JPH09236202A - Apparatus and method for controlling fuel of boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the stable steam temperature characteristics by providing fuel signal correcting means for correcting a fuel flow command signal by predicting the feed water temperature of a boiler in the case of switching a steam power single mode for stopping a gas turbine and a combined mode for operating the turbine. SOLUTION: A feed water flow signal 20 at the time of switching a steam power single mode and a combined mode, a generator output signal 21 for indicating a boiler load and a gas turbine exhaust gas temperature 22 are input to an estimate calculator 19, which calculates and outputs a predicted feed water temperature signal 23 previously predicted at the feed water temperature of the boiler. This signal and a boiler feed water temperature signal 25 are input to a subtracter 26, and subtracted. Further, a fuel flow correction signal 29 is output as a correction signal for a boiler fuel flow command signal 16 by a functional generator 27, and added to the signal 16 by an adder 30. Thus, since the correction is conducted and the boiler combustion amount command signal is output, stable boiler main steam temperature control can be executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boiler fuel control apparatus and method for an exhaust gas re-combustion type combined cycle boiler, and more particularly, to a stable steam characteristic when switching between steam alone mode and combined mode during steam turbine load operation. The present invention relates to an obtained boiler fuel control device and method.

[0002]

2. Description of the Related Art FIG. 5 is a system diagram of a boiler fuel control apparatus or method according to the prior art. The boiler input signal 4 is a command signal for a load required for the boiler, and is a signal for determining the base fuel flow rate corresponding to the boiler water supply and the fuel load. The function generator 5 and the function generator 6 are connected to the boiler input signal 4
Is input to determine the base fuel flow rate of the boiler in the load static state. The function generator 5 is for the steam alone mode, and the function generator 6 is for the combined mode. By adding the fuel boiler input acceleration signal 9, which is a boiler fuel flow rate advance command, to the base fuel flow rate signal with the adder 10, the advance control is performed with respect to the main steam temperature change when the steam turbine load changes, and the boiler main steam I try to keep the temperature constant.

Further, when a main steam temperature deviation 12 occurs between the main steam temperature set value and the actual main steam temperature value, a correction amount is calculated by a function generator 13 for the fuel flow rate according to this temperature deviation, and the sum is added. The main fuel flow rate is corrected by the device 14 to stabilize the main steam temperature. The fuel flow rate command signal 16 after the adder 14 to which the above correction is added is used as the final boiler combustion amount command signal 31, and the main steam temperature at the boiler outlet is kept constant even when the load on the steam turbine changes. I am trying. Reference numeral 7 is a switch.

[0004]

However, the gas turbine exhaust gas in the boiler fuel control device or method according to the above-mentioned prior art is used for heating the boiler feed water by the high pressure gas feed water heater, but in the combined mode operation, the high pressure gas is used. Since the feed water temperature at the outlet of the feed water heater is controlled to be almost the same as the outlet temperature of the high pressure feed water heater when operating in the steam power only mode, there is almost no change in heat input to the boiler, and as a factor for changing the boiler generated steam temperature. Has almost no effect.

Exhaust gas from the boiler heats combustion air and exchanges heat with condensate by a low-pressure gas feed water heater,
It is used to heat the condensate, but since the low-pressure gas feedwater heater is heat exchange in the boiler steam turbine heat exchange cycle, it has almost no effect as a steam temperature fluctuation element as boiler heat input.

However, when the operation for shifting from the steam power mode operation to the combined mode operation is performed, the temperature fluctuation at the confluence of the high pressure gas feed water heater and the high pressure feed water heater transiently occurs at about 50 ° C. Boiler feedwater temperature is transiently 5
When the temperature changes by 0 ° C, it becomes a disturbance factor to the boiler-generated main steam temperature.

In the conventional boiler fuel control apparatus or method, when the main steam temperature deviation occurs, the combustion flow rate command is corrected according to the deviation amount. It takes 10 to 15 minutes until the main steam temperature is stabilized by adjusting the boiler combustion amount, which may delay the boiler steam temperature control. That is, if the boiler feedwater inlet feed water temperature changes by 50 ° C, the main steam temperature becomes ± 1
It greatly exceeds the turbine-side control value ± 8 ° C of 5 to 20 ° C. Thus, the conventional boiler fuel control device or method,
The change in boiler heat input due to the change in boiler feed water temperature has not been taken into consideration, and the high pressure gas feed water heater and high pressure feed water heater outlet when switching between steam alone mode and combined mode like the exhaust reburn type combined cycle. When the feed water temperature changes, the total steam heat input and the feed water amount are out of balance and the main steam temperature deviation becomes large.

