JPH11182808A - Steam temperature control device for boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control a steam temperature safely without damaging a superheating reducer even against the load change of a wide range by contriving the reduction of the number of times of on/off of a pouring water flow rate regulating valve. SOLUTION: In order to contrive the reduction of the number of times of on/off of a pouring water flow rate regulating valve 8 for a desuperheating device, the limits of opening degree 17, 18, 20 are provided so that the opening degree of the pouring water flow rate regulating valve 8 will not become lower than 10% upon starting a unit under low-load operation and high-load operation while an opening degree limiting circuit is excluded when a steam temperature has been reduced to a value lower than the set value and the number of times of on/off of the pouring water flow rate regulating valve can be reduced by about 1/10 compared with that in a conventional device by the operation of gradually closing circuits 21, 22, gradually closing the pouring water flow rate regulating valve when the opening degree of the same valve has become lower than 10%. As a result, the regulation of the steam temperature can be effected safely without damaging the desuperheating device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boiler steam temperature control having an overheat reducer, and more particularly to a steam temperature control device capable of coping with a wide range of load changes.

[0002]

2. Description of the Related Art As shown in FIG. 3, a conventional water injection control system diagram of a superheat reducer is such that when the steam temperature by a steam temperature detector 10 rises above a specified value specified by a signal set value 12, a subtraction is performed. The water injection flow control valve 8 is controlled via the heater 11, the proportional integrator 13, and the automatic manual switching device 16 to open the control valve 8, and when the steam temperature falls below a specified value, the water injection flow control valve 8 is controlled. Operates fully closed.

[0003] Since the boiler static characteristics in the low load zone and the high load zone maintain the characteristic that the water injection flow rate is small, the opening of the water injection flow control valve is about 10%, which is the control lower limit of the control valve. (See the lower diagram of FIG. 4).

In such a state, if the steam temperature drops and fluctuates due to a load change, the opening of the water injection flow rate control valve becomes almost fully closed (off) by the control operation (the dotted line operation in the lower diagram of FIG. 4). ), The water injection flow control valve 8 is repeatedly turned on and off.

Accordingly, a thermal shock is applied to the overheat reducer, and there is a concern that the overheat reducer may be damaged. There has been a demand for a steam temperature control device capable of safely adjusting the temperature without damaging the superheat reducer with respect to a wide range of load changes.

[0006]

The prior art described above does not take into account the damage of the overheat reducer, and has a problem that a wide range of load change is restricted and it is difficult to adjust the steam temperature.

SUMMARY OF THE INVENTION An object of the present invention is to reduce the number of times the water injection flow control valve is turned on / off for a wide range of load changes (about 1/10 as compared with the prior art) and to safely adjust the steam temperature without damaging the overheat reducer. Will be planned.

[0008]

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

In the steam temperature control device for controlling the steam temperature of the boiler by adjusting the flow rate of water injected into the superheat reducer installed near the superheater of the boiler, the flow rate of water injected to the superheat reducer is adjusted. A valve control system is provided with valve opening lower limit limiting means for setting a valve opening lower limit of the control valve, and when the valve opening command to the control valve is equal to or less than the valve opening lower limit, the valve opening A steam temperature control device provided with gradually closing means for releasing a lower limit and gradually closing the control valve.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. Here, 1 is a boiler feed pump, 2 is a high pressure feed water heater, 3 is a economizer, 4 is a drum,
5, 6 are superheaters, 7 is a spray line, 8 is a water injection flow rate control valve, 9 is a superheat reducing device, 10 is a steam temperature detector, 11 is a subtractor, 12 is a signal setting device, 13 is a proportional integrator, 14 Is an adder, 15 is a preceding circuit operation unit, 16 is an automatic manual switching unit,
17 is a signal limiter, 18 is a switch, 19 is a signal setter (for 0% opening), 20 is a signal setter (for minimum opening), 21 is a speed converter, 22 is a function generator, and 23 is Arithmetic circuit.

FIG. 1 shows a basic system for an embodiment of the present invention. The boiler system supplies water from the deaerator with a water supply pump 1, a high pressure water heater 2, a coal saver 3, a drum 4,
It is configured to be sent to the turbine via superheaters 5 and 6. The spray system for adjusting the steam temperature by the superheat reducer 9 installed between the superheaters 5 and 6 of the boiler is constituted by a water injection flow control valve 8 of a spray line 7 taken out from the boiler feed pump outlet 1. At the time of low load and high load when the unit is started, the spray is supplied through the water injection flow rate control valve 8 and the superheat reducer 9 of the spray line 7 taken out from the outlet of the water supply pump 1.

