JPH05322101A - Device for controlling temperature of steam in variable-pressure once-through boiler - Google Patents

Abstract

PURPOSE:To reduce the swelling caused by the fluid through a change in the condition for the fluid for an elevation in the temperature of the fluid in tubes of a boiler and prevent variation in the steam-separator tank level. CONSTITUTION:The pressure in the system is detected by a pressure detector 9 at the outlet of a steam separator; the saturation temperature for the pressure in the system is selected by a pressure-temperature function setter 10; and a deviation between the saturation temperature and the actual measured temperature of the steam at the outlet of a vaporizer, which is by a temperature detector 1 at the outlet of the vaporizer, is calculated by a subtracter 11. When a monitor relay 13 detects that the deviation has become a value within alpha deg.C, a fuel charge corresponding to a reduction to be made in the rate of the elevation of the temperature as preset by a function setter 12 for the bias of fuel charge is added as a minus bias in an adder 6. The value added as a minus bias in the adder 6 is inputted to an adder 8 and added with a BID signal, and a restrained value of fuel charge is outputted to an FRD. In this way the fuel charge at the start-up of a boiler is restrained and the temperature of the fluid in the rate of the elevation is moderated so that disturbance to the feedwater system can be prevented.

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 apparatus for a once-through type boiler, and more particularly to a steam temperature control apparatus for a once-through type boiler, which is suitable for controlling the temperature of a fluid at startup.

[0002]

2. Description of the Related Art When starting and stopping a transformer once-through boiler of a conventional thermal power plant, the steam temperature fluctuates greatly, and a large temperature difference occurs between the temperature of a pressure member constituting the boiler such as a boiler steam pipe and the steam temperature. Occurs. In particular, in the thick wall portion of the boiler such as near the superheater outlet header pipe, the temperature difference in the thickness direction becomes large. Therefore, thermal stress is generated in the pressure member, and the risk of damage due to fatigue increases. This danger is particularly great during intermediate load operation in which start-stop operation is repeated rapidly and frequently. This is because the fatigue of pressure members such as steam pipes becomes severe. Therefore, in order to prevent fatigue of the pressure member during the start / stop operation of the boiler, the amount of fuel input is kept within a certain regulation range.

As shown in FIG. 2, a conventional transformer once-through boiler for a thermal power plant, for example, sets a fuel input amount in a boiler starting process by a program to set a fuel input amount for each start mode in response to a boiler input signal. The control circuit was designed to raise and lower the evaporator outlet temperature to a specified value.
That is, in FIG. 2, the vapor temperature detected by the evaporator outlet temperature detector 21 is the temperature setting function setting device 22 and the switching device 2.
4 and the adder 25 and the ratio set by the ratio setter 26 is sent to the adder 27. In the adder 27, the fuel injection amount function setters 28 to 30, the switcher 31 or the switcher 32, and the high selection are selected. It is added with the boiler input command (BID) signal input via the device 33, and the fuel request command (FRD) of the set value is output. During the steady operation of the boiler, the amount of fuel input is controlled by a signal from the constant value function setting device 23 instead of the temperature raising function setting device 22.

[0004]

However, the above-mentioned prior art has not taken into consideration the change in fluid during the temperature rising process. That is, in the conventional technology, when the main steam pressure at startup is increased to a specified value, the program is set so that the fuel injection amount is specified by the state at startup of the boiler so that the temperature rises within the allowable stress value of the thick wall portion of the boiler. Although the fuel is injected based on the value, no consideration was given to the suppression of the temperature rise state with respect to the boiler pipe fluid, so there was a problem that the steam / water separator tank level fluctuated due to the swelling of the pipe fluid. An object of the present invention is to mitigate the fluid swelling phenomenon due to changes in fluid conditions and prevent fluctuations in the steam / water separator tank level with respect to the temperature rise state of the fluid in the boiler pipe.

[0005]

The above objects of the present invention can be achieved by the following constitutions. That is, in the transformer once-through boiler whose water supply system to the furnace is a combined feed water system of a water supply system and a recirculation system, the steam temperature control of the once-through boiler with the fluid temperature rise rate suppressing means provided in the fuel injection setting means at startup. It is a device. Here, the fluid temperature rise rate suppressing means may be configured to operate when the deviation between the evaporator outlet temperature and the saturation temperature at the outlet pressure of the steam separator falls within a set value.

