The direct reduced iron briquette is generally considered a relatively safe load to transport. Hot-moulded briquette iron is dense, castable at 650°C, and has a limited surface area exposed to oxidation and water reactions.
Direct cast iron briquettes are generally considered a relatively safe load.
Iron is formed into dense castings at 650 degrees Celsius and has a limited surface area exposed to oxidation and water reactions. But when the briquettes are broken, the content of active iron increases, which is exposed to the oxidation process.
They heat and react with water to release hydrogen.
The attached image shows the extent to which the briquettes were broken in this case, especially the large number of fines that were present. The fine particles increase the surface area exposed to oxidation and reaction with water or moisture present in the holding atmosphere. In a marine environment, all water or moisture contains salt, which accelerates its oxidation and hydrogen evolution.
At the time of discharge, the healthy portion of the cargo was estimated to be 25%, so 75% of her cargo consisted of broken briquettes and debris, resulting in a significant increase in fresh surface exposure to oxidation and reaction with water. estate. There is water because dehydration records show that 178,873 tons were pulled up from the sea.
Furthermore, as the cargo tanks are vented almost continuously to release the hydrogen produced, moist sea air is drawn into the cargo tanks and condensed throughout the cargo, accelerating the oxidation of HBI and the release of hydrogen.
Sponge iron or reduced iron (DRI) is a type of iron that can be obtained directly through the reduction process. This is why it is called directly reduced iron. Iron ore is brought into contact with many different reducing agents, such as natural gas or coal gas, to produce sponge iron.
In addition, sponge iron can be produced in many types of blast furnaces, oxygen furnaces and coal furnaces. Sponge iron has several advantages over other forms of molten iron. Sponge iron is much richer in iron than pig iron. Therefore, it has many applications in electric ovens.
Sponge iron is a metallic material obtained by reducing (separating) oxygen from iron oxide (iron ore) at a temperature below the melting point of iron. Sponge iron is produced using reducing gases, mainly a mixture of hydrogen and carbon monoxide. The corresponding temperature in the process is significantly lower than the temperature used in the furnace, and its basic requirements are also lower. DIR is so named because of its spongy texture.
Suitable raw materials for the production of sponge iron
For the production of this iron, high-grade iron ore (at least 70% iron content) or rusted steel scrap is used, and the main component is iron. Of course, these materials still cannot be used in induction furnaces because reduction is a chemical reaction and induction only melts pure reduced metals.
Hot Sponge Iron (HDRI)
The hot iron is immediately fed into an arc or induction furnace to save energy. When HDRI is exposed to air, it can quickly oxidize and explode.
DRI allows us to take what two industries (iron ore mining and preparation and refining for steel production) fundamentally create and reduce their footprint. Most importantly, DRI is an excellent source for EAF steelmaking. This means that we can transfer the advantages of steelmaking in electric arc furnaces, which we see in scrap metal recycling, to new steelmaking using direct reduced iron.
Sponge iron provides an alternative steel production method to Scrap-EAF and BF-BOF methods. Iron ore is broken down to solid form in DRI (except in the BF process, where liquid metal is formed during reduction). DRI can be converted into steel in an electric arc furnace.
DRI production is very common in the Middle East, South America, India and Mexico. India is one of the world’s largest producers of sponge iron and has many small and medium mineral resources.
According to statistics provided by the World Organization, the global annual production of sponge iron reached the highest level of 100 million tons in 2018, doubling for two consecutive years. India and Iran together account for more than half of the world’s production of the metal.
Sponge iron is a special and attractive metal due to its small investment and good compatibility with local raw metal conditions. As a result, production has grown rapidly over the past three years. However, small DRI operators are also a barrier to investment in energy efficiency.
Natural gas and coal are the two main fuels used to make this iron. While more than 90 percent of the world’s DRI plants use low-grade natural gas to produce the metal, production in India is done from coal. The energy consumption of producing DRI from natural gas is very common, but this production method results in the emission of carbon dioxide gas.
The emission of carbon dioxide gas per ton of steel production varies from 0.77-0.92 tons, depending on the type of electricity used in the production process. The most common technologies used to produce DRI are the MIDREX and HYL III technologies, both of which use natural gas.
direct reduced iron briquettes
The briquettes are direct reduced iron or iron sponge in compressed way. Compression of sponge iron during production can eliminate some of its defects and produce higher quality steel. So much so that many factories today use iron sponges as raw material to replace scrap. There are three types of briquettes: cold, hot and soft, each with their own characteristics.
The many advantages of sponge iron ball make it widely used in the steel industry.
- Replacement of iron scrap in arc furnaces and induction furnaces
- Improve product quality and reduce coke consumption in blast furnaces
- Replacement of iron scrap in steelmaking converters as coolant
- Alloy steel can be produced due to low carbon content and impurities
Cold briquette or CBI
If the raw material in the briquetting process enters the briquetting machine at normal temperature, the end product is called cold briquetting. Cold briquettes are also produced using tunnel kilns, and coal is used in the production process. Coal plays the role of carbon monoxide regeneration gas.
