JPH01168824A - Production of reduced ore pellet - Google Patents

Abstract

PURPOSE:To improve reduction ratio of pellet by containing calcium chloride in the pellet at the time of drying, heating and reducing ore-contained green pellet in a reduction furnace. CONSTITUTION:The finder and water having prescribed ratio are added to chromium ore and coke crushed at the prescribed grain size and kneaded with a pug mill 7, and humidity conditioning and pelletizing are executed with a disk pelletizer 1, to form the green pellet having 10-15mm size (about 15-17wt.% carbon content). This green pellet is conveyed with grate conveyor 3 and dried and heated with a pre-heater 2 and sent into a rotary kiln 4 and reduced by heating with a burner 6 and cooled with a cooler 5, to make the reduced chromium ore pellet. Then, the calcium chloride is beforehand added to the green pellet at about 0.1-0.5wt.% as CaCl2. By this method, the reduction ratio of the reduced chromium ore pellet is improved, and many kinds of unit consumptions at the stainless steel blowing process in a converter are reduced and blowing time is shortened and the productivity, etc., is improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention involves drying, heating, and drying green pellets containing ore in a reduction furnace equipped with a preheater and a rotary kiln.
The present invention relates to a method for producing reduced ore pellets by reduction.

[Conventional technology] Using a reduction furnace with a preheater and a rotary kiln,
An example of a process flow sheet for producing reduced chromium ore pellets is shown in FIG.

First, a small amount of a caking agent, such as bentonite, was added to chromium ore and coke that had been crushed to a predetermined particle size in a predetermined ratio, and water was added to about 8 to 9% by weight in a mixing machine such as Pug Mill 7, and the mixture was mixed. The material is humidified and granulated using a disc pelletizer 1 to form green pellets of about 10 to 15 mm.

Here, the coke that is the interior carbon material is Cr in the chromium ore.
, it is common to add 5 equivalents to reduce Fe oxide to metal, and the carbon content in green pellets is 15
It is about 17% by weight.

The granulated green pellets are dried and heated in a preheater 2 while being conveyed by a great conveyor 3. Preheater 2 is usually divided into three chambers.

The gas temperature is, for example, 220℃ in the third chamber and 550℃ in the whip second chamber.
The temperature of the first chamber is 1000° C. In particular, the combustion exhaust gas from the rotary kiln 4 directly enters the first chamber as shown by the broken line arrow, so the gas temperature is the highest.

The pellets preheated by a preheater 2 enter a high-temperature rotary kiln 4, are heated by a burner 6, are reduced by an internal carbon material, and are then cooled by a cooler 5 to become reduced chromium ore pellets as a product.

However, the combustion exhaust gas composition of the rotary kiln 4 is 1, for example, H2O: 15.6% by volume, GO2: 13.5% by volume,
CO: 4.1% by volume, N2: 66.8% by volume, which contains about 30% by volume of oxidizing gas (GO2+I(20)), and the gas temperature is as high as about 20°C.
In the first chamber of the preheater 2, the carbonaceous material present in the surface layer of the pellet is decarburized by the reaction C+820=GO+H2C+C02=2GO. Since this amount generally reaches about 20% by weight of the total carbonaceous material, conventional processes have reached the limit of achieving a reduction rate of 80% for reduced ore pellets.

Conventionally, there was no decisive measure to suppress decarburization from pellets in the preheating machine, and the solution was to increase the blending ratio of the interior carbon material to compensate for the amount of carbon lost in the decarburization reaction. Increasing the amount of carbonaceous material has the fatal disadvantage of significantly lowering the strength of the pellets and increasing the powder ratio, and this also applies to methods for producing reduced ore pellets other than reduced chromium ore pellets.

[Problem to be Solved by the Invention 1] The present invention provides a method for minimizing the amount of decarburization in a preheater without causing problems such as a decrease in the strength of reduced ore pellets and an increase in powder ratio. The purpose is to make it possible to dramatically improve the reduction rate of reduced ore pellets.

