Characteristics of PEFC / Woody Biomass Engine Hybrid Microgrid and Exergy Analysis

Characteristics of PEFC / Woody Biomass Engine Hybrid Microgrid and Exergy Analysis

DOI: 10.4018/978-1-4666-5796-0.ch008
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Abstract

This chapter consists of three sections, ‘Dynamic Characteristics of PEFC / Woody Biomass Engine Hybrid Microgrid’, ‘Exergy Analysis of the Woody Biomass Stirling Engine and PEFC Combined System with Exhaust Heat Reforming’ and ‘Exergy Analysis of A Regional Distributed PEM Fuel Cell System’. The chapter describes the exhaust heat of the combustion of woody biomass engine using a Stirling cycle that was used for the city gas reforming reaction of a PEFC system. The response characteristic of PEFC and woody biomass engine is investigated by the experiment and numerical analysis. Finally, a combined system that uses the exhaust heat of the woody biomass Stirling engine for the steam reforming of city gas and that supplies the produced reformed gas to a PEFC is proposed.
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General Introduction

The summary of the 1st section is as follows. The combustion exhaust heat of woody biomass engine using Stirling cycle is a high temperature. This exhaust heat is used for the city gas reforming reaction of a PEFC system. The woody biomass engine generator has the characteristic that the greenhouse gas amount of emission with power generation is greatly reducible. In this study, the microgrid system that introduces PEFC / woody biomass engine hybrid cogeneration (PWHC) is proposed. It depends on the dynamic characteristics of the grid for the power quality at the time of load fluctuation being added to the microgrid. Especially, the dynamic characteristics of the independent microgrid are important on security of power quality. So, in this study, the response characteristic of PEFC and woody biomass engine was investigated by the experiment and the numerical analysis. Furthermore, the response characteristic of the PWHC independent microgrid including auxiliary machinery was investigated by the numerical simulation. Moreover, an improvement of dynamic characteristics is proposed using the method of adding proportional-plus-integral control to PWHC. If woody biomass engine is introduced into a house, 10.2s will be required to stabilize power quality at the maximum. On the other hand, when woody biomass engine corresponds to a base load and PEFC corresponds to the load exceeding the base load, settling time is less than 1.6 s. In this study, relation between the system configuration of the PWHC microgrid and the dynamic characteristics of the power was clarified.

The summary of the 2nd section is as follows. The woody biomass Stirling engine (WB-SEG) is an external combustion engine that outputs high-temperature exhaust gases. It is necessary to improve the exergy efficiency of WB-SEG from the viewpoint of energy cascade utilization. So, a combined system that uses the exhaust heat of WB-SEG for the steam reforming of city gas and that supplies the produced reformed gas to a PEFC is proposed. The energy flow and the exergy flow were analyzed for each WB-SEG, PEFC, and WB-SEG / PEFC combined system. Exhaust heat recovery to preheat fuel and combustion air was investigated in each system. As a result, (a) improvement of the heat exchange performance of the woody biomass combustion gas and engine is observed, (b) Reduction in difference in the reaction temperature of each unit, and (c) removal of rapid temperature change of reformed gas are required in order to reduce exergy loss of the system. The exergy efficiency of the WB-SEG / PEFC combined system is superior to PEFC.

The summary of the 3rd chapter is as follows. The exergy flow and exergy efficiency of a 3kW PEFC were investigated, and the regional characteristic of the distributed energy system was considered. In the environmental temperature range of 263K to 313K, the difference of the total efficiency of the proposed system was 6%. On the other hand, the difference of the exergy total efficiency of the same temperature range was 30%. Moreover, as a result of examining how to improve the exergy efficiency of this system, certain improvement methods were proposed. (a) Preheat the city-gas and air supplied to the system using exhaust heat, and raise the combustion temperature, (b) Preheat the water supplied to the system using exhaust heat, (c) Change the catalyst material of each unit and reduce the amount of cooling of the reformed gas, (d) Examination of combined cycle power generation. The exergy efficiency, in the case of introducing the proposed system into individual homes in Sapporo, Tokyo, and Kagoshima, was evaluated. Consequently, when the system was introduced into a community with low outside air temperatures, exergy efficiency increased compared with communities with high outside air temperatures.

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