A new 100 kW test plant with a novel dual fluidised bed steam gasification concept was built at the Vienna University of Technology. The new concept is designed for the gasification of a broad range of solid fuels even with difficult physical and chemical properties. Before the novel test plant will be operated with fuel, cold flow investigations were carried out to prove the fluid dynamics in the reactors. Therefore, the fluidisation flows of the reactors and the bed material mass were varied. The pressure profiles were used to analyse the proper function of the reactors. An optimum operation range for the fluidisation flows was found. The results are in accordance with previous investigations on a smaller acrylic glass cold flow model. The results achieved confirm the successful scale up of the dual fluid gasification concept from cold flow model scale to test plant scale.