Compound Microgrid of City-Gas Engine and Proton Exchange Membrane Fuel Cell

Compound Microgrid of City-Gas Engine and Proton Exchange Membrane Fuel Cell

DOI: 10.4018/978-1-4666-5796-0.ch006

Abstract

This chapter consists of two sections, ‘Amount of CO2 Discharged from Compound Microgrid of Hydrogenation City-Gas Engine and Proton Exchange Membrane Fuel Cell’ and ‘Power Characteristics of a Fuel Cell Microgrid with Wind Power Generation’. In the 1st section, a microgrid composed from a PEFC and a hydrogenation city gas engine is investigated using numerical simulation. The system which combined base-load operation of PEFC and load fluctuation operation of hydrogenation city gas engine is the most advantageous. The independent PEFC power supply system relating to hydrogen energy is investigated in the 2nd section. The hybrid cogeneration system (HCGS) that uses a PEFC and a hydrogen mixture gas engine (NEG) together to improve power generation efficiency during partial load of fuel cell cogeneration is proposed.
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General Introduction

The summary of the 1st section is as follows. The independent microgrid is considered to be a technology in which maximum distributed energy is realizable. However, there are many subjects, such as the stability of the dynamic characteristics of power and development of an optimal design method. If the fuel cell system of the capacity corresponding to a load peak is installed, equipment cost will be high and energy cost will not be able to get any profile commercially. By increasing the hydrogen concentration at the time of low load, the power-generation efficiency of a city-gas-engine-generator improves, and carbon dioxide emissions decrease. So, in this study, a microgrid composed from a PEFC and a hydrogenation city gas engine was investigated using numerical simulation. The system with a small load factor of NEG and with a large load factor of PEFC system has few CO2 emissions. The system which combined base-load operation of PEFC and load fluctuation operation of hydrogenation city gas engine is the most advantageous for the comprehensive evaluation of equipment cost, power generation efficiency, and CO2 emissions. When the optimal system was installed into the urban area model of 20 buildings and analyzed, power generation efficiency was 25% and CO2 emissions were 1,106 kg/Day.

The summary of the 2nd section is as follows. Development of a small-scale power source not dependent on commercial power may result in various effects. For example, it may eliminate the need for long distance power-transmission lines, and mean that the amount of green energy development is not restricted to the dynamic characteristics of a commercial power grid. Moreover, the distribution of the independent energy source can be optimized with regionality in mind. This study examines the independent power supply system relating to hydrogen energy. Generally speaking, the power demand of a house tends to fluctuate considerably over the course of a day. Therefore, when introducing fuel cell cogeneration into an apartment house, etc., low-efficiency operations in a low-load region occur frequently in accordance with load fluctuation. Consequently, the hybrid cogeneration system (HCGS) that uses a PEFC and a hydrogen mixture gas engine (NEG) together to improve power generation efficiency during partial load of fuel cell cogeneration is proposed. However, since facility costs increase, if the HCGS energy cost is not low compared with the conventional method, it is disadvantageous. Therefore, in this section, HCGS is introduced into 10 household apartments in Tokyo, and the power generation efficiency, carbon dioxide emissions and optimal capacity of a boiler and heat storage tank are investigated through analysis. Moreover, the system characteristics change significantly based on the capacity of PEFC and NEG that compose HCGS. Therefore, in this study, the capacity of PEFC and that of NEG are investigated, as well as the power generation efficiency, carbon dioxide emissions and the optimal capacity of a boiler and heat storage tank. Analysis revealed that the annual average power generation efficiency when the capacity of PEFC and NEG is 5 kW was 27.3%. Meanwhile, the annual average power generation efficiency of HCGS is 1.37 times that of the PEFC independent system, and 1.28 times that of the NEG independent system respectively.

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