Boiler combustion system and operation method therefor

A boiler combustion system comprising:

• a boiler equipped with a burner configured to burn fuel with combustion gas and a two-staged combustion gas input port configured to supply combustion gas to a neighborhood of a combustion area of the burner;
• a flue gas treatment system configured to treat flue gas discharged from the boiler;
• first and second flue gas supply devices configured to each supply the flue gas extracted from the flue gas treatment system to the boiler;
• supply lines configured to supply the flue gas supplied from the first flue gas supply device, including a combustion gas supply line configured to supply the flue gas as combustion gas to the burner and a two-staged combustion gas supply line configured to supply the flue gas as two-staged combustion gas to the two-staged combustion gas input port;
• a fuel carrier gas supply line configured to supply the flue gas as fuel carrier gas used to transport the fuel to the burner, the flue gas being supplied from the second flue gas supply device;
• an oxygen supply device configured to produce oxygen-rich gas and supply the oxygen-rich gas to the combustion gas supply line and the fuel carrier gas supply line via respective flow regulators;
• a first combustion air supply device configured to supply combustion air to the combustion gas supply line and the two-staged combustion gas supply line;
• a second combustion air supply device configured to supply combustion air to the fuel carrier gas supply line;
• a first damper configured to regulate a flow rate of gas supplied from the combustion gas supply line to the burner;
• a second damper configured to regulate a flow rate of gas supplied from the two-staged combustion gas supply line to the two-staged combustion gas input port;
• and
• a control unit configured to control openings of the first damper and the second damper, switching operation between the first and the second flue gas supply devices and the first and the second combustion air supply devices, and start of operation of the oxygen supply device, wherein
• when switching from oxygen combustion mode to air combustion mode, the control unit performs control so as to switch from operation of the first and second flue gas supply devices to operation of the first and second combustion air supply devices and yet open the first damper and the second damper, and when switching from air combustion mode to oxygen combustion mode, the control unit performs control so as to switch from operation of the first and second combustion air supply devices to operation of the first and second flue gas supply devices, start operating the oxygen supply device, and yet close the second damper with the first damper kept open.