JP2002081607A - Steam temperature controller for variable pressure once-through boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct the water/fuel ratio of a boiler so that the outlet temperature of an evaporator may maintain a degree of superheat and may not rush into saturation. SOLUTION: A steam temperature controller for a variable pressure once- through boiler is provided with a facility which sprays water upon a desuperheater installed at the outlet of the superheater of each section from the outlet portion of an economizer and controls (proportionally and integrally) the steam temperature of the boiler while the boiler is operated in an once- through mode by adjusting the water/fuel ratio which is the ratio of the quantity of feed water to the quantity of supplied fuel and the quantity of the sprayed water. The controller secures the degree of superheat of the outlet temperature of the evaporator by controlling the steam temperature by correcting the water/ fuel ratio based on the deviation of the fluid temperature at the outlet of the evaporator.

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 of a once-through boiler, and more particularly to a steam temperature control device of a boiler suitable for performing stable control of a steam temperature when a load changes.

[0002]

2. Description of the Related Art The steam temperature at the outlet of a superheater, which is extracted from a water supply system upstream of a furnace water wall inlet and divided into one or more stages in a steam system downstream of a furnace water wall outlet, is determined. In a boiler having a desuperheater for injecting the extracted water into a steam flow by spraying so as to have a predetermined value, the steam temperature at the final superheater outlet (hereinafter referred to as main steam) among the steam temperatures at the superheater outlet Control).
The PI is controlled by the water-fuel ratio and the spray amount, but it is controlled by the spray which has a high responsiveness to the correction of the transient change of the main steam temperature. I have.

The water-fuel ratio control is to control the main steam temperature to a predetermined value by changing the ratio between the amount of water supplied to the boiler and the amount of fuel to the boiler. This is a control in which the fuel combustion amount is commanded by adding the deviation of the main steam temperature to the fuel combustion amount command value corresponding to the command value (see the route of the boiler input command and the fuel combustion amount command in FIG. 2).

As shown in FIG. 4, the spray control uses a main steam temperature set value created by the function generator 2 based on the load command value from the load command 200 and an actual temperature from the main steam thermometer 300. The proportional / integral operation (1 → 7 → 8 → 21 → 20) is performed based on the deviation subtracted by the subtractor 1, but when there are a plurality of superheaters (three stages in FIG. 4), each superheater A correction value of the outlet temperature set value is obtained, and this correction value is added to the main steam temperature set value generated based on the load command 200 to create a temperature set value, and the spray is set so as to have the generated set value. A two-stage PI control system (cascade control system) that operates a valve is used.

When the load is settled, the spray amount is kept at the boiler balance point, and constant spray correction is performed so as to secure a control margin by spraying. In the case of gas- and oil-fired boilers, the heat collection characteristics do not change, so a constant ratio control is performed to keep the ratio of the spray amount to the load constant. However, in the case of coal-fired boilers, furnace collection by coal type (mainly fuel ratio) is performed. In order to cope with the change in the amount of heat, the program for setting the ratio of the spray amount to the load is made variable to cope with the change.

[0006] In the case of a variable-pressure boiler, a saturation temperature control set value based on steam pressure is created so that the inlet temperature of the superheater maintains the degree of superheat (saturation temperature + margin value), and the lower limit operation is performed on the inlet temperature setting. Is considered to give.

Next, a specific configuration of a conventional steam temperature control apparatus will be described with reference to FIGS. 4 and 2. FIG. FIG.
FIG. 2 is a control block diagram showing creation of a main steam temperature control bias in the prior art, and FIG. 2 is a control block diagram for creating a fuel combustion amount command using the main steam temperature control bias. The command represents one of the water-fuel ratio controls. (In the water-fuel ratio control, in addition to the fuel combustion amount, the water supply amount to the boiler (total amount of the water supply to the furnace and the water supply to the desuperheater) Control). The control block diagram of FIG. 2 is a common control block diagram applied to both the present invention and the prior art.

