Product and services

Le Mousseur - Introduction


This simple device runs automatically the carbon injection and optimise dynamically the foaming slag. Nothing comparable to all you have seen before !
Scheme of the foaming slag automation device The Rogowski coil and its integrator (optional) are measuring the electrode current with a very wide band. Only one phase needs to be measured. The existing CT's could be used. Rogowski signal is filtered and send in the PLC to be treated . A foaming slag index is first elaborated . The slag index Si is displayed on an indicator installed on the furnace control pulpit. Considering the furnace process status established in the Mousseur software or the operator selection, the injection is inhibited or allowed. Finally, a fuzzy logic regulator is sending "open" or "close" signal to the injector valve. Additional functions of the regulator include for example a safety model to prevent clogging of the carbon injection pipe as well as exhaust gas system overload. Eventually, the slag index is send to the main data base for further reporting or trending.
In electric steel making, foaming slag is a very important practice which provides tremendous improvements on energy consumption, metallic yield, productivity and refractory consumption. It is obtain by the reaction of carbon and iron oxide (FeO + C -> Fe + CO), which produces gaseous CO creating small bubbles in the slag. Practically, it is realised by carbon injection into the slag, supposing that, in any case, oxygen is injected in parallel into the steel bath. Until now, carbon injection is performed manually by the furnace operator. Thus carbon injection is submitted to human behaviour and it is nearly impossible to obtain reproducible conditions and reach the optimum each time. Some attempts have been made to estimate the foaming slag quality with the harmonic content of the electrode current. However, this indicator is only significant of the physical status of the arc foot substrate. The "Mousseur" (FSM) takes the harmonic range, which is really specific to the slag thickness. Furthermore FSM is able to regulate the carbon flow rate in order to keep a constant and adjustable foaming slag thickness. So that, for each heat and at any time, both targets are achieved: lowest carbon consumption and sufficient slag thickness.
The curve shows the behaviour of FSM over 2 consecutive heats realised in a furnace using 30 to 35% hot metal (average 25 minutes power on time): The blue line indicates that foaming slag is too good (above the middle of the slag door), the yellow line indicates a "good" foaming slag (approx. 700 mm) and the red line a "bad" foaming slag with sparks and noise. The red curve shows the carbon flow, which is regulated by FSM. There is no C required on the first heat as hot metal is used in this furnace. And the Fe content of the slag for this heat remained below 19%.