JPH1073205A - Controller for once-through boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize the degree of superheating of the inlet temperature of a steam separator during load change by providing a superheating degree control circuit for increasing and decreasing the set value of SH spray quantity and a water-fuel ratio command so as to cancel the deviation between the upper and lower limit set values of the inlet temperature of the steam separator calculated from the detected value of pressure of the steam separator and actual temperature. SOLUTION: When the deviation between the inlet temperature 4 of a steam separator and the upper and lower limit set values of the inlet temperature of the steam separator calculated from the pressure 1 of the steam separator is plus, output signals through function generators 7 and 8 are converted into minus. The minus output signals are added to the set values of primary and secondary SH spray quantities, so that the primary and secondary SH spray quantities are decreased, and water flow rate supplied through a water wall part is increased. In addition, the total of the output signals of the function generators 7 and 8 is also added to a water-fuel ratio signal so that a fuel command signal is decreased. As a result, the outlet fluid temperature of the water wall is lowered. Conversely, when the deviation of the degree of superheating is minus, the outputs through the function generators 7 and 8 are converted into plus. The degree of superheating of the inlet temperature of the steam separator is preferably maintained in a similar way.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spray flow rate control device and a steam temperature control device for a once-through boiler, and more particularly to a control device suitable for appropriately maintaining the degree of superheat at the inlet temperature of a steam separator when a load changes.

[0002]

2. Description of the Related Art A conventional flow rate control device for a once-through boiler is provided with a regulator for detecting a temperature and a pressure at a furnace outlet and outputting a control signal for superheat degree at a furnace outlet. It is connected to an upstream spray control system via a vessel (JP-A-59-212607). The control device is shown in FIG.

The spray control device comprises a feed water pump 1, a furnace wall 2, a steam separator 3, superheat reducers 4, 6, 8, superheaters 5, 7, 9, spray control valves 10, 11, 12 and first. Superheater outlet temperature setting device 13, second superheater outlet temperature setting device 1
4. Third superheater outlet temperature (main steam temperature) setting device 15, first superheater outlet temperature detector 16, second superheater outlet temperature detector 17, third superheater outlet temperature detector 18, subtractor 19 ,
20 and 21, controllers 22, 23 and 24, a furnace outlet temperature detector A, a furnace outlet pressure detector B, a superheat temperature calculator C, a subtractor D, a controller E, and a high signal selector F.

The superheat temperature with respect to the furnace outlet pressure detected by the furnace outlet pressure detector B is calculated by a calculator C, and is set as a set value. The difference from the actual furnace exit temperature from the furnace exit temperature detector A is obtained in the subtracter D, and a control signal for eliminating the deviation is formed in the controller E, and the degree of superheat of the furnace exit temperature is insufficient. At this time, the signal from the controller E is selected, and the spray control valve 10 controls the superheat degree at the furnace outlet.

[0005]

However, the prior art described above does not consider the following three points.

(1) If the degree of superheating of the furnace outlet temperature is insufficient, the signal of the controller E is selected, and during that time, the steam temperature cannot be controlled and the state quantity becomes unstable.

(2) Since the change of the set value of the first superheater outlet temperature setting device 13 is not considered in accordance with the fluctuation of the spray flow rate, it takes time to determine the steam temperature.

(3) Since the upper limit of the superheat degree is not set, the spray flow rate is reduced in order to prevent an increase in the temperature of the fluid at the furnace outlet, the flow rate of the water supply to the water cooling wall is increased, and the control for preventing the increase in the superheat degree is performed. Circuit is not considered.

An object of the present invention is to add or subtract a deviation of the superheat degree of the inlet temperature of the steam separator to a set value of the spray flow rate and a command of the water-fuel ratio so that the superheat degree of the inlet temperature of the steam separator at the time of load change. It is an object of the present invention to provide a once-through boiler control device capable of improving stability and improving boiler characteristics.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a once-through boiler having a spray facility for controlling the steam temperature at the outlet of each superheater, the upper and lower limits of the inlet temperature of the steam separator calculated from the detected value of the steam separator pressure. Calculate the deviation between the set value and the actual inlet temperature of the steam separator, and set S in the direction to eliminate this deviation.
This is achieved by providing a superheat control circuit that increases or decreases the H spray amount set value and the water-fuel ratio command.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention calculates a deviation of the degree of superheat from the set value of the inlet temperature of the steam separator calculated from the pressure of the steam separator and the actual inlet temperature of the steam separator, and outputs a plus signal (overheat state). ), It is converted via a function generator, a minus command is added to the set value of the spray flow rate and the signal of the water-fuel ratio, the spray flow rate is reduced, the feed water flow rate passing through the water wall is increased, and the fuel flow rate is increased. The decrease prevents the furnace outlet fluid temperature from rising.

