The NF ladle furnace is used to superheat slags before the slag is treated in a separation plant. The slag is heated up via electricity by electrodes. In order to prevent an inhomogeneous temperature distribution in the slag, inert gas is injected into the water cooled stirring lance. Typical questions concerning the heating process are the flow rate of inert gas and cooling water, the optimum immersion depth of the electrode to produce intensive mixing, and the amperage to obtain the heating rate requested.