel ratio control program, a primary spray valve opening control program, a secondary spray valve opening control program, etc.) are stored in this auxiliary storage device, and the CPU assists. Various processes to be described later are realized by reading and executing the program from the storage device to the main storage device.

FIG. 2 is a functional block diagram in which functions related to water-fuel ratio control are developed out of various functions provided in the steam temperature control apparatus 10.
As shown in FIG. 2, the steam temperature control device 10 includes a first water / fuel ratio command determination unit 20. The first water-fuel ratio command determination unit 20 includes a set value correction unit 21, a first calculation unit 22, and a second calculation unit 23 as main components.

  The set value correction unit 21 corrects the superheat degree set value used in the first calculation unit 22 described later, based on the deviation between the inlet temperature Ti and the outlet temperature To of the secondary superheat reducer 5b. Specifically, the set value correction unit 21 calculates a correction value that matches the deviation between the inlet temperature Ti and the outlet temperature To of the secondary superheat reducer 5b with the target temperature difference, and uses the correction value to determine the degree of superheat. Correct the set value. Here, the target temperature difference is determined according to, for example, the required load of the steam turbine, and is set to a larger value as the required load is higher, for example.

  The first calculation unit 22 determines a first control command for the water / fuel ratio so that the superheat degree at the furnace outlet matches the superheat degree set value. The superheat setting value used here is the superheat setting value corrected by the set value correction unit 21. The degree of superheat at the furnace outlet can be determined by using, for example, the steam temperature Tw and steam pressure Pw at the furnace outlet and a Mollier diagram (ph diagram) having an isotherm.

  The second calculation unit 23 determines a second control command for the water / fuel ratio so that the outlet temperature of the tertiary superheater 4c, that is, the main steam temperature Tm matches the preset main steam temperature set value. In the present embodiment, the second calculation unit 23 can be omitted as will be described later.

  FIG. 3 is a diagram illustrating an example of the control logic of the set value correction unit 21. As shown in FIG. 3, the set value correction unit 21 receives the inlet temperature Ti and the outlet temperature To of the secondary superheat reducer 5b, and calculates the deviation between them, and the required load of the steam turbine. A function unit 32 for determining the deviation target value and a subtracter 33 for subtracting the deviation target value determined by the function unit 32 from the deviation output from the subtractor 31 are provided as main components. The deviation calculated by the subtractor 33 passes through the delay unit 34 and the proportional unit 35, is added with a predetermined delay amount and gain, and is output to the selection unit 36. The selection unit 36 outputs the value as it is if the input value from the proportional unit 35 is positive (plus), and outputs zero if it is negative (minus).

  The output value from the selector 36 is output to the multiplier 38, and multiplied by a gain corresponding to the required load of the steam turbine. Here, the gain to be multiplied corresponds to a so-called weighting coefficient that determines how much the correction amount based on the temperature difference in the secondary superheat reducer 5b is applied to the water-fuel ratio control. The deviation weighted by the multiplier 38 is output to the adder 40 via the PI control unit 39. In the adder 40, the superheat degree set value is corrected by adding the correction value from the PI control unit 39 to the preset superheat degree set value at the furnace outlet. The corrected superheat setting value is output to the first calculation unit 22 and used.

FIG. 4 is a diagram illustrating an example of the control logic of the first calculation unit 22 and the second calculation unit 23. As shown in FIG. 4, the first calculation unit 22 includes a subtractor 41 that calculates a deviation between the superheat degree at the furnace outlet and the superheat degree set value corrected by the set value correction part 21, and the load is changing. Set by the multiplier 42 that multiplies the output of the subtractor 41 by a gain that varies depending on whether the load is constant or a constant load, the first gain determination unit 43 that sets the gain according to the load, and the first gain determination unit 43. And a multiplier 44 for further multiplying the output of the multiplier 42 by the gain. The output of the multiplier 44 is output as a first control command to the adder 49 at the subsequent stage.
The gain set in the first gain determination unit 43 is for setting a weighting coefficient. In this embodiment, the gain is always 1 regardless of the required load, as indicated by the broken line in FIG. Is set.

