Recent Upgrading and Life Extension Technologies for Existing Steam Turbines

Abstract

Electricity generation utilities are increasingly looking for cost-effective solutions to maximise the value of aging steam turbine generator plant assets. To this end, retrofits of steam turbines after many years of operation have been carried out for the purpose of life extension of units, performance improvements, capacity up-rating, availability improvement, and improved environmental compliance. Major steam turbine manufacturers have continued to push forward the development of advanced technologies to satisfy demand from utilities by provided retrofit design that optimise the above criteria. This paper describes the advanced technologies adopted in the recent retrofits, including advanced steam path design and new last stage blades of improved efficiency, improved reliability, and of simplified or no maintenance. Retrofit case-studies of capacity up-rating and life extension are introduced to illustrate how these technologies have been applied and what has been the gain.

Investigation of the failure of the L-0 blades

“…According to [2,19], the steam turbine operation with low load/low vacuum is inducing L-0 blade excitation (vibration) by unstable flow developing high vibratory stresses. Fig.…”

“…The use of a continuously-coupled connection structure instead of the grouped blades has proved to significantly reduce the vibration stresses and is currently implemented in many retrofits of steam turbines [1][2][3][4][5]. The blades are continuously coupled 360 degrees around the row by an integral or loose cover segment at the tip and loose sleeve and lug at the mid-span.…”

“…During turbine operation at a low load/low vacuum, the L-0 blade vibration stresses are increasing abruptly. This increase (peak) of the blade vibration is induced by unstable flow with oscillation of a shock wave near the throat of the blade tip passage [1,2]. Operation at a low load like initial load-hold and other conditions shall be determined by considering such phenomena.…”