Building emission processing and/or sequestration systems and methods

A method for operating a combustion boiler to optimize removal of the CO2 from the combustion flue gas within a multi-unit residential or commercial building that is operably engaged to provide steam upon demand from at least one unit within the multi-unit residential or commercial building using domestic water to provide the steam for hot water, and/or steam supplied radiant building heater, the method comprising:

• upon demand for hot water or building heat by the at least one of the multi-unit residential or commercial building occupants providing air and natural gas to the combustion boiler;
• using the combustion boiler to receive domestic water and provide heated water for use by the building occupants and/or steam to provide radiant heat for the residential or commercial building;
• monitoring the amount of free oxygen in a combustion burner of the combustion boiler;
• controlling the amount of air and natural gas provided to the combustion burner to maintain a free oxygen amount in the combustion burner greater than 3% and combust the air and natural gas within the combustion burner to generate flue gas from the combustion burner, wherein the flue gas generated from the combustion burner has a CO2 concentration of at least about 10% and a water concentration of about 18%;
• and
• compressing and drying the flue gas to remove water from the flue gas to achieve a water concentration at or below 10 ppm before separating CO2 from N2 then liquifying the CO2 separated from the flue gas.