Steel, ubiquitous in its usage, is the second largest production material and carbon emitter behind concrete.
The 1.8 billion tonnes of steel currently produced per year emits approximately 3.3 billion tonnes of CO2 or 7% of total global emissions.
Steel is still predominantly made through the reduction of hematite ore using coke as a reductant in the blast furnace. The coke and some pulverised coal additions provide the heating and CO to drive the reduction process. As both materials are practically devoid of Cu, the resulting liquid product, containing dissolved carbon, silicon, phosphorous and sulphur, termed ‘hot metal’ or ‘pig iron’ when solid cast, requires further processing, typically through the Basic Oxygen Furnace (BOF) route.
In the BOF process, a high volume of O2 gas is injected into the liquid metal to remove the carbon and other impurities, utilising a basic slag to absorb and contain the resulting oxides. As this process is exothermic, low-cost scrap steels have been used to bulk up the ferrous volume and provide a cooling effect. This scrap addition (~15%) is generally charged prior to the ladling of de-sulphurised ‘hot metal’ (achieved through a minor pre-process) into the BOF furnace vessel. It is from this initial scrap addition that the industry introduces a low level of copper and other deleterious metals into the product, which can be minimised by the use of plant-arising scraps with known chemistry.
At this low, controlled level, these contaminants have little to no effect on the product but will raise the baseline of Cu, Sn, Ni, Cr, Mo, etc. once the material is recycled. However, as steel is recycled over time, these elements can increase to a point that renders steel scrap difficult to reuse for the manufacture of grades that demand low levels of residual elements to achieve their essential mechanical properties when in use.
The blast furnace process is highly efficient and versatile, having been refined to its current state over 2000 years (the first examples of this process date as far back as 1 AD in China), with major innovations in quality, efficiency and volume throughput being introduced from the industrial revolution to the turn of the century.
One of the major benefits of the blast furnace is its ability to easily process abundantly available ferrous ores which contain relatively low FeO content. However, modern ironmaking ores are focussed at the 62-65% FeO range to maximise productivity and minimise slag production from the remaining material.
Unfortunately, methods to convert the blast furnace to operate solely using ‘green’ reductants such as H2 is impossible without significant, undiscovered step-change technology, as the coke not only provides both exothermic heating and reduction but necessary mechanical stability to the raw material feed mechanism as it is processed down the length of the furnace. H2 reduction of iron ore is endothermic, requiring additional heating and generating excess H2O which is deleterious to the process and its containment.
The current drive to decarbonise steel is through electrical steelmaking technology, with the Electric Arc Furnace (EAF) being the sole contender for volume production. This assumes the eventual conversion from fossil fuel to renewable electricity generation and manifold increase in electrical infrastructure to compensate for supplementary, off-grid chemical energy sources currently used in industry.
Better utilisation of scrap
Without the blast furnace supplying ~66% of the Fe units supporting the world’s annual steel demand, we must rely upon greater usage of obsolete steel (OS) from end-of-life (EoL) products (scrap) and virgin iron produced from technologies such as Hot Briquetted Iron (HBI) and Direct Reduced Iron (DRI).
Unfortunately, virtually all scrap generated globally is already in use, feeding the demand for low-quality construction products and highly alloyed, tightly specified engineering steels for aerospace, defence, medical and chemical industries to name a few, although the latter tends to apply to much smaller volumes.
Historically and presently this resource was and is of poor bulk quality due to the scrap supply chain model being built upon throughput over quality. Very little effort has been placed into segregation by source causing gross loss of original product grade identification, segregation or appropriate fragmentation sizing to ensure complete separation from joining to non-ferrous materials such as Al, Cu, etc. and dissimilar steel grades.
This problem has visibly worsened over the last two decades with entrained Cu levels rising several points. If one considers the production source of EoL steel scrap for the UK, considering its sourcing from the global market, the alloyed Cu content can be estimated simply as presented in Table 1.
|Average Inherent Copper
This is an over-estimate, as the UK in general consumes more blast furnace-sourced steel than implied by the global production average.
