Isentropic and exergy analyses of marine steam turbine segments at several loads

Abstract

This research presents isentropic and exergy analyses of marine steam turbine segments at three loads. Turbine segment is a part of any cylinder which is placed between the steam entrance to the cylinder and first steam extraction, between steam extractions and finally between last steam extraction and steam exit from the cylinder. Division of each cylinder to the segments allows insight into the various cylinder parts operation and an observation is the cylinder properly balanced. The analyzed marine steam turbine is composed of two cylinders – High Pressure Cylinder (HPC) and Low Pressure Cylinder (LPC), while each cylinder has two segments. The dominant part of real mechanical power produced in HPC is actually produced in the first HPC part (segment 1), while in LPC, the dominant part of real mechanical power is produced in the last LPC part (segment 4). Segments 1 and 3 have the highest improvement potential (inlet segments of both HPC and LPC) due to the highest isentropic losses and exergy destructions. HPC is much better balanced cylinder because along with isentropic, also exergy efficiencies between its segments (segment 1 and segment 2) at all loads differ lower than 7%, while the same cannot be stated for the LPC which exergy efficiencies between segments (segment 3 and segment 4) at all loads differ more than 20%. Very low isentropic and exergy efficiencies of the segment 3, at all observed loads, indicate that this turbine segment is highly problematic and at least some of the turbine stages mounted in this segment have difficulties in operation or potential malfunction. In addition, segment 3 is also the highest influenced by the ambient temperature change in comparison to other segments. The ambient temperature increase from 5 °C up to 45 °C can decrease segment exergy efficiency between 1.31% and 3.17%, if all the segments and all loads of the analyzed marine steam turbine are observed.