In FIG. 4, the main steam temperature control is set by either a command (DPC) from the middle supply (central power supply command station) or a command (ALR) installed in the station (for each power station). A difference between the main steam temperature set value programmed by the function generator 2 based on the load command 200 and the actual temperature (MST) from the main steam thermometer 300 calculated by the subtractor 1 is used as a differentiator. 6 and outputs the result to an adder 8
In addition, the main steam temperature deviation and the spray flow rate deviation ΔS
After the PF is added by the adder 21, the PF is input to the integrator 20 and the output is passed through the rate-of-change limiter 22 to create a main steam temperature control bias. Here, the rate-of-change limiter limits the rate of change of the input signal so that its output has a buffer characteristic.

Since the response time constant and the amount of change of the main steam temperature due to the change in the fuel combustion amount fluctuate depending on the load, the proportional and integral components are corrected by the function generators 13 and 14 from the boiler input command (BID). .

The adder 8 has a proportional control signal obtained by adding a correction value by the function generators 15 to 17 from the boiler input command (BID) to the primary superheater, secondary superheater and tertiary superheater outlet temperature deviation. Is added to the adder 10 to add the correction.

Since the time constant of the steam temperature is long during the load change, if the transient temperature fluctuation is corrected, the water-fuel ratio after the end of the load change deviates from an appropriate value, which causes disturbance of the steam temperature. The input 20 is switched by the switch 18 to 0 generated by the signal generator 19, and the integration operation based on the deviation of the main steam temperature is blocked.

In FIG. 2, as the superheat control at the evaporator outlet, the upper and lower limits of the evaporator outlet temperature set by the function generators 5 and 6 based on the steam separator tank pressure 600 (STP), and evaporation. When the deviation of the actual temperature from the evaporator outlet thermometer 700 exceeds the specified value, the superheat degree at the evaporator outlet is controlled to be within the specified value by applying an increase / decrease bias to the fuel. The correction is performed only in the middle, and the correction value from the function generator 4 according to the boiler input command (BID) is used. During the load change, the correction value of the signal generator 7 is used. Here, as an example, in the superheat degree limit setting, the upper limit is set to the saturation temperature + 60 ° C, the lower limit is set to the saturation temperature + 10 ° C, and the temperature deviation is 2 T / H on the + side and 4.5 T / H on the-side.
It is set to the degree.

In such a main steam temperature control method, when the load is increased (in response to the demand for increased power demand,
In order to increase the steam flow while maintaining the predetermined steam pressure, the temperature of the exhaust gas from the furnace rises by increasing the fuel in order to increase the steam flow), and the heat absorption of the primary superheater, the secondary superheater and the tertiary superheater transiently. Increases, the temperature at the outlet of each superheater rises, and control is performed so that the spray flow rate at each section is increased to achieve each temperature set value. There is no correction to the water-fuel ratio control because the temperature deviation is small by following the spray,
The deviation due to the change in the spray flow rate is corrected as a de-bias for the water-fuel ratio control.

Further, since the amount of fluid to the furnace side decreases due to an increase in the spray flow rate (the water supply amount is the sum of the furnace part and the spray part, so that if the spray increases, the water amount to the furnace decreases accordingly. ), The evaporator outlet fluid temperature increases and the degree of superheat increases, so that the de-bias correction is included in the water-fuel ratio control from the superheat degree control.

Since the temperature deviation decreases as the load rise approaches convergence, the spray flow rate decreases, and the flow is returned so as to converge to the load balance point, so that the amount of fluid to the furnace increases. At that time, the steam temperature deviation correction and the spray flow rate deviation correction amount disappear, but the water-fuel ratio is in an unbalanced state (there is less fuel than the water supply).
The fluid temperature at the evaporator outlet drops.

In the water-fuel ratio control, the water-fuel ratio is biased by increasing the superheat at the evaporator outlet. However, it takes time to contribute to the fluid temperature. In this state, the temperature imbalance of the water wall portion and the heat load in the pipe of the primary superheater cause the imbalance.

This phenomenon is observed when the load change rate and the change width are large, and in the case of high fuel ratio coal (the higher the fuel ratio, the smaller the heat absorption in the furnace part and the larger the rear heat absorption amount).

