First demonstration program of solid oxide fuel cells in Japan at Aichi EXPO 2005

Transcription

1 23 rd World Gas Conference, Amsterdam 2006 First demonstration program of solid oxide fuel cells in Japan at Aichi EXPO 2005 Y. Mizutani K. Hisada M. Yasuhara K. Ukai and M. Yokoyama Fundamental Research Dept., Toho Gas Co., Ltd. JAPAN

2 ABSTRACT The 2005 World Exposition Aichi, Japan (EXPO 2005) was held from March 25 to September 25, 2005, in Aichi, Japan. Its main theme was Nature s Wisdom. Environmental issues were given high priority, and many environmental technologies were demonstrated at this Expo. NEDO (the New Energy Development Organization of Japan) promoted and demonstrated advanced new-energy applications such as SOFC, MCFC, PAFC, solar cells, NaS batteries, as well as others. Chubu Electric Power Co., Inc., demonstrated a 30kW SOFC CHP system co-developed with Mitsubishi Heavy Industries, and the Japan Gas Association (JGA) pavilion showcased a 1kW PEFC CHP system for residential use and a proof-of-concept 1kW SOFC CHP system. This paper describes the demonstration of a proof-of-concept solid oxide fuel cell (SOFC) system, a small-scale unit that combines heat and power (CHP) generation. This was the first SOFC system seen by the public in Japan. The SOFC CHP system was developed by Toho Gas, and was installed at the JGA pavilion. The system was successfully operated for 4,459 hours, from May to September Exhaust heat was recovered with oil serving as the heat transfer medium, and that heat was utilized for a desiccant type dehumidifying air conditioning system, cooling the JGA pavilion. This paper introduces Toho s state-of-the-art SOFC technologies based on its material, cell, and stack technologies. To reduce the operating temperature of the SOFC, scandia-stabilized zirconia (ScSZ) was employed as the electrolyte. A compact catalytic partial oxidation (CPOx) reformer was employed to reduce costs. As a result, an innovative compact stack was developed for the 1kW SOFC system. These results of our developments and the demonstration at EXPO 2005 serve as the basis for the discussion of important issues in the realization of high efficiency, cost-effective SOFC systems and future perspectives on SOFC systems.

3 TABLE OF CONTENTS 1. Abstract 2. Body of the Paper 1. INTRODUCTION 2. EXPO 2005 AND THE FUEL CELL DEMONSTRATION 2.1 The Aichi 2005 World Exposition in Japan 2.2 New Energy and Fuel Cells Demonstrated at EXPO TOHO S SOFC R&D AND PROOF-OF-CONCEPT 1kW SYSTEM 3.1 Toho s Solid Oxide Fuel Cell R&D 3.2 1kW SOFC CHP system 4. FUTURE PERSPECTIVES 3. References 4. List of Tables 5. List of Figures

4 1. INTRODUCTION Discussions of environmental problems have focused on the issue of global warming that may result from the heavy consumption of fossil fuels. The Kyoto protocol of the United Nations Framework Convention on Climate Change was put into effect on Feb. 16 th, 2005 in Japan. The objective of the protocol is to reduce carbon dioxide emissions by 6%, by 2010, as compared to a base emission level from However, in order to achieve that objective, Japan would have to reduce its carbon dioxide emissions about 12-14% by 2010, because its emissions have already increased by +6% to +8% over the 1990 level, as shown in Fig.1[1]. Therefore, multilateral effective solutions and management are strongly needed. The Japanese government adopted an action plan at a cabinet meeting in April 2005, with the goal of reducing energy-production-originated carbon dioxide by 4.8% or 1,056 million tons. Therefore, the government has instituted drives and promotions of renewable energy and energy saving technologies, such as solar cells, wind farms, biomass energy, fuel cells, etc. (see Table 1). Distributed power systems, with combined heat and power (CHP), are one of candidates for energy saving solutions, and fuel cells are recognized as a promising technology for solving global environmental problems. Fig. 1 Increasing CO 2 emissions and the Japanese government's plan for accomplishing the goals of the Kyoto protocol Table 1 Anticipated volume of new energy sources in Japan (converted into oil, in units of 10 million liters) FY 2002 FY2010 Target Solar Cells Power Generation (637MW) (4,820MW) Wind Farms 18.9 (463MW) 134 (3,000MW) Waste + Biomass (1,618MW) 586 (4,500MW) Solar heat Heating Waste heat Biomass heat Unused energy Pulp waste Total (% of primary energy) 923 (1.6%) 1,910 (3%) Utilization Clean Vehicles million Co-generation(CHP) - 4,640 MW Fuel Cells - 2,200MW

