Waste as a Renewable Source of Energy - CiteSeerX

Proceedings of IMECE’03 2003 ASME International Mechanical Engineering Congress & Exposition Washington, D.C., November 16-21, 2003 IMECE2003-55258

Waste as a Renewable Source of Energy: Current and Future Practices Karsten Millrath and Nickolas J. Themelis Earth Engineering Center, Columbia University and Waste-to-Energy Research and Technology Council, New York City Keywords: Waste-to-Energy, Combustion, Municipal Solid Waste, Integrated Waste Management, Renewable Energy

Abstract Municipal Solid Waste (MSW) has been recognized by several states as a renewable source of energy. Worldwide, about 130 million tons of MSW are combusted annually in waste-to-energy facilities that produce electricity and steam for district heating and also recover metals for recycling. While being linked to environmental pollution prior to the implementation of Maximum Available Control Technology (MACT) regulations, Waste-toEnergy (WTE) was recently named one of the cleanest sources of energy by U.S. EPA However, the WTE industry often faces resistance and preconceptions based on past experience rather than current performance. Due to economic considerations that do not include environmental benefits, most of the U.S. MSW still ends up in landfills despite the fact that for every ton of MSW landfilled greenhouse gas emissions increase by at least 1.2 tons of carbon dioxide. While implemented research and development strategies focused on emissions, there is still a tremendous need for more efficient yet durable combustion technologies including flue gas recirculation and oxygen enrichment, environmentally and economically competitive reuse options for WTE residues, and also public education. The importance of WTE in the universal effort for sustainable development and its need for research and development resources has led to the formation of the Waste-toEnergy Research and Technology Council. Its principal goal is to improve the economic and environmental performance of technologies that can be used to recover materials and energy from solid wastes. This paper provides an overview of the current worldwide

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Copyright © 2003 by ASME

WTE practices, predominant technologies, and current research for advancing WTE as a renewable source of energy in the U.S. and elsewhere.

Waste as a renewable source of energy In the traditional sense, renewable sources of energy are those that nature can regrow, such as wood, crops, or other plants (biomass), that are available through the Earth’s unique physical set-up, such as wind, water, and solar radiation. However, the term biomass often includes one manmade good that is the byproduct of industrialization: waste [1]. The U.S. EPA repeatedly called MSW renewable. Although it is desirable to minimize the amount of waste during production and distribution of goods, it is almost certain that a minimum quantity of waste will be generated. Because it is believed that the global community will continue to produce industrial products, there will be a continuous stream of new waste, which therefore could be considered to replenish the previously generated garbage. After its generation waste has to be managed appropriately. In the past, the dominant technique to deal with the waste stream was the disposal or dumping in landfills, either controlled or without any regulation. It was soon realized that the waste dumped would turn the land into unusable space and means to reduce the MSW volume were sought. Waste was incinerated or separated into different fractions that could be reused directly or treated to become reusable. At some point, it was recognized during combustion energy was generated and first waste-to-energy plants were established. While the energy demand has grown rapidly since the beginning of industrialization, the environmental impacts of our consuming society started to be investigated mainly in the second half of the 20th century. Incineration gained a negative image through toxic air emissions and become less favorable. Fossil fuels have remained the dominant means of generating energy. Today, many authorities and the respective communities are very aware of MSW problems and seek environmentally acceptable solutions in integrated waste management approaches that include source reduction, recycling, composting, combustion, and, least desirably, landfilling. The U.S. EPA [2] made an effort to quantify the energy benefits for various MSW management options. The net energy savings for selected materials are summarized in Table 1. It can be seen that source reduction and recycling are very effective

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for materials that require energy intensive processes during manufacturing of goods from virgin resources. Improving the efficiency of energy generation during waste-to-energy processes would result in higher savings. However, environmental effects and costs for land use, transportation, collection, separation, and cleaning (if required) also have to be considered for inclusive comparison. Table 1:

Net energy savings for various MSW management options in million BTU/ton (after [2]) Material

Landfilling

Source reduction*)

