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Nov 06, 2024

Decarbonizing Flat Glass - Insights and Inspirations

While I was in the United Kingdom (UK) this summer, I took advantage of being in the same time zone to reconnect with the NSG Group’s UK team members working on float glass decarbonization: David

While I was in the United Kingdom (UK) this summer, I took advantage of being in the same time zone to reconnect with the NSG Group’s UK team members working on float glass decarbonization: David Cast, Paul Skinner and Chris Dye. I started my career 30 years ago this year with Pilkington (now part of the NSG Group) at its European Technology Centre in northwest England. I have great memories of playing pick-up football (soccer) after work with David and our other colleagues. I was, of course, much younger then!

Work is currently being done in Europe to decarbonize the highly energy-intensive float glass process. Many of the major European flat glass manufacturers have developed a low-carbon float glass option (NSG Group, AGC, Saint-Gobain), which tends to be only available in low quantities because of the current challenges in scaling decarbonization strategies and market demand. This is a great starting point and a critical development because approximately 70% of the embodied carbon in insulating glass comes from the float glass itself.

I was interested in learning more about the NSG team’s strategy because they have been implementing what seems to be broad and comprehensive. They explained that they seek to achieve their corporate goal of carbon neutrality by 2050. Before diving into the details of my discussion with the NSG team, it is important to understand why Europe is moving faster than North America in commercializing low-carbon glass.

The Driver: Legislation

European climate change legislation (directives) drives market demand for low-carbon construction materials and highly efficient buildings. Directives have been designed to funnel cheaper capital to companies and/or construction projects that are aligned with reducing climate change, increasing climate adaptation, participating in the circular economy, reducing other ecological impacts and addressing social and governance topics. As a result, design teams are being driven to specify and construct increasingly lower-carbon buildings, focusing on embodied and operational carbon.

Now operating outside the European Union, London has recently required an embodied carbon analysis to be submitted with every application for planning permission.

Embodied Carbon Levers

The NSG Group’s team noted that three main levers can be used to reduce carbon emissions from float glass production:

NSG’s approach to achieving net-zero carbon has been broad-based, addressing many levers simultaneously. The team has been most prominent amongst their peers for championing fuel switching. Since scope one emissions (those emitted in the manufacturing process rather than the supply chain) account for 40% of the embodied carbon emissions, addressing this contribution is essential. Cast asserted that combining all three strategies plus other activities, such as collaboration in the value chain, is essential to achieve net zero.

Fuel Switching

In 2021, Pilkington United Kingdom Limited, part of the NSG Group, announced that it had successfully made float glass with hydrogen instead of natural gas–the world’s first trial. A year later, the NSG Group’s team produced float glass from burning liquid bio-fuel. The NSG Group used a “sustainable biofuel made from organic waste materials” to “power the furnace entirely for four days, creating 165,000 square feet of the lowest carbon float glass ever made.”

The announcement noted that the fuel emits approximately 80% less carbon dioxide than traditional natural gas in float glass production. Pilkington’s original furnace designs allow it to have the flexibility to experiment with both gaseous and liquid fuels.

Hydrogen as an Alternative Fuel

Burning hydrogen produces 10 times fewer direct carbon emissions than natural gas (methane) and, as such, reduces the scope one emissions for float glass manufacturing close to zero. However, using hydrogen can add emissions from its manufacturing process (scope three emissions), so it is important to understand the source of hydrogen generation.

Several types of hydrogen are given names associated with the relative carbon emissions caused by making the hydrogen itself. Here are some common types:

Is hydrogen safe? Interestingly there is a perception that hydrogen is more dangerous than natural gas (methane), even though they are both explosive. According to the NSG team, hydrogen is already used in the float glass process, albeit in smaller quantities. They are familiar with the necessary controls, which do not present a barrier to fuel switching.

Global Hydrogen Capacity and Bridging Strategies

A global capacity issue currently limits hydrogen production expansion, which has significant implications for the timescale for widespread fuel switching. For example, to supply the hydrogen needed for the trial in 2021, the supply of hydrogen to other needs in the UK had to be curtailed. Government support may well be needed to drive the expansion of clean, economic hydrogen sources.

Using sustainable, low-carbon biofuels represents a bridging strategy for the NSG Group to the full hydrogen economy. Like the development and deployment of renewable energy, the NSG Group’s team predicts that hydrogen production will become more widespread, achieving needed economies of scale to attain cost parity with natural gas ultimately. It will just take time. In the meantime, biofuels can help augment sustainable fuel supply.

Decarbonized Electricity

In addition to natural gas, float lines typically use electricity for moving glass and power electric boosts for furnaces. About 10% of the energy to power a float line comes from electricity. There is an opportunity to decarbonize the electricity source by using renewable energy to create the electricity used.

Electrified Furnaces

Hybrid electric furnaces are also a future development opportunity. The balance of electricity to gaseous/liquid fuel increases in these furnaces and the electricity is derived from renewable sources. In 2023, Saint-Gobain and AGC announced their collaboration to develop a pilot hybrid furnace that targets 50% electrification (powered by low-carbon electricity), with the other 50% of energy supplied by oxygen and natural gas. There are understood to be constraints to the scaling of this concept to high quality, higher load, float production furnaces. Full electrification is a long-term development, and bridging strategies will be required to reduce carbon emissions before these furnace developments are widely deployed on regular float glass lines.

