JPH11241807A - Controller for boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To contrive the reduction of the increase of a metal temperature as well as a difference (maximum value-average temperature) due to unbalance of furnace heat absorption in a variable pressure once-through boiler. SOLUTION: In a variable pressure once-through boiler equipped with superheater temperature reducers 6, 8, the rise 25 of the maximum value of a furnace water-cooled wall metal temperature and/or the increase 24 of a temperature difference between the maximum value and an average value are detected to regulate the flow rate of passing fluid of the superheater temperature reducer 6 by the detecting output, whereby the flow rate of passing fluid of the furnace water-cooled wall is changed to reduce the maximum value of the furnace water-cooled wall metal temperature and/or a temperature difference between the maximum value and the average value. Further, in a variable pressure once-through boiler equipped with a gas re-circulation system, the rise of the maximum value of the furnace water-cooled wall metal temperature and/or the increase of a temperature difference between the maximum value and the average value are detected to regulate the flow rate of re-circulation of gas at the regulator 11 and change the heat absorbing amount of the furnace water-cooled wall, whereby the maximum value of the furnace water-cooled wall metal temperature or a temperature difference between the maximum value and the average value is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steam temperature control device for a once-through boiler of a variable pressure type, and more particularly to a control device suitable for improving the tolerance by reducing the thermal stress due to the tolerance to the design temperature of the furnace water cooling wall.

[0002]

2. Description of the Related Art In a conventional once-through boiler, a steam temperature control is performed by detecting a temperature and a pressure at a furnace outlet and outputting a controller for controlling a fluid superheat degree at a furnace outlet. FIG. 2 shows a spray control device connected to an upstream spray control system via the control unit.

[0003] The spray control device includes a water supply pump 1,
Furnace water wall 2, brackish water separator 3, desuperheater 4,6
8, superheaters 5, 7, 9 and spray control valves 10, 11, 1
2. First superheater outlet steam temperature setter 13, second superheater outlet steam temperature setter 14, third superheater outlet steam temperature (main steam temperature) setter 15, first superheater outlet steam temperature detector 1
6. Second superheater outlet steam temperature detector 17, third superheater outlet steam temperature detector 18, subtractors 19, 20, 21, regulators 22, 23, 24, furnace water cooling wall outlet fluid pressure detector A, It comprises a furnace water wall exit temperature detector B, a superheat degree calculator C, a subtractor D, a controller E and a high signal selector F.

The spray control valves 10, 11, and 12 control the temperature of each superheater outlet steam by using the deviation between the superheater outlet steam temperature and a set value as a control signal via a controller. Further, the degree of superheat with respect to the value detected by the furnace outlet fluid pressure detector A is calculated by a calculator C as a set value, and a subtractor D is used to obtain a deviation from the furnace outlet fluid temperature from the detector B, The controller E generates a signal in the direction of reducing this deviation, and selects the signal of the controller E when the furnace outlet fluid superheat is insufficient, and the spray control valve 10 controls the furnace outlet fluid superheat. That is, by appropriately distributing and supplying the amount of water supplied from the water supply pump 1 to the amount of water supplied to the furnace and the amount of water supplied to the spray control valve, the degree of superheat of the fluid at the furnace outlet can be controlled.

[0005] The control device is a variable-pressure once-through boiler,
An event in which the heat absorption amount of the furnace water wall becomes unbalanced due to the combustion characteristics, and the maximum value of the metal temperature at the relevant site increases or the temperature difference from the average temperature increases, and the thermal stress increases, has not been considered. 59-212607).

[0006]

The prior art described above has been a problem to be solved without considering the following points.

[0007] First, in a variable-pressure once-through boiler, the heat absorption of the furnace water cooling wall becomes unbalanced due to a burner pattern or the like, and the metal temperature of the portion where the heat absorption locally increases exceeds the design value. However, the prior art does not consider this point and has a problem in reliability.

The second point is that even if the maximum value of the metal temperature does not exceed the design value, thermal stress occurs due to a temperature difference between a portion where the amount of heat absorption locally increases and the average metal temperature, and the portion may be damaged. However, the prior art does not consider this point and has a problem in reliability.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the conventional control and to secure a margin for a design temperature of a furnace water cooling wall.
Another object of the present invention is to improve the reliability of the plant by reducing the thermal stress caused by the difference between the maximum temperature and the average temperature.

[0010]

In order to solve the above problems, the present invention mainly employs the following configuration.

In a variable-pressure once-through boiler provided with a superheater desuperheater, an increase in the maximum value of the temperature of the metal wall of the furnace water and / or an increase in the temperature difference between the maximum value and the average value are detected. A boiler control device that adjusts the flow rate of the fluid flowing through the heater desuperheater and changes the flow rate of the fluid flowing through the furnace water wall to reduce the maximum value of the metal temperature of the furnace water wall and / or the temperature difference between the maximum value and the average value. .

