Stiliana Georgieva

Waste-to-energy (WTE) technologies have been regaining popularity of late. In addition to meeting the continuously increasing electricity demand, WTE power plants divert municipal solid waste (MSW) from landfills, helping some municipalities increase diversion rates and ultimately decrease greenhouse gas emissions.

Diversion of materials from landfills and reduction of greenhouse gas emissions have been primary goals for both the United States and the rest of the world. According to 2009 statistics from the U.S. Environmental Protection Agency (EPA), Americans generated 243 million tons of MSW, including but not limited to paper and paperboard, yard trimmings, plastics, food scraps, metals, rubber, leather, textiles, wood and glass.

According to EPA, 82.02 million tons of that material were recovered through recycling. However, that left 66.2 percent of the waste stream unrecovered. According to EPA studies, nearly 12 percent of that unrecovered waste was used in waste-to-energy systems, while the remaining 54 percent was disposed in landfills.

Waste-to-energy systems can help address multiple global issues, including eliminating the need for additional landfills, reducing carbon dioxide (CO2) and methane emissions, and satisfying the projected 2 percent increase in electricity demand in 2012.

As stated in the Journal of Environmental Engineering, waste-to-energy negates approximately one ton of greenhouse gas emissions for every ton of MSW processed through the avoidance of:

While all waste-to-energy technologies offer some environmental benefit, certain systems, such as conversion technologies, provide the most. When taking into account overall efficiency, sustainability and financial feasibility, conversion technologies, including pyrolysis, gasification and plasma arc, are considered the most advanced.

Winning Converts

In 2008, after a decade-long study, the County of Los Angeles Department of Public Works published a fact sheet that illustrated the environmental superiority of conversion technologies over traditional solid waste management practices, such as landfilling. Among the report’s key findings was that conversion technologies are capable of complying with the most stringent air emissions standards. In addition, it showed that in operation these technologies produce dioxin and furan emissions in amounts far below EPA limits. It’s arguable that these systems actually make air cleaner by offsetting emissions from other sources.

In the same report, the California Air Resource Board’s Economic & Technology Advancement Advisory Committee (ETAAC) states that, “By conservative estimates, conversion technologies have the potential to reduce annual greenhouse gas emissions by approximately five million tons of CO2 equivalent in California alone.”

According to the U.S. Department of Energy, approximately 44.6 percent of all electricity used in the United States in 2009 was derived from coal combustion. Close to 11 percent was obtained from renewable sources, such as biomass (including wood and waste), solar, wind and geothermal.

Coal has the highest carbon intensity of all fossil fuels, which means coal-fired plants have the highest output rate of CO2 per kilowatt hour. As a result, emissions from coal combustion for electricity account for nearly 32 percent of the total U.S. CO2 discharge.

Conversion technologies are expected to grow significantly in the next five to six years. The U.S. Department of Energy’s 2010 Worldwide Gasification Database shows 144 operating plants with a total of 412 gasifiers in operation and a current gasification capacity of 70,817 megawatts thermal (MWth) of syngas output. Nine of the 144 gasification facilities use biomass/waste as feedstock and are operating successfully in Asia, Australia and Europe.

Gasification conversion technologies are located in 29 different countries around the globe. Asia and Australia lead the market with 37 percent of the total operating capacity. There are currently 37 gasification facilities operating in North America. The DOE’s National Energy Technology Laboratory predicts North America will lead the world’s regional growth with an 63 percent increase in capacity by 2016, which means the United States will see a significant increase in the demand and supply for gasification systems.

Additionally, conversion technologies surpass traditional WTE in their ability to integrate with optimal recovery of recyclables before gasification takes place. An example of such a facility is the Oneida Energy in Green Bay, Wis. Final approvals for the plant from the Wisconsin Department of Natural Resources and DOE are expected in May, with construction set to begin on June 1. A conditional use permit has already been approved. The plant is slated to be fully operational by December 2011.

The proposed facility will receive 150 tons of MSW per day from local municipalities, acting as a materials recovery facility on the front end and using gasification by pyrolysis on the remaining waste to create product gas and generate five megawatts of electricity per hour.

After the material is received and dumped inside the 65,000-square-foot building, it will be placed in a shredder by a grapple hook. As the material moves down a conveyor, overhead magnets will remove all of the steel and aluminum. A ballistic separator will divide material into two separate lines, where two-dimensional materials (paper, cardboard, plastic sheets, etc.) and three-dimensional materials (bottles, coffee cups, and other items that “bounce”) will be hand sorted into different types of recyclables. Non-recyclable materials will be recombined and run through a second shredder. The resulting material will be placed in metering bins and conveyed to the pyrolytic gasification equipment.

The processed MSW is fed into the gasifier and heated to 900 – 1,400 degrees Farenheit. The created gas is cleaned and processed, after which it is compressed and sorted in reciprocating engine generators for future use. The gas is used to fuel electric generators, which discharge that electricity onto the local distribution grid.

This conversion technology to be used at the Oneida Energy facility demonstrates 365, 24/7 operation of continuous-feed gasification in a closed-loop system. Additionally, it will produce clean, high-quality gas, reduce landfill consumption by 85 percent, decrease greenhouse gas emissions, increase recycling rates, and yield three or more potential revenue streams.

The operator of the facility will not only produce electricity, while diverting MSW from landfills, but also be energy self-sufficient and obtain a significant return on investment from tipping fees, sale of recyclables and sale of electricity.

While still developing, conversion technologies represent a promising solution to many of today’s most pressing global problems, including waste management, recycling and electricity generation. They also make economic sense. This is why they are expected to make significant inroads in the United States and the rest of the world in the next five years.

Stiliana Georgieva works as director of marketing and business development at Dae Sung Alliance LLC and Alliance Construction & Design. The firms specialize in advanced waste-to-energy systems, specifically conversion technologies, such as pyrolytic gasification.

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