Dual fluidized bed systems are increasingly used in different technical fields, especially for biomass steam-gasification. Their aim is to produce a nitrogen free product gas with high caloric value. These systems consist of two fluidized bed reactors. The first reactor (air reactor) provides heat for the second reactor (fuel reactor), where gasification takes place, by burning part of the biomass. Heat transport is realized through circulating bed material. It is advantageous that the product gas from the fuel reactor and the off gas from the air reactor are not mixed. A bubbling fluidized bed (fuel reactor) combined with a circulating fluidized bed (air reactor) is typical for the classical design. However, it is disadvantageous for gasification that the bubbling fluidized bed consists of two parts: the bed itself and a freeboard, where only gas and no catalytic active solids exist. The new concept replaces the freeboard with a counter current reactor: hot catalytic active bed material, coming from the air reactor, falls downwards and gas flows upwards. Additional geometric modifications of the counter current reactor lead to improvement of gas-solid interactions and longer residence time of solids. This thesis points out the positive impacts of the new design regarding bed material distribution on the basis of cold flow model investigations, especially pressure measurements. As a medium of fluidization air and as bed material bronze (64 µm) are used. Furthermore, a characteristic diagram of operation is presented. It shows, with regard to the operation of an industrial sized plant, that the field of operation is sufficient for reasonable operation of the system. Finally, the thesis contains experimental results of mass circulation measurements.