An object of the present invention is to solve the above problems,
It is an object of the present invention to provide a boiler fuel control apparatus and method for an exhaust gas re-combustion combined cycle, which can obtain stable steam temperature characteristics when switching between a steam power only mode and a combined mode.

[0009]

In order to achieve the above object, the present invention discharges a combustion turbine exhaust gas that uses steam generated in a boiler and combustion exhaust gas mixed with combustion air that is pushed into a furnace of the boiler. A boiler for an exhaust gas re-combustion combined cycle having a gas turbine, the fuel flow rate to a furnace based on a fuel flow rate command signal output by correcting a boiler input signal for commanding a load required for the boiler. In the boiler fuel control device for controlling the above, when switching between the steam power alone mode for stopping the gas turbine during the steam turbine load operation and the combined mode for operating the gas turbine, the feed water temperature of the boiler is predicted to predict the fuel flow rate. The fuel signal correcting means for correcting the command signal is provided.

Fuel signal correction means for predicting the feed water temperature of the boiler and correcting the fuel flow rate command signal when switching between the steam alone mode for stopping the gas turbine under the steam turbine load operation and the combined mode for operating the gas turbine Those equipped with can match the total heat input of the boiler with that required for the boiler regardless of the state of the gas turbine, that is, whether it is started or stopped. The temperature does not fluctuate beyond the specified range, and good boiler main steam temperature control with a small time delay can be performed.

Further, in the above boiler fuel control device,
The fuel signal correction means has a prediction calculator that predicts the feed water temperature of the boiler. The one having a prediction calculator for predicting the boiler feed water temperature, in addition to the operation of the boiler fuel control device, accepts various heat input data of the boiler and reliably predicts the boiler feed water temperature.

In the boiler fuel control device, the fuel signal correction means includes a subtractor for inputting the predicted feed water temperature signal output by the predictive computing unit and the boiler feed water temperature signal, and an output signal of the subtractor. A function generator that outputs a fuel flow rate correction signal that corrects the fuel flow rate command signal based on the above, an adder that adds the fuel flow rate correction signal to the fuel flow rate command signal, and the steam alone mode and the combined mode. And a switching device that outputs the fuel flow rate correction signal to the adder based on a switching signal output when switching.

The fuel signal correction means inputs a predicted feed water temperature signal and a boiler feed water temperature signal, a function generator which outputs a fuel flow rate correction signal, and adds the fuel flow rate correction signal to the fuel flow rate command signal. Having an adder for outputting a fuel flow rate correction signal to the adder based on the switching signal further increases the reliability of control with a simple control device in addition to the operation of the boiler fuel control device. .

Further, the boiler of the exhaust reburn type combined cycle has a steam turbine which uses steam generated in the boiler and a gas turbine which discharges combustion exhaust gas mixed with combustion air to be pushed into the furnace of the boiler. And a boiler fuel control method for controlling a fuel flow rate to a furnace based on a fuel flow rate command signal output by correcting a boiler input signal for instructing a load required for the boiler, during the steam turbine load operation. When switching between the steam power alone mode for stopping the gas turbine and the combined mode for operating the gas turbine, the feed water temperature of the boiler is predicted, and calculation is performed based on the predicted feed water temperature and the feed water temperature of the boiler before prediction. The fuel flow rate command signal is corrected by the output fuel flow rate correction signal.

When switching between the steam alone mode and the combined mode during the steam turbine load operation, the state of the gas turbine is corrected by correcting the fuel flow rate command signal based on the predicted feed water temperature and the pre-predicted boiler feed water temperature. ,
That is, regardless of whether it is started or stopped, the total heat input of the boiler can be matched with that required for the boiler,
Therefore, the temperature of the steam generated from the boiler does not fluctuate beyond the specified range, and good boiler main steam temperature control with a small time delay can be performed.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a boiler fuel control apparatus and method according to the present invention will be described below with reference to the drawings.