The second computing unit 23 is a subtractor 45 that calculates a deviation between the main steam temperature Tm and a preset main steam temperature set value, and a gain that varies depending on whether the required load is changing or is in a constant load state. Is multiplied by the output of the subtractor 45, the second gain determining unit 47 for setting the gain according to the load, and the output of the multiplier 46 is further multiplied by the gain set in the second gain determining unit 47 And a multiplier 48.
The gain set in the second gain determination unit 47 is for setting a weighting value. In the present embodiment, as indicated by a solid line in FIG. 5, the gain is always 0 regardless of the required load. (Zero) is set. Accordingly, since the second control command output from the second calculation unit 23 is always zero, the second calculation unit 23 can be omitted.

The first control command for the water / fuel ratio determined by the first calculation unit 22 and the second control command (= 0) for the water / fuel ratio determined by the second calculation unit 23 are added by the adder 49. The multiplier 51 multiplies the gain according to the required load of the steam turbine, and outputs it as a water-fuel ratio command via the integrator 52.
And based on this water-fuel ratio command, the rotation speed of the feed water pump 18 and the supply flow rate of the fuel containing carbon such as coal are controlled, and the degree of superheat at the furnace outlet is adjusted.

  In addition, the steam temperature control device 10 controls the primary spray valve 15a and the secondary spray valve 15b. For example, for the primary spray valve 15a, the valve opening degree is controlled so that the outlet temperature of the secondary superheater 4b, that is, the inlet temperature Ti of the secondary superheat reducer 5b becomes a predetermined temperature. The secondary spray valve 15b controls the valve opening so that the outlet temperature of the tertiary superheater 4c, that is, the main steam temperature Tm becomes a predetermined temperature.

As described above, according to the power generation system 1 and the steam temperature control method thereof according to the present embodiment, the deviation between the inlet temperature Ti and the outlet temperature To of the superheat reducer 5b at the final stage depends on the required load of the steam turbine 3. A correction amount that matches the determined predetermined deviation set value is obtained, and the superheat degree set value at the furnace outlet is corrected using this correction amount. Therefore, the superheat degree at the furnace outlet is set to the value of the superheat reducer 5b at the final stage. The degree of superheat can be controlled in consideration of the temperature difference between input and output.
Thereby, as shown in FIG. 6, the temperature difference Td in the secondary superheat reducer 5b can be sufficiently secured, and it is possible to provide a margin for the temperature reduction adjustment of the secondary superheat reducer 5b. As a result, the inlet temperature of the tertiary superheater 4c can be adjusted to an appropriate temperature, and in addition to the quick response characteristics in the superheat control, there is a margin for the temperature reduction adjustment in the fluctuation of heat generation and load change. Therefore, the main steam temperature can be matched with the main steam temperature set value.
Furthermore, according to the present embodiment, since the water / fuel ratio is controlled by feeding back the degree of superheat at the furnace outlet, the responsiveness can be improved compared to the conventional method of feeding back the main steam temperature and controlling the water / fuel ratio. it can.

[Second Embodiment]
Next, a power generation system and a steam temperature control method thereof according to the second embodiment of the present invention will be described. As shown in FIG. 7, the steam temperature control device 20 ′ in the power generation system according to the present embodiment has a second water-fuel ratio command determination unit 60 and a water in addition to the first water-fuel ratio command determination unit 20 shown in FIG. 2. A fuel ratio determining unit 65 is provided. The second water / fuel ratio command determination unit 60 includes a third calculation unit 61, a fourth calculation unit 62, and a fifth calculation unit 63.
The third calculation unit 61 determines a third control command for the water / fuel ratio so that the furnace outlet superheat degree matches the superheat degree set value. The fourth calculation unit 62 determines a fourth control command for the water / fuel ratio so that the main steam temperature matches the main steam temperature set value. The fifth calculation unit 63 determines a fifth control command for the water / fuel ratio so that the main steam temperature matches the main steam temperature set value.
The water / fuel ratio determining unit 65 uses the first water / fuel ratio command from the first water / fuel ratio command determining unit 20 and the second water / fuel ratio command from the second water / fuel ratio command determining unit 60 to obtain a final water / fuel ratio command. To decide.

