Non-premixed combustion in rotary kilns using OpenFOAM: the effect of conjugate heat transfer and external radiative heat loss on the reacting flow and the wall

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The wish to reduce the environmental footprint and to enhance economic gains of rotary kilns pushes the numerical simulation of combustion to include conjugate heat transfer. In this paper we study the influence of the refractory wall and radiative heat loss to the ambient, on the combustion process of a reference kiln model. Numerical results show that the inclusion of the refractory lining and the external radiative heat loss allows the inner wall temperature distribution to vary, with 60 % difference between its minimum and maximum. This is in sharp contrast with models that assume a fixed temperature at the wall. Consequently the maximum inner wall temperature increases by more than 200 %, the maximum flame temperature by nearly 13 % and maximum freeboard gas temperature by up to 90 %. It is thus important to account for these effects when modeling rotary kilns.