| OCR Text |
Show DISCUSSION - Page 6 - The oxy-fuel burner is positioned directly above the crucible furnace and the flame directed towards the cold material inside the crucible. Once the material is melted the oxy-fuel burner is immediately switched off. However, the air to the burner at the bottom of the crucible is continually enriched with oxygen and this burner is only switched off just before tapping i.e. once molten metal has reached superheat temperature. The blast air to the bottom burner was enriched up to 101 02 at which level the protective glaze around crucible started to melt. The oxy-fuel burner positioned above the furnace, on the other end, was 1001 oxygen and 100*s Sasol Gas. 3.1. The Influence of Oxygen on the Combustion Process In conventional combustion processes, ambient atmospheric air is used as the oxidising agent. Because of the nitrogen ballast which constitutes approximately 19% by volume of the combustion air, only low flame temperatures can be achieved as the inert nitrogen must be heated up additionally. As a result, substantially lower combustion efficiency is obtained at high waste gas temperatures, as the heat content of the waste gas volume is very great on account of the high nitrogen ballast. The use of pure oxygen or the reduction of the nitrogen ballast by enriching the combustion air with oxygen therefore represents an economic alternative. Very high flame temperatures are achieved as the waste gas volume is reduced by virtue of ballast-free, complete combustion with pure oxygen. This maximum possible difference between the temperature of the flame and that of the material also serves to improve convective heat transfer and optimise the amount of useful heat. The complete or partial elimination of the nitrogen ballast means that, in addition to increasing the temperature, the gas radiation properties are improved as well. |
