A steam-generating combustion system includes an oxygen enriched gas provided as at least part of an oxidant stream. A combustion chamber receives and combusts a fuel in the oxidant stream and generate steam. The combustion chamber generates flue gas having a flue gas volume which is smaller than a volume of flue gas generated by the combustion chamber when operated with air as the oxidant stream. A flue gas pollutant control system receives the flue gas from the combustion chamber and reduces at least one of particulate matter, SO_x, NO_x, and mercury. The reduction in flue gas volume allows the implementation of much smaller pollutant control equipment, since the size of the pollutant control units is mainly based on the volume or mass flow rate of flue gas to be treated. Moreover, the system including oxygen-enriched gas in the oxidant will lead to concentrated levels of the pollutants in the flue gas. The high concentrations of pollutants will enhance their absorption in the different pollutant control systems, improving removal efficiency for all species.