JP2022501497A - A method for utilizing side currents containing metal oxides in the ferrochrome smelting process. - Google Patents

Abstract

The present invention is intended to briquette metal oxide dust and fine materials with a cement-based binder. After this, briquettes can be supplied to the arc furnace for ferrochrome production through the already existing inlet system. [Selection diagram] Fig. 1

Description

The present invention relates to the recycling of metal oxides to recover metals by using cement-based briquettes in a submerged arc furnace for ferrochrome production. In this method, side currents from ferrochrome and fine steel production are formed into briquettes with cement, which briquettes can be fed to the submerged arc furnace through a standard inlet system and through a preheating furnace. In submerged arc furnaces, metal oxides are reduced to metals, primarily carbon, and the metals are recovered in ferrochrome products.

In a ferrochrome furnace, materials with a small particle size cannot be used because they do not reach the reaction region but are stopped by the gas flow present on the charge layer. The metal oxide dust produced in the production of ferrochrome and stainless steel is typically very fine and cannot be supplied to a submerged arc furnace or the like. In addition, the fine metal oxides increase the conductivity of the charge layer inside the furnace and reduce the production capacity. For these reasons mentioned above, all fine materials must be agglomerated before being supplied to the submerge arc furnace for ferrochrome production.

The material (s) formed into the briquette are typically mixed with cement and water in a concrete mixer. The mixture is used to form a briquette of the desired size on a briquette machine and dried for the desired period to reach the required strength. The manufacturing method described herein is the same as that used for manufacturing cement-based stone plates.

Under selected conditions, metal oxides from ferrochrome production that can be reduced in a submerged arc furnace can be used to form briquettes. In fine steel production, suitable debris are, for example, dust from filter plants, flakes from casting and rolling mills, slurry from water treatment, shot blast dust from cold rollers, and acids in annealing-pickling processes. It is a metal precipitate formed by the treatment. In ferrochrome production, a suitable debris is, for example, a fine material formed during pelletization and furnace feeding. In order to improve the metal yield, a suitable reducing material such as carbon can be added to the briquette to accelerate the reaction rate.

The potential of the present invention in ferrochrome production is to improve chromium yields, reduce waste, better use of raw materials, and avoid landfill costs. By modifying the composition of the briquette, the composition of ferrochrome can be modified as desired by the customer. In fine steel production, it would be advantageous to improve the current recycling of sidestreams and recycle cheaply.

Previous solutions to problems related to recycling sidestream were based on a separate dust smelter to form briquettes with organic binders, and a direct reduction process. Dust smelters and direct reduction processes are difficult due to the large investment required and the potential for high running costs. The use of organic binders such as molasses can result in briquette disintegration before reaching the reaction region of a submerged arc furnace for ferrochrome production. In fine steel production, the use of these briquettes in an arc furnace reduces energy efficiency and thus yields.

U.S. Pat. No. 8,409,320 (B2) briquette oxide-containing steelmaking sidestreams with syrup and supply them to the arc furnace of a smelting plant, where the metal is reduced and the slag is boiled. It discloses that. This patent does not cover using cement to briquette the oxide material and supply the briquette to a submerged arc furnace for ferrochrome production or to an arc furnace for steel production.

US Patent Application Publication Nos. 2014/0352496 and 2013/192422 disclose the preparation of cement and molasses-based briquettes and their use in arc furnaces for the production of fine steel. This patent focuses on boiling slag with briquettes in an arc furnace. This patent does not cover the use of briquettes in submerged arc furnaces used in ferrochrome production.

There is no publication presenting prior art using submerged arc furnaces used in ferrochrome production. Submerged arc furnaces cannot create conditions for boiling slag and are not suitable for reducing material from boiling slag by reaction in the reduction zone and turbulent gas.

The solution according to the invention is based on supplying the ferrochrome furnace with material from the sidestream of ferrochrome and fine steel production, which would be difficult to use with any other technique. In addition, it is possible and rational to supply other sidestreams containing metal oxides that can be reduced with carbon from the metal and mining industries to the ferrochrome arc furnace.

The chemical composition of the main calibration components of the feed material is presented in Table 1.

Using the materials according to Table 1, the mixture is formed with cement and water. In addition to cement as a reinforcing material, for example, blast furnace slag may be used as desired. For example, the mixture is cast as a 60 x 60 x 60 mm size briquette with 6 corners. Typically, the finished briquette contains 2-30% cement, some of which (10-70%) may be replaced, for example, with blast furnace slag. The size of the briquette depends on or is influenced by the supply or inlet system of the submerged arc furnace used. Briquettes are dried under outdoor conditions for about 4 weeks to reach their final strength before being fed to the furnace. It is also possible to use an accelerator and heat to adjust the hardness. If desired, a 0-25% reducing agent (coke, ferrosilicon, aluminum, silicon carbide) may be added to the briquette, thereby reducing the reducing agent itself as it is physically close to the metal oxide. It will be better.

