JP2002323203A - Vapor temperature control method and device for once- through boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vapor temperature control method and control device for a once-through boiler, in which main vapor temperature is controlled in a stable manner even under a great change of load between a sprayed water control loop of a final superheat reduction device and a fuel flow control loop. SOLUTION: The final desuperheater spray water control loop controls the outlet vapor temperature (main vapor temperature) of a final super-heater and the fuel flow control loop controls the front flow side temperature of the final desuperheater device. When heat is apt to be insufficient to lower the vapor temperature, the main vapor temperature is controlled, by the immediately effective desuperheater spray water control loop to be stable. However, the front flow side temperature of final desuperheater falls due to the feature of the once-through boiler that the front flow side temperature at a position where the sprayed water is supplied falls, when the sprayed water is decreased, in addition to a tendency that the temperature falls due to the shortage of heat by a burner. The fuel flow is increased by the fuel flow control loop for controlling it, which can contribute to the substantial recovery of thermal balance and the main vapor temperature can be controlled in a stable manner. When hart is excessive and temperature is a tendency to rise, effects are reverse to the above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for controlling the steam temperature of a once-through boiler, which is particularly suitable for improving the stability of the main steam temperature.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional superheated steam temperature control mechanism of a once-through boiler. In the main system of a once-through boiler in which an evaporator (including a furnace heat transfer wall) 1, an upstream superheater group 2, and a final superheater 5 are sequentially arranged, an upstream superheater group 2 and a final superheater 5 are provided.
The final superheat reducer 4 is disposed between the first and second superheaters, and no superheat reducer is provided downstream of the final superheater 5. The steam whose temperature has been adjusted by the final superheat reducer 4 is supplied to the boiler steam supply device ( A steam turbine etc. 7) is provided.

[0003] The conventional superheated steam temperature control of a once-through boiler is as follows.
The feedback control with the integral operation of subtracting the output value of the function generator 52 based on the measured value of the final superheater outlet steam thermometer 6 and the output value of the function generator 52 based on the boiler load command 51 by the subtractor 53 and adjusting by the proportional-integral controller 54, The amount of fuel burned by the burner 32 was controlled by adjusting the fuel flow rate adjusting operation end 31.

In addition, a part of the feed water is supplied to the final desuperheater 4 by bypassing the evaporator 1 and the upstream superheater group 2 of the main system (water and steam system) of the once-through boiler pipe and sprayed from the spray nozzle. A spray water pipe 8 is provided as a final superheat reducer to be supplied as water, and the flow rate of the spray water is adjusted by increasing or decreasing the flow rate adjusting operation end 9 of the spray water.
The control of the spray water flow rate by the flow rate control operation end 9 uses the measured value of the final superheater outlet steam thermometer 6 to subtract the output value of the function generator 55 based on the boiler load command 51 by a subtractor 56.
Is performed by feedback control with an integral operation of adjusting by the proportional-integral adjuster 57 by subtracting.

In the above prior art, the fluctuation of the steam temperature (main steam temperature) at the outlet of the final superheater is controlled by a control loop of the spray water of the final superheat reducing device having a high immediate effect because the spray water is sprayed directly into the steam. The concept is to adjust the temperature to a specified value by a fuel flow rate control loop that determines the balance value of the final superheater outlet steam temperature in the long term.

That is, the final superheater outlet steam temperature must be adjusted to a temperature range required by a steam demander such as a downstream steam turbine, and spray water having an immediate effect is effective for that purpose. . However, some adjustment is necessary because the factor of the steam temperature fluctuation from the upstream side has not been removed.

[0007] Specifically, since a part of the water supplied to the evaporator 1 is sprayed as spray water, the amount of water supplied to the evaporator 1 decreases when the amount of water extracted is increased. The amount of heat absorbed by the combustion gas generated by the combustion of the fuel in the evaporator 1 disposed in the flue portion through which the exhaust gas flows and the amount of heat absorbed by the evaporator 1 is reduced, and the superheater group 2 disposed on the upstream side of the flue portion Due to the increased heat absorption, the final superheater outlet steam temperature will return to the temperature before conditioning with spray water over time. The converse is true if the spray water is reduced.

