Coal Without Combustion

Coal Without Combustion

Apr 11 - Mechanical Engineering

By Samuelsen, Scott; Babcock, Amy

Researchers want to put it into fuel cells instead of boilers, for cheaper, cleaner electricity.

The 19th century is seen as the age of coal, and with good reason. It was then that engineers first put coal to work on a large scale, first as fuel for steamboats and locomotives, and later in electrical power plants. Other energy sources were available- petroleum came on the market in the middle of the 19th century, and wood and water still had important roles-but burning coal was dominant.

So it may be a shock to realize that in 1839, as the coalfired Industrial Revolution was in full swing, English scientist William Grove invented the first fuel cell. Grove used what was considered reverse electrolysis to generate electricity from hydrogen and oxygen. The efficiencies of the early fuel cells were low, and investigators were stumped as to how to make them more practical. With the advent of the internal combustion engine, interest in fuel cells fell away. They were curiosities, mostly, or relegated to specialized applications, such as powering manned spacecraft.

Now, many years later, scientists and engineers are working fervidly to make fuel cells a practical replacement for combustion. What's changed? For one, the cheap fuel that made the industrialization in the 19th and 20th centuries possible is becoming harder to find. And we've come to realize that how we use the fuel is an important consideration: Uncontrolled combustion can spew toxic metals or climate-changing gases into the atmosphere. Fuel cells can improve on combustion on both those fronts. Fuel cells are electrochemical, so they are not bound by the Carnot limit on efficiency, and they can be designed to capture any harmful metals or gases produced.

One of the most ambitious projects is the Solid State Energy Conversion Alliance, created by the U.S. Department of Energy to clear the technical hurdles that have kept fuel cells impractical. Launched in 2000, and managed by the National Energy Technology Laboratory and the Office of Fossil Energy in Pittsburgh, SECA is a collaboration among government, the private sector, and the scientific community to pursue a vision of cost-effective, near- zero-emission solid oxide fuel cell technology for commercial applications.

Already, the systems developed are making great advances. One small prototype system has exceeded benchmarks for efficiency, and has an estimated cost within a factor of two of existing commercial power stations.

And in what is an odd twist, the solid oxide fuel cells being developed are designed to run on gasified coal. The future of coal, in fact, may well be tied to a technology that it has overshadowed for nearly 170 years.

Compared to other government research programs, secA has an unusual structure. The program unifies a number of organizations to work toward a common goal, yet retains a healthy spirit of competition to drive progress and spur innovation. Private sector businesses are grouped into industry teams with vested interests in developing solid oxide fuel cell systems as commercial products. All of these teams work to spin off early products achieving the targeted reductions in SOFC system costs and to establish the needed material and manufacturing infrastructure.

The SECA industry teams are supported by the core technology program, comprising leading universities, national laboratories, and businesses across the country. These groups are working on dozens of competitively selected SOFC projects to provide vital research and development solutions to the industry teams in five areas: materials, manufacturing, fuel processing, power electronics, and computer simulation. Research priorities are constantly evaluated and updated as new knowledge and technology advances are achieved. This shared R&D portfolio is intended to reduce redundancy and the cost to the federal government by making results available to all industry teams through special intellectual property provisions that enhance technology transfer. As a result, the secA industry teams- potential competitors in the marketplace-benefit mutually from the collective ingenuity of the core technology program to pursue innovations independently in fuel cell design.

The United States' Office of Management and Budget recently cited the SECA program as a leader in government-industry partnerships, noting that its structure "has generated a high level of competition between the [industry teams] and an impressive array of technical approaches. The SECA program also develops certain core technologies that can be used by all the industry teams to avoid duplication of effort."

Clean, Quiet, and Consistent

There are, of course, many fuel cells in use today, so why do we need such a large-scale program? The fuel cells on the market have many advantageous qualities, to be sure: They are exceedingly clean, relatively quiet, and can operate for long periods without maintenance and oversight. But compared to standard combustion generating equipment, commonly used fuel cells-which use molten electrolytes such as sodium bicarbonate or phosphoric acid-have a capital cost many times greater. And they have been largely limited to fuels such as natural gas or pure hydrogen. As a consequence, fuel cells have yet to break into mainstream power applications.

