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Vitrification of Municipal Solid Waste Incinerator Fly Ash Using Brown’s Gas Kwinam Park, Jangsoo Hyun,† Sanjeev Maken, Seokheung Jang, and Jin-Won Park* Department of Chemical Engineering, Yonsei Centre for Clean Technology, Yonsei University, 134 Shinchon-dong, Seodaemoon-ku, Seoul, Korea, 120-749 Received February 19, 2004. Revised Manuscript Received September 15, 2004
Municipal solid waste incinerator (MSWI) fly ash was vitrified at ∼1450 °C, for the first time, using Brown’s gas. Vitrification of pelletized fly ash (fly ash + water glass) results in a decrease of the leaching of toxic heavy metals to much below the Korean regulatory limit values, although melted fly ash was a poorly vitrified product that had a dark gray appearance. The addition of glass cullet to the fly ash increased the silica content and decreased the basicity. It was determined that a decrease in basicity from 2.94 to 0.28 leads to good vitrified products that have an amorphous glassy structure that is dark brown in color. Leaching all of the potentially hazardous heavy metals present in fly ash also decreased as the basicity decreased. It was determined that all the heavy metals (zinc, lead, chromium, arsenic, copper, manganese, and cadmium) were efficient in regard to substituting for parent Al and Ca ions in the silicate structure. It was further confirmed by scanning electron microscopy and X-ray diffractometry studies that the initial crystalline structure of fly ash was transformed to an amorphous glassy structure upon vitrification. The vitrified products of fly ash and its mixtures with glass cullet were determined to be nonhazardous in nature and glassy in appearance; therefore, they could be considered as construction and road-building materials in the future.
Introduction Modern society generates large amounts of waste. Waste management systems include waste collection and sorting, followed by one or more of the following options: recovery of secondary materials (i.e., recycling), biological treatment of organic waste (i.e., production of marketable compost), thermal treatment (i.e., incineration to recover energy in the form of heat and electricity), and landfilling.1-4 Landfilling of municipal solid waste (MSW) releases volatile organic compounds, along with leachable toxic heavy metals, into the surrounding environment.5-10 Over the years, the incinera* Author to whom correspondence should be addressed. Telephone: +82-2-364-1807. Fax: +82-2-312-6401. E-mail:
[email protected]. † Currently with Institute of Energy & Environment Corporation, Hae-chang-ri, Paltan-myon, Hwa Sung City, Kyongki-Do, Korea 445914. (1) Broadbelt, L. J.; Chu, A.; Klein, M. T. Polym. Degrad. Stab. 1994, 45, 57-70. (2) Kruse, T. M.; Woo, O. S.; Broadbelt, L. J. Chem. Eng. Sci. 2001, 56, 971-979. (3) Sakai, S.; Sawell, S. E.; Chandler, A. J.; Eighmy, T. T.; Kosson, D. S.; Vehlow, J.; Van der Sloot, H. A.; Hartlen, J.; Hjelmar, O. Waste Manage. (Oxford) 1996, 16, 341-350. (4) Chandler, A. J.; Eighmy, T. T.; Hartlein, J.; Hjelmar, O.; Kosson, D. S.; Sawell, S. E.; Van der Sloot, H. A.; Vehlow, J. Municipal Solid Waste Incinerator Residues; Elsevier Science: Amsterdam, 1997. (5) Barlaz, M. A.; Ham, R. K.; Shaefer, D. M. J. Environ. Eng. (N.Y.) 1989, 115, 1088-1102. (6) Kjeldsen, P.; Barlaz, M. A.; Rooker, A. P.; Baun, A.; Ledin, A.; Christensen, T. H. Crit. Rev. Environ. Sci. Technol. 2002, 22, 297336. (7) Lin, K. L.; Wang, K. S.; Tzeng, B. Y.; Lin, C. Y. Waste Manage. (Oxford) 2004, 24, 199-205. (8) Sanin, F. D.; Knappe, D. R. U.; Barlaz, M. A. Water Res. 2000, 34, 3063-3074.
tion of waste to generate energy has become the most common method of dealing with combustible waste efficiently, because it decreases the volume and mass of MSW. The incineration of MSW generates fly ash (FA) and bottom ash (BA), which comprises ∼10%-30% of MSW.11 Recent research has shown that these ashes release leachable toxic heavy metals, dioxin, furans, and volatile organic compounds.12-15 Stringent environmental regulations are being imposed to control the environmental impact of MSW and incinerator residues. Thus, there is a need of ensuring effective long-term deposition of ashes and other residual products from the waste incineration process. The total amount of MSW generated by Korea was 48,499 tonnes per day in the year 2001.16 Approximately 4.6 million tonnes of total waste is being incinerated per year, which leads to the generation of a large amount of solid residues, including FA and BA.17 BA is (9) Tchobanoglous, G.; Theisen, H.; Vigil, S. Integrated Solid Waste Management; McGraw-Hill: New York, 1993. (10) Christensen, J. B.; Christensen, T. H. Water Res. 2000, 34, 3743-3754. (11) Park, Y. J.; Heo, J. J. Hazard. Mater. 2002, 91, 83-93. (12) Abe, S.; Kanbayashi, F.; Kimura, T. Organohalogen Compd. 1997, 31, 348-353. (13) Eusden, J. D.; Eighmy, J. T. Appl. Geochem. 1999, 14, 10731091. (14) Song, G. J.; Kim, K. H.; Seo, Y. C.; Kim, S. C. Waste Manage. (Oxford) 2004, 24, 99-106. (15) Li, M.; Hu, S.; Xiang, J.; Sun, L. S.; Li, P. S.; Su, S.; Sun, X. X. Energy Fuels 2004, 18, 1487-1491. (16) Kim, K. Y. Korea Environmental Policy Bulletin; Ministry of Environment Institute, Republic of Korea, 2003, Vol. 1, Issue 1. (17) State of Operation for MSWI in Korea; Ministry of Environment Report, Seoul, Republic of Korea, 2000.
