JPS5831027A - Controlling method for atmosphere in heating furnace for steel material - Google Patents

Abstract

PURPOSE:To improve the yield and quality of steel materials from suppressed formation of scale and decreased quantity of scale loss in the stage of heating the steel materials in a heating furnace by controlling the concn. of CO in an atmosphere in a soaking zone automatically. CONSTITUTION:Many steel materials W are passed through the heating zone 1a and soaking zone 1b of a heating furnace 1, whereby the materials are heated to working temps. for rolling, etc. In an arithmetic controller 14, the rate of supplying fuel necessary in the zone 1b is operated and is outputted to a flow rate controller 13 for fuel, by which a fuel control valve 52 is controlled. Here, the ratio and quantity of air are operated so as to control the concn. of CO in the zone 1b analyzed with a CO analyzer 9 to 0.5-1.5% and are outputted to a flow rate controller 12 for air, by which an air control valve 51 is controlled. In the zone 1a, on the other hand, the concn. of O2 in a gaseous atmosphere analyzed with an O2 analyzer 8 is inputted to an arithmetic controller 14 which controls an air control valve 41 and a fuel control valve 42 by means of a flow rate controller 10 for air and a flow rate controller 11 for fuel so as to improve combustion efficiency and to decrease fuel consumption.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention suppresses scale formation in steel materials in a method of heating steel materials such as steel ingots and billets in order to perform processing such as rolling. This paper proposes a method for controlling the atmosphere in a steel heating furnace that reduces the amount of heat generated.

In general, steel materials such as steel ingots and billets are oxidized during heating to produce schools, and the steel material loses its weight accordingly. The amount of steel material burnt out due to this scale loss varies greatly depending on the heating temperature and heating atmosphere. Looking at the relationship with heating temperature, the amount of burnout in steel materials starts to become noticeable at around 900°C, and increases significantly above 1100°C, but when heating steel materials as a pretreatment for processing such as rolling, heating to 1000°C or higher is recommended. This is necessary, and the amount of heat loss per steel material cannot be ignored. For example, when the temperature for extracting steel material from the heating furnace is about 1000 to 1100°C,
Conventionally, the amount of burnout of steel materials is about 0.9%, and if the above-mentioned extraction tolerance is even higher, the amount of burnout of steel materials increases rapidly. When scale occurs and the amount of burnout of the steel increases, it affects the material yield, and if the scale does not peel off and is carried over to subsequent processes, it causes scale defects on the surface of the steel, reducing the quality of the steel. urge

To overcome this, in conventional steel heating furnaces, the atmosphere inside the furnace is controlled by tio gas concentration, but this control is not aimed primarily at reducing the amount of burnout, but rather at reducing the fuel consumption per unit of production. As a result, the temperature at which the steel material is extracted from the heating furnace is lowered as much as possible to the extent that it does not interfere with subsequent processes.As a result, the amount of steel material burned out is reduced, and the amount of steel material burned out is reduced. Restraint could not be desired.

The present invention has been made in view of the circumstances, and it is possible to suppress the scale formation of steel materials without deteriorating the fuel consumption rate or causing pollution, and to reduce the amount of burnout of the steel materials, thereby increasing the material yield of the steel materials. and to improve quality.

The method for controlling the atmosphere in a steel heating furnace according to the present invention is characterized in that a soaking zone is made into a reducing atmosphere by adjusting the flow of air and fuel or by blowing H reducing gas.

The method of the present invention will be explained below based on drawings showing examples thereof. FIG. 1 is a schematic diagram showing an embodiment of the method of the present invention.
The inner button of the heating furnace 1, which is a continuous furnace, has a skid rail 2 installed from its population 1c to the exit 1d''!
The workpiece W is sequentially pushed into the furnace by the pushing force of the pusher 3 attached to the inlet rc side, and the workpiece W is slid on the skid rail 2 and is moved in the direction of the white arrow inside the heating furnace 1 in a predetermined direction. When the work w is moved at a high speed and reaches the outlet 1d, it is pushed out of the furnace and discharged. The heating furnace 1 consists of two heating zones, a heating zone 1a and a soaking zone 1b.The workpiece W, which is gradually heated from the surface to the inside in the heating zone 1a, is kept uniformly heated in the soaking zone 1b. It has become. A detector 6 is installed in the heating zone 1a.
and a burner 4 are installed, the detector 6 is connected to an O1 analyzer 8, and the burner 4 is connected to an air control valve 4.
1 and a fuel tank (not shown) through a fuel control valve 42, respectively. On the other hand, the soaking zone 1bK is similarly equipped with a detector 7 and a burner 5, and the detector 7 is connected to the FiCO analyzer 9, and the burner 5 is connected to the proa (
(not shown) are respectively connected to a fuel tank (not shown) via a fuel control valve 52. Incidentally, the furnace gas in the heating furnace 1 is configured to be discharged to the outside of the furnace through a flue 1e opened on the side of the furnace inlet lc.

The air control valve 41 is connected to the air flow control device 11) 10 (for the heating zone), the fuel control valve 42 is connected to the fuel flow control device 11 (for the heating zone), and the air control valve 51 is connected to the air flow control device 12 (for the soaking zone). ), the fuel control valve 52 is connected to the fuel flow control device 13 (
for the soaking area), and both of these are connected to the arithmetic and control unit 14. The operation III Goso @
The data obtained by the above-mentioned 02 analyzer 8 and CO analyzer are input to 14, and based on the data, the air flow control device [10, 12 and the fuel flow control device 11] is inputted. .13 control calculations are performed and output to each device.

