Contribution of Steel to the Circular Economy

Contribution of Steel to the Circular Economy

There are two types of economies which exist around the world. These are (i) linear economy, (ii) circular economy. A circular economy is an alternative to a traditional linear economy in which the resources are kept in use for as long as possible, extracting the maximum value from them while in use, and then recover and regenerate products and materials at the end of each service life. Since the last industrial revolution, economic growth has been strongly coupled to primary resource consumption; circular economy models attempt to decouple economic growth and resource use since it is recognized that current global consumption patterns are not sustainable. A shift is in progress presently from linear economy system to circular economy system. As steel is everywhere in our lives and is at the heart of our sustainable future, the steel industry is an integral part of the global circular economy.

Throughout its evolution and diversification, the industrial economy has never moved beyond one fundamental characteristic established in the early days of industrialization. The industrial economy is based upon a linear model of resource consumption which follows a ‘take-make-dispose’ pattern. The linear ‘take-make-dispose’ model relies on large quantities of easily accessible resources and energy, and as such is increasingly unfit for the reality in which it operates. Organizations extract materials, use them in the production of products, sell the products to customers who later discard them when the products life is over and no longer serve their intended purposes. This is the norm in the case of linear economy concept (Fig 1), without concerns for externalities which can take place. In addition, this behaviour is built on the assumption that resources are endless, and the external input is needed to support economic growth.

Fig 1 Linear economy concept

In the linear economy concept, the focus has been on efficiency improvements along this straight line. A higher efficiency results in lesser materials and resources needed, which in turn leads to less externalities per produced unit. However, working towards efficiency alone i.e. a reduction of resources and fossil energy consumed per unit of manufacturing output, does not alter the finite nature of the stock of resources but can only delay the inevitable. A change of the entire operating system seems necessary.

However, the mind-set is slowly changing now. The dependence on the linear economy concept is getting weaker in the wake of powerful disruptive trends which are going to shape the economy for years to come. These trends are (i) resource scarcity and tighter environmental standards are here to stay, (ii) possession of the information technology which allows the shift, and (iii) witnessing of a pervasive shift in consumer behaviour.

The circular economy concept is a reaction to the linear approach. It comes from the understanding that our planet’s resources are not endless, and that growth and value can be created without the input of external virgin materials. Instead of discarding materials, energy and products at its end of life, the concept of circular economy aims to bend this straight line, reconnecting the end with the start, with the aim to form a closed loop. This concept is nothing new, but is something which has been forgotten as people become more affluent and organizations to make profit out of people having to buy new updated products. The circular economy aims to rebuild capital, whether it is financial, manufacturing, human, social or natural. This approach enhances the flow of goods and services.

The circular economy concept has deep-rooted origins and cannot be traced back to one single date or author. Its practical applications to modern economic systems and industrial processes, however, have gained momentum since the late 1970s as a result of the efforts of a small number of academics, thought-leaders, and businesses. The general concept has been refined and developed by the several schools of thought such as (i) regenerative design, (ii) performance economy, (iii) cradle to cradle framework, (iv) industrial ecology, and (v) biomimicry which relies on three key principles of nature as model, nature as measure, and nature as mentor.

A circular economy is an industrial system which is restorative or regenerative by intention and design. It is based on the premise, where products or parts are repaired or remanufactured, reused, returned and recycled. It replaces the ‘end-of-life’ concept with restoration, shifts towards the use of renewable energy, eliminates the use of toxic chemicals, which impair reuse, and aims for the elimination of waste through the superior design of materials, products, systems, and, within this, business models. Fig 2 shows the circular economy concept.