5 During this period the Aichi 2005 World Exposition in Japan (EXPO 2005) was held, with Japan's message being Nature's Wisdom. Many advanced technologies for environmental solutions were demonstrated, including fuel cell systems. Of note were three demonstration programs about Solid Oxide Fuel Cells (SOFCs), introduced at EXPO the first chance for people in Japan to see SOFC systems. This paper outlines Toho s SOFC R&D program, its state-of-the-art 1kW SOFC CHP system, and the experience of witnessing a field demonstration at EXPO 2005, at the Japan Gas Association s (JGA s) pavilion. 2. EXPO 2005 AND THE FUEL CELL DEMONSTRATION 2.1 The Aichi 2005 World Exposition in Japan EXPO 2005 was held in Aichi, Japan from the 25 th of March through the 25 th of September 2005 (185 days). There were 125 officially participating countries and over one hundred thousand volunteers. More than 22 million people visited from all over the world during this period. The Japan Gas Association (JGA) pavilion showed a live entertainment program based on the theme Flame [2], and had 2 million visitors. Fig. 2 Site Map of EXPO 2005 and the JGA Pavilion To achieve sustainable development, Nature's Wisdom was offered as the main message, and environmental issues were a high priority at EXPO These themes ran throughout the site planning, construction, during the EXPO itself, and even after its conclusion. Many environmental issues were explained to citizens of the world, including the assessment of environmental impact and site planning, the introduction of advanced technologies promoting the eco-community, the introduction of the 3Rs (Reduce, Reuse, Recycle), promotion of transportation that has minimal environmental impact, and environmental education programs. 2.2 New Energy and Fuel Cells Demonstrated at EXPO 2005 At EXPO 2005, many new technologies were presented and some were demonstrated. IT (Information technologies) were used for the systems serving core functions at the exposition (reservations, visitor support and navigation, and visitor information). Next-generation vehicles (a Maglev linear-motor railway system, fuel cell vehicles, etc.) were in use or on display. State-of-the-art image technology, technologies for life styles of the future (biomass use, new energy systems, IC chips, etc.) were also on display [2].

6 Environmental technologies were exhibited, such as biomass energy use (methane fermentation, waste conversion to gas), solar power systems, gas co-generation (CHP), photo catalytic materials, bio-degradable plastic, water recycling, etc. Fuel cells were a center of interest among new energy systems. Fuel cell hybrid buses (FCHV) provided daily transportation between two EXPO areas. Toho Gas provided the hydrogen refueling station and the hydrogen fuel supply as part of its participation in the JHFC (Japan Hydrogen & Fuel Cell Demonstration Project) program. NEDO (New Energy Development Organization, Japan) promoted the advanced new-energy demonstration. SOFC, MCFC, PAFC, Solar cells, NaS batteries, etc. were simultaneously synchronized to meet real-time energy demands[3]. Chubu Electric Power Co., Inc. demonstrated a 30kW model SOFC co-generation system that was co-developed with Mitsubishi Heavy Industries. The Japan Gas Association demonstrated a 1kW PEFC CHP system for residential use and a proof-of-concept 1kW SOFC CHP system developed by Toho Gas, both shown at the JGA pavilion. Fig.3 Fuel cell hybrid bus and hydrogen refueling station Fig. 4 Advanced new-energy power generation plant supported by NEDO

7 3. TOHO S SOFC R&D AND PROOF-OF-CONCEPT 1kW SYSTEM 3.1 Toho s Solid Oxide Fuel Cell R&D Fuel cells are recognized as an important technology for environmental solutions because of their superior characteristics. Solid oxide fuel cells (SOFCs) have the highest electricity efficiency of all fuel cells and have many desirable features. Among these is that their solid electrolyte lasts a long time and supports design flexibility. The oxide ion-conductive electrolyte will work with a wide choice of potential fuels, its high temperature operation supports internal reforming, and expensive platinum-based catalysts are not needed. The electrolyte is a key material in SOFCs, and the ohmic resistance of the electrolyte is the most significant portion of the internal resistance in the cells. Therefore, a highly conductive electrolyte can improve performance and reduce the operating temperature in SOFCs. Toho gas has developed scandia-stabilized zirconia (ScSZ), which has a higher ionic conductivity than yttria-stabilized zirconia (YSZ), and is one of the candidates for use in making high-performance SOFCs [4]. The electrochemical performance of planar type single cells with a ScSZ electrolyte has already been demonstrated, and an extremely high power density of 2 W/cm2 has been achieved [5]. In addition, Sc-TZP (Scandia doped tetragonal zirconia polycrystal) electrolytes have been developed that have high mechanical strength and great resistance to fractures. Toho Gas s electrolyte technologies have been transferred to DKKK (Daiichi Kigenso Kagaku Kogyo, the largest zirconia supplier in Japan). ScSZ and Sc-TZP materials are now available for mass production. Many SOFC developers are interested in these electrolytes. To achieve high performance SOFCs at low cost, a planar configuration and electrolyte supported cells were developed, using Toho s electrolyte and electrodes. The state-of-the-art cell, a highly reliable, high performance flexible cell based on Toho s technology, was developed for use by SOFC developers worldwide. Mass production of these cells is now progressing, in cooperation with Nippon-Shokubai Co., Ltd. Fig.5 Materials for SOFC and developed cells 3.2 1kW SOFC CHP system Cost-effective and reliable SOFC systems were developed for demonstrations at EXPO In this system, a planar SOFC stack was created that has multiple ScSZ disk cells with a radial gas co-flow design. The cells are interconnected with low-cost, thin, ferritic bi-polar stainless steel plates that have coaxial gas (air/fuel) manifolds. In the 1kW SOFC system, an innovative compact stack with a volumetric power density of 0.5kW/Liters was developed [6]. A simplified SOFC system was designed with a compact CPOx reformer, used for reforming natural gas fuel. In the polymer electrolyte fuel cell

