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5 Commercial and Industrial Practices for Activated Carbon Management COMMERCIAL AND INDUSTRIAL Demand for activated carbon in the United States USE OF ACTIVATED CARBON was 363 million pounds in 2005, split approximately equally between granulated activated carbon (GAC) Overview and powdered activated carbon (PAC). About 173 mil- lion pounds of activated carbon was produced domes- Activated carbon finds extensive use as an adsorbent tically; the remainder was imported. Demand grew for the removal of a wide range of contaminants from at an average annual rate of 1.3 percent from 2000 to liquids and gases. It is also used to adsorb a product, 2005. Annual growth of 2.3 percent is expected through such as a solvent, from a process stream, with the 2009. adsorbed product being subsequently desorbed on-site Liquid-phase applications greatly exceed gas-phase for reuse. This last step, known as âcarbon regenera- applications. The three largest liquid-phase applications tion,â differs from âcarbon reactivation,â which is a are treatment of potable water (37 percent), treatment treatment process whereby adsorbed materials (adsor- of wastewater (21 percent), and decolorization of sugar bates) on the carbon are destroyed and the structure (10 percent). The three largest gas-phase applications of the activated carbon is restored for reuse. The term are air purification (40 percent), automotive emis- âspent carbonâ is commonly used in commercial and sion control (21 percent), and solvent vapor recovery industrial applications to denote used carbon whose (12 percent). The three largest producers of activated adsorptive performance has diminished to the point carbon in the United States are Calgon Carbon, Mead- that it can no longer be used for its intended application Westvaco, and Norit Americas (Kirschner, 2006). without reactivation. Although sometimes used in the context of chemical agent de- Mercury Removal as an Emerging Market for militarization operations, the term âspent carbonâ has not been used Activated Carbon in this report to refer to the degree of adsorption of chemical agents on carbon because the adsorptive capacities of the various agent- In 2005, the U.S. Environmental Protection Agency exposed carbon sources under consideration have not necessarily issued the Clean Air Mercury Rule, which proposed to been exhausted. Moreover, agents are not the only materials that are extend emissions limits for mercury beyond munici- adsorbed on the carbon used at chemical agent disposal facilities, pal waste incinerators (MWIs) to fossil-fueled power and these other materials could possibly make the carbon âspentâ in plants. Because coal contains roughly two orders of the sense used in commercial applications. For these reasons, and to magnitude more mercury than petroleum (Linak et al., avoid confusion, this report has instead used the terms âexposedâ or âunexposedâ to distinguish carbon that has âseenâ chemical agent 2000), the Clean Air Mercury Rule affected mainly at least once from carbon that has never been exposed to agent but coal-fired power plants, which account for slightly less may contain other contaminants. than half of the stationary electric generating capacity 45
46 DISPOSAL OF ACTIVATED CARBON FROM CHEMICAL AGENT DISPOSAL FACILITIES in the United States. Although the experience of MWI sions ends up mixed with much larger quantities of fly operators was initially expected to be instructive in ash. Because the concentration of PAC in the admixture controlling mercury emissions at power plants, dozens as well as the concentrations of mercury on the PAC are of demonstration tests have shown that controlling low, overall concentrations of mercury in the admixture mercury emissions from coal-fired power plants is do not prohibit disposal in a landfill. Tests conducted both more difficult and more complex than had been on the fly ash-PAC mixture have shown that leaching of expected. Mercury concentrations resulting from coal the mercury once deposited in a landfill is not an issue combustion are several orders of magnitude lower than (Gustin and Ladwig, 2004; Senior et al., 2004; Wang those typical of MWIs. Whereas MWIs typically inject et al., 2007). Some power plants can also sell their fly PAC into a fabric filter to form a fixed sorbent bed, 90 ash as a replacement for portland cement in concrete, percent of power plants operate without such filters although they must limit the PAC