The BOF converter has a capacity of up to 400 t hot metal. In combined-blowing BOF converters the top lance features supersonic nozzles that accelerate oxygen to twice the speed of sound and blow it into the melt. A foamy emulsion is formed from melt and slag droplets and carbon monoxide bubbles. To ensure thorough mixing of the melt, inert gas is injected through bottom stirring plugs. Typical issues concerning the BOF process are the best vessel design, the process gas flow rates, the type, number and location of the supersonic nozzles and the bottom stirring plugs as well as their position in relation to each another, the mixing effects, and the post-combustion rate in the vessel´s top part.