[0006]

The swelling of the fluid in the boiler tube is a phenomenon caused by a sudden increase in the specific volume when the enthalpy rises and the saturated water enters the steam-water mixing region, and the fluid on the downstream side is pushed out. Therefore, calculate the saturation temperature by the system pressure,
Detecting the time when the difference between the saturation temperature and the evaporator outlet temperature is within the set value, and narrowing the fuel injection amount to reduce the fluid temperature rise rate, it is possible to mitigate the sudden increase in the specific volume. become. In this way, swelling into the drain tank of the steam separator is suppressed, and disturbance to the water supply system due to level fluctuation can be prevented.

[0007]

Embodiments of the present invention will be described with reference to the drawings. Figure 1
The steam temperature control circuit of the transformer once-through boiler of this embodiment is shown in FIG. In the steam temperature control of a normal transformer once-through boiler,
This is performed in the same manner as the steam temperature control of the transformer once-through boiler of the conventional thermal power plant shown in FIG. That is, the fuel input amount in the boiler starting process is controlled by the control circuit which sets the fuel input amount for each start mode in response to the boiler input signal by a program and raises and lowers the evaporator outlet temperature to a specified value. The vapor temperature detected by the evaporator outlet temperature detector 1 of FIG. 1 is the function setting device 2 for temperature rise, the switch 4 and the adder 5,
Adder 8 with the ratio set by ratio setter 7 via 6
To the boiler input command (BI) input to the adder 8 via a fuel input function setting device (not shown).
D) The signal is added to the signal to set the fuel demand command (FRD)
Is output. Also, during steady operation of the boiler, the amount of fuel input is controlled by a signal from the constant value function setting device 3 instead of the temperature raising function setting device 2, as in the steam temperature control circuit of FIG.

In this embodiment, in order to suppress the temperature rise rate of the fluid by controlling the fuel injection amount at the time of starting the boiler, the saturation temperature condition of the fluid is set based on the system internal pressure, and the temperature rise of the fluid near the saturation temperature is set. A control circuit for suppressing the rate is added to the steam temperature control circuit of FIG.

The pressure inside the system is detected by the steam / water separator outlet pressure detector 9, the saturation temperature relative to the inside pressure is selected by the pressure-temperature function setter 10, and the saturation temperature and the evaporator outlet temperature detector 1 are selected. The subtractor 11 calculates the deviation of the evaporator outlet vapor temperature from the measured temperature. When the monitor relay 13 detects that the deviation is within α ° C., the fuel input amount for the temperature rise rate narrowing set by the fuel input amount bias function setting unit 12 is added to the adder 6 as a negative bias. To do. The added value negatively biased by the adder 6 is input to the adder 8 and the boiler input command (BI
D) signal is added and the suppressed fuel input amount is output to the fuel request command (FRD). In this way, the amount of fuel input at boiler startup can be suppressed and the fluid temperature rise rate can be mitigated.
It has the effect of preventing disturbance to the water supply system.

The fuel injection amount bias is set to zero bias by the signal from the zero bias signal generator 17 by the switcher 15 when the monitor relay 14 detects the temperature deviation of the saturation temperature plus α ° C.

[0011]

According to the present invention, not only fatigue of the pressure member can be prevented but also the rate of temperature rise of the fluid can be mitigated, so that there is an effect of preventing disturbance to the water supply system at the time of startup of the variable pressure once-through boiler.

[Brief description of drawings]

FIG. 1 is a diagram showing a steam temperature control circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing a conventional steam temperature control circuit.

[Explanation of symbols]

1 ... Evaporator outlet temperature detector, 5, 6, 8 ... Adder, 9 ...
Air / water separator outlet pressure detector, 10 ... Pressure-temperature function setting device, 11 ... Subtractor, 13, 14 ... Monitor relay, 15
... Switch

Claims (2)

[Claims] 1. A variable-flow once-through boiler in which a water supply system to a furnace comprises a combined water supply system of a water supply system and a recirculation system, wherein a fluid temperature rise rate suppressing means is provided in a fuel injection setting means at startup. Steam temperature control device for transformer once-through boiler. 2. The transformer according to claim 1, wherein the fluid temperature increase rate suppressing means is activated when the deviation between the evaporator outlet temperature and the saturation temperature at the outlet pressure of the steam separator falls within a set value. Steam temperature controller for once-through boiler.