When heating steel materials such as steel ingots and slabs using the equipment configured as described above, first, the atmosphere in the soaking zone 1b, which is the most humid in the heating furnace 1 and where scale is likely to form, is made into a reducing atmosphere. However, the numerical value to be set as the control target and its basis will be explained. Figure 2 shows the relationship between the CO gas concentration determined in the actual furnace (measured value in the soaking zone 1b) and the amount of burnout (the amount of burnout Fj of the steel material actually processed in the heating furnace 1) on the horizontal axis. This is a graph in which the amount of burnout is plotted and the vertical axis is the CO gas concentration, and it can be seen that as the CO gas concentration increases, the burnout amount decreases. Figure 3 is a graph showing the relationship between Co gas concentration and fuel consumption rate (heat generated per unit weight of fuel) determined through experiments, with fuel consumption on the horizontal axis and KCOCO gas concentration on the vertical axis. However, it can be seen that the fuel consumption rate shows the highest value when the CO gas concentration is about 1.0%. Therefore, in order to reduce the amount of burnout without worsening the fuel consumption rate, the CO gas concentration should be set at 0.5 to 1.5% (preferably 0.8 to 1.5%).
1.2%) It is preferable to adjust K. Figure 4 shows the relationship between the CO gas concentration (measured value in soaking zone 1b) and the air ratio (air ratio in burner 5) determined in an actual furnace, with the air ratio on the horizontal axis and the CO gas concentration on the vertical axis. This graph shows that there is an inversely proportional relationship between the CO gas concentration and the air ratio, and this relationship can be used to adjust the air amount to adjust the air ratio to a predetermined value. By doing so, the CO gas concentration can be set to a desired value.

Therefore, the arithmetic and control device 14 first calculates the amount of fuel to be supplied according to the required amount of heat in the soaking zone 1b, outputs the data to the fuel flow rate control device 13, and controls the fuel control valve 52. Calculate the air ratio such that the CO gas concentration in the soaking zone 1b analyzed by the analyzer 9 is 0.5 to 1.5% based on the relationship shown in Figure @4, and calculate the air ratio and the above-mentioned The air supply amount is calculated based on the theoretical air amount determined by the fuel supply amount of .5 to 1.5%.

On the other hand, the heating zone 1a#'i is controlled to have an oxidizing atmosphere, and the reason for this is that the reducing gas (CO
This is because if the unburned portions of the fuel and gas are directly discharged from the furnace through the heating zone 1a and through the flue 1e, it will cause pollution and worsen the fuel consumption rate. Therefore, the O gas concentration in the heating zone 1a analyzed using the 02 analyzer 8 is inputted to the arithmetic and control device 14, and the arithmetic and control device 14 sets the conditions in which the heating zone 1a becomes an oxidizing atmosphere and also takes combustion efficiency into account. Based on the calculation results, the air conditioning valve 41 and the fuel regulating valve 42 are adjusted and controlled using the air flow control device 10 and the fuel flow i control device 11.

If certain controls are carried out, it is possible to suppress the scale formation of steel materials and reduce the amount of burnout of steel materials without causing a deterioration of the fuel consumption rate or the occurrence of pollution.

In this example, a method of controlling the air flow rate and the fuel flow rate was used as a means for making the atmosphere in the soaking zone 1b a reducing atmosphere, but a method of supplying an appropriate amount of reducing gas such as CO gas from the outside may also be used. Of course.

Next, the effects of the method of the present invention will be explained based on examples. Fifth
The figure is a graph comparing rimmed steel heated by the conventional method and heated by the method of the present invention. The horizontal axis shows the heating temperature, and the vertical axis shows the value obtained by dividing the burnout amount by the square root of the furnace time.The dashed line shows the CO gas concentration in the soaking zone, The solid lines represent the cases in which the CO gas concentration in the soaking zone is controlled to 1 to 2%, respectively. It was confirmed that the amount of burnout can be significantly reduced by the method of the present invention compared to the conventional method.

As described in detail above, in the case of the method of the present invention, the steel is heated in a reducing atmosphere in the soaking zone of the heating furnace, so it is possible to reduce burnout of the steel without causing deterioration of the fuel consumption rate or the occurrence of pollution. This has a great effect on improving yield and quality.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of the method of the present invention, and FIG. 2 is a C
Graph showing the relationship between O gas concentration and burnout amount, Figure 3 Clear showing the relationship between FiCO gas concentration and fuel consumption rate, Figure 4 graph showing the relationship between CO gas concentration and air ratio, Figure 5 The figure is clear showing the effect of the method of the present invention. 1...Heating furnace 1a...Heating zone 1b...Soaking zone 4.5...Burner 6.7...Detector 8...0
2 Analyzer 9...CO analyzer patent applicant: Sumitomo Metal Industries, Ltd. Agent Patent attorney: Noboru Kono

Claims (1)

[Claims] 1. A method for controlling the atmosphere in a steel heating furnace, characterized by creating a reducing atmosphere in the soaking zone by adjusting the flow rates of air and fuel or by blowing a reducing gas.