Research is reducing the gap between fuel cells and standard combustion generators, and one type of fuel cell promises to eliminate it altogether. Fuel cells made with a solid, porous ceramic electrolyte have the ability to use many types of fuels, and since they don't require precious metals or caustic chemicals, they have the potential to be made quite inexpensively. Solid oxide fuel cells are, in fact, a solid-state technology, with all the potential for reliability and compactness that the name implies.

What makes SECA groundbreaking is that it is working to develop a modular, low-cost, solid oxide fuel cell system specifically for use in a new kind of coal plant. To be sure, SECA fuel cells can also operate using natural gas, bio-fuels and diesel, and, of course, hydrogen. By developing fuel cells to operate efficiently and cost effectively on the fuels that dominate today's power industry, the hope is that the program can help meet pressing environmental and energy-security needs while building a bridge to a low-carbon economy. The SECA goal is to have SOFC power generation systems capable of mass production at $400 per kilowatt-a cost comparable to that of current stationary power systems-by 2010.

That ambitious vision is rapidly becoming a reality. Challenges to fuel cell technology remain, but they are being solved at an accelerated rate due to the intense focus of the alliance.

To tackle the perennial problem of the cost of fuel cells, SECA is blending established manufacturing processes developed in the semiconductor and electronics industry with state-of-the-art fuel cell technology and designs. The aim is that this will leverage the advantages of economies of production and scale in the coal plant of the future. What's more, SECA has set aggressive performance and cost targets for its private sector industry teams, driving them to new solutions to old problems. And by dividing the research and development into three phases, a comprehensive set of escalating benchmarks has been established for achieving breakthroughs in cost, reliability, and efficiency-the keys to commercial viability.

Ready for the Real Test

The results have been encouraging. The first round of system prototypes developed by several competing industry teams and manufactured with scalable mass-production techniques, has exceeded SECA's first set of escalating goals for efficiency, availability, and production cost. A typical system demonstrated an availability of 90 percent, and the small 3-10 kilowatt systems reached efficiencies in the 35-to-40 percent range-both marks surpassing SECA targets. Indeed, this level of efficiency in a small system demonstrates that much higher levels are achievable in larger systems. Most significantly, the independently audited system costs ranged from $691 to $784 per kilowatt-a big step toward achieving marketcompetitive costs. (These numbers represent aggregated results across six industry teams.)

These early developments are needed to ensure that established, mature, and cost-effective solid-oxide fuel cells are ready for the real test-demonstration in a coal plant. Three teams, in fact, are focused on delivering megawatt-scale systems. And another program within SECA seeks to leverage the program's success to date by ultimately extending the efficiency and environmental benefits of the technology to full-scale coal central power systems.

Nearly a quarter of the energy consumed in the United States comes from coal, and while domestic gas and oil supplies dwindle, the U.S. possesses a bonanza of coal. With 25 percent of the world's coal reserves, the United States is the Saudi Arabia of coal, and coal is a key part of the National Energy Policy put forth by the Bush administration a few years ago.

Such a large and secure energy resource will be of critical importance in the coming decades. But there is concern from many quarters about coal's viability as \a fuel. It has been implicated in the increase in atmospheric carbon dioxide and in the rise in global temperatures that follow from that. In addition, harmful materials such as sulfur and mercury are found in the raw emissions from coal-fired power plants.

One increasingly popular solution to the environmental impact of coal energy is capturing carbon dioxide and other products of coal combustion before they are released. The captured carbon dioxide can then be held-sequestered-in geologic formations. SOFCs are one of the key technologies being developed with an eye toward enabling the sequestration of carbon dioxide during power production. The ultimate goal is that at least 90 percent of the CO2 produced generating electricity will one day be captured, and that this technology will let coal plants meet environmental and permit requirements throughout the United States.

Such a system would see an SOFC and its associated components scaled up to a size appropriate for a central generating station and integrated with coal gasification technology. SECA plans to have megawatt-scale, coal-based SOFC systems ready for deployment by 2012, perhaps as part of FutureGen, another public-private partnership. When it's operational, the prototype will be the cleanest fossil fuel-fired power plant in the world.

The fuel cell has come a long way since its inception nearly 170 years ago. SECA's recent successes demonstrate that it's only a matter of time before solid oxide fuel cell technology achieves its commercial potential. Indeed, it's possible that SOFCs could reach high enough standards of efficiency and economy to entirely replace conventional combustion as the primary means of generating electricity in the U.S.

The coal age would continue, only now it would be converted electrochemically into electricity. And the fuel cell would move from being William Grove's laboratory curiosity to the mainstay of the modern world.

