Shinji Kimijima

Cycle Analysis of Gas Turbine–Fuel Cell Cycle Hybrid Micro Generation System

Small distributed generation systems are currently attracting much attention because of their high energy utilization efficiency. Among them, a hybrid system based on micro gas turbine (µGT) and solid oxide fuel cell (SOFC) is expected to achieve much higher efficiency than a traditional µGT. In this paper, we investigate the effects of cycle design parameters on the performance and feasibility of a µGT-SOFC hybrid system for small apartments and businesses. As a result, a general design strategy is found that less direct fuel input to combustor as well as higher recuperator effectiveness leads to higher generation efficiency, while higher steam-carbon ratio moderates requirements for the material strength. It is also confirmed that the hybrid system is much superior to the recuperated gas turbine in terms of its power efficiency and aptitude for small distributed generation. A conceptual design of a 30kW µGT-SOFC hybrid system, of which diameter and height are 750mm and 1500mm, respectively, is shown to give power efficiency over 65% (LHV) in the best possible case.

Performance evaluation of gas turbine-fuel cell hybrid micro generation system

Design-point and part-load characteristics of a gas turbine-solid oxide fuel cell hybrid micro generation system, of which total power output is 30 kW, are investigated for its prospective use in the small distributed energy systems. A cycle analysis of the hybrid system has been performed to obtain general strategies of highly efficient operation and control. The method of analysis has been compared with previous results, of which power output values are set in the range from 287 to 519 kW. Then, the part-load performance of the 30 kW system has been evaluated. Two typical operation modes, i.e., constant and variable rotation speed gas turbine operation are considered. It is found that the variable speed mode is more advantageous to avoid performance degradation under part-load conditions. Operating under this mode, despite of 10% adiabatic efficiency drop in the gas turbine components, the generation efficiency can be maintained over 60% (LHV) in the power output range from 50 to 100%.Copyright

Biomass Solid Oxide Fuel Cell-Microgas Turbine Hybrid System: Effect of Fuel Composition

Performance analysis of the solid oxide fuel cell-microgas turbine (SOFC-MGT) hybrid system has been made. We assume a fuel composition that is methane based with varying concentrations of other species that are expected to be present in biomass-derived gas streams in preparation for the study of biomass fueled SOFC-MGT hybrid system. This is based on the fact that the chemical composition of biomass fuel produced from different fuel production processes is diversified, i.e., in one case one chemical species rich in concentration and in another case another chemical species rich. In the analysis, the multistage model for internal reforming SOFC module developed previously with some modification is used. With this model, studies cover not only the performance of the hybrid system but also the spatial distributions of temperature and concentration of some chemical species inside the module, namely, in the cell stack and in the internal reformer.

Solid Oxide Fuel Cell–Micro Gas Turbine Hybrid System Using Natural Gas Mixed with Biomass Gasified Fuel

The effect on performance of a solid oxide fuel cell-micro gas turbine (SOFC-MGT) hybrid system on mixing or replacing natural gas, the normal fuel of such hybrid systems, with biomass gasified fuel (biofuel) was studied. It was found that the efficiencies of the SOFC module and of the hybrid system noticeably decrease when natural gas is completely replaced by biofuel but that the system can still be operated at a reasonable condition. To explain these results, changes in spatial distributions of temperature and concentration of certain chemical species inside an internal reforming type SOFC module are also discussed.

Experimental and numerical analysis of transport phenomena in an internal indirect fuel reforming type Solid Oxide Fuel Cells using Ni/SDC as a catalyst

This paper presents experimental and numerical studies on the fuel reforming process on an Ni/SDC catalyst. To optimize the reforming reactors, detailed data about the entire reforming process is required. In the present paper kinetics of methane/steam reforming on the Ni/SDC catalyst was experimentally investigated. Measurements including different thermal boundary conditions, the fuel flow rate and the steam-to-methane ratios were performed. The reforming rate equation derived from experimental data was implemented in into numerical model which was numerically solved in order to discuss this process in details.

Experimental study on the 300W class planar type solid oxide fuel cell stack: Investigation for appropriate fuel provision control and the transient capability of the cell performance

The present paper reports the experimental study on the dynamic behavior of a solid oxide fuel cell (SOFC). The cell stack consists of planar type cells with standard power output 300W. A Major subject of the present study is characterization of the transient response to the electric current change, assuming load-following operation. The present studies particularly focus on fuel provision control to the load change. Optimized fuel provision improves power generation efficiency. However, the capability of SOFC must be restricted by a few operative parameters. Fuel utilization factor, which is defined as the ratio of the consumed fuel to the supplied fuel is adopted for a reference in the control scheme. The fuel flow rate was regulated to keep the fuel utilization at 50%, 60% and 70% during the current ramping. Lower voltage was observed with the higher fuel utilization, but achieved efficiency was higher. The appropriate mass flow control is required not to violate the voltage transient behavior. Appropriate fuel flow manipulation can contribute to moderate the overshoot on the voltage that may appear to the current change. The overshoot on the voltage response resulted from the gradual temperature behavior in the SOFC stack module.

