DRI Briquetting process
Currently, most of the existing direct reduced iron production processes in the world use the briquetting process to solve the problems of DRI such as high powder content, low density, flammability, large dust, and insufficient latent heat utilization. Briquetting is the method of applying mechanical pressure to agglomerate the pellets or powdered DRI produced by direct reduction into dense closed blocks. Briquetting is divided into cold pressing process and hot pressing process.
Cold pressing process
The cold pressing process is a process of pressing cold DRI materials into a certain shape and size under the action of mechanical force and capillary force. The quality of cold pressing blocks is affected by the type of raw materials, physical and chemical properties, type and amount of binder, process parameters and operation of the briquetting equipment, etc. influence of factors. The role of the binder in this process is to improve the balling properties of the material and increase the molecular bonding force between the particles in the green balls, so as to increase the strength of the green balls. The cold pressing process equipment works at room temperature, and the briquettes have problems such as low strength, low density, large amounts of powder, high production costs after using binders, and difficulty in on-site environmental management. In particular, product quality cannot meet user requirements. Domestic rotary hearth furnace production lines have stopped production or dismantled the supporting cold pressing production lines.
Hot pressing process
The hot pressing process causes the hot DRI to plastically deform under the action of mechanical force within a certain temperature range, increasing its density and obtaining HBI products with certain dimensions and strength. The hot pressing process equipment works at high temperatures, and the process is relatively complex. The cost of imported equipment is high and the troubleshooting time is long. However, HBI has high strength, the quality fully meets user requirements, no binder is needed, and the production cost is lower than that of the cold pressing process. There are reports on the construction of supporting roller hot pressing processes for the rotary hearth furnace technology abroad, such as Japan's Nippon Steel, South Korea's Posco, etc.
The earliest rotary hearth furnace production line built in China was also equipped with a hot pressing process (a development and research project). The main equipment, the hot press, was imported from abroad and adopted a double-roller forming structure. After several debuggings, a qualified HBI was produced. However, due to insufficient understanding of the rotary hearth furnace and hot pressing process, the overall process design is not suitable. For example, there is no screening and cooling equipment in front of the hot press. It takes a long time to deal with production faults, which basically cannot meet the needs of normal production. Due to site and other conditions, Due to the restrictions, it could not meet the renovation requirements and had to be demolished shortly after it was completed.
In order to solve the problems that arise in the roller hot pressing process. A domestically manufactured mold hot press machine has strong adaptability to raw materials, simple process configuration, low cost, and easy operation and maintenance. It has been successfully used in particle steel processing production lines. Using DRI produced by a rotary hearth furnace of a domestic steel company, a simulated production test of HBI produced by DRI was carried out in a domestic hot press manufacturing plant. The test results are very satisfactory, and all indicators of HBI meet the requirements for steelmaking raw materials.
At present, there are two main types of hot pressing processes, namely the roll forming process and the mold forming process.
① Roller forming process. The typical process flow is: rotary hearth furnace discharging DRI (DRI>1000DRI℃) → cooling (cylinder cooler, 650~800℃) → high temperature transportation equipment → screening (≤25mm) → forced feeder (radioactive element material Level meter detects material level) → Roller forming hot press (interlocked with material level) → Crusher → Screening (powder ≤5mm accounts for about 5%) → Cooling → HBI.
② Mold forming hot press process flow. In 2016, after the domestic elimination of intermediate frequency furnace steelmaking capacity, the particle steel, rolled steel scale, steel scraps, etc. (iron content greater than 85%, metallic iron content greater than 82% DRI) produced by the production processes of steel, mechanical processing and other enterprises, the overall size is less than 40mm raw materials cannot directly enter the steelmaking production process and need to be made into blocks before they can be put into the furnace. For this reason, domestic companies have developed hot presses suitable for processing such raw materials, namely mold forming hot presses. At present, there are more than 100 mold forming and hot pressing production lines in production and operation in China, and their products can meet the requirements of steelmaking raw materials. The typical process flow of the HBI mold forming hot press for the production of solid waste raw materials such as particle steel is: solid waste raw materials such as particle steel (≤40mm) → heating (rotary kiln, 700~1050℃) → fixed-capacity automatic distributor → mold heating Press→HBI→cooling or hot feeding (chain plate machine).
