The steel industry contributes 8% of global CO2 emissions, with each ton of steel produced producing an average of 1.85 tons of CO2 emissions. Compared to iron ore mining, iron and steel production contributes significantly more to CO2 emissions. Decarbonization efforts in the steel industry begin with the use of renewable energy for smelting. Biomass-based fuels, such as charcoal, which has a high carbon value, can replace the use of coke derived from coal. The use of hydrogen from renewable energy sources is the ultimate decarbonization target for the steel industry.
Currently, the steel industry largely uses coal as an energy source or reducing agent. This coal is processed into coke and used in blast furnaces. It is estimated that approximately 70% of global steel production uses the blast furnace or BF-BO process, and in China, over 90% of steel production uses the BF-BOF process. To reduce carbon intensity, natural gas is used as the fuel. The use of natural gas as a gaseous fuel also acts as a transition medium and, because it is derived from fossil fuels, is also a carbon-positive fuel.
Nearly all CO2 emissions in the steel production sector come from blast furnaces (BFs), which refine iron ore into crude iron or pig iron. The challenge is significant: there are approximately 1,850 steel mills worldwide, with approximately 1,000 using blast furnaces, producing approximately 1.5 billion tons of pig iron annually.
The use of charcoal in a blast furnace not only reduces carbon dioxide (CO2) emissions but also sulfur dioxide (SO2) emissions due to its very low sulfur content (approximately 100 times lower) than coke. Likewise, the use of limestone is reduced, thereby automatically reducing slag production. This also makes the blast furnace's operation acidic.
The use of biomass-based carbon fuel (biocarbon) in the form of charcoal has a better climate impact because it is carbon-neutral. Furthermore, technically, because it is a solid fuel, similar to coke derived from coal, it requires little or no changes or modifications to the smelting furnace. However, the availability of high-quality charcoal, large volumes, and a continuous supply remain major constraints.
This makes the use of charcoal to replace coal-based coke in blast furnaces crucial. Charcoal, derived from biomass, is a renewable, sustainable material used as a reducing agent or fuel in blast furnaces. The chemical reaction separates oxygen atoms from iron atoms, emitting CO2. This converts iron ore (Fe2O3) into crude (pig) iron.
However, the difference lies in the fact that the carbon source used as a reducing agent or fuel in a blast furnace comes from renewable and sustainable sources, making it a carbon-neutral process. Conversely, using coke from coal, as it comes from a fossil fuel, is a carbon-positive process. Similarly, using natural gas as a carbon source for reducing agents or fuel in a blast furnace, although it is said to have lower carbon intensity, is also considered a carbon-neutral process.
The use of charcoal or biocarbon materials for metallurgy or steelmaking has actually been commonplace for some time. In the early 1900s, global charcoal production reached its peak, exceeding 500,000 tons. In the 1940s, charcoal production declined to nearly half its early 1900s levels due to the replacement of other carbon materials, such as coke from coal, in the manufacture of steel and other metals.
Charcoal is a fuel and reducing agent derived from biomass that has significant potential for use during this transition phase. Palm kernel shells (PKS) are a potential biomass raw material for charcoal production. Palm kernel shells (PKS) are available in the millions of tons, ensuring a reliable supply. Charcoal, a product of biomass carbonization or pyrolysis, has a high calorific value, high fixed carbon content, and stability. However, another factor, ash chemistry, influences the quality of the resulting steel. This is somewhat similar to the ash chemistry of wood pellets from calliandra or gliricidia energy plantations.
When used as a reducing agent in blast furnaces, charcoal must have a low phosphorus content, while wood pellets from calliandra or gliricidia energy plantations must have low potassium, sodium, and chlorine content. The potassium, sodium, and chlorine content of wood pellets affects the quality of the wood pellets and their use in power generation. Pulverized combustion power plants, widely used worldwide, will reject wood pellets with this quality. Similarly, blast furnaces will reject charcoal with a high phosphorus content.
To achieve this quality, low-phosphorus content, the palm kernel shells (PKS) must first be washed. After washing, the phosphorus content decreases, and they are then dried and pyrolyzed, or carbonized, to produce palm kernel shell charcoal (PKSC). The same applies to wood pellets. The only difference is that wood pellet production doesn't involve pyrolysis or carbonization; instead, after drying and achieving the desired particle size, the pellets undergo biomass densification in a pelletizer.
Steel production requires an average of 6,000 MJ of energy per ton (equivalent to 50 kg of hydrogen) or 200 kg of charcoal, and requires approximately 600-800 kg of woody biomass as raw material. With a calorific value nearly identical to woody biomass, this is equivalent to using palm oil mills (PKS), which are plantation or agro-industrial waste.
Meanwhile, demand for low-carbon steel is growing rapidly as steel industries and governments worldwide commit to reducing carbon emissions from fossil fuels. The use of charcoal or biocarbon in blast furnaces is a key component of low-carbon steel production, as 100% of the steel is not yet produced using renewable energy.
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