To provide a multiphase mixing apparatus having an improved quench injection for inducing a rotational flow.

A mixing system, wherein the multiphase mixing is improved by using a new quench injection means, is provided. This mixing system has a horizontal collection tray, a mixing chamber arranged under the collection tray, and at least one pathway extending into the mixing chamber through the collection tray. The mixing chamber and the collection tray define a two-phase mixing volume. The pathway guides a fluid from the upper part of collection tray to the mixing chamber. The mixing chamber has preferably at least one exit opening, wherein the fluid is delivered downward. In particular, when a preferable direction of the quench injection is selected such that a quench is introduced to an upper area of the collection tray, mixing of a quench fluid is significantly improved.