FIG. 2 is a system diagram of combustion air for an exhaust gas re-combustion combined cycle boiler which employs an embodiment of the boiler fuel control apparatus or method according to the present invention. Exhaust reburn type combined cycle boiler 1 of the present embodiment
In the combined mode in which the gas turbine 34 is operated, the boiler push-in fan 38 that supplies the combustion air 54a to the furnace 33 of the boiler body 41 via the wind box 40.
And a gas supplied to the furnace 33 by combining the combustion exhaust gas 55b, which is a part of the gas turbine exhaust gas 55a supplied through the high-pressure gas feed water heater 35, with the combustion air 54a through the gas turbine exhaust gas wind passage inlet damper 36. And a turbine 34. The gas turbine exhaust gas 55c, which is another part of the gas turbine exhaust gas 55a, is supplied to the boiler main body 4
The combustion gas at the outlet 67 of the first economizer 66 is joined via the boiler bypass damper 37. Boiler push fan 38
The combustion air 54a of the furnace 3 passes through the air preheater 39.
3 is supplied.

Further, the suction damper 48 is introduced from the economizer outlet 67.
Combustion gas is sucked in through a, and gas furnace inlet damper 4
A gas recirculation fan 48 for supplying air to the wind box 40 of the furnace 33 through the furnace 33 and the gas mixing damper 50 is provided. The combustion gas discharged from the economizer outlet 67 merges with the gas turbine exhaust gas 55c, and the denitration device 42
And a part of it enters the high pressure gas feed water heater 46 through the gas feed water heater inlet damper 45, and further enters the low pressure gas feed water heater 47 and the air preheater 39 through the inlet gas damper 43. In addition, the two are further merged and exhausted to the chimney 51 by the induction fan 44 via the induction fan inlet damper 52. The induction fan 44 is provided with an induction fan bypass damper 53. Also, the boiler exhaust gas supplied to the air preheater 39 is
Combustion air 5 supplied by the boiler forced draft fan 38
Preheat 4a.

In the system for combustion air of a boiler of the exhaust gas re-combustion type combined cycle, in the combined mode in which the gas turbine 34 is in operation, the gas turbine exhaust gas amount is fed to the boiler wind box 40 only for the amount required for combustion. Therefore, a gas turbine exhaust gas wind inlet damper 36 and a boiler bypass damper 37 are provided. In the case of the steam alone mode, the air is sucked in by the forced draft fan 38, heat is exchanged with the boiler exhaust gas by the air preheater 39, and then the gas is passed through the gas mixing damper 50 recirculated to the air side by the boiler gas recirculation fan 48. It is mixed with the boiler exhaust gas and passed through the wind box 40 to be used as combustion air.
Since the temperature of the gas turbine exhaust gas at the outlet of the high-pressure gas feed water heater 35 is almost the same as the temperature of the combustion air that has passed through the air preheater 39, the boiler heat input due to the temperature of the combustion air during both steam power alone mode operation and combined mode operation Since there is almost no change, there is no effect enough to correct the boiler fuel flow rate command signal.

FIG. 3 is a system diagram of a condensate / water supply system of an exhaust gas re-combustion combined cycle boiler adopting one embodiment of the boiler fuel control apparatus or method according to the present invention.
The high-pressure steam of the superheater 68 enters the high-pressure steam turbine 69, performs work, and then returns to the reheater 70. The low-pressure steam reheated by the reheater 70 enters the low-pressure steam turbine 71, performs work, and reaches the condensate pump 56 via the condenser 72. Boiler feed water from the condensate pump 56 reaches the deaerator 60 via the low pressure feed water heater 57 or the low pressure gas feed water heater 58 and the low pressure feed water heater distribution valve 59. During combined mode operation, boiler feed water from the deaerator 60 is supplied by the feed water pump 61 through the high pressure feed water distribution valve 62 to the high pressure feed water heater 6
3 or the high-pressure gas feed water heaters 64 and 65, and join to become the feed water flow rate of the boiler. In the steam alone mode operation, water is supplied from the high pressure feed water heater 63. The condensate system is similar to the water supply system.

