Decarbonization in the Steel Industry Part 2: Charcoal as Fuel and Reductant in Blast Furnace

Basically, the conditions in each steel industry vary so that the decarbonization process is also carried out using different and gradual routes to achieve net zero emission conditions. The conditions of each steel industry have a unique configuration of production technology, raw materials and energy sources, capacity and yield, regulatory requirements and so on. To achieve Net-zero by 2050, a number of things need to be done, such as efficient use of raw materials, increasing the portion of reuse and recycling, retrofit and advanced technology, and especially efforts to use renewable energy sources as fuel and reductant in the iron and steel industry. But the fact is that the construction of blast furnaces - basic oxygen furnaces (BF -BOF) is still being carried out, which should be EAF (Electric Arc Furnace) or currently only around 30% of the global iron and steel industry uses this EAF, but there are transition efforts that can be made as described below. The transition is influenced by market demand, policy interventions, and incentives given to producers to reduce emissions in steel production.

To create policies related to this transition, providing incentives to reduce emissions for producers and creating market demand for "green steel", a clear definition is needed between low emissions vs. almost zero emissions (near zero emissions) vs zero emissions (net-zero emissions). It is estimated that in 2021 CO2 gas emissions from this industry will be 3.8 Gt globally (this has not even taken into account methane emissions from coal mining). Meanwhile, for Net-zero 2050 conditions, direct CO2 emissions from the global iron and steel industry must be reduced to 1.8 Gt CO2 in 2030 and 0.2 Gt in 2050. It seems that a lot of hard work is still needed to achieve this target, even with the current conditions. Many people are pessimistic.

One use of biomass as a carbon neutral fuel in the iron and steel industry is the use of charcoal as a fuel and reductant. Biomass such as wood must be carbonized or pyrolyzed to become charcoal. The use of charcoal in blast furnaces not only reduces carbon dioxide (CO2) emissions, but also sulfur dioxide (SO2) emissions because the sulfur content of charcoal is very low (around 100 times lower) than coke. Likewise, the use of limestone will decrease so that slag production will also automatically decrease. Likewise, it makes the blast furnace operation acidic.

Apart from a number of advantages obtained as above, it turns out that there are drawbacks to using charcoal in blast furnaces, namely in large blast furnaces which causes operational problems because the strength of charcoal is usually lower than coke. As a solution, there are three methods of using charcoal in the blast furnace process. First, with pulverized charcoal injection (PCI). With this method the charcoal must be crushed into a powder and injected into the blast furnace. Second, with charcoal powder mixed with coke powder into pellets or briquettes called charcoke. By making this charcoke, its strength is sufficient for use in conventional blast furnaces. And third, by replacing coke with lump charcoal for small capacity blast furnaces (inner volume 60 – 550m3). In small capacity blast furnaces, the compression pressure on each charcoal particle is much smaller than in large capacity blast furnaces. Sintering and pelletisation are not required in this case.

Energy plantations or biomass plantations can be created specifically to supply raw materials for charcoal production. The energy plantation will also absorb carbon from the atmosphere (carbon sink) in a certain volume. The volume of carbon from the atmosphere can be maintained in such a way that its function as a carbon sink can be carried out, namely by the amount of wood harvested for charcoal production not exceeding the growth rate of the wood biomass. In this way, the energy plantation cannot be finished in one harvest but is sustainable while maintaining its volume or area.

With continuous pyrolysis technology, charcoal production can be optimized. With this continuous pyrolysis technology, apart from the large charcoal production capacity, multi-use by-products are also produced, such as gas products which can be used as an energy source as well as biooil. Biooil can also be used as a raw material in the chemical industry. Charcoal production of tens to hundreds of tons per day is also possible with continuous pyrolysis technology.

And especially in Indonesia, as the owner of the largest oil palm plantations in the world, which is estimated at more than 15 million hectares and with palm oil mills reaching around 1,000 units, there is a lot of palm oil waste that can be utilized, especially empty palm fruit bunches or EFB (empty fruit bunch). The potential for charcoal production from EFB is also very large. Apart from that, as the 5th largest coal producer in the world with production of around 570 million tons per year, coal also needs to be processed into coke. Charcoal from empty bunches or EFB can be made into powder for PCI or into charcoke by compacting it, namely making pellets or briquettes with coke.

