JPS6235001B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a boiler steam temperature control device, and more particularly to a boiler spray flow rate control device that controls temperature by spray flow rate.

As shown in FIG. 1, superheated steam is generally supplied to the turbine 10 by sequentially supplying the fluid discharged by the water supply pump 11 to a heated steam section 12 and a heating section 13. obtain. The temperature of the superheated steam is determined by the output of a steam temperature controller 15 that receives the output of a flow rate detector 14 that detects the amount of superheated steam supplied to the turbine 10, and the output of a load amount detector 16 that detects the amount of load on the turbine. A spray flow rate target value is determined by the calculation circuit 18 based on the load-spray flow rate conversion calculation circuit 17 which receives the signal inputted, and a manipulated variable for making the output of the spray flow rate detector 19 coincide with this spray flow rate target value is determined. Calculated by the adjustment calculation circuit 20, the operating end 21
Temperature control is performed by controlling the amount of cooling water supplied to the inlet of the heating section to maintain it at a predetermined value.

By the way, the reason why such a spray temperature control system is adopted is that the response of the steam temperature output from the boiler superheater 13 is very slow, and it is not possible to perform good control against disturbances using normal feedback control alone. Therefore, this feedback control system incorporates spray flow rate control in which the target value is the spray flow rate determined from the preceding load.
If only spray flow rate control is used, a steady-state deviation will appear in the main steam temperature. Therefore, the spray flow rate target value determined in advance is corrected using a steam temperature controller to remove the steady-state deviation and maintain the main steam temperature at a predetermined target value, but this still causes the following two points. Therefore, it is difficult to accurately set the load-spray flow rate conversion equation. First of all, the conversion equation changes due to aging of the boiler, changes in efficiency, disturbances, etc. Second, it is difficult to accurately determine the conversion equation through a test run of the boiler.

As described above, since the conversion equation is not optimal, the amount of spray determined in advance becomes excessive (insufficient), the main steam temperature becomes too low (high), and the temperature feedback control requires a large correction.

SUMMARY OF THE INVENTION An object of the present invention is to provide a spray flow rate control device for a boiler that can maintain superheated steam temperature at approximately a predetermined value despite load changes.

The outline of how to achieve this purpose is to calculate the spray flow rate correction amount at the load using a load-spray flow rate conversion calculation correction circuit that inputs the output of the load amount detector and the superheated steam temperature signal, and then converts the load-spray flow rate. The configuration is such that the characteristics are modified by changing the parameters of the arithmetic circuit, and the spray flow rate is adjusted accordingly. The corrected spray flow rate signal from the load-spray flow rate conversion calculation circuit is given to the spray flow rate adjustment calculation circuit, so the optimum spray flow rate is determined for changes in load, and this flow rate value is used to supply cooling water to the input side of the superheater. supply. As a result, the superheated steam temperature can be maintained at approximately a predetermined value even when the load changes.

