JPH04316919A - Ignition control method of combustion furnace - Google Patents

Abstract

PURPOSE:To prevent the generation of explosion when igniting a large number of burners by detecting the percentage of combustible gas concentration or explosion lower limit concentration of mixed gas, and increasing the amount of air fed to an exhaust gas collection section when this detected value exceeds a specified value and keeping the above percentage within the specified value. CONSTITUTION:There are installed a large number of radiant tube burners 2 in a heat treatment furnace 1. Fuel 3 and air 4 are respectively controlled by way of controllers 5 and 7 and control valves 6 and 8 so as to produce a constant mixing percentage and supplied to these burners 2. In this case, an attempt is made to detect the combustible gas concentration contained in the exhaust gas mixed in a collection pipe or a header 15 or the explosion range of the mixed gas therein by means of a sensor 22. This detected value is input into a combustible gas alarm 23 while an alarming signal will be issued when the detected value exceeds a specified value. An exhaust gas temperature controller 20 and a combustion air controller 7 or a ratio setting instrument 9 will be subjected to interruption control so as to increase the amount of dilution air and combustion air to the header 15, which makes it possible to hold the concentration of combustible gas lower than the explosion lower limit concentration.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ignition control method for a combustion furnace having multiple burners, such as a heat treatment furnace.

0002

2. Description of the Related Art The current method of igniting multiple burners and the state of combustible gas generation at that time will be explained with reference to FIG. A large number of radiant tube burners 2 are arranged in the heat treatment furnace 1, and several dozen to several dozen burners are grouped together, and the fuel 3 and combustion air 4 to the whole group are kept at a constant ratio. Adjust the amount and supply it to the burner. Here, reference numeral 5 denotes a fuel flow rate controller which directs the opening and closing of the control valve 6 to control the fuel flow rate to a constant level. 7 is a combustion air flow rate controller that controls the control valve 8. Instructions to increase or decrease the flow rates of fuel and combustion air are given by the furnace temperature controller 10, and at this time, instructions to set the flow rate at a constant rate for the fuel are sent to the combustion air side via the ratio setter 9. feed to controller 7.

When the burner is ignited using the combustion control system described above, the furnace temperature is too low for automatic furnace temperature control, so generally the fuel and combustion air controllers are manually controlled. , and open each valve 6,8. Next, the burners are ignited by opening the fuel valves 12a to 12x in front of the burners one by one to ensure ignition. Note that the combustion air valves 13a to 13x in front of the burner are all open. When igniting in order from a to x,
During the ignition of the first few burners, the fuel from the entire zone was concentrated and flowed into the burner with the fuel valve open, resulting in incomplete combustion, and the burner contained a large amount of combustible gases such as CO, H2, CH4, etc. Exhaust gas flows into the exhaust gas collecting pipe 15 through the exhaust gas pipes 14a to 14x.

Since air flows into the exhaust gas collecting pipe from the unlit burner, the above-mentioned mixed gas of combustible gas and air is formed. Although it varies depending on the setting of the combustion air flow rate at the time of ignition, the concentration of combustible gas in the mixed gas is within the lower explosive limit of the gas (for example, 4.0% for H2, 12.5% for CO, CH4
If the amount exceeds 5%), an explosion will occur if there is an ignition source such as sparks. Therefore, in order to minimize equipment damage at this time, an explosion hole 16 is generally installed using a thin metal plate such as Al. However, if the explosion hole is ruptured, it will take time to repair it, so a method to prevent this from happening has been desired.

In FIG. 1, 18 is an exhaust gas blower;
Reference numeral 19 is a thermometer for monitoring exhaust gas temperature to protect the exhaust gas blower from heat, and 20 is a temperature controller that controls opening and closing of a dilution air valve 21 for taking in outside air in order to maintain a constant exhaust gas temperature.

[0006]

[Problem to be Solved by the Invention] In a combustion furnace having a large number of burners, for example, a radiant tube combustion furnace which is a common type of continuous heat treatment furnace for strip steel, when the furnace is ignited, the first few burners Due to excess fuel, incomplete combustion occurs, and combustible gas is emitted in the exhaust gas. At this time, in the exhaust gas collecting area, the air flowing in from the unlit burner mixes with the flammable gas, and if the lower explosion limit is exceeded, an ignition source such as sparks may cause an explosion, causing equipment failure. . An object of the present invention is to provide a combustion furnace ignition control method that can prevent such a situation from occurring.

[0007]

[Means for Solving the Problems] The gist of the present invention is to provide an ignition control method for a combustion furnace having a large number of burners, in which the fuel and combustion air valves are opened to sequentially ignite the burners, and the exhaust gas collection section at that time is Detecting the flammable gas concentration or the ratio of the mixed gas of combustible gas and air to the lower explosive limit concentration,
A combustion furnace characterized in that when the detected value exceeds a specified value, the amount of air to the exhaust gas collecting section is increased to control the combustible gas concentration or the ratio of the mixed gas to the lower explosive limit concentration to be within the specified value. ignition control method.