Newspaper

0.00

31.93

17.01

3.35

Corrugated cardboard

0.00

18.77

13.51

3.02

Textbooks

0.00

35.38

1.52

2.91

Lumber

0.00

3.93

-0.07 (loss)

3.48

Fiberboard

0.00

11.71

-0.36 (loss)

3.48

Polyethylene (HDPE)

0.00

24.60

19.52

7.19

PET

0.00

35.38

22.73

3.99

Glass

0.00

7.02

2.66

0.45

Aluminum cans

0.00

103.78

185.52

0.41

Mixed MSW

0.00

*)

Recycling

Combustion

Does not apply

2.30

Source reduction mostly refers to multiple usages of products. The above numbers account for new material produced with some recycled inputs (current practice).

In Addition, the data from the U.S. EPA [2] suggest that the 2.3 million BTU for every ton of MSW that is combusted rather than landfilled translate into net energy savings of 16.5 gallons of oil. Assuming an efficiency of 0.33 during the generation of energy from oil, the combustion of one ton of MSW results in saving approximately 50 gallons of oil. EPA reported for 2000 a composition of the 232 million tons of MSW as follows [3]: •

37.4% paper (86.7 million tons)

•

12% yard trimmings (27.7 million tons)

•

11.2% food scraps (25.9 million tons)

•

10.7% plastics (24.7 million tons)

•

7.8% metals (18.0 million tons)

•

5.5% glass (12.8 million tons)

•

5.5% wood (12.7 million tons)

•

9.9% other materials (22.5 million tons)

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Of these materials, 15.8 million tons of yard trimmings were composted, 39.4 million tons of paper, 6.4 million tons of metals, and 2.9 million tons of glass were recycled. Some was combusted (14.5%), yet most of the MSW is still disposed of in landfills (55.3%) [3]. The energy recovery from MSW is a function of the heating value of a given material composition. The approximate heating value can be determined by modeling one organic compound that represents the MSW the best. However, these models deliver only boundary values. The heating value also strongly depends on the content of inert material and moisture, increasing percentages of which are associated with heat loss [4]. There has been extensive research on improving WTE processes, yet their overall market contribution to the worldwide energy generation is with 0.23% comparably small [after 1].

The American perspective on waste-to-energy In the early 70s, first WTE plants were constructed in the U.S. and with the 1985 Tax Reform Act a high growth rate was predicted. In 1987, U.S. EPA reported about 330 plants operating, under construction, or planned. However, the favorable tax credits soon disappeared. Increasing public resistance against incineration hindered the siting of new WTE facilities. Megafills with low tipping fees entered the solid waste market. Also, new regulations required air pollution control systems that drove up the costs to run WTE operations but most of all, the response of the WTE industry lacked consistency to make a nationwide impact [5]. Consequently, the Integrated Waste Services Association reported 146 WTE plants with a total capacity of 108,330 TPD in 1996 [6], of which only 98 were still operating with a combined capacity of 94,683 TPD in 2002 [7]. Hence, the overall number of U.S. WTE plants decreased by approximately 33% while the total capacity was only reduced by 13%. This deviation can be explained with increased efficiency and expansions of existing facilities, i.e. the addition of new combustion lines. One possible reason for extension is the growing public acceptance of already built WTE plants. Initially, it can be expected that host communities respond with the NIMBY (Not in my backyard!) syndrome. After a certain period of time, NIMBY may translate into proactive movement through civil participation and open communication between all parties involved [8]. However, the association with incinerators that were main sources of various

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pollutants left a heavy burden for advancing WTE processes. Because it almost impossible to site new plants the U.S. WTE market is not expected to expand in the near future. It has been and will be essential to improve the environmental performance of WTE facilities in order to overcome traditional preconceptions. In 1995, the U.S. EPA introduced the Maximum Achievable Control Technology (MACT) standards as part of the Clean Air Act. As a result, the air emissions decreased drastically; between 1990 and 2000 over 85% reductions in emissions of major pollutants released by U.S. WTE plants can be seen in Table 2, [9]). Similarly, for the five WTE plants in New Jersey (Camden, Essex, Union, Warren, and Gloucester) the combined mercury emissions decreased from 4,410 lbs/year in 1993 to 770 lbs/year in 1997 and 326 lbs/year in 1999 [4], a reduction of 92% within six years. Table 2:

*)

Emissions from U.S. WTE facilities [9] Pollutant

Annual emissions 1990

Annual emissions 2000

Reduction in %

Dioxins/furans, TEQ*)

4,260 g

12 g

99.7

Mercury

45.2 tons

2.2 tons

95.1

Cadmium

4.75 tons

0.33 tons

93.0

Lead

52.1 tons

4.76 tons

90.9

Hydrochloric acid

46,900 tons

2,672 tons

94.3

Sulfur dioxide

30,700 tons

4,076 tons

86.7

Particulate matter

6,930 tons

707 tons

89.8

Toxic equivalent (sum of substance amounts multiplied with toxicity equivalency factors)

In contrast to most other countries in the world, the U.S. WTE plants currently combine their bottom and fly ashes. Fly ash tends to attract pollutants and its placement alone is more difficult and costly. By combining fly ash with the less contaminated bottom ash, samples pass the required leaching tests and thereby are classified as non-hazardous. The residues are then mostly landfilled or used as daily cover/road base material in landfills. Outside-landfill applications are very limited. Several studies on beneficial uses have been conducted but no nationwide standards have been established. Only those specifications

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would promote the beneficial use, help solving liability issues, and ultimately, lead to more frequent reuse of WTE ash (current U.S. rate is below 10%, including reuse in landfill sites).

The European and global perspective on waste-to-energy Worldwide, approximately 130 million tons of MSW are combusted in over 600 WTE facilities in about 35 nations [10]. The combined capacity of these plants is 6,757 Megawatts (Table 3, [1]). The predominant WTE technology is mass burn because it is simpler and less costly than refuse derived fuel (RDF) or other technologies. Two manufacturers lead the mass burn grate market: Martin GmbH (Germany) with 59 million tons of installed annual capacity and Von Roll Inova Corp. (Switzerland) with 32 million tons [10]. In Europe, the market share of CNIM/Martin is 47% with an upward trend [11]. Table 3:

Worldwide energy production in WTE facilities [1]

Year Region

Net Capacity MW

Generated electricity TJ

Generated heat TJ

2000

1995

2000

1995

2000

World

6,757

92,300

130,968

119,155

181,849

Europe

2,629

27,202

54,439

94,087

102,141

North America

2,806

53,182

56,351

7,270

31,070

Rest

1,322

11,916

20,178

17,798

48,638

While the North American market seems to stagnate, the most recently built U.S. facility started operations in 1997 [12], the prospects for the global WTE market are promising. In Europe alone, in addition to the existing facilities, approximately thirteen mass burn plants are expected to be built each year from 2003 to 2009 [11]. Martin and Von Roll reported additional 47 plants installed or under construction worldwide since 2001 with a combined annual capacity of approximately 6 millions tons MSW [10]. The incentives to invest into alternative waste management options to landfilling are much higher in countries with strict physical limitations such as densely populated areas or islands. The European Union mandates in its 1999 landfill directive that the amount of biodegradable waste for landfilling has to be drastically reduced and all waste has to be

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treated prior to being landfilled [13]. Environmental awareness of the regulatory authorities and the broad public is probably the second most important reason to restrict landfilling. Recycling is often considered the environmentally soundest solution and WTE processes are regarded as its competitor that allows our society to continue being wasteful with our resources. However, a recent study showed that for the U.S. the percentage of recycled materials in communities with WTE facilities is approximately 5% higher than the U.S. average recycling rate of 28% [16]. In 2001, the German chemical company BASF sponsored a study comparing the environmental impacts of mechanical-biological treatment (aerobic digestion), waste-toenergy, and landfilling [14]. The main conclusions are that, for the German market, the costs of landfilling MSW are slightly less than for mechanical-biological treatment (8%) and 54% less than for WTE. Main reasons are high operating costs that increase with the technical complexity of the management option. However, for all environmental performance criteria (energy, material, and land consumption, air and water emissions, risks) but potential toxicity WTE seems to be the favorable solution. The ecological footprint of these three MSW management options is visualized in Figure 1 (see Ref. [14] for more details). In addition, the carbon dioxide emissions from landfills per ton MSW are at least 1.2 tons CO2. Landfills have a much higher contribution to greenhouse gas emissions than for WTE plants [10, 15].

