Steady State Off-Design and Transient Behavior of a Solid Oxide Fuel Cell/Gas Turbine Hybrid Power Plant With Additional Firing of the Gas Turbine Combustor

The purpose of the current work is to analyze and also to verify the operating behavior of a solid oxide fuel cell/gas turbine (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 a 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.