The features of the embodiment of the present invention will be described below with reference to FIG. The water injection flow control valve 8 is opened for adjustment to lower the steam temperature. At this time, the opening command of the water injection flow control valve 8 is limited. That is, under specific conditions, the opening of the water injection flow control valve 8 is limited so as not to be lower than 10%.

The spray valve lower limit setting switching operation circuit 23 determines from the output signal of the subtractor 11 that the steam temperature (actual temperature) has become higher than the set value, further determines the load condition, and calculates these. , The switching circuit 1 by the arithmetic circuit 23
8 and the output from the signal setting device 20 (10% opening setting) is applied to the signal limiter 17 so that the opening of the control valve 8 becomes 1
Restrict to not go below 0%. That is, the lower limit of the signal limiter 17 is limited to 10% opening so that the control valve 8 is not set to the fully closed state.

When the lower limit of the opening is applied and the steam temperature drops below a set value, it is necessary to control the control valve 8 in a closing direction to narrow the flow rate of water injection. When the steam temperature decreases by α ° C. with respect to the set value (see the middle diagram of FIG. 4), the switch 18 is switched by the arithmetic circuit 23 and the output of the signal setter 19 (0% opening setting) is changed to the signal limiter. To release the lower limit of the valve opening. This allows the control valve to be fully closed.

Further, when the opening of the water injection flow control valve 8 reaches 10% or less, the speed converter 21 and the function generator 22
The valve closing rate is slowed down so that the water injection flow control valve 8 is not frequently turned on and off. That is, the function generator 22 has the characteristics shown on the left side of FIG. 2, and has a characteristic that when the valve opening is 10% or less, the valve closing speed is reduced to, for example, about 2%. In the figure, when the valve opening is 11% or more, the valve opening speed is set to 100%. As a result, it is possible to safely operate the superheat reducer capable of controlling the steam temperature in a wide range of load changes without damage.

As described above, the opening of the water injection flow control valve is limited in the low load zone and the high load zone when the load changes in a wide range, and the opening limit is excluded when the steam temperature falls below the set value. At the same time, when the opening of the flow control valve reaches 10% or less, the flow control valve is gradually closed, so that the number of ON / OFF operations of the water injection flow control valve can be reduced by about 1/10 as compared with the conventional case, thereby preventing damage to the overheat reducer. Can be achieved.

As described above, the embodiment of the present invention is to eliminate the thermal shock of the overheat reducer, and to open the water injection flow control valve installed at the time of low load operation and high load operation when the unit is started. By installing a degree limiting circuit and a gradually closing circuit, the number of times of turning on and off the water injection flow control valve is reduced, and safe operation can be performed without damaging the overheat reducer.

That is, in order to reduce the number of times the water injection flow control valve of the superheat reducer is turned on and off, the operation of the water injection flow control valve must be 10% or less during low load operation and high load operation when the unit is started. The operation of the gradual closing circuit, which restricts the opening degree and removes the opening restriction circuit when the steam temperature falls below the set value, and gradually closes when the opening of the water injection flow control valve becomes 10% or less. Thereby, the number of times of turning on and off the water injection flow rate control valve can be reduced by about 1/10 compared to the related art.
As a result, it is possible to safely adjust the steam temperature without damaging the overheat reducer.

[0019]

According to the present invention, the number of times of turning on and off the water injection flow control valve can be reduced, so that the steam temperature can be safely controlled without damaging the overheat reducer even in a wide range of load change. It can be carried out.

[Brief description of the drawings]

FIG. 1 is a boiler system diagram according to an embodiment of the present invention.

FIG. 2 is a water injection control system diagram according to the embodiment of the present invention.

FIG. 3 is a conventional water injection control system diagram.

FIG. 4 is a diagram showing a change in the opening degree of a water injection flow control valve and a change in steam temperature when the output changes.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 boiler feed pump 2 high pressure feed water heater 3 economizer 4 drum 5,6 superheater 7 spray line 8 water injection flow control valve 9 superheat reducer 10 steam temperature detector 11 subtracter 12 signal setting device 13 proportional integrator 14 addition Unit 15 preceding circuit calculator 16 automatic manual switch 17 signal limiter 18 switch 19 signal setting device (for 0% opening) 20 signal setting device (for minimum opening) 21 speed converter 22 function generator 23 calculation circuit

Claims (1)

[Claims] 1. A steam temperature control device for controlling a steam temperature of a boiler by adjusting a flow rate of water injected into a superheat reducer provided near a superheater of a boiler, wherein water injection is performed to adjust a flow rate of water injected to the superheat reducer. The control system of the flow control valve is provided with valve opening lower limit limiting means for setting a valve opening lower limit of the control valve, and when a valve opening command to the control valve is equal to or less than the valve opening lower limit, the valve A steam temperature control device, characterized in that gradual closing means for releasing the lower limit of the opening degree and gradually closing the control valve is provided.