A Python model was established for thermal performance of the heavy-duty gas-steam combined cycle triple-pressure heat recovery steam generator. The model calculates the detailed heat recovery steam generator parameters under the condition of changing unit load

including main steam pressure and flow rate

heat and heat transfer coefficient of each heat exchanger

as well as power output and efficiency. As the effect of exhaust gas temperature and flow rate on the heat recovery steam generator is analyzed

how the ambient temperature

humidity and fuel heating affect the heat recovery steam generator output is also discussed when the unit is in part-load. It is verified that the model has good simulation accuracy and calculation efficiency. Simulations for one certain frame gas turbine combined cycle show that: When the unit load is reduced from full load 650 MW to partial load 250 MW

the triple main steam pressure and feed water flow rate of heat recovery steam generator decrease

the steam turbine power output decreases from 219.1 MW to 130.4 MW

and the efficiency of heat recovery steam generator increases from 89.3% to 92.1%; main-steam flow increases as the flue gas flow rate and temperature increase at the inlet of heat recovery steam generator; As the load of the random group decreases

the heat transfer coefficient and heat transfer amount of each heat exchange surface of the waste heat boiler decreases

but the proportion of heat exchanger between the flue gas and the high-temperature section heat exchanger in the total heat increases

and the heat transfer between the flue gas and the low-temperature section increases. The proportion of heat exchanger heat transfer in the total heat is reduced; when the unit load is reduced from 650 MW to 300 MW

the proportion of steam turbine shaft power increases by 1.67 percentage points

the proportion of heat loss in the chimney flue gas decreases by 2.63 percentage points.