JPS6240312A - Method for controlling atmosphere in furnace - Google Patents

Abstract

PURPOSE:To execute optimum control of the atmosphere in a furnace by freely movably inserting probes into the furnace, measuring the concns. of the gaseous O2 and CO in a waste gas at plural positions and correcting and controlling an air-fuel ratio according to the deviation between the average value thereof and the set value. CONSTITUTION:The respective probes 11a, 11b of a gaseous O2 densitometer and gaseous CO densitometer are inserted into the furnace 10 and are inserted by each specified length into the furnace 10 by a driving device 12. The atmosphere in the furnace is introduced into respective gas analyzers 13 via plural measuring points 24'-1-24'-n through measuring holes 24-1 provided at the top end of the probes 11a, 11b. The analyzed concn. values of the O2 and CO are inputted to a computer 14 by which the respective average concn. values are determined. The values are compared with the set value of the required combustion air volume of an air-fuel ratio controller 17. A combustion air control valve 22 is controlled according to the deviation therebetween by which the air-fuel ratio is decreased or increased.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method of controlling atmosphere in a furnace, and in particular,
The present invention relates to an atmosphere control method for accurately controlling the atmosphere in a steel heating furnace, heat treatment furnace, etc. by measuring the entire atmosphere inside the furnace.

[Conventional technology]

Conventionally, in controlling the atmosphere in a furnace, the oxygen concentration (hereinafter referred to as 0.gas afl) or carbon monoxide concentration (
When measuring the CO gas concentration (hereinafter referred to as CO gas concentration), probes for measuring each concentration are fixed at specific positions within the furnace.

For this reason, each measurement value obtained by measurement is the CO gas at a certain point in the furnace or 0. It merely indicates the gas concentration, and does not accurately reflect the atmospheric conditions or combustion conditions inside the furnace. Additionally, the flow of unburned gas and flue gas in the furnace is constantly changing due to fluctuations in combustion conditions, furnace pressure, etc.
The current method of measuring with a fixed probe is affected by the various fluctuations mentioned above, making it impossible to control the furnace atmosphere with high precision.

[Problem that the invention seeks to solve]

As stated on paper, the conventional method is to measure CO gas and O gas concentration values obtained by measuring at a specific point in the furnace, that is, at the insertion depth of each probe at a specific point. The method merely controls the atmosphere inside the furnace, and it has not been possible to always obtain optimal control of the atmosphere inside the furnace.

[Purpose of the invention]

The present invention was made in order to solve the above-mentioned conventional problems. Therefore, the O gas concentration and CO gas concentration in the waste gas in the furnace are always accurately measured, and based on the measured values, the concentration in the furnace is It is an object of the present invention to provide an atmosphere control method that can optimally control the atmosphere.

[Means for solving problems]

The present invention is a method for controlling the atmosphere in a furnace, in which each probe is movably inserted into the furnace to measure O, gas concentration, and CO gas concentration in combustion waste gas at a plurality of measurement positions. The above object has been achieved by determining an average concentration value based on each of the measured values, and correcting and controlling the air-fuel ratio according to the deviation between the average concentration value and the target setting value.

[For production]

In the present invention, 0. The measurement position of the gas concentration and CO gas concentration in the furnace was made variable, and the concentration at multiple points in the furnace was measured. It is possible to always accurately determine the average value of the CO gas concentration, and therefore it is possible to always perform optimal furnace atmosphere control based on these average values.

That is, in general, the 02 gas concentration [0,] in the waste gas during the combustion process is 21 of the excess air amount Qex that does not contribute to combustion.
It is expressed as % by the following formula.

C02) −〇, 21 X QexX / Qgx t
o.

= (0,21X (Qf-Ao-m(1-77+))
/(Qf-Go・773+Qr・Ao-m(1-η
+))

CCo) = (Qr(1773)・77,)/(Q
r-Go・na+Qf(1-n 3)+Qf-Ao
-m(i77 +))X +00(%)...
...(2) Here, Q is the fuel flow rate, AO is the theoretical air amount, Go is the theoretically generated gas, fftQg is the combustion gas amount, η is the efficiency of combustion air contributing to combustion, and η3 is the completeness of the combustion gas. The combusted proportion, η, is the proportion of CO in the unburned gas, and m is the air ratio.

Therefore, depending on combustion conditions, combustion load, air ratio, etc., the amount of unburned gas in the furnace and waste gas may vary. and CO gas concentration differs depending on the gas flow and measurement position.

