The fuel cell, located at the South Treatment Plant in Renton, WA, can consume about 154,000 cubic feet of biogas a day to produce up to 1 MW of electricity. That’s enough to power 1,000 households, but it’s being used instead to help operate the plant.

The fuel cell’s electric output will save the Wastewater Treatment Division (WTD) of King County’s Department of Natural Resources and Parks about $400,000 a year—money that otherwise would be spent to buy electricity from the local utility, Puget Sound Energy, a subsidiary of Puget Energy Inc., of Bellevue, WA. Other savings, yet to be determined, will come from waste-heat recovery and reduction of biogas scrubbing costs.

Moreover, says Gregory M. Bush, the WTD’s manager of planning and compliance, the fuel cell will be far cleaner than a combustion engine, emitting into the air about 200 times less oxides of nitrogen, 30 times less carbon monoxide, and 35 times less volatile organic compounds.

The crucial question, though, is whether these benefits will be realized at a cost that makes such technology affordable for other sewage plants elsewhere. “This is, after all, a demonstration project,” Bush notes.

The total cost of the project is $22.5 million, but King County’s commitment is just $2 million, plus in-kind labor. Of the remainder, King County so far has received $8.5 million from a $12.5 million congressional commitment to fund the project through the EPA’s Office of Wastewater Management. The manufacturer, FuelCell Energy Inc. (FCE) of Danbury, CT, is contributing the other $8 million.

An Important Milestone
“This is an important milestone,” explains Jerry D. Leitman, FCE’s chairman, president, and chief executive officer. “It’s the world’s first commercial 1-MW fuel cell plant. To the power industry, real men talk megawatts, and power companies talk thousands of megawatts. If you talk smaller, it doesn’t get their attention at all.”

Leitman notes that, although carbon dioxide is widely regarded as the foremost culprit in global warming, methane (the major ingredient in biogas) has 23 times more impact on the atmosphere. “Today,” he says, “a lot of plants still are venting methane into the atmosphere. If you flare it or burn it in an engine or boiler, you convert it to carbon dioxide—but the best way is to put it through a fuel cell.” He predicts that, over time, as such demonstration projects prove how well fuel cells perform, “the EPA will ratchet the regulations down to force wastewater plants to have such technology.”

“Chances are it’s going to work,” predicts Robert K. Bastian, an EPA senior environmental scientist who is that agency’s project manager. “The hope is this system will run at a reasonable efficiency over a sustained period of time, and recover the investment cost. Anything beyond that will be gravy if it shows significant savings.

“Fuel cell technology is being viewed as a technology of the future. We’re trying to deal with it today. This is a next-generation design, a fuel cell more efficient than others already in use. The biggest current problem is the high cost of initial installation. If we had hundreds being installed every month, costs would be lower.”

Leitman concurs. “In today’s low-volume, high-cost scenario,” he says, “no fuel cells will be economically feasible without some kind of incentive from the state or federal government. We’re bridging the gap to tomorrow’s high-volume, low-cost scenario.”

A risk exists that contaminants in the gas supply could coat the electrodes and poison the fuel cell. To avoid that, the King County fuel cell has elaborate equipment to clean the gas. “The Achilles heel could be that the gas cleanup doesn’t work well enough,” Bastian warns. “If the fuel cell fails, you would have to spend all that money over again to rebuild it. However, it has some real potential for energy savings and increased efficiency. If everything works out, we will have paid for the investment early on, and we’ll come out ahead over time.”

A Constant Supply
On a typical day, the toilets, sinks, and garbage disposals of some 700,000 King County residents discharge about one million gallons of what Bush delicately calls “influent” to the South Treatment Plant in Renton. It goes through screens to remove large sticks, rocks, and rags. Next, grit removal and primary settling remove about 60% of the solids. Then it moves on to secondary (biological) treatment, secondary settling, and disinfection.

What remains goes from the bottom of the primary and secondary settling tanks to anaerobic digesters. In this warm, wet environment—near 32?C (90?F)—bacteria break down the volatile organic material and pathogenic organisms, then die and fall to the bottom of the digesters. Their microscopic corpses form a largely inert, non-pathogenic, nitrogen-rich residue that is dried and used for fertilizer and composting.

In this process, the bacteria excrete biogas (also called digester gas). It’s about 60% methane and 38% carbon dioxide, plus some trace elements—nitrogen, oxygen, compounds of chlorine and sulfur, and siloxanes.

