Core Advantages of Low Sulfur Content
Using low-sulfur graphitized petroleum coke as a carbon raiser offers the following significant advantages:
- Improved Carbon Absorption Rate and Reduced Energy Consumption: In the steelmaking process, the carbon element in low-sulfur, high-purity graphitized petroleum coke can be absorbed by the molten steel more efficiently. The carbon absorption rate of ordinary carbon raisers may only be 60%, while the absorption rate of high-quality graphitized petroleum coke can reach over 90%. This means that less carbon raiser is needed to reach the target carbon level, saving raw materials and reducing the additional energy consumption caused by repeated additions and composition adjustments, directly reducing electricity consumption.
- Improved Steel Purity and Steel Performance: Sulfur is a strictly controlled impurity element in steel, which is extremely detrimental to steel performance. Using low-sulfur recarburizers avoids introducing additional sulfur into molten steel, thus: ►Preventing hot brittleness: Sulfur reacts with iron to form low-melting-point FeS, which distributes along grain boundaries during hot working of steel, leading to intergranular cracking, i.e., "hot brittleness."
►Ensuring the quality of ductile iron: Sulfur is a "harmful element" in ductile iron production. It reacts with spheroidizing agents (such as magnesium), consuming them and reducing the spheroidization rate. Therefore, producing high-quality ductile iron requires the use of low-sulfur (<0.05%) recarburizers.
- Reducing equipment corrosion and extending furnace life: Sulfur corrodes furnace linings and electrodes at high temperatures. Using low-sulfur recarburizers can effectively slow down the chemical corrosion of furnace linings and electrodes. For example, data shows that using high-quality graphitized petroleum coke can reduce electrode replacement frequency by 30% and reduce heat loss from the furnace wall.
- Meeting environmental requirements: Sulfur is one of the main sources of air pollutants (such as SO₂). Using low-sulfur raw materials is an effective way for steel companies to reduce pollutant emissions at the source and meet increasingly stringent environmental regulations.
Negative Impacts of High Sulfur Content
Using petroleum coke (or inferior carburizing agents) with excessively high sulfur content can cause a series of problems during steelmaking:
- Formation of Harmful Inclusions: High sulfur content leads to the formation of sulfide inclusions such as MnS in the steel. While a certain amount of MnS is beneficial for machinability, excessive inclusions reduce the steel's transverse mechanical properties, plasticity, and toughness.
- Increased Refining Burden: If the sulfur content in the molten iron or furnace charge is too high, deep desulfurization operations must be performed in subsequent refining processes (such as LF furnaces). This increases the consumption of refining slag (such as lime and fluorite), prolongs the smelting cycle, and increases production costs.
- Causes Casting Defects: In casting production, high sulfur content reduces the fluidity of molten iron and may lead to defects such as "hot cracking" in castings.
Summary and Solutions
In general, using low-sulfur graphitized petroleum coke is an essential choice for the production of high-quality and special steels in order to obtain clean molten steel, a stable production process, and excellent steel properties. However, in certain specific processes, high-sulfur petroleum coke is not entirely without its uses. For example, in some smelting reduction ironmaking processes that use petroleum coke as both fuel and reducing agent, the sulfur in the petroleum coke can ultimately be absorbed by slagging agents (such as limestone) and enter the slag, thus separating from the molten iron. However, this process places higher demands on subsequent environmental treatment.
In summary, in most carbon-enhancing scenarios, choosing high-quality graphitized petroleum coke with a sulfur content below 0.05% is the safest and most efficient option to ensure the quality of the final product.
