A mixing device (32) comprising a statically pressurized container (36) adapted to be arranged inside a tank or reactor vessel (34), and at least one vane (38) attached to said pressurized container (36), wherein the pressurized container (36) is connected to a liquid pumping system (31), wherein said liquid pumping system (31) is adapted to be able to pump liquid in and out of said container (36)； wherein gas (7) trapped in the pressurized container is arranged at the top portion of said container (36)； and wherein said vane (38) is configured to encompass the container (36) around substantially the entire circumference thereof and extending from said container to at least a portion of the diameter of said tank or reactor vessel (34).
