Session: 09-13-03: Design Analysis and Optimization of Energy Conversion Systems III

Paper Number: 171863

Implications of Thermal Integration Paths on a Solid Oxide Fuel Cell – Gasturbine (Sofc-Gt) Hybrid System When Using High Gt Power Share 

The solid oxide fuel cell – gas turbine (SOFC-GT) hybrid power-generation system employs twochemical-to-electrical conversion methods – a fuel cell and a recuperated combustion turbine –to provide dispatchable power to the grid. Because of the SOFC’s high energy conversionefficiency and because the two parts of the system are thermally integrated, the SOFC-GTsystem has been shown to generate its power output at high fuel efficiency at design point,part load, and during rapid load turndowns. Electrochemical losses from the reaction ofreformed fuel (e.g. methane) within the SOFC are rejected as high quality heat for the gasturbine cycle, and unutilized fuel and air are combusted to provide additional energy to theturbine. The turbine’s exhaust transfers heat to air entering the SOFC. This intensive thermalintegration offers tremendous opportunities for flexibility and efficiency in power generation.
The amount of spinning reserve available from the hybrid machine grows as the share of powerproduced at the GT increases with respect to the SOFC or total power. In these cases, the SOFCutilizes less of the fuel – its fuel utilization fraction (Uf) decreases. Machines with low Uf at theSOFC require split air-paths to accomplish temperature control of the SOFC and GT withopposing requirements. The airflow to the SOFC must support the electrochemical reaction butmust not overcool the stack. The GT, however, requires a higher air flow to prevent excessivetemperatures at the turbine inlet. This turbine inlet air is supplied by routing part of therecuperator-heated compressed air flow to bypass the SOFC and proceed to the turbine – a hotair bypass.
Thermal integration design of this machine has evolved from connection of only SOFC and GTto also thermally integrate with the reformer, which converts more common fuels for use inelectrochemical generation. The hot air bypass throughout this evolution has been routeddirectly to the turbine inlet. The current work presents design implications arising from a newhot air bypass entry point. The resulting geometry enables designs which do not requireextreme design efforts to accommodate very high temperatures when operating at a very lowSOFC Uf. A model of the SOFC-GT system with a thermally integrated reformer has beenstudied at design points supporting ultra-low fuel utilizations. Hot air bypass routing choiceshave been compared. Simulations have been executed using a coupled simulation, comprisinga 1D SOFC model in Simulink and a GT plus balance-of-plant-model in Ebsilon. This studyinvestigates the impacts of this new geometry to identify any significant efficiency oroperational changes arising from the routing choice for the hot air bypass.

Presenting Author: Danylo Oryshchyn National Energy Technology Laboratory, United States Department of Energy

Presenting Author Biography: Dan Oryshchyn is a Research Mechanical Engineer who performs mechanical design for experimental investigations, power cycle simulations, process design and development. He has served at NETL for 20+ years and has patents related to oxyfuel combustion, and CO2 capture.

Authors:

Danylo Oryshchyn National Energy Technology Laboratory, United States Department of Energy
Nor Harun National Energy Technology Laboratory, United States Department of Energy
Hao Chen Mälardalen University
Biao Zhang National Energy Technology Laboratory, United States Department of Energy
Nana Zhou National Energy Technology Laboratory, United States Department of Energy
David Tucker National Energy Technology Laboratory, United States Department of Energy