JPS61190281A - Method of controlling tunnel furnace in reduction baking - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a tunnel furnace in which a reduction zone maintained in a reducing atmosphere is provided in a part of the firing zone formed in the longitudinal center of a tunnel-shaped furnace body. Regarding control method.

Problems to be Solved by the Prior Art and the Invention As shown in FIG. 1, a tunnel furnace for reduction firing is a tunnel having an entrance 2 for carrying in the materials to be fired at one end and an exit 3 at the other end. A large number of burners 4 are installed in the longitudinal center of the furnace body 1.
The suction pipe 6 of the blower 5 installed near the entrance 2 is inserted into the furnace body 1,
In addition, the discharge pipe 8 of the blower 7 installed near the carry-out port 3 penetrates into the furnace body 1, and by driving both blowers 5.7, a pressure gradient is created where the pressure gradient is high on the carry-out port 3 side and low at the carry-in port 2. As a result, an airflow is generated in the furnace body 1 from the carry-in port 3 side to the carry-in port 2 side, and the high-temperature gas flowing from the baking zone β causes the fired material to be fired immediately after being carried into the carry-in port 2 side of the firing zone B. There is a preheating zone A for preheating materials, and a 1. In the firing zone B, cooling zones C are formed in which the objects to be fired heated to the maximum temperature are cooled by air blown from outside the furnace.
Toward the sides, there is a neutral zone B1 kept in a neutral atmosphere, a reducing zone B2 kept in a reducing atmosphere, and a reducing gas flowing from the reducing zone B2 by blowing outside air into the furnace body 1 with a blower 9 inserted through a discharge pipe 10. The atmosphere in each zone is determined by the air-fuel ratio of each burner, and the reducing zone B2 or neutral zone B1 has the highest temperature. is maintained.

The furnace temperature is detected for each zone, and if it deviates from the standard temperature due to load fluctuations, the fuel supplied to the burner 4 is increased or decreased to return it to the standard temperature, and the combustion air is increased in proportion to the fuel. The air-fuel ratio of each burner 4 is kept constant by increasing or decreasing the supply flow rate, but even if the air-fuel ratio of each burner is kept constant, the suction amount of the blower 5 on the loading port 2 side and the suction amount of the blower 5 on the loading port 3 side If the blowing amount of the blower 7 is constant, the atmosphere inside the furnace will change depending on the combustion amount of each burner 4, and especially in the reduction zone where changes in the atmosphere have a large effect on the quality of the product, it is important to control the atmosphere. needs to be done precisely.

Therefore, the applicant of the present application has developed a method to keep the reducing atmosphere concentration constant by controlling the flow rate of the air flowing inside the furnace from the discharge port side to the delivery port side based on changes in the reducing atmosphere concentration. A patent application was filed as No. 57-224605, and this control method made it possible to stabilize the reducing atmosphere concentration compared to the conventional method. Because the method used was to directly measure the atmospheric concentration and control the amount of gas discharged from the inlet and/or the amount of air supplied to the outlet based on the results, the concentration of the reducing atmosphere remained stable. It has not always been possible to fully satisfy the higher demands for technology.

In other words, subsequent research has revealed that if the air flow in the furnace is controlled by directly measuring the reducing atmosphere concentration in the reducing zone, a time delay will occur and the reducing atmosphere source will fluctuate to some extent. It is.

Purpose of the Invention The present invention was completed based on the results of such research, and its purpose is to provide a control method that can stabilize the reducing atmosphere concentration in the reduction zone with extreme precision. It is something to do.

EXAMPLE Hereinafter, an example of the present invention will be described based on the accompanying drawings.