In a variable-pressure once-through boiler provided with a gas recirculation system, an increase in the maximum value of the temperature of the metal wall of the furnace water and / or an increase in the temperature difference between the maximum value and the average value are detected. A boiler control device that adjusts a recirculation flow rate and changes a furnace water wall heat absorption amount to reduce a maximum value of a furnace water wall metal temperature and / or a temperature difference between the maximum value and an average value.

[0013]

An embodiment of the present invention will be described below with reference to FIG. The main steam temperature control device includes a feedwater pump 1, a economizer 2, a furnace water cooling wall 3, a steam separator 4, superheaters 5, 7, 9, a superheater desuperheater 6, 8, a gas recirculation fan 1.
0, furnace hopper damper 11, furnace water cooling wall metal thermometer 1
2. Computer 13, spray control valves 14, 15, controller 1
6, 17, 18, 19, subtractors 20, 21, 22, 2
3, 24, 25, adders 26, 27, 28, high value selector 29, first spray flow rate setting device 30, second superheater outlet steam temperature setting device 31, third superheater outlet steam temperature setting device 3
2. Furnace water cooling wall metal temperature difference upper limit setting device 33, furnace water cooling wall metal temperature upper limit setting device 34, furnace hopper damper opening degree setting device 35, first spray flow rate detector 36, second superheater outlet steam temperature detector 37, It comprises a third superheater outlet steam temperature detector 38.

During normal operation, the spray control valve 14
Controls the first spray flow rate by using the deviation between the first spray flow rate 36 and the set value 30 as a control signal through the controller 16 when the load is established, and when the load changes, the secondary superheater outlet evaporation temperature. The deviation between 37 and the set value 31 is used as a control signal via the controller 16 to control the secondary superheater outlet evaporation temperature. The spray control valve 15 controls the tertiary superheater outlet evaporating temperature by using a deviation between the tertiary superheater outlet evaporating temperature 38 and the set value 32 as a control signal via the controller 17.

The furnace hopper damper 11 normally and transiently and auxiliary controls the reheat steam temperature fluctuation by program control by the opening degree setting device 35. Although not shown in FIG. 1, the reheat steam temperature is mainly controlled by the gas distribution damper.

When the temperature difference between the furnace water cooling wall metal temperature and the average temperature increases, this is corrected by the following operation. The calculator 13 calculates the maximum value and the average value of the furnace water cooling wall metal temperature based on the temperature of each part detected by the furnace water cooling wall metal thermometer 12, and the maximum temperature is calculated by the furnace water cooling wall metal temperature upper limiter 34 by the subtractor 25. The value is compared with the set upper limit, and if the upper limit is exceeded, a correction signal is output to the high value selector 29.

Further, the temperature difference between the maximum temperature and the average temperature is calculated in the subtractor 23 and compared with the upper limit value set in the furnace water-cooled wall metal temperature difference upper limit setting device 33 in the subtractor 24, and exceeds the upper limit. If so, a correction signal is output to the high value selector 29.

In the high value selector 29, the subtractors 24 and 25 are used.
Is selected and output from the correction signal having the larger correction amount. Therefore, the correction signal is output both when the maximum value of the furnace water wall metal temperature increases and when the (maximum value-average temperature) difference increases, and the one with the larger correction amount is output. Become.

The selected correction signal is first sent to the controller 1
8, the first spray flow setting is reduced in proportion to the correction amount, whereby the first spray control valve is operated in the closing direction and the first superheater desuperheater fluid flow, ie the spray water flow, is reduced. As a result, the flow rate of the fluid passing through the furnace water cooling wall increases (the amount of water passing through the feedwater pump 1 is substantially constant),
Maximum value of metal temperature and (maximum value-average temperature)
The difference can be reduced.

More specifically, the upper limit value set by the setting unit 34 is compared with the detected temperature from the thermometer 12, and if the detected temperature does not reach the upper limit value, the subtractor 25 does not output the detected temperature. If the temperature exceeds the upper limit, a value corresponding to the temperature that has been exceeded is output. The subtractor 24 also has (maximum value-average temperature).
The difference is obtained and the set value is compared with the difference.
9 is similarly input, and the higher value is selected and output. The output from the high value selector 29 is input to the controller 18, and the input / output value including the sign is appropriately converted and output.

At the same time, the correction signal is added to the opening command set by the furnace hopper damper setting device 35 in the adder 27 via the controller 19, and the furnace hopper damper is operated in the opening direction, so that the low temperature gas recirculation flow rate is set. By reducing the furnace gas temperature and reducing the heat absorption of the furnace water wall mainly due to radiation, the furnace water wall metal temperature can be reduced, and the heat absorption unbalance can be reduced to reduce the metal temperature difference. It becomes possible.

Even in the state where the above-described correction operation is in operation, the main spray temperature is controlled by the second spray control valve 15, and the reheat steam temperature is controlled by the gas distribution damper. Therefore, the main steam temperature and the reheat steam temperature do not become uncontrollable.

In the above description, the control is performed by paying attention to both of the maximum value of the metal temperature of the furnace and the temperature difference between the maximum value and the average value. It goes without saying that the control may be performed by focusing on the detection target.

As described above, the embodiments of the present invention have the following configuration and operation.

