JPH0742906A - Method and apparatus for controlling temperature of steam in boiler - Google Patents

Abstract

PURPOSE:To provide a control system for controlling a temperature of steam of a boiler in which the number of ON-OFF times of a fed water flow rate adjusting valve is reduced in respect to a variation in load in high frequent operation and an adjustment of a temperature of steam is performed safely without damaging an over-heat reducing device. CONSTITUTION:A temperature of reheated steam is detected by a reheated steam temperature sensor 17 of a boiler when a boiler load is set, a degree of opening of a fed water flow rate adjusting valve 15 for an over-heating reducer for a reheater is controlled in response to difference between the detected value and a value of a steam temperature setting device 19. At this time, when the boiler load is set, the degree of opening of the valve is set to be zero. Then, when the load is varied in a high frequent manner, the adjusting valve 15 is not operated when a minute load is varied during an increasing of load, but a degree of opening of the adjusting valve 15 is determined in response to a signal of a reheated steam temperature setting device 24 for the variation of load under an operation of a changing- over device 23 only when the load is substantially changed during an increasing of the load. In this way, the number of times of ON-OFF of the adjusting valve 15 can be reduced by about 1/10 as compared with that of the prior art and further a thermal shock of the over- heating reducer can be eliminated.

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 system for a boiler having an overheat reducer, and more particularly to a reheat steam temperature control system for a boiler suitable for frequent load changes.

[0002]

2. Description of the Related Art A conventional superheat reducer water injection control system in a steam temperature control system for a boiler having a superheat reducer is shown in FIG.
Shown in. In the control system diagram of FIG. 3, control of the steam temperature is performed as follows. The steam temperature of the boiler is detected by the main steam temperature detector 16, the difference from the steam temperature set value of the steam temperature setter 19 is obtained by the subtracter 18, and this value is proportionally integrated by the proportional integrator 20 and then temperature controlled. In order to satisfactorily perform the above, the adder 21 adds the preceding signal from the preceding circuit calculator 22 such as a load, and the added value causes the manual-automatic switch 2
8 for controlling the water injection flow rate control valve 14 of the overheat reducer (not shown) of the boiler superheater.

In the steam temperature control system shown in FIG. 3, when the steam temperature of the boiler rises above a specified value, the superheater water injection flow rate control valve 14 opens, and when the steam temperature falls below the specified value, the water injection flow rate control valve 14 Is fully closed. The water injection flow rate control valve 14 is repeatedly turned on and off in response to a high frequency load change, and thermal shock is given to the overheat reducer of the superheater, which may cause damage to the overheat reducer. Although not shown, the water injection flow rate control valve of the overheat reducer of the reheater is also shown in FIG.
The reheat temperature is adjusted in the same manner as described above.

[0004]

The above-mentioned prior art has a problem in that damage to the overheat reducer is not taken into consideration and high-frequency load change is restricted. Therefore, an object of the present invention is to turn on the water injection flow control valve for high-frequency load changes.
It is an object of the present invention to provide a boiler steam temperature control method that reduces the number of times of turning OFF and safely adjusts the steam temperature without damaging the overheat reducer.

[0005]

The above objects of the present invention can be achieved by the following constitutions. That is, the steam temperature in the downstream portion of the boiler is detected, and based on the deviation between the detected value and the steam temperature set value, between the boiler and the superheater, or to the overheat reducer installed between the boiler and the reheater. In the boiler steam temperature control method for controlling the water injection flow rate, in the boiler load settling state, the water injection flow rate to the superheat reducer is not performed, and when there is a minute load change during load increase during high-frequency load changes. A boiler steam temperature control method that adjusts the water injection flow rate to the superheat reducer only when there is a large load change without adjusting the water injection flow rate, or a steam temperature detector that detects the steam temperature in the downstream part of the boiler. , A calculator of the deviation between the detected steam temperature value of the detector and the set value of the steam temperature, and is installed between the boiler and the superheater or between the boiler and the reheater based on the calculated value of the calculator Note to overheat reducer Do not operate the pouring water flow rate control valve that controls the flow rate of the pipe and the pouring water flow rate control valve in the boiler load settling state, and set the pouring water flow rate control valve only when there is a large load change during load increase during high frequency load changes. It is a boiler steam temperature control device provided with a water injection flow rate control device which is operated and adjusts the water injection flow rate to the superheat reducer.

