Biomass Chemical Looping Gasification (BCLG) represents an innovative process allowing the generation of non-nitrogen diluted synthesis gas with low tar content. The BCLG process is based on the partial oxidation of the fuel by means of an oxygen carrier to produce a high quality syngas. CO2 produced during the partial oxidation is present in the syngas, and it can be more easily captured. In this work, a theoretical model for the fuel reactor of a BCLG unit was used to perform a basic design of a CLG unit. The model was developed as simple as possible to simulate a high number of conditions in a relatively short period of time with low computing effort. However, it has the required complexity to consider the main processes affecting to the reaction of the biomass and the oxygen carrier, such as reactor fluid dynamics (1.5D macroscopic model) and the reaction pathway of biomass in the fuel reactor. The performance of a CLG unit under several operating conditions was predicted and a parametric study was performed by varying some operating conditions such as the solids circulation rate, the steam to biomass ratio, the fuel feeding rate or the reactor temperature. Optimum operating conditions were identified in order to maximize the syngas yield in the BCLG process. Thus, the model is a helpful tool for the design, optimization, and scale–up of the CLG process in order to obtain both high biomass conversion and high CO2 capture efficiency.