FIG. 8 is a diagram illustrating an example of the control logic of the second water / fuel ratio command determination unit 60.
As shown in FIG. 8, the 3rd calculating part 61 is provided with the structure substantially the same as the 1st calculating part 22 demonstrated with reference to FIG. 4 in 1st Embodiment, However As a superheat degree setting value of a furnace exit A point where a fixed value is used, that is, a point where the superheat degree set value is not corrected by the set value correction unit 21 (see FIG. 3), and a third gain determination unit 43 ′ is provided instead of the first gain determination unit 43. It differs from the 1st calculating part 22 shown in FIG.

  FIG. 9 shows an example of the gain function Fx3 used by the third gain determination unit 43 ′. In FIG. 9, the horizontal axis indicates the load, and the vertical axis indicates the gain (weighting coefficient). As indicated by a solid line in FIG. 9, the gain function Fx3 used in the third gain determination unit 43 ′ is set to a relatively high gain value in a low load region, and the gain decreases as the load increases. It is considered as a function.

  The fourth calculation unit 62 has substantially the same configuration as the second calculation unit 23 described with reference to FIG. 4 in the first embodiment, but the fourth gain determination unit 47 instead of the second gain determination unit 47. It differs from the 2nd calculating part 23 shown in FIG. The gain function Fx4 used in the fourth gain determination unit 47 ′ is set to a relatively low value in a low load region, for example, as indicated by a broken line in FIG. 9, and the gain increases as the load increases. It is a function that increases.

  The third control command that is the output of the third calculation unit 61 and the fourth control command that is the output of the fourth calculation unit 62 are added by the adder 49, and the multiplier 51 multiplies the gain according to the required load. , And output to the adder 74 via the integrator 52.

  The fifth calculation unit 63 sets a gain that is a weighting coefficient according to a required load of the steam turbine, a proportional differential control unit 71 that performs proportional differential control on the deviation between the main steam temperature and the main steam temperature set value. A fifth gain determination unit 72 and a multiplier 73 that multiplies the output set by the proportional differentiation control unit 71 by the gain set by the fifth gain determination unit 72. Here, the gain function referred to in the fifth gain determination unit 72 is set to a higher gain function because, for example, the load change rate is high in a high load zone. The fifth control command that is the output of the multiplier 73 is output to the adder 74 and added to the control commands from the third calculation unit 61 and the fourth calculation unit 62. The control command after the addition is output to the water / fuel ratio determining unit 65 shown in FIG. 7 as the second water / fuel ratio command.

  Here, according to the second water-fuel ratio command determination unit 60 described above, as shown in FIG. 9, in the region where the load is 0% to 30%, the gain function used in the third gain determination unit 43 ′. Fx3 is set to gain = 0.9, while the gain function Fx4 used in the fourth gain determination unit 47 ′ is set to gain = 0.1. Therefore, in the region where the load is 0% to 30%, the second water-fuel ratio command that largely reflects the third control command by the third calculation unit 61 is generated.

  On the other hand, in the region where the load is 50% or more, the gain function Fx3 used in the third gain determination unit 43 ′ is set to gain = 0, while the gain function Fx4 used in the fourth gain determination unit 47 ′. Is set to gain = 1.0. Therefore, in the region where the load is 50% or more, the second water-fuel ratio command that largely reflects the fourth control command by the fourth calculation unit 62 is generated.

  In the region where the load is 30% or more and less than 50%, the gain of the gain function Fx3 used in the third gain determination unit 43 ′ changes from 0.9 in a decreasing direction, while the fourth gain determination unit 47 ′. In the gain function Fx4 used in, the gain changes in the increasing direction from 0.1. Therefore, in the region where the load is 30% or more and less than 50%, in the region close to 30%, the third control command becomes the second water-fuel ratio command in which the third control command is reflected relatively stronger than the fourth control command. In the near region, the fourth control command becomes the second water-fuel ratio command in which the fourth control command is reflected relatively stronger than the third control command.

