In an apparatus for contacting a gas with a liquid, the gas is caused to flow upward through a vertical channel associated with a device for charging the channel with a foam containing the liquid. The channel contains upper and lower gas-permeable elements each arranged to support a layer of the foam covering the through-flow area of the channel, each element being formed to cause turbulence of the gas flowing therethrough. The two foam-supporting elements are located so close to each other that foam is entrained by the flowing gas from the space between the elements upwardly through the upper element to the upper side thereof, from which foam is returned through a passage to the space between the two elements. This return passage is shielded from upward flow of gas therethrough, so that a foam column in the passage can move downward.
In an apparatus for contacting gas and liquid comprising a substantially vertical column containing a number of substantially horizontal contacting trays in which each tray is provided with passages for gas and liquid, which apparatus further comprises a controller indicating the density of the mixture of gas and liquid at at least one contacting tray which controller communicates with means to control the flow of liquid from a lower contacting tray ("control tray"), upwards-flowing gas from the lowermost contacting tray and downwards-flowing liquid from an upper contacting tray are contacted, the improvement comprising that the density of the mixture of upwards-flowing gas and downwards-flowing liquid at least one contacting tray is monitored and said density is maintained at a desired level by controlling the flow of liquid from the control tray.
