Cogeneration is nothing new to the readers of CSE. However, applying wastewater to the process certainly merits discussion. The south-central Oregon community of Klamath Falls did just that three years ago by installing a 484-megawatt (MW) cogeneration plant that was built in conjunction with an upgrade to the community's wastewater treatment plant (WWTP).
Cogeneration is nothing new to the readers of CSE . However, applying wastewater to the process certainly merits discussion. The south-central Oregon community of Klamath Falls did just that three years ago by installing a 484-megawatt (MW) cogeneration plant that was built in conjunction with an upgrade to the community's wastewater treatment plant (WWTP). The result was an ideal marriage of technologies. Not only was wastewater treatment greatly improved, but the water itself became a source of good-quality cooling water.
With an average dry weather flow of 4.3 million gal. per day (MGD), the plant delivers a constant supply of cooling water to the cogen facility that has proved a financial boon for the community.
Power into dollars
When the project was conceived and built, it was the first time in many years that the West Coast had seen a major new merchant plant. For those unfamiliar with the vernacular, a merchant plant is a power plant whose energy is sold wholesale on the open market. Situated close to the Oregon-California border and generating enough electricity for 400,000 homes, the plant was a welcome addition for an energy-starved Northwest. Furthermore, Klamath Falls' location proved even more strategic due to its close proximity to major electric transmission lines and regional natural gas supply pipeline.
Natural gas, of course, is the plant's primary fuel source. According to Jan Johnson, spokesperson for Portland-based PPM Energy, the plant is unique. "It sets the standard for all gas-fired plants in Oregon."
What sets it apart, she adds, is complete redundancy of all major components, plus complete automation. Also, every piece of major equipment is indoors, reducing maintenance and improving performance.
A subsidiary of ScottishPower, PPM is an energy wholesaler that deals in a number of energy sources, primarily natural gas and wind power. While the city of Klamath Falls owns the facility, PPM markets the plant's products: electricity and steam.
"We have been very successful at securing long-term contracts for the ... plant output," says Terry Hudgens, PPM's CEO. "Customers value the location, low cost, efficiency and superior environmental characteristics."
The cogen plant sits on a former industrial site, once a log yard for a Weyerhaeuser lumber mill. The advanced combined-cycle cogen plant has two gas turbines that produce 165 MW of power. The plant's overall fuel efficiency—approaching 59%—is nearly twice the typical 34% achieved by the conventional coal-fired plants that supply about half of U.S. energy needs.
The cogen plant is also cleaner than coal with respect to emissions. The Oregon Dept. of Environmental Quality has set the maximum allowable NOx emissions for the plant at 4.5 ppm. To meet these requirements, the facility's processes use dry low-NOx combustion with selective catalytic reduction.
Wastewater serving a purpose
In order to use the WWTP effluent as cooling water for the cogen plant, it is essential that it meets the right quality standards. This is achieved by "super-chlorinating" the effluent to kill algae and removing phosphates—the source of which are detergents, car washes and the like. Because phosphates block and even corrode cooling system components, sodium hypochlorite is added to control bio-fouling. Treatment at the WWTP also includes the introduction of sodium bisulfite to the return blowdown from the cooling towers to remove sodium hypochlorite. Additionally, turbidity monitoring ensures that effluent quality does not deteriorate.
The WWTP provides the cogen facility with 2.8 to 4.2 MGD in cooling water. It uses no freshwater at all. "This is important in a region that has traditionally had water problems," says PPM's Johnson, referring to its high desert location.
Moreover, more than 65% of the water entering the cooling tower system, which consists of eight cells, is being evaporated into the atmosphere. This is an important environmental benefit. By recycling wastewater through the cogen, the evaporative process reduces the amount of effluent discharge into the Klamath River by two-thirds—approximately 2.3 MGD.
The water that remains, which is called blowdown, is returned to the WWTP. There, it is dechlorinated and the temperature reduced before it is discharged into the river. Remarkable as it may seem, wastewater effluent has become a profit center for the city. The revenue that it helps generate has been a boon to the city of Klamath Falls. And the city is using some of the revenue from the steam sales to operate and maintain its geothermal system.
As one might expect of two process facilities that are running in tandem, scheduling between the cogen plant and WWTP is a critical, sensitively timed issue. With the cogen plant dependent on the WWTP for cooling water, system designers had to build redundancy into all of the major plant components such as pumps, storage units and water treatment equipment.
As far as the cogen operation itself, water is also an important component here. The system uses heat recovery to create steam. Hot exhaust gases go from the gas turbines to two heat-recovery steam generators (HRSG), which power a steam turbine. The facility produces 275,000 lbs. of steam per hr.
The HRSGs together add 30 to 50 MW of power, depending on ambient conditions. The HRSGs don't use wastewater from the WWTP. Instead, they rely on potable, fresh well water that is further treated by a demineralizer.
This combined cycle produces net power at a very low heat rate—less than 7,000 BTU/kWh. Some steam is sold and piped to nearby industrial users, most notably Collins Wood Products. Collins, by the way, is a company that boasts its own environmental pedigree, with many of its own "green" initiatives.
According to local officials, the sale of steam to community businesses has been a win-win proposition for everyone. While providing Klamath Falls with customers for the steam that the facility generates, the businesses, in turn, can remain competitive by depending less on oil-, gas- and wood waste-burning boilers.
