JPS6324359Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to combustion devices such as boiler devices and various combustion furnaces, and particularly relates to a combustion control device thereof.

In a combustion device, the combustion state is greatly influenced by the ratio of combustion air to fuel (hereinafter referred to as excess air ratio). That is, if the fuel flow rate is larger than the air flow rate, incomplete combustion will occur due to lack of oxygen, combustion efficiency will be poor, and black smoke will be generated, which is undesirable in terms of pollution. On the other hand, if the air flow rate is too large relative to the fuel flow rate, nitrogen oxides, sulfur oxides, etc. will be produced in large quantities, and heat loss from the chimney will also increase. For this reason, the ratio between the fuel flow rate and the air flow rate, that is, the excess air rate, must be adjusted appropriately in response to the load of the combustion device, both in normal operating conditions of the combustion device and in transient conditions where the load changes. However, it must be controlled so that combustion occurs under optimal conditions.

A conventional combustion control system is shown in Figure 1. 1 in the diagram
is a main steam pressure transmitter, 2 is a main steam pressure regulator, 3 is an oxygen concentration transmitter, 4 is an oxygen amount regulator, 5 is a fuel amount regulator, 6 is a fuel amount control valve, 7 is a fuel amount transmitter, 8
9 is an air amount regulator, 10 is an air amount transmitter, 11 and 18 are high signal selectors, 12
and 17 is a low signal selector, 13 and 16 are subtracters, 14 and 15 are adders, 19 is a multiplier,
20 and 24 are ratio calculators, 21 is a low signal limiter, 22 is a square root calculator, 23 is a divider, 25 is fuel, 26 is combustion air, and 27 is a burner.

In this control system, the load change rate of the combustion device is detected by the main steam pressure transmitter 1, and the signal thereof is input to the main steam pressure regulator 2. A reference value is preset in the main steam pressure regulator 2, and the actual measured value from the main steam pressure transmitter 1 is compared with the reference value, and as a result, if there is a deviation, it is determined that the main steam pressure regulator 2, and its output signal is branched to the fuel system and air system.

In the fuel system, the signal is passed through a high signal selector 11 and a low signal selector 12 to be distinguished from the air system signal, and is input to the fuel amount regulator 5 as a setting signal. The signal from the fuel quantity transmitter 7 is also input to the fuel quantity regulator 5, which is compared with the signal from the main steam pressure regulator 2, and if there is a deviation, a corresponding signal is sent to the fuel quantity regulating valve. 6, and the fuel flow rate is adjusted to match the load.

On the other hand, the signal output from the main steam pressure regulator 2 to the air system is distinguished from the fuel system signal by passing through a low signal selector 17 and a high signal selector 18. The signal is then multiplied by the excess air ratio in the multiplier 19, the final correction from the oxygen amount regulator 4 is made in the ratio calculator 20, and after passing through the low signal limiter 21, it is input as a setting signal for the air amount regulator 8. Ru. The signal from the air quantity transmitter 10 is input to the air quantity regulator 8 via the square root calculator 22, and is compared with the setting signal. If there is a deviation as a result, a signal corresponding to the deviation is used to adjust the air quantity. The air flow rate is output to the valve 9 and adjusted to an air flow rate suitable for the load (fuel flow rate).

In addition, in the oxygen amount regulator 4, depending on the deviation between the setting signal from the multiplier 19 and the measured value of the oxygen concentration transmitter 3, a corresponding correction signal is outputted to slightly correct the excess air ratio. ing.

FIG. 2 is a characteristic diagram showing the relationship between load (fuel amount) and excess air ratio (μ) in this conventional combustion control system, taking an air system as an example. Line A in the diagram
indicates the normal combustion air amount, line B shows the upper limit air amount when the load decreases, and line C shows the lower limit air amount when the load increases.

In this figure, for example, the excess air fluctuation rate when the load changes at high load point X is x: (x-β) when the load increases, and x: (x + β) when the load decreases.
α). On the other hand, the excess air fluctuation rate during load fluctuation at low load point Y is y:(y
-β), and when the load decreases, it becomes y:(y+α).

By the way, in the conventional combustion control system, as shown in this figure, the allowable ranges α and β of the excess air ratio μ are always constant regardless of the load. This is not a problem when the load is high, but when the load is low, the fluctuation range of the excess air ratio becomes large, making the control system unstable, and moreover, the air tends to be too much, reducing combustibility and reducing energy savings. It has the disadvantage that it is difficult to obtain an effect.

