discussed below may go through a fan 117 to increase the pressure as needed hydrogen fuel 108 may be blended with primary hrsg fuel 109 and then burned in duct burner 110 as the exhaust gas 112 exits the heat recovery steam generator 111 instead of being completely exhausted into main stack 114 a portion of the flue gas 113 is recycled back to displace an equivalent volume of fresh air 115 the hydrogen or hydrogen co blended fuel 118 may go through a fan 119 to increase the pressure for better injection and mixing after being burned in duct burner 110 the heated gas stream enters heat recovery steam generator 111 where it mixes with gas turbine exhaust gas 103 the velocity with which blended fuels 118 are introduced into the duct burner 110 depends on the structure of duct burner the size and the geometry of the combustion zone of the heat recovery steam generator the velocity and the temperature of combustion gases and the structure of heat recovery steam generator a cross section 200 of duct burner 110 as it is positioned within the transition duct between gas turbine 102 and heat recovery steam generator 111 is shown in fig2 a portion of cross section 200 is occupied by the rows of duct burner 201 the mixture of air and flue gas 107 passes through the remaining portion of the cross section 203 the blended fuels 118 are injected through fuel nozzles 202 the optimal air fuel ratio velocity ratio and the turbulent intensities of the blended fuels 118 and or the mixture of air flue gas 107 are dependent on the configuration of the cogeneration system the advantages of this solution the ability to maintain an efficient.