To output this volume of energy, the equipment had to be large. In fact, the boilers are so large that they had to be assembled on site. And because the facility is located in a seismic zone, each of the three turbines sits on a base of 1,000 cu. yd. of concrete.
Environmental mission continues
The city of Klamath Falls has created a model for other communities trying to strike an equilibrium between protecting their natural resources and seeing to their economic needs.
They have also struck another kind of balance, with a partnership between the public and private sectors for developing the cogen facility and marketing the power that it generates. The facility was financed with revenues from a city-sponsored $300 million bond. For the most part, these bonds were purchased by institutional investors. In essence, the city used private money to build a large public project that, in turn, benefits private businesses up and down the West Coast—while also making money for the city. And it accomplishes all of this as an open book.
"Unlike a lot of power plants, everything at this plant is very transparent, because it is owned by the city, making everything a matter of public record," says Johnson. "The city is making about $1 million per year. They've received a cash distribution every year since year one and have been able to cut taxes."
"Because the cogen plant is owned by the city," says City Manager Jeff Ball, "it will realize the profits made by the plant." He explains that in the first few years, the city expected to make approximately $3 million with additional revenues going to early debt retirement. The city has used its project revenues in part to reduce taxes, build city services and improve the parks. In addition, the revenues have been used to encourage economic development by providing low-interest business loans and installing new infrastructure.
But the community isn't resting on its laurels. "There are all kinds of interesting [environmental] happenings in Klamath Falls these days," says Jan Johnson. "For example, there's the CO 2 mitigation program, and a truck-idling program associated with the new peaker plant. Also, the facilities have won two safety awards last year through a program with Oregon OSHA."
The CO 2 mitigation program that she is referring to was developed early on and became the model for an Oregon law that created the first CO 2 standard in the nation. The truck-idling initiative is a program to reduce the emissions from trucks, which often idle eight to 10 hours per day.
In fact, this program is at a new peaker plant that was built after the success of the first cogen facility. When the latter proved to be such a success, the city of Klamath Falls wasted no time in beginning the permitting process for another cogen plant at the same location. All the same public and private players are involved. PPM Energy spearheaded the development of this 100-MW gas-fired simple-cycle peaking unit that was sited near the first cogen plant. Once again, the city and PPM negotiated a site lease with Collins Wood Products, and PPM obtained permits and a legislative exemption needed to site the new peaker plant on an expedited basis.
The Klamath Cogeneration Project has gained international attention and won awards, including the Governor's Sustainable Oregon Award. And rightly so. The city of Klamath Falls and its partners in the project have proved that cost-efficient energy and environmental responsibility aren't mutually exclusive.
Engineering Triple Play
Geothermal technology is the final element that makes the Klamath Falls wastewater treatment plant (WTTP) and cogen combination such an effective engineering triple play. In the WWTP upgrade, the city's existing geothermal heat loop was extended to heat the WWTP control building, provide backup heat for the WWTP digester and even melt sidewalk snow.
The city was already using 180°F natural geothermal water—one of the benefits of the region's volcanic activity—to heat downtown businesses. But in adapting it to the plant, not only did geothermal pipe have to be routed to the facility, but it had to be done while the WWTP was fully operating.
All three technologies function together as a well-integrated mechanism. Wastewater goes to the cogen plant to produce process steam. Profits from steam sales support maintenance, operation and expansion of the geothermal system that in part serves the WWTP.
An Innovation is Born
When officials in Klamath Falls, Ore., first began to discuss a new power-generating facility, it was the late 1970s and talks with the utility focused on hydro projects. But with federal designation of the Klamath River as a "wild and scenic river," a hydroelectric dam was out of the question. Other environmental regulations initiated in the 1980s also pushed this old logging community to look for new sources of income.
By the mid 1990s, officials were thinking about a cogen power plant. But the environmentally sensitive state government was not wild about the notion. In fact, even after conceding to the concept, it set the condition that only one 500-MW plant could be built in Oregon. And the project that would win approval had to offer the best environmental mitigation package.
Klamath Falls' proposal not only won the endorsement of Oregon's Energy Facility Siting Council, but also attained the support of key local and regional environmental groups. City Manager Jeff Ball credits his predecessor, Jim Keller, who "worked very hard at building alliances and cooperative relationships."
Customers for Cogen Power
Not all of the megawatts generated by the Klamath Falls, Ore. cogen facility are sold by the city to energy wholesaler PPM Energy. The 240 megawatts not sold to PPM are sold under long-term contracts to municipal and public power utilities, as required by the city.
"As far as PMM is concerned, the plant is unbelievable for dispatch," says Jan Johnson, spokesperson for the company. "They are very flexible and reliable for delivering power."
Geared to react to energy market conditions, the cogen plant is designed for cycling and limited peaking using duct burners to quickly service the market. It can go from an off-line state to full production in two hours. In fact, it is what is referred to as a "one-button" start plant. An automated sequencing program starts up one or two units, adding or subtracting a unit from service, and shutting down the plant. Once made ready for initial startup, the plant is designed to be started, stopped and restarted the following day using two operators without the necessity of leaving the central control room. The quick restart process after an overnight shutdown is possible because of automatic sequencing of the plant stack dampers, vents and drains, and the use of sparging steam from an auxiliary boiler to keep the heat-recovery steam generators hot and pressurized while shut down.
One final note about plant versatility: Natural gas transmission lines that supply the turbines are owned by the utility, but the gas is supplied from several sources. This results in market options that allow the plant to find the best prices from gas suppliers.