Further, during the combined mode operation, the high temperature gas turbine exhaust gas discharged from the condensate pump 56 of the gas turbine is used by the high pressure gas feed water heaters 64 and 65 to heat the feed water from the water feed pump 61. To be done. In the steam alone mode operation, the high pressure feed water heater 63 heats the feed water from the water feed pump 61. It is necessary to switch between combined mode and steam power alone mode with a steam turbine load of about 50% or more in the system. When switching between steam power alone mode and combined mode, high pressure gas feed water heaters 64 and 65, high pressure feed water heating With the switching operation of the reactor 63 and the switching of the low-pressure gas feed water heater 58 and the low-pressure feed water heater 57, the fluctuation of the boiler inlet feed water temperature increases to about 50 ° C., and the influence on the boiler outlet temperature cannot be ignored.

FIG. 1 is a system diagram showing an embodiment of a control system of a boiler fuel control device or method according to the present invention. The boiler fuel control device or method 2 of the present embodiment is
A fuel signal correction means 18 is provided for predicting the feed water temperature of the boiler and correcting the fuel flow rate command signal when switching between the steam alone mode for stopping the gas turbine during the steam turbine load operation and the combined mode for operating the gas turbine. It is a thing.

When the start / stop operation of the gas turbine is performed during the steam turbine load operation, that is, the switching operation between the steam alone mode and the combined mode is performed, the base fuel flow rate command signal 15 is set to the steam alone mode or the combined mode. Boiler input signal 4 determined by the function generator 5 or 6 in consideration of the heat input to the boiler determined by the function generator 5 and determined by the steam turbine load in the steam mode alone mode or the steam turbine load signal 4 determined by the steam turbine load in the combined mode. Function generator 5 so that the boiler heat input according to
Or, it is output at 6. The base fuel flow rate command signal 15 is switched by the switch 7 in accordance with a mode switching signal in the steam alone mode or the combined mode.

On the other hand, the heat quantity of the boiler feed water system that actually enters the boiler is calculated as the product of the boiler inlet feed water temperature and the boiler feed water flow rate. The fuel signal correction means 18 predicts the boiler heat input based on the actual measurement, the feed water flow rate signal 20 at the time of switching between the steam alone mode and the combined mode, the generator output signal 21 indicating the boiler load, and the gas turbine exhaust gas temperature 22. The predicted feed water temperature signal 23, which is input to the calculator 19 and calculated to predict the boiler feed water temperature in advance, is output, and this signal and the boiler feed water temperature signal 25 are input to the subtractor 26.
The boiler fuel flow rate command signal 16 which is subtracted and further output by the function generator 27 as described in the prior art
A fuel flow rate correction signal 29 is output as a correction signal for the above and is added to the fuel flow rate command signal 16 by an adder 30. The fuel flow rate correction signal 29 is switched by the switch 28 so as to operate at the time of switching between the steam alone mode and the combined mode.

The above signal transmission system predicts a change in the boiler heat input when switching between the steam alone mode and the combined mode by starting and stopping the gas turbine, and based on the deviation from the measured value, the fuel flow rate command signal 16 is generated. Since the correction is made, the fuel flow rate command signal 16 can be made the boiler combustion amount command signal 31 which is the optimum value.

FIG. 4 is an explanatory diagram showing a change in boiler main steam temperature with respect to a change in feedwater temperature at the inlet of the economizer after about 20 minutes have elapsed after switching from the steam mode to the combined mode. A curve 74 (solid line) shows the main steam temperature change according to the present embodiment, and a curve 75 (broken line) shows the main steam temperature change according to the conventional technique. Curve 76 (solid line)
Indicates the change in feedwater temperature at the inlet of the economizer. As shown in this figure, it takes about 20 minutes for the boiler coal economizer inlet feed water temperature to reach a stable state after it has decreased by about 50 ° C. from the gas turbine startup time 77. On the other hand, the main steam temperature of the present embodiment is changed from the steam-only mode to the combined mode and the fuel flow rate command signal is set to the optimum value, so that the boiler main steam boiler outlet main steam temperature fluctuation is ± 5.
It is suppressed to around ℃, and it can be controlled within the turbine control value ± 8 ℃. On the other hand, in the conventional boiler fuel control device or method, as described above, when the main steam temperature deviation occurs, the combustion flow rate command signal is corrected according to the deviation amount. When the inlet water temperature of the charcoal changes by 50 ° C, the main steam temperature fluctuates significantly by ± 15 to 20 ° C, exceeds the turbine-side control value of ± 8 ° C, and it takes time for the main steam temperature to stabilize. It indicates that the temperature control is delayed.