[0008] However, when a factor that disturbs the balance of the main steam temperature such as a load change having a large change width continues to act, it exists in the control loop of the superheat reducer spray water that is highly responsive to the main steam temperature. Since the integral controller 57 continues to absorb this while the apparent main steam temperature does not fluctuate,
No fuel flow correction is made to balance the final main steam temperature. Then, since the absorption by the integral controller 57 is not performed immediately after the spray water becomes zero (when the spray water is reduced) or the capacity limit is reached, the main steam temperature sharply decreases or rises. From the point in time, the fuel flow rate will be corrected, but it will be too late to take effect, causing a significant drop or increase in the main steam temperature, falling outside the required range of the steam demander, and causing a serious accident. Also leads to.

[0009]

The above-mentioned prior art uses a feedback control loop with two different integral operations of a final superheater spray water control loop and a fuel flow rate control loop from the same process value of the main steam temperature. With this configuration, there is a problem that if a load change or the like having a large change width continues to act, the main steam temperature is greatly reduced or increased.

An object of the present invention is to provide a steam temperature control method and a control device for a once-through boiler for stably controlling the main steam temperature even in a load change in which a final superheat reducer spray water control loop and a fuel flow rate control loop have a large change width. It is to be.

[0011]

In order to solve the above-mentioned problems of the prior art, the present invention has a configuration in which the two control loops control different process values. That is, the final superheater reducer spray water control loop controls the final superheater outlet steam temperature (main steam temperature), and the fuel flow control loop controls the final superheat reducer upstream side temperature.

That is, the present invention comprises the following constitutions (1) and (2). (1) A plurality of superheaters are arranged in series, and the most upstream side of the plurality of superheaters is located between the last downstream superheater and the upstream superheater among the plurality of superheaters. A fuel pipe for supplying fuel to a burner for superheating the plurality of superheaters, connecting a superheat reducer for supplying spray water by bypassing the plurality of superheaters from a water supply pipe upstream of the superheater. In the once-through boiler steam temperature control method comprising, by feedback control based on the outlet steam temperature of the final superheater, the flow rate of spray water supplied to the superheat reducer is adjusted, and the outlet steam temperature of the final superheater is adjusted. And a feedback control based on the steam temperature on the upstream side of the superheat reducer to adjust the fuel flow rate to the burner to control the steam temperature on the upstream side of the superheat reducer. is there. More specifically, the present invention feedback-controls the outlet steam temperature of the final superheater based on the difference between the outlet steam temperature of the final superheater and a value corresponding to the boiler load command value, and controls the upstream side of the superheat reducer. This is a method of feedback-controlling the steam temperature on the upstream side of the superheat reducer based on the difference between the steam temperature and a value corresponding to the boiler load command value.

(2) A plurality of superheaters arranged in series in a pipe, and the plurality of superheaters between the last superheater on the most downstream side and the superheater on the upstream side of the plurality of superheaters. A superheat reducer for supplying spray water connected by bypassing the plurality of superheaters from the upstream side of the most upstream side superheater, a fuel pipe for superheating the plurality of superheaters, and a tip thereof In the steam temperature control device for a once-through boiler provided with a burner provided in the section, an outlet thermometer for measuring the outlet steam temperature of the final superheater, and a function for generating a function based on the boiler load command value. A first function generator, a first subtractor that calculates a deviation between a measured value of the outlet steam thermometer of the final superheater and an output value of the first function generator, and the first subtractor. A first controller (proportional product) in which a response signal is generated based on the obtained deviation value A first proportional-integral controller), and a spray-water flow control operation end for increasing / decreasing spray water supplied to the overheat reducer based on an output of the first controller (first proportional-integral controller). A steam thermometer for measuring the steam temperature on the upstream side of the superheat reducer, a second function generator for generating a function based on the boiler load command value, and a measurement of the steam thermometer on the upstream side of the superheat reducer. A second subtractor for calculating a deviation between the value and the output value of the second function generator, and a second controller (for generating a response signal based on the deviation obtained by the second subtractor). Second proportional-integral controller for proportional integration)
And a fuel flow rate control operation end provided in the fuel pipe based on the output of the second regulator (second proportional-integral regulator) to control the fuel supply amount.

