One of the most common misunderstandings people seem to have about steelmaking (metallurgical or coking) coal is why it is used, and why it continues to to have such market dominance when there are seemingly alternatives to its use.
As a result this leads to the opinion or conclusion that steelmaking coal’s market dominance is simply the result of a lack of political will, not physics, market forces or the fact it is just an exceptional feedstock.
Some confusion arises from the belief that steel mills can simply swap steelmaking coal as a feedstock for another product that generates significant heat (e.g., hydrogen or methane) or convert blast furnaces to electricity.
But it isn’t so simple.
A background on steelmaking coal.
Firstly, steelmaking coal is a specific subtype of coal that does a very specific task. For background: broadly, coal is classified into three main rankings (from lowest to highest): lignite (“brown coal”), bituminous coal, and anthracite. All are derived from ancient plant material that accumulated millions of years ago. Over time, burial, heat and pressure transform this plant material into coal. As the degree of heat and pressure increases, moisture and other volatile components are over time driven off, increasing the carbon content of the coal.
However, not all coal is suitable for steelmaking, this is because for steelmaking you first need to create something called coke. Lignite is too soft, while anthracite is generally too hard and brittle s for making coke. Therefore, only certain types of bituminous coal possess the qualities to produce coke. To produce coke, coal is heated in the absence of oxygen, suitable coals soften, become plastic, and then resolidify into coke, a strong, porous material.
In other words, coke is made from coal, but only very specific types of bituminous coal can be used to make high-quality coke for steelmaking.
The world’s primary feedstock for iron smelting and steel manufacturing is iron ore and metallurgical coal. Approximately 70%, or 1.3 billion tonnes, of steel is made with it annually. And virtually all iron ore used to make steel uses coal (more on that later).
Just like not all coal is the same, not all steelmaking coal is the same, and it comes in three major categories: Premium low volatile hard coking coal, mid-volatile hard coking coal, and semi-hard coking coal. Each include different physical and chemical qualities which no single type of coal can provide.
Therefore, the coke mills blend the different types of metallurgical coals together to achieve the specific blend that they want for use in their BF-BOF. A comparable process would be refineries blending light and heavy crude and or sweet and sour crude to produce specific products or meet refinery specifications, or even flour producers milling wheat types to produce specific blends.
For example, coke mills may blend premium hard coking coal with semi-hard (or a lower-tier) coking coal to get just the right blend for their furnace, or they may primarily use a mid-tier coal and blend it with soft or high-tier coal. In short, it is about getting the right blend at the best economics, and there is no one size fits all coal.
Once mills have coke, they combine it with iron ore in the blast furnace to produce hot iron, usually called pig iron, which is a precursor to steel.
And now to answer the primary question — Why the heck do we even use steelmaking coal?
Coke has three critical characteristics for which there is no direct 1:1 replacement.
- It is a reducing agent
- It supports the burden in the furnace, and
- It provides energy to the steelmaking process.
What is reduction, and why do we need it?
Iron ore isn’t pure iron. The iron bonds with oxygen forming iron oxide, and for steel mills to take iron ore and convert it to iron, they need to remove the oxygen and other impurities in the iron ore. This is done using coke and a flux (often limestone). Coke is ideal for this application because it is porous and strong and allows the iron ore to have high surface-area contact, which more efficiently removes the oxygen while the other impurities combine with the flux. If certain impurities remain, we can end up with brittle steel—and brittle steel isn’t particularly safe to build a high-rise or a bridge with.
The second important characteristic that coke has is supporting the burden.
In simple terms, the burden is the alternating layers of coke, iron ore and flux which is fed into the top of the blast furnace. This configuration is what facilitates the chemical reduction, the melting of the iron, and the separation of the slag (impurities). It is a structural necessity of iron smelting, and is what gives coking coal its productivity edge. The burden allows for gas flow, efficient transfer of heat, and appropriate reaction times for the removal of impurities.
Lastly, coke provides energy and heat.
This is the characteristic people most often think is the purpose of coking coal in steel smelting. After serving two other purposes in the furnace, the energy from the coke helps to melt the iron and flux (~2000C) which then partitions into hot ‘pig’ iron and the slag which float on top of the iron. These are ‘tapped’ from the furnace in different streams – hot iron to the basic oxygen furnace, slag to the slag heaps.
Coke isn’t used exclusively for its heating ability. For example, Electric arc furnaces (EAFs) can achieve greater heat than blast furnaces, with temperatures reaching over 3000C using electricity (sometimes coal generated electricty), they cannot carry out all the tasks that steelmaking coal can—namely reduction and supporting the burden. Which is why they are primarily limtied to using scrap steel to create new steel.
So when someone says we can simply swap steelmaking coal for an alternative fuel, they simply don’t quite understand the three specific roles that coal provides.
Coke cannot simply be swapped out for a different feed in today’s modern BF-BOF steel plants.
With this in mind, it is important to remember that EAFs do play an important role in meeting world steel demand. They account for approximately 29% of world steel production, and this is achieved through the recycling of scrap steel with minor amounts of very high-grade iron ore (which is rate) and which is pre-processed to reduce it to ‘sponge iron’ prior to being fed into the EAF.
Global scrap steel supply is low compared to steel demand so a full rollout of EAFs to replace BF-BOF furnaces is a mathematical and economic impossibility.
Recently, Algoma Steel in Ontario replaced their blast furnaces with EAFs, a process that will allow them to produce steel without coke. But it is critical to remember that this is also a process dependent on access to scrap steel.
Bringing it back to the feedstock debate, opponents of steelmaking coal often point to Direct Reduced Iron (DRI) as an alternative. They are correct that DRI is an important and growing steelmaking technology, but it is not a universal replacement for the traditional blast furnace route.
Unlike a blast furnace, DRI reduces iron ore in the solid state using a reducing gas derived primarily from natural gas ( and sometimes hydrogen). The resulting product, known as sponge iron or DRI, is then melted in an Electric Arc Furnace (EAF) to produce steel.
However, the DRI process has more specific feedstock requirements than a blast furnace. It requires high-grade iron ore with high iron content and very low levels of impurities. The ore must also meet tight physical specifications, often in the form of pellets or calibrated lump ore, which require additional processing and increase cost. As global DRI capacity expands, demand for these premium-grade ores is expected to grow, potentially placing further pressure on supply and pricing. At present, only about 4% of globally traded iron ore meets these specific demand requirements for DRI.
Because DRI does not produce molten iron and slag in the same way as a blast furnace, it cannot process the same broad range of iron ore qualities. The subsequent EAF also requires reliable, competitively priced electricity to remain economically viable. While DRI-EAF technology is an important pathway for reducing emissions where suitable ore, energy and infrastructure are available, it complements rather than replaces the blast furnace-basic oxygen furnace (BF-BOF) route, which continues to produce the majority of the world’s steel.
Steel creation is complicated, and steelmaking coal and its market dominance remain “sticky,” not because it is a cheap heat source, but because it has all the multiple physical and chemical properties required to smelt steel in the most economical manner.
So, when someone tells you steelmaking coal isn’t necessary, remember that, in a world with little need for steel, this may be true. But in a world with growing steel demand, finite availability of scrap steel and high-quality ore, we bump up against reality—and that reality means steelmaking coal will be necessary for decades to come.