JPH02157501A - Starting controller for once-through boiler - Google Patents

Abstract

PURPOSE:To shorten the starting time of an once-through boiler by providing a circuit effecting the regulation of recirculation of gas upon starting the boiler. CONSTITUTION:The amount of recirculated gas is regulated by changing the opening degree of a GRF entrance damper 5. A control signal for the GRF entrance damper 5 is given from a ratio of combustion commanding unit (FRD) 6 to a function generator 1 and an opening degree program, corresponding to DSS/WSS mode, is produced. A current/air converter 3 converts a current signal into an air signal to send the air signal to the control drive of the GRF entrance damper 5 and changes the opening degree of the damper. Signal generators 4 set the opening degrees of the GRF entrance dampers at brake points respectively. The opening degree program by the combustion command 6 is not produced before supplying steam and, therefor, the opening degrees of the GRF entrance damper for each steps of ignition, turbine starting and steam supplying are produced in the signal generator 4 with respect to each modes. According to this method, the starting time can be shortened and the reductions of an in-plant power as well as the fuel cost in a power plant can be contrived.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a control device for a once-through boiler, and particularly to a startup control device suitable for adjusting the temperature balance of various parts of a boiler at the initial stage of startup.

[Conventional technology]

Conventional equipment raises the temperature of each part of the boiler by keeping the fuel and air volumes at constant values until the boiler is ignited.

However, today, thermal power plants are required to operate under intermediate loads, starting and stopping on a daily basis or on weekends, and from the viewpoint of economic efficiency, it is required to shorten the starting time. Conventionally, this request was dealt with only by bias-adjusting the fuel amount according to the boiler temperature rise characteristics, but due to fuel amount fluctuation (especially when increasing), the temperature rises to the metal temperature limit value of each part of the boiler. However, there was a problem in which an alarm was generated.

In particular, raising the boiler heater outlet temperature to the turbine ventilation temperature early will shorten the startup time, but in the case of a once-through boiler, the heat capacity of the furnace ice wall is large, so adjusting the fuel amount is necessary at this time. Since constants must be taken into consideration, drastic changes in fuel amount cannot be made. In addition, in the case of a once-through boiler, boiler system loss is small in the low load range (25% MCR or less) and heating spray cannot be used.
Main steam temperature control is performed only by changing the amount of fuel. Therefore, in order to raise the temperature stably, it is necessary to optimally control the fuel amount, but as mentioned above, the metal temperature limit value of each part of the boiler can be a factor that causes the temperature to rise excessively. With conventional technology, it is extremely difficult to shorten the startup time. That is, there is a limit to the method of shortening the startup time by increasing the amount of fuel.

In addition, bias adjustment of the amount of fuel had to be done manually by the operator, which placed a considerable burden on the operator, and the start-up time also varied depending on individual differences.

[Problem to be solved by the invention]

In the above conventional technology, boiler temperature increase control is performed only by fuel adjustment, and no consideration is given to temperature balance adjustment of each part of the boiler. It was difficult to shorten the start-up time only by adjusting the fuel.

SUMMARY OF THE INVENTION An object of the present invention is to provide a once-through boiler startup control device that can shorten the startup time without issuing an alarm regarding the metal temperature of each part when the temperature rises when the boiler is started.

[Means to solve the problem]

The above purpose is to change the temperature balance of each part of the boiler (especially the furnace ice wall and heater) by adjusting the amount of gas recirculation, in addition to the conventional method of temperature increase control at boiler startup using bias control of fuel amount. achieved by

[Effect]

In the case of a once-through boiler, the amount of gas recirculated must be greater than the specified amount at the beginning of startup to protect the furnace ice wall.

Generally, when the amount of gas recirculation is increased, the amount of gas passing through the furnace (the sum of combustion gas and recirculated gas) increases, and the amount of heat absorbed by the heater increases due to the convection effect.

Similarly, the flame of the burner increases, the amount of heat absorbed in the furnace decreases, and the amount of heat in the heater increases.

The synergistic effect of these two causes the steam passing through the heater to rise. Reducing the amount of gas recirculation will have the opposite effect.