Preferably, the briquette is fed to the submerge arc furnace via a preheating oven that dries the briquette in a CO _{2 atmosphere and heats it to approximately 500 ° C.} This breaks the silicate bond and replaces it with a carbonate bond, but maintains the strength of the briquette. The briquette flows as a plug flow through the inlet pipe to the pot of the submerged arc furnace, and heating is started at the same time by the gas of the furnace. When the briquette reaches the melting zone, the metal oxide in the starting reduction is first partially reduced in iron oxide by the pot gas and finally in chromium oxide. In a submerged arc furnace for ferrochrome production, the cement contained in the briquette raises the pH of the slag and thus reduces the chromium content of the slag by approximately 0.5-5%. The reduced metal melts and dissolves in the metal in the furnace, the melt melts out of the furnace as a castable alloy, the composition of which depends on the metal content of the feed. In practice, for example, all Ni, Mo, and Fe debris in the feed are reduced to metal. The composition of the metal and slag is presented in Table 2.

一実施形態では、触媒などの様々な二次原料を、ブリケット原料として使用して、金属酸化物中の金属をフェロクロム中へと回収することを可能にする。これらの原料は、ニッケル、モリブデン、チタン、銅、マンガン、又はコボルト（cobolt）を含有する金属酸化物であり得る。

In one embodiment, various secondary raw materials such as catalysts can be used as briquette raw materials to allow the metal in the metal oxide to be recovered into ferrochrome. These raw materials can be nickel, molybdenum, titanium, copper, manganese, or metal oxides containing cobolt.

Next, the present invention will be described in more detail with reference to the accompanying drawings.
The Ellingham diagram which illustrates the reduction order of a metal oxide is shown. Changes in nickel and manganese levels in ferrochrome products during supply experiments are shown. The change in the chromium content of the ferrochrome product during the experiment is shown. The carbon and silicon contents of the ferrochrome product during the experiment are shown.

The reduction order of the metal oxide is defined by the Ellingham diagram of FIG. In the arc furnace under the selected conditions, different metals that can be reduced by carbon can be seen. Carbon is capable of reducing the metal above the line that presents the reaction of carbon. The reduction reaction itself depends on temperature and pressure. In practice, the rare element is reduced first, so the reduction order is Ni, Mo, Fe, Cr. The diagram also shows the reaction equations for reduction, eg, individual equations for different oxidation stages of iron, which vary with the oxidation stage.

According to the present invention, cement is the only binding material capable of assembling briquettes at preheating furnace temperatures of 400-600 degrees. In addition, it provides the briquette with adequate mechanical strength so that the briquette can be supplied into the furnace through the inlet system. The chemical bonds of the cement are transformed into carbonate bonds by the heat of the preheating oven, thereby maintaining the original strength of the briquette almost completely. Also, by using cement-based briquettes, lime is provided to the submerge arc furnace by increasing the pH of the slag, resulting in higher reduction and higher yield of chromium.

The particle size distribution of the briquette depends on the raw material used in the formation of the briquette. The particle size distribution should follow the Fuller curve as closely as possible, as it allows to minimize the amount of cement used and provide raw material savings. The amount of briquette added can be up to 20% by weight, preferably 3-10% by weight, of the total material supply, depending on the analysis of the currently obtained slag material.

The present invention is not limited to the raw materials presented above. By this method, other side currents containing metal oxides can also be economically used. For example, oxides from the nickel industry will blend nickel with ferrochrome, and ferrochromes thus formed will be better suited for the production of austenitic steel grades.

FIGS. 2-4 show the results of an experiment in which a cement-based briquette containing flakes from fine steel production was supplied to a submerged arc furnace used in ferrochrome production.

FIG. 2 shows that changes in the nickel and manganese content of ferrochrome products during supply experiments, i.e., metal oxides, are reduced to the final product.

FIG. 3 shows changes in the chromium concentration of ferrochrome products in the final product under experiment. Chromium concentration decreased as expected when the proportion of other metals increased.

FIG. 4 shows that carbon and silicon concentrations during briquette experiments remained at normal levels in the final product.

Claims (6)

A method for utilizing a sidestream containing an industrial metal oxide, wherein the material containing the metal oxide is cemented into a briquette and the briquette is supplied to a submerged arc furnace for ferrochrome production. The method to be characterized. The material containing the metal oxide is characterized by flakes from a foundry, flakes from a rolling mill, dust from a filtering operation, sidestream from water treatment, or a metal slurry from an annealing-pickling line. The method according to claim 1. The method according to claim 1 or 2, wherein the briquette is supplied through a preheating furnace. The method according to claim 3, wherein the temperature in the preheating furnace is 400 to 600 ° C. The method according to any one of claims 1 to 4, wherein the briquette is added so as to constitute up to 20% of the total supply amount. The material containing the metal oxide is characterized by containing an oxide of a metal selected from the group consisting of chromium, iron, nickel, titanium, cobalt, manganese, and copper, according to claims 1 to 5. The method described in any one of the items.

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