JPH0579622A - Method for controlling combustion by control of oxygen concentration in combustion furnace - Google Patents

Abstract

PURPOSE:To prevent pollution and realize an energy saving by a method wherein the most suitable oxygen concentration is set in reference to continuous measured values of NOx concentration in discharged gas in a chimney and an oxygen concentration, an air ratio is calculated in reference to a combustion area in a combustion furnace, a smoke passage and a difference in oxygen concentration in discharged gas in the chimney and a flow rate of air is controlled. CONSTITUTION:In the case that a temperature in a furnace 14 is set to become a temperature TSV, a temperature adjusting meter 1 takes a measured temperature signal TPV from a thermocouple 15 for use in measuring the temperature in the furnace 14 and gives a fuel flow rate set value FSV of the fuel flow rate adjusting meter 2 in such a way that a difference between it and the set temperature TSV becomes zero. The fuel flow rate adjusting meter 2 controls an adjusting valve 6 in such a way that the value becomes this set value. In turn, a NOx analyzer 11 and a CO analyzer 12 in a chimney measure each of concentrations of NOx and CO, respectively. The most suitable oxygen concentration O2SV2 is set through a CO analyzed value weight coefficient setting device 18, a NOx analyzed value weighing coefficient setting device 19, a subtractor 20, an integrator 22 and an adder 21. An amount of air is controlled by an oxygen concentration adjusting meter 10 in response to a difference between the most suitable oxygen concentration set valve O2SV2 and an oxygen concentration O2PV in the discharged gas in the furnace 14 detected by the oxygen analyzer 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion control method for a combustion furnace, and more particularly to a combustion control method by controlling oxygen concentration.

[0002]

2. Description of the Related Art Normally, in the temperature control of a metal heating furnace or the like, different heating temperatures are required for different products, so that the set temperature is remarkably changed and the amount of fuel varies greatly.

In the affected furnace, when the operator suddenly changes the set temperature, the fuel flow rate control system and the air flow rate control system are temporarily in excess of fuel or in excess of air due to a difference in response time between the fuel flow rate control system and the air flow rate control system.

In the prior art, as disclosed in Japanese Patent Publication No. 58-17373, an oxygen concentration controller for measuring the oxygen concentration in exhaust gas and adjusting the oxygen concentration to a relatively low set value is provided. By controlling the air-fuel ratio by the calculation output of the meter, control was performed so as not to cause excess fuel or excess air.

[0005]

However, in this conventional method, the operator must finely adjust the optimum oxygen concentration due to the change of the set temperature of the furnace temperature and the change of the combustion state in the furnace. The annoyance that didn't happen remained. Recently, from the standpoint of pollution prevention, it is necessary not only to simply prevent the generation of black smoke but also to suppress the generation of NOx and dioxins to a low level.
It is becoming difficult to set the optimal points and relying on the feeling of the operator. The present invention has been made in view of such drawbacks, and an object of the present invention is to automatically calculate the oxygen concentration that makes the NOx concentration and the CO concentration of exhaust gas after combustion low and optimal, and prevent pollution. And to provide a combustion control method suitable for energy saving.

[0006]

In order to achieve the above object, the present invention continuously measures NOx concentration and CO concentration in addition to oxygen concentration in exhaust gas from a combustion furnace to obtain NOx concentration,
It has an oxygen concentration controller for calculating and outputting an oxygen concentration set value that makes the CO concentration low and in an optimum state, and having an oxygen concentration controller that adjusts the oxygen concentration using the calculated output as a set value. It was done. At this time, gains can be set for the NOx concentration signal and the CO concentration signal, respectively, and the ideal ratio of NOx concentration and CO concentration possessed by each furnace can be set by adjusting the gain. did.

