Post-combustion and heat transfer at blowing of oxygen into a carbon monoxide containing slag foam

A combined post-combustion model (CPM) for smelting reduction processes was developed in a multi-national research project supported by the European C oal and Steel Commission. The project partners were CSM, Rome, Hoogovens, I jmuiden, MPI, Dusseldorf, and TUB, Berlin. This paper reports about a heat transfer model developed by TU Berlin within this project. The batch-type s melting reduction reactor has a two-layered slag: an upper foamy and a lowe r less foamy slag. A bubble stream of (CO+H-2) gas originating from the iro n oxide reduction reaction with coal in the lower slag flows upwards. The r ising (CO+H-2) gas is post-combusted by three oxygen jets blown horizontall y into the upper part of the slag. A flame zone, and above the flame a mixi ng and a bubble zone form, in which post-combustion reaction and transfer o f the post-combustion heat to the slag take place. The modelling of the fla me zone was the subject of a previous paper. The present report describes m odels of the mixing and the bubble zone and of the occurrences in the gas s pace above the slag. The macro-kinetics of the overall heat transfer proces s including slag recirculation and heat transfer from the upper foamy to th e lower dense slag are presented further. The model calculations provide in formation about the distribution of the post-combustion and the heat transf er processes over the single zones as functions of the important internal p rocess parameters. Further, the oxygen utilisation, the heat efficiency and the temperatures at various locations of the process are described as func tions of the ratio of post-combustion oxygen flow rate to (CO+H-2) evolutio n rate. In all the calculations a specific gas through-put of carbon monoxi de of 3 mol/t . s is assumed. This value corresponds to 510 mol/s for the a ssumed melt of 170 t. The model shows that heat transfer efficiencies of mo re than 90 % and slag temperatures of less than 1700 degrees C are possible , if the slag circulation rate is 300 kg/s. Lower circulation rates lead to higher slag temperatures and worse heat transfer efficiencies. Controlled slag circulation is thus an important process tool.