Proper management of sewage sludge becomes increasingly problematic due to legal requirements aiming at diminishing environmental impact, as well as rationalising the utilisation from the point of view of logistics. Steam gasification of sewage sludge can result in very good quality of the producer gas. So far, the works have been focused on the gasification in fixed bed gasifiers. However, this does not allow to take full advantage of the effect of scale, as scalability of fixed ed gasifiers is limited. Entrained flow gasifiers are scalable up to the order of magnitude of hundreds of megawatts, which was proven for gasification of coal. Therefore, it seems plausible to suspect that such scalability would allow building gasifiers big enough, to work as a part of bioenergy with carbon capture and storage plants, operating in economically feasible manner, fully utilising the effect of scale. However, optimised design of such units would require robust modelling. This work focuses on different models for sewage sludge steam gasification, allowing accurate predictions of the producer’s gas quality. Core part of this work is a comparison between the results obtained using advanced CFD model in Fluent, a 2D model in Chemkin, as well as two different equilibrium models. Results from all the models are experimentally validated, by entrained flow steam gasification in a 3 m long reactor, with addition of O2 and CO2.