14. Solid Oxide Fuel Cell (SOFC) AND MATERIAL RESEARCH
The goal of the DOE-sponsored Solid State Energy Conversion Alliance (SECA) is to develop commercially-viable ($400/kW) 3 to 10 kW Solid Oxide Fuel Cell (SOFC) systems by year 2010. SOFC power generation systems are attractive alternatives to current technologies in diverse stationary, mobile, and military applications. SOFC systems are very efficient, from 40 to 60 percent in small systems and up to 85 percent in larger co-generation applications. The electrochemical conversion in a SOFC takes place at a lower temperature (650 to 850ºC) than combustion-based technologies, resulting in decreased emissions – particularly nitrogen oxides, sulfur oxides, and particulate matter. These systems all offer fuel flexibility as they are compatible with conventional fuels such as hydrogen, coal, natural gas, gasoline, or diesel. Despite these advantages, advances in balance of plant (BOP) component design must be developed before the SECA program goal can be realized. This topic seeks to develop these key support technologies for SOFC systems. Grant applications are sought only in the following subtopics:
a. High-Temperature Anode Gas Recycle Blowers—SOFC systems that incorporate some recycling of the anode exhaust gas, which is mixed with incoming fresh fuel prior to entering the pre-reformer, have a higher efficiency and offer the potential for lower overall system cost. Grant applications are sought for the design and development of motor-driven blowers for the recycle of SOFC anode exhaust gas, with cost, manufacturability, and reliability being critical factors for meeting the SECA Program goal. The blower inlet gas temperature may vary from 600 to 850ºC and the inlet pressure is atmospheric. The pressure rise requirements is 4 to10 inches of H2O and the flow requirement is 100 standard liters per minute (slpm), which is nominally composed of 46 slpm H2O, 27 slpm CO2, 20 slpm H2,and 7 slpm CO. Overall efficiency should meet or exceed 40% under the aforementioned operating conditions. The unit should be capable of variable speed control with a flow turn-down ratio of 5 to 2. The blower unit must have a design life of 40,000 hours, with a 100% duty cycle and 10,000 hour maintenance interval. The unit must be able to tolerate at least 30 thermal cycles, between operating and room temperatures, over its design life. The unit cost, based upon a production volume of 50,000 units per year, should be estimated and is considered a higher priority than efficiency.
b. Low-Cost High-Temperature Heat Exchangers for SOFC Systems—The high-temperature heat exchangers used in SOFC are attracting increasing attention because of their adverse impact on overall SOFC system cost. The operating temperatures of these heat exchangers depend upon the fuel cell application, and range from 25 to 800oC on the sink side and from 300 to 1000oC on the source side, which is usually the fuel cell stack effluent. Grant applications are sought to develop novel, low-cost, high-temperature heat exchanger designs that address the cost issues and technical performance requirements for two distinct applications of SOFC systems: (1) where the sink side is an air preheater; and (2) where the sink side is a natural gas fuel preheater.
Where the sink side is an air preheater, the heat exchanger requires a very low differential pressure drop (<4-10 inches of water column on the air side; 3-5 inches on stack side), high effectiveness (approaching 90%), and long life (10,000 hour maintenance interval/40,000 hour lifetime). Although material sets such as high nickel alloys (i.e., 600 series Inconels) are currently being used, they are very expensive and prone to long term high temperature creep and sulfidation attack.
In the application where the natural gas fuel preheater is on the sink side, the concern is that the fuel stream contains up to 50 ppm of sulfur and small amounts of SO2 in the stack effluent. Currently, shell and tube or plate fin exchangers are being used for this application. However, ceramic materials would be considered a candidate, provided that the thermal shock/ramp rate can be adequately addressed.
c. 1 to 5 kW Diesel Reformer—SOFC systems should have a strong early market in Class 8 diesel trucks in the form of auxiliary power units (APUs), which allow for on-board power while the vehicle engine is off. In the near term, the choice of fuels for these applications will focus on diesel liquid fuels because of their availability, low cost, and existing distribution networks. However, commercially-available hydrocarbon-based liquid fuels such as diesel must be reformed in order to achieve the desired gas compositions (consisting of hydrogen, carbon monoxide, and moderate levels of methane (< 10 mole %)), required for acceptable SOFC electrochemical performance. Therefore, grant applications are sought to develop innovative, low-cost, compact, and reliable reforming technologies to meet this requirement, including integrated plasma-assisted partial oxidation, catalytic partial oxidation (CPOX) or autothermal (ATR) diesel reformers. Designs must explicitly address and include the diesel injection system, mixing chamber, reactor vessel, and catalyst bed. Additional design requirements include: (1) operation within the temperature range 600 to 1000 °C; (2) turndown capability maximized and limited to not less than 4 to 1; (3) pressure drops below 1 psi, throughout the device; (4) minimal water usage; and (5) maximum carbon suppression. Also, practical APU SOFC system applications require fast start-up, processed fuel reformate availability to accommodate power demand transients, and the ability to accommodate part-load operation – all with minimal hydrocarbon (preferably methane) slip.