An embodiment of the present invention will be described below with reference to the drawings. Circuits having the same functions as those of the circuit shown in FIG. 1 are given the same numbers, and the description thereof will be omitted. The difference in the circuit configuration in FIG. 2 from the circuit configuration in FIG. 1 is that a load-spray flow rate conversion calculation circuit 22 is used in which the conversion characteristics of the load-spray flow rate conversion calculation circuit 17 can be freely changed, and a load-spray flow rate conversion calculation circuit 22 is used. This is where an arithmetic correction circuit 23 is added. The load-spray flow rate conversion calculation correction circuit 2
3 inputs the output of the load amount detector 16 and the output of the steam temperature detector 14, and outputs a load-spray flow rate correction signal of ΔF when the load-spray flow rate conversion correction calculation formula is applied. The load-spray flow rate conversion calculation circuit 22 inputs the output of the load amount detector 16 and the output △F of the load-spray flow rate conversion calculation correction circuit, and initially operates as shown in FIG.
L ₁ , F ₁ , L ₂ , F ₂ , L ₃ , F ₃ , L ₄ , F ₄ and L ₅ , F ₅
The load passing through the point - spray flow rate conversion characteristics is set in advance, and the load - is determined by the output of the load amount detector 16.
The characteristics are modified so that the value obtained by adding the output ΔF of the load-spray flow rate conversion arithmetic correction circuit 23 to the spray flow rate value determined from the spray flow rate conversion characteristics becomes the spray flow rate under the load at that time. For example, FIGS. 4 and 5 show the case where the load L is between loads L ₂ and L ₃ and near the load L ₂ , and ΔF is output from the load-spray flow rate conversion calculation correction circuit 23. This will be explained with reference to. When the load is stable, it is determined whether the current load L is closer to either of the break points L ₂ , F ₂ , L ₃ , or F ₃ on both sides. Assuming that the current load L is close to the load L ₂ , find the points _L 2 and F ₂ where the straight line connecting L ₃ · F ₃ and L · F + △F passes through the load L ₂ , and instead of L ₂ · F ₂ The point L ₂・F ₂ ′ is included in the conversion function characteristics, and L ₁・
Load F ₁ , L ₂・F ₂ , L ₃ , F ₃ ′, L ₄・F ₄ , L ₅・F ₅ -
Modify the spray flow rate conversion function characteristics. Also, assuming that the current load L is close to L ₃ , L ₂・F ₂ , L・F
Find the point L ₃ · F ₃ ′ where the straight line connecting +△F passes through L ₃ ,
Then, instead of L ₃ · F ₃ , the point L ₃ · F ₃ ' is included in the conversion function characteristics, L ₁ · F ₁ , L ₂ · F ₂ , L ₃ · F ₃ ', L ₄ · F ₄ ,
Correct the conversion function characteristics so that L ₅ and F ₅ become the load-spray flow rate conversion function. Such a correction operation is always performed between the break points where the current load L is located, and a corrected spray flow rate signal corresponding to the load amount is output. Through such correction operations, it is possible to always set optimum conversion function characteristics in the load-spray flow rate conversion calculation circuit 22.

Next, the effects of the load-spray flow rate conversion calculation circuit 22 and the load-spray flow rate conversion calculation correction circuit 23 will be explained.

A load-spray flow rate conversion function as shown in FIG. 3 is set as an initial condition in the load-spray flow rate conversion calculation circuit 22. A correction calculation formula is set in the load-spray flow rate conversion calculation correction circuit 23.

By the way, the following three points are taken as conditions for the plant to be stable.

(1)｜Load change rate｜≦predetermined value (2)｜Steam temperature deviation｜≦predetermined value (3) Conditions (1) and (2) continue for a predetermined period of time or longer.