“We scrub out the carbon dioxide to produce pipeline-quality gas, which we wholesale to Puget Sound Energy,” Bush says. “For this fuel-cell project, we’re using two gases produced onsite. The first is a higher-quality methane, more pure than pipeline gas, that is produced by passing digester gas through pressurized wet scrubbers to remove the carbon dioxide and trace elements. The second is unscrubbed digester gas, which is treated for the fuel cell through a two-step process (SulfaTreat media followed by activated carbon to remove the sulfur compounds.”

Electrochemical Reaction
Both gases provide methane for the fuel cell. As the fuel cell pulls the hydrogen out of the methane, the hydrogen reacts with oxygen from the air in an electrochemical reaction.

All fuel cells blend hydrogen and oxygen in this manner. “A fuel cell is like a battery that never loses its charge,” Leitman says. “It’s the first time in the history of man that we can generate electricity without combustion.”

The King County fuel cell, a high-temperature molten carbonate type, consists of four 250-kW stacks of about 900 individual cells. Within each cell, stainless steel plates surround a porous ceramic matrix containing an electrolyte. At the anode (negatively charged electrode), carbon dioxide and oxygen combine with two free electrons to form a carbonate ion. Hydrogen then joins the carbonate ion, which migrates through the electrolyte to a cathode (positively charged electrode). At the cathode, the carbonate ion releases four electrons, two of which become electricity and leave the fuel cell. The other two electrons migrate back through the electrolyte and become part of another carbonate ion.

Byproducts of this reaction are carbon dioxide (although in far smaller quantities than a combustion engine releases) and water. Aboard the Space Shuttle, the astronauts drink potable water produced by their craft’s fuel cells.

The Renton installation, although rated at 1 MW of electrical output, actually produces slightly more. It consumes 90 kW to run its ancillary equipment, leaving a net output of 1 MW. The balance of the plant is designed for expansion later to produce up to 1.5 MW of electricity.

About 400 sewage treatment plants in the US have anaerobic digestion and receive at least 30 million gallons of influent a day, the minimum necessary to justify installation of a fuel cell the size of King County’s. For smaller treatment plants, FCE offers a 250-kW fuel cell that can be installed in multiples to produce 500 kW or 750 kW.

New Gas-Turbine Generator
The South Treatment Plant, among the 33 largest sewage plants in the nation, produces about 770,400 cubic feet of digester gas per day, but uses only 18% to 20% of this supply to run the fuel cell. Under ideal conditions, the rest of the gas is now sold to Puget Sound Energy—but by the end of 2005, most of it will be burned in a new dual-fuel gas-turbine generator capable of burning digester gas or natural gas.

The South Treatment Plant’s average daily power consumption is 7.5 MW, but during storms its demand can rise to a peak of 24 MW. Together, the 1 MW fuel cell and the new 8-MW gas-turbine generator will more than cover the plant’s entire electricity base load, though it will continue to rely on PSE for peaking power.

“We are committed to using the gas resources we produce in an environmentally effective manner,” Bush says, “and we like the security and independence we will have from fluctuating power prices.”

The fuel cell also is boosting the South Treatment Plant’s total heat supply by about 18%. A molten carbonate fuel cell operates at 650?C (1,200?F). “From its exhaust-gas stream at nearly 425?C (800?F), we’re capturing 1.2 million Btus of heat per day in the form of hot water,” Bush explains. “We could have gone to steam, but we use hot water in the plant to heat the digesters.”

Seven Years and Counting
The project began in 1998 when M.C. Power Corp. of Burr Ridge, IL, invited the WTD to serve as a site host. “We said that sounded like it would meet our business needs,” Bush recalls. “We’re interested in better utilization of our gas resources.

“We set out to raise grant funding, managed to entice the EPA to partner with us and M.C. Power, and got fairly well into the design process. Then, in 2000, M.C. Power went out of business. They were one of three major manufacturers working on high-temperature fuel cells, based largely on grant funding from the US Department of Energy (DOE). When the DOE performed a down-select process and continued funding for only two vendors, M.C. Power wound up with the short straw.

“We said, ‘We’ve got a $12.5 million funding commitment from the federal government. We’re not going to give the money back.’”

With the assistance of then-senator Slade Gorton (R-WA), the WTD retained the federal commitment while it issued a request for proposals and selected FuelCell Energy to provide the power plant and share in its cost. “FCE had an appealing technology that was still being funded by the DOE, and a track record of smaller demonstration projects,” Bush says.

Design and fabrication of the equipment took 28 months, from January 2001 to April 2003. FCE made the fuel cell stack. Fluor Corp. of Aliso Viejo, CA, designed the plant, wrote specifications, and helped FCE select its other subcontractors.

