Abstract: The present invention comprises a mixing system that provides improved mixing of quench gas and process fluids in a height constrained interbed space while not increasing pressure drop. In particular, the device improves the effectiveness of an existing mixing volume in mixing the gas phase of two-phase systems. The mixing system includes a horizontal collection tray, a mixing chamber positioned below the collection tray, at least one passageway extending through the collection tray into the mixing chamber, and a vapor slipstream passageway extending through the collection tray into the mixing chamber for directing a vapor slipstream from above the collection tray into the mixing chamber. The mixing chamber and the collection tray define a two-phase mixing volume. The passageway conducts fluid containing at least some vapor from above the collection tray into the mixing chamber. The mixing chamber preferably includes at least one outlet opening for the downward passage of fluid.