Ferrochrome is a ferroalloy mainly composed of lead and iron. As an additive to steel, ferrochrome can produce a variety of special steels with high strength, corrosion resistance, wear resistance, high temperature resistance and oxidation resistance. Such as: stainless steel, acid-resistant steel, heat-resistant steel, ball bearing steel, spring steel, tool steel, etc.
In 2020, the total production capacity of high-carbon ferrochrome in the country will be 12.858 million tons, of which Inner Mongolia’s production capacity will be about 5.85 million tons, accounting for 47%, nearly half of the country; followed by Sichuan and Shanxi, with production capacity reaching 1.07 million tons and 1.03 million tons respectively; by 2020 China imported 3.07 million tons of ferrochrome m.
The main smelting process of ferrochrome
With the massive mining of global chrome ore resources, high-quality lump ore resources are becoming less and less, and fine ore resources have become the main raw material for iron and steel smelting in China, and the amount of fine ore (-8 mm) accounts for about 80%; therefore, the fine ore treatment process It has become the main process of ferrochromium smelting in China.
However, when smelting high-carbon ferrochrome in submerged arc furnaces, too much powder ore will cause poor gas permeability of the furnace charge and deteriorate the furnace condition, seriously affecting technical and economic indicators such as safety, power consumption and chromium yield. At present, the mainstream chromium powder ore pretreatment and smelting processes are divided into oxidation method and reduction method. The mainstream processes of the oxidation method are: sintering method, Outokumpu method, and the mainstream processes of the reduction method are: SRC (rotary kiln + submerged arc furnace) method and DRC (rotary hearth furnace + submerged arc furnace) method.
Oxidation ferrochromium smelting process
The sintering method sinters the chromium powder ore into a block and puts it into a submerged arc furnace for reduction smelting. Although the sintering method has the advantages of simple equipment, low investment, and short process, it has poor product strength and high powder rate, and is not suitable for large-scale closed electric furnaces. , serious environmental pollution and other issues. The production of 200,000 tons of ferrochrome is equipped with a sintering machine of 24 square meters. According to the “Industrial Structure Adjustment Catalog M2019”) regulations: the belt-type chrome ore sintering machine of less than 24 square meters for ferroalloy production belongs to the elimination category. Since the reduction load is all in the mineral heat
In the furnace, the power consumption is high, about 3400 kWh/t, and the high energy consumption leads to high production costs.
Finnish Outotec technology, Outokumpu method is that the chromium powder ore is roasted in a belt roaster, and the mixture is sent to a preheating kiln for preheating to 500-600 °C, and then enters a submerged arc furnace for smelting. This technology is equipped with a charge preheating device on the top of the submerged arc furnace to heat the charge with self-produced gas to reduce power consumption. The power consumption for smelting is about 2800 kWh/t.
Ferrochrome smelting process by reduction method
Due to many problems in the oxidation method, the reduction method came into being. The main feature is that the function of the smelting process of the submerged arc furnace is advanced, and the pellets are pre-reduced before entering the submerged arc furnace, which effectively reduces the smelting power of the submerged arc furnace. consumption; the mainstream technology has SRC method and DRC method.
The SRC method uses the rotary kiln as a pre-reduction device to pre-reduce the chromium ore and reduce the smelting load of the submerged arc furnace, thereby reducing the power consumption of the submerged arc furnace. %), but there are the following problems:
1) Rings are easy to form in the rotary kiln, the kiln must be shut down for maintenance, the operation rate is low, and it is difficult to ensure stable production;
2) High requirements for chromium ore and coal burning (w (SiO2) of sawn ore < 6%, low coal ash content used);
3) It is very difficult to completely heat the pellets into the electric furnace for smelting. For this reason, cold lines are generally installed, so it is difficult to fully realize the advantage of hot charging to save electricity;
4) The pulverization rate of finished pellets is high;
5) Only one burner is installed at the kiln tail in the rotary kiln, the temperature and atmosphere are difficult to be effectively controlled, and the pre-reduction degree is low.
The DRC method adopts the dual technology of rotary hearth furnace and submerged arc furnace to connect and couple the advantages of rotary hearth furnace and submerged arc furnace. The hot charging temperature of ferrochrome DRI is about 850 °C, and the submerged arc furnace can effectively use Heat and more effective use of high reduction rate of pellets (comprehensive reduction rate 60%), reduce smelting power consumption (smelting power consumption 2150-2200 kWh/t), improve production efficiency, reduce production costs, and have obvious economic benefits benefits and market prospects.
As a low-carbon reduced ferrochrome smelting process, the DRC method has the following
(1) The raw material has wide applicability and can be adapted to various grades of sawn iron ore;
(2) The DRC method can truly realize the high-efficiency and low-cost comprehensive recovery of valuable metals, and the comprehensive utilization efficiency of resources is high, which is in line with the benefits of circular economy;
(3) The hot metallized pellets can be smelted directly into the gas-fired smelting furnace, which reduces the loss of heat energy. A large amount of gas is used as the heating source, which greatly reduces the power consumption of the process.
(4) The entire production process of the DRC method has low energy consumption and is environmentally friendly; it greatly reduces atmospheric smog and greenhouse gas emissions, and has significant energy-saving and environmental protection benefits. Each ton of product can effectively reduce energy consumption by 15% and CO emissions by 20%.