Recycled Content

Increasing recycled content by adding more cullet is another significant lever to reducing carbon emissions. However, many challenges exist with cost-effectively procuring enough high-quality cullet. While capturing and returning pre-consumer cullet (waste from downstream glass fabricators) is important, post-consumer recycled content will be key to reducing emissions.

This means glass must be recovered from construction sites, separated from the other waste streams, and transported back to the float line. Once the glass is mixed with other construction materials, it is almost impossible to use, so it is critical that there is education about the value of cullet and processes developed to separate the glass at the end of life.

The cost of cullet also needs to remain economical. Transportation costs are a significant issue. While the relative scale of the UK may lend itself more to cost-effective transportation back to the float line, the economic challenges of recovery and return become much greater for land masses the size of North America.

Currently, there is a lack of effective recovery and return systems. Government programs, such as the producer responsibility legislation in France, will help drive glass recovery and recycling.

As demand grows for more post-consumer cullet, cullet prices will increase due to relative scarcity in the glass recovery supply chain. This will challenge the economics. It will be important to balance supply and demand to maintain the economic viability of recycling.

Glass for Europe, the trade association for European glass makers, indicates that there is more than enough glass in the built environment to support high levels of recycling and cullet content. They have laid out policy recommendations to increase the availability of post-consumer cullet.

The NSG Group’s team noted that automotive manufacturers are being pushed to recycle automotive glass with the European Union’s End-of-Life Vehicle Directive. It requires removing 70% of vehicle glass before crushing to support recycling. Systems are currently in place to recover and recycle in the automotive industry, but nothing is currently implemented for construction glazing—at least not yet.

Potentially, the biggest challenge is cullet quality. The quality requirements for cullet to be used in float glass manufacturing are much higher than those for container glass or fiberglass applications.

Typically, container glass furnaces only need to last five to 10 years and contamination poses less risk to the furnace structure. Container glass already uses 60-80% cullet. In contrast, float furnaces must last 15-20 years and, therefore, need higher control of contaminants.

Newer inspection technology can be brought to bear to reduce some risks, but these higher requirements point to closed-loop recycling systems. Contamination not only impacts furnace service life; it also impacts the quality of the resultant glass.

Nickel contamination can cause spontaneous breakage in tempered glass from nickel sulfide inclusions (NiS). While heat-soaking tempered glass can reduce the risk of spontaneous breakage in buildings, if NiS is present in the glass batch, there will be a lot of glass waste due to breakage during heat soaking. This increases the effective embodied carbon of the glass.

How do we minimize breakage risk? Should we reduce the use of tempered glass and use laminated annealed or heat-strengthened glass instead? The latter option has its challenges with adding embodied carbon from the interlayer.

The challenge of sufficient quality cullet availability and relative economics underscores the need to follow the fuel-switching strategy in parallel.

Low-Carbon Glass

The NSG Group has reduced the embodied carbon of float glass by over 52% by using alternative fuels, 100% renewable electricity and high post-consumer recycled content without impacting its quality or performance. Its embodied carbon (global warming potential) is 5 kg CO2/m2 for 4mm glass, compared to approximately 10.3 Kg/m2 for its regular 4mm flat glass. The embodied carbon of EU-produced regular float glass is similar to the lowest published value for North American-made flat glass of 11 kg CO2/m2 for 4mm glass from Guardian Industries.

Because of the capacity challenges noted, the NSG Group has not yet fully implemented these carbon-reducing strategies, and the low-carbon glass is only produced in batches.

While it costs more than regular float glass, it does not show up as a significant cost adder when considering the impact on the total insulating glass unit cost.

Coming to the U.S.?

When will the fuel switching and higher post-consumer recycled cullet strategies come to North American float lines? According to the NSG Group’s team, there are plans to roll out similar approaches globally, but implementation will depend on the local availability and economics of technology.

In the fall of 2023, the U.S. government announced a $7 billion investment (part of the bipartisan infrastructure law of 2021) to create America’s first clean hydrogen hubs to accelerate the commercial-scale deployment of low-cost, low-carbon emission hydrogen. Hub locations are in:

Economic and quality-controlled closed-loop cullet recycling systems are not yet set up locally or regionally at scale in the U.S.

While renewable electricity is becoming increasingly available in the U.S.–over 20% of electricity generation in the U.S. was from renewable sources in 2022–it is still dependent on the supply of regional electric grids. It may not be available near many float lines.

To achieve step changes in float glass decarbonization at a scale that can fulfill the market capacity needs, acceleration in infrastructure development for alternative fuels, high-quality glass recycling and low-carbon electricity generation are essential. Government support and incentives can play an important, accelerating role, as they are doing in Europe.

Some first steps are being taken in that direction. The non-profit Northwest Ohio Innovation Consortium, a collective involving the NSG Group’s U.S. operations, O-I Glass, Owens Corning, Libbey, First Solar, local universities, and civic organizations, received a $31M grant from the state of Ohio to create an innovation hub for glass excellence. The consortium has a broad-based initiative to decarbonize the glass industry, including alternative energy sources. According to Kyle Sword, NSG Group’s North American research and development director, increased cullet processing technologies and use is a key objective.

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