Fig 2 Circular economy concept and waste management hierarchy

The essence of circular economy is to decouple value creation from the consumption of finite natural resources, and to replace the end-of-life concept in which products naturally end up as waste. With a change in product design, materials and systems, together with a change of the concept of ownership through new business models, waste can be limited and ultimately eliminated. Perhaps the most important underlying principle to achieve this is the recycling of materials, by which materials are reused to make new products instead of being disposed through incineration or land filled. But circular economy contains more than recycling. Achieving a circular system needs fundamental changes to fully support the recycling of materials, but also to maximize the value of the natural capital. This entails a set of new approaches, namely (i) materials recirculation, (ii) product materials efficiency, and (iii) new business models which all contribute to a reduced demand for virgin materials, leading to less extraction of raw materials and production with lower carbon dioxide (CO2) emissions.

The circular economy ensures that value is maintained within a product when it reaches the end of its useful life while at the same time reducing or eliminating waste. This idea is fundamental to the triple-bottom-line concept of sustainability, which focuses on the interplay between environmental, social and economic factors. Without a life cycle approach, it is impossible to have a genuine circular economy.

Circular economy concept is based on few simple principles. First, at its core, a circular economy aims to ‘design out’ waste. Waste does not exist in this concept. The products are designed and optimized for a cycle of disassembly and reuse. These tight component and product cycles define the circular economy and set it apart from disposal and even recycling where large amounts of embedded energy and labour are lost. Secondly, circularity introduces a strict differentiation between consumable and durable components of a product. Unlike today, consumables in the circular economy are largely made of biological ingredients ‘nutrients’ which are at least non-toxic and possibly even beneficial, and can be safely returned to the biosphere either directly or in a cascade of consecutive uses. Durables, such as engines or computers, on the other hand, are made of technical nutrients unsuitable for the biosphere, like metals and most plastics. These are designed from the start for reuse. Thirdly, the energy needed to fuel this cycle is to be renewable by nature, again to decrease resource dependence and increase system resilience (e.g., to oil shocks).

Within the circular economy, the end-of-life credentials of construction products are important. Also, it is important to understand the difference between reuse and recycling. This is particularly important in the case of the term recycling which has a loose definition in general parlance but a more specific definition within waste management and the circular economy. Recycling is the process of converting waste materials into new materials and products, which can be the same or different to the original material or product. Normally the recycling process needs energy. Recycling can be true or closed loop recycling or down cycling. On the other hand, reuse is the subsequent use of an object (in its original form) after its first life. It can be repurposed, but the object only has minor alterations, retaining a similar (or the same) form. It is also important to differentiate between two different types of recycling since the environmental or circular economy benefit (normally assessed using life cycle assessment) can vary significantly. In the ‘true or closed-loop recycling’ the products are recycled into products with exactly the same material properties. An example of true recycling is recycling steel by remelting. In the case of ‘down cycling’, the ‘down cycling’ process consists of converting materials into new materials of lesser quality and reduced functionality. Examples of’ down cycling’ is the crushing and grinding of refractory materials to produce refractory mortar.

The Ellen MacArthur diagram (Fig 3) conceptually ranks waste management options according to what is best for the environment. This has been a central concept in European Union waste policy frame-works for many years. Waste management hierarchy under this concept is shown in Fig 2.

Fig 3 Ellen MacArthur diagram for circular economy

Steel and circular economy

Steel has excellent circular economy credentials both as a material which is strong, durable, versatile and recyclable and, as a structural framing system, which is lightweight, flexible, adaptable and reusable. One of the key benefits of steel is that it can be designed to meet the specific strength, durability, and end-of-life recycling requirements of almost any application. The combination of strength, recyclability, availability, versatility and affordability makes the steel unique.

Present research is resulting into the production of new steels which are even stronger and lighter than those available today. Wind tower turbines, vital for producing clean wind energy, are already 50 % lighter than they were a decade ago. For a 70 metre tower, this translates into a 200 ton reduction in CO2 emissions. With their higher strength-to-weight ratio, the newer steels can be used to manufacture tower sections of upto 30-metres. This reduces emissions during transport and assembly.

