ANGWIN – The ability to generate mechanical energy, megawatts of electricity and heat in the same engine using a process called co-generation is increasing in popularity due to skyrocketing fuel prices and continued uncertainty over the future availability of global oil supplies.
At Pacific Union College (PUC) in Napa County, facilities managers anticipated this trend years ago and installed a $12 million gas turbine power plant that went into 24/7 continuous operations on Feb. 18, 2006.
Today PUC is more than half way toward realizing a complete return on its investment. This plant saves the college approximately $1 million a year in energy costs.
“During the past decade we experienced a series of rolling blackouts and sharply rising electricity rates,” said Dale Withers, director of facilities at PUC.
“By using 20 percent more natural gas than was historically used in our boiler to supply steam for our campus, PUC is able to supplement 90 percent of its electrical needs while also covering the campus’ steam use.”
The college installed a Kawasaki GPB-15X natural gas turbine, capable of generating 1.5 megawatts (MW) of power (1,490 kW).
This is enough energy to satisfy the needs of a campus with more than a million square feet of building space. These facilities include dormitories, classrooms, laboratories, offices, a cafeteria, library, gymnasium, and auditoriums, along with a student center and church occupied by more than 1,200 students, faculty and the administrative staff.
The gas turbine is similar in function to engines used in turbo prop airplanes that service Charles M. Schulz Sonoma County Airport. However, instead of a propeller, an electric engine is used on the gas turbine.
The gas turbine system is designed to last 30 to 35 years. The engine is overhauled every three years to keep the power plant operating at peak efficiency.
The exhaust from the turbine has temperatures approaching 1,000 degrees Fahrenheit. Hot air is captured in a heat recovery system that produces 10,000 pounds of steam per hour used in a variety of applications.
“With current utility grid prices, PUC could be paying 14 to 17 cents per kilowatt hour (kWh). However, using co-gen technology, our cost is about nine cents per kWh to produce electricity and six to seven cents per kWh for steam — when you consider the steam we are using for heat is a byproduct of co-generation,” according to Gayle Grove, co-generation manager at PUC.
Mr. Grove said when considering co-gen, it is important to sign up for an extended service agreement as well as long-term natural gas supplier contracts to fix maintenance and operating costs.
“The cost of natural gas can go up from 10 to 20 cents per decatherm, (1,000 square feet of natural gas equivalent to 100,000 BTUs, or British Thermal Units of heat energy). However, current natural gas prices are among the lowest in years and the U.S. has huge onshore reserves.”
This single, unified power system operating at 80 percent efficiency provides over 90 percent of the energy required for the entire campus when it comes to producing heat, hot water, steam, chilled water (for ventilation and air conditioning), lighting, as well as the steam needed to heat PUC’s indoor swimming pool and sanitize cafeteria equipment.
“PG&E is our backup. We import from 20 kW to 300 kW of electricity from them on a regular basis. They are there for us in the event that we have to take the co-gen plant offline for periodic maintenance. Most of the time we are virtually self-sufficient – except for rare occasions when PG&E’s breaker opens and we have to be on our own (by going into what we call Island Mode.)”
The large metal structure housing the co-gen plant on top of Howell Mountain also has pads for a backup boiler and a diesel generator currently located in another campus building.
With a full-time staff of two, including Mr. Grove and Associate co-gen plant manager Raulton Haye, plus seven to 10 students (who receive more than 40 hours of intensive training), the control gauges for this heavy-duty single combustion gas turbine are monitored around the clock. Student shifts are assigned to allow for class schedules.
Ultra low emissions, corrected to 15 percent O2, are a major co-gen benefit. The system emits only 1.14 parts per million volume dry (ppmvd) of nitrogen oxide (NOx) as a byproduct of flameless catalytic combustion, as well as 0.237 ppmvd of carbon monoxide and 0.323 ppmvd of Precursor Organic Compounds (POCs) as CH4 (methane) – levels well below allowable standards.
For example, the Bay Area Air Quality Management District has set a standard maximum of 2.5 ppmvd for NOx. Furthermore, the engine does not require frequent oil changes, coolants or selective catalytic reduction (SCR) ammonia-based agents.
Another way of looking at co-gen emissions is to compare them with those produced by commonly occurring natural phenomena.
A single lightning strike makes as much NOx as a catalytic combustion Kawasaki gas turbine produces in a year, according to the company website.
“As environmental regulations become more stringent, there is nothing more cost efficient and 99 percent reliable than co-gen, a technology that is improving with time. We are also looking at fuel cell and solar technologies for the future,” Mr. Withers said.
A few miles down the mountain at St. Helena Adventist Hospital, a fuel cell system is already in place within the facility’s cancer treatment center.
“We are far from being alone in adopting this green technology,” Mr. Withers said. “Other co-gen plants have been in stalled at Napa State Hospital and at the Veteran’s Home in Yountville. And I also know of several additional installations in the North Bay. It’s a technology whose time has come.”
There are some 550 co-gen plants in California producing two-thirds of all non-utility power in the state – a total of some 6,500 MW – according to the California Cogeneration Council.
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