Grantee Research Project Results
Final Report: Low-Cost Mercury Sorbents Derived From Waste Tires
EPA Contract Number: 68D02004Title: Low-Cost Mercury Sorbents Derived From Waste Tires
Investigators: Wojtowicz, Marek
Small Business: Advanced Fuel Research Inc.
EPA Contact: Richards, April
Phase: I
Project Period: April 1, 2002 through September 1, 2002
Project Amount: $69,999
RFA: Small Business Innovation Research (SBIR) - Phase I (2002) RFA Text | Recipients Lists
Research Category: SBIR - Pollution Prevention , Pollution Prevention/Sustainable Development , Small Business Innovation Research (SBIR)
Description:
This Phase I research project addressed two important environmental problems: (1) removal and recovery of mercury from combustion/incineration flue gas, and (2) reprocessing of waste tires into value-added products. Coal combustion and incineration of municipal and hazardous wastes result in air pollution due to emissions of trace amounts of heavy metals. Because of the high toxicity of these species, their emissions are or will be regulated. The high volatility of mercury makes control of this metal particularly difficult.
Scrap tires present formidable disposal problems as they are known to be immune to biological degradation. Landfilling of the 280 million tires that are generated each year in the United States is an unacceptable solution. In addition to the continuous flow of waste tires, there are approximately 2-3 billion tires already stored in piles throughout the country and illegal dumping also is a problem. The tires take up large amounts of valuable landfill space, provide breeding sites for mosquitoes and rodents, and present fire and health hazards.
The proposed approach to solving the problems described above is based on mercury adsorption on low-cost, sulfur-rich activated carbons derived from scrap tires. The sulfur added to tire rubber in the process of vulcanization makes the tire-derived sorbents particularly effective in mercury removal due to the high chemical affinity between mercury and sulfur. Two possible implementations of the process are envisaged: (1) sorbent injection into the flue gas duct (near-term applications), and (2) a patented regenerative scheme (long-term applications).
The overall objective of the project was to develop a novel and effective technology for mercury control using sorbents derived from waste tires. A specific objective of the Phase I project was to demonstrate the superior price-performance characteristics for waste tire-derived activated carbons under simulated industrial conditions, which was successfully accomplished. The objective of the Phase II project is to optimize sorbent properties as a function of carbon-preparation conditions, and to advance the product to pilot scale (Phase II Option). The main result of this research will be a novel technology for the removal of mercury from combustion/incineration flue gas combined with the simultaneous utilization of massive amounts of solid waste (scrap tires). The obvious applications for the process are coal-fired power plants as well as municipal, medical, and hazardous waste incinerators.
Summary/Accomplishments (Outputs/Outcomes):
Advanced Fuel Research, Inc. (AFR) performed the following tasks as part of the Phase I research project: (1) sorbent development, (2) sorbent testing, and (3) process assessment. The main results of the project include the following:
· Tire-pyrolysis char obtained from a pilot-scale facility was used as a starting material for sorbent preparation. Char activation resulted in an increase in surface area and an increase in sulfur content. Both findings are favorable for improved mercury removal. Higher surface area increases the effectiveness of mercury capture due to the improved contact with the carbon sorbent. The higher sulfur content is desirable because of a strong chemical affinity that exists between mercury and sulfur. Activated carbons developed in this work had a sulfur content of up to 6 weight percent; the typical sulfur content of waste tires is 1.1-2.1 weight percent.
· The tire-derived carbons were tested for elemental mercury adsorption at flue gas conditions simulating those of a low-sulfur Eastern bituminous coal. Except for the unactivated tire-pyrolysis char, all sorbents met the industrial requirement for effective mercury sorption (equilibrium sorption capacity higher than 150 µg Hg/g). The performance of non-optimized AFR sorbents must be viewed as promising, because the equilibrium sorption capacity was found to range from 276 to 829 µg Hg/g. In addition, most sorbents exhibited excellent initial adsorption capacity (up to 663 µg Hg/g). Mercury adsorption at early stages of sorbent exposure to mercury-laden gas is important due to the relatively low residence time of carbon in the flue gas duct (1-2 seconds). The above data compare favorably with previous results obtained using activated carbons derived from various carbonaceous precursors. The range of values for the equilibrium sorption capacity for these carbons was reported to be 40-847 µg Hg/g.
· Preliminary data obtained for the adsorption of mercuric chloride (HgCl2) on tire-derived carbons look very promising. Thus, the sorbents developed in this study are effective in capturing elemental mercury (Hg0) and mercuric chloride (HgCl2). Both species are major pollutants released during coal combustion and solid waste incineration.
· For the activated carbons prepared in this study, mercury-adsorption capacity was found to correlate with percent burn-off, specific surface area, and sulfur content. It is unclear at this time which of the above three factors has the strongest direct effect on mercury sorption. Elucidation of this point will be sought in the Phase II research project.
· For the tire-derived carbons used in this work, the mercury sorption capacity was found to be relatively insensitive to flue gas temperature in the range 135-200°C. This is a desirable result from the standpoint of flue gas clean-up as high gas temperatures usually result in the degradation of sorbent performance. This is due to the fact that the mercury-sorption equilibrium is shifted in the direction of desorption as temperature increases. The important practical implication is that the combustion flue gas will not have to be cooled prior to mercury removal and then re-heated, because of the good thermal stability of mercury surface species adsorbed on AFR sorbents.
Conclusions:
The feasibility of the proposed concept was demonstrated successfully, and the Phase I objectives were accomplished. The cost-performance analysis for the AFR sorbents is depicted in Figure 1. It can be seen that although Norit FGD performs better than AFR sorbents, its cost is rather prohibitive (Norit FGD is an activated carbon specially designed for optimum mercury sorption). Data in Figure 1 show that after product optimization in Phase II, there is a good chance that AFR sorbents will be competitive in terms of both price and performance.
Figure 1. The cost-performance analysis for AFR tire-derived mercury sorbents
Excellent mercury sorption capacity was found for a number of tire-derived sorbents. Based on preliminary mercury sorption data, AFR was invited to participate in full-scale mercury tests conducted at several power plants under a U.S. Department of Energy-funded demonstration project conducted by ADA-ES. This should be viewed as important recognition of AFR's Phase I results by an independent party.
Supplemental Keywords:
waste tires, solid-waste utilization, pyrolysis, value-added products, activated carbon, mercury emissions and their control, coal combustion, incineration, adsorption, sorption, SBIR., RFA, Scientific Discipline, Air, Toxics, Waste, Ecosystem Protection/Environmental Exposure & Risk, Sustainable Industry/Business, Chemical Engineering, Environmental Chemistry, air toxics, cleaner production/pollution prevention, HAPS, Monitoring/Modeling, Civil Engineering, Engineering, Chemistry, & Physics, Environmental Engineering, Incineration/Combustion, Futures, Exp. Research/future, coal combustion wastes, flue gas , combustion byproducts, mercury, medical waste incinerator, mercury emissions, clean technology, elemental mercury, flue gas, waste tires, emission controls, hazardous waste incinerators, emissions control, mercury sorbents, sorbents, Mercury Compounds, combustion, mercury recovery, flue gas emissions, coal combustion, pollution prevention, coal fired power plants, flue gases, clean combustion, heavy metals, mercury removalSBIR Phase II:
Low-Cost Mercury Sorbents Derived From Waste Tires | Final ReportThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.