content. These fac- (Brown et al., 1999) and instead seek to adsorb the tors all contribute to the conclusion that the disposal of mercury on PAC suspended within the flue gas. Coal activated carbon by the electric power industry offers combustion produces different species of mercury in little useful insight for the disposal of used activated proportions that vary by type of coal burned and the carbon from the destruction of mercury-contaminated configuration of the power plant. Each mercury spe- mustard agent (which is described in Chapter 6). cies exhibits different adsorption kinetics on activated carbon, kinetics that can be enhanced or inhibited by TREATMENT AND DISPOSAL OF the other species present in the flue gas. For this and ACTIVATED CARBON FROM COMMERCIAL other reasons, the control of mercury emissions from AND INDUSTRIAL APPLICATIONS power plants by the use of activated carbon is an area of active research. There are essentially three commercial treatment/ Activated carbon has been used for several decades disposal methods for the spent activated carbon result- to treat the gaseous products of combustion result- ing from its commercial and industrial use: ing from medical and municipal waste incineration facilities (collectively termed MWIs). These MWIs â¢ Reactivation, use activated carbon to adsorb volatile heavy metals â¢ Landfill, and such as mercury that survive the combustion process â¢ Incineration. and are present in the waste stream as well as unwanted combustion products such as dioxins and furans that Figure 5-1 summarizes the choices for disposition may be formed in the postcombustion region of an of the approximately equal amounts of GAC and PAC incinerator. In MWI applications, flue gas treatment used in commercial and industrial applications. Of the with activated carbon most often occurs in conjunction spent GAC generated from industrial and commercial with a fabric filter (baghouse). The filter material may use, approximately 10 percent is hazardous and 90 be constructed from fibers embedded with PAC or may percent is nonhazardous. Ninety percent of hazard- be continuously injected into the flue gas upstream of ous GAC is disposed of by reactivation, 7 percent by the baghouse, forming a sorbent bed on the filter that incineration, and 3 percent in landfill; the reactivation grows over time until it is dislodged during periodic is done entirely off-site at Resource Conservation and baghouse cleaning. In either case, the physical configu- Recovery Act (RCRA) permitted facilities. Disposition ration can be described as a fixed sorbent bed in which of the nonhazardous GAC is 66 percent by reactiva- long exposure times of the sorbent to the waste stream tion, 7 percent by incineration or thermal destruction result in the near-complete utilization of the adsorptive at cement kilns or waste-to-energy plants, and 27 capacity of the carbon. percent by landfill. Of the nonhazardous GAC that is Disposal issues for spent PAC at power plants are reactivated, approximately 40 percent is reactivated largely overshadowed by the disposal issues associated on-site by sweetener manufacturers like Cargill and with residual fly ash. PAC used to control mercury emis- Archer Daniels Midland Company, and the remainder is reactivated off-site. Spent wood-based GAC, used in For additional information, see the Energy Information Agency automotive applications, is not well suited to reactiva- Web site at http://www.eia.doe.gov/kids/energyfacts/sources/elec- tion and is mainly sent to landfills. tricity.html#Generation. Last accessed March 25, 2009. Spent PAC cannot be reactivated. About 5 percent of
COMMERCIAL AND INDUSTRIAL PRACTICES 47 Spent AC GAC PAC Hazardous Nonhazardous Hazardous Nonhazardous Reactivation Reactivation Incineration Incineration Incineration Off-site Landfill Landfill Landfill On-site Incineration Landfill FIGURE 5-1â General schematic of the fate of spent activated carbon from commercial and industrial sources. FIGURE 5-1.eps it is hazardous (it comes mainly from the pharmaceuti- Companies other than Calgon Carbon Corpora- cal industry) and is incinerated. The other 95 percent is tion that provide reactivation services include Norit nonhazardous and goes to landfills. Americas; Westates Carbon, a division of Siemens Figure 5-2 is a schematic diagram for carbon reacti- Water; and Cameron Carbon. These vendors offer two vation, which is carried out in either a rotary kiln or a options. One is to return the reactivated