Higher grade steels are also being developed for construction. They enable the construction of larger and taller buildings in a more efficient way and produce the lowest possible amount of waste. The use of higher grade steels is expected to reduce the quantity of steel used in construction. Transportation costs are also reduced thanks to the thinner and hence lighter, steel components. They also shorten the time needed for processing at plants and on-site construction, largely due to a reduction in the number of welds needed. Using these steels, it is possible to reduce the number of columns in building structures and make them thinner. This results in larger areas and provides opportunities for better design and use of space. Higher grade steels enable structures to be developed which incorporate dissipation mechanisms to absorb the majority of the seismic energy generated by an earthquake.

A circular economy promotes longer product lives. The longer a product lasts the lesser raw materials are needed to be sourced. Product durability contributes to reducing the depletion of raw materials. Maintaining products at their highest utility and value for as long as possible is a key component of the circular economy. Putting it simply, the longer a product lasts the lesser raw materials are needed to be sourced and processed and less waste is generated. Steel products are inherently durable meaning not only that they last a long time but also that several steels can be reused after their first life.

Steel also facilitates its own longevity. Steel-framed buildings can be easily adapted if the configuration of the structure needs to be changed. The building can be taken apart and rebuilt with minimal disruption to local communities and the environment. Strong, durable exterior steel structures can accommodate multiple internal reconfigurations to suit changing needs. Warehouses or industrial buildings made with steel can be easily converted into modern living or working spaces. This extends the useful life of the building (and the life of the steel it contains) to save resources and reduce costs.

Steel is a versatile material both in terms of its metallurgy / chemistry and as a product. It is infinitely recyclable material. Structural product elements s are durable, robust and dimensionally stable which can be bolted together to form assemblies which are inherently demountable and reusable. Steel structures can be easily extended and reconfigured in-situ.Steel is not a single material. There are several different grades of steel ranging from mild conventional steels to high-strength steels, advanced high-strength steels, and specialty steels such as stainless steels. Each grade of steel has properties designed for its specific application. In fact, there are more than 3,500 different compositions or grades of steel with different physical, chemical, and environmental properties. If the different product sizes and shapes are added to this, then the figure of 3500 gets increased several times. Each variety of steel is tailored to specific applications in sectors as diverse as packaging, engineering, white and yellow goods, vehicles and construction. Around 75 % of modern steels available today have been developed in the past two to three decades. If the Eiffel Tower is to be rebuilt today, the steel requirement is only one-third of the steel which has been originally used (in 1889) because of the strength and quality improvements achieved by the steel industry over the last century.

The versatility of steel promotes recycling since steel scrap can be blended, through the recycling process, to produce different types of steel (different grades and products) which meet changing demands over time. For example, steel from redundant industrial machinery can be recycled into more contemporary products such as automobiles or white goods which, in turn, can be recycled into new, maybe as yet undiscovered, applications in the future.

Extending the life of the products is another key aspect of the circular economy. In theory, all new steel can be made from recycled steel. However, this is not practically feasible due to the long life of steel products, given the strength and durability of the steel. Around 75 % of steel products ever made are still in use today. Buildings and other structures made from steel can last from 40 years to 100 years and longer if proper maintenance is carried out.

Extending the life of the products can be achieved by making the products which are both flexible and adaptable to change so that they can last longer and greater value can be extracted from the materials and resources used to produce them. The pace of change in all walks of life has never been greater. Changing work patterns, new building services and information technologies, changing demographics and new legislation are all putting new and different demands on the steel products. Sustainable products are to be flexible to change of use and adaptable to future needs and requirements whether they are regulatory or market driven.

Large, heavy structural steel components need planning for end-of-life management. However, with steel scrap having value, the incentive to recover and recycle these components is high and more cost effective than paying for them to be placed in landfill sites.

In a well-structured circular economy, the steel has significant competitive advantages over competing materials. Four keywords which define these advantages are (i) reduce, (ii) reuse, (iii) remanufacture, and (iv) recycle as shown in Fig 2.