Therefore, by adjusting the amount of gas recirculation from boiler ignition to combustion, and changing the balance of each part of the boiler, it is possible to avoid large changes in the amount of fuel (also, it is possible to control temperature rise, and to increase the metal temperature of each part of the boiler). can also be kept within limits.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 2 is a gas recirculation tg adjustment characteristic diagram.

During intermediate load operation of boilers, daily start/stop (hereinafter referred to as DSS)
) and Weekend Start-up and Shutdown (hereinafter referred to as WSS).

The vertical axis shows the gas recirculation amount, and the horizontal axis shows the break point from boiler ignition to the start of ramping. Also, in the figure,
T indicates the secondary heater outlet temperature, and T2 indicates the secondary heater outlet temperature. Further, the characteristics of the portion surrounded by the dashed line are set by a function generator l, which will be described later.

FIG. 1 shows a gas recirculation control system illustrating an example of the present invention.

The amount of gas recirculation can be changed for each operating mode (DSS/WSS) and for each startup step.

Further, FIG. 1 is a circuit diagram of the gas recirculation changes shown in FIG. 2. The amount of gas recirculation is adjusted by changing the opening degree of the GRF entrance rodan bar 5.

The GRF input Rozoro damper 5 control signal is the combustion amount command (FRD
) 6 to the function generator 1, and an opening program corresponding to each DSS/WSS mode is created (turbine load/damper opening). Each signal is switched by a switch 2 in an interlocking manner.

The electro-pneumatic converter 3 converts the current into air and sends an air signal to the GRF input rotary damper 5 control drive to change the damper opening degree. Each signal generator 4 sets the GRF input rotor damper opening for each break point. Since the opening degree program based on the combustion command 6 is not created before the combination, the GRF input rodan bar opening degree for each step of ignition, turbine startup, and combination is created for each mode by the signal generator 4.

As mentioned earlier, it is possible to change the temperature balance of each part of the boiler (ice wall and heater) by adjusting the amount of gas recirculation, so the fuel at the time of boiler ignition is
In order to keep the boiler temperature rise rate within the reheater protection range (as steam does not flow into the reheater until the turbine vents, the upper limit of fuel is more restricted than metal protection) and the boiler temperature rise rate is within the limit value,
Until the turbine starts, the fuel amount is basically constant, and in order to accelerate the temperature rise on the superheater side, the GRF input rodan bar opening is set to be equal to or higher than the recirculation gas amount determined by furnace protection (DS
(X+ opening for S, X2 opening for WSS), so that the steam temperature rises quickly until the time of turbine startup. Since the amount of fuel is constant, no metal temperature alarm occurs. At the time of turbine startup, the superheater outlet steam temperature rise has been increased, suppressing the temperature rise rate. Therefore, increase the opening of the GRF input rotary damper (X2 opening for DSS, Y2 opening for WSS).

If the temperature rise rate is not suppressed, the fuel amount will be controlled and increased to match the load signal from the time of addition, and the temperature rise rate of the superheater will become too high, causing a metal temperature alarm in the superheater. This is because there are concerns.

After joining, the GRF input rodan bar 5 is opened in accordance with the program signal generated by the function generator 1 in accordance with the combustion amount command 6.

Therefore, by setting the opening degrees X2 and Y2 set in the signal generator 4 in DSS and WSS to be the same as the opening degree programmed in the function generator 1 at the time of joining, signals can be switched smoothly.

The same effect can be obtained by adjusting the amount of secondary air using the same operation and control circuit as the gas recirculation adjustment shown in one example of the present invention.

(Effects of the Invention) According to the present invention, since the start-up time can be shortened, there is an economical advantage as the internal power and fuel costs of the power plant can be reduced.Also, there are economic advantages in terms of boiler operation management. This makes it possible to reasonably shorten startup time and reduce the burden on the operator.

[Brief explanation of the drawing]

FIG. 1 is a control system diagram of a once-through boiler startup control device according to an embodiment of the present invention, and FIG. 2 is a time chart showing the contents of GRF manipulator damper opening adjustment. 1...Function generator, 2...Switcher, 3...Electro-pneumatic converter, 4...Signal generator, 5...GRF input rotary damper...Combustion amount command. Figure 1 Figure 2

Claims (1)

[Claims] A once-through boiler startup control device characterized by having a circuit for adjusting gas recirculation when the boiler is started.