[0027]

According to the boiler fuel control device or method of the present invention, when switching between the steam mode alone mode for stopping the gas turbine during the steam turbine load operation and the combined mode for operating the gas turbine, the total flow into the boiler is reduced. By calculating the heat quantity, correcting the boiler fuel flow rate command signal, and outputting the boiler combustion quantity command signal, stable boiler main steam temperature control can be performed.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of a control system of a boiler fuel control device or method according to the present invention.

FIG. 2 is a system diagram of combustion air of an exhaust gas re-combustion combined cycle boiler adopting an embodiment of a boiler fuel control device or method according to the present invention.

FIG. 3 is a system diagram of a condensate / water supply system of an exhaust gas reburn type combined cycle boiler adopting an embodiment of a boiler fuel control apparatus or method according to the present invention.

FIG. 4 is an explanatory diagram showing a boiler main steam temperature change with respect to a coal economizer inlet feed water temperature change after mode switching.

FIG. 5 is a system diagram of a boiler fuel control device or method according to the prior art.

[Explanation of symbols]

 1 Boiler 2 Boiler fuel control device or method 4 Boiler input signal 16 Fuel flow rate command signal 18 Fuel signal correction means 19 Prediction calculator 23 Predicted water temperature signal 25 Water supply temperature signal 26 Subtractor 27 Function generator 28 Switcher 29 Fuel flow rate correction Signal 30 Adder 31 Boiler combustion amount command signal 33 Furnace 34 Gas turbine 69 High pressure steam turbine 71 Low pressure steam turbine

Claims (4)

[Claims] 1. A boiler of an exhaust reburn type combined cycle, comprising: a steam turbine that uses steam generated in a boiler; and a gas turbine that discharges combustion exhaust gas mixed with combustion air to be pushed into a furnace of the boiler. In the boiler fuel control device for controlling the fuel flow rate to the furnace based on the fuel flow rate command signal output by correcting the boiler input signal for instructing the load required for the boiler, during the steam turbine load operation. When the steam power alone mode for stopping the gas turbine and the combined mode for operating the gas turbine are switched, fuel signal correction means for predicting the feed water temperature of the boiler and correcting the fuel flow rate command signal is provided. A boiler fuel control device characterized by the above. 2. The boiler fuel control device according to claim 1, wherein the fuel signal correction means includes a prediction calculator that predicts a feed water temperature of the boiler. 3. The fuel signal correction means according to claim 2, wherein the fuel signal correction means is based on a subtractor for inputting the predicted feedwater temperature signal output by the predictive computing unit and the boiler feedwater temperature signal, and an output signal of the subtractor. A function generator that outputs a fuel flow rate correction signal that corrects the fuel flow rate command signal, and an adder that adds the fuel flow rate correction signal to the fuel flow rate command signal,
A boiler fuel control device comprising: a switch that outputs the fuel flow rate correction signal to the adder based on a switch signal that is output when switching between the steam alone mode and the combined mode. 4. The boiler of an exhaust gas recombustion combined cycle, comprising: a steam turbine that uses steam generated in a boiler; and a gas turbine that discharges combustion exhaust gas mixed with combustion air to be pushed into a furnace of the boiler. And a boiler fuel control method for controlling a fuel flow rate to a furnace based on a fuel flow rate command signal output by correcting a boiler input signal for instructing a load required for the boiler, during the steam turbine load operation. When switching between the steam power alone mode for stopping the gas turbine and the combined mode for operating the gas turbine, the feed water temperature of the boiler is predicted, and calculation is performed based on the predicted feed water temperature and the feed water temperature of the boiler before prediction. A boiler fuel control method, wherein the fuel flow rate command signal is corrected with an output fuel flow rate correction signal.