Biomass Hits the Campus
A lesson to higher education at the University of Iowa's onsite power plant.
The University of Iowa’s (UI’s) Department of Utility Management was certainly feeling its oats on Earth Day 2005. Thanks to a project that burns biomass along with coal, the university now boasts significantly lower pollution emissions and a newfound contribution to carbon sequestration. It all started with a recipe from the Quaker Oats Co., but millions of dollars and years of research and development went into adapting the university’s power plant to burn oat hulls, a pesky waste product for Quaker. Less pollution and carbon control make for great public relations, but was it worth the effort in terms of power generation and plant operations?
The University of Iowa has a strong record of distributed energy milestones. Their central plant fired up its first three coal boilers and two hydroelectric generators in 1926. By 1947, the addition of a controlled extraction steam turbine brought the benefits of cogeneration into full swing. The combustion conversion rate of 17% to 25% improved to a cogeneration rate topping out at 85%.
Speaking of topping, the cogeneration arrangement uses a “topping” cycle, where steam from the boiler powers the electric turbine first, then the steam exhaust is routed to space- and water-heating duties. A bottoming cycle reverses the location of the electricity turbine, so it gets steam after the space- and water-heating tasks.
Over the years, the power plant has grown to five boilers capable of 640,000 lbs/hr of steam, and three turbine generators with 24 MW of output. There are three chilled-water plants with 18 chillers totaling 29,755 tons of cooling. Additionally, UI is one of a small number of universities that operates its own water plant. Keeping up with the annual campus demand for 855 million gallons of purified water takes 3,816 MM Btu of steam and 2,104,000 kWh of electricity per year.
The plant’s overall capacity may sound like a lot, but UI has grown faster than its power generation. Located in Iowa City on 1,900 acres, the campus has approximately 14.5 million square feet of building space spread over 119 structures. More than 30,000 students, faculty, and staff rely on the power plant for 100% of their heating requirements, 50% of the cooling, and 30% of the electrical demands (peak campus load can reach 55 MW).
Of course, keeping everybody comfortable means maintaining the heat for those boilers. Before Quaker entered the picture, it was 85% coal (110,000 tons per year), plus 15% natural gas for peak and backup. With coal costs on the rise, and Quaker’s need to dispose of 350 tons of hulls per day, the company’s offer to supply oat hull biomass was more than welcome. But according to P. Ferman Milster, P.E., associate director of utilities for UI, it wasn’t as simple as just tossing the biomass into the coal.
When the project started in 2002, Quaker wanted to supply UI with Resifil, a coal substitute that is actually a byproduct of Furfural, an industrial material made from oat hulls. Quaker sold Resifil to Alliant Energy until new permit requirements forced the power generator to switch to low-sulfur coal.
The first project for the Resifil partnership was a 90-day test burn, but it proved less than attractive, recalls Milster. “The easiest experiment was to mix it in with the coal fuel stream, but we found out quickly that a small granular biomass lights off much earlier than the coal.”
Resifil has a lower ignition temperature than coal, and at a blend of 50/50 (by BTU levels, not weight), the coal feed chutes were the first to suffer due to dangerous pre-ignition heat levels. The fine black powder also had a tendency to collect moisture, making it acidic and corrosive to the fuel-handling equipment. Also, an expected drop in SO2 emissions didn’t materialize, due to Resifil’s high sulfur content. Milster and his staff decided on a maximum of 30% Resifil, and gave Quaker the nod to tackle UI’s strict requirements for dust-free loading at the plant.
Expensive pneumatic tanker trucks and vacuum loading provided a solution, but the global economy made short work of Quaker’s efforts. Cheap imports from China turned Furfural into a nonprofit product for Quaker, and the company faced the unpleasant prospect of paying for disposal of the oat hulls. With just three days worth of storage capacity for the waste, it came down to a choice of paying landfill fees, disrupting the plant’s scheduling, or finding a way to burn the oat hulls in UI’s furnaces. When Quaker returned to UI with the news, Milster and company were willing to give the oat hulls a try.
Milster wanted to take a new approach to solve the pre-ignition problem, and called in engineers from Foster-Wheeler, the boiler manufacturer. Accommodating the hulls proved to be a formidable challenge. According to Milster, the team had expanded, but so had the engineering requirements, which now included tasks to “design, procure, and install pneumatic blowers, fuel injection nozzles, transport piping and fittings, safety interlocks, and new boiler control–logic specifically designed for the biomass fuel.” If that weren’t enough, these modifications had to be done in a manner that would not negatively impact the existing coal systems.
The solution was a pneumatic fuel-injection system that put the oat hulls directly into the circulation fluidized bed (CFB) of the boiler, rather than loading them simultaneously with the coal. “We use a lean phase conveyed CFB that blows in limestone with the secondary air,” explains Milster. “Foster-Wheeler had to design a nozzle that went into the secondary air ports with sufficient velocity to actually penetrate the bed of the furnace because the hulls have got to go in and settle. It’s not like coal; it’s like burning oil or natural gas.”
