In the steel industry the injection of solids is of great importance. Fine grained solids have a big reaction surface, thus causing a short reaction time. In the present work, research was undertaken in the field of solid injection into iron and steel melts from the top, using the coherent jet technology. The aspects were the mathematical simulation of injection process from the top and the examination of the injection efficiency of various solids of different grain size.To analyse and clarify the physics behind top injection, mathematical simulation was conducted. The mathematical model gives a qualitative and quantitative description of the penetration and flotation process for an individual particle. It shows that the denser particles penetrate more deeply and as a result have the longer residence time in melt. The factors influencing the penetration depth are particle size, initial particle velocity, particle density and possible agglomeration of several particles in the melt.