The second water / fuel ratio command determined in this way is output to the water / fuel ratio determining unit 65. The water / fuel ratio determining unit 65 also receives the first water / fuel ratio command determined by the first water / fuel ratio command determining unit 20. The water-fuel ratio determining unit 65 outputs a sum of the first water-fuel ratio command and the second water-fuel ratio command as a final water-fuel ratio command.
Here, in the present embodiment, the weights of the respective control commands are determined by the first gain determination unit 43, the third gain determination unit 43 ′, the second gain determination unit 47, and the fourth gain determination unit 47 ′ described above. Therefore, the water / fuel ratio determining unit 65 determines the final water / fuel ratio command by adding the first water / fuel ratio command and the second water / fuel ratio command. Instead of such a mode, the final water-fuel ratio command may be determined by weighting the first water-fuel ratio command and the second water-fuel ratio command in the water-fuel ratio determination unit 65. Thus, the weighting of the water-fuel ratio control based on the degree of superheat at the furnace outlet and the weighting of the water-fuel ratio control based on the main steam temperature may be performed in each calculation unit, or the water-fuel ratio determination unit 65 It is good also as finally performing in.

  According to the steam temperature control apparatus 10 ′ according to the present embodiment as described above, the water-fuel ratio command output from the water-fuel ratio determination unit 65 is based on the degree of superheat at the furnace outlet in the region where the load is 30% or less. In the region where the fuel ratio control is strongly reflected and the load is 30% or more and less than 50%, the water fuel ratio control based on the main steam temperature gradually changes from the water fuel ratio control based on the superheat degree of the furnace outlet as the load gradually increases. However, in the region where the load is 50% or more, the water-fuel ratio control based on the main steam temperature is strongly reflected.

Next, the basis for weighting as described above will be described with reference to FIG. FIG. 10 is a diagram showing a general Mollier diagram (ph diagram). For example, in a power generation system having a once-through boiler, the pressure region is about 85 [kPa] to about 246 [kPa]. In a load zone where the load is 50% or less, there is a possibility of entering a saturated steam region depending on the enthalpy. When the steam at the furnace outlet becomes wet steam, the wet steam flows into the superheater, which is not preferable for operation. Therefore, the steam at the furnace outlet is required to be superheated steam.
For this reason, in the load zone where there is a possibility of entering the saturation region, control is performed with an emphasis on the degree of superheat at the furnace outlet, and the high load zone where the possibility of entering the saturation region is low (load is about 50% or more) In this area), control is performed with the main steam temperature more important than the degree of superheat.

  As described above, according to the power generation system and the steam temperature control method according to the present embodiment, the superheat degree at the furnace outlet is set to the superheat degree in a load zone (for example, an area of 50% or less) that may enter the saturation region. The weighting of the control that matches the value is increased, and the water-fuel ratio control based on the superheat degree is shifted to the water-fuel ratio control based on the main steam temperature as the load increases. Since such control switching is performed by continuously changing the weighting coefficient, the control switching can be performed seamlessly.

  In the second embodiment, the first water-fuel ratio command determination unit 20 includes a set value correction unit 21, a first calculation unit 22, and a second calculation unit 23, and the second water-fuel ratio command determination unit 60 has a third value. The calculation unit 61, the fourth calculation unit 62, and the fifth calculation unit 63 are provided, but instead of such a configuration, the first water-fuel ratio command determination unit 20 has a configuration based on the main steam temperature, that is, a second configuration. Only the configuration for determining the water / fuel ratio command so as to make the superheat degree at the furnace outlet coincide with the superheat degree set value by excluding the calculation unit 23, and the second water / fuel ratio command determination unit 60 is configured based on the superheat degree, that is, The third calculation unit 61 may be excluded and only the water / fuel ratio command may be determined so as to make the main steam temperature coincide with the main steam temperature set value. Thus, by completely dividing the roles of the water / fuel ratio command determination units 20 and 60, it is possible to simplify the weighting of the water / fuel ratio command and the like.

