Community asset

As communities across the country today consider options for recovering energy value from the waste stream and extending the life of their landfills, one community in Iowa had the foresight back in the 1970s to develop a system to accomplish both goals. That waste-to-energy (WTE) facility is still producing electricity today, and with a renewed contract and plans for a system upgrade, the facility is proving its staying power.

The city of Ames, Iowa, just celebrated the 40th anniversary of its Arnold O. Chantland Resource Recovery System in September 2015 and signed another 20-year agreement for the facility to continue to accept waste and provide energy to the local community.

The WTE facility, owned and operated by the city of Ames in Story County, Iowa, services 13 member organizations, including several municipalities in the county as well as the Iowa State University.

“We will have 60 years of cooperation between all these different communities of handling the municipal solid waste (MSW) from these communities and disposing of it in an environmentally sound manner,” says Bill Schmitt, the facility’s superintendent.

The resource recovery system manufactures refuse-derived fuel (RDF) from the MSW it receives. The RDF is cofired with coal in an electrical generation unit. The 55,000-ton-per-year facility employs 15 people and operates five days per week during the day and four 10-hour shifts a week at night.
 

A sound solution

Schmitt talks about the methodology behind opening the RDF facility all those years ago. “At the time, our landfill was starting to reach its capacity. We had the Oil Embargo and Oil Crisis of the early 70s, and there was some thought amongst some concerned citizens and government at that time about how we could better utilize rather than just bury our waste,” he says.

Schmitt adds, the community was not looking at becoming entirely energy independent, but to lessen its dependence on fossil fuels. “At that time they visited a facility down in St. Louis and determined that this was something that could work well for us,” he says.

RDF produced at the WTE facility is fed into the two pulverized coal boilers and the resulting steam is used to generate electricity. The RDF acts as a coal replacement and has about two-thirds the British thermal unit (Btu) value of coal. About 10 percent of the electricity generated by the city of Ames comes from the RDF.

According to Schmitt, most RDF or mass-burn WTE facilities have traveling grates, but with pulverized coal, there is a fireball in suspension with fixed grates. Therefore, the RDF needs to be able to burn in suspension, “So we have to make a fairly fine and a fairly uniform product to get the best utilization from our RDF.”
 

Quality counts

An ideal RDF product, according to Schmitt, is between 2 to 4 inches in size. To make MSW into a suitable fuel product, several steps are involved. First, material is dumped onto the tipping floor from outside haulers. It is then loaded into a primary shredder. A drum magnet pulls out the ferrous metals and the remaining material heads across a disc screen. Oversized material is separated from the grit, sand, gravel and glass. In addition to the drum magnet, Schmitt says, magnetized head pulleys are positioned throughout the facility to make sure as much ferrous material as possible is recovered.

The bottom fraction goes through an eddy current separator to recover nonferrous metals. Ferrous and nonferrous metals recovered from the separation process are sold into the secondary commodities markets. The overs are run through a secondary disc screen where the smaller material is ready to go to the power plant, and the oversized material goes through a secondary shredder for size reduction. The material is then run across an air knife for classification. Lighter material is separated out and pneumatically transferred by a 14-inch pipe to a storage bin at the power plant. Material is blown from the storage bin through an 8-inch pipe and injected into the fireball of the boiler.

“We have a wide range of equipment in here,” says Schmitt. The variety of equipment includes shredders from American Pulverizer and Komptech as well as a nonferrous recovery system from Steinert. The WTE facility is a union operation, notes Schmitt. Workers typically start out as entry-level process maintenance workers and can take classes to help them further their careers. With time and experience, Schmitt says, workers can move their way up to higher-level technician-1 and technician-2 positions. Over the years, the crew has taken much initiative.

Schmitt recalls about a year ago, the facility had a conveyor that kept plugging and jamming. “We looked at trying to source several different conveyors,” he says. Not one conveyor had all the options the facility needed in one package, so an employee suggested that the crew could build one themselves.

Schmitt says employees designed and constructed a new conveyor, removed the existing conveyor and put the new conveyor in place. “It has worked out exactly as we had hoped, and we were able to do it all in-house with the expertise they had, and they did a fantastic job with it,” he says.

