XeBOOST™ Solution: Helping Glassmakers Reduce CO2 Emissions in Electrically Boosted Furnaces

The implementation of enhanced boosting capabilities in the furnace bottom will require thicker paving tiles and the use of more durable refractory materials with tailored electrical properties to ensure reliable operation and a cost-effective furnace lifespan. 

The expected glass temperature increases of more than 60°C (Figure 1), will more than double the direct corrosion rate of refractories. With higher glass temperature, the furnace bottom can also experience glass infiltration, which could lead to the uncontrollable phenomenon of upward drilling beneath the paving tiles. The risk of glass infiltration is also augmented by the increased number of joints between tiles due to the higher number of electrodes in the paving.

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Additionally, the increased glass temperature and velocities in highly boosted furnaces are expected to accelerate the corrosion of the sidewalls. Recent designs for hybrid furnaces feature soldier blocks with increased thickness from 250mm to 300mm and are made with AZS exhibiting higher zirconia grades.

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With at least 3 times more electrodes implemented in hybrid melters compared to conventional furnaces, electrode blocks are now subjected to higher current density and increased glass velocity. As the soda contained in the glass diffuses deeply into the refractory over the furnace lifetime, the electrical resistivity of AZS refractories dramatically decreases from 150 ohm.cm down to ~20 ohm.cm (Figure 3). The refractory corrosion resistance also declines, accelerating the wear of the top of the electrode block. This phenomenon is amplified by higher temperatures and the glass convection currents. 

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When the electrical resistivity of the refractory material gets close to the electrical resistivity of melted glass, current can be deviated through the refractory and eventually could lead to shorts-circuits (also called floor tracking). This ultimately could lead to the melting and failure of the electrode block.  

Consequences could be dramatic for the glass furnace: power and pull rate limitations, potential glass leaks or glass defects. Any failure of an electrode block would require an increase in fossil fuel consumption to maintain the energy input, counteracting the initial goal of decarbonization. 

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Decades ago, isopressed zircon bricks and resistive fused cast High Zirconia (HZ) were the only materials known for their high electrical resistivity and were predominantly used for display glasses, reinforcement glasses, and specialty glasses. However, isopressed zircon cannot be used for sodalime glass because of its dissociation (ZrSiO₄à ZrO₂ + SiO₂) at approximately 1,400°C. Even though High Zirconia (HZ) could be a high-performing paving solution, the associated CAPEX difference is considerable, and their use is limited to niche applications.

Engineered by SEFPRO as part of the AZS refractory family, XeBOOST™ refractory aims to achieve higher reliability and safer operation. XeBOOST™ solution tackles the electrical boosting challenges mentioned earlier by providing three times greater electrical resistivity (Figure 4) than a standard AZS containing 40% ZrO₂. 

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Even after soda infiltration, the electrical resistivity of XeBOOST™ technology remains significantly higher than of AZS40. Figure 4 also evidences that the electrical resistivity of XeBOOST™ material remains at least one order of magnitude higher than that of sodalime and borosilicate glasses, suggesting that XeBOOST™ innovation can significantly strengthen the reliability of furnace boosting systems. 

With 46% of Zirconia, XeBOOST™ refractory is setting a new AZS standard for tank side wall blocks, usually made of AZS fused cast with a 36 % or 41% ranking of Zirconia. Laboratory-based qualification tests performed on a wide sample panel are predicting a total MGR corrosion resistance improvement of up to 15% compared to AZS 40 (Figure 5). 

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Furthermore, MGR dynamic corrosion tests are evidencing a significant improvement in corrosion at the glass line (Figure 6), by +20%. 

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SEFPRO developed a dedicated pilot glass furnace able to replicate melting conditions close to the ones in industrial glass furnaces. During test, this furnace was powered by electrodes with electrical input varying from 15 to 20kW and voltage up to 200 V. It features bottom electrodes embedded in refractory blocks, allowing the evaluation of corrosion not only for the electrode blocks but also for the sidewalls. The furnace was tested over a two-month period, achieving an average glass temperature of 1,420°C, with peaks at 1480°C to replicate the severe conditions of high boosting.

This pilot setup is able to evaluate up to three materials simultaneously for both locations (bottom paving and sidewalls). Post-mortem analyses and 3D scans confirmed that the glass line corrosion resistance of XeBOOST™ solution exceeds that of AZS 40 by 20%, resulting in enhanced performance for XeBOOST™ side wall blocks (Figure 7).

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XeBOOST™, a groundbreaking AZS refractory, is establishing a new standard, particularly under the demanding conditions expected in super boosted or hybrid soda-lime glass melting furnaces. Its exceptional properties, including high electrical resistivity and the highest corrosion resistance among commercial AZS refractories, make it an optimal choice for addressing challenges associated with increased glass temperatures and high electrical densities. Extensive laboratory qualification tests indicate a potential improvement in total corrosion resistance of up to 15% compared to AZS 40, along with a notable 20% improvement in glass line performance. 

As the industry shifts towards sustainability and reduced emissions, glass industry engineering teams should prioritize the adoption of advanced materials such as XeBOOST™ material to improve furnace reliability, facilitate higher electrification levels, and give sidewalls higher corrosion resistance.