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Olmsted Waste to Energy facility burns waste for savings

1213by Bill and Mary Weaver

Olmsted County, MN is now reclaiming space at their Kalmar Landfill. At the same time, they are making money from electricity and steam heat produced by their Olmsted Waste to Energy Facility (OWEF). They also glean profit from the sale of recovered ferrous metal that they salvage from the ash.

The choice facing county commissioners was either to open a new MSW cell and purchase a compactor for about $1.7 million, or to wend their way through the permitting process to expand their currently undersized Waste to Energy Facility, which had come online in 1987. Expansion would involve significant capital cost. In addition, if the expansion was undertaken, the County would need to purchase a shredder and screen at significant cost to handle bulky items and mined clean MSW.

They chose to apply for a permit for a new 200 Tons per day (TPD) burn unit, effectively doubling the capacity of the facility. Construction of the new burn unit was greatly simplified because when Olmsted County built their first two 100 TPD burn units, they had wisely built OWEF with more storage capacity than was currently needed. They prepared for the growth of the surrounding communities and the waste material that would eventually result from the new residents.

The pit where the waste was stored was to be far larger than needed at the time. The pit holds 2,000 tons, even though the two current burn units together could only handle 200 TPD. “So when we added the extra 200 TPD burn unit, all we had to do was put in the hopper for the new unit. We put the new unit on the back of the currently existing ones,” said John Helmers, director of Environmental Resources.

As construction began on the new burn unit, workers maintained two separate faces at the landfill. There, they separated the contaminated industrial waste from the clean MSW. The county planned use the MSW for fuel once the new burn unit was brought online in 2012.

Although the effort was considerable, workers sorted the material until the new burn unit came on line. “We maintained two separate faces at our landfill for over four years,” said Matt Anderson, OWEF plant engineer. “That effort has really paid off because of the fuel value of the clean MSW.”

The OWEF is a mass burn facility. “We take solid waste from households, the front end of businesses, and a little bit of industrial waste. Sixty per cent of the waste that is generated is recycled,” explained Helmers. “Of the amount not recycled, all but five percentg is burned to produce electricity and steam,” added Anderson.

“Before the expansion, we bypassed the WTE facility two to three days a week,” continued Anderson. “In 2014, we only had to bypass it 12 days total because it was operating at full capacity. That unused MSW was not permanently landfilled, and we’ve recovered it since.”

“We’re now recapturing landfill space,” added Helmers. “The goal is that we won’t have to go outside the permitted Kalmar area.” This is important, because much of the surrounding area has karst topography with fractured bedrock that makes it very difficult to site a landfill.

Anderson added, “The site was selected after a siting study due to the depth of the bedrock (>100-foot) and the low permeability of the onsite clay that acts as a natural liner below the engineered liners. With the three burn units, it should be well into the 2030’s until we have to expand into a new cell. That cell, which will still be in the permitted area, should last well into the next century. After that, we also have a currently unpermitted area at the same site.”

“We had been landfilling 40,000 tons per year. In 2013, we landfilled less than 8,000 tons,” Helmers added. “So far with the landfill recovery operation, the county has reclaimed space for 30,000 tons of waste!”

Energy production

The electricity to run the WTE Facility 1-1/2 megawatts,” explained Anderson. “The total we can generate is 9-1/2 megawatts. The other units, boilers and turbines produce steam and electricity respectively, for a considerable number of county and city buildings.” The steam heat is distributed using an underground steam heat tunnel system that was unused when the WTE Facility was built.
Some of the steam can also be used to create air conditioning. “Twenty seven county buildings use tax revenues to pay for their steam and electricity,” commented Helmers.  The County Commissioners have been very supportive in providing us the funds we need to maintain and run the facility properly,” he added.

