Biomass is used since ancient times as combustion fuel for cooking, keeping houses warm, etc. Biomass is cheap and available abundantly and it can be converted into energy and/or products using the suitable processes. So, biomass is considered a potential energy source which can be converted by gasification processes into a gas mixture known as synthetic gas (syngas). A gasification process is a thermo-chemical process which converts carbon material into syngas gas streams, mainly constituted by mixtures of hydrogen and carbon monoxide. Typically, hydrogen gas is chemically produced from natural gas reforming; the use of renewable energy sources such as biomass to produce hydrogen offers a promising alternative. This study is focused on the modelling, simulation and performance analysis of biomass gasification processes using UniSim software. UniSim Design is a process simulator especially suited for the design and simulation of chemical processes. The performance of the gasification processes was studied varying the reaction temperature, and the gasifying agents’ flows (air and steam) in order to obtain realistic hydrogen/carbon monoxide productions in the syngas stream. Almond shell was chosen as the biomass source. Two models were constructed and tested using different conditions of temperature, biomass mass flow, air mass flow, and steam mass flow. For the first model, the best result was obtained when steam was used as gasifying agent producing syngas streams with mole compositions of 0.34 and 0.5 H2 and CO, respectively. Using the second model, there were observed small deviations in hydrogen and carbon monoxide compositions in the synthesis gas stream. However, the best result was obtained using steam as gasifying agent producing syngas streams with mole compositions of 0.45 and 0.5 for H2 and CO, respectively.