[0007]

The NOx concentration and the CO concentration in the exhaust gas have a contradictory relationship with the O ₂ concentration in the furnace. That is, O _{2 in} the furnace
Since the higher the concentration of fuel burned in the form close to a complete combustion emissions of CO is reduced, excess O ₂ is much generation of NOx reacts with N ₂ in the combustion air, also O ₂ concentration If is low, the rate at which the fuel does not completely burn increases and CO
Many of generation, generation of a small excess O ₂ is divided NOx is reduced. From this principle, NOx concentration of exhaust gas and CO
If the NOx concentration becomes high by comparing the concentrations, it can be judged that the O ₂ concentration in the furnace is too high, and the O ₂ concentration in the furnace is controlled to be low, that is, the combustion air amount is controlled to be small, and the CO concentration is not high. It can be judged that the O ₂ concentration in the furnace is too low, and in the same manner, stable combustion can be maintained by performing control to increase the O ₂ concentration in the furnace.

[0008]

The present invention will be described in detail below with reference to the drawings. FIG. 1 shows an embodiment of a combustion control device for carrying out the combustion control method of the present invention. In FIG. 1, 1 is a furnace 1.
A temperature controller for keeping the temperature of 4 at a set temperature, 2 a fuel flow controller for adjusting the fuel flow rate according to a command from the temperature controller 1, 3 an opening / closing calculator, 4 an oscillator, 5 an orifice , 6 is a flow control valve, 7 is a pipe, 8 is an air-fuel ratio setter, 9 is an air flow controller for adjusting the combustion air flow rate according to a command from the air-fuel ratio setter 10, and 10 is an exhaust gas of the furnace 14. An oxygen concentration controller for controlling the oxygen concentration to a set concentration, 11 is a NOx analyzer, 12 is a CO analyzer, 13 is a combustion zone, 14 is a combustion furnace, 15 is a thermocouple, 16 is an oxygen analyzer, and 17 is mV. / I converter.

Reference numeral 18 is a CO analysis value weighting coefficient setting value for calculating the optimum O ₂ concentration setting value, 19 is also a NOx analyzer weighting coefficient setting device, and 20 is a subtracter for calculating an adjustment amount for the O ₂ concentration setting value. 21 is an adder for calculating the optimum O ₂ concentration set value from the basic O ₂ concentration set value and the O ₂ concentration set value adjustment amount. Reference numeral 22 is an integral calculator for integrating the adjustment amount. 23 is O
₂ Limiter for holding the value of the density setting value adjustment amount within a certain range.

The operation of the combustion control device having the above structure will be described below. Now, when the temperature of the furnace 14 is set to a certain temperature Tsv, the temperature controller 1 receives the measured temperature signal Tpv from the thermocouple 15 for measuring the temperature of the furnace 14 and receives the input deviation (Tsv-Tpv). The fuel flow rate set value Fsv of the fuel flow rate controller 2 is given so that becomes zero. In the fuel flow rate controller 2, the fuel flow rate measurement value Fpv obtained through the transmitter 4 that converts the differential pressure signal of the orifice 5 into a flow rate signal and the square root calculator 3 that squares the output of the transmitter 4 is the set value Fs.
The opening / closing of the control valve 6 is controlled so as to coincide with v.

On the other hand, the air flow rate controller 9 has an air flow rate set value As determined by the air-fuel ratio μ and the fuel flow rate set value Fsv.
When v is received from the air-fuel ratio setter 8, the control valve 6 is controlled so that the measured air flow rate Apv matches the set value Asv as in the case of the fuel flow rate controller 2.

In this way, the fuel flow rate and the air flow rate are adjusted according to the desired furnace temperature. However, if the air-fuel ratio set value is fixed, when the set temperature Tsv of the furnace 14 is changed, the fuel The oxygen concentration of the exhaust gas changes depending on the difference in response time between the flow rate control system and the air flow rate control system.

The relationship between the oxygen concentration O ₂ % and the NOx generation amount, CO generation amount and energy loss is as shown in FIG.

If the oxygen concentration in the exhaust gas in the furnace is low, the amount of CO generated will increase, the energy loss due to unburned fuel will increase, and if the oxygen concentration is high, the amount of NOx generated will increase, and excess air will cause the furnace to burn. Energy loss increases by cooling the inside. Therefore, the oxygen concentration is controlled to keep the oxygen concentration of the exhaust gas in the furnace at the optimum value. The oxygen concentration controller 10 is for that purpose, and is a PI controller that continuously performs proportional and integral operations. The oxygen concentration measurement value in the exhaust gas detected by the oxygen analyzer 16 is an input deviation so as to be maintained at a set value. Proportional and integral calculations are performed on (O ₂ pv−O ₂ sv) to give the air-fuel ratio set value μ to the air-fuel ratio setter 8.

