Welcome to the Glass Age

110 Sustainable responsible glass production & climate action (UN Goal 12&13) Melting glass requires considerable energy to reach the necessary high temperatures (>1500ºC). Glass production used to take place in “glass houses” where people had local resources —sand and wood ash as raw materials and wood from the forest for energy. Old glass houses can still be found in forested areas. As much as 150-200 kg of wood was needed then to melt a kg of glass [4]. Assuming wood burning generates about 19 MJ/kg, this equates to >2850 MJ for a kg of glass. Today’s result of 3.5 MJ/kg is astonishingly 800 times more efficient. Over the last century, the main energy source has shifted to fossil fuels such as oil and natural gas. Modern glass melting uses about 1% of all industrial energy [5] much less than for example steel production. Nevertheless, it is energy intensive and massive improvements have been made over the years. Asahi Glass Company have plotted these downward trends, and the reduction in pollutants such as NO x , SO x and dust emissions for flat glass production (Figure 7.1). Figure 7.1 also shows that since 2000 the relative specific energy line has flattened, suggesting little improvement in recent furnace designs. Furnace efficiency had increased because new refractories allowed higher combustion and crown temperatures, and increased melting temperatures. Furnaces became larger, producing more glass per m 2 of heat loss surface. Some flat glass furnaces now produce a remarkable 1200-1500 tons/day while container glass furnaces can melt a high 800 tons/ day. But furnace size is limited by the maximum crown span (width), the size of equipment, flame length, and other factors. Larger regenerators have increased heat regeneration from 50% to 70%, close to the theoretical maximum of 75%. This maximum arises from the difference in heat flow in the waste gas (greater mass and specific heat) than the air being preheated. Figure 7.2 shows the design of the most common U flame (end-fired) container glass melting furnace, Figure 7.1. Energy efficiency gains over 150 years and NO x , SO x and dust emissions for the last quarter century. Source: http://www.agc-glass.eu/sustainability/ environmental-achievements/air Relative specific energy Year