• Total Process Control Inc., of Red Bud, IL, fabricated and assembled much of the equipment, and packaged it on skids to facilitate shipping and installation.
• ABB Inc., of New Berlin, WI, a subsidiary of ABB Group of Zurich, Switzerland, manufactured and supplied the “electrical balance of plant,” including inverters and the control center.
• John Zink Co., LLC, of Tulsa, OK, part of the chemical technology group of Koch Industries Inc., of Wichita, KS, supplied the anode gas oxidizer.
• The G C Broach Co., of Tulsa, supplied the power plant’s integrated heat recovery unit.

Two engineering firms are helping King County coordinate and manage the project. CH2M Hill Companies Ltd., based in Englewood, CO, is the prime consultant. Engineers in its Bellevue, WA, office have provided the overall project coordination through design, and assistance during construction and start-up. Now they are involved in the testing program during the two-year operational demonstration. Engineers in the Seattle office of Brown and Caldwell of Walnut Creek, CA, were responsible for much of the onsite utility design.

Installation and Operation
All of the components were shipped to FCE’s Connecticut factory. There the plant was assembled and tested, then dismantled and placed on the skids—one for the fuel-cell assembly, one for the electrical balance of plant, and two for the mechanical equipment, which includes three separate desulfurizing devices to clean the gas supply. The equipment traveled 3,000 miles across the country, to Renton, on four flatbed trailers.

Meanwhile, the WTD was constructing reinforced concrete pads with a grounding grid, and bringing electricity, gas, and water hookups to the fuel cell’s half-acre site. Groundbreaking took place April 14, 2003. The pads and onsite utility work were completed August 6.

The skid-mounted equipment arrived August 11 and was bolted to the pads with anchor bolts arranged in a configuration that complies with Uniform Building Code requirements for local seismic and wind loading conditions. “Once the equipment reached our site, it was offloaded from the trailers and mounted on the foundation in three hours. It was really astounding,” Bush recounts.

The fuel cell itself occupies a pad 42 feet long and 40 feet wide. The gas-conditioning equipment rests on another pad that is 17 feet long and 14 feet wide. A third pad, for heat-recovery equipment, is 16 feet long and 12 feet wide. The entire installation stands 12 feet tall, except for a vent stack that rises to a height of 29 feet.

Work at the plant during the next seven months included piping and wiring connections, painting, modifying several components to meet local codes, and onsite fabrication of an additional heat recovery unit designed by WTD. Start-up testing began March 25, 2004. Operations testing began June 2004 and is scheduled to continue through spring 2006.

“Between June and mid-September of 2004,” Bush reports, “we logged about 2,000 hours of operation with 93% availability. Then we shut down for a little over one month due to other construction activity at the treatment plant that forced us to move our main power line. We started up again in November.”

Monitoring the demonstration is a 20-person peer-review panel, with representatives from the EPA, King County, the Puget Sound Clean Air Agency, the Electric Power Research Institute, an energy company, other wastewater utilities, and academic engineers. They will analyze the fuel cell’s performance and emissions data, and report to the EPA, which in turn will provide the information to other prospective users who are considering the use of fuel-cell technology.

At the end of the demonstration project, King County will own the fuel cell. It has a design life of 30 years, but the fuel cell stacks will need replacement every three to five years.

“That’s something we’re demonstrating,” Bush says. “I don’t know the cost to replace them. My contract isn’t specific on that, although it says I’ll get a favorable rate. This is FCE’s first 1-MW plant, so they haven’t restacked any yet.”

Annual operating expenses are estimated at $80,000 a year, for equipment maintenance and fresh carbon for the scrubbing vessel that purifies the digester gas.

Early-Adopter Strategy
FCE shipped its first commercial fuel cell to the Kirin Brewery in Japan in 2003, and now has 34 others located around the world—all smaller than the Renton installation.

Leitman says the company’s new-technology rollout strategy entails targeting selected customer groups—wastewater treatment plants, hotels, universities, prisons, manufacturing plants, and mission-critical facilities. The latter category includes commercial data-processing and telecommunications installations, and government clients, such as military bases and defense installations, veterans’ hospitals, emergency-management centers, regional air traffic control centers, and homeland security facilities.

“We want to get fuel cell technology into each of those segments with early-adopter customers, and make sure it meets their expectations,” Leitman says. “Then those early-adopter customers will bring in the broad market.”

GEORGE LEPOSKY is a science and technology writer based in Miami, FL.

DE - November/December 2005