[0018]

In such a main steam temperature control method, temperature control is performed by changing a spray flow rate in response to a transient temperature change. (The amount of fuel is less than the feed water), and the superheat degree of the fluid temperature at the evaporator outlet cannot be secured, and it temporarily enters the saturation region. Therefore, the temperature imbalance of the water wall occurs and the primary superheater There is a problem that the heat load in the pipe becomes unbalanced because the air-water mixture state occurs in the pipe, and the superheater tube is damaged.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a circuit for correcting the water-fuel ratio so as to maintain the degree of superheat so that the evaporator outlet temperature does not enter saturation.

[0020]

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

The system has a facility for spraying water from a water supply system upstream of the furnace water wall inlet, for example, from the outlet of the economizer to the desuperheater at the outlet of each superheater. A steam temperature control device of a variable-pressure once-through boiler for controlling steam temperature during once-through operation with a water injection amount, wherein the steam temperature is controlled by correcting the water-fuel ratio based on a deviation of an outlet fluid temperature of an evaporator. A steam temperature control unit for a variable-pressure once-through boiler that ensures the superheat of the outlet temperature.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A steam temperature control apparatus for a variable-pressure once-through boiler according to an embodiment of the present invention is shown in FIGS.
This will be described below. FIG. 1 is a view showing a fluid path of a variable-pressure once-through boiler and a state of correction of a main steam temperature during a once-through operation. FIG. 2 is a view showing a control block for creating a fuel amount command leading to water-fuel ratio control. FIG. 1 is a diagram showing a configuration of a steam temperature control device for creating a main steam control bias according to an embodiment of the present invention.

In FIG. 1, the fluid (steam) path is shown through an evaporator 51 → a steam separator 52 → a primary superheater 53 → a secondary superheater 54 → a tertiary superheater 55 → a final superheater 56. Not supplied to the turbine. The point at which the steam temperature is adjusted is that spray water is injected into the desuperheaters 60, 61, and 62 installed at the outlets of the primary superheater 53, the secondary superheater 54, and the tertiary superheater 55, and the superheated steam and water Is controlled by adjusting the steam temperature by changing the amount of water injected in response to changes in the amount of heat absorbed by each superheater.

The main steam temperature during the once-through operation is controlled by PI (proportional + integral) with the water-fuel ratio and the spray.
The correction of the transient change of the main steam temperature is controlled by the above-mentioned spray (spray water injection amount), and statically when the main steam temperature is settled by bias operation to the water / fuel ratio (ratio of feed water and fuel consumption). The temperature is stabilized by correcting it so that it becomes the balance point of the planned value.

In FIG. 1, when the deviation of the outlet temperature of the primary superheater, the secondary superheater and the tertiary superheater in the prior art shown in FIG. If the steam at the inlet enters saturation and the deviation of the evaporator outlet temperature is employed as the main steam temperature control bias in the embodiment of the present invention shown in FIG. 3, the steam at the inlet of the primary superheater does not enter saturation. Is shown.

According to FIG. 3 showing the embodiment of the present invention, the main steam temperature control for the steam immediately before the turbine is performed in the same manner as in the prior art by the command from the middle supply (DPC) or the command (ALR) set in the plant. Load command 200 set by either
The difference between the main steam temperature set value programmed by the function generator 2 (corrected value for ensuring the degree of superheat at the evaporator outlet) and the actual temperature MST from the main steam thermometer 300 is calculated by the subtractor 1. The deviation from 1 is input to the differentiator 6 and the output thereof is added by the adder 8. Further, the spray flow rate deviation .DELTA.SPF is added to the main steam temperature deviation by the adder 21, and then input to the integrator 20, The output is passed through the rate-of-change limiter 22 to create a main steam temperature control bias.

Further, since the response time constant and the amount of change of the main steam temperature due to the change in the fuel combustion amount fluctuate depending on the load, the function generator for the integral and proportional components of the deviation of the main steam temperature from the boiler input command (BID). 13 and a function generator 14. Further, a proportional control signal obtained by adding a correction value by the function generator 16 from the boiler input command (BID) is added to the adder 8.

