Modified fuel might be answer for UMM gasifier
By Tom Larson
After months of trying to figure out how to change its unique biomass gasifier to operate using corn stover as fuel, University of Minnesota, Morris officials are trying instead to change the fuel to fit the burner.
A test burn of UMM's experimental biomass gasification system is scheduled for later this month using dense, compressed biomass "logs." If the experiment is successful, not only will the system be ready for every-day use, a new biomass industry could be spawned.
Officials hope that the new fuel adaptation will solve nagging problems that have kept the gasifier from providing steam for heating and eventually cooling campus buildings, and has kept the community wondering what's happening with a million-dollar system that was expected to be on-line last fall.
"The community has been patient but curious," said Lowell Rasmussen, UMM's Vice Chancellor for Finance and Facilities. "What are we running? What are we doing? This has generated a lot of interest, but it's still a research project."
The $9 million project is intended to offset 80 percent of UMM's fossil fuel needs and help the university meet its goal of being energy self-sufficient and carbon neutral by 2010.
But when the system was fired up last fall, operators learned that gasifying loose stover posed substantial problems.
A Walking Trailer moves the stover into the burner, where air is blown through from the bottom of the burner for combustion.
But the loose stover has a density of three pounds per cubic foot and the air moved it around in the burner and created a hole in which all the air would move through instead of maintaining a steady flow, Rasmussen said.
Most solid fuel gasifiers burn heavy density wood at a temperature of about 3,000 degrees, and the ash produced can only be used for limited purposes, such as wallboard.
UMM's goal is to create the first gasifier that incinerates the fuel temperatures of 1,000 degrees or lower, producing gas that can be used to create steam for UMM's system while also preserving minerals in the ash so it can be used in soils.
"A critical part of the project from day one was making ash that could be used as a soil nutrient," Rasmussen said.
But operators were unable to keep a consistent and even bed temperature, and modifications to the burner proved ineffective.
"Fuel-flexible gasification is more difficult than it seems," Rasmussen said.
"That's the fun of being first," said Jim Barbour, of UMM's Plant Services department.
Unable to work out ways to alter the gasification system, operators turned to altering the fuel.
They worked with a company in Emily, Minn., to compact the stover into a form similar to compressed sawdust fireplace logs. The new stover "logs" have a density of 50 pounds per cubic foot compared to the three pounds per cubic foot of loose stover. The density is expected to help the fuel remain in place in the burner and even out the heat and air distribution in the gasification process.
The first stover logs are several inches long, but they eventually could be cut down to roughly the size of hockey pucks.
"It behaves more like wood and gasifiers are used to handling wood," Rasmussen said.
There are costs with the process, but potential benefits, as well, said Joel Tallackson, Biomass Gasification Coordinator for the West Central Research and Outreach Center.
For example, a full load of stover transported to be compressed at the plant in Emily came back taking up about one-fifth of the space in the trailer, Tallackson said.
"It's too early to tell because this is a prototype," Tallackson said. "But if we can have five semis of stover in one, we should be able to see a gain on transportation costs and fuel."
Rasmussen said that if the new fuel stock works well, it could create business opportunities in the area.
"If we can economically densify, now we're on an equal footing with anyone in the forest products area," he said.
UMM has about 12 tons of the compressed stover logs, and wants to gasify about 80 tons in the July test burn.
Despite the setbacks, interest in the technology and the process remains high. There are about $4 million worth of grants from federal and state agencies and individual patrons waiting on the research, Rasmussen said.
"The manual isn't written on how to do this stuff," he said. "We'll probably be the authors when this is done."