KR101145325B1 - Control logic on tranfer to follow up mode in the HP turbine bypass control - Google Patents

Abstract

In a turbine bypass system that controls the boiler pressure at the time of starting the turbine by discharging the steam generated from the boiler before the turbine ventilation to the condenser through reheating, and prevents the excessive pressure rise of the boiler during the normal operation, , The method of switching the overheated steam coming from the header of the superheater of the boiler superheater to the follow-up mode of the turbine bypass termination in the constant pressure control mode of the high pressure bypass system, which bypasses the high pressure turbine to the low temperature reheater, We plan driving.

Description

[0001] The present invention relates to control logic for switching a high-pressure turbine bypass control to a follow mode,

Field of the Invention The present invention relates to a turbine bypass system, and more particularly to a control logic for switching a high pressure turbine bypass control to a follow mode.

Generally, the turbine bypass system controls the boiler pressure when the turbine is started by discharging the steam generated from the boiler before the turbine aeration to the condenser through reheating, and prevents the excessive pressure rise of the boiler during normal operation It bypasses the steam generated from the boiler during the emergency operation of the power plant without passing through the turbine, thereby functioning to independently operate the boiler regardless of the state of the turbine. The turbine bypass system shortens the startup time at start-up and adjusts the boiler pressure by discharging the steam generated from the boiler in the case of sudden load change to the condenser so that the difference between the steam temperature and the turbine metal temperature due to the rapid temperature change can be quickly Minimize turbine thermal stress by keeping it optimally. It also improves the load characteristics, separates the boiler and the turbine from each other, prevents erosion of turbine blades by solid particles, and improves stability against system transients. The main steam pressure at boiler start-up is regulated by the high-pressure turbine bypass system, in particular the high-pressure turbine bypass valve. In order to increase the main steam pressure, the controller operates in the direction of closing the high pressure turbine bypass valve. The pressure controller of the high-pressure bypass system controls the main steam pressure from the initial boiler startup to the system feed-in pressure, then closes the high-pressure turbine bypass valve as the turbine is started and steam is introduced into the turbine, (Main steam pressure + bias) is set to a set value in order to prevent the steam from being opened again.

1 is a diagram showing an example of a pressure operation curve of a general high-pressure bypass system. In order to perform the same operation as in the pressure operation curve shown in FIG. 1, the pressure controller of the high-pressure bypass system controls the main steam pressure to the system feed-in pressure by changing the main steam pressure control set value as the combustion rate increases at the start- Thereafter, the high-pressure turbine bypass valve is closed as the turbine is started and steam is introduced into the turbine. When the valve is closed, it operates in the following mode in which the value is set to a value higher than the main steam pressure by a bias value in order to prevent the valve from being opened.

Referring to the high-pressure bypass pressure operation curve of FIG. 1, after the set value of the high-pressure bypass pressure reaches the system feed-in pressure of the constant-pressure control mode, the high-pressure turbine is forward flow, If the opening degree of the valve is less than 2%, the mode is switched to the follow mode.

2 is a view showing the concept of the pressure control logic of the high-pressure bypass system at the time of switching the follow-up mode of the conventional controller.

As shown in Fig. 2, the set value demand (a) acts as a set value requirement value before the follow mode switching, and at the time of the initial start operation as a value generated by the set value generation logic satisfying the operation curve of Fig. In the constant pressure control mode, the system feed-in occurs, and when the turbine becomes a forward flow, the turbine flow rate increases and the main steam pressure decreases. Accordingly, the high-pressure bypass valve is gradually closed to maintain the pressure, and when the valve opening degree is 2% or less, the mode is switched to the follow mode. When the mode is switched to the follow mode, the value of the main steam pressure (b) acts on the output of the analog transfer (c) at the previous stage of the speed limiter (D), and the adder The value of the bias (e. G., 15 kg / cm 2) acting as the second input of the analog input signal (e) acts as the output of the analog transfer (), and the set value becomes (main steam pressure value + bias) Ⓘ) set value (ⓗ). In order to increase the main steam pressure, in consideration of the fact that the controller operates in the closing direction of the high-pressure turbine bypass valve, the set value becomes larger than the process value in the steady state so that the turbine bypass valve is closed.

