Technologies to Mitigate the Climate Impacts of Steel

Jeffrey Dewey, Beam Project

Steel has made modern society, but it’s also a huge contributor to climate change. Want to know how do we keep building on steel’s strength while cutting the climate impact? Read on.

The impact of steel on modernity cannot be overstated. Modern steel processing was born in the 1940s, leading to the mass production of skyscrapers, industrial and agricultural machinery, automobiles, and deadly weapons. Steel is durable, versatile, and most significantly, strong; if I encountered a warlock that converted and reshaped my mass of ~150 pounds (if we round down a bit 😉) into steel shelving, then my cursed form could proudly support at least 20,000 pounds of brews and cauldrons. However, as with many amazing 20th century inventions, climate change demands we rethink the 3 gigatons of CO2 expelled by steel production.

Contemporary Steel: Uses, Players, and Climate

Let us first understand the current uses and climate impacts of steel. According to worldsteel.org, the world used 1.7 gigatons of steel in 2018, with 51% used in construction, 15% in mechanical equipment, 12% in automobiles, 11% in metal products, and 5% or less in transport, domestic appliances, and electrical equipment. The lifespan of steel is very long. Steel lasts on average 52 years when used for its primary purpose of construction, and a minimum of 11 years when used in appliances or trucks. This means steel consumption rises dramatically as a country develops, and then cycles around a baseline disrupted only by major infrastructure replacement projects. For example, the democratic nominee for president, Joe Biden, is calling for $2 trillion investment in nationwide infrastructure, which will undoubtedly require increased consumption of construction materials such as steel and cement.

The current climate implications of steel use today are distressing. In 2018, the production of steel accounted for roughly 3 gigaton equivalents of CO2, or 7–9% of global emissions. To put this in perspective, steel production alone produced more CO2 than the aviation, aluminum, and plastics sectors combined. Processing one ton of crude steel produces on average 1.9 tons of CO2. Why? Steel is simply iron that has been purified and supplemented with a small amount (.05–2%) of carbon. The purification process involves melting impure iron at 2000–3000 degrees Fahrenheit in a blast furnace and adding large amounts of coke, a refined form of coal, to chemically react with oxides and other impurities in the iron, producing steel, CO2, and heat. Coke production and use accounts for 50–75% of emissions while energy accounts for the remaining 25–50%. It is clear that steel production is an emissions problem; what can we do to address it?

Changes in the behaviors and policies of the largest steel producers and consumers will have a greater impact than others. When talking about contemporary steel production and consumption, China must be mentioned. As a superstar of economic development, China has been both the number one producer and consumer of steel by a long shot. In 2000 China alone produced and consumed roughly 15% of the world’s steel. In 2018 that figure grew to a staggering 50%, trailed by India, Japan, The United States, South Korea, and Russia each producing merely 4–6% of global steel. This reality is critical to understanding which solutions can realistically curb emissions from steel production.

Exhausted Solutions: Efficiency and Recycling

One method to reduce emissions is to improve energy efficiency. In the case of steelmaking, however, profit has already motivated manufacturers to reduce their costly energy consumption. Over the last 50 years, the industry has reduced energy consumption by 61%, but efficiency has plateaued since 2005. Unfortunately, the most energy intensive step, melting the steel in a blast furnace, is only 20–30% away from its theoretical efficiency limit. While the basic-oxygen furnace (BOF), which relies on burning of coke and impurities to reach the necessary temperatures, is traditionally used, electric arc furnaces (EAFs) represent an increasingly green alternative as the energy grid is replaced with renewable sources. Unfortunately, EAFs require an additional iron purification step to remove impurities normally removed by coke. This step can be made greener using coke alternatives, such as natural gas, hydrogen gas, or even electricity (these discussed later!), which can decrease overall CO2 emissions by at least one quarter.