8 (PEFC) systems, complex multi-stage reforming systems are required because of the limitations of proton conductive electrolytes and platinum-based electrodes, and these elements are responsible for much of the large cost of a BOP system. On the other hand, many types of reforming options, i.e., steam reforming, partial oxidation reforming, auto-thermal reforming, and dry (CO 2 ) reforming can be used in SOFC systems, because carbon monoxide can be used as a fuel for SOFCs. The 1kW class SOFC CHP systems were developed in FY 2004 and installed on the 21 st of December, 2004 outside the JGA pavilion (see Table 2). Many safety controls and a remote supervisory telemetry and control system were employed. The SOFC system was monitored all the time it was operating. Exhaust heat was utilized for a desiccant type dehumidification air conditioning system. System operation commenced in March 2005, corresponding to the start of EXPO A carefully designed internal manifold 80-cell stack produced an output of 955W using city gas (mainly natural gas) fuel and thermal self-sustaining conditions. Maximum electrical efficiency and thermal efficiency were both 35% (LHV). The system was successfully operated for 4,459 hours (96.4% up-time) from the 16 th of May to the 25 th of September, Fig.6 1kW SOFCCHP system demonstrated at EXPO 2005 Table 2 Specifications of the SOFC system demonstrated at EXPO Item Specifications Comments Output 1kW DC Not grid connected SOFC Operating 1053K (average) Designed using the heat resistance of the Temperature metal interconnection plate Fuel City Gas 13A 4L/min Connected to a city gas pipeline (13A natural gas-based fuel) Reformer Catalytic partial oxidation Air/Gas = 0.35 of stoichiometric combustion Air 160L/min Supplied by air blower SOFC stack 80 cells: 12cm diameter ScSZ per cell With ferritic stainless steel interconnection plates Pre-heater Electric heater 3kW Used for startup (Startup time is less than 4hrs.) Dimensions 700W*530D*1230H Not including controlling & heat recovery units Heat recovery system Heat recovery temp. is Recovery heat was transferred by oil 200

9 Fig.7 Typical changes in operating parameters over time 4. FUTURE PERSPECTIVES SOFCs have a number of beneficial characteristics such as high electrical efficiency, low pollutant emissions, quiet operation, and a wide choice of potential fuels. SOFC CHP systems are more efficient than the conventional combination of a central power station and distributed heating systems. Domestic and commercial customers constitute the future potential markets for SOFC CHP systems. SOFCs are particularly suitable for small-scale applications, because of their lower material costs and simplified fuel processing. Residential CHP is already commercialized in the form of a 1kW gas engine generator, and PEFC CHP systems that have an electrical efficiency of 35% have just been introduced for commercialization. Daily start-up (heating) and stop (cooling) cycle operations are required for residential use, and that is a weakness of the SOFC system because of the high temperature needed during that operation. Therefore, the first market for SOFC may be in commercial use, such as for restaurants, hospitals, and hotels. Toho gas is planning to develop a 5-10kW SOFC CHP system for the commercial market, applying the technology developed for the 1kW SOFC system shown at EXPO Many innovative SOFC systems are also being developed in Japan under government supported programs and private programs. Cogeneration systems from 10kW to several hundred kilowatts are planned to begin operation during FY Also, Osaka Gas started a field test of Kyocera s 1kW SOFC CHP for residential use in FY To promote infrastructure improvement, a de-regulation program was launched in 2005 for SOFCs by the Japan Gas Association and the Japan Electrical Manufactures Association. This is a government (NEDO) supported effort. 1. Koizawa, K., (2006). Proceedings of the Fine Ceramics Symposium 2006, Japan Fine Ceramics Center:

10 Mizutani, Y., Tamura, M., Kawai, M., and Yamamoto, O., (1994). Development of high-performance electrolytes in SOFC, Solid State Ionics, 72, p Mizutani, Y., Kawai, M., Nomura, K., Nakamura, Y., and Yamamoto, O., (1997). Performance of Sc2O3-ZrO2 electrolytes in planar solid oxide fuel cell, Solid Oxide Fuel Cells V, U. Stimming, S. C. Singhal, H. Tagawa, and W. Lehnert, eds., Electrochemical Society PV97-40, Pennington, USA, p Mizutani, Y, Hisada, K, Ukai, K, Yokoyama, M, Sumi, H, (2005). Experiences with the first Japanese-made SOFC system, Journal of Fuel Cell Science and Technology, ASME, Vols 2-3, p