On the other hand, if the deviation of the degree of superheat is a negative signal (the state at the inlet of the steam separator is low), the operation is the reverse of that at the time of the plus signal, and the inlet temperature of the steam separator does not become saturated. That is, the furnace outlet fluid temperature is increased by increasing the spray flow rate and decreasing the flow rate of the water supply through the water wall.

Hereinafter, a specific description will be given with reference to the accompanying drawings. 1 and 2 are control circuit diagrams of a once-through boiler according to a specific example. The control circuit includes function generators 2 and 3, subtractors 5 and 6, function generators 7, 8, 10, 12, 15, and 1.
8, an adder 9, 14, 16, 19, and a change rate limiter 13. 1 is the pressure of the steam separator, 4 is the inlet temperature of the steam separator, 17 is the set value of the primary SH spray amount, and 20 is 2
This is the next SH spray amount set value.

As an example, the upper and lower limit set values of the steam separator inlet temperature calculated from the steam separator inlet temperature 4 and the steam separator pressure 1 (the static characteristic value of each load, The variation width is set in consideration of the actual results; when a deviation occurs in the function generators 2 and 3), if the deviation is plus (overheated), the output signal via the function generators 7 and 8 ( The output signals of the subtracters 5 and 6 in FIG. 1) are converted to minus and added to the primary SH spray amount setting value 17 and the secondary SH spray amount setting value 20, and the primary and secondary SH spray amounts decrease. In this case, the flow rate of feedwater passing through the water wall increases.

In addition, the sum of the output signals of the function generators 7 and 8 (the output of the adder 9) is also added to the water-fuel ratio signal (the output of the adder 14), and the fuel command signal 21 decreases.
As a result, the temperature of the fluid at the outlet of the water wall decreases, and the degree of superheat of the inlet temperature of the steam separator (the sum of the output signals of the function generators 7 and 8 (the output of the adder 9) is 0) is preferably maintained. It is. Conversely, if the deviation between the actual steam separator inlet temperature 4 and the upper / lower limit set value calculated from the steam separator pressure 1 is minus (insufficient overheating), the output signal via the function generators 7 and 8 Is converted to a positive value and added to the primary SH spray amount setting value 17 and the secondary SH spray amount setting value 20, so that the primary and secondary SH spray amounts increase and the water supply flow rate passing through the water wall decreases. At the same time, it is added to the water-fuel ratio signal, and the fuel command 21 is increased. As a result, the water temperature at the water wall outlet is increased, and the superheat degree of the steam separator temperature is suitably maintained. Therefore, it is possible to improve the stability of the steam temperature characteristic when the load changes.

A deviation between the upper and lower limit values of the inlet temperature of the steam separator calculated from the pressure 1 of the steam separator and the actual inlet temperature 4 of the steam separator, that is, the degree of superheat is calculated, and the primary degree is set to eliminate the difference. By increasing / decreasing the water / fuel ratio correction signal in addition to the SH spray amount set value 17 and the secondary SH spray amount set value 20, it is possible to suitably maintain the superheat degree of the brackish water separator inlet temperature. Alternatively, controllability and stability of static characteristics (after aging) are improved.

[0017]

According to the present invention, the deviation of the superheat degree of the inlet temperature of the steam separator is added to the primary SH spray amount set value, the secondary SH spray amount set value, and the water-fuel ratio correction signal to add the primary SH spray amount. By increasing / decreasing the spray amount set value, the secondary SH spray amount set value, and the water-fuel ratio correction signal, it is possible to appropriately maintain the degree of superheat of the steam changer inlet temperature at the time of load change and static characteristics,
This has the effect of improving boiler characteristics.

[Brief description of the drawings]

FIG. 1 is a control circuit diagram of a once-through boiler according to a specific example of the present invention.

FIG. 2 is a control circuit diagram of a once-through boiler according to an embodiment of the present invention.

FIG. 3 is a control circuit diagram of a once-through boiler according to a conventional example.

[Explanation of symbols]

 17 Primary SH spray amount setting value 20 Secondary SH spray amount setting value 21 Fuel command signal

Claims (2)

[Claims] 1. A once-through boiler having a spray facility for controlling the steam temperature at the outlet of each superheater, the upper and lower set values of the inlet temperature of the steam separator calculated from the detected value of the steam separator pressure and the actual steam separator. A once-through boiler control device, comprising: calculating a deviation from an inlet temperature, and providing a superheat degree control circuit for increasing / decreasing an SH spray amount set value and a water-fuel ratio command in a direction to eliminate the deviation. 2. The superheat control circuit according to claim 1, wherein the superheat control circuit adds a minus signal to the SH spray amount set value and the water-fuel ratio command when the deviation value is a plus signal, and when the deviation value is a minus signal, A once-through boiler control device that performs control for adding a plus signal to an SH spray amount set value and a water-fuel ratio command.