Steady State Off-Design and Transient Behavior of a SOFC/GT Hybrid Power Plant With Additional Firing of the GT Combustor

Abstract

The purpose of the current work is to analyze and also to verify the operating behavior of a SOFC/GT hybrid system in order to derive necessary requirements for an appropriate control system. The studies are carried out with a control oriented simplified dynamic model of a 25 MWe hybrid system based on a conceptual design previously presented in literature. As specific feature additional firing of the GT combustor is investigated. First the design point is defined. Then the off-design performance is presented in terms of characteristic performance maps. Based on operating map investigations an appropriate part load operating curve is defined with considerations given to constraints (e.g. stack temperature or surge margin), efficiency and operational flexibility. The load range goes from 40% part-load to 105% overload. To investigate the transient behavior five open loop simulations are carried out changing different model inputs, as well as all model inputs applying a 30% load change according to the operating curve. The simulated behavior reveals that the inputs should be changed with specific care to avoid critical situations during load change.