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112 Other furnace designs Other technologies include the recuperative and the oxy-gas furnace. Oxy-gas furnaces use pure oxygen, extracted from air and may seem more energy efficient than the best regenerative furnaces. A correct analysis though requires the energy and cost of separating the oxygen be considered and usually favors a regenerative furnace. However, oxy-gas furnaces can bring other benefits - NO x reductions and a smaller footprint. Recently, two industrial gas suppliers have reduced energy consumption by preheating the fuel and oxygen. Linde (Praxair) developed the OptiMelt TM technology to save another 20% of energy by preheating the natural gas with waste gas from the oxymelter to create a syngas (CO + H 2 ) formed by cracking CH 4 with CO 2 in the waste gas [6]. An interesting side benefit is that CO tends to reduce foam on the glass surface, increasing heat transfer and lowering seed counts. Air Liquide designed HeatOx technology with heat exchanging recuperators using furnace waste heat to preheat the natural gas and oxygen indirectly to 400-500ºC, giving 9-10% additional energy savings [7-9]. Should this technology be installed in a conventional regenerative float furnace converted to oxy-gas firing, a total of 20-25% energy savings may be achieved. A side effect would be a major NO x reduction. Finally an oxy-gas furnace is apparently converted to burn hydrogen more easily than an air-fired furnace. Burning hydrogen with air gives higher Figure 7.3. A cross-fired regenerative 600 TPD float glass melting furnace. Source: Courtesy of Glass Service a.s. (www.gsl.cz) .