The present disclosure relates to a boiler system that includes an oxyfuel boiler in which a stream of oxygen and a fuel are combusted to generate a stream of flue gas. A flue gas condenser condenses the cleaned flue gas. A flue gas compression unit produces a stream of pressurized carbon dioxide rich flue gas. A pressure control system measures and controls the pressure after the flue gas conditioning system to a predetermined set value. A flow control system measures and controls the flow after the flue gas compression unit to a predetermined set value. The present disclosure further relates to a method of operating such a boiler system for an oxy-fuel process as well as to a power plant comprising such a system.