If liquid metals cannot proceed to the next processing step via gutters, torpedoes, distributors or ladles are used for transportation. To increase the life of the refractory lining and avoid costly overheating of the metal bath, these vessels are pre-heated. Preheating temperatures up to 1200°C are uneconomical with cold air burner systems and those above 1200°C are difficult to achieve.
In the case of oxyfuel burner systems there is a distinction between their use for pre-heating vessels which are circulated during the production process, and for drying new vessels made of refractory material. The reason for this is the different heat transfer mechanisms at different temperature levels.
Drying newly delivered vessels:
Newly delivered vessels must be preheated slowly, according to predetermined heating curves from the refractory material producers. The annoying smoke or odour arising during the expulsion of the refractory binder can be prevented by internal post combustion.
At the lower temperature range, firing is carried out using oxyfuel with air enrichment, or exhaust gas recirculation. When refractory binders start being expelled, additional oxygen is used for internal post-combustion in the vessel. At the end of expulsion of the refractory binders, stoichiometric combustion using pure oxygen as the oxidation medium takes place.
Natural gas savings with oxyfuel: 30% - 40%
Pre-heating of ladles during production cycle:
Rapid, energy-conserving stoichiometric combustion with pure oxygen as the oxidation medium
Natural gas savings with oxyfuel: 40% - 70%