It`s time to take fuel cells seriously (Part II)
Industry/DOE demonstration partnerships in higher temperature fuel cells add impetus to the technology`s development
By J. H. Hirschenhofer, Gilbert/Commonwealth
Part I of this article described lessons learned from low-temperature phosphoric acid fuel cell installations. Higher temperature fuel cell development also has gained momentum through the work of important industry and Department of Energy (DOE) demonstration partnerships.
One such technology is the molten carbonate fuel cell (MCFC). Its 1,200 F operating temperature offers several benefits: a major cell component can be stamped out of common sheet metal for low cost fabrication; cell reactions occur with nickel catalysts instead of precious metal catalysts; reforming can take place within the cell if a reforming catalyst is added (produces a gain in efficiency); CO is directly usable in the cell and does not have to be shifted to hydrogen; and rejected cell heat is high enough to drive a gas turbine and/or produce high pressure steam for cogeneration or turbine use.
Already being built at commercial size, MCFC cells also are starting tests in full height stacks. Short stacks with full-size cells and full height stacks with smaller cells have demonstrated lifetimes of 9,000 hours. Projections, based on individual cell component tests, see MCFC stacks achieving a life expectancy of 40,000 hours when operated at atmospheric conditions. This has yet to be demonstrated.
The 40,000-hour goal appears achievable. However, at 10 atmospheric cell pressure, only approximately 5,000 to 10,000 hours may be possible with presently available NiO cathodes. This issue needs to be resolved prior to building large power plants.
Systems concepts are defined and a 100-kW power system was tested on a limited, non-integrated basis. Efforts now focus on developing acceptable commercial systems. Studies indicate that materials used in MCFCs will result in a stack cost of $400/kW, which is on target to yield a total system cost of $1,000/kW. Two companies in the United States–M-C Power Corp. and Energy Research Corp. (ERC)–receive U.S. DOE and private sector funding to develop this technology.
On December 2, 1994, the IMHEX® team led by M-C Power Corp. dedicated a 250-kW MCFC process development plant at UNOCAL`s Fred L. Hartley Science and Technology Center in California (Figure 1). M-C Power produced the stack and managed the project; Stewart and Stevenson Services Inc. designed and packaged the balance of plant skid; and Bechtel Corp. handled process design, plant engineering and procurement. The Institute of Gas Technology, the major stockholder of M-C Power, developed the cell technology.
After shakedown testing, the plant was scheduled to begin 7,000 hours of planned operation in April 1995. Each stack contains 250 cells with an active area of 1 square meter yielding 1 kW per cell. The plant operates at three atmospheres of pressure. One program goal is to successfully demonstrate low-cost, stamped, sheet metal fuel cell components. M-C Power can produce 10 MW of cell stacks each year.
UNOCAL`s plant is not fully integrated and uses an existing, non-optimized fuel processor that will be replaced after the first demonstration. The plant, which is slightly more than 30 percent efficient lower heating valve (LHV) uses external fuel reforming.
A second 250-kW plant will have fully integrated components. It is due for construction at the U.S. Naval Air Station at Miramar, Calif., and efficiency is expected to improve to approximately 45 percent (LHV). San Diego Gas and Electric Co. plans to begin operation in 1995.
Both 250-kW plants are intended to demonstrate MCFC technology prior to design and operation of a 1-MW commercial plant that M-C Power and Southern California Edison plan to operate by 1998. DOE supports the project (Figure 2).
Groundbreaking took place in April 1994 at a City of Santa Clara (Calif.) Municipal Electric site for an ERC 1.8-MW net (2-MW gross) MCFC utility demonstration (Figure 3). This plant will demonstrate the high-efficiency internal fuel reforming concept, referred to as the direct fuel cell. It is expected to achieve 50 percent efficiency (LHV) and is scheduled to operate for 10,000 hours starting in the third quarter of 1995. The $46 million program is funded by host City of Santa Clara Municipal, five California utilities, DOE, Electric Power Research Institute (EPRI) and the National Rural Electric Cooperative. The balance of plant, designed by Fluor Daniel, was completed in January 1995. Fuel cell modules will be delivered starting in mid-1995. The 16 125-kW internal reforming stacks contain 258 cells. Each cell has an active area of 5,600 square centimeters (6 square feet).
