In the first of this series of articles on emerging trends toward integrated systems of waste management (MSW Management, June 2012), we spotlighted plans by both the city and county of Los Angeles to utilize waste conversion to clean energy technology (WTCE) to help reduce landfill volume, meet state diversion regulations and mine the energy potential of the MSW stream. Although, when completed, these projects will be among the first of their kind in the United States, the fact is that biological and mechanical conversion technology has been available on a commercial scale and has been used in Europe and Asia for over 20 years.
It has been reported that in the European Union, 70 conversion technology facilities that treat biowaste or MSW were installed between 2006 and 2010, bringing the total to approximately 200 facilities in 17 countries for an expected combined capacity of 6 million tons per year. The movement toward conversion of solid waste into energy, fuel and other products is in response to Europe’s high-density population, which makes siting landfills problematic, dwindling natural resources and high energy costs, along with high tipping fees (regulatory fees in the European Union can drive the cost of landfill disposal up to a reported $200 per metric ton), international climate change initiatives and landfill bans against unprocessed waste and materials that may contain energy value.
In Japan, 80% of nonrecyclable waste is currently either incinerated or gasified in community-based facilities that combine locally controlled solid waste management with electricity generated for local use. Japan, which has faced problems similar to Europe’s in regard to managing solid waste, has in fact become a leader in the kind of thermal conversion technology that figures in the installations that are being planned for Southern California or that are in development or commercial operation elsewhere in North America.
While thermal and biological conversion technologies are effective and well established-and over 30 emerging and developmental technologies are working their way into the marketplace-the US currently has no statutory incentives such as federal or state regulations against landfilling organic waste, and communities investigating these options often come in through the back door, seeking alternatives for dwindling landfill space and high electricity costs or under mandates to generate renewable energy in states like California. The city of Los Angeles, for example, will divert energy from the its planned WTCE facilities to the Department of Water and Power to help the agency meet the state’s 20% renewable energy goal.
What Are We Talking About?
Good question. While definitions have been technically established, general terminology is far from standardized. The City of Los Angeles Bureau of Sanitation includes traditional mass-burn/incineration technology under the banner of alternative technology and uses the term advanced thermal recycling to differentiate newer generation mass-burn/incineration facilities from older 1980s technology. The Los Angeles County Department of Public Works Alternative Technology Subcommittee defines conversion technology as any technology capable of converting post-recycling residual solid waste into useful products and chemicals, including green fuels like ethanol and biodiesel, and clean renewable energy. Although the county’s definition doesn’t specifically exclude mass-burn technology, Southern California’s tough air quality requirements have resulted in a focus on non-incineration.
According to international WTCE consultant Eugene Tseng, the types of WTCE technologies in most common use to date can be classified into three broad categories: 1) thermal; 2) biological/biochemical; and 3) what he describes as secondary manufacturing, which is the use of specific components of the mixed-MSW stream to manufacture new, value-added products. Instead of recycled glass being used to manufacture new glass containers, for example, it is fabricated into completely new products such as foamed glass or glass/ash bricks and tiles for construction. (A similar approach is on the docket for the city of Lancaster in Los Angeles County).
Thermal technologies, which include fluidized bed gasification, gasification, and gasification/plasma, use high heat (greater than 700°C) in an oxygen-deficient environment to convert the organic fraction of a wastestream into fuel gas, primarily carbon monoxide, hydrogen, and methane, which can then be used to produce electricity and heat via a steam boiler and turbine plant, gas turbine, fuel cell, or an internal combustion engine or generator. Syngas can also be used to produce fuel products and other chemicals by chemical reactions such as Fischer-Tropsch synthesis. Feedstock is typically low-moisture organics such as paper and other carbon-based materials, including not-readily-decomposable plastics and rubber, industrial biomass waste products, and, sometimes, sewage sludge.
In Westbury, QC, for example Montreal-based Enerkem has constructed a demonstration-scale, 1.3 million-gallon-per-year thermal conversion facility that will convert treated wood from used telephone and electricity poles to biomethanol and, eventually, cellulosic ethanol. Locating the installation close to a sawmill that recycles the used poles assures the operation a regular supply of feedstock. The same company recently signed a 25-year agreement with the city of Edmonton to build and operate a facility that will produce and sell biofuels from non-recyclable and non-compostable municipal solid waste. The city has committed to supplying 100,000 dry metric tons of sorted MSW per year, and expects the project will increase its residential landfill waste diversion rate to 90%. The installation is scheduled to begin operations in 2013. In this country, Enerkem has entered into an agreement with the Three Rivers Solid Waste Management Authority of Mississippi to site a facility at a landfill to sort material and convert the post-recycled portion into ethanol. According to Enerkem, the installation has received $50 million from the US Department of Energy and conditional commitment for an $80 million loan guarantee by the US Department of Agriculture (USDA).
