The present invention relates to a method for carrying out melting, melt-metallurgical and/or reduction-metallurgical processes in a plasma melting furnace, in whose interior freely burning plasma torches are produced between plasma burners guided through the lid or through the side walls of the furnace body and a bottom electrode, and fluxes and reactive substances to be melted and reacted, respectively, are charged into the region of the plasma torches, as well as to an arrangement for carrying out the method.
Methods of this kind are known, with argon, nitrogen, helium or hydrogen usually being used as plasma gases. These gases have different electric voltage gradients (E=U.multidot.cm.sup.-1), argon having the lowest and hydrogen having the highest voltage gradient. The lengths of the plasma torches forming depend on the value of the voltage gradient, which means that the plasma torch is longer with a gas having a lower voltage gradient under otherwise equal conditions. Thus, when using argon as the plasma gas and a voltage of about 800 V, the plasma torch has a length of up to about 1 m, whereas, when using hydrogen as the plasma gas at the same voltage and current intensity, the torch has a length of about 10 cm only.
When carrying out melting and reduction processes by using plasma torches as energy carriers, the energy of the plasma torches given off by radiation has not been utilized in a desired manner, because the highest energy density of the plasma torches is developed near the plasma burner mouths. The plasma jet, the farther away from the mouth, is fanned out and thus gets poorer in energy, because the energy given off continuously decreases in dependence on the distance from the mouth. Hence it follows that, particularly, with melting processes in which a sump is formed by melting lumpy charging materials, less and less energy is supplied to the bath in the course of the melting process, while an undesirably large portion of energy is given off to the furnace inner walls. To follow with the plasma burner has little effect, because the arcs thereby become shorter and the energy given off decreases with a decreasing voltage.
The invention aims at avoiding these disadvantages and has as its object to provide a method as well as the pertaining means for increasing the energy supply to the charges to be melted or reacted and thus improving the thermal efficiency and the kinetics of the process. The invention resides on the knowledge that, by the formation of plasma torches containing various gases with different voltage gradients, it is possible to regulate, in particular increase, both the lengths of the torches and the discharge of energy.