[Third Embodiment]
Next, a power generation system and a steam temperature control method thereof according to a third embodiment of the present invention will be described. Although the power generation system according to the first embodiment described above has one steam turbine 3, the power generation system according to the present embodiment includes a high pressure steam turbine 3a and a low pressure steam turbine 3b as shown in FIG. And. In this figure, the same components as those in FIG. 1 are denoted by the same reference numerals and description thereof is omitted. As shown in FIG. 11, the steam that has finished work in the high-pressure steam turbine 3 a is guided to the reheater 19 and is reheated again by the reheater 19. The steam superheated again by the reheater 19 is guided to the low-pressure steam turbine 3b and used to drive the low-pressure steam turbine 3b. The steam after driving the low-pressure steam turbine 3 b is guided to the condenser 8 and returned to water (liquid) by the condenser 8.

  Moreover, in the combustion gas cycle in this embodiment, the combustion gas produced | generated by the furnace 2 is a water cooling wall (not shown), the tertiary superheater 4c, the secondary superheater 4b, the reheater 19, and the primary superheater 4a. At least one of these passes through the economizer 14, and then a part thereof is recirculated to the furnace 2. Here, gas dampers are respectively provided upstream of the combustion gas flows of the reheater 19 and the primary superheater 4a, and the reheater 19 and the primary superheater are adjusted by adjusting the degree of opening of the dampers. The ratio of the fuel gas supplied to the container 4a can be changed.

  Further, an inlet gas damper is provided on the downstream side of the combustion gas flow of the economizer 14, and the amount of gas recirculated to the furnace 2 and discharged to the atmosphere again by adjusting the degree of opening of the inlet gas damper. It is possible to adjust the gas flow rate. Thus, by adjusting the gas flow rate to be recirculated, it is possible to adjust the heat absorption amount in the water cooling wall, each of the superheaters 4c, 4b, 4a and the reheater 19.

  In the power generation system having such a configuration, the water-fuel ratio control by the temperature control devices 10 and 10 'according to the first or second embodiment described above is applied, but if applied as it is, the reheater 19 There is a possibility that the overheat at the time becomes insufficient and the outlet steam temperature Ts of the reheater 19 deviates from a predetermined temperature set value. Therefore, in the present embodiment, the following three methods are adopted in order to set the outlet steam temperature Ts of the reheater 19 within a predetermined temperature range.

[Delay adjustment of superheat setting]
At the time of load drop, the degree of superheat at the furnace outlet is apparently lowered with a predetermined time delay. In this way, by providing a predetermined time delay in the superheat degree at the furnace outlet, it is possible to avoid a sudden drop in the superheat degree setting at the furnace outlet, and for a certain period after the required load decreases, On the other hand, it is possible to change the steam temperature setting gradually so as to maintain a high degree of superheat. As a result, it is possible to prevent the reheat temperature from rapidly decreasing, and it is possible to improve the control followability of the reheat temperature when the load drops.

FIG. 12 is a diagram showing a configuration example of a correction unit for giving a predetermined time delay to the degree of superheat at the furnace outlet. As shown in FIG. 12, the correction unit 80 includes a function unit 81, a delay circuit 82, a selection unit 83, and a deviation calculation unit 84.
The function unit 81 calculates a saturation temperature at the pressure from the furnace outlet steam pressure. The delay circuit 82 causes a predetermined time delay in the output from the function unit 81. The selection unit 83 receives the output of the function unit 81 and the output of the delay circuit 82, outputs the input from the function unit 81 in a normal time, and outputs the input from the delay circuit 82 in a load drop. The deviation calculation unit 84 calculates the degree of superheat at the furnace outlet by subtracting the output of the selection unit 83 from the furnace outlet steam temperature.

[Adjustment of primary spray valve]
In the first and second embodiments described above, the primary spray valve 15a is set so that the outlet temperature of the secondary superheater 4b, that is, the inlet temperature Ti of the secondary superheat reducer 5b becomes a predetermined temperature. The valve opening was controlled. In the present embodiment, by adding a predetermined correction value to the valve opening thus determined, the valve opening of the primary spray valve 15a is controlled to open. Here, the predetermined correction value may be a fixed value or a value that is changed according to the required load.