In the embodiment of the present invention, the correction value based on the furnace water cooling wall metal temperature is added to the upstream desuperheater spray valve opening command, and the furnace water hopper damper (gas recirculation flow rate control damper) command value is added to the furnace water cooling command. It has a configuration for adding a correction value based on the wall metal temperature.

Regarding the operation, the correction value is added to the command value of the spray valve of the upstream desuperheater according to the deviation between the maximum value of the furnace water wall metal temperature and the set value, so that the flow rate of the fluid passing through the desuperheater is reduced. Decreasing and increasing the flow rate of fluid through the furnace water wall promotes metal fluid heat transfer and reduces the overall temperature of the furnace water wall metal.

In addition, since the gas recirculation flow rate is increased by adding the correction value to the furnace hopper damper command value, the furnace gas temperature decreases due to the increase of the recirculated gas having a low temperature, and most of the heat absorption in the furnace is performed. The amount of radiant heat transfer that occupies (the amount of radiant heat transfer is determined by the temperature difference between the gas temperature and the metal temperature) is reduced, thereby reducing the amount of heat absorbed in the furnace water wall and reducing the overall temperature of the furnace water wall metal. Does not exceed the design value.

Further, a correction value is added to the command value of the spray valve of the upstream desuperheater according to the difference between the (maximum value-average temperature) difference between the furnace water cooling wall metal temperature and the set value, and the flow rate of the fluid passing through the desuperheater is adjusted. The (maximum-average temperature) difference decreases in proportion to this temperature drop because the furnace water wall metal temperature is reduced overall by decreasing and increasing the furnace water wall passing fluid flow rate.

Further, since the recirculation flow rate is increased by adding the correction value to the furnace hopper damper command value, the furnace gas temperature decreases due to the increase of the recirculated gas having a low temperature, and occupies most of the heat absorption in the furnace. Since the amount of radiant heat transfer (the amount of radiant heat transfer is determined by the temperature difference between the gas temperature and the metal temperature) decreases, the heat absorption amount of the furnace water wall decreases, so the heat absorption unbalance itself also decreases, and the temperature of the furnace water wall metal temperature decreases. The (maximum-average temperature) difference is reduced and the thermal stress does not increase with temperature.

[0030]

By using the control system of the present invention,
The metal temperature rise at the relevant site due to the furnace heat absorption imbalance, which is the basic problem of the once-through boiler, and (maximum value-
(Average temperature) difference is reduced, the tolerance for the design value of this part can be improved, and the stress can be reduced due to the temperature difference, and the reliability of the plant can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a main steam temperature control system of a variable-pressure once-through boiler according to an embodiment of the present invention.

FIG. 2 is a diagram showing a prior art variable-pressure once-through boiler main steam temperature control system.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 feed water pump 2 economizer 3 furnace water cooling wall 4 steam separator 5,7,9 superheater 6,8 superheater desuperheater 10 gas recirculation fan 11 furnace hopper damper 12 furnace water cooling wall metal thermometer 13 computer 14,15 Spray control valve 16, 17, 18, 19 Controller 20, 21, 22, 23, 24, 25 Subtractor 26, 27, 28 Adder 29 High value selector 30 First spray flow rate setting device 31 Second superheater outlet steam Temperature setting device 32 Third superheater outlet steam temperature setting device 33 Furnace water cooling wall metal temperature difference upper limit setting device 34 Furnace water cooling wall metal temperature upper limit setting device 35 Furnace hopper damper opening degree setting device 36 First spray flow rate detector 37 Second superheating Steam outlet temperature detector 38 Third superheater outlet steam temperature detector

Claims (3)

[Claims] 1. A variable-pressure once-through boiler provided with a superheater desuperheater, wherein an increase in the maximum value of the temperature of the metal wall of the furnace water and / or an increase in the temperature difference between the maximum value and the average value are detected. Adjusting the passing fluid flow rate of the superheater desuperheater and changing the passing fluid flow rate of the furnace water wall to reduce the maximum value of the furnace water wall metal temperature and / or the temperature difference between the maximum value and the average value. A boiler control device. 2. A variable-pressure once-through boiler equipped with a gas recirculation system, comprising detecting an increase in the maximum value of the temperature of the metal wall of the furnace water and / or an increase in a temperature difference between the maximum value and the average value. A boiler control device comprising: adjusting a recirculation flow rate and changing a furnace water wall heat absorption amount to reduce a maximum value of a furnace water wall metal temperature and / or a temperature difference between the maximum value and an average value. 3. A variable-pressure once-through boiler comprising a superheater desuperheater and a gas recirculation system, wherein an increase in the maximum value of the furnace water wall metal temperature and / or an increase in the temperature difference between the maximum value and the average value are detected. By the detection output, adjusting the passing fluid flow rate of the superheater desuperheater, changing the passing fluid flow rate of the furnace water cooling wall, adjusting the gas recirculation flow rate, changing the furnace water cooling wall heat absorption amount, A boiler control device for reducing a maximum value of a furnace water wall metal temperature and / or a temperature difference between the maximum value and an average value.