Therefore, in the present invention, the probes of the 02 densitometer and the CO densitometer are moved for measurement, thereby making it possible to eliminate the influence of the measurement position, thereby making it possible to perform more accurate control.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

In this embodiment, as shown in FIG. 1, the present invention is applied to a preheating zone.

A description will be given of a method applied to a typical example of a heating zone combustion control device in a heating furnace 10 consisting of a heating zone and a soaking zone.

A fuel flow meter 20 for measuring the fuel flow ff1Qf is disposed in a fuel pipe for feeding fuel to a burner (not shown) disposed in the heating zone. The fuel flow ff1Q' measured by the fuel flow meter 20 is determined based on the deviation between the furnace temperature measurement value Tm of the furnace temperature measurement device of the heating zone (not shown) and the target furnace temperature set value Ta, and is calculated based on the deviation. Fuel flow regulator 16
outputs a control signal to control the fuel flow control valve 21 to maintain the furnace temperature at the target set value.

The air-fuel ratio setter 17 sets the required combustion air fiAom(1±
Calculate α).

A signal of the required combustion air fflAom(1±α) (α is the total excess coefficient of the air-fuel ratio) is output to the combustion air flow rate regulator 18, and the signal is output to the combustion air flow rate regulator 18, and the signal is sent to the air piping for feeding to the burner (not shown). Based on the deviation between the measured value of the combustion air flow meter 23 that measures the air amount Qa and the set value of the combustion air flow rate regulator 18, the combustion air control valve 22 is controlled to eliminate the deviation. There is. On the other hand, the atmospheric gas inside the furnace was sampled and 0. Gas concentration meter 13a and CO gas concentration meter 13
On the tip side of the introduction pipe 26 leading to the inlet pipe 26, there are probes 13a and 11b (in the figure, one Ol and CO gas concentration meter), each of which has a variable insertion length into the furnace. (representatively shown in the figure). each probe 11a.

A probe moving drive device 12 is provided outside the furnace 11b to make the length of insertion into the furnace variable. Also, each probe l
A seal cylindrical body 25 is attached that seals the cylinder by a length corresponding to the movement of 1a and 1b. Then, the rack L2a connected to a motor (not shown) and the pinion 12b fixed to each probe 11 mesh with each other, and the pinion 12b is sent into the furnace at a constant length according to a command from an in-furnace insertion length control device (not shown). The atmosphere inside the furnace at n measurement points (24'-1 to 24'-n) in the furnace is sequentially measured through the measurement hole 24-1 provided on the tip side of the probe 11 through the introduction pipes 26 on each side for each gas analysis. Total 1
Introduced in 3. Alternatively, the maximum insertion length Itma of the probe into the furnace may be determined based on a command from the furnace insertion length control device.
measurement holes 24'-1 to 24'-n corresponding to each measurement position provided in the cylindrical body of the probe 11.
The atmosphere inside the furnace is introduced into each of the gas analyzers 13 at once.

Each gas introduced in this way is analyzed by each gas analyzer 13 to measure the atmospheric gas at each measurement point in the furnace.
The measurement hole 24 is normally located at the tip of each probe 11.
-1 is located 11 m1n from the furnace wall.

Maximum insertion length into the furnace II m only during zumbling measurement
a x, and set this insertion setting position to l(max
Measurement hole 24' on the furnace wall side of each probe 11 at this time
-n corresponds to the position of Hmin, which is constantly measured, and Co9 and 0. It is possible to make a correspondence between the gas concentration and the gas concentration at each measurement hole 24'-1 to 24'-n.

In other words, each gas concentration is constantly measured by the measurement hole 24-1, and the relationship between the measured value and the measurement value measured by each measurement hole 24'-1 to 24'-n is determined in advance by sampling ff1ll.
You can always monitor the atmosphere in the furnace using the measured values from the 24 measurement holes of the valley probe for CO and 02 gas concentrations. When the maximum insertion length II m a x or a certain length is sequentially sent into the furnace and the measurement is delayed, certain changing conditions such as combustion load and air-fuel ratio are changed to 1:? <
Perform the measurement when adding up, and always measure each probe 11 at the position of 11m1n. Alternatively, Zumbling measurement may be performed at regular intervals.

The atmosphere inside the furnace sampled in this way was 0. Gas and Co gas concentration meters 13a and 13ti were analyzed, respectively, and 02 gas concentration values (02) for each of 41 fixed points.

[02) t, -(02) nl(O scum concentration value (C
O),.

