JPH03217787A - Electric heating type rotary kiln - Google Patents

Abstract

PURPOSE:To contrive the improvement of producibility and thermal efficiency by a method wherein a rod type electric heater is provided on the center line of a rotary kiln and the inner wall of the rotary kiln is constituted of a simple and durable structure sam as an ordinary rotary kiln while material to be heated is heated directly by radiation heat and convection heat from the electric heater as well as the heat transfer of conduction from the inner wall of the kiln. CONSTITUTION:Heat insulating bricks 2 are wound along the inside of the cylindrical steel skin 1 of a rotary kiln 14 while a round rod type electric heater 3 is provided along the center line at the center of the rotary kiln 14. Material to be treated is supplied quantitatively by a material supplying device 10 from a material hopper 9 into the rotary kiln 14 through a material supplying chute 11. The material, supplied into the rotary kiln, is heated by the transfer of heat from the heater 3 and the wall surface of the bricks 2 while being rolled, then, is discharged from a product discharging hole 12 and is taken out after being collected by a product chute 13. In this case, combustion flame is not used and, therefore, the product will never receiver oxydizing effect. The inner wall of the rotary kiln is constituted of simple and durable structure same as an ordinary rotary kiln in such a manner that the improvement of producibility as well as thermal efficiency can be brought further.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an electric heating rotary furnace for efficiently heating a large amount of workpieces in any atmosphere using electric heat. .

[Conventional technology]

When heating granular materials, the most efficient and economical method is to burn fuel to produce high-temperature gas and exchange heat with the combustion gas.

However, combustion gas contains gas components that react with substances, and the substances and gas components react at high temperatures.
Economic means may not be available.

For example, when reducing ore by heating it to a high temperature, if fuel is used as the heat source, the combustion gas of the fuel contains gas components such as oxygen that have an oxidizing effect on the processed material. Exposing the ore to the atmosphere goes against the original purpose. This method uses a rotary kiln to generate high-temperature combustion gas using coal, heavy oil, LPG, etc. as fuel, and reduces the ore in this process.This method is widely used because it uses cheap energy and can process large quantities continuously. Used for smelting.

However, as mentioned above, the combustion gas contains oxidizing gas components such as excess oxygen, creating an oxidizing atmosphere that is the opposite of a so-called reducing atmosphere, which is not always satisfactory for the purpose of improving the reduction rate. It's not a thing.

Methods of isolating the object to be treated from the oxidizing combustion air flow include coating the object itself, wrapping the combustion flame in a ceramic tube, and using radiation and conduction through the ceramic tube to indirectly isolate the object. A heating method is used, for example, as disclosed in US Pat. No. 1,871.848, Fig. It is disclosed in 3.

However, in the method as disclosed in the USP,
Thermal and mechanical strength becomes a problem at high temperatures, and it is difficult to manufacture large diameter and long ones. Temperature-wise, at most 10
It is only practical at temperatures below 00°C and can only be used to reduce iron oxide. In addition, the length is at most 2 to 3 m, making it impossible to completely surround the combustion flame and making it difficult to effectively isolate the object to be treated from the combustion gas atmosphere.

Therefore, it was unsuitable for the reduction treatment of ores containing metals such as chromium, which have a strong affinity for oxygen and are easily affected by combustion air currents.

[Problem to be solved by the invention]

The present applicant previously developed a rotary furnace with a large processing capacity that was designed to effectively isolate the processed material from the combustion gas of the fuel.
The iH4 structure was provided (Japanese Patent Application No. 62-219232).

However, if a completely indirect heating method is adopted using this equipment, the heating efficiency is poor and the fuel consumption rate is low.

In addition, if an attempt is made to raise the temperature to promote the reaction, damming of the raw material to the partition wall will occur, so there is a natural limit.

The present invention provides a method in which the inner wall of the rotary kiln has the same simple structure and durability as a normal rotary kiln, in place of the above-mentioned external heating rotary kiln, and which further improves productivity and thermal efficiency. It is intended for this purpose.

[Means to solve the problem]

In order to solve the above problems, in the present invention, a rod-shaped electric heater is installed on the center line of the rotary furnace, and the inner wall of the rotary furnace is made of the same simple structure and durability as a normal rotary kiln. We adopted a structure that aims to improve productivity and thermal efficiency by directly heating the object to be heated using radiation and convection heat transfer from the heater and conductive heat transfer from the inner wall of the kiln.

The present invention will be explained in detail below based on the drawings.

FIG. 1 shows a cross section perpendicular to the rotation axis of an example of an electric heating rotary furnace according to the present invention.