Unlike with plastics and other commonly used materials, steel is a recycling success story. Globally, a remarkable 80–90% of steel is recycled. The problem is that steel recycling cannot keep up with the explosion in demand from China and other developing nations. Roughly 630 million tons of steel were recycled in 2019, but that only accounts for 34% of global steel demand. Recycling is only a feasible solution to reducing steel-related emissions if society can reduce its demand for steel. In addition, furnace type matters greatly when it comes to recycling. EAFs can be loaded with 100% scrap steel, whereas BOFs can only accept 20–30% scrap. As mentioned earlier, BOFs rely on coke for heating, increasing emissions from the recycling process. The bad news is China’s steel production, and therefore most steel production, relies almost entirely (90%) on BOFs.

The Typical Climate Solution: Use Less!

Reducing single-use plastics, meat consumption, and fossil fuel extraction: all are feasible “less is more” societal changes to reduce greenhouse gas emissions. Unfortunately, steel is critical to the most important aspects of our society’s very survival. Machines made from steel cut and harvest crops; steel buildings efficiently and economically house millions of people; factories and equipment made from steel manufacture solar panels and wind turbines. Using less steel will be a challenge for our society. Can we replace steel with sustainable materials?

As strong as steel, but five times lighter, carbon fiber is a material that should not be ignored. Even 62 years after its initial discovery, however, carbon fiber is rarely used in our society. Despite continuous advances in its efficient production, carbon fiber still costs roughly 25 times more than steel. This cost disparity starves carbon fiber demand. Although millions of tons of carbon fiber would be needed to replace steel, a mere 110,000 tons were produced globally in 2012. Even worse than its costs and limited production, carbon fiber is made from fossil fuels that are synthesized into plastic and superheated. It requires an astonishing 24–31 tons of CO2 to generate 1 ton of carbon fiber. Even accounting for carbon fiber’s lower weight, steel emits fewer CO2 emissions by far. The economic and climate costs of carbon fiber restrict its ability to replace steel in construction, manufacturing, and packaging. However, carbon fiber could play a role in transportation. For cars and trucks, the Department of Energy found replacing steel with carbon fiber could increase fuel efficiency 35–50%. Air travel emissions are highly dependent on weight, making airplanes an excellent candidate for carbon fiber replacement. One study found replacing steel or aluminum with carbon fiber in aircrafts would provide climate benefits after just 5 hours or 93 hours of air travel respectively. Therefore, it seems that carbon fiber could play only a limited, albeit significant, role in steel replacement. Carbon fiber will only play a role in our society when its economic and climate costs are addressed.

Steel reinforced concrete is an area in need of replacement; 17% of all steel is used to reinforce concrete. Replacing all steel reinforced concrete with a net zero emission material would reduce global CO2 emissions by 505 million tons/year. Bamboo could be that material! For millennia bamboo has been used in construction, but can it really compare to steel? Despite being 20 times lighter than steel, bamboo has a similar tensile strength (force needed to stretch apart) and modulus of rupture (force needed to snap in half). Unlike carbon fiber, bamboo is already grown and harvested in enormous quantities. In 2005 alone 389 million tons of bamboo were cultivated globally. Check out professor Dirk Hebel’s work from ETH Zurich on bamboo’s potential as a steel replacement for a more in depth look. Bamboo reinforced concrete was tested as early as 1914, but careful studies revealed the bamboo lacked a key property of steel: durability. Over time bamboo absorbs and releases moisture causing swelling and contracting. Repeated rounds of this process create space between the bamboo and concrete, weakening the material overall. Adding more concrete can counter this effect. However, as Ryan Duncombe from Beam has written, concrete, more specifically cement, currently produces enormous amounts of CO2. Researchers at Visvesvaraya Institute of Technology designed bamboo strips with evenly spaced ridges to counter bamboo’s poor adhesion to concrete. This resulted in reinforced concrete blocks with equal strength to steel. Similarly, 2020 research by Prof. Hebel uses epoxy resin to tackle the durability challenge. These recent breakthroughs will hopefully translate to a trusted bamboo product that can quickly replace steel in reinforced concrete.