From recent sampling and assaying of scrap available in the UK, it has been demonstrated that the Cu average for a range of scrap products currently purchased by the UK Steel Industry, i.e. OA, 1, 2, 3B, 6A, 7A/B (see BMRA Scrap Guide publication for definitions) is 0.2-0.38wt% making it an unsuitable replacement raw material for the 6 million tonnes of product currently manufactured by blast furnace for strip and long products in the UK.
Given that the UK generates 10.2 million tonnes of scrap annually and the domestic steel manufacturing use total is approximately only 7.2 million tonnes, we are missing a huge opportunity to lead the global charge in circularity and going ‘green’.
Due to the high copper content, which could evidently be minimised to a level close to that shown in Table 1 with appropriate pre-segregation and processing, this valuable material is predominantly exported to countries such as Turkey and India where it is downcycled to produce low-value rebar.
Alternatively, rather than employing a 100% scrap charge model for EAF steelmaking, the UK could follow the progression of US steelmakers, where EAF steelmaking has overtaken blast furnace/BOF via the financially competitive surge in Mini-Mill plants since the 1970’s.
Led by Nucor, EAF plants have not only improved the quality and relevance of scrap product grades through the partnership and purchase of scrap collection and processing organisations, but have utilised pig-iron and DRI as a dilutant to reduce concentrations of deleterious elements such as Cu to overcome the remaining mixing and contamination problems.
Unfortunately, the cheap electricity and natural gas prices found in the US are not enjoyed by the UK and Europe, making DRI domestic production uneconomical, particularly when dilution of up to 50-80% is required for bulk Cu contamination of scrap between 0.15-0.4wt% to produce strip and high-end long product applications.
This is complicated even further by the looming phase-out of fossil fuels, requiring the replacement of natural gas-powered DRI/HBI plants with green fuels such as H2, which brings a far higher cost, compounded by the scarcity of supply in the current market.
Production scale-up of H2 of several orders of magnitude would be required to make this a possibility, with green H2 production volume being towards the bottom of the many sources (‘colours’) of H2 production, with each colour having a variable impact upon CO2 emission.
Focussing upon both scrap and DRI on a global level, another major issue is encountered. As Western steel manufacturers transition away from the blast furnace, with its readily available, cheap and accessible supply of iron ores, the demand for limited availability raw materials such as scrap and DRI process-matched iron ore (>67% FeO), demand will outstrip supply and quickly raise the open market price.
As mentioned earlier, virtually all of the globally available scrap is already in use, accounting for ~30% of global steel demand.
DRI quality iron ore accounts for only 3-5% of the ore currently mined and shipped, with the remaining ores that are easily processed by the blast furnace unable to be used. This is due to the inability of DRI furnaces to effectively eliminate the mineral impurities during the process.
Expensive additional processing and beneficiation techniques have been hypothesised together with the mining of magnetite ores to augment the abundant hematite ores that are favoured by today’s market. However, analysts have opined that this may only increase supply by a further ~40% by 2030 (an increase from 104mt to 152mt per annum).
Optimistic speculation of DRI-suitable ores predicts that production could ramp up to 889mt per annum by 2050, with global scrap availability rising to 900-1200mt per annum. However, when considering the actual Fe yield of both scrap (~89%) and DRI ( ~63%) in the EAF, a significant shortfall still remains between this number and the predicted global steel consumption of 1.8-2.4 billion tonnes per annum.
It is opined that, together with an unprecedented rise in ‘green’ ferrous raw material prices, there will be a global shortfall of over 50% in green steel, with prices further compounded by the high cost and low availability of H2.
The historically low cost of steelmaking and its commodity status that has enabled cheap product manufacture over the last 80 years may be at an end.
The insufficient supply of ‘green’ raw materials and resulting price increase, driven by unrelenting market demand for steel products, may place a further strain on the transitioning Western steel manufacturing industry as developing nations are also encouraged to transition.
