Abstract: A gas, for example, oxygen which has low solubility in water is efficiently dissolved and reacted with a substance in a flowing liquid medium by injecting the gas into the flowing liquid at spaced apart points such that a bubble flow condition is maintained and the injected gas is dissolved and substantially consumed by reaction with the substance in the interval between adjacent injection points; in this way the gas is injected at a point at which the aqueous liquid has maximum dissolving capacity and the number of injection points can be minimized; in another embodiment oxygen injection is controlled to maintain a desired oxygen:liquid ratio effective for efficient dissolving of the oxygen while maintaining the bubble flow condition, however, this requires more injection points.

Abstract: An inert gas such as helium is employed as a tracer gas in a pulp and paper mill to determine the utilization of oxygen by an aqueous cellulosic pulp particularly, as well as other parameters, in an oxygen delignification or extraction in which oxygen is dissolved in the pulp and reacted to solubilize lignins and reduce the requirement for chlorine-based bleaching chemicals.