An object of the present invention is to eliminate the drawbacks of the prior art and provide a combustion control device that always performs stable combustion control.

In order to achieve this objective, the present invention provides a load detection means for detecting the load of a combustion device, an excess air rate setting means for setting an excess air rate, and an excess air rate set by the excess air rate setting means. A fuel flow rate adjustment means and an air flow rate adjustment means for adjusting the fuel flow rate and the combustion air flow rate supplied to the combustion device according to the rate, and the excess air rate as the load decreases based on a detection signal from the load detection means. and an allowable width changing means for reducing the allowable width of.

Next, an embodiment of the present invention will be described with reference to FIGS. 3 and 4. FIG. 3 is a diagram showing the combustion control system.

In order to enable combustion with a certain range of excess air ratio when the load fluctuates, in the fuel system when the load increases, the main steam pressure regulator 2 - low signal selector 12 - adder 14 - fuel quantity regulator 5 - fuel The quantity transmitter 7-fuel quantity control valve 6 system increases the fuel flow in proportion to the air flow. In the air system, main steam pressure regulator 2 - subtractor 16 - high signal selector 18 - multiplier 19 - ratio calculator 20 - low signal limiter 21 -
The air flow rate is increased in proportion to the fuel flow rate by the system of the air amount regulator 8, the air amount transmitter 10, the square root calculator 22, and the air amount adjustment valve 9.

On the other hand, when the load decreases, the main steam pressure regulator 2 - subtractor 13 - high signal selector 11 -
The system of fuel quantity regulator 5 - fuel quantity transmitter 7 - fuel quantity regulating valve 6 reduces the fuel flow rate in proportion to the air flow rate. In the air system, main steam pressure regulator 2 - adder 15 - low signal selector 17 - multiplier 19
- Ratio calculator 20 - Low signal limiter 21 - Air amount regulator 8 - Air amount transmitter 10 - Square root calculator 22 - Air amount control valve 9 system reduces the air flow rate in proportion to the fuel flow rate.

In addition, the multiplier 19, the ratio calculator 20, the divider 2
3. The ratio calculator 24 is a correction system for excess air ratio based on the oxygen concentration in the combustion gas.

28 is a function calculator that can change the allowable range of excess air ratio (μ) according to the load, and the main steam pressure regulator 2
As shown in FIG. 4, the permissible range (values of α and β) decreases as the load decreases. Specifically, in FIG. 3, -
The β value and/or the +α value in adders 14 and 15 will change depending on the load. In other words, when the load is high, the +α and -β values are the same as before, but as the load decreases, the +α value increases.
The value and the -β value are set gradually smaller.

The present invention has the above-mentioned configuration, and maintains an appropriate excess air ratio even under low loads, eliminating the instability of combustion caused by high excess air at low loads, heat loss due to exhaust gas, and blackout. A combustion control device with stable combustibility and controllability can be provided by eliminating smoke generation and the like.

[Brief explanation of the drawing]

Fig. 1 is a conventional combustion control system diagram, Fig. 2 is a conventional characteristic diagram showing the relationship between load and excessive air ratio correction width, and Fig. 3 is a combustion control system diagram according to an embodiment of the present invention. Figure 4 is a characteristic diagram of the function calculator in the combustion control system. 1... Main steam pressure transmitter, 2... Main steam pressure regulator, 5... Fuel quantity regulator, 6... Fuel quantity control valve,
7...Fuel quantity transmitter, 8...Air quantity regulator, 9...
...Air amount control valve, 10...Air amount transmitter, 13,
16...Subtractor, 14, 15...Adder, 19...
... Multiplier, 20, 24 ... Ratio calculator, 25 ...
Fuel, 26... Combustion air, 27... Burner, 2
8...Kan number calculator.

Claims (1)

[Scope of utility model registration request] load detection means for detecting the load of the combustion device; excess air rate setting means for setting an excess air rate; and fuel supplied to the combustion device according to the excess air rate set by the excess air rate setting means. a fuel flow rate adjustment means and an air flow rate adjustment means for adjusting the flow rate and the combustion air flow rate; and an allowable range changing means for reducing the allowable range of excess air ratio as the load decreases based on a detection signal from the load detecting means. A combustion control device comprising: