Source: United Kingdom – Executive Government & Departments
Scientists comment on the British Steel factory situation.
Dr Julian Steer, a Research Fellow from Cardiff University’s School of Engineering, said:
How hot do the blast furnaces get? How do the blast furnaces work? And why do we need these certain ores/materials to keep them running?
“The hottest part of the furnace can get to temperatures of up to 2200°C; the blast furnace converts Iron Oxide, supplied as Iron ore, to Iron by a counter current chemical reduction reaction where raw materials descend through the furnace as hot gases rise up through the furnace. The blast furnace is a very well optimized process that requires the reactions to occur at an even rate throughout the process. To do this, raw materials are selected based on the properties needed to produce iron continuously and efficiently.”
Why are the blast furnaces so difficult to switch back on if they turn off?
“The size, dimensions, and complex reactions in the blast furnace mean that heat distribution and heat transfer through the furnace are absolutely critical to stable iron production. Raw materials are continuously added to the top of the furnace as hot molten iron is continuously tapped from the bottom, the shear scale of this process means that the distribution of the heat through the furnace is critical at all times.”
Why is it crucial that they need to mobilise these supplies of fuel etc.?
“The production efficiency and stability of the whole process of iron production requires careful raw material selection to maintain consistent, and uniform reactions through the furnace and process.”
What can the government do if these blast furnace turn cold?
“If the furnace goes cold, the molten materials inside become solid, blocking the furnace and making any form of restart very difficult, costly and potentially terminally damaging to the furnace.”
Dr Abigail K Ackerman, Royal Academy of Engineering Research Fellow, Department of Materials, Imperial College London, said:
Blast Furnace Operation:
“A blast furnace is used to convert iron ore (hematite, Fe2O3) to pig iron (Fe) by mixing it with coke (carbon), limestone and hot air.
“Limestone is used to remove impurities, forming slag which is a waste material. The slag collects impurities, primarily silica, and is removed and used in construction materials like cement.
“The coke, which is a derivative of coal, reacts with the hot air, which is blown in at the bottom of the furnace at around 1000degC, and forms carbon monoxide (CO). The carbon monoxide reacts with the iron ore to produce molten iron and CO2, which is released as gas.
“The resultant molten liquid iron ore is tapped out at the bottom of the furnace, and is referred to as pig iron.”
Blast Furnace Temperatures:
“Blast furnaces have ‘heat zones’ in order to drive the different chemical reactions which occur within the furnaces. They are set up in a large chimney like structure and have 3 main zones:
“Top (throat) – 200degC to 600degC – Raw materials are poured in
“Middle (Stack) – 600degC to 1200degC – Iron ore starts to reduce forming gases (mainly CO) and the initial reduction of iron ore occurs. The initial reaction has the iron ore (Fe2O3) eventually reducing to FeO.
“Middle (Bosh) – 1200degC to 1600degC – The main chemical reaction occurs, where FeO reduced to Fe. The slag forms here, where limestone reacts with impurities.
“Bottom (Hearth) – up to 2000degC – Hot air (1000degC to 1200degC) is blown in at the bottom of the furnace, which causes the coke to combust and release heat and CO2.
“The molten iron and slag are collected. The slag is lighter that the molten iron so is floats on top of it and can be collected by tapping, or drilling a hole, above the molten iron and allowing the slag to flow out..
“The molten pig iron is removed by tapping, or drilling, a hole in the bottom of the furnace, and flows through guide channels to be collected and transferred to a basic oxygen furnace (BOF) to mix with carbon and make steel.
“Tap holes are made roughly every couple of hours, and then plugged back up with a clay mixture to contain the heat and molten materials in the furnace.
Essential Materials:
“Coking coal, iron ore and limestone are essential to keep the blast furnaces in Scunthorpe running, and these are the critical raw materials that are being sourced. Without these materials in the correct amounts, the chemical reaction will be disrupted and the furnace will cool as the chemical reaction absorbs heat, which is provided by the burning of coke.”
Why can’t you let it go cold?
“The high temperature of the blast furnace means the iron and slag are molten at the bottom, they are in liquid form at around 1500degC. If the furnace is allowed to cool, these materials solidify and can stick to the interior of the furnace. When the metal cools it contracts, which can cause the lining of the furnace to become damaged resulting in expensive repairs to the furnace interior before it can be heated up again.
“Additionally, blast furnaces have various inlets and outlets for pumping in hot air and extracting the molten material. When this solidifies, these can become blocked and are extremely difficult and costly to fix.
“The chemical reaction is disrupted when the furnace goes cold, and restarting this reaction can be complicated due to the heat required to melt the solicited materials, and the balance of gas and materials needed to obtain the correct chemical reaction.
“Finally, a large amount of fuel is required to restart a furnace, which is costly, and it can take anything from days to weeks to get the furnace back up to temperature and getting the correct chemical reaction to occur. It takes much more energy to melt the materials back down than to keep them at temperature. And, of course, there’s a loss of production which costs money.”
Why is it crucial to keep the Scunthorpe furnaces running?
“The Scunthorpe blast furnaces are the last remaining blast furnaces operating in the UK, and therefore the only method for the UK to produce ‘virgin’ steel, which is steel that has not been used in any other process. Other steel producers in the UK, such as TATA, have moved to using recycled steel and electric arc furnaces (EAF). Without the Scunthorpe plant, there will be an impact of the supply chain of steel to essential services such as construction, rail and defence. There will also be an impact on the Scunthorpe community, with a loss of work for the many steelworkers.”
What can the Government do if they turn cold?
“If the furnaces go cold, the options are to restart the furnaces, which will be more costly that obtaining the raw materials required to continue steel production due to the damage that will occur within the furnace from the solidification of the iron and slag, and the large amount of energy required to restart the furnaces.
“The government can choose to change the type of steel production to, for example, recycled steel using EAFs, like Port Talbot, however this will most likely result in job losses, economic impact on the people of Scunthorpe and the UK economy, and significant disruption to the UK supply chain. There is also not enough scrap steel to supply EAFs, so primary virgin steel will need to be sourced from elsewhere. The National Grid is also not set up to supply the energy required to fuel EAFs at this scale so it would be a timely and costly option.
“There is also the option to start producing green steel, which uses hydrogen as a reduction agent rather than coal based coke. However, this requires a large amount of hydrogen and the UK hydrogen economy is not set up for this scale of production currently. Nevertheless, this is the best option for long term CO2 goals.
“Finally, there is the option to close British Steel. This would again have a significant impact on the UK economy, supply chain and the local area. The loss of steel sovereignty could impact the supply chain in the long run as there would be an increased dependence on external steel suppliers, which is impacted by geopolitics.”
Prof Barbara Rossi, Associate Professor of Engineering Science, University of Oxford, said:
“Steel is the most commonly used metal in the world. Blast furnaces and electric arc furnaces are present everywhere, all over the world. There is worldwide 1.9 billion tonnes of crude steel produced per annum. UK in 2020 (then still a EU member state) was the 8th largest steel producer in the European union, which produced in total >150 million tonnes of steel in 2019, only 8% of the world total. Japan alone produced roughly 100 million tonnes, while the biggest steel producing country is currently China, which accounted for above 50% of world steel production in 2020. Globally, the steel industry emits 25% of all industrial greenhouse gases, which is more than any other industrial sector.
“The construction sector is the largest steel using sector and that is not likely to change. It accounts for more than 50% of the world steel demand, with the other major uses being the manufacture of vehicles, industrial equipment and final goods. The global population is forecast to increase to more than 9 billion people over the next 40 years. The population growth rate in Europe (and the UK) is only expected to start decreasing slightly by 2050. And, by then, about 75% will live in cities (~50% today). We still have to build the buildings and infrastructures for these cities and replace those that are damaged. When our country needs more and more new homes, new buildings, new infrastructure, we will have to go higher, more slender and leaner in dense populated areas and the need for ultra-strong and highly ductile materials like steel will become increasingly pressing.
“Steel is indefinitely recyclable, and, while it is recycled, it does not lose its performance which is an extraordinary ability inexplicably often ignored. It isn’t the case of most construction materials: other than steel, aluminium or stainless steel, you can only recycle glass indefinitely provided that you sort the type of glass appropriately. Steel is not just downcycled into a less noble material, just like an old jewel can be turned into a new one, steel can be melted over and over again.
“Recycled steel is one of the industry’s most important raw materials. We have accumulated almost 1 billion tonnes of steel only in the UK, all of which must be recycled, and, today, we generate about 10 million tonnes of scrap a year. Studies show that in the next 10-15 years, that availability of steel scrap will rise from 10 million to 20 million tonnes (global flow of steel scrap are likely to treble in the next 30 years) because all the steel made in the past will be recycled. In 2018, in Europe, this exceeded 110 million tonnes, showing that there is no scrap shortage. Despite its weak position in the scene of steel production, this is one of the advantages by which the UK could profit in the current global change of steel production.
“We have already produced the steel that we will need tomorrow. With increased availability of scrap and under our nation’s commitment to cut its domestic emissions by 2050, we can anticipate a global shift from blast furnace to electric arc furnace production. Roughly 2/3 of today’s liquid steel is made from iron ore, with the rest made from scrap, but at present >50% of the scrap originates from the manufacturing process, rather than from end-of-life recuperation. This is even though (1) on average, steel products have an approximate life horizon of 35-40 years, before being scrapped, and (2), apart from ~10% of steel that is buried (e.g., oil pipes or in building foundations), most end-of-life steel can be easily collected for recycling. Even if the total demand for steel production will increase, one can demonstrate that if most old steel is recycled, future requirements could be met entirely through increased production from scrap via electric arc furnaces. In America today, >50% of all domestic steel demand is already made by recycling domestic scrap. And since steel recycling causes significantly less greenhouse gas emissions than blast furnaces (topped by the fact that the UK already produces low emissions electricity grid, with high potential for further improvement, so recycling steel in the UK today leads to a reduction in emissions of > 2/3 compared to global average primary steel), UK need for steel recycling can be expected to grow significantly and rapidly. This will increase with more renewable generation capacity and will grow strategically important as global pressure to alleviate climate change increases.
“UK’s commitment to decarbonization need to address the emissions which are released from within UK borders. Although closing steel plants in the UK would lead to a reduction in the emissions, our future demand for steel may lead to higher global emissions if the emissions intensity in other countries is greater than that in the UK. Rather than providing extensive efforts in technologies allowing reduced emissions in primary production which require major capital investment, a more effective contribution to global mitigation would be to produce our domestic steel through electric arc furnaces combined with a massive decrease of their emissions which are directly linked to the emissions intensity of local electricity generation.
“There is nonetheless a technical limitation on the extent to which scrap can be substituted for iron ore: contaminants. Scrap composed of large pieces such as that from construction, have well controlled composition while scrap collecting from mixed waste streams have higher levels of contamination. The latter is usually sourced when scrap prices are high. As a consequence of contamination, the degree to which recycled steel can replace primary steel is capped by the inability of (a) imperfect control of metal composition in scrap steel collection and (b) today’s technologies to adjust the chemical composition of liquid steel produced with electric arc furnaces. Therefore, steel scrap supplies have to date been mostly absorbed by the lowest grade products (such as reinforcement bars).
“It is possible to vaporise unwanted metal contaminants from liquid steel by vacuum arc re-melting. This is already a commercial strength in the UK and used for making some of the highest quality steels for e.g., aerospace components. The innovation opportunity is to replicate this success at higher speed and lower cost. Other processes than vacuum arc re-melting have been tested in research laboratories but were abandoned due to lack of economic incentive. The UK, with its high volumes of scrap and its commitment to act on climate mitigation is well placed to lead the development of these technologies.
“We cannot replace steel, it’s ridiculously cheap, ultra-strong and highly ductile, and completely recyclable, fitting into any story about a circular economy. Not a single construction material taken alone can compete with steel today. But we can produce low carbon steel and build better structures, lasting longer, not harming our environment. If UK would recycle its own scrap to deliver high-quality steel satisfying its domestic demand in a closed loop it would lead to massive decrease of UK Iron and Steel emissions. This necessitates to (a) establish low-carbon steelmaking plants based on electric arc furnace, (b) develop technologies to make high quality steel from recycled scrap, i.e., examine and mitigate the causes of scrap contamination and develop the opportunities to control the chemical composition of liquid steel made via electric arc furnace, and (c) develop innovative business models to allow UK downstream steel supply-chains to prosper.”
Declared interests
Dr Julian Steer: in receipt of funding from British Steel to measure, and optimise, the performance and selection of their injection coals.
For all other experts, no reply to our request for DOIs was received.