Dry low NOx staged combustion system

A dry staged combustion system, comprising:

• a fuel nozzle comprising:
• a purge gas tube configured to feed a purge gas;
• a diffusion combustion fuel tube fitted over the purge gas tube, and having an end provided with a diffusion combustion fuel swirler;
• an isolation gas tube fitted over the diffusion combustion fuel tube;
• a premixed combustion fuel tube fitted over the isolation gas tube;
• and
• a premixed combustion air tube fitted over the premixed combustion fuel tube, and provided with a premixed passage swirler to divide an interior of the premixed combustion air tube into a premixed combustion air passage upstream of the premixed passage swirler and a premixed chamber downstream of the premixed passage swirler;
• and
• a combustion compartment located downstream of the fuel nozzle and communicated with the purge gas tube, the diffusion combustion fuel tube, and the premixed chamber, respectively;
• wherein the premixed combustion fuel tube is provided with a cut-off plate on a same section as the premixed passage swirler to divide an interior of the premixed combustion fuel tube into a premixed combustion fuel passage upstream of the cut-off plate and a secondary passage for an isolation gas downstream of the cut-off plate, and the premixed combustion fuel passage is communicated with the premixed chamber through the premixed passage swirler;
• wherein the isolation gas tube defines an isolation gas passage upstream of the cut-off plate and a main passage for the isolation gas downstream of the cut-off plate, and the isolation gas passage is communicated with the secondary passage via an aperture formed in the isolation gas tube downstream of the cut-off plate;
• wherein an end of the secondary passage coincides with an end of the fuel nozzle;
• and
• wherein the combustion compartment is communicated with the main passage and the secondary passage, respectively.