Damage is a crucial characteristic of refractory castables and has to be considered to simulate correctly the behaviour of refractory structures. But, damage modelling by finite element simulations remains difficult. Indeed, the use of a continuum damage model with softening leads to strain localization phenomena. Numerical results depend on the mesh. Several numerical methods allow solving this meshing dependence by introducing an internal length in the material constitutive laws. In this paper, a regularization method has been applied with the damage plasticity model, considering a scalar value for damage. This model enables to take into account permanent strains due to plasticity and damage before and after the peak stress in tension and compression. Thermomechanical simulations are performed with this model to predict damage in a gas-burner. The damage level is evaluated after a thermal simulation generating high temperature gradients. Interests to take into account damage in the refractory structures are discussed. Sensitivity of results to material properties is studied. This work gives an example of using thermomechanical simulations to improve the design of refractory castable structures and to help in the material choice.