Nowadays, according to new environmental regulations, a reduction of waste volume is required. Because of this limitation, only two ways of elimination will be considered: incineration and land application. In this context, a global energetic study of a wastewater and sewage sludge treatment pilot station is carried out in order to build a real-time simulation tool of incineration processes [1,2]. A part of the investigation was focused on the pyrolysis characteristics. Indeed, thermolysis or pyrolysis kinetics are very complex and depend on many factors, such as sludge composition and its characteristics in the furnace input or such as its previous treatment. The thermal degradation of a complex material in an inert atmosphere or vacuum, causes organic material to change into three phases (liquid, gas and carbon), the proportion of which depends not only on the heat transfer speed, temperature, pressure, turbulence and reactor residence time, but also on the effluent nature (pH, OM%, DM%). Humid or pasty sludge incineration (10-30% DM) in a fluidised bed reactor can be used in conjunction with a natural gas combustion source when sludge auto-combustion is not complete or when the bed temperature is not high enough to destroy all the dangerous components. The modelling of the process in the incinerator is being developed to allow a numerical study of the reactor performance and to better understand the mechanisms of the pyrolysis and locate the different load transformation zones.