The environmental and air quality benefits of the facility are dependent on its being well maintained and operated. “For example, all three burn units emit less than a pound of mercury per unit per year,” said Helmers. “According to the EPA report on greenhouse gases, the facility is preventing the emission of large amounts of these gases, both compared to a solid waste landfill system which emits landfill gases, and by producing heat and electricity from the MSW. This process produces smaller amounts of greenhouse gases than if coal or oil were burned. We are into the negative numbers on greenhouse gas emissions.”

MSW contains more BTU’s than most people realize. According to Helmers, a 30 gallon garbage can of compacted municipal solid waste contains 247,500 BTU’s, about equivalent to 20-pounds of bituminous coal, or 2.7 gallons of propane.

Mining the landfill

The separate face of the landfill where the clean MSW was stored for more than four years is now being deconstructed and mined for the BTU’s it contains. After it’s mined, the waste is fed into a Doppstadt Slow Speed Shredder.

They chose this unit after Doppstadt U.S. allowed a two week trial on site through the Hayden-Murphy Equipment Co. It was delivered in early 2012 and was followed by a Doppstadt SM 726 trommel. The Doppstadt DW 3060K is designed to operate at a slow 34 RPM, with a high torque, single shaft tooth and comb design.

The mined or bulky MSW goes from the shredder to a 1-1/4-inch Doppstadt Trommel Screener, which is used with two sizes of trommel screens: 5/8-inch to remove the fines from the ferrous metal recovered from the ash and 1-3/4-inch to remove metal from shredded MSW before it is transported to the burn units.

The Doppstadt Shredder has also been useful for efficient handling of an item that is the bane of landfill operators everywhere: mattresses. After the mattresses are shredded by the Doppstadt into pieces less than 10-inches in size, the material makes great fuel for the burn units, as do old carpets, carpet padding and upholstered furniture. All of these are also shredded by the Doppstadt.

“Fort McCoy disposed of 3,800 mattresses here,” said Carl Struckmann, who heads the crew at the landfill. “They dropped off one to two semi loads of mattresses a day, and we shredded them as fast as the workers threw them off the truck.”

The ash generated by the burn units is removed on a vibrating conveyor at the bottom, and has been stored in dedicated landfill cells. It is possible the ash may not be stored in the landfill in the future.

“We’re exploring uses for bottom ash,” continued Helmers. “In Europe, it’s used in roadways as base material and to replace aggregate in asphalt and concrete. In fact, Polk County MN is now permitted to use bottom ash in roadway construction.

County officials believed when the new burn unit came online that they had about four years’ worth of stockpiled fuel to mine and burn for energy until they would be down to burning just the MSW that comes in each day, providing the capacity to accommodate growth in the area. There are no plans to mine a larger area because of the proximity to possible asbestos and contaminated industrial waste, which could pose health hazards.

The Kalmar Landfill is operated by five workers, and they hustle. “Although we have curbside recycling, about five percent of the metal is removed at the landfill by workers before the MSW is burned,” said Anderson. Loads that contain metal are dumped on the ground at a specific area, and the operator jumps off his machine and picks out the larger pieces of metal, stockpiling them temporarily in a large dumpster.

Objects containing metal are disassembled when necessary. “We have a fee schedule for that,” explained Struckmann.

The recovered ferrous metal is currently contracted to CIMCO Resources, with the option to renew every year. Eighty percent of the ferrous metal that goes through the burn unit is recovered by sifting through the ash using an excavator with a magnet on the bucket. The metal brings a higher price if it has first been screened. The money received from the sale of that metal is on track to pay for the capital improvements to the facility in only a few years. The cost per household for garbage service in Olmsted County is about $30 a month, similar to the cost in areas that landfill only.

The secret of Olmsted County’s success

Why is Olmsted County’s Facility succeeding in paying for itself and more, while other WTE facilities have bankrupted both themselves and their municipalities? John Helmers stated the reason clearly. “Our board has kept the WTE Facility and the other parts of the county’s integrated solid waste management system as an enterprise fund, separate from other city and county moneys.” This is something other facilities should emulate. “Keeping it as a separate enterprise ensures that adequate resources are available to maintain the facility and operate it at a high standard.”


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