Hybrid Fuel Cell Gas Turbine System Design and Optimization for SOFC

Author(s):  
Dustin McLarty ◽  
Scott Samuelsen ◽  
Jack Brouwer

Fuel Cell–Gas Turbine (FC-GT) hybrid technology portends a significant breakthrough in electrical generation. Hybrid systems reach unprecedented high efficiencies, above 70% LHV in some instances, with little to no pollution, and great scalability. This work investigates two high temperature fuel cell types with potential for hybrid application ranging from distributed generation to central plant scales; sub MW to 100MW. A new library of dynamic model components was developed and used to conceptualize and test several hybrid cycle configurations. This paper outlines a methodology for optimal scaling of balance of plant components used in any particular hybrid system configuration to meet specified design conditions. The optimization strategy is constrained to meet component performance limitations and incorporates dynamic testing and controllability analysis. This study investigates seven different design parameters and confirms that systems requiring less cathode recirculation and producing a greater portion of the total power in the fuel cell achieve higher efficiencies. Design choices that develop operation of the fuel cell at higher voltages increase efficiency, often at the cost of lower power density and greater stack size and cost. This work finds existing SOFC technology can be integrated with existing gas turbine and steam turbine technology in a hybrid system approaching 75% fuel to electricity conversion efficiency in optimized FC-GT hybrid configurations.

Author(s):  
Ji Ho Ahn ◽  
Tong Seop Kim

Owing to the increasing consumption of fossil fuels and emission of greenhouse gases, interests in highly efficient and low carbon emitting power systems are growing fast. Several research groups have been suggesting advanced systems based on fuel cells and have also been applying carbon capture and storage technology to satisfy the demand for clean energy. In this study, the performance of a hybrid system, which is a combination of a molten carbonate fuel cell (MCFC) with oxy-combustion carbon capture and an indirectly fired micro gas turbine (MGT) was predicted. A 2.5MW MCFC system that is used in commercial applications was used as the reference system so that the results of the study could be applicable to practical situations. The ambient pressure type hybrid system was modeled by referring to the design parameters of an MGT that is currently being developed. A semi-closed type design characterized by flow recirculation was adopted for this hybrid system. A part of the recirculating gas is converted into liquefied carbon dioxide and captured for storage at the carbon separation unit. Almost 100% carbon dioxide capture is possible with this system. In these systems, the output power of the fuel cell is larger than in the normal hybrid system without carbon capture because the partial pressure of carbon dioxide increases. The increased cell power partially compensates for the power loss due to the carbon capture and MGT power reduction. The dependence of net system efficiency of the oxy-hybrid on compressor pressure ratio is marginal, especially beyond an optimal value.


Author(s):  
Ji Ho Ahn ◽  
Tong Seop Kim

Owing to the increasing consumption of fossil fuels and emission of greenhouse gases, interests in highly efficient and low carbon emitting power systems are growing fast. Several research groups have been suggesting advanced systems based on fuel cells and have also been applying carbon capture and storage technology to satisfy the demand for clean energy. In this study, the performance of a hybrid system, which is a combination of a molten carbonate fuel cell (MCFC) with oxy-combustion carbon capture and an indirectly fired micro gas turbine (MGT), was predicted. A 2.5 MW MCFC system that is used in commercial applications was used as the reference system so that the results of the study could be applied to practical situations. The ambient pressure type hybrid system was modeled by referring to the design parameters of an MGT that is currently being developed. A semi-closed type design characterized by flow recirculation was adopted for this hybrid system. A part of the recirculating gas is converted into liquefied carbon dioxide and captured for storage at the carbon separation unit (CSU). Almost 100% carbon dioxide capture is possible with this system. In these systems, the output power of the fuel cell is larger than in the normal hybrid system without carbon capture because the partial pressure of carbon dioxide increases. The increased cell power partially compensates for the power loss due to the carbon capture and MGT power reduction. The dependence of net system efficiency of the oxy-hybrid on compressor pressure ratio is marginal, especially beyond an optimal value.


2004 ◽  
Vol 126 (4) ◽  
pp. 755-762 ◽  
Author(s):  
Hideyuki Uechi ◽  
Shinji Kimijima ◽  
Nobuhide Kasagi

Hybrid systems, which are based on a micro gas turbine (μGT) and a solid oxide fuel cell (SOFC), are expected to achieve much higher efficiency than traditional μGT’s. In this paper, the effects of cycle design parameters on the performance and feasibility of a μGT-SOFC hybrid system of 30 kW power output are investigated. It is confirmed that the hybrid system is much superior to a recuperated gas turbine in terms of its power generation efficiency and aptitude for small distributed generation. General design strategy is found that less direct fuel input to a combustor as well as higher recuperator effectiveness leads to higher generation efficiency, while higher steam-carbon ratio moderates requirements for the material strength. The best possible conceptual design of a 30-kW μGT-SOFC hybrid system is shown to give power generation efficiency over 65% (lower heating value).