(CO)2.[:C0)n is measured 5 times. Each of the measured values is inputted to the calculator 14, and the average value of each measured value is corrected or weighted by a coefficient Ki that takes into account the gas flow in the furnace, etc. to calculate the integral value for each section of the furnace. Multiplying the cross-sectional area An gives the value of 0. Equivalent f of gas amount and CO gas amount
Find f1X (0,), X (Co). Based on the respective equivalent fftX Co, ),
In U15, the average concentration value of 02 gas% and CO gas% is calculated.

The calculation is, for example, CO,)-02 gas%=XCO,']/
Σ(Qf+Qa), (Co) -CO gas%=x
Calculated as (Co)/Σ(Qf+Qa). The average concentration value (0,) (Co) obtained in this way is the required combustion air amount A for the combustion fuel amount of the air-fuel ratio regulator 17.
The correction values (0,) and (Co) are added to the set value of om (1±α), and when the gas concentration reaches 0 and the dead zone β1 set for each furnace zone or more, combustion is performed to reduce the air-fuel ratio. Controls the air control valve 22.

Also, the CO gas concentration is a dead zone β set for each furnace zone.

If it is above, increase the air-fuel ratio. Combustion air control valve 2
Control 2.

In addition, the average concentration value Σ(
0,) /n, Σ[CO)/n and assuming that the gas flow in the furnace is the same, the average concentration value [0,] and [CO]
Therefore, the CPt 115 calculates the relationship between the air-fuel ratio and 00% and 07% shown in FIG. 2, and controls the air-fuel ratio to be corrected by inputting it to the air-fuel ratio regulator 17 so that the target O7 and CO gas concentrations are achieved. Zuro.

This correction control is not shown in Figure 2.
Based on the relationship, for example, the average concentration value 1 of [0,] in the heating zone
．． 0% is obtained as the above-mentioned measured value, the target setting is 0, the gas concentration is 0.6%, and the air-fuel ratio regulator 17 sends a control command to the combustion air flow rate regulator 18 to control the air ratio to 1.03. The output is output to throttle the combustion air control valve 22 to adjust the flow rate.

In this way, by measuring the CO, O, and gas concentrations in the furnace by varying the insertion position of each probe 11, it is possible to accurately know the O7 and CO gas concentration distribution and perform optimal atmosphere control.

In addition, although the above embodiment is applied to a continuous billet heating furnace having a pre-heating zone, a heating zone, and a soaking zone, the application of the present invention is not limited to this, and is applicable to atmosphere control in a furnace such as a heat treatment furnace. It can also be applied to Furthermore, when measuring the gas concentration, it is also possible to use a zirconia analyzer for direct insertion.

Of course, this atmosphere control may also be performed by controlling the flow rate of the combustion fuel instead of controlling the combustion air.

[Effects of the Invention] As explained above, according to the present invention, the 0° gas and CO gas concentrations in the furnace can be measured at each measurement position, so that the atmosphere can always be controlled accurately. This measurement method also has the advantage of allowing accurate combustion control.

[Brief explanation of drawings]

FIG. 1 shows CO gas and CO gas in the heating furnace according to the present invention.
．． Diagram explaining gas concentration measurement and furnace atmosphere control method,
FIG. 2 is a diagram showing the relationship between CO gas and O in the furnace, gas concentration, and air-fuel ratio. Symbol lO...Heating furnace [1...Gas concentration measurement probe lta, llb...02 and CO gas concentration measurement probe 12/probe movement drive device 12a...Rack 12b...Pinion 13...Gas analysis Total L3
a, 13b...02 gas and CO gas concentration analyzer 1
4... Arithmetic unit 15... CI'0 1G... Fuel flow rate regulator 17... Air-fuel ratio regulator 18... Air flow rate regulator 19... Fuel flow rate transmitter 20... Fuel flow rate Total 21...Combustion fuel control valve 22...Combustion air control valve 23...Combustion air flow meter 24...Measuring hole 25...Seal cylinder

Claims (1)

[Claims] When controlling the atmosphere in the furnace, each probe for measuring the oxygen concentration and carbon monoxide concentration in the furnace is movably inserted to measure the oxygen concentration and carbon monoxide concentration in the furnace atmosphere gas at a plurality of measurement positions. A method for controlling the atmosphere in a furnace, characterized in that each concentration is measured, each average concentration value is determined based on the measured values, and the air-fuel ratio is corrected and controlled according to the deviation between the average concentration value and a target setting value. .