Demonstration Of 5mw Pafc Power Plant

Yutaka Usaml

Phosphoric Acid Fuel Cell Technology Research Association (PAFC-TRA) 3-3-3. Tenjinbashi, Kita-ku, Osaka 530. Japan

Toshio Takae 1

New Energy and Industrial Technology Development Organization (NEDO) 3— 1— 1. Higashiikebukuro, Toshima-ku, Tokyo 170, Japan

Introduction

Phosphoric Acid Fuel Cell Technology Research Association, established in May 1991 by Japanese 10 electric power and 4 gas companies, started a new project in 1991 FY, with the object of PAFC realization and aiming the development of 5MW—class PAFC power plant for urban energy center and 1MW—class power plant for onsite use. This project is carried out as 6 years plan jointly with New Energy and Industrial Technology Development Organization. The targets of the project are to evaluate and resolve the development task, such as a high reliability, compactness and cost reduction throughout the engineering, manufacturing and field testing of PAFC power plants.

PAC tests and power generating test operations of 5MW plant were completed in 1994. Conducting the 2 years continuous operations and studies since 1995, the plant operational performance, system control characteristics, waste heat recovery and environmental advantage will be demonstrated.

Development of RMW Plant

Engineering of 5MW plant, manufacturing and installing of the major components except the cell stack assemblies and inverter were completed in 1991 and 1992, respectively. Inverter was produced and set up in 1993, cell stack assemblies were also made in 1993 and introduced in January 1995, after the PAC tests completion. In PAC tests, carried out since August 1994, temperature, pressure, flow rate and compositions at each location were tuned with the components in operation.

The initial power generation was performed in February 1995, 5MW plant passed the Japanese MITI inspection at rated load in March 1995 after the control system adjustment tests. Demonstrational operations and studies have been continueing from April 1995.

Concept and Structure of 5MW Plant

Considering a dispersed power source placed in an urban energy center, 5MW plant was developed based on the following concept:

• Dispersed power source settled in urban areas

• High efficiency power plant

• An advantage in environment

• Effective use of waste heat

Major structual features of 5MW plant were listed next:

• Adopted large capacity, area and high current density cell stacks

• A large axi—symmetric mono tube type reformer was chosen

• Air compressor and gas turbine were separatedly used

Process flow diagram of 5MW plant was shown in Fig. 1. Plant specifications were listed in the previous abstract Regarding an urban area application, most part of components were

assembled within doors, which had three hierarchical structure. Foot prints were reduced by means of adopting plate-fin type heat exchanger, etc. Exhaust chimney, cooling tower, water treatment system and nitrogen supply system were installed outside for their useful management.

Pressurized high performance cell stacks were taken up to achieve a high generating efficiency, also a short stack testing was carried out to prove the characteristics and reliability of the cell prior to a practical use. Aiming the growth of methane conversion rate and thermal efficiency in fuel processing system, the mono tube type reformer was selected. Three dimensional impellers were introduced to the separated air compressor and gas turbine to accomplish a more higher efficiency, on the other hand, direct steam injection to the gas turbine was planned to increase the generating efficiency.

The separated air compressor and gas turbine afford an advance in plant controllability and the limitation of direct fuel combustion only to a spent fuel, so as to the lower NOx emission simillar to the level at the convensional «¡generation system de— NOx outlet was performed. In the waste heat recovery system, surplus steam (174°C) and hot water (48—9 2°C) were recovered in each stage to adequately respond to the cooling, heating and hot water demands.

Demonstration of 5MW Plant

Cumulative generating hours and generated electric energy from the initial power generation to August 1996 are 3061 hours and 6899MWh, respectively. Cell voltage was unexpectedly decreased in some parts of cell stack assemblies, the reformer tube pressure drop was (»incidentally increased, so that the disassembled inspection of cell stack assemblies and reformer was carried out from June 1995. Three damaged cell stacks were

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