Bituminous coal has powered the United States for more than a century. The SECA program aims to find a cleaner way to use this resource.

Projects and Progress

here is a snapshot of just a few of the projects being undertaken by some of the dozens of universities, national labs, and businesses that are part of the Solid State Energy Conversion Alliance.

The National Energy Technology Laboratory: The research team at NETL independently tests prototype fuel cell systems devised by the SECA industry teams and validates various aspects of performance relative to SECA targets. Although the systems are intended for stationary power and mobile auxiliary power unit applications and fueled with natural gas or diesel, they demonstrate the fundamental SOFC technology required for large coal-fueled central power generation applications.

"We're now looking at how the systems and-material sets can evolve from gas-fired technology in order to be viable with coal," said research group leader Randall Gemmen. "It's great to see this much significant progress."

Pacific Northwest National Laboratories: Muhammad Khaleel, director of the computational sciences and mathematics division at PNNL, and his team use sophisticated computer models to reduce the expensive trial and error traditionally inherent in ceramic fuel cell R&D and engineering design. The goal is to validate design concepts in a virtual realm, efficiently guiding development, design, and manufacturing activities by the SECA industry teams. The PNNL team studies the various SOFC materials and the complex thermal- mechanical interactions between those materials, as well as general stack design for reliability and durability.

The PNNL team is also working-with Oak Ridge National Laboratory and ASME to generate a structural design basis document. The goal of that collaboration is to bring ASME's codes and standards expertise to bear on the considerable SOFC material property database and design knowledge acquired over the past four years by the secA core technology programs at Pacific Northwest and Oak Ridge, and by the industry teams. That document will serve as a repository for laboratory and operational learnings regarding the design of robust, reliable fuel cell stacks, with emphasis on knowledge and experience with SOFC failure mechanisms and associated failure criteria. Khaleel said, "We need more global guidelines. That's what we're trying to do with the ASME guide, to establish more consistent guidelines that give us consistent levels of reliability." University of Florida: Eric Wachsman's group at the University of Florida, a satellite of SECA's high-temperature electrochemistry center, studies electronically and chemically functional ceramics- specifically, solid ion-conducting materials and electrocatalysts- and their application in improving energy efficiency. The group also performs modeling and simulation, and delivers software modules used by SECA core technology and industry teams. Before SOFCs can be deployed into industrial and consumer markets, key hurdles, especially the mechanical, chemical, and transient stability need to be cleared.

National Fuel Cell Research Center: The center is characterizing compressor and turbine maps to support stable gas turbine operation at various pressure ratios for the fuel cell/gas turbine hybrid power block contained within an advanced IGCC power plant. As a leader in hybrid technology, the NFCRC has developed an advanced dynamic model of the FC/GT block that comprises a pressurized SOFC, feed air from a gas turbine compressor, and a high-pressure and high- temperature exhaust flow to a gas turbine expander.

Unlike other FC/GT hybrid systems, which typically operate on natural gas and are on the scale of 100 kW, advanced systems operate on nearly pure hydrogen generated from coal syngas with CO2 sequestration, and are on the order of 100 MW. A significant goal is the specification of a gas turbine that matches the FC/GT performance requirements, including design and control of the turbine in order to avoid compressor surge.

Lawerence Berkeley National Laboratory: Steve Visco, a principal investigator at Lawrence Berkeley, and his team have been working on SOFCs for more than 15 years. Their efforts have bettered SOFC performance at lower temperatures, and have improved tolerance to contaminants like sulfur.

"We try to come up with solutions-longer life, higher power, sealing technology-that are all geared to cost reduction for industry commercialization," Visco said. His group has started to do more technology transfer and is creating a standard test platform SOFC stack to validate SECA's core technology program innovations. Mis team is also working on infiltration, introducing nanostructured catalysts into cathode microstructures to boost fuel cell performance.

"We've had some breakthroughs in designing a cathode that only takes a single processing step," Visco said, which enhances stability and simplifies the manufacturing process.

These ceramic parts, which were designed at the Pacific Northwest National Laboratory, may form the heart of an advanced SOFC.

This article was written in cooperation with the U.S. Department of Energy's National Energy Technology Laboratory.

Scott Samuelsen is the director of the National Fuel Cell Research Center at the University of California. Irvine. Amy Babcock is president of STG2, a technical marketing firm, in Honeoye Falls, N.Y.

Copyright American Society of Mechanical Engineers Apr 2007