JPS5811723A - Heating furnace - Google Patents

Abstract

PURPOSE:To reduce thermal loss and to economize energy by forming gas circulating flow between a heating chamber and a circulating line by means of a circulating fan, and recovering the sensible heat of the gas flowing out from the heating chamber and heating the gas flowing into the heating chamber by means of air permeable solids. CONSTITUTION:An upper vent port 9 and a lower vent port 7 partitioned respectively with air permeable solids 8 are provided in the upper and lower part of a heating chamber 5, and a circulating pipeline 13 communicating the port 9 and the port 7 is provided. A circulating fan 14 is provided in the pipeline 13 to circulate the gas in the chamber 5 through the port 9 then through the line 13 and the port 7 into the chamber 5. Therefore, the high-temp. gaseous flow is generated in the chamber 5, by which the soaking of objects to be heated and the heat transfer to said objects are accelerated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heating furnace for heating or heat treating objects to be heated, such as steel pieces and plates.

In a heating furnace, which heats or heat-treats the object to be heated in a heating chamber equipped with a heating device such as a burner or heater, the temperature at the top of the heating chamber tends to be higher than the temperature at the bottom, resulting in a temperature difference of 50°C or more. often occurs. In this case, a temperature difference also occurs in the object to be heated, making uniform heating difficult. Therefore, in heat treatment furnaces and the like that require uniform heating, a fan is installed in the furnace to stir the gas in the furnace in order to equalize the temperature in the furnace and promote convective heat transfer. However, according to this method, the upper limit of the applicable furnace temperature is 800 to 900° C. due to the high temperature strength of the impeller portion of the fan that rotates at high speed.

This invention was made in view of the above points, and it is possible to equalize the temperature of the heated object in the furnace and promote heat transfer to the heated object, even when the temperature inside the furnace is high. The purpose is to provide an applicable heating furnace.

However, the gist of the present invention is to provide a heating furnace that heats objects to be heated in a heating chamber equipped with a heating device, in which upper and lower vents are provided at the upper and lower parts of the heating chamber, respectively, and are partitioned by air-permeable solid material. A circulation path is provided that communicates the upper vent and the lower vent, and the gas in the heating chamber is introduced into the circulation path from the upper vent through the lower vent. The heating furnace is characterized by being equipped with a circulation fan that circulates the air within the heating chamber.

In the present invention, the term "breathable solid" refers to a solid made of a heat-resistant material such as metal or ceramic, and formed into a shape having air permeability such as a net shape, a honeycomb shape, a folded shape, a porous shape, etc., and having an appropriate thickness. This air-permeable solid is considered to be equivalent to a large number of small spheres or small diameter wires, so its effective surface area is extremely large, and when gas is passed through this air-permeable solid, the convective heat transfer coefficient is significantly larger.

An embodiment of the present invention will be described below with reference to FIGS. 1 to 4.

In the figure, 1 is a batch-type heating furnace, 2 is a box-shaped furnace body, and 3 is a batch-type heating furnace.
is the hearth. 4 is a furnace side wall, 5 is a heating chamber formed by being surrounded on all sides by the furnace side wall 4, and 6 is a radiant tube attached to penetrate this heating chamber. 7 is a lower vent at the bottom of the heating chamber 5, and 8 is a partition plate-like breathable solid piece attached to this lower vent, which is made of stainless steel wire mesh (wire diameter 0.
5jIjI.

14 meshes) were laminated in 15 layers to a thickness of 13 mm, the edges were reinforced with a stainless steel frame, and the four peripheries were held by the furnace side wall 4. Reference numeral 9 denotes an upper vent of the heating chamber 5, and 10 denotes a partition plate-like breathable solid that is detachably attached to the upper vent and has the same structure as the breathable solid 8. 11 is an upper chamber formed between the breathable solid 10 and the furnace lid 3; 12 is a lower chamber formed between the breathable solid 8 and the furnace bottom; 18 is the upper chamber 11 and the lower chamber 1;
2 is a circulation pipe whose both ends are open, and 14 is a circulation fan provided in the middle of this circulation pipe. The circulation fan 14 is composed of a high temperature fan, and its discharge port is connected to the lower chamber 12 side. Note that a grate for placing objects to be heated is provided in the heating chamber 5, but its illustration is omitted.

In the heating furnace I having the above configuration, if the object to be heated is charged into the heating chamber 5 and the heating chamber is heated by the radiant tube 6, radiation heat transfer from the radiant tube 6 is achieved. The object to be heated is heated.

In addition, the atmospheric gas (hereinafter simply referred to as gas) in the heating chamber 5 is heated to 1000 to 1200°C by radiation and convective heat transfer from the radiant tube 6, and the object to be heated is heated by convective heat transfer from this gas. The gas, whose temperature has risen as it is heated, flows upward from the upper vent 9 due to the draft effect caused by the decrease in specific weight, and the suction effect of the circulation fan 14, which is more powerful than the draft effect. At this time, since the air-permeable solid IO has a large surface area, convective heat transfer causes high temperatures (approximately 1000
°C), and the gas passes through the upper chamber 11, the circulation pipe 18, the lower chamber 12, and the lower ventilation lower in a state where the temperature has decreased by 200 to 400 °C.
Due to the pushing action of , it circulates and flows into the heating chamber 5 again. At this time, the air-permeable solid 8 is at a high temperature due to radiation heat transfer from the radiant tube 6, so when the low-temperature gas passes through the air-permeable solid 8, which has a large surface area, its temperature is raised by 200 to 400°C due to convective heat transfer. It flows into the heating chamber 5 as a high-temperature gas and heats the object to be heated by convection heat transfer.