Benefitting from significantly lower operational costs and subsidised by national government financial support, countries such as China, India, etc. will logically utilise their higher profit margins to outbid the West for DRI and scrap, making it increasingly difficult for Europe, the UK and the US to compete without political countermeasure.
Such intervention is already in preparation across Europe with border taxes and scrap movement control nearing completion (see EU Carbon Border Adjustment Mechanism (CBAM)).
Although the global situation is difficult, the UK is potentially in an advantageous position given we accumulate more scrap than we currently produce steel. Furthermore, this scrap steel is viewed as high quality when compared with the global mean.
Analysis is key
To be successful, the UK must exploit this surplus and not rely upon dilution with virgin iron such as DRI/HBI. This leads to the final and most important factor in ensuring both sovereign capability and sustainability in the face of the ensuing chaotic global market: analysis.
Together with efficient pre-segregation, processing through fragmentation and shredding and post-processing/separation using conventional means, a robust and reliable analysis/sorting technique is essential to our success.
Not only do we need to separate the steel from non-ferrous and non-metallic contamination, but we also need to ensure that differing steel grades and alloys are identified, appropriately separated and grouped.
There are ~3500 grades of steel that are currently in use, with various alloy chemistries. These alloys are typically blended to satisfy the high throughput required by the scrap industry, resulting in poor matching to recycled end-product chemistries, particularly for strip which is, essentially, pure, uncontaminated iron plus a small amount of carbon and other beneficial alloys.
Some of the alloyed elements can be removed by deoxidation during the EAF and secondary steelmaking processes, which requires energy and additional cost, while others such as Cu, Sn, Ni, and Mo are not thermodynamically or economically possible.
Several techniques utilising XRF, LIBS and PGMAA are being trialled or used in limited applications to identify and remove contamination by external elements and segregate alloys for direct and controlled mixing. However, further effort is required to also focus this technology on alloy identification.
If a higher level of control is demanded from the UK scrap supply chain, together with dedicated grade analysis and separation, it will be possible for the UK to take the global lead in decarbonised steelmaking in a profitable manner.
Research conducted by Swansea University’s ERDF/WEFO-funded FlexisApp-iSpace project and the EPSRC-funded SUSTAIN Future Manufacturing Hub has indicated that the material within the UK’s scrap mix could satisfy all of the UK’s current steel manufacturing portfolio, with room for volume and product expansion, if the above factors are implemented successfully.
This would of course rely upon the application of appropriate policies to control the influence of the global market’s access to the UK’s high-quality scrap ‘mine’, minimising the effects of developing and newly developed nations from outpricing this sovereign resource as discussed.
Tough legislative controls like tariffs and subsidies, however, only provide an easy, short-term solution to what will become a bigger, long-term problem.
Sustainable development will only be achieved by motivating the market to want and support change; the first major issue would be how the yearly accumulation of 3.3 million tonnes of UK scrap oversupply will get to the wider market.
The key solution is to prevent the global steel manufacturing market from out-buying the UK companies without stifling the scrap industry and accumulating material we cannot sell, while the steel industry grows to accommodate.
To this end, sustainable solutions must be found to the following questions:
- How do we motivate investment into developing the supply chain to react to quality and not quantity?
- How do we financially drive the UK market to become a domestic mine of manufacturing raw materials?
- How do we create the first financially motivated and effective circular economy?
- How do we create sustainable and worthwhile employment for the redundant primary steelmakers?
Ultimately, success for steel and other materials production industries can only be achieved by making money for individual companies and UK PLC while creating a positive change for an industrial heritage we are passionate about.
The provision of cheap, abundant green energy will also be essential, but potential solutions to this issue are also being explored.
i-Space is a collaboration between Swansea University and UK Steelmakers, to develop a technically and commercially viable source of raw material from domestically arising end-of-life components, and for this reclaimed material to re-enter the UK Steel Industry and other UK Foundation Industries. Find out more about the iSpace project by visiting their page on the Swansea University website: www.swansea.ac.uk/science-and-engineering/research/i-space
Find out more about the SUSTAIN programme by visiting their website: www.sustainsteel.ac.uk