Aiming at solving the gas wall blockage problem occurred in the 5 MW class supercritical carbon dioxide(S-CO_2) boiler of Xi'an Thermal Power Research Institute Co.

Ltd.(TPRI) during start up process

cause analysis was carried out combining with the field situation. It was found that

during gas charging process of the unit

the working medium throttled and expanded for many times

the cooling effect was remarkable

and the water in the header at the bottom of the gas wall froze. The CO_2 temperature decreased and the pressure gradually increased

resulting in liquefaction and sealing of the header. After ignition of the boiler

the liquefied CO_2 and frozen water closed the through-hole and blocked the flow of the working medium

thus the gas wall could not be effectively cooled

and the metal wall temperature of the boiler rose sharply. Based on the above analysis

improvement measures such as small fire heater

depressurization flash

end drainage and optimization of working medium filling parameters were implemented

and good effects were achieved. After debugging and adjustment

the ignition and start-up of the S-CO_2 boiler turned normal

and the metal wall temperature rise rate was reasonable. The relevant experience can provide reference for similar units in the future.