material to the multiple hearth furnace. As the carbon travels through generator. The other is to combine it with the reacti- the furnace, water and other solvents evaporate, volatile vated carbon from other sources for reuse or resale. halides and hydrocarbons vaporize, and other impurities Of the hazardous spent carbon reactivated off-site, are destroyed by calcination or pyrolysis. The calcined product is reactivated by steam gasification at around 1800Â°F (980Â°C). The process is carried out in a low- oxygen environment consisting of flue gas and steam. Offgases go through an afterburner and a scrubber prior Spent to discharge to the atmosphere. Approximately 10-15 activated Dryingâ percent of the carbon is lost through oxidation during carbon water/solvent reactivation. removal Appendix A provides tabulated criteria from Calgon Dried spent Carbon Corporation for determining if used GAC is carbon suitable for reactivation. It is noteworthy that Calgon Devolatilization/vaporization does not accept material contaminated with mercury process (less than 1000Â°F) at any concentration and has limits on the acceptable Devolatilized concentration of sulfur. If Calgon accepts a material product for reactivation, the company will, on request, pick it Calcination/pyrolyzation process (greater than 1000Â°F) up from the site of generation and assume responsibil- ity and liability for the reactivated product. If Calgon Calcined Activation process Reactivated product steam gasification carbon product rejects a material for reactivation, the company will assist the generator in finding an alternative method of disposition, but liability remains with the generator. FIGURE 5-2â Calgon Carbonâs process for reactivation of spent carbon. FIGURE 5-2.eps redrawn as vector
48 DISPOSAL OF ACTIVATED CARBON FROM CHEMICAL AGENT DISPOSAL FACILITIES approximately 80 percent is released for resale and the are being burned successfully at Veoliaâs incinerator in vendor assumes all subsequent liability. Reactivation Port Arthur, Texas. is attractive principally because it is less costly than disposal and/or the purchase of freshly made activated Finding 5-1.â Reactivation is an attractive alternative to carbon. landfilling or incineration for disposing of unexposed Landfilling is less expensive than incineration and carbon if the carbon reactivation contractor accepts is the preferred option if the carbon is not suitable liability for subsequent use and disposal. for reactivation. However, the contaminants adsorbed on the carbon can leach out, and the generator can be REFERENCES expected to retain liability for the landfill operation. Permitted hazardous waste landfills suitable for dis- Brown, T., D. Smith, R. Hargis, Jr., and W. OâDowd. 1999. Mercury measurement and its control: What we know, have learned, and need posal of spent activated carbon include several oper- to further investigate. Journal of the Air and Waste Management As- ated by Clean Harbors, Waste Management Inc., and sociation 49(6): 1-97. American Ecology. Gustin, M., and K. Ladwig. 2004. An assessment of the significance of mer- cury release from coal fly ash. Journal of the Air and Waste Management Incineration is the most expensive of the three Association 54(3): 320-330. options but the one with the least potential liability. Kirschner, M. 2006. Ethylene. Chemical Marketing Reporter 270(4): 34. At least two commercial hazardous waste incinerators, Linak, W., C. Miller, and J. Wendt. 2000. Comparisons of particle size dis- tributions and elemental partitioning from the combustion of pulverized Clean Harbors in Aragonite, Utah, and Veolia in Port coal and residual fuel oil. Journal of the Air and Waste Management Arthur, Texas, are permitted to burn spent activated Association 50(8): 1532-1544. carbon and have experience in doing so. Permits might Senior, C., C. Bustard, M. Durham, K. Baldrey, and D. Michaud. 2004. be required to handle activated carbon contaminated Characterization of fly ash from full-scale demonstration of sorbent injection for mercury control on coal-fired power plants. Fuel Processing with the agent by-products discussed in Chapter 4, Technology 85(6-7): 601-612. although there is no question that they would be Wang, J., T. Wang, H. Mallhi, Y. Liu, H. Ban, and K. Ladwig. 2007. The destroyed by incineration. The agent by-products are role of ammonia on mercury leaching from coal fly ash. Chemosphere 69(10): 1586-1592. similar to those in the hydrolysate from Newport that