JPS6350588Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an exhaust gas concentration control device used in an air-fuel ratio control device for a combustion furnace.

FIG. 1 is a schematic diagram showing an example of the configuration of such an air-fuel ratio control device. In the figure, 1 is a package boiler, 2 is a brackish water drum, 3 is a water supply pipe, 4 is a steam pipe, 5 is a burner, 6 is a fuel supply pipe, 7 is a blower,
8 is an exhaust gas duct, 10 is an automatic combustion control device (ACC), 12 is a control motor, 13 is a load detector, 14 is a link mechanism, 15 is a fuel valve, 1
6 is an air damper, 19 is an oxygen gas concentration analyzer (O ₂ sensor), 20 is an O ₂ controller, 21 is a variable speed control device for the electric motor, VVVF (Variable Voltage
Variable Frequency), 22 is an interlock line,
It is.

In the figure, fuel supplied from a fuel supply pipe 6 and a blower 7 are supplied to the combustion chamber of a package boiler 1.
The air supplied by the burner 5 is blown into the burner 5 and combusted. The generated steam is supplied from the brackish water drum 2 to the load through the steam pipe 4. From the steam pipe 4 of the package boiler to the automatic combustion control device (hereinafter referred to as
The steam pressure is led to 10 called ACC),
Depending on the level of this pressure, the ACC 10 sends a signal to the control motor 12, and the lever, which is linked to the control motor 12 by a link 14,
They are starting to move in unison. A fuel valve 15 and an air damper 16 are jointed to this link 14. If the characteristics of these valves and dampers are roughly adjusted in advance, fuel injection into the boiler can be mechanically controlled by the movement of the control motor 12. O ₂ inserted inside the exhaust gas duct 8
The sensor 19 measures O ₂ (oxygen concentration). When the O ₂ concentration in the exhaust gas is detected by the _{O 2 sensor} 19, the excess air rate for combustion can be determined. It acts on the VVVF 21 and controls O ₂ so that the O ₂ value is maintained.

Now, the air-fuel ratio control device for a combustion furnace as described above controls the O ₂ gas concentration in the exhaust gas in relation to load fluctuations, so it has a large energy saving effect.
It has the advantage of saving fuel in the combustion furnace, but on the other hand, if the O ₂ gas concentration in the furnace drops below the limit value, even temporarily, due to a sudden change in load, it may become incomplete. There is a risk of combustion and, in some cases, explosion.

The situation during this period will be explained below with reference to FIG. 2, which shows an example of a combustion characteristic curve of a certain boiler.

In Fig. 2, the horizontal axis shows the fuel valve opening degree (0 to 100%) as a load, and the vertical axis shows the O ₂ gas concentration (0 to 100%).
~10VOL.%) and VVVF frequency (30~50Hz).

The curve showing the _O2 concentration set value is from 0 to 100% load.
The target value should be O ₂ if the O 2 changes over time.
The curve showing the gas concentration and the frequency of the VVVF shows the frequency of application to the VVVF necessary to achieve the target O ₂ concentration as described above.
The relationship is that if the frequency applied to the VVVF is increased, the amount of air sent from the blower into the furnace will also increase. The curve showing the limit O ₂ value represents the limit value indicating that if the O ₂ concentration value in the furnace decreases below this value, problems such as incomplete combustion will occur.

Now, in Figure 2, the load is now between 40% and 60%.
Suppose there is a sudden change to Then, from the viewpoint of combustion characteristics, the frequency of VVVF needs to increase by ΔHz at this time. If the _O2 concentration setting value is set, the setting value SV _o-1 when the load is 40% to the setting value SV _o when the load is 60%.
The difference is given by ΔO ₂ . Because the set value decreases in this way, in the conventional O ₂ gas concentration control device, the control operation acts in the direction of lowering the frequency of VVVF in an attempt to lower the O ₂ gas concentration in the furnace.

