JPH0315082B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a control device for a boiler that performs gas recirculation, and particularly to a control device for controlling a boiler that performs gas recirculation, and in particular controls the temperature of reheated steam using a gas recirculation fan inlet damper (hereinafter abbreviated as GRF input damper). The present invention relates to a boiler control device that reduces nitrogen oxides (hereinafter referred to as NOx) through optimal opening/closing control of a primary gas inlet damper, a mixed gas inlet damper, and a furnace hopper inlet damper.

[Conventional technology]

Figure 1 shows a schematic diagram of the smoke duct of a thermal power plant.

In the figure, an automatic boiler control device 1 controls a fuel control valve 12 and a damper 9 of a forced draft fan 8 in accordance with load requirements, and guides fuel and air in accordance with this to a burner 13 for combustion. on the other hand,
The generated combustion gas passes through the furnace 14, a part of which is returned to the furnace again by the gas recirculation fan 3, and the rest is discharged into the atmosphere. In addition, in Figure 1, 2
4 is a boiler, 4 is a GRF inlet damper, 5 is a furnace hopper inlet damper, 6 is a primary gas inlet damper, 7 is a mixed gas inlet damper, 10 is a flow rate detector, 11 is a temperature detector, and 15 is a reheater.

A conventional recirculation gas control system will be explained with reference to FIG. In the same figure a, the reheat steam temperature 16 detected by the temperature detector 11 is compared with the reheat steam temperature set value 18 determined by the signal generator 17,
The deviation 19 is calculated by a proportional integrator 20.
A preceding signal generated by the function generator 221 from the boiler load command 21 is added to this signal to operate the GRF inlet damper and control the reheat steam temperature.

In addition, the exhaust gas recirculated by the GRF inlet damper is distributed by the mixed gas inlet damper, primary gas inlet damper, and furnace hopper inlet damper and returned to the furnace. That is, in FIG. 2b, the mixed gas flow rate value 23 detected by the flow rate detector 10 is compared with the mixed gas flow rate set value determined by the function generator 222 based on the load command value 21, and the deviation 24 is proportional to , are calculated by the integrator 20.
This signal is applied to the function generator 223 from the load command 21.
Add the preceding signal created by , and operate the mixed gas inlet damper. Similarly, the primary gas inlet damper and the furnace hopper inlet damper are operated by a signal obtained by adding biases 25 and 26 to the mixed gas inlet damper opening command.

[Problem that the invention seeks to solve]

The drawback of this method is that in advance program control based on load commands, the mixed gas inlet damper, primary gas inlet damper, and furnace hopper inlet damper are uniformly opened and closed in response to the opening and closing of the GRF inlet damper.

That is, while the reheated steam temperature tends to rise when the load increases, the GRF inlet damper is controlled to close in advance, so the recirculation gas flow rate decreases. On the other hand, since the mixed gas damper, primary gas inlet damper, and furnace hopper inlet damper only open uniformly, the mixed gas flow rate and primary gas flow rate are insufficient for the load command, and the oxygen concentration in the combustion air increases. However, this has the disadvantage that the NOx value increases as a result.

An object of the present invention is to improve the above-mentioned drawback that NOx increases when the load increases in a boiler that performs gas recirculation.

[Means for solving problems]

For this reason, the present invention absorbs fluctuations in the amount of recirculated gas especially when the load increases with the furnace hopper inlet damper, and adopts a control system that suppresses the fluctuations. This paper proposes a control device that reduces NOx by controlling the oxygen concentration in the combustion air to match the load.

[Effect]

According to the present invention, for example, when the load increases, the furnace hopper inlet damper is controlled in the direction of closing in advance,
Since the mixed gas flow rate and the primary gas flow rate can be adjusted to match the load, the oxygen concentration in the combustion air can be suppressed and the NOx value can be reduced.

〔Example〕

An embodiment of the invention is shown in FIG. Components that are the same or equivalent to those shown in FIG. 2 are given the same reference numerals.

In this embodiment, as is clear by comparing FIG. 2b and FIG. 3, the furnace hopper inlet damper opening command 27 (comparable to the recirculation gas amount command to the furnace) is
It is characterized in that the rate of change of the load command 21 is detected by the differentiator 28, a gain commensurate with this rate of change is created by the function generator 224, and the gain is corrected by the multiplier 29. With this system, whereas conventionally the mixed gas damper, primary gas damper, and furnace hopper inlet damper were uniformly opened and closed by the same preceding signal when the load increased, by narrowing down the furnace hopper inlet damper, the amount of recirculated gas is increased. The feature is that even if there is a decrease in the mixed gas flow rate and primary gas flow rate, the decrease in the mixed gas flow rate and the primary gas flow rate is prevented.

According to this embodiment, in a boiler that performs gas recirculation, the reheated steam temperature is controlled by a GRF inlet damper, and further by a mixed gas inlet damper, a primary gas inlet damper, and a furnace hopper inlet damper.
When controlling NOx, especially when the load increases, by preemptively throttling the furnace hopper inlet damper,
The GRF inlet damper is throttled to control the temperature of reheated steam, making it possible to prevent a decrease in the amount of mixed gas and primary gas even if the amount of recirculated gas decreases.

〔Effect of the invention〕

As described above, according to the present invention, the oxygen concentration in the combustion air is always made to match the load command,
A rise in NOx value can be prevented and suitable recirculation gas control can be obtained.

[Brief explanation of the drawing]

Figure 1 shows a schematic diagram of the smoke duct of a thermal power plant.
FIG. 2 shows a conventional recirculation gas control system, and FIG. 3 shows a recirculation gas control system according to the present invention. 16...Reheat steam temperature, 17...Signal generator,
18...Reheat steam temperature setting, 19...Temperature deviation,
20...Proportional integrator, 21...Load command, 23...
...Mixed gas flow rate, 24...Mixed gas flow rate deviation, 2
5, 26...Bias, 221, 222, 22
3,224...Function generator.

Claims (1)

[Claims] 1. A boiler control device having a structure in which a part of the combustion gas is divided and recirculated to the furnace and the combustion material supply section, which includes a control element that receives a load command signal and generates a control signal corresponding to fluctuations in the load command. and a control system that controls the amount of recirculated gas to the furnace in accordance with this control signal so as to suppress a decrease in the amount of recirculated gas to the combustion material supply section based on fluctuations in the load command. A boiler automatic control device featuring: