An inertial gas-solid separator has been specifically designed to collect the recycling products from solids in CFB reactors operating at very high gas velocities. The main feature of this device is an integrated layout of the riser separator set that allows gas retention times as short as 3 ms and maximum inlet solid/gas mass ratios up to 30. The separation efficiency and the pressure drop for different particle sizes, gas velocities and solid mass flow rates has been determined and their dependence on solid loading and design features has been discussed.