Further, the evaporator superheat control, which controls the deviation between the upper and lower limits of the evaporator outlet temperature set by the program from the steam pressure of the steam separator and the evaporator outlet temperature to be within a specified value, The proportional control signal obtained by adding the correction value of the function generator 17 from the boiler input command (BID) to the correction value (ΔCEI) of the above is also added to the main steam temperature control bias in the adder 8. Here, the evaporator outlet superheat correction ΔCEI is created based on the steam separator tank pressure STP and the evaporator outlet temperature SIT in the control black diagram for creating the fuel amount command shown in FIG.

Further, constant spray control is performed by adding the spray flow rate deviation .DELTA.SPF to the proportion of the main steam temperature deviation by the adder 22.

Since the time constant of the steam temperature is long during the load change, if the transient temperature fluctuation is corrected, the water-fuel ratio after the end of the load change deviates from an appropriate value and becomes a disturbance of the steam temperature. The input to the signal generator 2 is switched by the switch 19
On the 0 side, switching to 0 is performed to block the integration operation.

The main difference of the steam temperature control apparatus according to the present embodiment from that of the prior art is that the prior art corrects the proportional calculation value of the deviation of the main steam temperature by the sum of the deviations of the outlet temperatures of the superheaters. (1SHOT, 2SHOT, 3S in FIG. 4)
(Refer to HOT), however, by making a correction at the evaporator outlet temperature, the correction will be made so that the evaporator outlet temperature will maintain the degree of superheat under any heat absorption conditions. is there. That is, the evaporator outlet temperature set value programmed by the function generator 3 from the actual measured value of the evaporator outlet temperature EVT and the target load command (the temperature that does not enter saturation)
Is added to the adder 8 to create a main steam temperature control bias, and this main steam temperature control bias is applied to the fuel amount command FRD shown in FIG. 2 and used for water-fuel ratio control.

As described above, according to the embodiment of the present invention, it is possible to prevent the primary superheater inlet temperature from entering the saturation region even when the load changes, by securing the degree of superheat at the evaporator outlet temperature. Can prevent damage to the superheater.

[0033]

According to the present invention, the superheat degree at the outlet of the evaporator is ensured even if the water-fuel ratio balance at the time of load change is lost. Is not likely to enter the saturation region,
It is possible to prevent the superheater tube from being damaged.

Accordingly, the material of the primary superheater pipe can be reduced, and maintenance due to extubation can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a fluid path of a variable-pressure once-through boiler and a state of correction of a main steam temperature during a once-through operation.

FIG. 2 is a diagram showing a control block for creating a fuel amount command that leads to water-fuel ratio control.

FIG. 3 is a diagram illustrating a configuration of a steam temperature control device that creates a main steam control bias according to an embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a conventional steam temperature control device.

[Explanation of symbols]

 1,4 Subtractor (FIG. 3) 2,3,11,14-18 Function Generator (FIG. 3) 5,7,9,12,13 Multiplier (FIG. 3) 6 Differentiator (FIG. 3) 8,10 , 22, 24 Adder (FIG. 3) 19 Switcher (FIG. 3) 20 Signal Generator (FIG. 3) 21 Integrator (FIG. 3) 23 Rate-of-Change Limiter (FIG. 3)

Claims (1)

[Claims] 1. A facility for spraying water from a water supply system upstream of a furnace water wall inlet to a desuperheater at a superheater outlet in each section, wherein a water-fuel ratio, which is a ratio of feedwater to fuel, and a spray water injection amount flow through. A steam temperature control device for a variable-pressure once-through boiler for controlling a steam temperature during operation, wherein the steam temperature is controlled by correcting the water-fuel ratio based on a deviation of an outlet fluid temperature of an evaporator, and a degree of superheat of the evaporator outlet temperature. A steam temperature control device for a variable-pressure once-through boiler, characterized in that the temperature is maintained.