[Means for Solving the Problems J] As a result of repeated research in order to solve the above-mentioned problems of the prior art, the present inventors have found that when calcium chloride is added to the green pellets, the strength of the green pellets decreases and the pellets become powdery. The present invention was achieved by obtaining the knowledge that it is possible to reduce the decarburization rate and improve the reduction rate without causing an increase in the decarburization rate.

[Operation] The present invention will be explained using an example in which chromium ore is used as the ore.

Chromium ore = 79 parts by weight Coke = 18 parts by weight Bentonite: For the blended raw material consisting of 3 parts by weight, calcium chloride CaCβ2
Add 0.1 to 1.0% by weight as green pellets with a diameter of 10 mm, and calculate the calcium chloride addition rate and decarburization rate.
The relationship between preheated pellet strength and reduction rate was tested.

Figure 1 shows the relationship between the decarburization rate and the calcium chloride addition rate when the green pellets were left for 60 minutes in an atmosphere of 30% CO2 and 0% N2 by volume at 1000°C. The decarburization rate decreases markedly when adding .1% by weight or more, but even greater effects can be obtained even when adding 0.5% by weight or more.

The test results show that adding up to 0.5% by weight of calcium chloride is sufficient to suppress decarburization in the preheater.

Figure 2 shows the relationship between the strength of each pellet and the addition rate of calcium chloride when left in a N2 atmosphere at 900°C for 40 minutes. Addition of calcium chloride up to 0.5% by weight causes almost no change in pellet strength. is not observed, 0.7% by weight
It seems that the strength decreases when the above amount is added.

Figure 3 shows CO2: 30% by volume and N2 near 0 at 1000℃.
After holding the volume% atmosphere for 60 minutes, switch to N2 atmosphere 1
The relationship between the reduction rate and the addition rate of calcium chloride is shown when the temperature is raised to 300°C and held for 45 minutes.The reduction rate improves with the addition of calcium chloride, but even if it is added at 0.5% by weight or more, it does not increase. effect cannot be obtained.

Although the reason why calcium chloride exhibits the above effect is not clear, it is thought to be due to the effect of protecting the green pellets from oxidizing gases by chlorine gas.

The effect of adding calcium chloride to reduced ore pellets can be obtained in substantially the same way with ores other than chromium ore.

[Example J Using a blended raw material consisting of 9 parts by weight of chromium ore nia, 18 parts by weight of coke, and 3 parts by weight of bentonite, CaCβ2 relative to the blended raw material was used.
0.3% by weight of calcium chloride was added as an aqueous solution to the raw materials in the pug mill, and the raw materials were humidified and kneaded, then humidified and granulated using a disk pelletizer to form green pellets.

The green pellets were dried, heated, and reduced under the following operating conditions, and the reduction rate and the -5 mm powder rate are shown in Table 1, along with a comparative example in which calcium salt was not added.

Table 1 By adding calcium chloride, an effect of improving the reduction rate by about 5% was obtained, and no increase in the powder ratio was observed.

[Effects of the Invention] The method of the present invention improves the reduction rate of reduced ore pellets.1 For example, the improvement of the reduction rate of reduced chromium ore pellets reduces the unit consumption of each cypress in the stainless steel blowing process in a converter, and reduces the blowing time. The usefulness of the present invention is extremely large, such as the improvement of productivity by shortening the time, and the present invention is effective not only in the production of reduced chromium ore pellets but also in the production of other reduced ore pellets.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between calcium chloride addition rate and decarburization rate, Figure 2 is a graph showing the relationship between calcium chloride addition rate and preheated pellet strength, and Figure 3 is a graph showing the relationship between calcium chloride addition rate and reduction rate. FIG. 4 is a diagram showing an example of a process flow sheet for producing reduced chromium ore pellets. l... Desk pelletizer 2... Reserve area 1m 3... Great conveyor 4... Rotary kiln 5... Cooler 6... Burner 7... Pug mill 8... Kiln exhaust gas applicant Kawasaki Steel Kawatetsu Mining Co., Ltd.

Claims (1)

[Claims] 1 Green pellets containing ore are dried, heated, and
A method for producing reduced ore pellets, characterized in that the green pellets contain calcium chloride. 2. The method for producing reduced ore pellets according to claim 1, wherein the ore is chromium ore.