Figure 1:

Ecological footprint of three MSW management options (after [14]); NOTE: the larger the footprint becomes the less preferable is the alternative 7


Similar to the MACT standards in the U.S., emissions from WTE plants are rigorously controlled by the responsible authorities worldwide. As a result, in Sweden (and elsewhere) far less pollutants such as dioxins and furans are released into the environment (Figure 2). In 1999, all 22 Swedish WTE plants together emitted 3g of dioxins to the air while 5g were released in the bottom ash and 110-120g in the fly ash [17]. This example confirms the general trend that flue gas and bottom ash can be considered clean but the fly ash may require special measures. At the same time, the efficiency of energy generation in the WTE plants increased. With only a slight increased in the tonnage of incinerated MSW the generated energy almost doubled (Figure 2). One possible means is the co-generation of steam and electricity such as suggested in the WTE plant in Brescia, Italy [18]. The data in Table 3 for North America also suggest that here higher efficiency was achieved after 1995; while the production of electricity was fairly constant, far more heat was generated in 2000 [1]. As noted above, the capacity of MSW tonnage decreased during that period.

Figure 2:

Energy production, incinerated tonnage of MSW, and dioxin air emissions of Swedish WTE plants [17] 8


Conclusions and outlook New technologies and challenges are stimulating the current global WTE market. Public perception and education, tax incentives, regulatory changes, new technologies, or improved operations could revitalize the WTE market in the U.S. Ongoing research focuses on gasification/pyrolysis, oxygen enrichment, flue gas recirculation, corrosion phenomena, further improvement of air pollution and operational control systems, carbon dioxide sequestration, and beneficial reuse WTE ash. The WTE market will change as technologies grow and innovations establish themselves. For example, it is expected that 16 gasification plants will be added in Europe with a combined capacity of approximately 1 million tons MSW from 2004 to 2006 [11]. Martin [19] recently introduced pilot studies for the Martin Syncom-Plus process that employs a reverse-acting Martin grate, oxygen enrichment, flue gas recirculation, infrared camera controls, recirculation of incompletely sintered bottom ash, wet-mechanical bottom ash treatment, and fly ash recirculation. The process results in reduced flue gas flow, less than 7kg fly ash per tonne MSW, completely sintered bottom ash (that can be beneficially used), and a total dioxin output of less than 0.005 mg/tonne waste [20]. It shows the importance of a holistic approach to WTE plant design; from the feed to the combustion residues, the process should be optimized. In 1999, the Integrated Waste Services Association [21] and the Earth Engineering Center at Columbia University [22] founded the Waste-to-Energy Research Council (WTERT, [23]). It is the mission of the WTERT to “bring together engineers and scientists from industry, federal, state and local government, and universities from around the world. These dedicated individuals believe in the Integrated Waste Management of Solids and strive to increase the global recovery of materials and energy from used solids. In particular, the mission of the WTERT Council is to advance both the economic and environmental performance of waste-to-energy technologies” [23]. Especially in the United States, advanced, environmentally friendly technologies and simultaneous public education are main factors in promoting waste-to-energy in a scheme of integrated waste management with minimized landfilling practice. The implementation of

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nationwide standards for WTE processes, residues, and beneficial uses thereof are needed, yet (governmental) economic incentives are the most important driver to strengthen the current position of WTE in the renewable energy market.

Acknowledgements The WTERT council and its sponsors should be gratefully acknowledged; we would also like to thank our research partners and promoters: American Ref-Fuel, ASME, Covanta Energy, Delft University of Technology, Energy Answers, Earth Institute at Columbia University, IWSA, Martin GmbH, Sheffield University, State University of New York at Stony Brook, Temple University, Wheelabrator, and all others supporters.

