Oxy fuel boiler system and a method of operating the same
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.
1. A boiler system comprising
an oxyfuel boiler in which a stream of oxygen and a fuel are combusted to generate a stream of flue gas,
a flue gas compression unit for producing a stream of pressurized carbon dioxide rich flue gas,
a flue gas condenser for condensing cleaned flue gas,
a pressure control system in which the pressure before the flue gas condenser is measured and controlled to at least one predetermined set value, and
a flow control system in which the flow after the flue gas compression unit is measured and controlled to a predetermined set value,
wherein the pressure control system establishes a pressure value at which the boiler system operates, and controls the boiler system to operate in an air inlet mode when the pressure value at which the boiler system operates is below a predetermined first set value, and controls the boiler system to stop operation in the air inlet mode when the pressure value at which the boiler system operates is at or above the predetermined first set value, said air inlet mode including introducing air from the atmosphere as an air stream to at least part of a carbon dioxide containing stream from the flue gas condenser to be forwarded to the flue gas compression unit.
2. The boiler system according to claim 1 , further comprising a recirculation system, operative at least for a period of time in a recirculation mode, in which at least a part of the stream from the flue gas compression unit is returned to an inlet of the flue gas condenser.
3. The boiler system according to claim 2 , further comprising a recirculation controlling device and a recirculation regulating device which controls the recirculation system to operate in the recirculation mode based on a measured load on the boiler system.
4. The boiler system according to claim 1 , wherein the flow control system further comprises a flow controlling device and a flow regulating device which controls a bypass stream to operate in a bypass mode based on a measured flow value in the boiler system after the flue gas compression unit.
5. The boiler system according to claim 1 , wherein the pressure control system further comprises a pressure controlling device and a high pressure regulating device which controls an evacuation stream to operate in an evacuation mode based on a measured pressure value in the boiler system before the flue gas compression unit.
6. The boiler system according to claim 1 , wherein the pressure control system further comprises a low pressure regulating device which together with the pressure controlling device controls an air stream from the atmosphere to operate in an air inlet mode based on a measured pressure value in the boiler system before the flue gas compression unit.
7. A method of operating a boiler system comprising an oxy-fuel boiler in which an oxygen stream and a fuel stream are combusted to generate a flue gas stream, a flue gas condenser for condensing cleaned flue gas, a flue gas compression unit for producing a stream of pressurized carbon dioxide rich flue gas, said method comprising:
monitoring the pressure before the flue gas condenser and controlling the pressure before the flue gas compression unit to at least one predetermined set value by a pressure control system, and
monitoring the flow after the flue gas compression unit, and controlling the flow after the flue gas compression unit to a predetermined set flow value by a flow control system,
wherein the pressure control system establishes a pressure value at which the boiler system operates, and controls the boiler system to operate in an air inlet mode when the pressure value at which the boiler system operates is below a predetermined first set value, and controls the boiler system to stop operation in the air inlet mode when the pressure value at which the boiler system operates is at or above the predetermined first set value, said air inlet mode including introducing air from the atmosphere as an air stream to at least part of a carbon dioxide containing stream from the flue gas condenser to be forwarded to the flue gas compression unit.
8. The method according to claim 7 , further comprising operating the boiler system, at least for a period of time, in a recirculation mode, during which at least a part of a carbon dioxide stream from the flue gas compression unit is returned to an inlet of the flue gas condenser.
9. The method according to claim 7 , further comprising:
establishing whether the boiler system operates at a first load or at a second load, wherein the second load is a lower load than the first load,
controlling the boiler system to operate in a recirculation mode when the boiler system operates at the second load, and controlling the boiler system to stop operation in the recirculation mode when the boiler system operates at the first load.
10. The method according to claim 8 , wherein the recirculation mode of the boiler system is controlled using a recirculation controlling device and a recirculation regulating device.
11. The method according to claim 7 , wherein a measured load on the boiler system is measured on a stream from a fuel storage before the oxy-fuel boiler.
12. The method according to claim 7 , wherein the flow control system establishes a flow value at which the boiler system operates, and controls the boiler system to operate in a bypass mode when the flow value at which the boiler system operates is below the predetermined set flow value, and controls the boiler system to stop operation in the bypass mode when the flow value at which the boiler system operates is at or above the predetermined set flow value, said bypass mode including forwarding at least a part of a carbon dioxide stream from the flue gas compression unit as an evacuation stream to a stack or to a stream from a carbon dioxide separation unit forwarded to the stack.
13. The method according to claim 12 , wherein the bypass mode of the boiler system is controlled using a flow controlling device and a flow regulating device.
14. The method according to claim 7 , wherein the pressure control system controls the boiler system to operate in an evacuation mode when the pressure value at which the boiler system operates is above a predetermined second set value, and controls the boiler system to stop operation in the evacuation mode when the pressure value at which the boiler system operates is at or below the predetermined second set value, said evacuation mode including forwarding at least part of a carbon dioxide containing stream from a flue gas conditioning unit as a stream to a stack.
15. The method according to claim 14 , wherein the predetermined second set value for pressure is higher than the predetermined first set value.
16. An oxy-fuel combustion power plant comprising the system according to claim 1 .