After regeneration of this gas, sponge iron is mixed with water and glue and placed in a high-pressure briquetting machine to make briquettes.
Cold briquettes are spherical and hollow and differ from hot briquettes in size and shape.
hot briquettes or HBI
The production process of hot-pressed ball is a continuation of the production process of sponge iron, which is produced by direct reduction furnace.
In these furnaces, the temperature of the sponge iron rises to 650 degrees Celsius and, after a gas regeneration process, it is brought into the briquetting machine. The high temperature of iron ore makes the briquette made from it denser than cold briquette. Also, the shape of the hot briquettes looks like a rectangle.
Hot briquetting balls are the most widely used type of sponge iron briquetting balls, mainly used in rolling mills equipped with electric arc furnaces. Compared to sponge iron, this product has lower porosity and is the safest briquette in the world.
soft briquettes
Soft briquettes are the same as dust or softballs produced during direct reduction production of sponge iron. This dust is collected and converted into sponge iron briquettes in the same way as cold briquette production. Due to more impurities and different chemical compositions, soft briquettes are of lower quality than other briquettes but are still used as raw material by many steel mills.
What are the advantages of briquettes?
The advantages of briquettes show us why the price of iron made from it is higher than the price of iron made from sponge iron. Below are just some of the benefits of iron sponge balls:
- Smaller size compared to sponge iron
- Easier to store and transport than sponge iron
- Low oxidation rate
- Possibility of alloying during production
- Easy export by land and sea
- Possibility to adjust the percentage of carbon in its structure from 0.02 to 1%
- Uniform quality due to non-degradation of metal grades
- Metal quality over 96%
- Compact and non-porous for high ignition resistance
- High steel production efficiency due to low oxygen content
- High mechanical strength and no dust formation due to rapid crushing in the oven
Process carried out at DRI:
- Cylindrical furnace
- rotary kiln
- Rotary oven
- fluid bed reactor
Since there is no slag stage or smelting stage in the production of sponge iron, all the waste elements of the iron ore remain in the sponge iron itself, which requires separation with slag in the arc furnace method.
Compared to the scrap melting method, this method increases the electrical energy consumption of the arc furnace method. If the hot sponge iron is immediately transferred to the EAF melting section, the heat generated by the process directly reduces the cost of DRI melting in the EAF process, significantly reducing energy supply and electrode consumption costs.
The temperature load for sponge iron production is mainly related to coal quality and to a lesser extent rock degradability. DRI plants in India typically use a high percentage (32% on average) of coal’s combustible content (ash and moisture), resulting in higher energy consumption.
Coal consumption in Indian factories varies from 1.2 to 1.5 tons per ton of sponge iron. And the coal consumption of advanced plants is between 1.05 and 1.2, which is obviously much higher than the coal used in South African plants, which use 16% non-combustible coal.
Non-parallel flow rotary kilns for sponge iron production in India allow only 60% of the heat to be used for production, while the remaining 40% of the heat removed from the furnace has been re-evaluated as having great potential. to improve energy efficiency.
Most gas-based direct crackers are part of small integrated steel plants located near electric arc furnace steel plants. Sponge iron enters the arc furnace in the form or cold state.
Small steel companies transfer this iron from their DDCs to nearby metal works and small quantities of DRI are sold in the market. In India, a large number of small rotary kilns use coal as energy to produce sponge iron.
Transportation
Since DRI metal is a highly reduced and decomposed metal, it has a strong tendency to deoxidize and exothermic reactions. Therefore, there is a risk of fire and self-heating if its special conditions are not observed and suitable tanks for transporting this metal are not considered. Many international shipping companies use the DRI storage method in tanks containing an inert gas such as nitrogen.
Application of iron sponge
Powdered sponge iron can be combined with many other metals to make a variety of ferrous products. For example, wrought iron can be made from sponge iron. This is the type of iron we use to make decorative items such as garden furniture. The latest method of making sponge iron is made with reducing gas, so it does not require melting in a melting furnace.
Sponge iron or cast iron?
Sponge iron is different from pig iron. Pig iron is actually another form of iron made by melting iron ore or coal and limestone under very high pressure. The product obtained after cooling is called pig iron. This iron has a high carbon content. Therefore, it is so fragile and unstable that it cannot be used directly in this way.
However, this type is mainly used to produce wrought iron, steel, and cast iron by melting and mixing. This iron was first discovered by the Chinese in the 11th century. Although pig iron cannot be used in its original form, after more modification and processing it becomes an important and useful metal, such as cast iron and steel, and is one of the most widely used metals in the world.
Without protection, DRI is prone to oxidation and rust and generally corrodes faster than steel. Unlike pig iron, which is almost pure metal, DRI contains some siliceous impurities that must be removed during the steelmaking process.
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