  By increasing the valve opening degree of the primary spray valve 15a, the water supply supplied to the furnace 2 can be reduced. When the amount of water supplied to the furnace 2 is decreased, the water-fuel ratio increases, and the degree of superheat at the furnace outlet can be increased more than the degree of superheat determined according to the required load. Thereby, the amount of heat input at the time of load fall can be increased, and it becomes possible to prevent the outlet steam temperature Ts of the reheater 19 from being lowered.

FIG. 13 shows a configuration example for realizing this aspect. FIG. 13 is a diagram illustrating a configuration example of the correction unit 90 that corrects the valve opening degree of the primary spray valve 15a. As shown in FIG. 13, the correction unit 90 outputs 0% during normal time, and selects and outputs the output of the multiplier 44 (see FIG. 4) of the first calculation unit 22 during load drop. And an adder 92 that adds the output from the selector 91 to the outlet steam temperature deviation of the secondary superheater 4b. The output of the addition unit 92 is output to a command generation unit that generates a primary spray valve opening command, and finally a primary spray valve opening command is generated by performing PID control or the like.
Thus, when the load drops, the output of the multiplier 44 of the first computing unit 22 is added to the secondary superheater outlet steam temperature deviation, so that the valve opening of the primary spray valve 15a can be increased. It becomes.

  Although it is possible to cope by increasing the valve opening of the secondary spray valve 15b instead of the primary spray valve 15a, the primary superheat reducer 5a controlled by the primary spray valve 15b is Since it is installed at a position close to the furnace 2 in addition to the secondary overheat reducer 5b, the influence on the steam temperature is small when the spray amount is increased. Therefore, a higher effect can be obtained by adjusting the valve opening degree of the primary spray valve 15a.

[Adjustment of the amount of combustion gas supplied to the reheater]
As described above, the gas dampers are provided on the upstream side of the combustion gas flow of the reheater 19 and the primary superheater 4a, respectively, and the reheaters 19 and 1 are adjusted by adjusting the degree of opening of the dampers. The inflow ratio of the fuel gas to the next superheater 4a can be changed. From this, when the load drops, the amount of combustion gas flowing into the reheater 19 is increased by controlling the damper of the reheater 19 to be more open than usual. Thereby, a large amount of heat input in the reheater 19 can be taken, and a decrease in the outlet steam temperature Ts of the reheater 19 at the time of load drop can be suppressed.

DESCRIPTION OF SYMBOLS 1 Electric power generation system 2 Furnace 3 Steam turbine 3a High pressure steam turbine 3b Low pressure steam turbine 4a Primary superheater 4b Secondary superheater 4c Third superheater 5a Primary superheat reducer 5b Secondary superheat reducer 10, 10 'Steam temperature control Device 15a Primary spray valve 15b Secondary spray valve 19 Reheater 20 First water-fuel ratio command determination unit 21 Set value correction unit 22 First calculation unit 23 Second calculation unit 60 Second water-fuel ratio command determination unit 61 Third calculation Unit 62 fourth calculation unit 63 fifth calculation unit 65 water-fuel ratio determination unit

Claims (10)