Decarbonization in the Steel Industry

World steel production reached 1.9 billion tons in 2020, with China accounting for around half and followed by European Union countries. Germany, with annual production of around 42 million tonnes, is the largest steel producer in Europe or around a quarter of European steel production, while the other quarter is Italy and France, followed by Belgium, Poland and Spain. The steel industry contributes 8% of CO2 globally, each ton of steel production produces an average of 1.85 tons of CO2 emissions and compared to iron ore mining, iron and steel production contributes much more to CO2 emissions. Efforts to decarbonize the steel industry begin with the use of renewable energy for its smelters. Biomass-based fuel in the form of charcoal which has a high carbon value can replace the use of coke derived from coal. And the use of hydrogen from renewable energy sources is the ultimate target for decarbonization in the steel industry. 

Currently, the steel industry mostly uses coal as fuel using blast furnaces. To reduce carbon intensity, natural gas is used as fuel. The use of gas fuel in the form of natural gas is also a transition medium and basically because it comes from fossil fuels it is also a carbon positive fuel. Apart from that, the use of CNG in the form of natural gas is also a transition fuel before switching to hydrogen from renewable energy. The use of biomass-based carbon fuel in the form of charcoal has a better effect on the climate because it is a carbon neutral fuel. Apart from that, technically, because it is a solid fuel, the same as coal, practically there is not much or even no need for changes or modifications to the smelting furnace. The availability of high quality charcoal, large volumes and continuous supply are still the main obstacles.

The use of charcoal for metallurgy or steel making has actually become commonplace for some time. In the early 1900s, world charcoal production experienced its heyday with production of more than 500 thousand tons. In the 1940s, charcoal production decreased to almost half of what it was in the early 1900s, due to other carbon materials, namely coke from coal, replacing charcoal in the manufacture of metals.

With the current conditions of using coal as the main fuel in smelting furnaces or blast furnaces, slag will be produced. Slag or GGBFS (Grounded Granulated Blast Furnace Slag) from the steel plant is used in cement plants as a cement additive or SCM (supplementary cementious material) thereby reducing the portion of clinker in cement production. In the cement plant itself, the more slag or SCM used, the more clinker use is reduced, thereby also reducing CO2 emissions. In cement production, the clinker production section contributes the most to the CO2 emissions produced, so the use of slag or SCM is part of decarbonization in cement plants. It is estimated that around 70% of world steel production uses the blast furnace or BF-BOF process which produces quite a lot of GGBFS, even in China more than 90% of steel production uses the BF-BOF process. It is worth noting that the decarbonization of the steel sector is resulting in a shift away from blast furnaces, which will impact the availability of GGBFS worldwide in the coming decade. However, this change will occur slowly and gradually and, in the meantime, there are a number of GGBFS that will be available for use as SCM to reduce the carbon footprint of cement and concrete.

To be able to produce charcoal in large quantities, raw materials are also needed in large quantities. Raw materials in the form of biomass, especially wood, can be produced from energy plantations. Energy plantations from fast growing species and short rotation crops will be suitable to meet the need for raw materials because apart from the fast harvest period they also have high productivity. Apart from that, there is no need to replant every time it is harvested and it is easy to grow and easy to maintain. To produce steel per ton, an average of 6,000 MJ of energy is required (equivalent to 50 kg of hydrogen) or the equivalent of 200 kg of charcoal and requires around 600-800 kg of wood biomass as raw material. Apart from raw materials from energy plantation wood, raw materials from agricultural and plantation wastes can also be used.

The future palm oil industry could produce hydrogen from biogas. Each ton of steel will require 50 kg of hydrogen, while each palm oil mill with a capacity of 30 ffb/hour can produce 1 MWh of electricity, while the production of 1 kg of hydrogen requires 50 KWh, so that with the capacity of the palm oil mill it can produce 20 kg of hydrogen. Areas with a high concentration of palm oil mills such as Riau province could create a hydrogen pipeline network for environmentally friendly steel mills.

With higher prices for steel produced with renewable energy (green steel), market share is also limited. Currently, only certain uses, such as automotive, buy such premium or green steel. Decarbonization efforts in steel industries can also be carried out in stages, along with the development of renewable energy. With the increasing supply of renewable energy, the price will decrease so that environmentally friendly steel (green steel) will also become more competitive in price. New steel industries can be built close to these cheap renewable energy sources so that green steel production can become competitive.