However, if the set value of the oxygen concentration controller 10 is set to a fixed value, even if the set temperature of the furnace changes and the temperature in the furnace rises and the amount of NOx generated for the same amount of oxygen changes, Unless the operator re-adjusts the set value of the oxygen concentration, a large amount of NOx continues to be generated or a large amount of air continues to be blown, resulting in energy loss.

In order to solve this problem, in the present invention, the set value of the oxygen concentration controller is automatically changed according to the CO concentration and NOx concentration in the exhaust gas. That is, if the amount of NOx in the exhaust gas increases, the adjustment amount calculation value calculated by the 20 subtractor becomes a negative value and this value becomes 22
The oxygen concentration is set by the integral calculator, and the basic oxygen concentration setting value O ₂ s
v1 and the adder 21 are added, and as a result, a value obtained by subtracting the oxygen amount with respect to the amount by which the NOx amount is increased from the basic oxygen concentration set value, the optimum oxygen concentration set value O ₂ sv2 is calculated, and the oxygen concentration is adjusted. It is set as the setting value of the meter.

It is known that the relationship between the NOx concentration and the CO concentration when the O ₂ concentration is increased or decreased is generally a contradictory relationship as shown in FIG. The ratio between the NOx concentration and the CO concentration can be determined from the economical efficiency of the furnace and the range permitted as the environment. Generally, there is a tendency to prioritize environmental issues even if economic efficiency is somewhat poor. 1 from these ratios
It is possible to freely set the relationship between the NOx concentration and the CO concentration by performing weighting using the 8 and 19 coefficient setting devices.

[0018]

As described above, the set value of the oxygen concentration controller is changed in accordance with the NOx concentration and the CO concentration, and this is fed back to maintain a good combustion state.

As is apparent from the above description, according to the present invention, the NOx concentration and the CO concentration in the exhaust gas can be maintained at relatively low desired values, and the set value of the oxygen concentration can be the NOx concentration and the C value.
Since it is adjusted according to the O concentration, the control meter is stable, and it is possible to avoid the generation of an unburned state, reduce NOx, and save energy. Also, the fine adjustment of oxygen concentration by the operator, which was necessary every time the furnace temperature was changed, was eliminated.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a combustion control device for carrying out a combustion control method according to the present invention.

FIG. 2 is a diagram showing a relationship between oxygen concentration in exhaust gas, NOx generation amount, and energy loss.

[Explanation of symbols]

1 ... Temperature controller, 2 ... Fuel flow controller, 8 ... Air-fuel ratio setter, 9 ... Air flow controller, 10 ... Oxygen concentration controller, 11
… NOx analyzer, 12… CO analyzer, 13… Combustion zone, 1
4 ... Combustion furnace, 15 ... Thermocouple, 16 ... Oxygen analyzer, 17 ...
mV / I converter, 18 ... Weighting coefficient setting value of CO analysis value,
19 ... NOx analysis value weighting coefficient setter, 20 ... Subtractor, 2
1 adder, 22 ... integrator, 23 ... limiter.

Claims (1)

[Claims] 1. When controlling a fuel flow rate and an air flow rate supplied to a combustion zone of a combustion furnace according to a desired furnace temperature, one of the flow rates is set to a set value from a furnace temperature adjusting means so that a flow rate measurement value matches. In the combustion control method of controlling in accordance with the above, the NOx concentration and the CO concentration in the exhaust gas in the chimney are continuously measured, the optimum oxygen concentration set value in the operating state of the furnace is determined from these values, and the combustion range of the combustion furnace, Continuously measure the oxygen concentration in the exhaust gas in the flue or chimney, calculate the air ratio by performing proportional and integral calculations on the deviation between the measured value and a predetermined set value, and based on this, calculate the flow rate. The combustion control method by oxygen concentration control in a fuel furnace, characterized in that the other of the above is continuously controlled.