Two ERC subsidiaries are involved–Fuel Cell Engineering Corp. handles power plant design, sales and services, and Fuel Cell Manufacturing Corp. produces the stacks. Potential production capacity is 10 MW/year. Also, ERC and Fluor Daniel`s Power Group recently announced joint marketing activities. Plans are to follow the Santa Clara demonstration with production of plants totaling 100 MW and commercialization by 1998-1999. A group of 37 utility and industrial fuel cell users have indicated their commitment as potential customers.
These fuel cells could some day be used to produce power in large-scale plants fueled by natural gas or coal. In 1994, ERC participated in an EPRI- and DOE-supported demonstration. A 20-kW stack was tested with Destec Energy Systems` coal gasification plant in Plaquemine, La. The stack was integrated with a gas cleanup and thermal management module fabricated by Haldor Topsoe of Houston, Texas.
The system was fed a slipstream of the 245 Btu/cubic foot coal gas from Destec`s two-stage entrained bed gasifier. The plant operated for 4,000 hours with 1,700 hours in the power mode. Post-test analysis continued at this writing. The stack hardware showed clean metal with no adverse effects and corrosion was within goal. The fuel cell stack and balance of plant was designed to operate on other gases such as landfill, digester or biogas.
IFC, the major phosphoric acid fuel cell (PAFC) developer, does not receive government support for MCFC activities. However, the company apparently is continuing previous government supported development of MCFC with Toshiba and Ansaldo under private funding.
Solid oxide fuel cell
Because the electrolyte is a solid, the solid oxide fuel cell (SOFC) can be cast into flexible shapes, such as tubular, planar or monolithic. The cell`s solid construction alleviates corrosion problems common to liquid electrolyte cells and is impervious to gas cross-over between electrodes. The absence of liquid also eliminates electrolyte movement or flooding in the electrodes. Cell kinetics are fast and CO is a directly usable fuel. At the temperature of presently operating SOFCs (1,832 F), natural gas can be used directly with no reforming catalysts.
One type of SOFC, the tubular configuration produced by Westinghouse Corp.`s Science and Technology Center in Churchill, Pa., has been in continuous development in the United States longer than PAFCs, proton exchange membrane or MCFCs. System concepts for this cell are more integrated and less complex than other cells. Several 25-kW units are being tested. However, there are questions whether the present tubular design can be cost competitive. Reaching cost goals represent a major challenge. Westinghouse is pursuing scaling of the tubular cell to longer lengths and development of alternative SOFC concepts.
Westinghouse produced two 25-kW SOFC plants that were installed at utilities in Japan in 1992. One plant set a record SOFC operating time of 7,064 hours. The manufacturer quickly found that a laboratory environment doesn`t exist on plant sites here and faced unanticipated glitches in small items from fan belts to transportation packaging.
Westinghouse found that customers with problems need timely technical support and remote monitoring to maintain a degree of knowledge, comfort and control over unit operation. Further, the company found that, although the seismic sensors on the shipping containers tripped during transportation, the units survived intact.
Two other demonstrations now are underway. The first, a nominal 20-kW, was shipped to Southern California Edison`s Highgrove substation (Figure 4). Operation had exceeded 5,300 hours as of March 1995. The SOFC bundle is equivalent to a fuel cell stack. The second plant will have a nominal capacity of 100 kW (maximum 150 kW). It will be supplied to a group of Dutch and Danish utilities and located in the Netherlands. Operation is scheduled in approximately two years. Both plants are considered precursors of larger units.
At least four other U.S. companies are developing alternative SOFC flat component cell configurations. They are Allied Signal, Ceramatec, ZTEK and Technology Management Inc. Most of these SOFCs are in early stages of development.
The high temperature of the SOFC has its drawbacks. There are thermal expansion mismatches among materials, and sealing between cells is difficult in the flat configurations. High temperatures needed to fabricate components alters material properties, placing severe constraints on materials selection and fabrication processes. These issues led researchers to consider cells at a reduced temperature of 1,200 F, but the electrical resistivity increases in current solid electrolyte material. Research continues on alternate materials.