A furnace for burning a fuel containing carbon such as coal;
A steam turbine that generates electric power by rotating the turbine using steam generated in the furnace;
A steam pipe for supplying the steam from the furnace to the steam turbine;
An N-order superheater (N is an integer of 3 or more) provided in series with the steam pipe;
An N-1 primary superheat reducer provided between the Nth superheater and the N-1 primary superheater among the Nth superheaters provided in the steam pipe;
Control means for controlling the water-fuel ratio, which is the ratio of the calorific value of fuel in the furnace and the amount of water supply,
The control means includes
First calculating means for determining a first water-fuel ratio command for matching the superheat degree at the furnace outlet with a superheat degree set value;
A power generation system comprising: a set value correcting means for correcting the superheat degree set value based on a deviation between an inlet temperature and an outlet temperature of the N-1 primary superheat reducer.   The set value correction means calculates a correction value that makes the deviation between the inlet temperature and the outlet temperature of the N-1 primary superheat reducer coincide with a target temperature difference, and uses the correction value to set the superheat degree setting value. The power generation system according to claim 1 which corrects.   The power generation system according to claim 2, wherein the target temperature difference is determined according to a required load of the steam turbine. The control means includes
First control means comprising the first calculation means and the set value correction means, and determining a first water-fuel ratio command;
A second control means for determining a second water-fuel ratio command for causing the main steam temperature to coincide with the main steam temperature set value;
Gain determining means for determining a weighting coefficient of the first water-fuel ratio command and the second water-fuel ratio command;
The final water-fuel ratio command is determined using the first water-fuel ratio command determined by the first control means, the second water-fuel ratio command determined by the second control means, and the weighting coefficient determined by the gain determination means. The power generation system according to any one of claims 1 to 3, further comprising a water-fuel ratio determining unit that determines In the high load zone, the weighting coefficient of the second water-fuel ratio command is set higher than the weighting coefficient of the first water-fuel ratio command,
5. The power generation system according to claim 4, wherein a weighting coefficient of the first water-fuel ratio command is set higher than a weighting coefficient of the second water-fuel ratio command in a low load zone. A low pressure steam turbine driven at a lower steam pressure than the steam turbine;
Reheating means for resuperheating the steam used in the steam turbine and supplying the steam to the low pressure steam turbine;
An inflow amount adjusting means for adjusting an inflow amount of the combustion gas generated in the furnace to the reheating means,
The power generation system according to any one of claims 1 to 5, wherein the inflow amount adjusting means increases the passage distribution of the amount of combustion gas that flows into the reheating means when the load drops. A low pressure steam turbine driven at a lower steam pressure than the steam turbine;
Reheating means for resuperheating the steam used in the steam turbine and supplying the steam to the low pressure steam turbine;
An overheat reducer provided between adjacent superheaters disposed in the steam pipe;
A spray pipe branched from the water supply line to the furnace and fed to the superheat reducer;
A spray valve provided in the spray pipe for adjusting the amount of spray supplied to the overheat reducer;
The control means includes
Opening degree determining means for determining the opening degree of the spray valve based on the outlet temperature of the nearest superheater provided on the downstream side of the steam flow from the superheat reducer;
The power generation system according to any one of claims 1 to 5, further comprising an opening degree correcting unit that increases the opening degree of the spray valve determined by the opening degree determining unit when the load is lowered.   The power generation system according to claim 7, wherein the overheat reducer is provided between the primary superheater and the secondary superheater. A low pressure steam turbine driven at a lower steam pressure than the steam turbine;
Reheating means for reheating the steam used in the steam turbine and supplying the steam to the low pressure steam turbine,
The first calculation means includes correction means for correcting the superheat degree at the furnace outlet so as to have a predetermined time delay at the time of load drop, and the superheat degree at the furnace outlet after correction is set to the superheat degree set value. The power generation system according to any one of claims 1 to 5, wherein a first water-fuel ratio command that matches is determined. A furnace for burning a fuel containing carbon such as coal, a steam turbine for generating electricity by rotating a turbine using steam generated in the furnace, and a steam pipe for supplying the steam from the furnace to the steam turbine An N-order (N is an integer greater than or equal to 3) superheater provided in series with the steam pipe, and the N-order superheater and the N− of the N-order superheaters provided in the steam pipe. The present invention is applied to a power generation system that includes an N-1 primary superheat reducer provided between a primary superheater and a control unit that controls a water / fuel ratio that is a ratio of a calorific value of fuel and a water supply amount in the furnace. A steam temperature control method,
A first calculation step of determining a first water-fuel ratio command that makes the superheat degree at the furnace outlet coincide with a superheat degree set value;
A steam temperature control method for a power generation system, including a set value correction process for correcting the superheat degree set value based on a deviation between an inlet temperature and an outlet temperature of the N-1 primary superheat reducer.

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