Abstract Biomass and low rank fuel gasification is a very promising process for conversion of fuels to a high quality fuel (Syngas). In the present paper research work on the design of a high pressure entrained flow gasifier for biomass based fuels is shown. Atomization quality of twin fluid nozzles as a function of gas velocity and reactor pressure is analyzed. The developed and characterized atomizers are used in an atmospheric entrained flow gasifier, to detect the influence of spray quality on gasification process. Furthermore, a CFD model of a high pressure entrained flow gasifier was developed. A significant influence of gas velocity and reactor pressure on Sauter Mean Diameter (SMD) of the produced spray was detected. Increasing gas velocity decreases the SMD, whereas increasing reactor pressure leads to the increase in drop diameter. An influence of SMD on gasification process was observed from organic carbon and methane concentration measurements as well as from the radial temperature profiles at various positions along the reactor centerline. Finally the CFD model of high pressure entrained flow gasification of biomass based slurries shows a very pronounced influence of drop size distribution on gasification quality.