Gas Turbine Load Limited due to High Exhaust Temperature Deviation

Abstract

This case study presents an incident of sudden exhaust temperature spread increase of a medium power range Gas Turbine Generator (GTG) during normal operation. The analysis of exhaust temperature spread, field troubleshooting and recommended solution are presented to share the key learnings. A routine planned inspection on the GTG was conducted to assess the machine condition. The external fuel gas filter coelescer was swung from the running Filter B to standby Filter A due to increase in differential pressure. After GTG restart and running for a month, the turbine exhaust temperature (T7) deviation was found increased from 15�C up to 40�C which then caused GTG auto unloading to about half load. In the process of troubleshooting, the exhaust temperature spread at different loading was tested and the results rendered were analyzed systematically by both user and OEM. Cold spots were indicated from the spread which suggested burners clogged up. It was a challenge to identify the clogged burners due to the complexity of turbulent flow at the turbine exhaust. A thorough fuel gas manifold inspection was performed and particles were found downstream at different sections of the system. Sample collected and sent for EXD testing which revealed presence of rust particles. The internal and external fuel gas system were clean purged with instrument air in the subsequent planned maintenance window. GTG restarted back successfully after the corrective action and the average turbine exhaust had been normalized to ~10�C.