References [1]

International Energy Agency, 2002, “Renewables Information 2002.” International Energy Agency (IEA), Paris Cedex, France.

[2]

Choate, A. and Ferland, H., “Waste Management and Energy Savings: Benefits by the Numbers.” U.S. EPA, Washington, DC, online-version, http://yosemite.epa.gov/oar /globalwarming.nsf/UniqueKeyLookup/SHSU5C3J2J/$File/energy.pdf.

[3]

U.S. Environmental Protection Agency, 2002, “Municipal Solid Waste in the United States: 2000 Facts and Figures.” U.S. EPA, Washington, DC.

[4]

Earth Engineering Center and Urban Habitat Project at Columbia University, 2001, “Life After Fresh Kills: Moving Beyond New York City’s Current Waste Management Plan.” Columbia University, New York, NY.

[5]

Hickman, Jr., H. L., 2001, “A Brief History of Solid Waste Management During the Last 50 Years, Part 9b: A Reverse Marshall Plan.” MSW Management, 11 (7), onlineversion, http://www.forester.net/msw.html.

[6]

Taylor, A. and Zannes, M., 1996, “The 1996 IWSA Municipal Waste Directory of United States Facilities.” Integrated Waste Services Association, Washington, DC.

[7]

Kiser, J.V.L and Zannes, M., 2002, “The 2002 IWSA Directory of Waste-To-Energy Plants.” Integrated Waste Services Association, Washington, DC.

[8]

Scharff, C., 2003, “The waste site story - exploring the NIMBY syndrome.” Waste Management World, 3 (3), pp. 47-53.

[9]

Stevenson, W., 2002, “Emissions from Large MWC Units at MACT Compliance.” Memorandum to Docket A-90-45, U.S. EPA, Research Triangle Park, NC.

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[10] Themelis, N.J., 2003, “An Overview of the Global Waste-to-Energy Industry.” Waste Management World, submitted for publication. [11] Barker, M., 2003, “European Waste to Energy Plants Markets.” Frost & Sullivan, New York, NY, online-version, http://frost.com. [12] Dunne, R., 2002, “Waste-to-Energy Trends: Review of 12 of the Most Recently Constructed WTE Facilities.” MSW Management, 12 (6), pp. 82-89. [13] European Union, 1999, “Council Directive 1999/31/EC of 26 April 1999 on the landfill of waste.” Official Journal of the European Communities, pp. L182/1-19. [14] Schmidt, I., Kircherer, A., and Zwahr, H, 2001, “Eco-Efficiency Analysis of Waste Management Options – Mechanical-Biological Treatment, Waste-To-Energy, and Landfilling (in German).” BASF, Ludwigshafen, Germany. [15] Batchelor, D., Eeraerts, D., Smits, P., 2002, “Greenhouse Gas Abatement: Assessing WTE and Landfill Disposal.” Waste Management World, 2 (5), pp. 43-47. [16] Kiser, J.V.L., 2003, “Recycling and Waste-to-Energy: The Ongoing Compatibility Success Story.” MSW Management, 13 (4), pp. 92-103. [17] Rylander, H., 2002, “ISWA Statistics on Energy Supply from Waste in the EU.” Presentation at the FEAD International Conference, Bruges, Belgium. [18] Bonomo, A., 2003, “WTE Advances: The Experience of Brescia.” Presentation at the 11th North American Waste-to-Energy Conference, Tampa, FL. [19] Martin GmbH, “Homepage.” Munich, Germany, http://www.martingmbh.de. [20] Gohlke, O. et al., 2003, “New grate-based waste-to-energy system produces inert ash granulate.” Waste Management World, 3 (3), pp. 37-46. [21] Integrated Waste Services Association, “Homepage.” Washington, D.C., http://www.wte.org. [22] Earth Engineering Center, “Homepage.” Columbia University, New York, NY, http://www.columbia.edu/cu/earth. [23] Waste-to-Energy Research and Technology Council, “Homepage.” New York, NY, http://www.columbia.edu/cu/wtert.

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