Reduce means reducing the weight of products, and hence the amount of material used. It is an important key to the circular economy. Through investments in research, technology and good planning, steel producers have drastically reduced the amount of raw materials and energy needed to make steel over the past 50 to 60 years. In addition, the steel producers are actively promoting and developing the use of high-strength and advanced high-strength steel grades for several applications. These grades contribute to the light weighting of applications ranging from wind turbines to automobiles to construction panels. Because of it, lesser steel is required for providing the same strength and functionality.

Reuse characteristics of steel is because of its durability. Steel can be reused or repurposed in many ways, with or without remanufacturing. This already occurs with automotive components, buildings, rails and many other applications. Reuse of steel is not limited to its original application. It dates back to ancient times when swords were converted into plough-shares. Reuse is normally done in the areas where it is technically possible without reducing safety, mechanical properties and / or warranties. Rate of reuse is going to increase as eco-design, design for reuse and recycling, and resource efficiency become more popular.

Reuse is advantageous as little or no energy is needed for reprocessing. The durability of steel ensures several products which can be partially or fully reused at the end of their life. This can extend the life cycle of the steel product considerably. However, initial design based on life cycle thinking is critical if reuse is to succeed.

The construction industry has been one of the first to embrace the reuse of steel components such as structural beams, roofing, and wall elements. Increasingly these elements are being designed for reuse. Although reinforcement steel is presently recycled rather than being reused, opportunities exist to create modular reinforced concrete elements such as standard floor slabs.

Reuse through repurposing involves a specially designed collection and reprocessing system to make the product fit for a new application. The quantity of energy and resources needed for reuse applications can be considerably lower than producing a new application from raw materials. For example, steel plates used to build ships can be re-rolled and used in the construction of new vessels. The only input is the energy needed to reheat, re-roll, and transport the steel.

Remanufacture of several steel products can be done. A wide range of steel products are already being remanufactured. They include machine tools, electrical motors, automatic transmissions, office furniture, domestic appliances, automobile engines and wind turbines. Re-manufactured for reuse is done to take advantage of the durability of steel components. Re-manufacturing restores durable used products to like-new condition. It differs from repair, which is a process limited to making the product operational, as opposed to thorough disassembly and restoration with the possible inclusion of new parts.

Remanufacturing restores durable, used products to like-new condition. It involves the disassembly of a product, during which each component is thoroughly cleaned, examined for damage, and either reconditioned to original equipment manufacturing (OEM) specifications or replaced with a new part. The product is then reassembled and tested to ensure proper operation. This process differs from repair, which is limited to making the product operational as opposed to thorough restoration. Further, by designing steel products for reuse or remanufacturing, even more resources can be conserved.

Recycling of steel has been carried out in the steel industry since steel was first made. It ensures that the value of the raw materials invested in steelmaking lasts far beyond the end of the life of a steel product, and that the steel remains a permanent resource for society. All the steel products are inherently recyclable and structural steel elements are also inherently reusable. Further, steel is 100 % recyclable and can be recycled over and over again to create new steel products in a closed material loop. Recycled steel maintains the inherent properties of the original steel. The high value of steel scrap ensures the economic viability of recycling. Because of this, steel is today the most recycled material.

Two main raw materials for making steel are iron ore, one of Earth’s most abundant elements, and recycled (scrap) steel. Once steel is produced (from iron ore), it becomes a permanent resource for society, as long as it is recovered at the end of each product life cycle, because it is 100 % recyclable without loss of quality.

The magnetic property of steel ensures its inexpensive and easy recovery for recycling. Using magnetic separation, the steel scrap from post-consumer products can be easily retrieved from almost any waste stream. A world steel review showed that recovery rates for different sectors range from 50 % for small electrical and domestic appliances, upto more than 90 % for machinery. Levels of upto 98 % for structural steel in commercial and industrial buildings are being achieved.

