Polymer powder vessel having a silo including a main vertical cylinder and a hopper at the bottom of the cylinder, a polymer powder which occupies the full volume of the hopper and at least a part of the volume of the cylinder, a polymer powder silo inlet pipe connected to the silo at a height located above the polymer powder, and a polymer hopper withdrawal pipe is also connected to the hopper. The polymer powder hopper withdrawal pipe is also connected to the silo at a location above the polymer powder for recirculating a part of the polymer powder within the silo.