Introduction Developing technology to ensure that the use of coal is an economic energy source while maintaining America’s ever tightening environmental and climate requirements is of crucial U.S. national importance for solving today’s energy security concerns. The U.S. Department of Energy’s (DOE) is sponsoring the research and development (R&D) of solid oxide fuel cells (SOFCs) under the Solid State Energy Conversion Alliance (SECA). SECA is leading the way to low-cost, environmentally-friendly, fuel-flexible SOFCs and coal-based SOFC power generation systems for stationary markets. SECA is managed by the DOE’s National Energy Technology Laboratory (NETL) Program Office, in partnership with private industry, educational institutions and national laboratories. SECA has three major focus areas: Cost Reduction, Coal-Based Systems, and Core Technology R&D. The SECA Cost Reduction goal is to reduce the manufactured cost of SOFC power systems to $400 per kilowatt by 2010. Concurrently, Coal-Based Systems is pursuing the scaling, aggregation, and integration of the technology for use in large Integrated Gasification Fuel Cell (IGFC) systems for central power generation applications in order to efficiently and cleanly utilize the nation’s large coal reserves. The performance of IGFC systems will be consistent with Fossil Energy’s Advanced Power Systems goals, including over 45 percent efficiency (coal higher heating value HHV to electricity) with 90 percent carbon capture. Megawatt-class proof-of-concept systems will be demonstrated no later than 2012 to 2015. In support of these goals, SECA Industry Teams are establishing the requisite manufacturing base, and the SECA Core Technology Program is providing vital R&D to further improve on the substantial progress made through the SECA program. The first series of SOFC system prototypes fielded by the SECA Industry Teams surpassed SECA’s intermediate-targets for efficiency, reliability and production cost. Performance improvements and testing show continued progress. Furthermore, NETL analyses show that an IGFC system with a pressurized SOFC and catalytic gasification with recycle permits a high net efficiency approaching 60 percent HHV with carbon capture greater than 90 percent. Separate fuel and air streams to the SOFC substantially reduce the amount of water required to condense, recycle and reuse process water, and without a steam cycle, there is virtually no external water requirement. The high efficiency maintains an economic cost of electricity (COE) due to less fuel per megawatt hour and a smaller plant. Meeting SECA goals results in the lowest COE coal option with environmental regulation compliance and the ability to capture greater than 90 percent of the carbon. This technology makes substantial strides in permitting clean, economic energy production from coal in any state in the U.S. Clean Economic Energy in a Carbon Challenged World The DOE’s Office of Fossil Energy has established a set of aggressive technology goals to advance coal-fired power generation. SECA directly addresses the goals highlighted in italics. By 2010, coal-fired power systems will have the following characteristics: • 45-50% efficiency • 99% SO2 removal • NOx emissions < 0.01 lb/MMBtu • 90% Hg removal By 2012, these coal-fired power systems will improve: • 90% CO2 capture • < 10% increase in the cost of electricity (COE) with carbon sequestration By 2015, further improvements include:
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Multi-product capability (e.g. power and H2) 60% efficiency (w/o CO2 capture)
A primary reason the Department’s SECA program has focused on the SOFC is its very substantial synergism with coal plant integration. The importance of carbon capture and reduced water requirements for coal power plants, together with the development of new more powerful low-cost SOFC technologies, asks the question of what impact SECA fuel cells will have on the cost, efficiency, and environmental performance of advanced coal power plants and if SECA fuel cells integrated with a coal gasification process, known as an Integrated Gasification Fuel Cell (IGFC) Cycle, addresses carbon capture and reduced water requirements in an effective way. As shown below, the benefits of SOFC systems become readily apparent: The Importance of Increased Efficiency – Why this is Important?
Smaller Power Plant - Higher efficiency means a smaller power plant and reduced feedstock throughput. This leads to a reduction in capital cost which, when compounded by the financial considerations associated with the construction period, is a major component, along with feedstock, of the ultimate cost-of-electricity. Reduced Emissions - Higher efficiency translates to reduced emissions of product gas such as carbon dioxide and unwanted by-products such as mercury and sulfur that require removal and appropriate disposal. Reduced emissions mean smaller systems and parasitic power requirements to mitigate emissions reducing cost-of-electricity.
Synergism with a Coal Plant – How a SECA Fuel Cell Fits
Oxygen Separation Membrane - The SOFC electrolyte permits the flow of oxygen to the fuel but does not permit electrons to travel in the reverse direction. This is essential to the function of the SOFC but also permits keeping the fuel and air separate. This leaves only CO2 and water in the fuel stream allowing easy capture by condensing the water. This permits the use of methane in the fuel cell with post-fuel cell capture, a unique feature. Water Gas Shift Reactor – The SOFC fuel electrode (anode) will “shift” CO to CO2 by reaction with water producing H2. This eliminates the need to shift CO to CO2 in a separate reactor. Steam Reformer – The SOFC fuel electrode (anode) will reform methane and to some degree higher hydrocarbons to CO and H2.
High Methane Fuels - Why this is Important?
Higher methane fuels are important because in general the lower the gasification temperature the higher the gasification efficiency; less energy is lost to keep the gasifier hot. The methane also reduces the amount of air required to cool the SOFC because the steam reforming occurring inside the SOFC (rather than in a separate external reactor) consumes heat. The coupled efficiency improvement in the gasification and the fuel cell is significant. The discussion and systems analysis performed to date indicates IGFC plants will achieve between 50% to 60% efficiency (based on HHV) depending on gasification and fuel cell operating conditions.
Water Use – How SECA Fuel Cells Help
Higher efficiency reduces water use per unit of coal feed.
Separate fuel and air streams means a smaller or virtually no steam cycle and condensing water from the separate fuel stream requires little condensing medium, i.e., water.
Bibliography W. Surdoval, DOE’s SECA Program: Progress & Plans, 25th Annual International Pittsburgh Coal Conference, September 29 – October 2, 2008. W. Surdoval, SOFC Development in the USA, 8th European SOFC Forum, Lucerne, Switzerland, June 30 –July 4, 2008.