JPH0321808B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a combustion control device that can perform optimum control at a low excess air rate in a combustion process of a boiler or the like.

<Conventional technology> In combustion processes, issues of energy conservation and pollution prevention must be considered. FIG. 3 is an explanatory diagram showing the relationship between these and the amount of air. In the figure, the horizontal axis is the air ratio (actual combustion air amount/theoretical air amount),
The vertical axis represents thermal efficiency (left vertical axis) and heat loss (right vertical axis). The solid line represents the exhaust gas heat loss from the chimney, the dashed line represents the heat loss due to incomplete combustion, and the dotted line represents the total heat loss. The two-dot chain line represents the corresponding thermal efficiency.

In the excess air region A, the exhaust gas heat loss increases with increasing air ratio. Furthermore, in this region NOx,
Pollution substances such as SOx and metal corrosive substances will gradually increase.

In the air-deficient region C, heat loss due to incomplete combustion increases, and black smoke is generated due to unburned substances, causing pollution.

When thermal efficiency and pollution are considered, the optimum combustion region is the low excess air ratio region B, and combustion control may be performed at the air ratio in this region.

Conventionally, devices shown in FIGS. 4 and 6 are known as devices that perform combustion control at a low excess air ratio.

In Fig. 4, 1 is an O ₂ concentration meter attached to the flue of a combustion furnace (not shown in this figure).
For example, a zirconia type O ₂ concentration meter is used. 2
3 is a flow meter that detects changes in the load of the combustion furnace, such as steam flow rate and fuel flow rate; 3 is a function generator that generates an O ₂ setting signal based on the load signal from flow meter 2; 4 is an O ₂ setting signal. A bias generator for manually setting the signal, 5 an adder for adding the signal from the function generator 3 and the signal from the bias generator 4, 6 the output from the adder 5 as the _O2 setting signal SV; ₂ This is a regulator to which the O ₂ concentration signal from concentration meter 1 is added as a process variable PV, and a PID regulator, intermittent integral regulator, dead time compensation regulator, etc. are used depending on the load characteristics. 7 is limit.

With this configuration, in order to perform optimal combustion control even at low loads, the load signal is converted into a function generating function that generates an O ₂ setting signal that has a large O ₂ value at low loads, as shown in Fig. 5. A manual setting signal from the bias generator 4 is added to the O ₂ setting signal to obtain a setting signal that can realize optimal combustion control in the low excess air ratio region B. This setting signal is applied to a regulator 6, and the output from this regulator is applied via a limiter 7 to an air flow control system (not shown in FIG. 4).

By the way, in such a device, O ₂ in the exhaust gas
Since the concentration is monitored as the amount of change and combustion control is performed based on this, it is not possible to detect if an abnormality occurs in the burner and combustion becomes incomplete, and even if black smoke is generated, this can be dealt with. I couldn't do it.

On the other hand, the device shown in FIG. 6 has been proposed to eliminate such drawbacks, and in the figure, the same elements as those in FIG. 4 are given the same reference numerals. 8 is a CO concentration meter that detects the CO concentration in exhaust gas, 9 is a setting signal generator that generates an optimal CO setting signal, and 10 is a CO concentration signal from CO concentration meter 8 that is added as a process variable PV to generate a setting signal. A regulator to which the CO setting signal from the device 9 is added as a set value SV, 11 is a limiter, 12 is a regulator 6, 1
This is a high selector that selects the output that increases the air flow rate from among the outputs from 0 and supplies it to the air amount adjustment system in the subsequent stage.

With this configuration, the CO concentration in the exhaust gas has a close relationship with the generation of black smoke caused by an increase in unburned substances, and the optimal CO value remains approximately constant regardless of the type of furnace. . In this conventional example, in addition to a combustion control system based on O ₂ concentration (part D surrounded by a dashed-dotted line), a CO concentration control system based on CO concentration (part E surrounded by a dashed-dotted line) is provided to achieve a low excess air rate. Combustion control is performed in the area, and when the CO concentration increases abnormally due to a burner-related failure, the control system works to increase the amount of air and lower it to prevent the generation of black smoke.

However, in such a configuration, two control systems are provided, and the output of one of these control systems is selected under predetermined conditions, so the two control systems cannot be adjusted sufficiently. However, there is a drawback that the high selector 12 selects the wrong output of the control system.

<Problems to be Solved by the Invention> The technical problems to be solved by the present invention are to provide a single control system, eliminate the difficulty of adjusting multiple control systems, and achieve combustion control at a low excess air rate. The purpose is to prevent the generation of black smoke due to abnormalities or disturbances in the combustion system.

<Means for solving the problem> The structure of the present invention is to reduce O ₂ in the exhaust gas from the combustion furnace.
means for detecting the concentration; means for detecting load fluctuations in the combustion furnace; and a first function generator that generates an O ₂ setting signal that increases the O ₂ value when the load is low based on the load signal. means for detecting the CO concentration in the exhaust gas; and a means for detecting the CO concentration in the exhaust gas;
a second function generator that generates an O ₂ setting signal that increases O ₂ according to the O 2 value; a bias generator that manually sets the O ₂ value; and O ₂ from the first and second function generators. an adder for adding the setting signal as well as the O ₂ manual setting signal from the bias generator;
The O ₂ concentration signal from the O ₂ concentration detection means is given as a change amount, the output signal from the adder is given as a setting signal, and the controller is provided with a regulating output to an air flow rate regulating system.