Steel is the most recycled material in the world. Around 650 million ton of pre- consumer and post-consumer scrap are recycled annually, leading to significant savings in energy and raw material use. All scrap from steel production and downstream processing (frequently referred to as pre-consumer scrap) is collected and recycled directly in the steel production processes. The recycled content of any steel product can range from 5 % to 100 %. More than 23 billion tons of scrap has been recycled since steel production began.

The use of the term ‘recycling’ is required to be clarified. All types of steel can be recycled back into new steel of various grades, keeping its inherent material properties. Thus, steel scrap from lower value steel products can also be converted into high value steels by using appropriate processing and metallurgy. For other materials, this is not typically possible. Indeed the quality of recycled material is frequently downgraded or down cycled, as in the case of concrete, wood and aluminum.

Recycling is important in the circular economy as it conserves valuable resources. In addition to steel industry efforts to increase recovery rates, there are also initiatives, in conjunction with other metal industries and research institutes, to identify losses throughout product life cycles. The goal is to minimize these losses and further improve the recycling rate of steel and other materials.

The steel industry continues to further integrate these advantages into its operations in order to highlight the benefits of steel to those people who are making decisions on material choices. Co-operation from the whole production chain is essential for ensuring that reused or remanufactured products have the same properties as new steels. Also, to further contribute to the circular economy, a number of key areas which the steel industry is required to focus on include the following issues.

  • Water used in the production process is required to be handed back to the society in the same or better condition as it was received, and that emissions to atmosphere are to be minimized as much as possible.
  • Regarding the raw materials consumed, such as coking coal and iron ore, strict adherence to sustainability is impossible as raw materials, once consumed, can clearly not be replaced and as such reduces the ability of future generations to produce steel in the same way as today. This challenge can be bridged by the construct of reuse, remanufacture and recycling, to design products for easy reuse and to recycle as much steel from the products at the end of their life as possible to make new steel products. Clearly this needs that in time, sufficient quantities of reusable and recyclable steel are available to satisfy market demand for steel. In addition, the concept of responsible sourcing needs to be addressed further, taking consideration for the sourcing of materials in the supply chain.
  • Emissions into the atmosphere (e.g. CO2 and other green house gasses) can be reduced by ensuring that the application of steel leads to reduced emissions during the product use phase. This can be done through the use of, for example, high-strength steels or more efficient steels used in motors.
  • Many competing materials have ‘light-weight’ properties (more specifically lower density materials) and can help reduce the emissions of energy intensive products in the use phase. However, these materials are frequently so much more energy and CO2 intensive to produce than steel products, negating the use phase benefits which these alternative materials offer. 

Life cycle thinking

Steel is everywhere in the lives of peoples today and is at the heart of the sustainable future. The steel industry is an integral part of the global circular economy. The circular economy promotes zero waste, reduces the amount of materials used, and encourages the reuse and recycling of materials, all fundamental advantages of using steel. A life cycle approach is very important in delivering true sustainability.

Normally policies are presently being made on the premises which only affect the ‘use phase’ of the life of a product, for example energy consumption for a refrigerator or CO2 emissions while driving an automobile. This focus on the ‘use phase’ can lead to more expensive alternative lower density materials being employed but which typically have a higher environmental burden when the whole life cycle is considered. This use phase limitation cannot continue. Life cycle thinking (LCT) is required for all the manufacturing decisions.

Every product which is sold and bought has a life cycle. Every product is manufactured, used, and then can be reused, recycled or disposed off at the end of its useful life. Further, steel which enters the waste stream can be easily separated and collected from other materials for recycling, by the use of magnets. LCT is a term which is used for describing the holistic thinking which is required for the sustainable solving of the problems of the society. It needs consideration of the raw materials used, energy consumption, waste, and emissions of a product across each phase of its life. This starts with design and finishes at the point where the product reaches the end of its useful life. In LCT, it is anticipated that a well-designed, steel-containing product is subjected to reuse or recycling of its components at the end-of-life.