According to the Bioenergy Producers Association, other thermal conversion projects in this country include Silva Gas, which used woody biomass from an adjacent C&D landfill as feedstock for a WTCE demonstration plant in Burlington, VT, and the Coronal WTE Project, undertaken in partnership with the Koochiching Minnesota Development Authority, which will convert MSW, woody biomass, and sludge from a wastewater treatment plant to synagas that will be directed to a neighboring sawmill, enabling it to significantly decrease its consumption of natural gas. In Columbus, MS, Kior Inc. has begun construction on its first commercial-scale facility, which will produce syngas and diesel blend stocks from southern yellow pine woody biomas, the site chosen in part for its proximity to abundant locally grown feedstock, and will process 500 bone-dry tons of sustainably harvested biomass a day to produce an annual 11 million-plus gallons of gasoline, diesel and oil blend stocks. A second, larger facility planned for Natchez, MS, will process 1,500 tons of feedstock a day-three times the size of its sister facility-planned to take advantage of the economies of scale.
And in Vero Beach, FL, ground has been broken for the Indian River Bioenergy Center, a joint venture between INEOS Bio and New Planet Energy. The $130 million facility will convert yard, vegetative, and household waste into what the company says will be the first facility to commercially produce cellulosic ethanol in the US plus 6 MG of renewable power, 2 MG of which will go directly to the local community. The federal DOE and Department of Agriculture and the state of Florida have provided support in the way of incentives and loans.
Thermal Conversion Versus Mass Burn
It’s important to distinguish non-combustion thermal technologies of the type being used in these projects from the kind of mass-burn incinerators that originated in Europe, where some 400 combustion-based energy plants are reported to consume 55 million tons of MSW annually, many in large-scale regional facilities. In mass-burn installations, heat is generated by direct combustion, and no useful intermediate fuel gases, liquids, or solids are generated. The drivers are volume reduction (typically 10 to 1, but up to 20 to 1 depending on the feedstock) and electricity (produced in boilers and steam-driven engines or turbines). And although no preprocess sorting is required, mass-burn technology may produce as much as 30% to 35% ash, which then must be disposed of. In Japan many of the newest thermal gasification facilities have in fact been designed to reprocess the inorganic bottom ash from incinerators into a glassy slag that can be used as building material. Currently in the United States, 80 mass-burn facilities consume 30 million tons of MSW a year (but without the benefit of conversion technology to process the combustion waste).
Biochemical conversion processes include aerobic conversion (composting), anaerobic decomposition, which produces a biogas containing mostly methane and carbon dioxide that can be burned directly for heat or steam or converted to electricity, and anaerobic fermentation, which converts cellulose-derived sugars to ethanol. The biogas produced can be upgraded to biomethane and used as a vehicle fuel or injected into the natural gas transmission system or reformed into hydrogen fuel. Feedstock for both anaerobic digestion and fermentation includes readily biodegradable components including foodwaste, greenwaste, paper, etc. Plastic and rubber have to be sorted out, along with woody and ligneous materials.
Currently there are no such commercial facilities operating on MSW in the United States, although the same type of anaerobic digestion systems are in use in wastewater treatment plants. For example, the Orange County Sanitation District and the US Department of Energy are currently involved in a three-year demonstration project at the district’s Fountain Valley wastewater treatment facility to use biogas from its digesters to fuel a fuel cell from Fuel Cell Energy. The trigeneration facility generates 250 kW of electricity, heat and hydrogen, which is then used to fuel a fleet of hydrogen-fueled automobiles, enough for 25 to 30 fill-ups of county vehicles a day.
A review of WTCE facilities worldwide suggests a number of design and operating principles.