[0006]

[Operation] The superheated steam temperature of the boiler is detected by the detector installed in the superheated steam piping, and the flow rate of water injected to the superheater overheat reducer is adjusted based on the deviation between the detected value and the value of the superheated steam temperature setting device. The opening of each control valve is controlled. At this time, in order to reduce the number of ON-OFF of the water injection flow rate control, the valve opening is set to zero at the boiler load settling, and the load is increasing during frequent load changes. In the case of a small load change, the water injection flow rate control valve is not operated, and the opening degree of the water injection flow rate control valve is changed to a value according to the load change only when a large load change occurs while the load is increasing. In this way, the number of times the water injection flow rate control valve is turned on and off can be reduced to about 1/10 of that of the conventional case, and the thermal shock of the overheat reducer can be eliminated. As a result, it became possible to adjust the superheated steam temperature safely without damaging the superheat reducer. The above superheated steam temperature control method can be applied to control the reheated steam temperature, and the reheated steam temperature can be adjusted while preventing damage to the superheat reducer of the reheater.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. A boiler system diagram of this embodiment is shown in FIG. The water supplied to the boiler 4 is first sent from the water supply pump 1 to the high-pressure feed water heater 2 and heated, and then sent to the boiler 4 via the economizer 3.
The steam generated in the boiler 4 is sent to the high-pressure turbine 7 via the primary superheater 5, the superheater superheat reducer 12 and the secondary superheater 6. The exhaust of the high-pressure turbine 7 is systematically configured to send steam to the intermediate-pressure turbine 10 via the primary reheater 8, the reheater overheat reducer 13 and the secondary reheater 9. The steam discharged from the intermediate-pressure turbine 10 is recovered in the condenser 11. A main steam temperature detector 16 is provided in a pipe of steam supplied to the high-pressure turbine 7, and a reheat steam temperature detector 17 is provided in a pipe of steam supplied to the intermediate-pressure turbine 10. Further, a part of the feed water heated by the high-pressure feed water heater 2 and supplied to the boiler 4 is extracted from the inlet of the economizer 3, and is discharged from the branch pipe provided with the superheater water injection flow rate control valve 14 to the superheater. It is supplied to the overheat reducer 12. Further, a part of the low-pressure water supply from the middle stage of the water supply pump 1 can be extracted and supplied to the reheater overheat reducer 13 from the branch pipe provided with the reheater water injection flow rate control valve 15.

In this embodiment having the above structure, the superheater / superheat reducer 12 adjusts the main steam temperature to a specified value on the basis of the detected main steam temperature of the main steam temperature detector 16 to superheater water injection flow control valve 14 Adjust. On the other hand, the reheated steam temperature is determined by the reheated steam temperature detector 17 and the reheater water injection flow control valve 15
Is adjusted to the specified value. A steam temperature control system diagram according to the present embodiment is shown in FIG. The reheated steam temperature is detected by the reheated steam temperature detector 17, and the difference between the detected steam temperature and the steam temperature setter 19 of the rated temperature is subtracted by the subtracter 1
An opening adjustment signal is created by 8. The preceding circuit calculator 22 such as a load and the adder 2 in order to perform good steam temperature control
1 to control in advance.

In the boiler load settling state, the steam temperature setting device 19 is a steam temperature setting device that operates only in an emergency, so that the reheater water injection flow rate control valve 15 is fully closed.
Also, when the load increases during high-frequency load changes, the amount of fuel to the boiler increases in proportion to the load, and the reheat steam temperature tends to rise. The reheat steam temperature is adjusted to a specified value by setting the set temperature of the temperature setter 24 to the value of the rated temperature + α so that the water injection flow rate control valve 15 is operated by the switch 23. The reheat steam temperature setter 24 has a predetermined rate (a ° C.) for the temperature rise rate of the reheat steam temperature.
/ Min or more, and since it is configured to operate only when there is a large load change, the reheater water injection flow rate control valve 15 is not operated even when the load is high, even when the load is high. . Therefore, in the steam temperature control method of the present embodiment, as in the conventional steam temperature control method shown in FIG. 3, the pouring water flow rate control valve 15 sets the ON-OFF frequency to a small load change at the time of a high frequency load change. It does not repeat and therefore does not damage the reheater overheat reducer 13.