In FIG. 1, the rotary furnace 14 has a cylindrical iron shell 1 wrapped around an insulating brick 2, and a round bar-shaped electric heater 3 is installed along the center line of the furnace. Both ends 3a, 3b of the electric heater 3 are held by holding terminals 4, and in the example shown in FIG. 1, the holding terminals 4 are held by a raw material hood 5 and a product hood 6, which are separated from the rotary furnace. When the furnace length is short, the holding terminal 4 may be attached to the rotary furnace body l4 and rotated integrally with the rotary furnace body. In addition, the expansion due to heat of the heater 3 and the holding terminal 4
Bushers are installed at both ends of the holding terminal 4 to absorb shrinkage.
7 and always press down with constant pressure. Further, power is supplied to the holding terminal 4 by a water-cooled power supply conductor 8.

The material to be treated is quantitatively cut out from the raw material hopper 9 by the raw material supply device 10 and is supplied into the rotary furnace 14 through the raw material supply chute 11 .

The raw material supplied into the rotary furnace is transferred to the heater 3 while being transferred.
It is heated by heat transfer from the wall surface of the brick 2, is discharged from the product discharge hole 12, and is collected and taken out by the product shoe 13. In this case, since no combustion flame is used, there is no oxidation effect. Furthermore, by introducing gas into the rotary furnace, the raw material can be heated in any atmosphere.

If there is gas generated, it is discharged from the system through the gas vent duct 17. The rotary furnace 14 is supported by support rollers 16 via a support ring 15, and is driven and rotated by power (not shown).

The rod-shaped heater 3 and the holding terminal 4 are made of graphite or silicon carbide, etc., and have a strong bending strength of 150 kg/c or more, a high heat resistance of 1600°C or more, and 10-2 to 10-4 Ω.
Appropriate materials are those that have a uniform, appropriate electrical resistivity and are less abrasive at high temperatures. If you use a heating element like the one above, 2
A high temperature of 000°C or higher can be easily obtained.

It is preferable to use graphite, which has low electrical resistance, for the holding terminal 4.

When graphite is used for the heater 3, if the diameter of the heater 3 portion is made smaller than the holding terminal 4, heat generation in a portion of the heater will increase. Connection of heater 3 using holding terminal 4
The holding method may be a screw type, a spherical contact type, or any other type that provides as little contact resistance as possible.

As described above, the holding terminals 4 and raw material supply chute 11 may be held by a hood that is separated from the rotary furnace, or as shown in FIG. It may be held in

A spring plate type seal or a sliding type seal mechanism is suitable for the seal 18 for preventing leakage of gas in the furnace and inflow of gas from the outside.

[Function] As explained above, if an electric heater is installed in the center of the rotary furnace and the raw material inlet, product outlet, electric heater insertion part, etc. are structured to prevent outside air from entering, the raw material can be efficiently heated in large quantities in any atmosphere. Heating is performed using radiation heat transfer from the electric heater and conduction heat transfer from the rotary furnace wall.

〔Example〕

The inside of a rotary furnace with an outer diameter of 2.5 (m) and a length of 5 (m) as shown in Figure 1 was lined with 25cII 1-thick alumina bricks, and a graphite heater with a diameter of 25G was installed in the center. . A raw material prepared by mixing 3 or less chromium ore and coke with the composition shown in Table 1 at the mixing ratio shown in Table 1 is supplied to this electric heating rotary furnace at a rate of It/h, and the heater is heated at 1t/h.
Supplying 200kW of electricity to power the electric rotary furnace at 0.2r
When the reduction reaction was carried out while rotating at pm, the reduction rate of the resulting product was 98.4 (%) for FeO, and 98.4 (%) for C.
“The return rate of 203 was 90.4 (%).

Table 1 By using the heating furnace of the present invention, a mixture of chromium ore and coke of 3 seconds or less can be subjected to a reduction reaction without being affected by oxidizing combustion gas, and the reduction rate is 90%. The reduction rate can be increased significantly compared to about 30% in a method in which the oxidizing combustion gas and the raw material are in direct contact with each other.

〔effect〕

By using the apparatus of the present invention, a large amount of raw materials can be efficiently heated at high temperatures in any atmosphere.

In other words, since the heat generating part is located in the center of the furnace, there is less heat radiation loss.
An insulated furnace structure can be easily obtained. Furthermore, since the ratio of the furnace internal volume to the raw material throughput is reduced, the apparatus becomes compact.

[Brief Description of the Drawings] Fig. 1 is a sectional view for explaining one embodiment of the present invention;
FIG. 2 is a diagram showing another embodiment of the heating element support structure.

Claims (1)

[Scope of Claims] 1) An electric rotary furnace characterized in that a rod-shaped electric heater is installed in the center of the rotary furnace along a rotation axis. 2) The electric heating rotary furnace according to claim 1, wherein the electric heater is a graphite heating element.