The radiant energy emission state in 10 parts of the breathable solid will be explained using the schematic diagram in FIG.
Since the layer has a thickness X in the gas flow direction, a temperature gradient shown by a curve 15 is generated within the layer due to convective heat transfer with the passing gas. And each layer Xi,! 2,...
・At x6, the radiant energy emitted to the upstream side (1) and downstream side (4) of the gas is indicated by arrows y1, y2, etc.
・y5, and Zl, Z2, ... Z5, but among these, the radiant energy z1, Z2.74,
Since y6 is attenuated by the shielding effect of the breathable solid, the main part of the radiant energy 16 is directed toward the upstream side of the gas in the ■ direction, and is effectively used to prevent temperature drop by heating the heated object and being absorbed by the gas. It is. Due to the same phenomenon in 8 parts of the breathable solid (however, the gas flow direction is opposite to that in Figure 3), the main part of the radiant energy is directed inward to the heating chamber 5, and is effectively used for heating the object to be heated, etc. .

In this way, the heating chamber 5, the upper chamber 11 and the circulation pipe 18
A circulating flow of gas is formed between the upper and lower chambers 12 by the draft action and the pumping action of the circulation fan 14, which is more powerful than this, and the high temperature gas flows in the heating chamber 5 as an upward flow. , the temperature distribution within the heating chamber 5 becomes uniform, and convective heat transfer to the object to be heated is further promoted. In addition, since the breathable solid 8.10 creates a significant temperature difference before and after it and functions as a kind of heat insulating material, the gas temperature outside the heating chamber becomes low, and the heat resistance limit of the circulation fan 14 is
The temperature may be 200 to 400°C lower than the gas temperature inside.
Furthermore, heat loss from the furnace bottom, furnace lid 3, circulation pipe 13, etc. is reduced.

Next, the heating furnace 1 with the above configuration (heating chamber length 1900',
The results of the inventor's experiment using the same height (950f11, 1000111f) are shown below. When the combustion amount of the radiant tube 6 was set to 85,000 kcal per hour, and the object to be heated W11W2 (both cube-shaped ordinary steel materials with a − side of 1100 t) placed at the positions shown in FIGS. 1 and 2 was heated,
A temperature rise curve of the heated object as shown by the solid line in FIG. 4 was obtained.

In addition, as a comparative example, the broken line in the figure shows the upper chamber 11 and lower chamber 12 in which the circulation fan 14 is not used in FIG.
This is a temperature rise curve of the heated object in the case of directly connecting through the circulation pipe 20 (other conditions are the same as above). As can be seen from FIG. 4, according to the apparatus of the present invention, the temperature difference between the heated objects W1 and W2 placed in the upper and lower parts of the heating chamber 5 is 9. °C
The temperature reached by the object to be heated was also about 40°C higher than that of the comparative example (both after 3 hours), and the temperature uniformity in the heating chamber and heating performance due to the present invention were improved. improvement,
A decreasing trend in heat loss is clearly demonstrated.

Although the above description has been made for a batch-type heating furnace, this invention can also be applied to a continuous-type heating furnace, and the heating device for the object to be heated can be a heating device other than a radiant tube, such as a direct flame burner or an electric heater. may also be used.

As explained above, according to the present invention, a circulating flow of gas is formed between the heating chamber and the circulation path by the circulation fan, and the sensible heat of the gas flowing out of the heating chamber is recovered by the air-permeable solid and transferred to the heating chamber. Since the temperature of the inflowing gas is raised, a high-temperature gas flow is generated in the heating chamber, and it is possible to equalize the temperature of the object to be heated and promote heat transfer to the object. In addition, since the circulating gas outside the heating chamber is lower temperature than the gas inside the heating chamber, heat loss is reduced and energy savings can be achieved, and the present invention can be applied without problems even when the temperature in the heating chamber exceeds the heat resistance limit of the circulation fan. It can be done.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a heating furnace showing an embodiment of the present invention;
2 is a cross-sectional view taken along the line A-A in FIG. It is a temperature rise diagram of a hot substance. 1... Heating furnace, 5... Heating chamber, 6... Radiant tube, 7... Lower vent, 8... Breathable solid,
9...Top vent, 10...Breathable solid, 11...
・Upper chamber, 12...Lower chamber, 13...Circulation pipe, 1
4... Circulation fan. Applicant: Ryozo Echigo, Daido Steel Co., Ltd. Agent: Masao Inui

Claims (1)

[Claims] In a heating furnace that heats an object to be heated in a heating chamber equipped with a heating device, upper and lower ventilation holes are provided at the upper and lower parts of the heating chamber, respectively, and are partitioned by a breathable solid material. A circulation path communicating with the lower vent is provided, and a circulation fan is installed in the circulation path to circulate gas in the heating chamber from the upper vent, through the circulation path, the lower vent, and into the heating chamber. A heating furnace characterized by: