Master's Thesis : Recycling of sludges in high-temperature furnaces for circular economy

Abstract

High furnaces are used since centuries in the field of metallurgy. They have been upgraded in term of capacity, efficiency, size, and environmental footprint. Indeed, while processing, iron and steel making produce by products such as sludges, dusts, and slags. Nowadays cold biding technologies start to be studied in the field due to the potential save of energy and the problem of resources depletion. In first time, studies have been made to analyze the global behavior of pure iron pastilles in a simulation of BF process. 2 different binders has been used : FE14 (organic) and cement combined with bentonite (non-organic). As planned, their behaviors were totally different. The mechanical properties of samples containing Alcotac FE14 tended to decrease a lot just after the increase of temperature, in contrary to the recipes with cement and bentonite. However after 700°C, others physicals phenomenon like sintering start to counterbalance the effect of binder. Also, the addition of anthracite (carbon) in some recipes has as effect to decrease the (or at least slow down the increase) the quality of the samples due to the evaporation of mater (Boudouard reaction). In a second time, a large panel of recipes containing a large panel of binders/binder combinations were briefly studied in order to not loose too munch time. The results in term of mechanical properties led some interesting point : - CB11 binder seems to have acceptable mechanicals properties at high temperature (700°C) despite the fact that is an organic material. - Carbon addition seems to have an effect before its degradation with boudouard reaction. - Cement added with other component than bentonite gives bad results. - Using by products tends to decrease a lot the quality of the samples

In a last time, deeper studies on recipes from 2nd campaign revealed the fact that, not only the quality (in term of mechanical properties) of the agglomerate change by using secondary resources, but also its behave all along the BF treatment. Thus, making extrapolations of what would happen to samples containing by products (sludges, dusts,…) from data coming from experiments made on pure iron agglomerates seems to not be judicious. This 3rd campaign also revealed better the necessity to control the amount of carbon in the recipe. Indeed, agglomerated containing to munch carbon were not characterizable due to their degradation inside the crucible after 900°C.