<Operation> The technical means described above operates as follows. That is,
The main adjustment operation was an O ₂ adjustment operation using an O ₂ concentration meter, and a correction operation for the O ₂ setting signal based on changes in CO value was added to this. When the combustion furnace is operated at the optimum CO value and at a low excess air rate that is optimal for load fluctuations, no correction is made to the O ₂ setting signal, and when the CO concentration increases beyond a predetermined value, the CO
A correction signal related to the value was added to the O ₂ setting signal.

<Examples> Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention.
In the figure, the same elements as those in FIGS. 4 and 6 are given the same reference numerals, and explanations thereof will be omitted. The signal from the O ₂ densitometer 1 is adjusted to an appropriate range by the range changing means 13, and then is applied to the regulator 6 via the first-order delay circuit 14. The signal from the flow meter 2 that detects changes in the steam flow rate, fuel flow rate, etc. that become a load on the combustion furnace is adjusted to an appropriate range by the range changing means 15, and then applied to the function generator 3. There is. As explained earlier, the characteristics of this function generator are as shown in FIG.

The signal from the CO concentration meter 8 is the range changing means 16
After being adjusted to an appropriate range by , it is applied to a function generator 18 via an upper limit alarm setting device 17 . As shown in FIG. 2, the characteristics of this function generator are to generate an O ₂ setting signal that increases O ₂ in accordance with the CO value after the CO concentration signal exceeds a predetermined value. The signal from the function generator 18 is added to the O ₂ setting signal provided from the function generator 3 and the bias generator 4 in the adder 5 as a correction signal based on the CO value.

O ₂ setting signal SV and O ₂ concentration signal from adder 5
The output of the regulator 6 given PV is the output of the calculator 1
At step 9, the output is corrected so that it becomes 50% output with zero deviation, and is output to the air flow rate adjustment system 20 via the limiter 7. The air flow rate adjustment system 20 uses the output of the regulator 6 to correct the air ratio or air-fuel ratio set value.

With such a configuration, in the optimum operating state with a low excess air rate, the O ₂ setting signal is changed only in relation to the load signal given from the flow meter 2 without any correction by the CO value being applied to the O ₂ setting signal. Combustion control is performed by the signal.

If the CO concentration signal increases beyond the predetermined value (S1 in Figure 2) due to an abnormality or disturbance in the combustion system,
The O ₂ correction signal increases according to the curve in Figure 2 _.
Add to setting signal.

The curve in Figure 2 was obtained from the relationship between the previously measured CO concentration and the O ₂ concentration at that time.
Optimal CO concentration (corresponding to S1), e.g. 80ppm
If the CO concentration increases beyond this level, the amount of O ₂ correction required to achieve the optimum CO concentration is determined and plotted.

<Effects of the Invention> According to the present invention, the main adjustment operation is the O ₂ adjustment operation using the O ₂ concentration meter, and the O ₂ adjustment operation based on the CO value.
Combustion control is performed by one control system in addition to the correction operation of the setting signal, and there is no difficulty in controlling the control systems when multiple control systems are used.

Furthermore, according to the invention, monitoring the CO concentration;
This adds correction to the O ₂ setting signal, so
It is possible to prevent the generation of black smoke due to abnormalities or disturbances in the combustion system, and because it can approach the low excess air ratio region to the limit, the energy saving effect is enhanced and the generation of pollutants such as NOx is effectively suppressed. can be suppressed.

Furthermore, according to the present invention, a zirconia O ₂ concentration meter with quick response can be used as the O ₂ concentration meter, so a control device with good response to load fluctuations can be realized.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of the device of the present invention, FIG. 2 is an explanatory diagram of the operation of the embodiment of the device of the present invention in FIG. 1,
Fig. 3 is an explanatory diagram showing the relationship between the energy saving effect and pollution prevention for the amount of air in the combustion process, Figs. 4 and 6 are the configuration diagrams of the conventional device, and Fig. 5
The figure is an explanatory diagram of the operation of the conventional device. 1... O ₂ concentration meter, 2... Flow meter that detects the amount of change that becomes the load of the combustion furnace, 3... Function generator, 4
...Bias generator, 5...Adder, 6...Adjuster, 8...CO concentration meter, 18...Function generator, 2
0...Air flow rate adjustment system.

Claims (1)

[Claims] 1 A means for detecting the O ₂ concentration in the exhaust gas from the combustion furnace, a means for detecting the load fluctuation of the combustion furnace, and a nonlinear characteristic that is large at low load and small at high load based on the load signal. a first function generator generating an O ₂ setting signal having an O 2 setting signal;
A means for detecting CO concentration, and a CO concentration signal is given as an input signal, unless the CO value in a region where heat loss increases due to incomplete combustion or black smoke is generated due to unburned material is reached. A second function generator that generates an O ₂ setting signal according to the CO value when it exceeds this value, and a manual setting of the O ₂ value that achieves optimal combustion control in the low excess air rate region. a bias generator for adding the O ₂ setting signals from the first and second function generators and _{an O 2 manual} setting signal from the bias generator; a regulator to which the O ₂ concentration signal is given as a change amount and the output signal from the adder is given as a setting signal, and which gives a regulating output to an air flow regulating system, so that the combustion furnace can control the optimum CO
When the operation is performed at the optimal low excess air rate condition according to the value and load fluctuation, no correction is applied to the O ₂ setting signal, and when the CO concentration increases beyond the predetermined value, a correction signal related to the CO value is applied. A low excess air rate operation control device for a combustion process, characterized in that combustion control is performed by adding the above O 2 setting signal to the O ₂ setting signal.