JPS6051606B2 - Air-fuel ratio control device for heating furnace for exhaust gas denitrification - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for automatically controlling the air-fuel ratio of a heating furnace for exhaust gas denitrification.

As shown in Fig. 1, exhaust gas denitrification using the ammonia catalytic reduction method involves passing exhaust gas of about 100 to 1800C through a heat exchanger 1 to raise the temperature to around 300℃, and then passing it through a mixing chamber 2 to a heating furnace 3. The mixture is mixed with the combustion gas generated in the reactor 4, heated to the denitration reaction temperature (340-400°C)
The reactor is reacted with ammonia inside the reactor to remove nitrogen, and then the temperature is lowered through the heat exchanger 1 and discharged to the outside.

In this method, in the heating furnace 3, air is conventionally mixed with fuel gas to produce combustion gas at a temperature of 1,600 to 100°C, and exhaust gas is mixed with this, but recently, air is mixed with fuel gas. A method has been proposed in which a portion of the exhaust gas is mixed and combusted.

This method focuses on the fact that the exhaust gas, especially the sintering exhaust gas, contains a large amount of oxygen. By using this exhaust gas, it is possible to float the fuel gas required to heat the air, and the Co content in the exhaust gas can be reduced. Since oxidation heat is generated, fuel can be saved accordingly. However, when exhaust gas is used, there are the following problems.

In other words, in the conventional method of mixing air, the air-fuel ratio of the burner is kept constant over the turndown range, but in this case, the oxygen content in the air is sufficiently high.
Furthermore, since there are no fluctuations in oxygen concentration or temperature, there is no problem in controlling in this way. On the other hand, in the method of mixing exhaust gas, the oxygen content in the exhaust gas is lower than that of air, and the fluctuations in oxygen concentration and temperature are also large (for example, 10 to 16% in the case of sintering exhaust gas). , room temperature ~ 3300C
It fluctuates. ) If the air-fuel ratio is kept constant as in the past, there is a drawback that stable combustion cannot be achieved. The present invention has been made in view of the above circumstances, and its purpose is to calculate an excess air ratio according to fuel load fluctuations,
Also, an air-fuel ratio control device that measures the oxygen concentration and temperature of exhaust gas and automatically controls the flow rate of exhaust gas and the flow rate of air blown in as needed based on these measured values to ensure stable combustion at all times. It provides:

That is, the present invention provides an exhaust gas denitrification heating furnace that burns a mixture of fuel and exhaust gas or the gas and air, and an adjustment calculator that calculates an air ratio according to fluctuations in the fuel gas, and an exhaust gas temperature measuring device. , an exhaust gas oxygen concentration measuring device, a flow rate controller that controls the flow rate of exhaust gas based on these calculated and measured values, and a distribution ratio between exhaust gas and air based on the measured value of the oxygen concentration measuring device. The device is equipped with a setting device for setting.

The present invention will be described below with reference to illustrative embodiments.

FIG. 2 shows a heating furnace for exhaust gas denitrification and its air-fuel ratio control device, where 11 is a heating furnace and 12 is a burner.

An exhaust gas pipe 13 is connected to the temperature rising furnace 11, into which exhaust gas containing a relatively large amount of oxygen, such as sintering exhaust gas, flows. An exhaust gas branch pipe 14 is branched off from the exhaust gas pipe 13 and connected to the burner 12 . Furthermore, the burner 12 is provided with an air blowing pipe 1 along with the exhaust gas branch pipe 14.
5 and a fuel gas suction pipe 16 are connected. The exhaust gas branch pipe 14 includes an exhaust gas prower 17 and an oxygen concentration measuring device 1.
8. A temperature measuring device 19, an exhaust gas flow rate measuring device 20, and an exhaust gas flow rate control valve 21 are installed.

Further, the air blowing pipe 15 is equipped with an air blower 22, an air flow measuring device 23, and an air flow regulating valve 24. Furthermore, fuel gas injection pipe 16. A fuel flow rate measuring device 25 and a fuel flow rate regulating valve 26 are attached to the unit. An oxygen concentration measuring device 18 attached to the exhaust gas branch pipe 14 is connected to a ratio setting device 27 and a selector 28, and inputs an oxygen concentration detection signal to these ratio setting device 27 and selection device 28.

The temperature measuring device 19 and the exhaust gas flow rate measuring device 20 attached to the exhaust gas branch pipe 14 are each connected to a flow rate correction calculator 29, and the flow rate correction calculator 29 corrects the exhaust gas flow rate based on fluctuations in the exhaust gas temperature. I'm getting used to it. The signal from the four flow rate correction calculators 29 is sent to the exhaust gas flow rate controller 30.
is being input. On the other hand, the fuel flow rate measuring device 25 attached to the fuel gas injection pipe 16 sends its detection signal to the fuel flow controller 3.
1 and the addition/subtraction calculator 32, and the fuel flow controller 31 gives a control command to the fuel flow control valve 26 to control the flow rate of fuel gas.

The addition/subtraction calculator 32 calculates the air ratio (μ) based on the flow rate of fuel gas, that is, the amount of combustion, and the calculation is performed using the relationship between the amount of combustion and the air ratio as shown in FIG. . This addition/subtraction calculator 32 inputs an output signal to the ratio setting device 27. The ratio setter 27 sets the flow rate of the exhaust gas from the air ratio and the oxygen concentration in the exhaust gas, and this set value is input to the selector 28. The selector 28 selects whether the oxygen concentration of the exhaust gas is equal to or higher than a predetermined value (for example, 12
% or more), a signal is input to each distributor 33, 34 so that only exhaust gas flows and no air flows, and if the oxygen concentration is less than a predetermined value, exhaust gas and air are input to ensure the required amount of oxygen. Each distributor 33
, 34. The exhaust gas distributor 33
inputs the signal to the exhaust gas flow rate controller 30, and the exhaust gas flow rate controller 30 adjusts the exhaust gas flow rate based on the exhaust gas flow rate setting signal from the distributor 33 and the corrected exhaust gas flow rate from the flow rate correction calculator 29. The control valve 21 is operated to control the flow rate of exhaust gas. The air distributor 3
4 inputs the signal to the air flow controller 35,
The air flow controller 35 operates the air flow control valve 24 based on the air flow setting signal from the distributor 34 and the air flow from the air flow measuring device 23 to control the air flow. According to the above-described air-fuel ratio control device, when a fuel gas load fluctuation occurs, the computing unit 32 measures the excess air ratio, and the exhaust gas flow rate can be controlled to an appropriate value based on this measured value.

Furthermore, even if the exhaust gas temperature fluctuates, the flow rate can be corrected to accurately control the flow rate. In addition, the oxygen concentration of the exhaust gas decreases, and υ [if stable combustion cannot be achieved with gas alone,
The selector 28 sends a predetermined amount of air to the burner 1 together with the exhaust gas.
2, allowing stable combustion to occur regardless of the oxygen concentration of the exhaust gas. In summary, the present invention automatically controls the flow rate of exhaust gas (or exhaust gas and air) in accordance with changes in fuel gas load and flue gas properties, so that even when exhaust gas is used for combustion, the burner Stable combustion can be achieved over the turndown range.

[Brief explanation of the drawing]

Fig. 1 is an overall schematic diagram showing conventional exhaust gas denitrification, Fig. 2 is a block diagram of an air-fuel ratio control device showing an embodiment of the present invention, and Fig. 3 shows the relationship between the combustion amount of the burner and the air ratio. FIG. 11...Temperature rising furnace, 12...Burner,
13...Exhaust gas pipe, 14...Exhaust gas branch pipe, 1
5... Air blowing pipe, 16... Fuel gas blowing pipe, 18... Oxygen concentration measuring device, 19...
...Temperature measuring device, 20...Exhaust gas flow rate measuring device,
21...Exhaust gas flow rate control valve, 23...Air flow rate measuring device, 24...Air flow rate control valve, 2
5...Fuel flow rate measuring device, 26...Fuel flow rate adjustment valve, 27...Ratio setting device, 28...
... Selector, 29 ... Flow rate correction calculator, 30
...Exhaust gas flow rate controller, 31...Fuel flow rate controller, 32...Arithmetic unit, 33, 34...
...Distributor, 35...Air flow rate controller.

Claims (1)

[Claims] 1. A heating furnace for exhaust gas denitration that burns a mixture of fuel and exhaust gas or the gas and air is equipped with an adjustment calculator that calculates the air ratio according to fluctuations in the fuel gas, an exhaust gas temperature measuring device, and an exhaust gas temperature measuring furnace. an oxygen concentration measuring device, a flow rate controller that controls the flow rate of exhaust gas based on these calculated and measured values, and a setting section that sets the distribution ratio between exhaust gas and air based on the measured value of the oxygen concentration measuring device. An air-fuel ratio control device for a heating furnace for exhaust gas denitrification, comprising: and controlling the flow rate of exhaust gas and air.