A non-ordinary type of solid fuel gasification reactor, which was under development for the few past decades and it is briefly described as indirect heat rotary kiln gasifier, seems to be capable of sufficiently satisfying the incorporated gasification needs in the most challenging contemporary power technologies using solid fuels, like IGCC and CLC combustion. The design of such a gasifier emerges in this work, while the focus is mostly on the presentation of the relevant theoretical model. Moreover, model predictions are compared and optimized with respect to experimental data that were acquired in a pilot scale gasification unit including the suggested type of gasifier. Comparisons showed successful predictions of such a marginal error that could be characterized as quite sufficient for a primary model validation. However, the model flexibility to a wide variety of different solid fuels, rotary kiln configurations and operating conditions has to be verified by assessment of further experimental results. (C) 2011 Elsevier B.V. All rights reserved.