FIG. 2 shows the ignition control method of the present invention. The function of the present invention is to install a sensor 22 that detects the combustible gas concentration in the exhaust gas mixed in the exhaust gas collecting pipe or the explosion range of the mixed gas, and inputs this detected value to the combustible gas alarm 23. A combustible gas alarm will notify the operator if the concentration of combustible gas in the exhaust gas exceeds a specified value (generally set at 1/4 to 1/2 of the lower explosive limit concentration). issue an alarm. At the same time, one or both of the exhaust gas temperature controller 20 and the combustion air flow rate controller 7 or ratio setter 9 is controlled to control either the dilution air amount or the combustion air amount to the exhaust gas collecting pipe. Or, by increasing both, control is carried out to maintain the combustible gas concentration at a value sufficiently lower than the lower explosive limit concentration. In this way, the concentration of combustible gas in the exhaust gas can always be kept at a sufficiently low value for safety during the ignition operation.

[0009]

[Main components...H2: 53.3%, CH4: 28.2%, CO: 5.7%, C2 H4: 3.6%, N2: 6.3%, CO2: 2.9%]

Calorific value 4480kcal/Nm3 Combustion control zone: 2 zones (21 units/zone) Ignition procedure: Each zone
COG flow rate 100Nm3 /h Air flow rate 6
The flow rate was adjusted to 00 Nm3/h. The air valve in front of each burner is fully open, and a predetermined amount of air is flowing to the burner. The valves in front of the COG burners were all closed, then opened one by one to ignite them.

H2 in the exhaust gas collecting pipe until the end of all ignition
, when the CO concentration was measured, the conventional method reached a maximum of 12% for H2 and 3% for CO, as shown in FIG. Since the lower explosive limit concentration of H2 is 4%, it was a dangerous situation with a high possibility of explosion. Applying the control of this method, H
As a result of setting the upper limit of 2 to 1% and igniting in the same way, as shown in Figure 4, H2 was suppressed to a maximum of 1.5% and CO to a maximum of 0.5%, maintaining sufficiently safe concentrations. I was able to do that.

[0011] At this time, an exhaust gas dilution valve in the collecting pipe portion having a diameter of φ300 was used, and the opening of this valve reached its full opening when three burners were ignited. After that, the flow rate increase control is applied to the combustion air flow rate adjustment, and the maximum value is 1250N when 6 burners are ignited.
After reaching m3/h, it decreased thereafter and returned to the initial setting of 600 Nm3/h when the 12 burners were ignited. After the ignition of 16 burners was completed, the exhaust gas dilution valve in the collecting pipe also returned to the fully closed state. Although this example shows an example in which combustible gases such as H2 and CO are detected, the same control is possible using a commonly used combustible gas detector that detects the ratio of combustible gas to the lower limit of explosion. .

0012

[Effects of the Invention] According to the combustion furnace ignition control method of the present invention, when a large number of burners are ignited, there is no explosion due to combustible gas etc. in the exhaust gas collecting section, there is no equipment failure due to explosion, and the effect is It is extremely large.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a conventional combustion furnace ignition method.

FIG. 2 is an explanatory diagram showing an ignition control method for a combustion furnace according to the present invention.

FIG. 3 is a diagram showing a change in combustible gas concentration during ignition according to a conventional method.

FIG. 4 is a diagram showing a change in combustible gas concentration during ignition according to the method of the present invention.

[Explanation of symbols]

1 Heat treatment furnace 2 Radiant tube 3. Fuel 4 Combustion air 5,7 Controller 6, 8 Control valve 9 Ratio setter 10 Furnace temperature controller 12 Fuel valve 13 Air valve 14 Exhaust gas pipe 15 Collecting pipe 16 Explosion hole 18 Exhaust gas blower 19 Thermometer 20 Temperature controller 21 Dilution air valve

Claims (1)

[Claims] Claim 1: In a method for controlling ignition of a combustion furnace having multi-stage burners, valves for fuel and combustion air are opened to sequentially ignite the burners, and the concentration of combustible gas in the exhaust gas collecting section at that time or the ratio between combustible gas and air is controlled. The ratio of the mixed gas to the lower explosive limit concentration is detected, and when the detected value exceeds the specified value, the amount of air to the exhaust gas collection section is increased to raise the combustible gas concentration or the ratio of the mixed gas to the lower explosive limit concentration to the specified value. 1. A combustion furnace ignition control method characterized by controlling the ignition so that the ignition enters the combustion furnace.