In advanced steam-turbine power plants, pre-heating is an essential means by which the
thermodynamic efficiency of the Rankine cycle can be improved. The high-pressure preheater
is one of the last steps of pre-heating before the feedwater is fed into the steamgenerator.
This paper presents an analysis of GKN I’s HP pre-heater. Steam bled from the highpressure
turbine and condensate from the re-heater flow on the shell-side of the
component and account for a 35°C temperature rise of the feedwater.
A thermal model predicting the tube and shell outlet temperatures on the basis of all the
boundary conditions and the geometrical characteristics of the component is presented.
Head losses and static pressure variations inside the heat-exchanger are also calculated.
The velocity distributions inside the shell and the tube-bundle were estimated on the basis
of a thermally-driven flow of the steam through the component. The results of this
analysis were then used later on to determine if the heat-exchanger was prone to damage
caused by fluid-elastic instabilities or vortex shedding in the condensation zone or in the
subcooling enclosure (Kühlkasten).
Finally, a simplified Rankine cycle with one stage of pre-heating was simulated in order
to understand the impact of heat-exchange area variations inside the pre-heater on the
performance of the plant. The entropy generation and exergy destruction of the various
components of the cycle were studied and general guidelines for the design of the HP
pre-heater were deduced.