JPS58193328A - Continuous heat treating furnace - Google Patents

Abstract

PURPOSE:To heat a strip in excellent heat efficiency, in heating the strip by a direct firing combustion gas, by arranging a gas permeable solid at a proper angle in the advancing direction of the strip. CONSTITUTION:In heating a strip 2 in a direct firing non-oxidative furnace comprising plural stages, the strip 2 is directly heated by a baking gas containing a non-combustion component and a minute amount of free oxygen generated by combustion due to a burner 4 in an air ratio of 1 or less. After the strip 2 is preheated by the high temp. exhaust gas from a heating furnace, it is heated by direct fire of a weakly oxidative combustion gas in the heating zone equipped with the burner 4. At this time, a gas permeable solid 7 comprising a foamed metal, a sintered metal or porous ceramics is arranged at right angles or a certain angle with respect to the advancing direction of the strip 2 and the combustion exhaust gas is passed through the gas permeable solid 7 to convert the heat contained in the exhaust gas to solid radiant heat. As the result, the strip can be heated in excellent heat efficiency and a heating apparatus itself can be also miniaturized.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous heat treatment furnace for heating a material to be heated with direct combustion gas. The continuous heat treatment furnace will be explained below using an example of a direct fire non-oxidation furnace (hereinafter referred to as NOF and including a preheating furnace).

The present invention improves the heat transfer efficiency of NOF, an example of a general device shown in FIG. 1, and saves energy.

■ Reduce equipment costs by increasing heat transfer rate and shortening equipment length.

For this purpose, as shown in Figures 2 and 3 of the embodiment of the present invention, a permeable solid is installed at right angles to the strip material (heated material) or at an appropriate angle in a direction that blocks the gas flow in the furnace. This article relates to a continuous heat treatment furnace characterized by the following.

Generally, heating methods for strip material include indirect heating using a radiant tube in a reducing atmosphere and direct heating in a slightly oxidizing combustion gas.

As one line, the former is based only on indirect heating;
There are cases where the low temperature section is heated directly by the latter, and the high temperature section is heated indirectly by the former.

The former type of indirect heating is heated in a reducing atmosphere, so it does not oxidize the strip material and is advantageous in improving the surface texture, but because it is indirect heating, the heating rate is limited and the thermal efficiency is low.

The latter direct heating uses unburned matter burned at an air ratio of 1 or less,
The strip material is oxidized because it is heated in a weakly oxidizing atmosphere containing a trace amount of Free-02 (unreacted 02). However, it has the advantage of higher heating speed and thermal efficiency than indirect heating. Therefore, it is expected that direct heating will be used more frequently in the future, but to achieve this, it is necessary to suppress oxidation of the strip material and further increase the heating rate and thermal efficiency.

First, let's start with a typical direct-fired non-oxidizing furnace (
NOF) will be explained with reference to FIG. Reference numeral 1 designates a furnace wall having thermal insulation properties and refractory properties, 2 a strip material, 3 a conveyor roll for the strip material, and 4 a heating device with one burner that burns at an air ratio of 1 or less. Reference numeral 5 denotes a heating chamber for heating the strip material with the combustion gas supplied from the heating device 4. Normally, the combustion gas from the heating chamber 5 preheats the strip IJ strip material, so a preheating chamber is provided on the front side of the heating chamber. It has 6.

The solid arrows in the figure indicate the flow of combustion gas.

The furnace temperature is set at a maximum of 1,200 to 1,300°C, and heat transfer to the strip material is mainly performed by gas radiation. The temperature of the furnace wall surface is generally 100 to 150℃ compared to the furnace temperature.
Solid radiation from the furnace wall is small. Further, the amount of heat transferred by convection is very small compared to the amount of heat transferred by radiation. Therefore, in order to increase the heat transfer rate, it is necessary to increase the thickness of the gas layer, but this is limited by equipment space and cost.

The present invention is a continuous heat treatment furnace in which materials to be heated are heated with directly fired combustion gas, in which a permeable solid is installed at right angles or at a certain angle to the direction of movement of the material to be heated, and the combustion gas flows to the front through the permeable solid. In particular, it aims to convert the energy of combustion exhaust gas into solid radiation from an air-permeable solid and transfer it to the heated material, thereby increasing thermal efficiency and heat transfer rate.

Note that the breathable solid here refers to a porous material that has good air permeability and a suitable pressure drop.Metallic materials include foamed metal, sintered metal, etc., and refractory materials include ceramic porous materials and porous S.
There are products such as iC and alumina ball composite.

