The production process of ferrochromium

Ferrochrome production process High-carbon ferrochrome production methods include electric furnace method, shaft furnace (blast furnace) method, plasma method and smelting reduction method. The shaft furnace method currently only produces low-chromium alloys (Cr<30%), and the shaft furnace production process with higher chromium content (eg Cr>60%) is still in the research stage; the latter two methods are emerging processes that are being explored ; Therefore, the vast majority of commercial high-carbon ferrochromium and remanufactured ferrochromium are produced by the electric furnace (submerged arc furnace) method. Electric furnace smelting has the following characteristics:

(1) Electric furnaces use electricity, the cleanest energy source. Other energy sources such as coal, coke, crude oil, natural gas, etc. inevitably bring the associated impurity elements into the metallurgical process. Only an electric furnace can produce the cleanest alloys.

(2) Electricity is the only energy source that can obtain arbitrary high temperature conditions.

(3) The electric furnace can easily realize the thermodynamic conditions such as oxygen partial pressure and nitrogen partial pressure required by various metallurgical reactions such as reduction, refining, and nitridation.

Process flow

1. Selection of raw materials

The raw materials for smelting high carbon soldering iron are chrome ore, coke and silica. Among them, coke and silica are used as reducing agents.

2. Reducing agent

In alloy production, one of the cheapest reducing agents is most commonly used - metallurgical coke "cracks" (under-sieve coke after blast furnace coke has been screened). Due to the different quality of coking coal and coke production conditions in coking plants, the quality of crushed coke blocks is also different. But they have a common disadvantage, that is, the resistance is not high, the reaction performance is not good, the content of ash, sulfur and phosphorus is high, and the moisture content is also high, and it is not stable. The sulfur contained in the coke is mainly organosulfur and a large amount of sulfide, as well as a small amount of sulfate and a very small amount of elemental sulfur that exists in the state of solid solution in carbon. The phosphorus content of coke also varies. The coke block has a spongy structure and a lot of cracks, its porosity fluctuates in the range of 35%-55%, and the apparent density of the coke is 0.8-1t/m3.

3. Smelting operation process: The continuous operation method is adopted for the production of high carbon ferrochromium by the electric furnace flux method. The raw materials are batched in the order of coke, silica, and chrome ore, so as to facilitate uniform mixing. The open furnace feeds the material around the electrode through the feeding trough, and the material surface is a large cone. The closed furnace directly feeds the material into the furnace from the feeding pipe. Whether it is an open furnace or a closed furnace, new materials should be replenished in time with the sinking of the charge in the furnace to maintain a certain height of the material surface.

The main process of the chemical reaction in the electric furnace to produce high-carbon ferrochromium is: the starting temperature of carbon reduction of chromium oxide to form Cr3C2 is 1385K, the starting temperature of the reaction to generate Cr7C3 is 1453K, and the starting temperature of the reaction to reduce to form chromium is 1520K, so in When carbon reduces chromium ore, chromium carbides are obtained instead of metallic chromium. Therefore, only high carbon ferrochromium with higher carbon content can be obtained. And the level of carbon content in ferrochromium depends on the reaction temperature. It is easier to form carbides with high carbon content than carbides with low carbon content. In actual production, during the heating process of the charge, part of the chrome ore reacts with coke to form Cr3C2, which increases with the temperature of the charge. Most of the chrome ore reacts with coke to form Cr7C3, the temperature further increases, and chromium trioxide plays a role in refining and decarburization of the alloy.

The starting temperature of the reduction reaction of iron oxide is lower than the starting temperature of the reduction reaction of chromium trioxide, so the iron oxide in the chromium ore is fully reduced at a lower temperature, and is mutually soluble with the chromium carbide to form a composite carbide, which reduces the melting point of the alloy. At the same time, since chromium and iron are dissolved in each other, the reduction reaction is easier to carry out.

[Reprint must retain the source – Changjiang Nonferrous Net]

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