In the present invention, the control target of the fuel flow control loop is not simply the steam temperature in the upstream of the superheat reducer, but the steam temperature in the upstream of the final superheat reducer. Because he did. (A) By measuring the steam temperature as close as possible to the final superheater outlet, which is the final control target as the main steam temperature control device, the control disturbance received by the superheater arranged on the upstream side of the fluid path is also reduced. This can be detected and corrected by appropriate control actions, which is better served by the purpose of controlling the main steam temperature of the present invention. (B) Since the steam flowing through the superheater has the characteristic that the higher the temperature is, the lower the specific heat is (in other words, the fluctuation of the temperature is large with respect to the same specific enthalpy fluctuation), the same thermal disturbance Even if the temperature is measured on the downstream side of the superheater, the fluctuation of the steam temperature can be detected more remarkably, and in the case where immediate effect is required as in the problem of the present invention, it is more convenient as a control object. It is.

[0015]

According to the invention, the main steam temperature is controlled by reducing the spray water by means of a rapid-acting superheat reducer spray water control loop, for example, when the steam temperature tends to decrease due to insufficient heating, Transition to stable. However, in addition to the tendency of temperature decrease due to insufficient heating by the burner, the characteristics of once-through boilers, in which the steam temperature on the upstream side decreases when spray water decreases, combine with the characteristics of the once-through boiler before the final desuperheater. Although the steam temperature on the downstream side drops, the fuel flow rate is increased by the fuel flow rate control loop that controls this, which can contribute to the recovery of the essential heat balance, and stable main steam temperature control can be expected. When the heating amount is excessive and the steam temperature tends to increase, the reverse is true.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a superheated steam temperature control mechanism for a once-through boiler according to the present invention will be described with reference to FIG.
1, in the main system of the once-through boiler pipe in which the evaporator 1, the upstream superheater group 2 and the final superheater 5 are sequentially arranged, as in the conventional superheated steam temperature control mechanism shown in FIG. The final superheater 4 is disposed between the final superheater 5 and the final superheater 5, and the superheat reducer is not provided downstream of the final superheater 5. A steam supply destination device (steam turbine or the like) 7 is provided with a device for demanding steam.

In the above superheated steam temperature control mechanism, the set value of the final superheater outlet steam temperature determined by the function generator 55 based on the boiler load command 51 and the temperature measured by the final superheater outlet steam thermometer 6 are compared by a subtractor 56. , A control signal is transmitted by the proportional-integral controller 57, and the position of the final superheat reducer spray water flow rate control operation end 9 is operated by the control signal. The flow rate of the spray water flowing through the final superheat reducer spray water pipe 8 is adjusted by increasing / decreasing the final superheat reducer spray water flow rate adjusting operation end 9 provided in the middle of the pipe 8, and is provided upstream of the final superheater 5. Water is injected into the main system through the provided final superheat reducer 4 and contributes to increase and decrease of the steam temperature.
That is, as described above, when the injection amount of the spray water is increased, the temporary superheater outlet steam temperature measured by the final superheater outlet steam thermometer 6 is temporarily reduced, and conversely, the spray water injection amount is increased. When the temperature decreases, the temperature is temporarily increased.

The superheated steam temperature control mechanism shown in FIG. 1 is different from the conventional superheated steam temperature control mechanism shown in FIG. 2 in that a upstream side of the final superheat reducer is located between the upstream superheater group 2 and the final superheat reducer 4. The subtractor 53 subtracts the thermometer 3 from the output value of the function generator 52 based on the boiler load command 51 and the measured value obtained by the thermometer 3 on the upstream side of the final superheat reducer. In other words, the proportional-integral adjuster 54 controls the fuel flow rate adjusting operation end 31 by feedback control with an integral operation based on the deviation value to control the amount of fuel burned by the burner 32.

With the configuration shown in FIG. 1, when a disturbance is generated in a direction in which the superheated steam temperature rises due to, for example, a load change, the temperature measured by the final superheater outlet steam thermometer 6 rises. The output signal of the subtractor 56 operates relatively in the positive direction, and accordingly, the proportional-integral controller 57 operates in the direction of increasing the output signal. In response to this signal, the degree of opening of the final superheat reducer spray water flow control operation end 9 is increased,
Temporarily the steam cooling effect is effective, and the final superheat reducer 4
Since the temperature measured by the final superheater outlet steam thermometer 6 located on the downstream side of the heater decreases, the control by the spray water has little delay and the response is good, the final superheater outlet steam temperature is relatively quick. Then, the value increased by the above-described disturbance can be returned to the original value, and stable control is continued.

