Smelting of High Carbon Ferrochrome

Smelting of High Carbon Ferrochrome

The smelting of high carbon ferrochrome mainly adopts the electric furnace method, which uses carbon to reduce the chromium and iron oxides in the chromium ore. The reaction temperature determines the carbon content of the product. The main raw materials include chromium ore, coke and silica, and there are strict requirements on the grade, particle size and purity of the raw materials. The smelting process requires precise control of parameters to ensure product quality.

Basic Principles of Smelting

The basic principle of smelting high carbon ferrochrome by electric furnace method is to use carbon to reduce the chromium and iron oxides in the chromium ore in the high temperature zone heated by electric arc. It is called electric carbon thermal method. The submerged arc reduction electric furnace is a kind of electric furnace, which is used for reduction smelting of ore and other furnace materials in ferrochrome production. Its main point is that the electric arc is always buried in the furnace material during normal smelting.

According to the high carbon ferrochrome furnace mouth form, it is divided into high smoke hood open type, low smoke hood open type (after lowering the high smoke hood, the short net is introduced from the upper part of the smoke hood), semi-enclosed type and enclosed type (see Figure 3 below). The first two forms are used in the early days and are gradually being eliminated. At present, the semi-enclosed and closed types are widely used.

Among them, the semi-enclosed reduction electric furnace is the most widely used. This type of electric furnace (especially medium and small ones) is easy to observe and adjust the furnace conditions, can adapt to different raw material conditions, and is conducive to refining varieties. The electric furnace smoke hood is mostly a semi-enclosed hood evolved from a low smoke hood. 

Usually, several furnace doors with adjustable opening and closing degrees are set on its side, so that it can be opened when it is necessary to add materials and pound the furnace, and the air intake can be controlled as required, and the furnace gas temperature can be adjusted to achieve flue gas dust removal and even waste heat utilization. The closed reduction electric furnace is a closed electric furnace with a furnace cover. The coal gas generated in the furnace is led out by a duct and can be recycled after purification. 

In order to facilitate operation and maintenance and ensure safe operation, several covered peek, maintenance and explosion-proof holes are set on the closed electric furnace cover. This type of electric furnace has high requirements for operation and control technology. Figure 2 shows a cross-sectional view of a fully enclosed reduction electric furnace smelting workshop, which is mainly composed of a batching station, a main plant and auxiliary facilities.

Smelting Operation

The basic principle of smelting high carbon ferrochrome by electric furnace is to use carbon to reduce the oxides of chromium and iron in chrome ore in the high temperature zone heated by electric arc. It is called electric carbon thermal method. Submerged arc reduction electric furnace is a kind of electric furnace, which is used for reducing smelting of ore and other furnace materials in ferrochrome production. Its main point is that the arc is always buried in the furnace material during normal smelting.

Smelting operation process: The production of high carbon ferrochrome by electric furnace flux method adopts continuous operation method. The raw materials are batched in the order of coke, silica and chromium ore to facilitate uniform mixing. The open furnace adds the material around the electrode through the feeding trough, and the material surface is a large cone. The closed furnace directly adds the material into the furnace through the feeding pipe. Whether it is an open furnace or a closed furnace, new materials should be added in time as the furnace material sinks in the furnace to maintain a certain material surface height.

The main process of producing high carbon ferrochrome by chemical reaction in the electric furnace is: the starting temperature of carbon reduction of chromium oxide to generate Cr3C2 is 1385K, the starting temperature of the reaction to generate Cr7C3 is 1453K, and the starting temperature of the reaction to generate chromium is 1520K. 

Therefore, when carbon reduces chromium ore, chromium carbide is obtained instead of metallic chromium. Therefore, only high carbon ferrochrome with high carbon content can be obtained. Moreover, the carbon content in ferrochrome depends on the reaction temperature. It is easier to generate carbides with high carbon content than carbides with low carbon content. In actual production, part of the chromium ore reacts with coke to generate Cr3C2 during the heating process of the charge. As the temperature of the charge increases, most of the chromium ore reacts with coke to generate Cr7C3. The temperature further increases, and chromium trioxide plays a refining and decarburizing role on the alloy.

The starting temperature of the iron oxide reduction reaction is lower than that of the chromium trioxide reduction reaction. Therefore, the iron oxide in the chromium ore is fully reduced at a lower temperature, and is miscible with chromium carbide to form a composite carbide, which reduces the melting point of the alloy. At the same time, since chromium and iron dissolve in each other, the reduction reaction is easier to proceed.