Ultra cleaning of combustion gas to near zero concentration of residual contaminants followed by the capture of CO2 is provided. The high removal efficiency of residual contaminants is accomplished by direct contact cooling and scrubbing of the gas with cold water. The temperature of the combustion gas is reduced to 0-20 degrees Celsius to achieve maximum condensation and gas cleaning effect. The CO2 is captured from the cooled and clean flue gas in a CO2 absorber (134) utilizing an ammoniated solution or slurry in the NH3—CO2H2O system. The absorber operates at 0-20 degrees Celsius. Regeneration is accomplished by elevating the pressure and temperature of the CO2-rich solution from the absorber. The CO2 vapor pressure is high and a pressurized CO2 stream, with low concentration of NH3 and water vapor is generated. The high pressure CO2 stream is cooled and washed to recover the ammonia and moisture from the gas.