A comparative study of two various empirical methodologies for deriving kinetics of methane/steam reforming reaction

Despite methane/steam reforming is the conventional method for hydrogen production, there are widespread disagreements between formulations of the process kinetic derived in the literature. In the present research, the mathematical baseline of the classical calculation methodologies of the reaction kinetic are presented and compared. They include methodologies based on: I) the assumed constant partial pressure of steam and methane and II) the minimization of the summed relative standard deviation of the calculated reaction constant. Their results are compared with generalized least squares approach. The calculation methodologies are correlated with the planed experimental measurement set. This paper aims for the clarification of the observed differences and pointing the most suitable methodology for the decreasing the overall uncertainty of the model.

An attempt to minimize the temperature gradient along a plug-flow methane/steam reforming reactor by adopting locally controlled heating zones

Plug flow reactors are very common in the chemical process industry, including methane/steam reforming applications. Their operation presents many challenges, such as a strong dependence of temperature and composition distribution on the inlet conditions. The strongly endothermic methane/steam reforming reaction might result in a temperature drop at the inlet of the reactor and consequently the occurrence of large temperature gradients. The strongly non-uniform temperature distribution due to endothermic chemical reaction can have tremendous consequences on the operation of the reactor, such as catalyst degradation, undesired side reactions and thermal stresses. To avoid such unfavorable conditions, thermal management of the reactor becomes an important issue. To carry out thermal management properly, detailed modeling and corresponding numerical analyses of the phenomena occurring inside the reforming system is required. This paper presents experimental and numerical studies on the methane/steam reforming process inside a plug-flow reactor. To optimize the reforming reactors, detailed data about the entire reforming process is required. In this study the kinetics of methane/steam reforming on the Ni/YSZ catalyst was experimentally investigated. Measurements including different thermal boundary conditions, the fuel flow rate and the steam- to-methane ratios were performed. The reforming rate equation derived from experimental data was used in the numerical model to predict gas composition and temperature distribution along the steam-reforming reactor. Finally, an attempt was made to control the temperature distribution by adopting locally controlled heating zones.

Numerical analysis on the dynamic behavior of a solid oxide fuel cell with a multivariable control strategy

The paper describes the dynamic analysis of the operation of a solid oxide fuel cell (SOFC) with a multivariable control strategy. Developing a control strategy shall be essential for the practical use of SOFCs in the future. The system needs to be operated flexibly to load change. DC power output control of the SOFC by adjusting the density of the current has been studied previously and the quick response of the SOFC estimated [1]. However, in that study the performance degradation of the SOFC under part-load operation was estimated. To achieve effective operation of the SOFC under the partload condition in the present study, system operation with multivariable control was adopted. The numerical modeling of the SOFC system analysis was done by solving the steady mass balance and the unsteady energy equations including heat transfer (the electrochemical reaction is spontaneous and mass diffusion is a relatively faster transient phenomenon than heat transfer due to the high heat capacity of the system components). Feedback control methodology was used to build the system control strategy. Fig. 1 shows the feedback loop of the SOFC targeted to control of the DC power output. In order to achieve multivariable control of the SOFC as shown in Fig. 2, the DC power output and cell operating, the fuel utilization factor and Steam/Carbon (S/C) ratio were adopted as process variables. For this control purpose, the current density, the air mass flow rate, the fuel mass flow rate and the steam mass flow rate were adopted as the manipulated variables. The relationship between the process variables and the manipulated variables are shown in Fig. 2.

Experimental and analytical evaluation of the drying kinetics of Belchatow lignite in relation to the size of particles

Water removal is a key technology for enhancing efficient utilization of lignite in power generation. An inherent characteristic of lignite, attributed to the large amount of water kept within the fuel, is the factor decreasing the thermal efficiency of lignite-fired power plants. This paper presents the research results on investigating the drying kinetics of Belchatow lignite excavated in the Central Poland in prior to developing a water removal system. Lignite drying test was conducted in superheated steam atmosphere at the temperature range of 110-170 °C. Spherically shaped samples, of which the diameter is 2.5 mm, was used. The experimental results were then analysed with previously conducted measurements of 5, 10, 30 mm samples to investigate the influence of particle size. The presented analysis shows the agreement of the evaluated drying rate at the CDRP to the experimental data. The obtained experimental results were used to predict the drying behaviour of the group of particles. The proposed investigation clarifies the size dependence of the drying characteristics of the multisize group of lignite particles.