On the other hand, the temperature measured by the thermometer 3 on the upstream side of the final superheater also rises due to disturbance, but the flow rate of steam flowing through the main system decreases due to an increase in the spray water of the final superheat reducer. The upstream temperature further increases, and this temperature increase can be detected in a remarkable manner. The signal of the temperature measured by the thermometer 3 on the upstream side of the final superheat reducer 3 rises, and the output signal of the subtractor 53 operates relatively in the minus direction (note the plus and minus directions of the subtractor 53). In response, the proportional-integral controller 54 operates in a direction to decrease the output signal. In response to this signal, the fuel flow rate adjusting operation end 31 acts to reduce the fuel flow rate, reduce the combustion amount of the burner 32, and return the steam temperature to the direction of reducing the long-term balance fluctuation of the steam temperature.

[0021]

According to the present invention, the fluctuation of the boiler heat balance is accurately detected and operated by the fuel flow control loop, so that the main steam temperature can be stably controlled.

[Brief description of the drawings]

FIG. 1 is a diagram showing a superheated steam temperature control mechanism of a once-through boiler according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a superheated steam temperature control mechanism of a once-through boiler according to the related art.

[Explanation of symbols]

1 Evaporator (including furnace heat transfer wall) 2 Upstream superheater group 3 Final superheat reducer upstream thermometer 4 Final superheat reducer 5 Final superheater 6 Final superheater outlet steam thermometer 7 Boiler steam supply device ( 8 Spray water piping for final superheat reducer 9 Spray water flow control operation terminal 31 Fuel flow control operation terminal 32 Burner 51 Boiler load command 52, 55
Function generators 53, 56 Subtractors 54, 57
Proportional integral controller

Claims (3)

[Claims] 1. A plurality of superheaters are arranged in series, and a most superheater of the plurality of superheaters is disposed between a most downstream superheater and a superheater upstream of the plurality of superheaters. A superheat reducer that supplies spray water by bypassing a plurality of superheaters from a water supply pipe upstream of the upstream superheater is connected, and further supplies fuel to a burner for superheating the plurality of superheaters. In a once-through boiler steam temperature control method provided with a fuel pipe, the flow rate of spray water supplied to the superheat reducer is adjusted by feedback control based on the outlet steam temperature of the final superheater, and the outlet steam of the final superheater is adjusted. A once-through flow characterized by controlling the temperature, and further controlling the fuel flow to the burner by feedback control based on the steam temperature on the upstream side of the superheat reducer to control the steam temperature on the upstream side of the superheat reducer. Boiler steam temperature Your way. 2. A feedback control of an outlet steam temperature of the final superheater based on a difference between an outlet steam temperature of the final superheater and a value corresponding to the boiler load command value, so that a steam temperature and a boiler load upstream of the superheat reducer are provided. 2. The steam temperature control method for a once-through boiler according to claim 1, wherein the steam temperature on the upstream side of the superheat reducer is feedback-controlled based on a deviation from a value corresponding to the command value. 3. A plurality of superheaters arranged in series in a pipe,
A plurality of superheaters from the upstream of the most upstream superheater in the plurality of superheaters between the most downstream final superheater and the upstream superheater in the plurality of superheaters. In a steam temperature control device for a once-through boiler comprising a superheat reducer for supplying spray water connected by bypass, a fuel pipe for superheating the plurality of superheaters, and a burner provided at a tip end thereof. An outlet steam thermometer of the final superheater for measuring the outlet steam temperature of the final superheater; a first function generator for generating a function based on the boiler load command value; and an outlet steam thermometer of the final superheater. A first subtractor for calculating a deviation between a measured value and an output value of the first function generator; a first controller for generating a response signal based on the deviation obtained by the first subtractor And supplying the superheat reducer based on the output value of the first controller. A spray water flow control operation end for increasing or decreasing the spray water, a steam thermometer for measuring a steam temperature on the upstream side of the superheat reducer, and a second function generator for generating a function based on a boiler load command value. A second subtractor for calculating a deviation between a measured value of the steam thermometer upstream of the superheat reducer and an output value of the second function generator; and a deviation obtained by the second subtractor. A second regulator that generates a response signal based on the value, and a fuel flow rate adjusting operation end that adjusts a fuel supply amount provided in the fuel pipe based on an output value of the second regulator. A steam temperature controller for once-through boilers.