Since the heating unit often runs under off-design conditions

an off-design calculation model was established for the heating unit. Taking the Quanzhou 300 MW condensing heating retrofit unit as an example

the thernodynamic characteristics of the heating unit running under off-design condition were analyzed. The exergy efficiencies and local exergy loss ratios of the heating unit under off-design conditions were calculated quantitatively from the perspective of energy grade. The results showed that

under certain thermal user conditions

with the increase of the main steam flow rate

the total thermal efficiency of the thermal power plant decreased

while the power generation thermal efficiency and exergy efficiency increased. When the main steam flow rate remains unchanged

with the increase of the first stage heating extraction steam flow rate

the exergy efficiency of thermal power plants increased first and then decreased

and there was an optimal first stage heating extraction steam flow

which made the thermal performance of the unit optimal. In the actual work of the steam turbine unit

the appropriate main steam flow and heating extraction steam flow can be selected according to the specific heat user requirements and the thermal characteristics of the unit

to ensure that the thermal power plant maintains a high exergy efficiency.