First, the design and technology selected must be compatible with the priorities and purpose established for the project, which in turn must be balanced against available feedstock. For example, to achieve optimum results in a thermochemical conversion technology, materials such as glass, metals, and ceramics should be eliminated. However, if the goal of a project is maximum landfill diversion, these materials would likely be included in the feedstock, along with additional non-optimal materials such as sewage sludge and/or bottom ash from other facilities, despite the fact that these will predictably reduce fuel value, require additional blending and mixing procedures, and result in additional bottom and fly ash that will require additional technology for conversion into a useful product.
One solution for situations where project goals may be in conflict would be to combine a range of thermal conversion technologies, each with its unique processing advantage. Likewise combining an incinerator with a gasifier would accommodate the need for flexibility in feedstock material while allowing for maximum landfill diversion through the vitrification of the ash with the gasification technology (keeping in mind the facility would then require the installation of two processing lines).
Second, because each type of technology has a preference for particular components in the mixed MSW stream, and depending on the level of source separation of recycles, there will be requirements for various amounts of preprocessing in order to optimize the feedstock and produce a high-quality product that needs no further processing. In this kind of scenario, materials such as plastics, which would be considered non-processable in biochemical or biological conversion technology, would be sorted out as an ideal source of high-fuel content feedstock for gasification. The value of preprocessing shouldn’t be underestimated, because it will not only improve the reliability of overall system performance, but in thermal gasification conversion technology projects, emissions will be improved. The trend in preprocessing is toward automation and continually more sophisticated technology that can separate out smaller and smaller bits of material. In this same way, emissions of heavy metals such as mercury can be reduced by removing components of the trash stream that are the sources of the metals.
Finally, preprocessing provides an opportunity to recover additional recyclables such as ferrous and nonferrous metals, glass, etc. While these don’t contribute to the energy value of the feedstock, they do have marketable commodity value as a recyclable raw material.
Ancillary to these considerations is that various types of technology can be assembled in ways that are mutually beneficial to each other. For example, a project could use a thermochemical process on a high-fuel value portion of the processed wastestream in combination with a biochemical process on the high-moisture, readily decomposable, and compostable portion of the wastestream, or a facility that uses thermal gasification of MSW to produce synthesis gas in the first stage could then use this as a feedstock in a biochemical process to produce ethanol in the second phase. The rationale for this type of integrated approach is to treat each fraction of the wastestream as efficiently as possible and thereby obtain maximum value.
Which is another way of applying the fourth principle of conversion technology, which is the highest and best use of all materials, the ideal being an integrated materials recovery facility that combines source-separated recycling with additional materials recovery preprocessing, followed by biological conversion technology and, at the end, energy recovery. Such an operation has the combined benefit of maximum landfill diversion and the highest rates of traditional materials recovery from recycling, with clean energy generation effectively a byproduct.
Integration and Ecoparks
The trend within the European Union and in Japan has in fact been development of integrated facilities that process not only post-recycled MSW, but greenwaste, construction-and-demolition waste, and sewage sludge combined with the necessary facilities for secondary manufacturing. Such an approach is in operation in the regional-scale integrated facility that serves the city of Marseille, France, and its surrounding cities and communities. The first step is the recovery of additional recyclables from the mixed waste stream and processing of the residuals into an organic fraction for anaerobic digestion, which produces biogas, and a processed engineered fuel fraction that is used as feedstock for thermal conversion for energy recovery. Source-separated greenwaste is separately composted or can also be anaerobically digested with or without foodwaste.
A variation on this approach will be used in the city of Palmdale, CA, which will forego source separation of recyclables in favor of a single mixed stream that will be separated onsite in a sophisticated MRF capable of separating 20 different materials, including hazardous and medical waste and divert it to the appropriate type of conversion technology, leaving residuals to be remanufactured onsite.
Assembling the Components
According to Tseng, the capital cost estimate for developing and constructing an integrated waste management facility, including the required preprocessing MRF to optimize feedstock and a combination of anaerobic digestion and thermal conversion technologies to generation electricity, can range between $350,000 and $1 million per ton per day of throughput capacity, depending upon the size and the types of technologies utilized, and not including the cost for land. Generally speaking, facilities at 1,000 tons-per-day or greater input tonnages are considered to be at a level where economy of scale makes a difference. Based on budgetary estimates from various project developers and case studies of existing facilities, and again depending on the size of facility and the mix of selected conversion technologies, Tseng estimates operational and maintenance costs at $150 to over $200 per ton for an integrated MRF that includes anaerobic digestion and thermal conversion technology.