Hearth protection in blast furnace operation by injection of TiO2 materials

The protection of blast furnaces by charging ilmenite with the burden is common practice in BF-operation [1] - [4]. The shielding effect is caused by the precipitation of solid titanium carbonitride at the contact between the Ti-containing HM and the carbon BF-hearth lining. The addition of ilmenite leads to a raised total titanium charge. Due to the partial reduction of the ilmenite the slag and HM are enriched with titanium oxide and titanium respectively. The distribution of Ti between HM and slag under those conditions is rather poor. The titanium content in the slag got to be significant higher than in the HM. Depending on operation conditions it can be up to more than an order of magnitude. As the desired effect is locally necessary and caused by the titanium in the HM only a minute fraction of the added ilmenite is efficient. By far the largest amount of the added titanium leaves the blast furnace without shielding effect. Due to the burden residence time it also takes much more time to increase the titanium content in the HM by ilmenite addition to the burden than by tuyere injection. For that reason this RFCS project focused on investigations to the tuyere injection of TiO 2 materials in order to assist the BF operators to optimise their hearth protection. The main focus of the investigations was set on the technical aspects of titanium injection for hearth protection. An economical evaluation and comparison of charging titanium (ilmenite) with the burden and injecting it on tuyere level was not carried out because the aims of both practices are totally different. The titanium charging with the burden is a preventive measure for hearth protection leading to overall effects in the BF hearth whereas titanium injection is a local measure at acute damages/hot spots in the BF hearth with only local effects. Within the RFCS project thermochemical calculations concerning the titanium solubility in HM and the distribution of titanium in HM and slag were carried out with a commercially available thermodynamics simulation tool. The thermochemical calculations indicate that the solubility of titanium in HM increases with raising HM temperature. Investigations concerning the dependence of accompanying components on the titanium solubility in HM showed that Si and Mn do not have a significant effect whereas the titanium solubility in HM decreases rapidly with an increasing content of P and S in the HM. The calculations concerning the titanium distribution between HM and slag showed that the temperature has a most important impact on the titanium distribution. With increasing temperature the titanium content in the HM raises and the titanium content in the slag is reduced. A high Si content in the HM has a positive effect on the titanium distribution between HM and slag in terms of high titanium content in the HM and comparable low titanium content in the slag. S has a negative impact on the titanium distribution which means, that a high S content in the HM leads to a sinking titanium content in the HM and raising content in the slag. A comparison of the results of the thermochemical calculations with BF data of the BF operators showed, that tendencies and general dependence of titanium solubility and titanium distribution in HM and slag are well reproduced.