In other words, if the above three conditions are satisfied,
The value obtained by adding the output of the temperature controller 15 to the output of the load-spray flow rate conversion calculation circuit 22 having the characteristics of the load-spray flow rate conversion calculation function shown in FIG. 3 is shown to be the optimum spray flow rate for this load in the steady state of the plant. . However, there are differences between the load-spray flow rate conversion calculation function characteristics obtained through boiler test runs and the actual load-spray flow rate conversion calculation function characteristics.
In addition, changes appear in the characteristics of the load-spray flow rate conversion calculation function due to changes in the boiler over time, efficiency changes, disturbances, etc. Therefore, the load-spray flow rate conversion calculation circuit 22 is set as an initial value as shown in Figure 3. The calculated load-spray flow rate conversion calculation function characteristics are not necessarily optimal. load-
If there is a difference between the spray flow rate conversion calculation function characteristic and the plant load-spray flow rate characteristic, it will appear on the steam temperature detector 14. A load-spray flow rate correction signal ΔF is outputted from the load-spray flow rate conversion calculation circuit 23 and inputted to the load-spray flow rate conversion calculation circuit 22 . Assume that the current load L is between load L ₂ and load L ₃ and is greater than load L ₂ . In this load-spray flow rate conversion calculation circuit 22, if the spray amount determined by the initial load-spray flow rate conversion calculation function characteristics is F and the corrected spray flow rate F', a signal of F'=F+△F is sent to the addition/subtraction circuit 18. Output. At this time, the load-spray flow rate conversion calculation function characteristics are modified as follows. In other words, the current load L is the break point on both sides L ₂ , F ₂ , L ₃・F ₃
Determine which one is closer to. If the load L is close to the load _L2 as shown in Fig. 5, _L3・_F3 and L,
Find the point L ₂ ·F ₂ ' where the straight line connecting F+△F passes through the load L ₂ . The initially set break points L ₂ and F ₂
As L ₂・F ₂ ′, L ₁・F ₀ , L ₂・F ₂ ′, L ₃・F ₃ , L ₄・
F ₄ , L ₅ and F ₅ are modified so that they become load-spray flow rate conversion function characteristics. The current load L is the break point of the break points L ₂・F ₂ and L ₃・F ₃ on both sides.
In the case of L ₃・F ₃ , L ₂・F ₂ and L, F+△F
Find L ₃・F ₃ ′ that intersects L ₃ by connecting them. Assuming the initially set break point L ₃ F ₃ as L ₃ F ₃ ′, L ₁ F ₀ ,
Load connecting L ₂・F ₂ , L ₃・F ₃ ′, L ₄・F ₄ , L ₅・F ₅ -
The initial load-to-spray flow rate conversion function characteristic is modified to be the spray flow rate conversion function characteristic. By repeating such corrections, the characteristics of the load-spray flow rate conversion calculation circuit are corrected to those of the load-spray flow rate conversion function characteristics with a small correction amount.
Then, the load-spray flow rate conversion calculation circuit obtains the optimum function characteristics by matching the actual load-spray flow rate conversion function characteristics of the plant.

The vertical axis shows load, spray flow rate, and steam temperature.
The conventional method and the present invention will be compared and explained with reference to FIG. 6, in which time is plotted on the horizontal axis. FIG. 6A shows how the load increases from a stable state and moves to another stable region, and FIG. 6B shows how the spray flow rate changes as the load changes. Characteristics of the conventional device are shown using dotted lines. FIG. 6C shows how the steam temperature changes as the load changes, with the solid line representing the invention of the present invention and the dotted line representing the conventional system. The spray flow rate is controlled by the amount of change in load that precedes the steam temperature response, and the actual load-spray flow rate conversion calculation function characteristics of the plant are set in the load-spray flow rate conversion calculation circuit, so the steam temperature We were able to eliminate what would appear as a change in

[Brief explanation of the drawing]

Fig. 1 shows a boiler spray flow rate control device in a block configuration, Fig. 2 shows the main parts of the present invention in a block configuration, and Fig. 3 shows the characteristics of a conventional load-spray flow rate conversion calculation circuit. Figures 4 and 5 are diagrams for explaining how the characteristics of the load-spray flow rate conversion calculation circuit in the present application are modified, and Figure 6 is a diagram showing the effects of the present invention and the conventional one. It is a figure for explaining. 22...Load-spray flow rate conversion calculation circuit, 23
...Load-spray flow rate conversion calculation correction circuit.

Claims (1)

[Claims] 1 In a device that adjusts the spray amount of cooling water injected into the steam before the superheating section in accordance with the load amount of the superheating section, there is a temperature detector that detects the steam temperature input to the load, and a load that detects the load amount. a detector;
a load-spray flow rate conversion calculation correction circuit that outputs a spray amount correction signal corresponding to the load from the temperature detection signal and the load detection signal; and a load-spray flow rate characteristic that is set in advance is corrected by the spray amount correction signal; A correction load for the load - a load that outputs a spray flow rate signal determined by the spray flow rate characteristics - a spray flow rate conversion calculation circuit, and a steam temperature adjustment calculation circuit that calculates the adjustment amount to make the temperature of the steam temperature detector match the target temperature. A spray flow rate control device for a boiler, comprising: a spray flow rate adjustment calculation circuit that adds and subtracts the output of the load-spray flow rate conversion calculation circuit and the output of the steam temperature adjustment calculation circuit to obtain a target value of the spray flow rate. .