Abstract
Abstract In this work, operation and load of Once-Through Steam Generators (OTSG) in a combined cycle power unit offshore are investigated in terms of load changes for the gas and steam turbines as well as OTSG start-up sequences. This is connected to remaining life-time analysis of OTSG components, focusing on the influence of the OTSG design parameters on dynamic operation and equipment fatigue. The reference offshore combined cycle power plant configuration consists of two SGT750 gas turbines with a steam bottoming cycle for power production. Two bottoming cycles were designed, one based on a compact OTSG design with a tube diameter of 1”, and one based on an OTSG with a larger tube diameter of 1¾”. The main results of this work highlight the total weight reduction with the use of smaller tube diameters, as well as smaller settling times to changes in operating conditions with and without process controls. OTSG startups were investigated and found to be the main contributors to lifetime consumption. A slower startup sequence, with gradual adjustment of the inlet feed water flowrate increases lifetime of the system in about 3 orders of magnitude when compared to an instant change in operating conditions for start-up.