JPS63130726A - Method and device for operating rotary kiln for reducing chromium ore - Google Patents

Abstract

PURPOSE:To accelerate reduction of ore pellets and to prevent reoxidation by providing a suction fan near a drop part where the reduced pellets of chromium ore are discharged from a rotary kiln. CONSTITUTION:The reduced pellets 4 of the chromium ore formed by burning fuel in the rotary kiln 1 by a burner 2 are taken out via a chute 5 of a firing port hood 3 and are introduced into a cooler 30. The suction fan 7 for sucking the air in the hood 3 is provided near to the juncture between the hood 3 and the cooler 30 or to the cooler 30 side. The leakage of the air into the rotary film 1 or the suction of a large amt. of the vapor, etc., generated by the cooler 30 into the kiln 1 is thereby prevented and the high reducibility of the pellets 4 is maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and apparatus for operating a rotary kiln for reducing chromium ore, and more particularly to measures for improving the reduction rate of chromium ore in a rotary kiln.

[Conventional technology]

An example of a process flow sheet for reducing chromium ore using a rotary kiln is shown in Figure 2.

Powdered chromium ore such as chromium sand is passed from the storage tank 11 to the belt conveyor 13, and is charged into the granulator 14 together with the mixed material from the other material tank 12, where it is granulated into an appropriate size, for example, 15 to 20 mm. be done.

The granulated ore is dried and heated within the preheater 20 while being conveyed by a grate conveyor 21 or the like. The preheater 20 is divided into classrooms and is connected by fans from each room.
．． 24 to suck the hot air.

The preheater is divided into, for example, three chambers, and the gas temperature is
Room 200℃, 2nd room 550'C1 3rd room too~10
It's like 50 degrees Celsius. These gases are dissipated into the atmosphere through the electrostatic precipitator 25, the main suction fan 26, and the chimney 27, or are used as other heat sources.

The raw material dried and heated in the preheater 20 is transferred to the hopper 2
8 to the rotary kiln 1 together with the exterior carbon material supplied via the chute 29.

In the rotary kiln 1, fuel is combusted by the burner 2, and the raw material is heated to 1300 to 1400'C and reduced. The target reduction rate at this time is, for example, 50% or more for Cr, Fe
85% or more (X).

The reduced pellets heated and reduced in the rotary kiln pass through a hood 3 and a chute 5 and enter a cooler 30, where they are cooled and turned into finished products.

[Problem that the invention seeks to solve]

As described above, in the chromium ore reduction process, the chromium ore that has been heated and reduced by the burner in the rotary kiln 1 is discharged from the rotary kiln, and is supplied to the cooler 30 through the hood 3.

In this case, as shown in Fig. 1, near the outlet where the chromium ore reduced pellets 4 are discharged from the rotary kiln 1 and inside the burner hood 3, the ejector effect of the mainstream flow of the main stream 2 and the chute due to temperature. 5, upward flow within hood 3, seal between hood 3 and kiln shell, cooler 3
An oxidizing atmosphere is created due to air intrusion from the inlet seal portion of the cooler and other places, and a large amount of steam generated in the cooler. This oxidizing atmosphere inhibits the reduction of the chromium ore pellets 4 and oxidizes their surfaces. Even if this oxidized layer is thin, since it is a large area of the outer surface of the pellet, the amount of oxidation (volume) becomes large and the reduction rate decreases significantly.

Chromium oxide is inherently difficult to reduce, so it is important to maintain a high temperature and a reducing atmosphere. In particular, in a rotary kiln, the air sucked in or the steam generated by the cooler is an oxidizing gas, which consumes the coal contained in the pellets in the kiln or preheater, reducing the amount of carbon material contributing to reduction.

Possible ways to prevent such a decrease in the reduction rate are: (1) Eliminating the oxidizing atmosphere; (2) Containing a large amount of reducing agent; and (2) Not maintaining the temperature at high temperatures.

If the reducing agent is contained in an excessive amount in the pellet, the strength of the beret will decrease and it will cause powdering, so it is limited. Therefore, the present invention focuses on the above-mentioned point (1) and provides a means to prevent air leakage into the rotary kiln or suction of a large amount of steam generated by the cooler into the rotary kiln, thereby promoting the reduction and reoxidation of the chromium ore pellets. The aim is to prevent this and maintain a high return rate.

[Means for solving problems]

The method of the present invention is a method of operating a rotary kiln for reducing chromium ore, which is characterized by maintaining the airflow on the raw material charging side of the rotary kiln in a reducing atmosphere to improve the reduction rate of chromium ore. Further, the apparatus of the present invention for suitably carrying out this method, as shown in FIG. The above object is achieved by connecting a suction fan 7 for suction.

[Effect]

According to the present invention, the carbonaceous material in the chromium ore pellets is not consumed in the preheater or the low-temperature part of the kiln.
Reduction by the carbonaceous material progresses in the reduction reaction zone.

The device of the present invention releases the pressure inside the firing hood 3 and sucks in a large amount of air or steam generated by the cooler from each gap in the hood 3, so that the internal coal is not consumed in the kiln or preheater. The reduction rate of chromium ore berets can be increased.

〔Example〕

The present invention was carried out by attaching a suction fan to the hood on the firing side of a rotary kiln for reducing chromium ore.

Table 1 shows a comparison of the specifications before and after implementation.

By suctioning the oxidizing gas in the hood, the suction air around the tweed is drawn by the suction fan without entering the kiln. Therefore, the estimated intake air amount calculated from the kiln exhaust gas composition is reduced, and the reduction rate of the discharged pellets is improved.

However, if the suction amount is increased to such an extent that the amount of suction air becomes O, the amount of coke oven gas burned will increase at the same reduction rate, which is not a good idea.

As is clear from Table 1, by implementing the method of the present invention using the apparatus of the present invention, it was possible to improve the reduction rate of chromium ore pellets.

〔Effect of the invention〕

The present invention has improved the reduction rate of chromium ore pellets when using a rotary kiln.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the vicinity of a kiln hood showing an embodiment of the present invention, and FIG. 2 is a process flow sheet for reducing chromium ore using a rotary kiln. 1... Rotary kiln' 2... Burner 3... Burner hood 4... Chrome ore reduction pellets 5... Chute 7... Suction fan

Claims (1)

[Claims] 1. A method for operating a rotary kiln for reducing chromium ore, characterized by maintaining the air flow on the raw material charging side of the rotary kiln in a reducing atmosphere to improve the reduction rate of chromium ore. 2. A rotary kiln for reducing chromium ore comprising a rotary kiln connected to a combustion chamber hood, characterized in that the combustion chamber hood is equipped with a suction fan for sucking leaked air.