Abstract
A dynamic model of an integrated solid oxide fuel cell (SOFC) combined heat and power (CHP) system has been developed. The model was developed by modifying a previously developed generic 5 kW simple-cycle SOFC system. Fuel cell model modifications include changes in methods and constants for estimating over-potentials to better simulate a modern anode-supported planar SOFC. In addition to scaling up and modifying the fuel cell model, a thermal energy storage (TES) tank, exhaust gas duct burner and hot water exhaust gas recuperator model were integrated into the system model. The fully integrated system model can effectively simulate an SOFC-CHP system and evaluate the system performance and efficiency in meeting building electricity and heating demand profiles. For the present effort, dynamic building electricity and heating data from a hotel operated in Orange County, southern California during the months of July and August 2008 were analyzed. Specifically, tradeoffs between SOFC performance and thermal energy storage have been investigated. The simulation results show that the SOFC-CHP system has the ability to follow the dynamic electrical load with appropriate system design and controls. Due to thermal power mismatch during electricity load-following operation, supplementary exhaust gas duct burner heat and/or a TES is required to independently dispatch the fuel cell power and meet the hotel heating demand. However, if the fuel cell is sufficiently sized, the system can achieve greater than 70% efficiency with only a small TES tank and without the need to fire the duct burner. The dynamic model and integrated SOFC-TES concept are shown to be useful for developing integrated CHP systems and to evaluate performance.
Highlights
Combined Heat and Power (CHP) systems based on integrated solid oxide fuel cells (SOFC) are considered to be attractive future energy systems [1,2,3,4,5,6]
SYSTEM OPERATION STRATEGIES Three basic operating strategies have been considered for the current SOFC-combined heat and power (CHP) system to meet local dynamic electricity and heating load demands
This section includes three main sets of results that are important for SOFC-CHP system development: 1) dynamic heating demand and supply trends, 2) system performance in terms of thermal and electrochemical efficiency of the system, and 3) the effects of Thermal energy storage (TES) capacity and SOFC scale on the system performance
Summary
Combined Heat and Power (CHP) systems based on integrated solid oxide fuel cells (SOFC) are considered to be attractive future energy systems [1,2,3,4,5,6]. After these modifications, the generic 5 kW simple-cycle system model was scaled up for the desired operating system power by increasing the number of fuel cell stacks, and balance of plant component sizes (e.g. heat exchanger plates, exhaust gas duct burner, and reformer). (4) Between control volumes, only mass transport and conductive heat transfer is considered Based on these assumptions, the molar flow rate and temperature of each control volume of the TES are determined from the appropriate transient energy and mass conservation equations of the same general form. The second control loop maintains the TES outlet temperature above 350 K (the hotel’s minimum hot water temperature requirement) by controlling the duct burner fuel flow rate (Figure 5). Note that the duct burner is only fired when the TES outlet temperature is below the demand temperature
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