Catalyst-based reformers, which mostly operate in the temperature range 700 to 900°C, carry their own set of issues. In an ATR or CPOX reactor, where the fuel is sprayed into preheated steam and/or air, the fuel must be mixed as a vapor before entering the catalyst. Great care must be taken when exposing the diesel fuel to the catalyst surface, in order to avoid cracking and pyrolysis reactions that can lead to carbon deposition. (The high vaporization temperature of the heavy hydrocarbon compounds present in diesel fuel favors pyrolysis and carbon deposition in the preheat zones of the reactor.) Preventing this carbon formation, as well as autothermal ignition, requires that the local steam-to-carbon (S:C) and oxygen-to-carbon (O:C) ratios be maintained within a given range. Failure to uniformly mix the fuel with the air and/or steam prior to entering the reactor can result in hot spots, carbon fouling of the reactor, and deactivation of fuel reforming catalysts via localized carbon deposition. Finally, the diesel reformer catalyst itself must be able to handle up to 50 ppmv of sulfur in the fuel without sulfur poisoning and provide stable, long-term operation (> 5,000 hours) before maintenance is required.
References:
Subtopic a: High-Temperature Anode Gas Recycle Blowers
1. Systems Development for Planar SOFC- Based Power Plant, prepared by ALSTOM Research and Technology Centre for UK Department of Trade and Industry, 2002. (Full text available at: http://www.dti.gov.uk/energy/renewables/publications/pdfs/f0100195.pdf)
2. Conceptual Design of POX/SOFC 5kW net System, Final Report, U.S. DOE National Energy Technology Laboratory, January 2001. (Full text available at: http://www.tiax.biz/industries/pdfs/fuelcells/sofc_pox_0108-01.pdf)
3. Clark, T. and Arner, M., PEM Fuel Cell Air Blowers: DOE Merit Review, UTC Fuel Cells, May 2003. (Full text available at: http://www.eere.energy.gov/hydrogenandfuelcells/. In search box at the top enter “PEM Fuel Cell Air Blowers.”and then select the second entry “Motor Blower Technology for …”)
4. Fuel Cell Handbook, prepared by EG&G Services, Parsons, Inc., and SAIC for U.S. Department of Energy, October 2000. (Full text available at: http://www.osti.gov/dublincore/gpo/servlets/purl/769283-sD4TGw/native/769283.pdf)
5. Shaffer, S., “Development Update on Delphi’s Solid Oxide Fuel Cell System”, 2004 SECA Annual Workshop and Core Technology Program, Boston, MA, May 11-13, 2004. (Full text available at: http://www.netl.doe.gov/publications/proceedings/04/seca-wrkshp/Delphi%20-%20Shaffer.pdf)
Subtopic b: Low-Cost High-Temperature Heat Exchangers for SOFC Systems
6. Shaffer, S., “Development Update on Delphi’s Solid Oxide Fuel Cell System,” 2004 SECA Review Meeting, Boston, MA, May 11-13, 2004. (See above)
7. Minh, N., “SECA Solid Oxide Fuel Cell Program,” 2004 SECA Annual Workshop and Core Technology Program, Boston, MA, May 11-18, 2004. (Full text available at: http://www.netl.doe.gov/publications/proceedings/04/seca-wrkshp/GE%20Energy%20-%20Minh.pdf)
8. Vora, S. D., “SECA Program at Siemens Westinghouse,” 2004 SECA Review Meeting, Boston, Ma. May 11-13, 2004. (Full text available at: http://www.netl.doe.gov/publications/proceedings/04/seca-wrkshp/Siemens%20Westinghouse%20-%20Vora.pdf)
9. Norrick, D., “10 kW SOFC Power System Commercialization Program Progress,” 2004 SECA Review Meeting, Boston, Ma. May 11-13, 2004. (Full text available at: http://www.netl.doe.gov/publications/proceedings/04/seca-wrkshp/Cummins%20-%20Norrick.pdf)
10. Bessette, N., “Status of the Acumentrics SOFC Program,” 2004 SECA Review Meeting, Boston, Ma. May 11-13, 2004. (Full text available at: http://www.netl.doe.gov/publications/proceedings/04/seca-wrkshp/Acumentrics%20-%20Bessette.pdf)
11. Patel, P., “Thermally Integrated High Power Density SOFC Generator,” 2004 SECA Review Meeting, Boston, Ma. May 11-13, 2004. (Full text available at: http://www.netl.doe.gov/publications/proceedings/04/seca-wrkshp/Fuel%20Cell%20Energy%20-%20Patel.pdf)
Subtopic c: 1 to 5 kW Diesel Reformer
12. Hartmann, L., et al., Cool Flame Evaporation for Diesel Reforming Technology,” Proceedings of the 8th International Symposium on Solid Oxide Fuel Cells: SOFC VIII,, 8:1250, Pennington, NJ: The Electrochemical Society, Inc., 2001. (ISBN: 1-56677-377-6)
13. Solid State Energy Conversion Alliance(SECA), U.S. Department of Energy. (http://www.seca.doe.gov/. Provides information on SECA SOFC development goals and status as well as conferences, meetings and individual fuel processing projects)
14. Ahmed, S. and Krumpelt, M., International Journal of Hydrogen Energy, 26:291, 2001. (ISSN: 0360-3199)
15. Flytzani-Stephanopoulos, M. and Voecks, G. E., International Journal of Hydrogen Energy, 8:539, 1983. (ISSN: 0360-3199)
Return to the Complete List of Topics.
| Program Information, Instructions and Requirements | Technical Topic Descriptions | View Example Forms | Download Program Information | Download Technical Topics |