Producing a quality RDF for the boilers starts with getting quality materials coming into the facility. For example, the city of Ames has worked to keep organics out of the waste stream, since its moisture content is not ideal for the RDF process.

“For us trying to create a product that will burn in suspension, the organics are not a beneficial product for us to utilize in our system,” Schmitt says.

To reduce the amount of organics entering the WTE facility, the city of Ames has worked with area grocery stores and Iowa State University to send their source-separated organics to a local composting firm, Chamness Technologies, rather than the WTE facility. “So it is working in cooperation with our customers to make sure that we are able to get the best recovery from product that comes in our doors,” Schmitt explains.

Residuals from the RDF facility are landfilled. Reducing the amount landfilled is a priority for the facility. One of the variables in the waste stream is the student population at Iowa State University. The population of the city, which is about 60,000, increases by 30,000 when school is in session.

Students moving into or out of town “can be very taxing on the waste stream,” says Schmitt. Also, many less than desirable materials for producing RDF can show up at the facility, namely textiles and furniture. To address this, Schmitt says the city has worked with the university to try to separate out material that is not beneficial to the WTE facility.

The city and the university have been working together on developing a swap or garage sale where students can donate items when they move out that other people can buy “to divert material from landfill and raise awareness on reuse and recycling rather than just putting it on the curbside and getting rid of it,” Schmitt explains.

The city also initiated a glass recycling program several years ago because glass would cause slag buildup in the boilers. Schmitt says the program has been very well received and the facility is recovering about 180-190 tons of glass out of the system, which is sent to Ripple Glass in Kansas City, Missouri.

Since the WTE facility was founded, 1.3 million tons of material have been diverted from landfills. Schmitt says, that may not sound like a lot in comparison to some larger facilities, but it is still significant. “We are a very small facility, but we handle all of our material here locally so that is a beneficial and environmentally sound way of managing it for us.”
 

Changes on the horizon

Big changes are underway for the city of Ames’ electric generation boilers. The power plant is going through a conversion from coal to natural gas, due to new requirements from the U.S. Environmental Protection Agency. The city is in the process of taking one of the two boiler units through that conversion, which is expected to take about three months.

Schmitt says the facility will have a better understanding of how the conversion will affect operations after the transition is complete. “We can see what the fuel will look like and how it will react with the natural gas.” The second boiler will be retrofitted to natural gas as soon as the first one is complete.

Schmitt knows cofiring RDF with natural gas is a unique situation, “We are not aware of anyone else cofiring RDF with natural gas,” he says. “We will kind of have to do some on-the-fly kind of adaptations and make sure we can improve the product and get it into the best quality fuel that can be recovered.

Other RDF facilities sell their material to a separate end user, but the arrangement in the city of Ames works well, according to Schmitt. “With us it has been nice to have the symbiotic relationship both being owned by the same organization,” he says.

Schmitt has a great appreciation for the pioneering vision his predecessors had to develop the WTE facility well before the era of curbside recycling or the mantra of “reduce, reuse recycle.” “It was nice to know that they were that forward-thinking at that time, to embrace it and to utilize the technology that was available and then to continue to grow with that technology as time progressed.”

Schmitt has been with the city of Ames’ WTE facility for three years, first as assistant superintendent and the last eight months as superintendent. He says his business philosophy is to engage all parties involved to help make them part of the process. “We are not here to tell people how to do things, we are here to help them accomplish their goals.”

He adds, I’ve always been pretty passionate about environment and sustainability. This was a real good fit to be able to put those passions into play every day. The crew we have here is very professional, dedicated and fun to work with. It is nice to work with a group of people with like minds who have a common goal in mind to make sure the citizens’ needs are met and to do it in a cost-effective means.”

As for the future, Schmitt says the facility and the city will continue to look at upgrading its processes and increasing our recovery rates. “We will continue to keep abreast of industry standards and options that are out there. We want to be responsible, we want to be sustainable and we want to have local solutions.”

The author is editor of Renewable Energy from Waste and can be reached at ksmith@gie.net.