3 is a diagram for explaining a block used in the control logic of FIG.

In Fig. 3 (a), the analog transfer (c) becomes OUT = IN1 when Logic is 0, and OUT = IN2 when Logic is 1. 3 (b), the rate limiter (D) sets an input change rate limit value using the internal parameter, and reflects the input change only in the set change rate limit value.

The high pressure bypass pressure operation curve of FIG. 1 is an ideal curve, but in actual situations, the slope of the main steam pressure set value and the valve opening degree can vary greatly depending on the boiler combustion rate controlled by the operator. A PI controller that is responsible for more than 90% of the plant control loop can take various forms based on the ideal analog PI controller algorithm of Equation (1). The ideal analog PI controller algorithm,

As shown in Fig.

In Equation (1), u (t) denotes a controller output, K denotes a proportional constant, Ti denotes an integration time, and e (t) denotes an error, which is the difference between the set value SP and the process value PV .

In order to utilize Equation (1) in the digital controller, discretization process is required. By approximating the integral term by square sum and taking the speed type algorithm, the following equation (2) can be obtained.

In Equation (2), DELTA u (k) represents the difference between the current step and the previous step as the amount of change in the controller output. That is,? U (k) = u (k) - u (k-1). T denotes a sampling period.

In the conventional logic of FIG. 2, when the combustion rate can not be followed up due to a malfunction of the boiler, the main steam pressure drops, and the bypass valve is closed to switch to the follow mode. In this case, the pressure setting of the controller is changed from the system feed-in pressure (main steam pressure value + bias). In the case of a high-pressure bypass controller, the controller operates in the direction of closing the high-pressure turbine bypass valve to increase the main steam pressure. Thus, the error in the controller will act as a process value-set value. When the main steam pressure is switched to the follow mode in a state in which the increase of the burning rate due to the driving operation can not follow, that is, when the main steam pressure is lower than the current set value by the bias, the set value is decreased, And the high-pressure bypass valve is opened again by the equation (2) to return to the constant-pressure control mode.

As described above, when the main steam pressure is lower than the system feed-in pressure according to the burning rate according to the boiler operating state at the time of switching to the follow-up mode, the pressure control valve is opened again as the set value of the controller input decreases, In order to operate the bypass system steadily, logic for preventing such a case is required.

The present invention has been made to solve the above-described problems of the prior art that occur in the process of switching from the constant pressure control mode to the follow mode at the time of high pressure turbine bypass pressure control. In the constant pressure control mode, When the high-pressure bypass valve is closed as the steam pressure drops, the phenomenon of switching back to the follow-up mode and then returning to the constant-pressure control mode due to the lowering of the burning rate due to mis- It is an object of the present invention to provide a control logic capable of stably operating a bypass system.

In order to achieve the above object, the switching control logic according to the present invention can be implemented by two methods as control logic for switching the high-pressure turbine bypass control to the follow mode. The control logic for switching the high-pressure turbine bypass control implemented in the first method to the follow-up mode switches to the follow-up mode, which is a bypass operation termination condition in operation of the high-pressure turbine bypass system, (Large value + bias) using the larger of the main steam pressure and the current set pressure as the set value of the follow-up mode, stable switching to the follow-up mode is enabled, and the pressure is restored The pressure acts as a large value, thereby enabling stable bypass operation.

The control logic for switching the high-pressure turbine bypass control to the follow mode implemented in the second method is such that when switching to the follow-up mode which is an operation termination condition of the high-pressure turbine bypass system, (Current steam pressure value + bias) is smaller than the current set value, it is possible to prevent the switching to the follow mode, that is, to prevent the difference between the present set pressure and the main steam pressure from being changed to the following mode To the follow-up mode switching condition, thereby stably operating the bypass system.

Furthermore, it is desirable to provide a user interface that displays whether or not a condition is satisfied due to a difference between the main steam pressure value and the current set pressure value, which is a switching condition to the follow-up mode, and thereby stably performs bypass operation.