Though the hulls burned like gas, they were far different in terms of volume---roughly the size of sunflower seeds, but lighter and stickier. Compared to coal, at 55 pounds per cubic foot, the hulls are 9--11 lbs per cubic foot. Happily, the injection system accommodated the hulls, but an existing coal silo couldn’t convey the sticky hulls fast enough. Again, Quaker stepped up, this time with a geometrically designed silo, a radical alternative to the traditional round shape used for coal.
After eight months of testing, the system produced impressive results in every area of performance. The efficiency improvements were especially notable, in light of the fact that the university had invested in two high-grade boilers. Boiler #11 is the circulating fluidized bed unit, installed with technology for controlling sulfur dioxide with limestone injection and a particulate-collecting bag house. Before the biomass fuel project, it consumed 60,000 tons of coal annually. The university currently purchases the hulls at about half the price for an equivalent amount of energy from coal, thus eliminating 25,000--35,000 tons of coal, and saving $500,000 annually.
Moreover, those savings were based on 2004 prices. “We’re now burning somewhere around 130 to 140 tons of coal per day,” says Milster. “Originally we estimated that we would save about $500,000, now it’s more like $700,000, because coal prices have really shot up.”
The coal comes from two sources. Fuel-bed coal out of Southern Illinois---where current supplies appear to be strong---has to be transported by truck and is vulnerable to diesel fuel prices. The university has seen prices rise 30% in two years. The stoker boiler’s coal comes from Appalachia, where prices have doubled in the last two years, with just one bidder willing to offer product.
Although the stoker boiler uses a fundamentally different combustion process, Milster and crew believe it is feasible to burn oat hulls in it. They plan to partner with UI’s College of Engineering to study the stoker boiler combustion process using computational fluid dynamics computer modeling.
All told, Milster believes the rewards for the project far outweighed the expense. “We spent a million dollars over two years,” he says. “But the project brought the College of Engineering, the administration, and the power plant a lot closer together. And we certainly had the environmental folks and students interested in what we’ve accomplished.”
For the College of Engineering, the project created a model for the University’s students and faculty, and now provides hands-on learning, plus environmental and economic performance data. The program is the basis for a case study by the International District Energy Association, and the university continues to get favorable publicity, such as its recent carbon sequestration announcement for Earth Day 2005
PHOTO: P. FERMAN MILSTER
A pneumatic fuel-injection system feeds oat hulls to the boiler's CFB.
Equally important, the success with biomass has contributed to the power plant’s momentum in upgrades and innovations. “I have been here since 1991, and I’ve seen some radical changes over the decade,” says Milster. “We have invested in automation with distributed controls and other automation devices.” Automation allows a smaller staff to operate the boilers, turbines, and other equipment with the click of a mouse from their desktops.
Milster notes that although the system requires less staff, it offers more operational data. In his early years at the university, the plant’s system would “trip” and boilers just shut down, leaving Milster and crew with many unsolved mysteries as to the causes. “Now we have the ability to go in and analyze and determine what condition caused the equipment to trip and start fixing things one at a time,” explains Milster. “It’s at a tremendous change in the reliability once people understand why the system is acting the way it does.”
The automation has proved so successful that Milster scheduled similar upgrades for pumps on backup standby boilers for steam heating. Milster also wants to increase the use of variable fans and motors for the system.
The pumps don’t run often, but Milster expects a tremendous energy savings from a minimal investment. “They have solved problems with harmonics and prices have really fallen,” he notes. “We can buy 300-horsepower motors and variable-speed drive for about $17,000. Just a few years ago, these used to sell for $100,000.”
Further out, the power plant is looking at two additions---one based on technology that’s very new, one that’s very old. On the cutting edge, plant engineers now have a solid fuel boiler in conceptual planning stages. It would be a biomass burner capable of 1,800 pounds of pressure in a topping cycle configuration. An extraction turbine would reduce pressure to 500 pounds. “The efficiency of that cycle is really attractive,” says Milster. “But we would really be pushing the boundaries for this kind of a district energy plant.”
Milster won’t have to push many boundaries for another power project. Other than quite a few tons of earth. New construction at the university’s water pumping facility has created an opportunity to revive a hydroelectric power generator that was retired in the early 1960s. The water pumping modernization will expose a pit formally used for hydroelectric power. The structure itself is still standing, and with minimal cost, hydroelectric generation could be restored with a 500-kW unit. Milster has already secured a temporary permit with FERC for the project.
The hydroelectric system would help with peak demand, but the university also favors its value as part of a renewable energy program---which brings us full circle back to the subject of Earth Day 2005. The university and the Iowa Farm Bureau used the occasion to announce “an historic transaction to help reduce the emission of carbon dioxide, a greenhouse gas.” Administrators noted that UI was the first Iowa-based commercial entity to become a member of the Chicago Climate Exchange, the multi-national and multi-sector market for reducing and trading greenhouse gas emissions. Each ton of oat hulls displaces 0.6 tons of coal, and prevents 2.5 tons of new CO2 from being created by burning coal. Along with the economic savings from an increased biomass burn rate in 2005, the university also expects to become a seller of renewable energy credits. So, ultimately, Milster says the time and money were well spent, and all parties are happy with the performance and economics of the project.
Author's Bio: Writer Ed Ritchie specializes in energy, transportation, and communication technologies.