Stewardship of Glass Products

Ethically and socially responsible sourcing for tomorrow’s buildings

Float Glass Furnaces

As discussed in the previous section, forming molten glass requires uninterrupted extremely high temperatures. Therefore, glass furnaces require a lot of energy to operate and are a resource-intensive part of glassmaking.

A float glass manufacturing furnace typically has a lifespan of 16-20 years. After that time, it can be rebuilt from the ground up in what is known as a Cold Tank Repair (CTR).

It’s difficult to make major modifications to the furnace outside of a CTR, as the furnace is rarely, if ever, allowed to cool down. While a furnace is active, automation and the responsible use of resources are the two key aspects manufacturers can focus on to help improve its energy efficiency and reduce the system’s greenhouse gas emissions.

In a float glass manufacturing plant, there are several technologies a manufacturer may consider installing on the furnace during a CTR to help improve energy efficiency and reduce greenhouse gas emissions. Some of these technologies have already been implemented in industrial-scale plants globally and other technologies are relatively new to the industry and their feasibility is still being evaluated.

In a traditional furnace, air is used for combustion. Oxygen combustion technology replaces the air with pure oxygen through a modified geometry of the burner. This substitution reduces the amount of natural gas required to generate the same amount of heat, which is needed to melt the batch materials. By reducing the amount of natural gas consumed, the technology helps improve a furnace’s energy efficiency and decreases the associated greenhouse gas emissions.

Hydrogen-blending technology can replace a percentage of natural gas with hydrogen, using existing furnace infrastructure and burner positions. The burners use a blend of natural gas and hydrogen, which reduces the amount of natural gas consumed by the furnace.

Depending on the type of hydrogen used, this technology can also reduce some of the environmental attributes associated with the extraction and processing of raw materials phase. For example, green hydrogen—hydrogen produced via electrolysis using water and renewable energy such as solar or wind—has a lower embodied carbon value than hydrogen produced with natural gas. However, it’s important to note that implementing green hydrogen technology has both advantages and drawbacks. For example, the electrolysis process consumes large amounts of water. It is also worth noting that the availability of green hydrogen is currently limited.¹⁰

Supply Chains and Glass EPDs

Section three covered how carbon emissions can be calculated through Life-Cycle Assessments (LCAs) and reported through Environmental Product Declarations (EPDs). Implementing these tools is a learning curve for any industry, but there are some additional challenges specific to the building industry.

When considering actual environmental attribute factors, a distinction needs to be made between product-specific and industry-wide EPDs.

Industry-wide EPDs provide aggregated or average environmental data for a particular sector of industry. They are often used to establish benchmarks or average environmental performance across that sector. They are valuable to stakeholders because they communicate the environmental attributes associated with a product or product category associated with that industry sector.

Product-specific EPDs are particular to an individual product or a closely defined product line. They provide detailed information about the environmental attributes associated with the covered product or product line and its associated life cycle phases. These EPDs offer comprehensive and specific information to stakeholders interested in the environmental performance of a product. Therefore, they allow builders, designers, and architects to make more precise, informed decisions about the environmental attributes of the materials they use.

But there is another helpful level of EPD. Product-specific EDPs can be specifically created for regions or individual manufacturing plants. In the case of float glass, it may be more appropriate to design with regional-specific EPDs because of the complexity of the supply chain of float glass.

When it comes to float glass, there is a small number of companies making the majority of products used in the U.S. Because of that small number, and the nature of float plants, revealing facility-specific data (as opposed to regional average manufacturer data) could reveal proprietary information that could be used by competitors such as information about specific products. This raises proprietary, anticompetitive, and antitrust concerns.

Facility-specific EPDs may create a burden for manufacturers, fabricators, and the associated supply chain. For general stock products that contain common glass types, fabricators often do not segregate their stock based on which plant or manufacturer supplied the glass. Many fabricator’s systems are not sophisticated enough to make this distinction and would require upgrades, or a new system, to be able to track manufacturer and plant information for these products.

To ensure a project’s demand and schedule are met, float glass manufacturers often supply glass from multiple plants. Fabricators do not have control over which plants the glass manufacturers select; a fabricator places a purchase order for a specific product and then the manufacturer supplies it from one or more of its plants based on stock availability, logistics, transportation, and other considerations. This flexibility is eliminated if glass sourcing requirements must adhere to product-specific, facility-specific type EPDs.

Unpredictable complications like rolling blackouts and winter weather could impact a manufacturer’s ability to produce and supply float glass from a specific facility. Again, facility-specific EPD requirements could restrict a manufacturer’s ability to maintain supply using its other plants and could delay a project.

The National Glass Association made comments regarding these challenges on the U.S. GSA’s pilot program requiring the use of low embodied carbon construction materials in GSA projects funded by the Inflation Reduction Act of 2022, referenced in section one of this article.

So, while industry-wide EPDs can provide general transparency for the industry on a whole, regional EPDs are more practical and appropriate. Regional EPDs offer better information specifically on the material likely to be used for a project without the risk of sharing proprietary information from individual manufacturing plants.

Alternate Furnace Designs

Similar to hydrogen-blending technology, hydrogen-combustion technology replaces the natural gas with hydrogen. But instead of replacing only a percentage of the fuel source, hydrogen replaces 100% of the natural gas. The main difference between the two technologies is that hydrogen combustion cannot use the existing furnace technology. A special furnace design and refractories are required. The research associations and universities working on this technology are typically using a lab scale or pilot scale furnace. By replacing the natural gas with hydrogen, this technology maximizes the reduction of the greenhouse gas emissions associated with the combustion of fuel.

It's important to note that additional research and infrastructure is needed to make hydrogen technology a viable alternative.

With the current furnace technology, direct heating with electricity—electrical boosting—can replace a percentage of the energy needed from natural gas. The furnace is modified to install electrodes directly in the furnace melt. This option takes advantage of glass’s electrical conductivity in the molten state and uses the freely moving sodium ions as charge carriers. The applied electrical voltage heats the glass with the help of the friction forces of ion immigration.

Instead of using combustion, direct electric melting relies on 100% electric melting. As with hydrogen-combustion, electrical melting uses a different furnace design. This design has been extrapolated to a production scale furnace; however, with current technological bottlenecks, electrical melting tanks are typically limited to 200 tons per day. The standard capacity of a float glass plant is around 600 to 1,000 tons of product per day. Researchers continue to look for a solution that will allow a larger scale.

By replacing natural gas with electricity, the direct electric melting technology eliminates the carbon emissions generated by the furnace combustion process. This technology also has an efficiency of approximately 95%. This is higher than the efficiency of combustion, which is typically around 50%.

As with the other technologies mentioned, the use of electricity helps reduce the amount of fuel consumed by the furnace and reduce the greenhouse gas emissions associated with the combustion of fuel. When exploring this option, the manufacturer should consider the mix of energy in the electrical grid, on-site energy options (e.g., solar) and virtual options (e.g., power purchase agreement) as the energy mix used by a furnace—whether mostly non-renewable sources, renewable sources or a mix—will influence the reduction in greenhouse gas emissions.

The list presented here is not exhaustive, and it is likely that the "furnace of the future" will use a hybrid solution, or it might use a technology not discussed here or that has not yet been discovered.

Graphic courtesy of Guardian Glass

Potential solutions to help reduce embodied carbon within a float glass plant include cullet recycling, optimizing transportation, reducing water consumption, and improving furnace efficiency.

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Originally published in June 2024

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