[Objective] With the deepening of global carbon reduction trends and the promotion of large-scale hydrogen application

the retrofitting of hydrogen blending combustion technology for existing gas turbine units is an important and promising approach to achieving the low-carbon energy transformation in the power and heating sectors. [Methods] This study constructs a thermal system model based on the Ebsilon thermal system simulation platform for an SGT800 dual-pressure non-reheat combined cycle unit of a combined heat and power(CHP) cogeneration gas turbine power plant. The influence laws of hydrogen blending ratio(0～50%

mass basis) and gas turbine load rate on the system operating parameters as well as thermal performance of the combined heat and power system are investigated systematically under the condition of keeping the total fuel heat input and turbine inlet temperature constant. [Results] The results show that as the H2 blending ratio increases

the fuel mass flow rate gradually decreases. To keep the turbine inlet temperature unchanged

the excess air coefficient at the turbine inlet must be reduced accordingly. However

the turbine exhaust temperature

flow rate and heat do not monotonically change with the increase of hydrogen blending ratio. This is the result of the dynamic adjustment of the cooling air flow rate of the system to maintain a constant turbine inlet temperature. Under the 100% gas turbine load rate and maximum extraction-condensing working condition

the gas turbine power generation efficiency and the combined cycle system efficiency reach their maximum values of 41.05% and 80.79% at nearly 20% hydrogen blending ratio respectively

which are 1.38% and 1.16% higher than those in the pure-natural-gas combustion working condition. Further examination of the influence of hydrogen blending combustion under variable load conditions of the unit on system operating parameters reveals that

when the hydrogen blending ratio increases from 0 to 50%

the gas turbine power generation efficiency increases by 1.38%

1.28% and 1.12% at gas turbine load rates of 100%

80% and 60% respectively

and the combined cycle system efficiency increases by 1.16%

1.08% and 0.92% respectively. [Conclusion] Overall

the effect of hydrogen blending combustion on the performance of the CHP gas turbine combined cycle unit exhibits a complex and dual-dimensional load-dependent characteristic. In the high-load range

hydrogen blending provides optimization to the combustion process to maximize the absolute efficiency gain of the unit

and in the low-load range

hydrogen blending raises the performance baseline of the unit to ensure its economic feasibility in deep peak-shaving working conditions.