Takao Nakagaki

Development of Chemically Recuperated Micro Gas Turbine

Micro gas turbines (MGTs) are subject to certain problems, notably low thermal efficiency of the system and high emission including NO x . The chemically recuperated gas turbine (CRGT) system introduced in this paper is one of the most promising solutions to these problems. The CRGT system we propose uses an endothermic reaction of methane steam reforming for heat recovery. It is usually thought that the reaction of methane steam reforming does not occur sufficiently to recover heat at the temperature of turbine exhaust, but we confirmed sufficient reaction occurred at such low temperature and that applications of the chemical recuperation system to some commercial MGTs are effective for increasing the efficiency.

Development of methanol steam reformer for chemical recuperation

The purpose of the present work is to establish the design method of methanol steam-reformer for application to chemical recuperation in a gas turbine system. The reaction rate of the methanol steam-reforming was measured with a small amount of catalyst using the gaseous mixture of methanol, water, hydrogen and carbon dioxide as a simulated product gas. The reaction rate equation could be expressed by power law of methanol mole fraction and total pressure. The reaction and heat transfer in the catalyst-packed bed was analyzed numerically using the reaction rate equation. The analytical results of temperature distribution and conversion were compared with the experimental results using a reforming tube. These results agreed well except for the region of high methanol conversion.

Effect of gas channel height on gas flow and gas diffusion in a molten carbonate fuel cell stack

An investigation is made of the relationships between the gas channel height, the gas-flow characteristics, and the gas-diffusion characteristics in a plate heat-exchanger type molten carbonate fuel cell stack. Effects of the gas channel height on the uniformity and pressure loss of the gas flow are evaluated by numerical analysis using a computational fluid dynamics code. The effects of the gas channel height on the distribution of the reactive gas concentration in the direction perpendicular to the channel flow are evaluated by an analytical solution of the two-dimensional concentration transport equation. Considering the results for uniformity and pressure loss of the gas flow, and for distribution of the reactive gas concentration, the appropriate gas channel height in the molten carbonate fuel cell stack is investigated.

Distributed Cogeneration of Power and Heat within an Energy Management Strategy for Mitigating Fossil Fuel Consumption

Distributed energy sources, such as self‐power generation, steam boilers, and combined heat and power production (CHP), are operated to manage the supply of energy by optimizing the costs of meeting the demand for electricity and heat. This article was written in conjunction with reports by the United Nations Environment Programs International Resource Panel that quantifies and compares the environmental and natural resource impacts and benefits of using demand‐side efficient technologies for greenhouse gas mitigation scenarios from now until 2050. In this article, we examine the potential of using distributed energy sources in future energy systems. First, we reviewed the existing research into several energy technologies, especially into cogeneration systems for CHP, using a bibliometric analysis. The current energy supply/demand in the demand‐side sectors in Japan is also reviewed using available statistical data, and an investigation into the energy requirements of industrial manufacturers was performed. After systematizing the results of our review on progress in current research, a scenario analysis was conducted on the potential of distributed energy sources to clarify the contribution of the various technology options. A mismatch between the quality of energy produced, especially heat, or any benefits arising from scale from other energy technologies, can decrease the incentive to implement distributed energy technologies. As a requirement of a regional energy system design and management, distributed energy sources should be considered so that the appropriate technology options can be adopted for the desired energy supply in the demand‐side sector. The possibility exists to replace conventional single‐generation technologies, such as boilers or power generators, with multigeneration technologies. A change in the grid power mix is one of the most sensitive parameters affecting the performance of cogeneration technologies.

Pressure losses at dividing and combining junctions in a molten carbonate fuel cell stack

The pressure losses at manifold junctions in a molten carbonate fuel cell (MCFC) stack depend on the stacking positions of the cells and the flow rate in the manifold. These pressure losses affect the uniformity of gas flow rate in each stacked cell and consequently also affect the cell performance. In this study, the pressure losses at dividing and combining junctions in a plate heat-exchanger type MCFC stack were examined by numerical analysis. A stack consisting of 100 cells was assumed, and the junction pressure losses at various stacking positions of cells were calculated under various flow rate conditions ranging from the minimum possible flow rate (80% utilization of fuel gas) to the maximum possible flow rate (10% utilization of oxidant gas). The results were arranged according to the equations for loss coefficients, and were compared with the experimental results of previous studies.

Thermal Power Generation

Thermal power plants will be a promising power source even in the 2050s, because they can generate a vast amount of electricity with low cost, high reliability, and stability. The plants will also have strong flexibility and controllability to compensate the gap between power demand and supply with coexistence of a certain amount of unstable renewable power sources. Coal, oil, and liquefied natural gas (LNG) are mainly used for thermal power generation in the electricity business and are evenly mixed because of energy security, the so-called best mix. After the Great East Japan Earthquake, thermal power generation of all electric companies drastically increased by 164 TWh (+33.9 %), to compensate their nuclear power generation.

Exergy Recuperation of Mid and Low Quality Heat by Chemical Reactions

Conventional thermal power generation, as typified by gas turbines, has steadily increased power generation efficiency by elevating temperature of heat, but there is a limit to the maximum availability of electric energy. Exergy rate is a unified index indicating the quality of energy in deferent forms. We have no way in thermal conversion to extract all of the availability, while almost hydrocarbon fuels have exergy rate around 95%. 25% of exergy is inevitably lost through the combustion process from chemical to heat at maximum temperature of 2000°C. Hydrogen’s low exergy rate provides “exergy recuperation” in which degrading 12% from 95% to 83% can take low quality heat up to availability of 83% as a kind of chemical heat pump. Chemically Recuperated Gas Turbine (CRGT) is a specific example, and dimethyl ether (DME) is one of the most suitable fuels because steam reforming occurs around 300°C. Electrochemical partial oxidation (EPOx) is another way to convert mid-quality heat into electric energy as much as difference between change in Gibbs free energy and change in enthalpy. This paper reports concept and industrially-feasible applications of this unconventional and non-cascadic use of heat.Copyright

溶融炭酸塩型燃料電池用ガスシール構造に関する研究 : 第2報,ガスシール構造の実験的検討(熱工学,内燃機関,動力など)

A reactant gas seal is one of critical issues to achieve the reliability of the MCFC stack which is a key equipment in MCFC power plant. The wet-gas seal with carbonate melted at operating temperature (650°C) is generally expected to be suitable for such a seal. We develop the wet seal configuration composed of thin sheet metal parts to be cost-competitive with other power plants. In this report, the proposed configuration of wet-gas seal using thin sheet metal parts is produced for trial, which is assembled in single cells. The leak rates from wet seals were examined under the condition of MCFC operating temperature. Then, the superior seal performance was found and it is confirmed that the wet seal configuration composed of thin sheet is reliable.

溶融炭酸塩型燃料電池用ガスシール構造に関する研究〔熱工学, 内燃機関, 動力など〕

Molten carbonate fuel cells (MCFCs) are expected to be large-scale, highly efficient energy sources in the future. A reactant gas seal is one of the critical issues in achievement of reliability of the MCFC stack, which is a key piece of equipment in an MCFC power plant. At present, the wet gas seal with carbonate molten at the operating temperature (650°C) is generally considered to be suitable as such a seal. On the other hand, to be cost-competitive with existing power plants, the MCFC stack must consist almost entirely of thin sheet metal parts. In this report, a wet gas seal configuration composed of thin sheet metal parts is proposed. Then, the long-term performance of the wet gas seal in an actual MCFC is evaluated.