Possibilities of counter-current scrap pre-heating with melting by use of 100% fossil energy

It shall be found out, how far scrap can be heated without too much oxidati on in a shaft with counter-current flow of scrap and heating gas if the hea ting gas is stepwise post-combusted during its rising in the shaft. The scr ap is a mixture of plates, cylinders and spheres obeying a log-normal distr ibution function of the size. Heat transfer is by convection and radiation. Scrap oxidation kinetics is determined by the phase boundary reaction and by diffusion in the oxide layer. The model calculates the temperature of th e scrap size classes and of the gas, and the oxidation of the scrap along t he shaft height. The preheated scrap is melted in a smelter. It was found t hat under steady-state conditions with a moving scrap heap, about 60% post- combustion difference between bottom and top of the shaft is possible if th e scrap initially has room temperature and is then heated up as far as poss ible without melting. Scrap oxidation in the shaft is only 0.2% of the prod uction. This is possible by the shot? residence time of a moving scrap heap in the hot post-combustion planes where the oxidation rate is high. Calcul ations for a stationary heap, where the scrap residence time in the hot zon es is much longer, showed that here, the oxidation is more than 10 times hi gher.