Abstract: Processes and apparatus are disclosed for the separation and collection of contaminants from combustion chamber flue gas by means of heterogeneous nucleation and droplet accretion. The embodiment of the invention is based on: (1) A means of saturating the flue gas proportional to the contaminant volume. (2) A conception of a nucleation chamber where cold gas is added to establish and maintain a continuous supersaturated state throughout its volume. (3) A cold heat exchanger which lowers the partial pressure of the nucleation chamber and assists in maintaining a state of supersaturation. (4) A turbulent and inertial means of collecting the large drops together with the contaminant particles.