Only by calculating the resources and energy used, and the waste and emissions produced at every stage along this journey, the true environmental impact of a product can be defined. This also enables the identification where its long-term environmental sustainability can be improved. For instance, the small increase in energy consumption or the addition of alloying elements needed to produce high-strength steels is compensated several times over when the life cycle of the product is considered. Using these high-strength steels means that products can be lighter and hence frequently save energy during the use phase of their life, for instance, when applied to the automobile sector it provides fuel economy, and over the entire life cycle of the product, less energy is used.

There is another reason why life cycle thinking is very important. By knowing the actual impact of each stage of the life of a product, the best decisions can be made on which materials are to be used. As an example, in addition to high-strength steels, low density materials such as aluminum, carbon fibre, magnesium, or plastics are sometimes used to make applications lighter. At first glance, these materials weigh less or, more precisely, have a lower density than steel and because of it can appear to be interesting alternatives. However, when the total life cycle of the material is taken into account then steel remains competitive, owing to its strength, durability, recyclability, versatility and cost. Comparison of CO2 emissions of these materials is shown in Fig 4. Further, at the end of the life of the product, these materials can need to be sent to landfill since there is no economical way for recycling or reusing the material. Alternatively, they can be down cycled to a lower grade product. It is important that this information is known before key material decisions are made. The whole life cycle, from raw material extraction through to end-of-life recycling or disposal is to be considered.

Fig 4 Comparison of CO2 emissions

A life cycle approach is required to be considered within the concept of the circular economy to create a more resource-efficient world, focusing on waste minimization. The steel industry has been doing the waste minimization since a long time for economical reasons. The circular economy promotes zero waste, reduces the amount of materials used, and encourages the reuse and recycling of materials, all fundamental advantages of using steel. A life cycle approach is very important in delivering true sustainability.

Steel by-products

Material efficiency is an integral part of the modern steelmaking process. The goal is to use all raw materials to their full capacity and eliminate waste from steelmaking. This approach includes industrial symbiosis in which almost every by-product formed during steelmaking is used in new products. This minimizes the amount of waste sent to landfill, reduces emissions, and preserves raw materials.

As with all large-scale manufacturing processes, the production of iron and steel generates by-products. On average the production of 1 ton of steel results in 200 kg (scrap-electric arc furnace route) to 400 kg (blast furnace- basic oxygen furnace route) of by-products. The main by-products produced during iron and steel production are slags (90 %), dusts and sludges. The worldwide average recovery rate for slag varies from over 80 % for steelmaking slag to nearly 100 % for ironmaking slag. Slag is used to make a range of products including cement, fertilizers, and asphalt. Process gases from ironmaking and steelmaking are typically used within the steelmaking plant, replacing steam and electricity, or exported to the local grid. Other by-products such as dust are reclaimed for their high metallic content. The generation of the by-products and their uses are shown in Fig 5.

Fig 5 By-product generation and their uses

In order to achieve better results, over the last few years, several initiatives and activities have been undertaken in order to apply new approaches and techniques aiming at by-product management in iron and steel plants for increasing their recycling. For example, the internal recycling of some of the by-products in the sintering and pelletization processes for achieving high quality of sinter and pellets while simultaneously reducing the environmental impacts and operating costs. In addition, dust recovered from electric arc furnace gas treatment has been used for substituting clays in traditional brick manufacturing, for the purpose of energy savings, environmental impact reduction and possible economic benefits. Furthermore, simulation models development has allowed identifying the slag quality of basic oxygen furnace, electric arc furnace, and ladle furnace to be internally reused and to provide significant economic and environmental improvements, compared to the present slag use in the steel plants. However, there is still significant room for improvement for increasing the recovery rate of by-products, achieving environmental and economic benefits, also according to the principles of industrial symbiosis.

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