Thermomechanical modelling of a blast furnace hearth

A blast furnace hearth is made of several refractory layers and materials. To improve its design and to determine the most sensitive zones, a thermomechanical finite element model was built. The material properties are temperature dependent. The carbon ramming mix, a compacting material which absorbs part of the thermal expansion, is represented by a modified Cam-Clay model. The masonries with mortar joints (in the bottom and in the ceramic cup) are replaced by an orthotropic material that has a behaviour equivalent to that of the masonries. Since failure can occur either in mortar joints or brick/mortar interfaces, different joint states are considered (according to the "open" or "closed" state of the joints in each direction). The interface strength, determined experimentally, was taken into account through a Mohr-Coulomb criterion. The equivalent material parameters were obtained, for each joint state, using a periodical homogenization method. The simulation was performed in two steps: first, computation of the thermal field, and second, computation of the displacements and stress fields. The comparison with experimental measurements on a real blast furnace showed that the model produces satisfactory results. The results also showed the importance of the initial ramming mix density and the influence of joint openings.