Although it is necessary to increase the frequency of VVVF from the viewpoint of combustion characteristics, in actual control operation
As the VVVF frequency decreases, there is a risk that the O ₂ gas concentration in the furnace will temporarily become insufficient, causing incomplete combustion. The control then detects that the O ₂ gas concentration in the furnace has dropped too much and performs control operations to recover it, but as described above, the O ₂ gas concentration in the furnace may temporarily decrease. The drawback was that the concentration could drop below the limit, creating a risk of explosion in some cases.

The present invention was devised to eliminate the safety drawbacks of the prior art as described above, and therefore, the purpose of the present invention is to provide a temporary Let's go inside the furnace
It is an object of the present invention to provide an exhaust gas concentration control device that prevents the O ₂ gas concentration value from decreasing below a limit value and eliminates the possibility of occurrence of danger.

The essential point of the configuration of the present invention is an exhaust gas concentration control device for a combustion furnace, comprising a variable speed control device for controlling the motor of a blower for sending air to a combustion furnace, an oxygen gas concentration analyzer for detecting the oxygen gas concentration in the exhaust gas from the combustion furnace, and an oxygen gas concentration regulator for correcting the amount of air supplied to the combustion furnace by controlling the variable speed control device so that the oxygen gas concentration in the exhaust gas approaches the set value, using a load detector for the combustion furnace and a function value of the load of the combustion furnace detected by the load detector as a set value, the oxygen gas concentration regulator comprising a load/ _O2 setting converter for converting the load amount output by the load detector into an oxygen gas concentration set value, a comparator for comparing the detected oxygen gas concentration value output by the oxygen gas concentration analyzer with the load amount, and a PID controller for receiving an error voltage output by the comparator and outputting a calculation result to the variable speed control device.
In the device equipped with a PID calculator, when the oxygen gas concentration set value is changed due to a sudden change in load, only when the change in the set value is positive, that is, the current set value is lower than the previous set value, a function amount of the change in the set value is input in the _additive direction to the integrating circuit of the PID calculator.
A feedforward control means is provided in parallel with the comparator to prevent incomplete combustion from occurring in the combustion furnace.

Next, I will explain one embodiment of the present invention.
Before that, for the sake of comparison, the configuration of a conventional O ₂ gas concentration control device is shown in a block diagram in FIG.

In the figure, 33 and 35 are amplifiers, respectively.
34 is a linearizer. The linearizer 34 converts the signal voltage output from the O ₂ sensor (not shown) and amplified by the amplifier 33 into linear characteristics since it has non-linear characteristics with respect to the O ₂ gas concentration. This is a circuit for output. 36 is a load/O ₂ setting converter, that is, a converter that changes and outputs the set value of O ₂ concentration according to the magnitude of the load. 37 is a PID calculator.

Briefly explain the operation. A signal voltage representing the O ₂ gas concentration from an O ₂ sensor (not shown) is amplified by an amplifier 33, linearized by a linearizer 34, and then output from a converter 36 depending on the magnitude of the load. It is compared with the O ₂ gas concentration set value, and the error voltage is input to the PID calculator 37. The calculation results are sent to VVVF and O ₂ gas concentration control is performed.

It has already been explained that in such a conventional O ₂ gas concentration control device, there is a risk that the O ₂ gas concentration in the furnace may drop below a limit value when the load suddenly changes, causing a danger.

FIG. 4 is a block diagram showing one embodiment of the present invention. The configuration shown in this figure differs from the conventional configuration shown in FIG. 3 in that a feedforward circuit 38 is additionally connected as shown.

The operation of the feedforward circuit 38 will be explained.
The circuit 38 is connected to the converter 36 due to a sudden change in load or the like.
Detects changes in the O ₂ concentration set value output from the
The amount of change is positive (i.e., the previous set value SV _o-1
Therefore, the current set value SV _o is lower, and SV _o-1 − SV _o =
Only when the value of ΔO ₂ is positive), for example, add the addition amount ΔSV _F to the integrating circuit I of the PID calculation circuit 37,
Performs feedforward control of VVVF to prevent incomplete combustion in the combustion furnace.

Here, the addition amount ΔSV _F is expressed as follows.

