Phosphoric acid fuel cell power plants

J. M. King, N. Ishikawa, "Phosphoric Acid Fuel Cell Power Plant Improvements and Commercial Fleet Experience," Nov. 96 Fuel Cell Seminar. www.intemationalfuelcells.com. 

Tokyo Electric Power Company, Inc. (Principal Investigator K. Shibata), Demonstration Testing of 11 MW Phosphoric Acid Fuel Cell Power Plant—from Planning to Power Generation. Interim Report for Electric Power Research Institute, Palo Alto, 1992. 

Toward the end of the 1990s, interest in power plants based on phosphoric acid fuel cell power plants gradually waned, despite the success that had been achieved the relatively large number of intermediate-power PC-25 plants were built and the installation of several megawatt-sized power plants took place in a number of places. 

PAFCs are the first fuel cells to be commercially available. The major manufacturers of these fuel cells are UTC Power, Toshiba Corporation, HydroGen Corporation, Fuji Electric Corporation and Mitsubishi Electric Corporation. UTC Power introduced for sale a 200 kW PAFC system in 1991, and over 260 units were delivered to various customers worldwide. The design operational lifetime for these units was 40,000 h and most of the fielded units have met or exceeded this requirement A number of these units are still operational today with fleet leader at Mohegun Sun in Uncasville, Connecticut, USA, accumulating more than 76,(X)0 h [48]. Fuji s phosphoric acid fuel cell power plants, launched in 1998 have also demonstrated 40,000 h of life in field and some units after overhaul have exceeded 77,000 h of operational lifetime [1]. 

Fhosphoric acid does not have all the properties of an ideal fuel cell electrolyte. Because it is chemically stable, relatively nonvolatile at temperatures above 200 C, and rejects carbon dioxide, it is useful in electric utility fuel cell power plants that use fuel cell waste heat to raise steam for reforming natural gas and liquid fuels. Although phosphoric acid is the only common acid combining the above properties, it does exhibit a deleterious effect on air electrode kinetics when compared with other electrolytes ( ) including such materials as sulfuric and perchloric acids, whose chemical instability at T > 120 C render them unsuitable for utility fuel cell use. In the second part of this paper, we will review progress towards the development of new acid electrolytes for fuel cells. 

Medium-temperature phosphoric acid fuel cells (PAFCs). The electrolyte is 85 to 95% phosphoric acid the working temperatures are 180 to 200°C. Such systems were used to build numerous autonomous power plants with an output of up to about 250 kW, and even some with an output of up to 4 MW, in the United States, Japan, and other countries. 

Progress continues in fuel cell technology since the previous edition of the Fuel Cell Handbook was published in November 1998. Uppermost, polymer electrolyte fuel cells, molten carbonate fuel cells, and solid oxide fuel cells have been demonstrated at commercial size in power plants. The previously demonstrated phosphoric acid fuel cells have entered the marketplace with more than 220 power plants delivered. Highlighting this commercial entry, the phosphoric acid power plant fleet has demonstrated 95+% availability and several units have passed 40,000 hours of operation. One unit has operated over 49,000 hours. 

Operators of the Tokyo demonstration plant have concluded that phosphoric acid fuel cell technology is ready for commercialization. The project demonstrated that (I) fuel cells can be sited in urban areas which are regulated by strict environmental constraints (2) performance and operational characteristics were very close to design goals and (3) utility personnel can efficiently operate and maintain fuel cell plant equipment with minimal additional training. As a consequence of the demonstration plant success, a new 11 -MW power plant will be developed and marketed. A comparison of the new 1 C 23 Unit with the 4,5 MW demonstration plant is given in Table 4. 

Phosphoric acid fuel cell (PAFC) 200 Phosphoric acid Hydrogen, reformed methane 35-45 1 up to 100 MW power plants, 5-500 kW heating power station... 

The efficiencies of the different energy conversion systems are compared in Fig. 3 as a function of the size of power plants. Figure 3 shows that the efficiencies of two types of fuel cell systems (phosphoric acid fuel cell, PAFC, see Sect. 8.1.3.1.3 andsolid oxide fuel cell, SOFC, see Sect. 8.1.3.2.2) are higher than those of engines and conventional power plants of comparable size. 

Among the dozens of demonstration plants, subsystems, test facilities, and other related hardware constructed or planned in the United States, Europe, and Japan in those years, three examples stand out. The first was the first megawatt-class fuel cell power plant the PC-19 phosphoric acid plant, built by United Technologies in South Windsor, Connecticut and tested during the first half of 1977. 

In February 1977, as PC-19 began churning out electricity, the US Department of Energy, in cooperation with the Electric Power Research Institute, issued a request for proposals to build a big (4.5 megawatts) phosphoric acid demonstrator fuel cell power plant in New York City. Consolidated Edison was picked as the host utility. 

Phosphoric acid fuel cell (PAFC) Phosphoric acid H2 O2 (in air) 200 Stationary power plants, cogeneration plants... 

The first information on medium-temperature phosphoric-acid fuel cells (PAFC) came out in 1961. Highly concentrated phosphoric acid (85-95%) is the electrolyte in these cells. The working temperature in these cells is in the range of 180-200 C. These fuel cells quickly aroused great interest and found wide distribution. On the basis of such cells, numerous power plants of up to 250 kW were built and used as an autonomous power supply for individual operating units such as hotels and hospitals. Also, in the United States, Japan, and other countries, megawatt plants were built... 

The first data about fuel cells based on concentrated phosphoric acid solutions date from the mid-1960s. After three decades, since about 1995, very few papers on phosphoric acid fuel cells have appeared in the scientific literature. Of course, many of the numerous intermediate and large-size power plants that had been built in prior years still function, but work toward their further development and improvement has practically ceased. 

The cell stack assembly is the heart of the power plant which produces both electrical and thermal energy by electrochemically combining H2 in fuel and O2 in air. The basic description of a phosphoric acid fuel cell is shown in Fig. 12.2. 

The first cogeneration power plant on phosphoric acid fuel cell (PAFC)-basis comes into service in Hamburg... 

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