A study of thermal effort during half-hour start-up and shutdown of a 400 MW steam power plant spherical Y-pipe

Abstract

The subject of considerations is a spherical Y-pipe made of the 91 steel, which is an element of a coal-fired power plant unit working with a 18K370 turbine. Two scenarios for such a unit have been adopted: a fast scenario, in which the turbine is shutting down to a warm state three times in 24 h and an ultra-fast scenario, analyzing the one load peak with 30 min start-up and shutdown. These actions are dictated by new challenges in the field of electricity network regulation, caused by increasing share of renewable energy sources. A one-way numerical thermal-FSI analysis performed for each scenario focuses on hoop stresses as the most significant for the Y-pipe durability. The waveforms of these stresses at two points – at inner and outer surface of the Y-pipe sphere have been presented. Mechanical stresses derived from pressure and thermal stresses derived from temperature changes have been isolated. It has been shown that depending on the thermal load, some areas of the cross section are compressed while adjacent ones are stretched and vice versa. Thus, the thermal stresses can be reduced under certain conditions by mechanical stresses. It has been indicated that the Y-pipe could withstand given extreme loads.