Kousuke Nishida

Analysis of entropy generation and exergy loss during combustion

The analysis of entropy generation and exergy loss is used for optimizing the performance of energy conversion systems such as gas turbines. Exergy loss in the combustor of 20%–30% is the largest of all component losses in the gas turbine systems. The sources of the large exergy loss during the combustion process can be evaluated by analyzing local entropy generation of irreversible processes. Multicomponent flow with chemical reactions such as combustion involves four irreversible processes: viscous dissipation, heat conduction, mass diffusion, and chemical reaction. In this study, we analyzed local entropy generation and exergy loss due to these processes in premixed and diffusion flames in order to clarify the reasons for large exergy destruction during combustion processes, taking into account detailed chemical kinetics and multicomponent diffusion. The effects of fuels, equivalence ratio, and inlet fluid temperature on local entropy generation and exergy loss were evaluated for premixed flames. Chemical reaction is the dominant process for exergy loss in premixed flames, and the fraction of it changes in relation to the flame structure modification and temperature. On the contrary, for diffusion flames, heat conduction instead of chemical reaction is the major process for exergy loss.

Performance Evaluation of Multi-Stage SOFC and Gas Turbine Combined Systems

Solid oxide fuel cell (SOFC) and gas turbine hybrid power generation systems have gained more and more attention with regard to the development of the high performance distributed energy systems. The SOFC can be combined with a gas turbine because the SOFC operating temperature of about 1000°C matches the turbine inlet temperature. In this study, we proposed the multi-stage type SOFC/GT combined system and compared the system performance of it with that of other combined systems using the thermal efficiency and exergy evaluation. It is noted that the thermal efficiency of the 3-stage type SOFC/GT combined system can reach more than 70% (HHV) at low pressure ratio.Copyright

Performance Analysis of Regenerative Steam Injection Gas Turbine (RSTIG) Systems

There is a demand for developments of a distributed energy system using a small scale gas turbine. The steam injection configurations can improve the performances of the simple and regenerative gas turbine cycles. In this study, the thermal efficiency and exergy loss of two types of regenerative steam injection gas turbine (RSTIG) system are analyzed, and the performances of them are compared with those of the regenerative, water injection and STIG systems. It is noted that the optimum pressure ratio of the RSTIG systems becomes relatively low. The thermal efficiency of the RSTIG systems is higher than that of the water injection and STIG systems. The specific power of them is larger than that of the regenerative cycle. The steam injection configurations can be applied to the flexible heat and power generation system. The total efficiency of the heat and power generation of the RSTIG systems reaches more than 70% (HHV).Copyright

Analysis of Electrochemical Performance and Exergy Loss in Solid Oxide Fuel Cell

A solid oxide fuel cell (SOFC) is expected to be applied to the distributed energy systems because of its high thermal efficiency and exhaust gas utilization. The exhaust heat from the SOFC can be transferred to the electric power by a gas turbine, and the high efficiency power generation can be achieved by constructing the SOFC and gas turbine hybrid system. In this study, the local processes in the electrodes and electrolyte of unit SOFC are analyzed taking into account the heat conduction, mass diffusion, electrode reactions and the transport of electron and oxygen ion. The temperature and concentration distributions perpendicular to the electrolyte membrane are shown. The effects of the operating conditions on the cell performance are also shown. Furthermore, the entropy generation and exergy loss of each process in the electrodes and electrolyte are analyzed and the reason for generating the exergy loss in the SOFC is clarified. It is noted that two electrode reactions are responsible for the major exergy loss.Copyright