In general, this type of breathable solid is porous, so the heat transfer phenomenon between the breathable solid and the passing gas approximately approximates the heat transfer in a packed bed of granular material. The equivalent diameter is 0.01 to 1. If it is about Ovrm, it is 102 to 10
Since a large convective heat transfer coefficient of "kca17'm"H'c is obtained, the upstream surface temperature of the breathable solid is almost instantaneously heated to near the gas temperature. Furthermore, it is known that solid radiation from the permeable solid to the upstream side of the passing gas is extremely large.

Therefore, as shown in Fig. 4, facing the stretch material 2,
A structure in which a breathable solid body 7 is installed and combustion gas is discharged as shown by the actual arrow line can be considered. In this structure, the strip material 2
It is possible to convert the entire furnace wall surface facing the air-permeable solid into a gas-permeable solid, and all the combustion gases generated in the heating device 4 can be discharged through the gas-permeable solid. In addition, when the line is decelerated, cooling gas is blown in from the heating device or a separately provided cooling gas inlet, and the cooling gas passes through the breathable solid to lower the temperature of the wall facing the strip material in a short time. Overheating of the strip material can be prevented.

As mentioned above, the structure shown in Figure 4 has many advantages, but on the other hand, the superficial velocity (
gas passing rate) is limited. Generally, the greater the superficial velocity of gas passing through the gas permeable solid, the greater the amount of heat transfer can be obtained (Figure 5).

The structure shown in FIG. 4 has the drawbacks of a small superficial velocity and a small heat transfer coefficient.

The present invention aims to improve the above-mentioned drawbacks, and one embodiment will be described below with reference to FIGS. 2 and 3.

In the example of the present invention shown in FIGS. 2 and 3, permeable solids 7 are attached to both sides of the strip material in a direction perpendicular to the traveling direction of the strip material 2 in the NOF furnace. Here, strip material 2
In order to prevent damage to the air permeable solid 7 due to flopping, poor shape, etc., and to avoid scratches on the plate, the distance between the strip material 2 and the air permeable solid 7 is generally 100 to 15 Q mm.
It is necessary to take an interval of

Combustion gas generated by the heating device 4 flows toward the front facing the strip material 2. The temperature of the upstream side of the air-permeable solid 7 through which the combustion gas has passed is almost equal to the combustion gas temperature, and the solid radiation from the air-permeable solid 7 is larger than the conventional gas radiation. 2, more energy is transferred than the amount of heat transferred by conventional gas radiation, and the heat transfer rate increases. At the same time, the temperature of the combustion gas after passing through the air permeable solid 7 is lower than in the absence of the air permeable solid 7, and the thermal efficiency is increased.

In addition, when the air permeable solid 7 is arranged as shown in Fig. 2, r is
The superficial velocity of the combustion gas passing through is 0.25-1.9 Nm
/S, the above-mentioned superficial velocity conditions shown in FIG. 5 can be fully satisfied.

Above, the case of the strip material 2 as the material to be heated has been explained using a vertical continuous heat treatment furnace, but the same applies to a horizontal type, and also to continuous heat treatment furnaces for round steel, bulges, etc.
Application of the present invention may be possible.

The present invention is a continuous heat treatment furnace characterized by installing an air permeable solid having a heat transfer promoting effect at right angles or at a certain angle to the direction of progress of the material to be heated. And as shown in Figure 4, compared to a furnace installed parallel to the air-permeable solid material to be heated, it is possible to improve the heat transfer rate and thermal efficiency, so the length of the furnace equipment can be reduced for the same heating T/H. Alternatively, it can be treated in a continuous heat treatment furnace that has many features such as being able to lower the exhaust gas temperature.

[Brief explanation of drawings]

Fig. 1 is a longitudinal sectional view of a conventional continuous heat treatment furnace, Fig. 2 is a longitudinal sectional view of a continuous heat treatment furnace of the present invention, Fig. 3 is a partial detailed view of the present invention, and Fig. 4 is a continuous heat treatment other than the present invention. Furnace example vertical cross-sectional view,
FIG. 5 is a comparison diagram of heat transfer coefficients between the present invention and the device example shown in FIG. ■... Furnace wall, 2... Strip material, 3...
・Conveyance roll, 4...Heating device, 5...Heating chamber, 6...Preheating chamber, 7...Patent attorney representing the applicant for the breathable solid patent Tomoyuki Yafuki (and one other person) Figure 1 1311 Figure 4

Claims (1)

[Claims] In a continuous heat treatment furnace that heats the material to be heated with direct combustion gas, a permeable solid is placed at an appropriate angle to the direction of movement of the material to be heated, and the combustion gas is combusted by flowing toward the front through the permeable solid. A continuous heat treatment furnace that converts the energy of exhaust gas into solid radiation from an air-permeable solid and transfers it to the heated material, increasing thermal efficiency and increasing the heat transfer rate.