A numerical model is developed to describe the hydrothermal decomposition of municipal solid waste (MSW) in the pilot scale facility. The modelling process involves the use of high-pressure steam to directly heat MSW to the temperature and pressure at which decomposition reactions occur. This process converts the organic matter into solid coal-like fuel having properties suitable for co-firing or co-gasification with coal. The model used in the present work uses the Combustion Mathematics and Energy Transport (COMMENT) code. In order to appropriately simulate the behaviour of the inherent batch process, a transient model is developed. The model facilitates the calculation of important process parameters such as the temperature, the pressure, the gas flow and the composition with respect to time. The model is also used to determine the possible operational scenarios of the proposed pilot scale test. Based on the calculated results, the numerical predictions of the model are compared with the experimental profiles obtained in the base case of the hydrothermal treatment, which shows a good agreement. Considering its advantages, the innovative hydrothermal treatment process can be considered as an alternative to MSW treatment and can be used to produce safe, usable and low-chlorine content solid fuels.