Thermodynamic Model of the Influence of N2 Leakage on Heat Rate in Power Plant

Abstract

The steam leakage in HP&IP (high pressure and intermediate pressure) turbine through midspan packing (N2 packing) is called N2 leakage for short. When this leakage changes, its effects on the turbine’s power, superheating heat, reheating heat, and heat rate are analyzed by using the small deviation theory, with the main steam flow kept constant. It was proved that as N2 leakage changed, the HP turbine power and reheating heat changed significantly while that of IP&LP (intermediate pressure and low pressure) turbines changed little. Besides, the calculations pertaining to a supercritical 660 MW steam turbine in variable conditions are carried out. The results indicated that when N2 leakage increased, the change of those parameters was nearly linear, which agreed with the theoretical analysis. The results also demonstrated that the leakage affected the heat rate mainly by changing the HP turbine power and reheating heat. However, as the LP turbine power accounted for a large proportion of the total power of turbines, the impact of its change on the heat rate also should be taken into account.

Keywords:

• Supercritical steam turbine
• N2 leakage
• Linearity
• Variable conditions
• Heat rate