Optimised blast furnace slag water quenching with sulphur compounds control

The main result of this research work is a concept for low emission operation of a typical industrial slag quenching system with reference to emissions of steam and subsequently gaseous sulphur compounds such as H 2 S and SO 2 . Extensive operational measurements have been carried out in order to collect basic data on steam emissions, sulphur compounds emissions and operational conditions at an industrial INBA slag granulation plant. The measurements aimed at a definition of typical emission values in dependence on plant configuration, measuring point and certain operational conditions like for example slag flow. The following topics have been investigated: Effect of new invented short circuit opening inside the condensation tower on diffuse steam emissions. Typical H 2 S emission values, temperatures and pressures at different measuring points and different slag flow rates. Proportionality between H 2 S emission value at certain measuring point and slag flow rate. Further data collection at an industrial INBA slag granulation plant has been performed in order to evaluate the correlation between sulphur compounds emissions and slag properties and to set up a mathematical model for prediction of sulphur compounds emissions. A correlation was found between sulphur loss of granulated slag and slag basicity, K 2 O/Na 2 O content, viscosity and slag temperature. Since within the industrial range of variations of physical-chemical parameters the sulphur loss was nearly constant, no suitable mathematical model could be developed. Primary means for reduction of H 2 S emissions by control of the chemical reactions were developed in laboratory trials. The first step of these investigations aimed in understanding the reaction mechanism of gaseous sulphur compounds generation and in development of countermeasures. The most promising countermeasure was to stabilise sulphur in the slag as sulphate either by addition of oxidising additives to the liquid slag or to the granulation water. In a set of trials efficient additives for this purpose have been chosen and tested on their ability to decrease H 2 S emissions during slag water quenching. As secondary mean for reduction of H 2 S emissions, different methods of exhaust air treatment were investigated. Extensive operational measurements have been performed at an industrial INBA slag granulation plant in order to evaluate the effect of modified condensation water nozzles inside the condensation tower and of exhaust air scrubbing with water and NaOH solution. NaOH scrubbing showed a good H 2 S absorption in the operational trials. For this reason thermodynamic calculations on H 2 S absorption were carried out in order to determine optimised absorption parameters. In laboratory trials, ferric EDTA scrubbing was successfully tested for H 2 S absorption. Influencing the thermal conditions at the granulation head could be another primary means to reduce H 2 S generation. Calculations showed that the degree of slag dispersion is the main influence on the solidification rate of blast furnace type slags. In order to improve the emissions situation at an industrial INBA plant, the granulation head / tank design has been modified. The aim was an improved slag-water-contact, which strongly reduces steam and H 2 S generation. On basis of all the results, a concept for economical and low-emission operation of industrial slag granulation plants was developed.