When SV _o-1 −SV _o ≧0, ΔSV _F = K{SV _o-1 −SV _o ...... (1) When SV _o-1 −SV _o <0, ΔSV _F = 0... (2) However, K is a constant.

For example, if the load suddenly changes from 40% to 60% (see Figure 2), the feed forward circuit 38
The addition amount ΔSV _F added to the product circuit I of the PID calculator 37 is expressed by the following equation based on the above equation (1).

ΔSV _F = K・ΔO ₂ By setting the value of the constant K to an appropriate value, it is possible to achieve control that maintains the O ₂ gas concentration in the furnace in a steady state without reducing it even if there is a sudden change in load. can do.

Conversely, if the load suddenly changes from 60% to 40% in the decreasing direction, as mentioned above, SV _o-1 - SV _o < 0 (in this case, the O ₂ concentration setting value is in the increasing direction). ), ΔSV _F =0, but the O ₂ gas concentration in the furnace does not decrease even if this is done.

In addition, in FIG. 2, the frequency of VVVF tends to increase in the right side area with respect to the position of 40% load, and tends to decrease in the left side area. However, even in this left-hand region, due to the balance between the rate at which the O ₂ concentration setting value decreases and the rate at which the VVVF frequency decreases in response to sudden changes in the direction of increase in load, the O ₂ gas concentration in the furnace falls below the limit value. As a safety measure, there is a risk that the
It is better to implement O ₂ gas concentration control.

An example of how to add the addition amount ΔSV _F to the integration circuit I is to charge an electric charge corresponding to the addition amount ΔSV _F to both ends of the capacitor in an integration circuit consisting of a Miller integrator consisting of an amplifier and a capacitor. , a method of increasing the initial value of the integral operation can be mentioned. There are various ways to add the addition amount to the PID calculator, and the method is not limited to the above method.

The present invention can be easily implemented by using a microprocessor and configuring it with software technology.

According to this invention, a sudden change in load is treated as a change in the exhaust gas concentration set value, and the change is fed forward to the control amount only in the direction of increasing load. This has the advantage that even if a sudden change occurs, safe combustion control can be achieved without the O ₂ concentration value in the furnace reaching below the limit value.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing an example of the configuration of an air-fuel ratio control device for a combustion furnace, Figure 2 is a graph showing an example of a boiler combustion characteristic curve, and Figure 3 is a diagram showing the configuration of a conventional O ₂ gas concentration control device. FIG. 4 is a block diagram showing one embodiment of the present invention. Explanation of symbols, 33...Amplifier, 34...Linearizer, 35...Amplifier, 36...Load/ _O2 setting converter,
37...PID calculator, 38...Feedforward circuit.

Claims (1)

[Claims for Utility Model Registration] A variable speed control device 21 that controls the motor of the blower 7 that sends air to the combustion furnace 1, and an oxygen gas concentration analyzer 1 that detects the oxygen gas concentration in the exhaust gas of the combustion furnace 1.
9, a load detector 13 of the combustion furnace 1, and a function value of the load of the combustion furnace 1 detected by the load detector 13 as a set value, and the oxygen gas concentration in the exhaust gas approaches the set value. An exhaust gas concentration control device for a combustion furnace, comprising an oxygen gas concentration controller 20 that controls a speed change control device 21 to correct the amount of air supplied into the combustion furnace 1, the oxygen gas concentration controller 20 compares the load/O ₂ setting converter 36 that converts the load amount output from the load detector 13 into an oxygen gas concentration setting value with the oxygen gas concentration detection value output from the oxygen gas concentration analyzer 19. A device equipped with a comparator 39 and a PID calculator 37 which receives the error voltage output from the comparator and outputs the calculation result to the variable speed control device 21. When a change occurs, only if the set value change is positive, that is, the current set value is lower than the previous set value, the function amount corresponding to the set value change is added to the PID calculator. The load/O ₂ setting converter 36 and the PID calculator 37 are input to the integrating circuit.
An exhaust gas concentration control device for a combustion furnace, characterized in that a feedforward control means 38 is inserted in parallel with the comparator 39 to prevent incomplete combustion from occurring within the combustion furnace 1.