Method and system for gas initiated natural circulation vertical heat recovery steam generator

A vertical heat recovery steam generator system comprising:

• a steam drum;
• one or more downcomers;
• an evaporator with a plurality of evaporator tubes arranged perpendicular to a flow of hot gas;
• one or more risers having an inlet end and an outlet end, the outlet end fluidly coupled to the steam drum;
• a header having a header inlet fluidly coupled to the outlet end of the plurality of evaporator tubes, and a header outlet fluidly coupled to the inlet end of the one or more risers;
• a gas flow connector assembly configured to introduce a gas into the system at the one or more risers to reduce an average density of a fluid therein to initiate natural circulation flow of a fluid therein, for flow circulation in a direction from the one or more risers directly to the steam drum;
• and
• a secondary gas flow connector assembly configured to introduce a secondary gas into the system at the header outlet to reduce the average density of the fluid in the system to initiate natural circulation flow of the fluid therein, for flow circulation in the direction from the one or more risers directly to the steam drum.