Switching from the emergency steam temperature setting device 19 to the reheat steam temperature setting device 24 by means of the switching device 23 means that the reheat steam temperature is equal to or higher than the temperature rise rate a ° C./min, the load signal and the load. The difference between the signal and the output signal from the delay operation unit 25 is calculated by the subtractor 26, and the signal detector 27 detects that it corresponds to a large load change. Thus, even if the boiler changes its load at a high frequency, the reheater water injection flow rate control valve 15 does not operate when the change in load is minute. However, when there is a large change in load and the reheat steam temperature tends to rise, the water injection flow rate control valve 15 is operated by setting the set temperature of the reheat steam temperature setter 24 to the value of the rated temperature + α. It becomes possible to adjust the reheat steam temperature to a specified value. Further, in the boiler load settling state, since the switching device 23 switches to the emergency steam temperature setting device 19 side, the water injection flow control valve 15
Is fully closed and does not hinder operation.

In this way, in the steam temperature control system of this embodiment, the water injection flow rate control valve 15 does not repeat the ON-OFF times for a minute load change of the high frequency load change of the boiler, and the reheater overheat reducer is not required. There is no danger of damaging 13. In addition, the steam temperature control method of the present embodiment can be applied to the water injection flow rate control valve 14 of the superheater / overheat reducer 12 as well, and the number of times the water injection flow rate control valve 14 is turned ON / OFF is not repeated. There is also no risk of damaging the superheater overheat reducer 12. Although the boiler water injection system diagram of FIG. 1 illustrates the control method of the reheated steam temperature, the steam temperature set value is a rated value as a method for reducing the number of ON-OFF times of the water injection flow rate control valves 14 and 15. There is a way to lower it. However, this control method cannot be said to be a very suitable method because the operation is performed in a state where the steam temperature is lowered and the plant efficiency is lowered. However, this control method can be adopted when the reduction in plant efficiency is acceptable.

[0012]

According to the present invention, the water flow rate control valve is turned on.
Since the number of times of OFF can be reduced, the steam temperature can be adjusted safely even if the load changes frequently, without damaging the overheater overheat reducer or the reheater overheat reducer.

[Brief description of drawings]

FIG. 1 is a boiler water injection control system diagram of an embodiment of the present invention.

FIG. 2 is a general boiler system diagram used in one embodiment of the present invention.

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

[Explanation of symbols]

1 ... water supply pump, 2 ... high pressure water heater, 3 ... economizer, 4
... Boiler, 5 ... Primary superheater, 6 ... Secondary superheater, 7 ... High pressure turbine, 8 ... Primary reheater, 9 ... Secondary reheater, 10 ... Medium pressure turbine, 11 ... Condenser, 12 ... Superheater overheat reducer,
13 ... Reheater overheat reducer, 14 ... Superheater water injection flow rate control valve, 15 ... Reheater water injection flow rate control valve, 16 ... Main steam temperature detector, 17 ... Reheat steam temperature detector, 19 ... Steam temperature setting Unit, 22 ... Advance circuit calculator, 23 ... Switching unit, 24 ... Reheat steam temperature setting unit

Claims (2)

[Claims] 1. Superheat installed between a boiler and a superheater, or between a boiler and a reheater, based on a deviation between a detected value and a steam temperature set value, the steam temperature being detected downstream of the boiler. In the boiler steam temperature control method that controls the flow rate of water injected to the reducer, in the boiler load settling state, the flow rate of water injected to the overheat reducer is not performed, and when the load changes frequently, there is a small load change during load increase. In case of not adjusting the water injection flow rate,
A boiler steam temperature control method, wherein the flow rate of water injected into the superheat reducer is adjusted only when there is a large change in load. 2. A steam temperature detector for detecting a steam temperature in a downstream portion of a boiler, a calculator of a deviation between a steam temperature detection value of the detector and a steam temperature set value, and a calculation value of the calculator. A water injection flow rate control valve that controls the flow rate of the water injection pipe to the superheat reducer installed between the boiler and the superheater or between the boiler and the reheater, and the water injection flow rate control valve is operated in the boiler load settling state. In the case of a high frequency load change, the water injection flow rate control device that operates the water injection flow rate control valve only when there is a large load change during load increase and adjusts the water injection flow rate to the superheat reducer is provided. Characteristic boiler steam temperature control device.