Building emission processing and/or sequestration systems and methods

A method for separating carbon dioxide from flue gas generated from a natural gas combustion boiler within a commercial or residential building having multiple units, the method comprising:

• within the commercial or residential building, and upon demand for hot water or heat by at least one unit occupant, using a natural gas combustion boiler to generate flue gas from the combustion of air and natural gas, wherein the commercial or residential building includes a cooling tower;
• using the natural gas combustion boiler to generate hot water and/or steam for use by commercial or residential building heating systems to provide the hot water or heat to the at least one unit;
• cooling the flue gas using cooling water from the cooling tower to reduce the water in the flue gas to less than 3% water and provide cooled flue gas;
• providing at least a portion of the cooled flue gas to a desiccant dryer assembly to lower the water content of the flue gas to less than 10 ppm;
• after providing the cooled flue gas to the desiccant dryer assembly, providing the less than 10 ppm water flue gas to a pressure swing adsorption assembly and removing at least some of the nitrogen from the less than 10 ppm water flue gas to produce greater than about 95% carbon dioxide using the pressure swing adsorption assembly;
• and
• using the nitrogen removed from the flue gas by the pressure swing adsorption assembly to remove water and regenerate spent desiccant of the desiccant dryer assembly.