Overall, fuel cells have attained different degrees of advancement toward commercial use. Technical concepts common to all have been proved by individual cell and stack tests. No technical or economic showstoppers have emerged that would prohibit the use of various cells in early power plants fueled by natural gas. Depending on the cell type, it is now a matter of refining the cell materials and design configurations, scaling the cells to full area and stacks to full height, integrating the fuel cell stack with its system, and improving developed power plants to meet the commercial goals of life, reliability and cost. An important fact is that users are installing units in a real-world environment. These installations are providing the fuel cell manufacturer with valuable data on what is important to the user and how to interact. Users are finding that fuel cells are a viable technology worthy of consideration and that field type products are becoming available. END
Fuel Cell Program and Abstracts, 1994 Fuel Cell Seminar, San Diego, Calif., Courtesy Associates, Washington, D.C., November 1994.
Proceedings of the Fuel Cells `94 Contractors Review Meeting, U.S. DOE Morgantown Energy Technology Center, Morgantown, W.Va., August 1994.
An EPRI/GRI Fuel Cell Workshop on Technology Research and Development, Cosponsored by the Electric Power Research Institute (EPRI) and the Gas Research Institute, Proceedings by EPRI, Palo Alto, Calif., March 1994.
McClelland, Dick, “First Commercial Fuel Cell Fleet: Experience, Lessons Learned and Future Perspective,” 1994 Fuel Cell Seminar, San Diego, Calif., November 29, 1994.
Proceedings, Intersociety Energy Conversion Engineering Conference, Vols. 2 & 3, American Institute of Aeronautics and Astronautics, Washington, D.C., August 1994.
Hirschenhofer, J.H., “International Data Book of Fuel Cell Activities 1993,” prepared by Gilbert/Commonwealth Inc. for U.S. DOE/FE, 1994.
Hirschenhofer, J.H., Stauffer, D.B., and Engleman, R.R., Fuel Cells, A Hand-book, Rev. 3, prepared by Gilbert/Commonwealth Inc., for DOE under Contract DE-AC01 88FE61684, January 1994.
John Hirschenhofer serves as manager of various fuel cell and coal technology projects at Gilbert/Commonwealth, a subsidiary of The Parsons Corp. The company currently is technical support contractor to the Department of Energy in fuel cell technology. Hirschenhofer is the American Society of Mechanical Engineer`s (ASME) vice chairman of the Advanced Energy Systems Division and was past chairman of ASME`s Fuel Cells Power Systems technical committee. Hirschenhofer holds a bachelor`s of science in mechanical engineering from Mississippi State University and a master`s of science in mechanical engineering from the University of Connecticut.
Figure 1. Full-scale 250-kW MCFC fuel cell stack. Photo courtesy of M-C Power.
2-MW Energy Research Corp.
Molten Carbonate Unit
in Santa Clara, Calif.
Westinghouse SOFC 25-kW Generator
Most asked questions about fuel cells
Many of these questions relate to material presented in Part I of this report in the June 1995 issue of Power Engineering on page 30.
Q. How much space do fuel cell plants require?
A. The footprint of the PC-25C PAFC 200-kW unit is 200 ft2. A 2.85-MW MCFC plant is expected to require 4,500 ft2.
Q. What are typical startup times?
A. The startup times are approximately two hours from cold and one hour from hot standby for the PC-25.
Q. What are the life issues?
A. The major life issues for fuel cell power plants are stack and fuel processor replacement. These components need to be overhauled every 5 to 10 years. Several days of shutdown are required to replace these components.
Q. What other maintenance is required and what does that mean in terms of downtime?
A. PAFCs require that water treatment beds and filters be replaced every three to six months. No shutdown is required. An annual, two-day shutdown is required for inspection of relief valves, vessels and pressure piping.
Q. Are there any unusual dangers or surprises?
A. A hydrogen-rich fuel is produced for the cells. But the fuel contains carbon dioxide, carbon monoxide, water and some residual methane. The danger from the fuel should be no different than any typical fuel and precautions are similar.