Sponge iron is also called direct reduced iron. It uses high-quality ore and uses the principle of redox reaction to remove it by filtration. It can corrode dissolved oxygen in pipelines, boilers and circulating water. After water treatment, the dissolved oxygen content can reach 0.05mg / L or less. With low backwash frequency, high compressive strength, no chalking, no compaction, large specific surface area. High activity and good regeneration effect.
Sponge iron (mainly iron oxide) is a low-carbon porous product obtained by low-temperature reduction of iron ore (or iron oxide pellets) in a rotary furnace, shaft furnace or other types of reactors. It is pulverized, magnetically separated, and pressed into agglomerates, which are used as the smelting metal charge.
This iron retains a large number of micro pores formed during oxygen loss, and it looks like a sponge under a microscope, so it is named sponge iron. The content of elements that can oxidize and generate heat such as silicon, carbon, and manganese is very low. Cannot be used for converter steelmaking, but suitable for electric arc furnace steelmaking
Its main quality indicators are:
(1) Silica (
) Content, generally less than 2.5%;
(2) Metallization rate, that is, the percentage of metal-containing iron in total iron, which is generally about 92%;
(3) Carbon content is generally 0.5 ~ 2.0%.
Sponge iron is relatively pure. Increasing its proportion in the EAF steelmaking charge can play a purification role and improve the quality of steel. In addition, if used in a continuous feed method, it can shorten the smelting cycle and increase production. However, most or all of the steel is made of sponge iron, which has more slag and consumes more energy. [2]
(1) Iron-phosphorus reduction method: rolling steel
name
index
name
index
Active iron
98%
Bulk density
2.2g / cm3
There are many ways to produce sponge iron, mainly four. That is: back to the kiln method, shaft furnace method, vertical tank method, belt machine method.
The following uses the rotary kiln method as an example to explain its production process. The rotary kiln method (also known as the "SL / RN" method) uses solid fuel as a reducing agent and a rotary kiln as a reactor. The reducing agent and pellets (pig iron or pellets consolidated after oxidation roasting) enter the rotary kiln at the same time. Reduction roasting. Generally, the degree of metallization can reach more than 90%, and the sponge iron with a particle size of 5 to 15 mm is usually used as a raw material for steelmaking.
The process of this method is: if the iron-containing raw materials are lump ore or oxidizing pellets, the iron-containing raw materials, reducing agents and other raw materials can be directly entered into the rotary kiln, and dried and preheated in the kiln before reduction. If the iron-containing raw material is powder or concentrate, dry grinding or wet grinding is required. After pelletizing, the raw balls are added to a chain caster to be dried and preheated, and then added to a shorter rotary kiln for reduction roasting. .
The working principle of the rotary kiln is: the raw material composed of solid carbon and ore particles (pellets) moves forward continuously in the rotary kiln of the inclined furnace body, during which the charge is preheated by the gas generated by the countercurrent or cocurrent flow combustion method (<800 region) and reduction (900 1000 region), and finally the product-solid sponge iron.
The SL / RN rotary kiln method can handle a variety of different iron-containing raw materials (such as lean iron ore, vanadium-titanium magnetite, and dust from steel plants, etc.). Many types of energy can also be used, especially non-coking coal that can use abundant storage but cannot be used in blast furnaces. The price of coal is lower than natural gas and oil, so the energy cost is also low. Therefore, this method has broad development prospects. The selection of reduced coal is very important. Coal types with low ash content (<20%), low S content (<1%), good reactivity, high fixed carbon, suitable volatile content, and good fusibility of coal ash should be selected. reducing agent.
However, the method has huge equipment, high investment cost, long trial run time, lower productivity than gas reduction, and high energy consumption. [3]
