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Show DIRECTIONAL LANCING techniques are used in cases where more specific, localised heating or melting is required and general enrichment is not the optimum method, e.g. in cupola operation where the oxygen is introduced to supplement the capability of the airstream used to produce molten iron from the composite charge coke, iron and steel. A great deal of work has been done to ensure that the most efficient method is used for such applications and sub-tuyere technique and through tuyere have been developed to optimise results. There are still units which are best served by general combustion air enrichment and from an operational point of view these will always remain. The danger can often be in trying to introduce more sophisticated technology when the process does not warrant it. OXY FUEL BURNERS have made an increasing impact in the past decade with the major emphasis in the steel industry where this system is an accepted aid to productivity and power savings in the electric arc melting units. There is still a reluctance in other industries to move wholeheartedly to this technique and in the majority of applications the use is of an "add-on" nature. The full advantages of a system using only oxygen to interact with a fuel will only be gained when melting units are designed solely for oxy-fuel combustion. These are becoming available in limited areas and proving cost-effective from a design and operational stand-point. Whether they become universally acceptable in all industrial sectors depends on the user's willingness to commit his production units to a system which depends not only on an external supplier for fuel but also on an external supplier for oxygen. The current source of oxygen, from air, is not something which is subject to third party influence. DEVELOPMENT of new techniques is on-going to improve and modify ways in which oxygen can be introduced. For instance one of the problems with any oxy-fuel burner may be the intensity of the flame which needs to be "softened" if it is to achieve the required end result when melting finely divided particles. In different parts of the cycle, different flame shapes and intensities will be required. A burner will need to operate with a varying level of oxygen to achieve this requirement. There is a big gap between the low level enrichment techniques and the 100% oxy-fuel burner in terms of oxygen levels used and little work to date has been done to discover whether for instance 60% level of oxygen enrichment could be more cost-effective. This has been due to the need to combine features of air/fuel burners and oxy-fuel burners in one unit and the subsequent engineering and cost problems. The same effect has been achieved by firing an oxy-fuel burner inside 247 a conventional burner to achieve a variable oxygen level. Work is on-going on techniques such as using oxygen to atomise the oil in air/oil burners to produce a flame retaining many of the characteristics of an air/fuel flame but with some of the preferred benefits of oxygen. It has been very successful in achieving increased heat transfer to a melt without any measurable difference in refractory temperature thus producing a considerable fuel saving. CASE STUDIES SOUTH AFRICA - In South Africa several steel industries have investigated the use of oxyfuel burners for assisted melting in induction furnaces. To meet the physical limitations imposed by the relatively small size of the induction furnaces, burner design was modified to produce narrow, penetrating flames which ensure high thermal efficiency without potential refractory damage from radiation. The system is designed to ensure that the hottest part of the flame is in contact with the scrap during the initial melt down period. As the scrap melts and the level drops new scrap is continuously charged into the furnace. During the last few minutes of melting the burner is lifted up to about sOOmm above the molten metal surface to prevent hot metal splashing the burner. When all the metal has melted, the burner is retracted and the molten metal is superheated by electrical energy alone. The oxy-fuel burner gives several operating advantages which lead to a greater effi'ciency of the induction furnace. 1) Quickly creates a molten heel by melting the charge from the top 2) Increases the coupling efficiency by welding the scrap pieces to each other 3) Raises the metal temperature quickly and therefore the magnetic permeability will decrease giving a higher penetration depth These points lead to a reduction in the size of liquid heel required and frees more metal for tapping. Increased production rates are thus possible and in one case the increase was such that a 4 tonne casting can now be produced using a 1.5 tonne furnace. The oxy-fuel burner system thus gives either: |