Steam Turbines for Flexible Load Operation in the Future Market of Power Generation

Abstract

In a liberated electricity market with a steadily growing percentage of fluctuating renewables the load related requirements of modern steam power plants are noticeably changing. Whereas the past has seen mainly coal-fired units being operated in base load now highly efficient part load behavior becomes more and more important as well as quickly responding frequency support at minimized investment costs. …In the article various approaches will be identified, discussed and evaluated under economical criteria focused on the above described challenges for future power generating technologies. One central idea is to shift the pure sliding pressure mode down to an intermediate load range where the upper limit is reached at around 70% and optimize the blade path efficiency according to this point. Along with this strategy concepts are presented which allow frequency support from primary to hour- reserve of maximized load steps. Moreover it shall be explained how it is principally possible to use the same cycle conditions for load steps and increasing part load efficiency at the same time. Another idea is to improve the plant performance at lower load ranges by raising the main and reheat steam temperature accompanied by special maintenance concepts. The ideas presented in this article are mainly derived from a steam turbine point of view. Nevertheless some requirements and effects on the overall plant are taken into account additionally. The presented approaches can be applied for new apparatus as for the upgrade of existing units. As the drivers for a more flexible operation of steam plants are especially strong in markets which do not guarantee an attractive utilization of the plant in produced MWhrs/year, investment decisions for new plants have been delayed or cancelled due to the difficult market conditions. Therefore special attention will be paid in this paper to the application of the new flexibility features in power plants which are already in operating and which have been designed originally with the main focus on highest efficiencies in base load operation. The difficulties and limitations given with the existing plant design will most likely be compensated by the economical advantages of the more flexible plant operation after the modernization.