According to the switching control logic of the present invention, in the process of switching to the follow mode, it is possible to prevent the phenomenon of returning to the positive pressure control mode again after switching to the follow mode due to the decrease of the burn rate due to wrong operation, It becomes possible to operate stably.

Hereinafter, the switching control logic according to the present invention will be described in detail with reference to the accompanying drawings.

In the present invention, in order to switch to the turbine bypass operation termination condition, the operating conditions that can occur in view of the PI controller that has been most widely employed in the industrial field are examined, and a method for stable operation is sought, Switching control logic.

The technique to be implemented in the present invention is as shown in Fig. 4 and Fig. FIG. 4 is a diagram illustrating the pressure control logic of the high-pressure bypass system implemented by the first method, and FIG. 5 is a diagram illustrating logic including the switching mode switching condition of the high-pressure bypass system implemented by the second method.

The logic of FIG. 4 is an input of a speed limiter that selects a larger value among a set value demand and a main steam pressure value, which are set values in the constant pressure control mode, and determines a controller set value. In switching to the follow mode, The switching to the constant pressure control mode due to the decrease in pressure does not occur, and stable bypass operation becomes possible.

5 adds a condition of " (main steam pressure value + bias) " to the existing following mode switching condition, and when the main steam pressure value + bias is smaller than the present set value, So that stable switching can be achieved.

FIG. 6 is a diagram for explaining a control block used in the logic of FIG. 5; FIG.

6, OUT1 = 1 when the input IN is equal to or higher than the upper limit set value, and OUT2 = 1 when the input IN is equal to or lower than the lower limit set value.

On the other hand, in the present invention, a user interface is provided for stable operation of the high-pressure turbine bypass system. For this user interface, the difference between the set value and the process value in the constant pressure control mode is set in the follow- If the bias value is smaller than the used bias value, a user interface for satisfying the automatic switching condition to the follow-up mode in the constant pressure control mode may be added to the structure for helping the combustion rate adjustment and the bypass operation.

As described above, in the switching control logic according to the present invention, in the process of switching to the follow mode, it is possible to prevent the phenomenon of returning to the positive pressure control mode after switching to the follow mode due to a decrease in the burning rate due to mis- It is possible to stably operate the path system.

According to the present invention, the turbine bypass system in a power plant can be continuously applied as an indispensable system for an initial operation and a stable power generation operation. The present invention is applicable to a coal-fired power plant, And nuclear power plants.

1 is a diagram showing an example of a general high-pressure bypass system pressure operation curve.

FIG. 2 is a diagram illustrating the concept of pressure control logic of a conventional high-pressure bypass system.

3 is a diagram for explaining a control block used in the control logic of FIG.

Figure 4 is a diagram of the pressure control logic of the high pressure bypass system implemented in a first method.

FIG. 5 is a diagram illustrating the follow-up switching mode logic of the high-voltage bypass system implemented in the second method.

FIG. 6 is a diagram for explaining a control block used in the logic of FIG. 5; FIG.

Claims (3)

As the control logic (Fig. 4) for switching the high-pressure turbine bypass control to the follow mode, When the set value of the main steam pressure is calculated by switching to the follow-up mode which is the bypass operation termination condition in the operation of the high-pressure turbine bypass system, the main steam pressure (b in Fig. 4) and the current set pressure ) (Fig. 4, ⓒ) is used as the set value (ⓓ in Fig. 4) so that stable switching to the follow mode is made. As the control logic (Fig. 5) for switching the high-pressure turbine bypass control to the follow mode, 5) and the main steam pressure (b in Fig. 5) used in the follow-up mode when the mode is switched to the follow-up mode which is the operation termination condition of the high-pressure turbine bypass system (D) of FIG. 5) is added so as to stably operate the bypass system. The control system according to claim 2, further comprising a user interface for displaying whether or not the condition (D in FIG. 5) is satisfied due to the difference between the main steam pressure value and the current set pressure value, And the switching control logic.

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