Bamboo may be able to replace steel rods, but what about beams and sheets? Researchers at the University of Maryland may have found an answer in 2018. Trees did not evolve to be walls in our homes, and so they contain many micrometer-scale pores. These scientists determined if these pores were eliminated while retaining the wood’s general structure fibrous structure, the resulting material would be much stronger. They eventually accomplished this by chemically weakening and then compressing wooden blocks. The final product was five times lighter than steel, twice the specific strength (ability to withstand pressure), and, when laminated, could stop a bullet (it’s too bad Superman Man of Wood doesn’t quite roll off the tongue). This technology still needs to address many questions. What are the other material properties of densified wood? How durable is it? Can the process scale and compete with steel’s cheap price? Can the material be efficiently recycled? Despite is early stage, this new material, similarly to bamboo, has the potential to not only reduce GHG emissions from steel, but also store CO2 in our infrastructure.

Greenifying Steel Production

The replacement strategies we’ve discussed so far would cover roughly 70% of all steel use (in construction and transportation), but what about its other uses? Two strategies in particular have the potential to eliminate all direct emissions from steelmaking!

Steelmaking’s only emissions that aren’t related to energy consumption come from reacting coke with raw iron to chemically reduce oxide impurities such as iron oxide (aka rust). Replacing coke with a non-carbon source is one solution to steel’s CO2 footprint. Hydrogen gas is a powerful chemical reductant that reacts with oxides to produce water instead of CO2. Furthermore, hydrogen gas has a near zero carbon footprint when produced from a fully renewable electric grid. Steelmakers have investigated using hydrogen for decades, but it is only in the next year that several large-scale (100,000 tons/year) hydrogen-based iron ore reducing plants are expected to open. Also, a joint venture between three companies in Sweden called HYBRIT seeks to completely eliminate all steelmaking emissions by 2050. The technology is well validated and scalable, but there are still technical questions that impact its success, such as scaling hydrogen storage and consistency of steel quality. Furthermore, HYBRIT estimates the process will require 15 TWh of renewable energy, or a 2.5% increase in Sweden’s total output. That’s roughly equal to 2 million household solar panels. The energy consumption is huge, but steelmaking currently uses an unfathomable 10% of the world’s energy, with 75% of that energy coming from coke and coal power. As pilot facilities begin mass production, we will soon find out whether hydrogen-based steel production can match global demand.

Hydrogen gas and coke, fundamentally, are electron donation sources. If we need electrons, why not get them straight from the electric grid? Researchers at MIT made a breakthrough in 2013 to do just that, leading to a startup called Boston Metal. The technology, called molten oxide electrolysis, uses an electric current to directly convert iron oxides into iron and oxygen gas. This eliminates the need for capital-intensive hydrogen gas or coke production facilities. The major challenge was finding an anode material that itself did not corrode or oxidize from the intense conditions. It turns out a mixture of chromium, the metal that gives stainless steel its anticorrosion properties, and aluminum oxides does the trick. The technology is still in its infancy (Boston Metal proudly reports over one ton of metal alloys produced so far), and questions of steel properties, scalability, and energy consumption need to be addressed. However, molten oxide electrolysis has the potential to completely eliminate CO2 emissions from steel while reducing capital and operational costs to a bare minimum.

Key Takeaways

As with many Beam articles, we’ve covered a lot of material! Here are some key takeaways:

· Half of all steel is used in construction.

· China produces and consumes roughly half of global steel

· Steel production in 2019 generated 7–9% of global emissions.

· Steelmaking efficiency and recycling rates are near their theoretical limits

· Electric arc furnaces (EAFs) produce steel with fewer emissions while basic oxygen furnaces (BOFs) rely on burning coke

· Each ton of carbon fiber is expensive and produces 24–31 tons CO2. However, it provides huge climate benefits in aviation.

· Bamboo can replace steel reinforcement in concrete to reduce ~1.5% global emissions, but only if bamboo’s durability is addressed.

· Densified wood is an innovation that can stop bullets and could replace steel in construction, but many questions about its durability and scalability remain.

· The direct emissions from steel production can be eliminated if coke is replaced with a green chemical reductant, and with a 100% renewable energy grid.

· Large-scale hydrogen-based steel plants are coming online in the next 5 years, but they require enormous amounts of electricity and infrastructure.

· Steelmaking uses approximately 10% of global energy.

· Electrons are used to replace coke or hydrogen in molten oxide electrolysis (MOE). The technology is in its earliest stages, but could eliminate CO2 emissions and reduce costs.

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