Control strategy for a SOFC gas turbine hybrid power plant

Abstract

Today, gas steam combined cycle plants are the most efficient power plants converting chemical energy into electrical energy with installed powers of usually several hundred MW. They are technologically mature reaching electrical efficiencies of 60 % (based on the lower heating value). Hybrid power plants consisting of solid oxide fuel cells (SOFC) and a gas turbine (GT) can reach higher electrical efficiencies and can be built at lesser installed power. The general concept of a SOFC/GT hybrid power plant is to use the hot SOFC exhaust gases to drive a gas turbine. High electrical efficiencies are achieved if SOFC and gas turbine match well. In the past few years a hybrid power plant with an electrical power output of 30 kW has been designed and is currently under construction at DLR. One challenge concerning the operation of the hybrid power plant is the control of the hybrid system. Stand-alone gas turbines can react comparatively fast to load changes and quickly reach a new stationary operating point. SOFC system temperatures react much slower due to their large thermal capacity. The operating strategy of the hybrid system needs to ensure a safe and reliable operation and allow for high electrical efficiency in a wide power range. Furthermore, dynamic operation like start-up, load changes, shut-down and emergency procedures are also considered. This work will give an overview of the control concept and show how the requirements are met.