|Courtesy: Stanley Consultants|
As part of the University of Iowa Research Park’s efforts to promote renewable energy use, the new campus power plant’s engine generators are designed to operate primarily on landfill gas when the pipeline from the Iowa City Landfill is completed, with natural gas as a secondary fuel source. To make it more efficient, the plant’s waste heat recovery system captures waste heat from the gas engine generator’s cooling and exhaust systems to produce hot water for heating, or chilled water for cooling, campus facilities.
The new 2.8-MW Tri-Generation Power Plant exemplifies the University of Iowa Research Park’s (UIRP) commitment to sustainable energy and its green initiative for the future of its campus and surrounding community. The plant helps reduce the campus’s carbon footprint by reusing an existing heating plant building; by its choice of fuel sources and emission controls; and by centralizing the cooling, heating, and electrical service in one location. It also creates a hands-on teaching environment for the university’s engineering school.
With its versatile design, the plant will cut both carbon emissions and energy costs. “Even at partial completion we are receiving benefits. We can use the engine generators to offset load limitations from Alliant Energy. During testing phases at the new University of Iowa Information Technology Center, electrical demands often would have exceeded Alliant’s demand limit set for our campus. The engine generators are turned on to reduce the demand from the electric company, saving [the campus] thousands of dollars each time,” Steve Kottenstette, plant manager told POWER in July.
Using landfill gas is similar to using anaerobic digester gas, according to Tom Hickey, PE, who works for Stanley Consultants and is the project manager of the UIRP plant project. It is common for municipalities to utilize digester gas created in the breaking down of sludge at a wastewater treatment facility as a fuel supply for boilers or engine generators. Incorporating this process into the energy plan at an educational facility, however, is uncommon and is being made possible through a partnership between the University of Iowa, MidAmerican Energy, and Iowa City.
The plant has two 1.4-MW engine generators and operates as a peak-shaving plant to reduce the cost of peak demand electricity purchases each day. With current low natural gas prices, plant managers find it more cost-effective to generate power than to purchase grid power. In addition, they are trying to cut peak consumption on campus to lower the current usage demand that the utility, in turn, will use to set next year’s peak usage demand.
Since the plant entered service in June 2011, it has produced 911,660 kWh. In the first six months of the very warm summer of 2012, production was 455,389 kWh.
The engine generators are currently using natural gas while a complex, 6-mile-long pipeline originating at the Iowa City Landfill is being planned (Figure 1). When the pipeline is completed, the generators will be switched to run on landfill gas as a primary fuel for load demands up to 1.275 MW (the landfill gas limit). If demand exceeds that amount, the generators will automatically switch the fuel source to natural gas.
|1. Switch-hitter. The University of Iowa Research Park power plant contains two 1.4-MW General Electric Jenbacher engine generator sets capable of powering all the campus facilities at peak output. These generators are designed to operate using either biogas or natural gas. Courtesy: Stanley Consultants|
Stanley Consultants was the engineer of record for the UIRP project. Tricon Construction Group of Dubuque, Iowa, constructed the plant. Major subcontractors were American Piping Group Inc. and Price Industrial Electric Inc.
Equipment installed at the UIRP plant included:
- Gas engine generators: 1.416-MW GE Jenbacher 420 series engines
- Chiller: York YK 600-ton chiller
- Exhaust gas heat recovery unit: Cain
- Radiators: Guntner USA
- Medium-voltage (15 kV) switchgear: ABB
- Low-voltage (600 V) switchgear: Eaton Cutler Hammer
- Motor control center: Eaton Cutler Hammer
- Programmable logic controller system: Allen Bradley
- Backup campus heating system heat exchanger: Mueller
- Campus heating water supply pumps: Gould
- Ventilation equipment: Greenheck
- Fire alarm system: Simplex Grinnell
“The timing of this project was very unfortunate due to a devastating flood in 2008 that affected the Iowa City community heavily, including the Main Campus of the University of Iowa,” Hickey said. “Due to flood damage recovery efforts, local supplies and materials were diminished, forcing the university to ship in materials and pay increased prices for construction.”
Because this project is located on the UIRP campus, university management decided to reuse an existing building to house the engine generators and support equipment. That building had previously been used as an incineration facility, so it needed to be completely reconfigured to house engine generators. Provisions were incorporated into the design to install future equipment in the building through access doors instead of lifting it into place by crane.
Overcoming Engineering and Permitting Obstacles
The plant’s plan to use excess landfill gas in the future will reduce the amount of flaring and emissions from the local landfill. However, a significant challenge arose while engineering the control system for the use of landfill gas as a primary fuel source and natural gas as a secondary fuel source, according to Hickey. “The system must detect inconsistent flows and pressures of the landfill gas so the engine generators will have a consistent flow of fuel to operate efficiently during all load conditions. If the landfill gas supply becomes insufficient, the controls must switch the fuel source to avoid equipment down time,” he said.
Because landfill gas quality can vary significantly from area to area, it was professionally tested to confirm that it would be a good fuel source for the plant. High levels of hydrogen sulfide and silica dioxide (similar to sand) were detected, which could be catastrophically damaging to engine generators. Because of these potential problems, the university was required to purchase specific engine generators that are capable of handling small amounts (parts per billion) of these particulates without damage or frequent maintenance.
Hickey explained, “In an effort to reduce these particulates, the university will take additional precautions by filtering the landfill gas before it is supplied to the engines. This filtration brings the landfill gas to near pipeline quality and is better for the generators to use.”
The design of the campus electrical interconnection that switches electricity from a supplied source (Alliant Energy) to generated electricity from the plant presented additional challenges. The complex control systems must ensure that if the plant is unable to provide sufficient power to meet demand, the campus would seamlessly switch back to supplied power. Hickey said that as a result, with the coordination of Alliant Energy, the initial switch was uneventful and the designed controls worked “flawlessly.” Now that the switching process has been designed, implemented, and tested, it could pave the way for future, similar projects.
The project team also encountered difficulties in obtaining the plant’s air emissions permit. Hickey said, “Since the university maintains only one permit for the main campus and the UIRP campus, the new plant emissions are in addition to the university’s overall emissions output—not as an individual element but as a cumulative value of all the facilities that the university operates. This required the design to include oxidation catalysts to properly treat the exhaust system and emissions from the engine generators.”
Heat Recovery System Overview
One aspect of this project is the plan to use absorption chillers, which will reuse waste heat from the engine generators to chill water for cooling UIRP campus buildings.
The exhaust gas heat recovery units are configured with modulating bypass dampers that allow the units to vary the amount of exhaust heat that is recovered, depending upon the need for campus heating. Each heat recovery unit is supplied with an individual primary heating water pump, which allows for additional units to be added to the system in a similar configuration without disruption to the current control scheme.
By using a primary-secondary heating water flow scheme and decoupling heat exchangers tied to the engine radiator glycol water cooling loop, the heating water temperature control scheme has the ability to either recover heat from the engines or dump excess heat from the campus heating system to the radiators. Hickey noted: “This system provides a safe, straightforward method of maintaining precise water supply temperature control to the campus.”
— Angela Neville, JD is POWER’s senior editor.