10.1021/ef049953z CCC: $30.25 © 2005 American Chemical Society Published on Web 11/03/2004
Vitrification of Solid Waste Incinerator Ashes
landfilled in Korea, provided that the leaching concentration of lead does not exceed the Korean regulatory limit.18 FA is considered to be hazardous waste and disposed of in a special landfill. However, it is becoming increasingly difficult to obtain more land for landfilling purposes, because of the small land area and high population density of Korea. Moreover, Korean municipal solid waste incineration (MSWI) FA contains low silica and has a high chloride content, which makes it difficult to vitrify. Melting of these ashes at high temperature (vitrification) can lead to a further volume reduction to one-half or one-third of the original amount19 and destruction of >98% of polycyclic organic compounds,20,21 and it also makes the heavy metals less leachable.22 Melting of MSWI ashes at high temperature modifies the state of the ash and transforms it to a type of glass that is innocuous to the environment and a valuable source of secondary raw material with applications in the construction and road-building industries.22-26 This technology consumes a large amount of energy; however, research is being focused on reducing the energy consumption. In the past, Brown’s gas was used to detoxify radioactive nuclear waste27 and for welding.28 These considerations prompted us to use an economical, energy-efficient, and environmentally friendly Brown’s gas as a fuel in an ash-melting furnace to stabilize the toxic heavy metals that are present in MSWI fly ash. Experimental Methods The fly ash used in this study was collected from a stokertype incinerator at Pyong-chon (Kyung-ki Province, Korea), operated by Dongbu Cooperation. Its capacity was 200 tons of MSW per day. In the incinerator, MSW was burned in the combustion chamber at ∼ 850 °C and the flue gas was cooled through a waste heat boiler and treated through a spray-dry absorber and baghouse filter. Thermal energy recovered therefrom was used to generate electricity and for district heating. The MSWI fly ash was melted in an ash melting furnace (E&E Company, Korea). It uses Brown’s gas, which is a stoichiometric mixture of atomic hydrogen and oxygen,29-31 as a fuel and can melt 5 tons of ash per day. A flow diagram of the ash-melting process is shown in Figure 1. Brown’s gas was (18) Regulatory of Waste Management; Ministry of Environment Report, Seoul, Republic of Korea, 2000. (19) Kinto, K. Waste Manage. (Oxford) 1996, 16, 423-430. (20) Ito, T. Waste Manage. (Oxford) 1996, 16, 453-460. (21) Kuo, Y. M.; Lin, T. C.; Tsai, P. J.; Lee, W. J.; Lin, H. Y. Chemosphere 2003, 15, 313-319. (22) Pelino, M.; Cantalini, C.; Sun, H. J. Glass-Ceramic Materials Obtained by Recycling of Industrials Wastes. In Glass-Ceramic MaterialssFundamentals and Applications; Manfredini, T., Pellacani, G. C., Rinco´n, J. Ma., Eds.; Series of Monographs on Material Science, Engineering and Technology; Mucchi Editore: Modena, Italy, 1997; pp 223-242. (23) Jimbo, H. X. Waste Manage. (Oxford) 2003, 16, 417-422. (24) Pelino, M.; Karamanov, A.; Pisciella, P.; Crisucci, S.; Zonetti, D. Waste Manage. (Oxford) 2002, 22, 945-949. (25) Pisciella, P.; Crisucci, S.; Karamanov, A.; Pelino, M. Waste Manage. (Oxford) 2001, 21, 1-9. (26) Polettini, A.; Pomi, R.; Sirini, P.; Testa, F. J. Hazard. Mater. 2001, 88, 123-138. (27) Haley, D. Transmutation of Radioactive Materials with Brown’s Gas. Planet. Assoc. Clean Energy Newsl. 1993, 6 (4), 8-9. (28) Michrowski, A. Yull Brown’s Gas. Planet. Assoc. Clean Energy Newsl. 1993, 6 (4), 10-11. (29) Brown, Y. Welding. U.S. Patent No. 4,014,777, March 29, 1977. (30) Brown, Y. Arc-Assisted Oxy/hydrogen Welding. U.S. Patent No. 4,081,656, March 28, 1978. (31) Oh, H. K. J. Mater. Process. Technol. 1999, 95, 8-9.
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Figure 1. Flowchart of the ash-melting process. generated by a Brown’s gas generator (E&E Company, Korea) via the electrolysis of water. A schematic diagram of the ashmelting furnace and the Brown’s gas generator is shown in Figure 2. This generator produces 300 m3 of Brown’s gas per hour and each burner consumes 25 m3 of Brown’s gas per hour. The ash-melting furnace contains six Brown’s gas burners, four of which were used simultaneously during ash melting and two were kept as standby equipment. Thirty five cubic centimeters of water glass (a mixture of sodium and potassium silicate) was added to 1 kg of fly ash before melting, to avoid the flying of fly ash. Glass cullet was used as an additive to adjust the basicity of the slag and as a glass-forming material. The fly ash (FA), bottom ash (BA), and slags were dried at a temperature of 110 °C for 24 h. After drying, these were pulverized to a size of
