Embodied CO2 in Float Glass
Glass manufacturing is an energy-intensive process and results in significant CO2 emissions. However, the overall CO2 balance is favorable when large operational energy savings are considered.
In the Float Glass Process, raw materials and energy are the single largest elements of cost. Silica sand is the main component by weight of the ‘batch’ (raw material mixture). Soda ash is one of the most expensive raw materials used in glass manufacturing. It represents about 16 percent of batch weight, but around 60 percent of batch cost and approx 75 percent of embodied CO2 in raw material manufacture.
Recycled glass (cullet) represents, on average, around 15 percent of the materials used. Cullet usage of 10 percent leads to a 3 percent furnace energy reduction.
Since the 1960s the glass industry as a whole has reduced specific energy consumption by approximately 1.5 percent per year.
The diagram below shows analysis of CO2 emissions from a typical European float line.
- In total, the manufacture of 1 tonne of packed float glass results in the emission of approx 1.2 tonnes of CO2.
- Quarrying and processing of raw materials results in supplier emissions of approx 0.3 tonnes CO2 per tonne glass packed. (1)
- Natural gas and heavy fuel oil are used to melt the raw materials. This combustion process emits approx 0.5t CO2 per tonne of float glass. (2)
- Carbonate raw materials decompose when heated to emit approx 0.2t CO2 per tonne glass.
- The electricity required to heat the float bath and annealing lehr emits approx 0.2t CO2 per tonne glass at the electrical suppliers’ generation site.
- Modified properties can be produced by means of surface coating (on or off-line). On line coating contributes an additional 0.7kgCO2 per m2 (1m2 of 4mm float glass weighs 8kg).
- Plies of glass are bonded or laminated together with a layer of polymer film in between for use in safety and security applications. Glass can also be heat-treated (toughening), shaped, bent, silvered (mirrors), surface-worked, installed in multiple glazed units and, in Automotive, assembled in modular systems.
- The carbon emissions for these additional processes are not listed here but will be the focus of next year’s Sustainability Report.
(1) External data.
(2) European Emission Trading Scheme – externally verified CO2 emission data.
Float glass and environmental impact
Glass and CO2
The manufacture of one square meter of low-e double glazing leads to the emission of 25 kg of CO2.
However, industry studies show that the CO2 saved by replacing one square meter of single glazing with low-e double glazing in a typical European building is 91 kg per year, offsetting the CO2 emitted during manufacture after only 3.5 months in use.
If ordinary double glazing is replaced by low-e double glazing, the offset period is typically 10.5 months.
The NSG Group emitted (direct and indirect) 4.7 million tonnes of CO2 in 2009.
Independent studies show that savings of more than 100 million tonnes of CO2 could be achieved annually if all Europe’s buildings were fitted with advanced energy-saving glass.
For more information go to http://www.glassforeurope.com