Glass production requires sand, soda, and lime - raw materials which occur in nature in almost unlimited quantities - as well as a considerable amount of energy. Temperatures of over 1,500°C are needed in order to melt the mixture of raw materials in large oil-fired or gas-fired glass-melting tanks. For instance, around 7 gigajoules are used to produce one ton of flat glass, which corresponds to the heating value of around 200 cubic metres of natural gas.

The optimisation factors for the production process include not only energy consumption, but also emissions. In particular, nitrogen oxides can present problems during glass manufacture, because at the high combustion temperatures, oxygen not only reacts with the natural gas or oil, but also with the nitrogen in the combustion air.

Flameless burners, which are already providing considerable energy savings and emission reductions in the metal industry, have now been adapted to the special requirements of glass production by the research institute Gaswärme-Institut in Essen, Germany. Together with industrial partners, the researchers investigated how these burners, which operate on the principle of flameless oxidation, can be used to fire glass-melting tanks.

Compared to conventional burners, the use of flameless oxidation achieves a more uniform temperature distribution in the combustion chamber. At the same time, the burners operate with high efficiency, because the hot exhaust gases are channelled past the supply air, thus recuperatively preheating the combustion air.Experience gathered in other industries can only be transferred to a very limited extent, because the structure of glass-melting tanks differs greatly from that of other industrial furnaces.

The glass industry remains wary of straying from the beaten path, because it requires a great deal of experience to optimise the product quality as well as the throughput of the glass-melting tanks. The intention of this research project, sponsored by the German Bundeswirtschaftsministerium (Federal Ministry of Economics and Technology), is to demonstrate with a retrofitted glass-melting tank, that at least the same product quality and productivity can be achieved with this technology, with improved consumption and emission values.