A gas injection and heating device and method for the bubbling of a gas into a body of hot liquid to be interacted with the gas. The device comprises an elongate heat exchange gas container, designed to be immersed in the hot liquid to pre-heat the gas in situ by heat exchange with the liquid. Cold gas is supplied to the elongate gas container, circulated therethrough to become heated to the liquid temperature, and then released from a nozzle into the depth of the liquid in the form of small bubbles of hot gas having a large liquid interfacial mass transfer area.