Author(s):  
Dustin McLarty ◽  
Jack Brouwer ◽  
Scott Samuelsen

Ultrahigh efficiency, ultralow emission fuel cell gas turbine (FC/GT) hybrid technology represents a significant breakthrough in electric power generation. FC/GT hybrid designs are potentially fuel flexible, dynamically responsive, scalable, low-emission generators. The current work develops a library of dynamic component models and system design tools that are used to conceptualize and evaluate hybrid cycle configurations. The physical models developed for the design analysis are capable of off-design simulation, perturbation analysis, dispatch evaluation, and control development. A parametric variation of seven fundamental design parameters provides insights into design and development requirements of FC/GT hybrids. As the primary generator in most configurations, the FC design choices dominate the system performance, but the optimal design space may be substantially different from a stand-alone FC system. FC operating voltage, fuel utilization, and balance of plant component sizing has large impacts on cost, performance, and functionality. Analysis shows that hybridization of existing fuel cell and gas turbine technology can approach 75% fuel-to-electricity conversion efficiency.


2014 ◽  
Vol 257 ◽  
pp. 412-420 ◽  
Author(s):  
Dustin McLarty ◽  
Jack Brouwer ◽  
Scott Samuelsen

Author(s):  
Nana Zhou ◽  
Chen Yang ◽  
David Tucker

Thermal management in the fuel cell component of a direct fired solid oxide fuel cell gas turbine (SOFC/GT) hybrid power system, especially during an imposed load transient, can be improved by effective management and control of the cathode air mass flow. The response of gas turbine hardware system and the fuel cell stack to the cathode air mass flow transient was evaluated using a hardware-based simulation facility designed and built by the U.S. Department of Energy, National Energy Technology Laboratory (NETL). The disturbances of the cathode air mass flow were accomplished by diverting air around the fuel cell system through the manipulation of a hot-air bypass valve in open loop experiments. The dynamic responses of the SOFC/GT hybrid system were studied in this paper. The evaluation included distributed temperatures, current densities, heat generation and losses along the fuel cell over the course of the transient along with localized temperature gradients. The reduction of cathode air mass flow resulted in a sharp decrease and partial recovery of the thermal effluent from the fuel cell system in the first 10 seconds. In contrast, the turbine rotational speed did not exhibit a similar trend. The collection of distributed fuel cell and turbine trends obtained will be used in the development of controls to mitigate failure and extend life during operational transients.


2012 ◽  
Vol 138 (4) ◽  
pp. 205-214 ◽  
Author(s):  
Hsiao-Wei D. Chiang ◽  
Chih-Neng Hsu ◽  
Wu-Bin Huang ◽  
Chien-Hsiung Lee ◽  
Wei-Ping Huang ◽  
...  

Author(s):  
Wei Jiang ◽  
Ruxian Fang ◽  
Jamil A. Khan ◽  
Roger A. Dougal

Fuel Cell is widely regarded as a potential alternative in the electric utility due to its distinct advantages of high energy conversion efficiency, low environmental impact and flexible uses of fuel types. In this paper we demonstrate the enhancement of thermal efficiency and power density of the power plant system by incorporating a hybrid cycle of Solid Oxide Fuel Cell (SOFC) and gas turbine with appropriate configurations. In this paper, a hybrid system composed of SOFC, gas turbine, compressor and high temperature heat exchanger is developed and simulated in the Virtual Test Bed (VTB) computational environment. The one-dimensional tubular SOFC model is based on the electrochemical and thermal modeling, accounting for the voltage losses and temperature dynamics. The single cell is discretized using a finite volume method where all the governing equations are solved for each finite volume. Simulation results show that the SOFC-GT hybrid system could achieve a 70% total electrical efficiency (LHV) and an electrical power output of 853KW, around 30% of which is produced by the power turbine. Two conventional power plant systems, i.e. gas turbine recuperative cycle and pure Fuel Cell power cycle, are also simulated for the performance comparison to validate the improved performance of Fuel Cell/Gas Turbine hybrid system. Finally, the dynamic behavior of the hybrid system is presented and analyzed based on the system simulation.


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