Furnace temperature and Co gas concentration detected by the temperature detector 22 and atmosphere detection tube 11 provided in the spaces C and C respectively formed between the object a to be fired in the reduction zone B2 and the ceiling surface of the furnace body 1 is measured by the thermometer 23 and the CO analyzer 12, respectively, and '
The measured value is input as an electric signal to the calculation device 24.15, and the output signal of one calculation device 24 adjusts the opening degree of the flow rate control valve 25.26 as shown in FIG. The flow rates of fuel and air supplied to the burner 4 are changed to control the temperature in the furnace to be kept constant, and the measured values of the fuel flow meter 27 and the air flow meter 28 are corrected by a calculation device. 29 and its correction calculation device 2
At step 9, the correction value calculated based on the previously input arithmetic expression is input to the other arithmetic unit 15, and its output signal is input to the rotation speed control device 20. Or a blower 18 installed near the firing zone B of the cooling zone C and having the suction pipe 19 penetrated into the furnace body 1.
The rotational speed of the burner 4 is changed to change the flow rate of air flowing into the firing zone B from the cooling zone C, and as the fuel consumption of the burner 4 increases, the actual atmosphere in the reduction zone B2 changes. The actual C detected by the CO analyzer 12 before
Assuming that the concentration has become higher than the o gas concentration, the rotation speed of the blower 7 on the outlet 3 side that blows air into the furnace body 1 increases, or the rotation speed of the blower 18 that discharges gas from the furnace body to the outside of the furnace increases. As the rotational speed decreases, the amount of air flowing from the cooling zone C to the firing zone B increases, and the excess CO gas in the reduction zone B2 due to the increase in fuel consumption is combusted, reducing its concentration, and vice versa. When the fuel consumption decreases, the rotational speed of the exhaust blower 18 increases before the Co gas concentration actually decreases, or the rotational speed of the blowing blower 7 decreases and cooling Control is performed in such a way that the amount of air flowing from zone C into firing zone B is reduced, and the decrease in CO gas concentration in reduction zone B2 due to the decrease in fuel consumption is corrected.

Note that if the fuel and combustion air are always controlled in proportion, only one of the flow rates may be input to the correction calculation device 29.

Further, the flow rate of the air flowing from the carry-in port 3 side to the carry-in port 2 side within the furnace body 1 may be controlled by controlling the rotational speed of the blower 5 on the carry-in port 2 side.

Structure and Effects of the Invention As specifically explained in the above embodiments, the method for controlling a tunnel furnace of the present invention includes arranging burners in a row in the longitudinal center of a tunnel-shaped furnace body to form a firing zone. A preheating zone is formed on the loading port side of the firing zone by maintaining the pressure inside the furnace body so that the pressure on the loading port side is higher than that on the loading port side and generating an airflow from the loading port side to the loading port side. A cooling zone is formed on the carrying-out port side, and a neutral zone kept in a neutral atmosphere and a reducing zone kept in a reducing atmosphere are arranged in order from the carrying-out port side to the carrying-in port side in the firing zone. , a tunnel furnace divided into a purification zone where air is blown into the furnace to completely burn the reducing gas flowing in from the reduction zone and an oxidation zone where an oxidizing atmosphere is maintained;
Alternatively, the gist is to control the flow rate of the air flow from the carry-out port side to the carry-in port side in the furnace body based on changes in the supply flow rate of combustion air, and the method is to , since the air flow in the furnace is controlled based on changes in the supply flow rate of fuel and/or combustion air,
This provides the effect of precisely controlling the atmosphere within the reduction zone to a constant level without causing any lag time.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a tunnel furnace used to carry out the method of the present invention, together with a block diagram of the control circuit.
The figure shows a cross-sectional view of the furnace body in the reduction zone along with a block diagram of the control circuit. 1: Furnace body 2: Loading port 3: Loading port 4: Burner 5.
7.9.18 Nibloa 11: C○ concentration detection tube 12
: Co concentration analyzer 15.24 = calculation device 20.2
1: Control device 22: Temperature detector 23: Thermometer 25
．． 26: Flow rate control valve 27. 28 Two flow meters 29 = Correction calculation unit W A: Preliminary zone B: Firing body C: Cooling zone Bl
Neutral zone B2: Reduction zone B3: Purification zone B4: Oxidation zone

Claims (1)

[Claims] A firing zone is formed by arranging burners in the longitudinal center of a tunnel-shaped furnace body, and the pressure inside the furnace body is maintained so that the pressure on the outlet side is higher than that on the carry-in port side. By generating an airflow toward the loading port side, a preheating zone is formed on the loading port side of the firing zone, and a cooling zone is formed on the loading port side, and the inside of the firing zone is moved from the loading port side to the loading port side. In this order, a neutral zone maintained in a neutral atmosphere, a reduction zone maintained in a reducing atmosphere, a purification zone in which air is blown into the furnace to completely burn the reducing gas flowing from the reduction zone, and an oxidizing atmosphere maintained in the furnace. In a tunnel furnace divided into an oxidation zone, the flow rate of the air flow from the outlet side to the inlet side in the furnace body is controlled based on changes in the supply flow rate of fuel and/or combustion air in the reduction zone. Tunnel furnace control method for reduction firing