Grantee Research Project Results
Final Report: Low-Cost Mercury Sorbents Derived From Waste Tires
EPA Contract Number: 68D03039Title: Low-Cost Mercury Sorbents Derived From Waste Tires
Investigators: Wojtowicz, Marek
Small Business: Advanced Fuel Research Inc.
EPA Contact: Richards, April
Phase: II
Project Period: May 1, 2003 through April 30, 2005
Project Amount: $224,678
RFA: Small Business Innovation Research (SBIR) - Phase II (2002) Recipients Lists
Research Category: SBIR - Pollution Prevention , Pollution Prevention/Sustainable Development , Small Business Innovation Research (SBIR)
Description:
The objective of this Phase II research project conducted by Advanced Fuel Research, Inc., was to address two important environmental problems: (1) the removal and recovery of mercury from combustion/incineration flue gas, and (2) the reprocessing of waste tires into value-added products. Coal combustion and incineration of municipal and hazardous wastes results 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.
Many of the technologies currently pursued for capturing mercury are based on the injection of sorbents into the flue gas, which results in the capture of mercury along with fly ash in electrostatic precipitators and baghouses. The problems associated with this approach are: (1) the high cost of sorbents (usually activated carbons with a market value of about $0.50/lb), and (2) disposal of the mercury-contaminated carbon and fly ash. Clearly, the current practice of sorbent injection and landfilling of the spent sorbent is only a short-term solution. Because the release of mercury eventually will be regulated in gas, solid, and liquid effluents, future-generation technologies likely will be regenerative. An additional complication is that air toxics control needs to be integrated with the existing SO2 and NOX abatement techniques to form a comprehensive multi-pollutant control system. Sorbent cost also is a critical factor and reducing it through the use of tire-derived carbons to $0.30–$0.35/lb is desirable.
Scrap tires present formidable disposal problems as they are immune to biological degradation. Landfilling of the 280 million tires generated each year in the United States is becoming an increasingly unacceptable solution. The estimated number of tires already stored in stockpiles across the United States is several hundred million. The tires take up large amounts of valuable landfill space and also present fire and health hazards. Tire-pyrolysis plants have been in operation for years, but the economics of their operation are poor, because of the low value of the end products, which usually are fuels (oil, pyrolysis gas, char). Reprocessing of waste tires into value-added products would improve the economic leverage.
The approach 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 envisaged implementations of the process are: (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. The objective of the Phase I project was to demonstrate the superior price-performance characteristics for waste tire-derived activated carbons under simulated industrial conditions; this was successfully accomplished. The Phase II objective was to optimize sorbent properties as a function of carbon-preparation conditions and to advance the product to pilot scale (Phase II Option). This was to be accomplished through the following tasks: (1) sorbent optimization, (2) sorbent performance, (3) product evaluation, and (4) pilot-scale testing (Phase II Option).
The technology developed in this project, if successfully advanced to full scale, should result in a novel technology for the removal of mercury from combustion and 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):
The Phase II objective (to optimize sorbent properties) was successfully accomplished. The Phase II Option objective (pilot-scale testing) had to be abandoned because of the inability to secure the required funds. The work performed is summarized below.
A number of activated carbons were prepared from waste tires using pyrolysis followed by char activation to different degrees of burn-off. The samples were characterized in terms of elemental composition and pore-structure characteristics (specific surface area, pore volume, pore-size distribution). Kinetic analysis of the char activation process was carried out. The mercury sorption performance of tire-derived activated carbons was tested in fixed-bed experiments, and the results were compared to the performance of a reference activated carbon, Norit FGD. A parametric study was conducted in which the effects of temperature and gas composition on sorbent performance were determined. In addition, a sample of tire-derived sorbent was tested at Conesville Station under the U.S. Department of Energy’s National Energy Technology Laboratory Mercury-Control Program run by ADA-ES, Inc. Product evaluation and an economic analysis were performed. A detailed economic model was created for the process and a sensitivity analysis was performed, including an analysis of oil prices and tire tipping fees.
Conclusions:
- Activated carbons with an internal surface area of 200–500 m2/g and a pore volume of 0.85–1.5 cm3/g were produced from waste tires.
- Mercury-sorption tests showed that 80–100 percent performance of Norit FGD reference sorbent was possible to achieve for tire-derived activated carbons that had the following characteristics: 40–50 percent burn-off, 300–500 m2/g surface area, and 5–8 weight percent sulfur (dry, ash-free basis). Thus, tire-derived activated carbons can match the performance of commercial activated carbons at a significantly lower cost.
- The economic analysis performed during this project showed that the price of tire-derived activated carbon in the range of $0.11–$0.36/lb was consistent with a profit margin of 20 percent. The cost-performance plot for tire-derived activated carbons for mercury control is shown in Figure 1.
Price ($/lb)
Figure 1. The Cost–Performance Analysis for AFR Tire-Derived Mercury Sorbents (based on information from literature references and elemental mercury sorption data from this study)
Journal Articles:
No journal articles submitted with this report: View all 3 publications for this projectSupplemental Keywords:
solid waste utilization, waste tires, emissions, pyrolysis, activated carbon, air pollution control, mercury sorbent, mercury control, combustion, flue gas, fly ash, coal-fired power plants, incinerators, small business, SBIR,, RFA, Scientific Discipline, INTERNATIONAL COOPERATION, Waste, INDUSTRY, POLLUTANTS/TOXICS, POLLUTION PREVENTION, Sustainable Industry/Business, Municipal, waste reduction, cleaner production/pollution prevention, Environmental Chemistry, Chemicals, recycling, Industrial Processes, Incineration/Combustion, Environmental Engineering, heavy metals removal, combustion byproducts, mercury, scrap tires, tires, waste minimization, cleaner production, environmentally friendly technology, clean technology, air pollution control, combustion emissions, flue gas, municipal waste, rubber tire, emission controls, waste tires, emissions control, heavy metal emissions, municipal solid waste landfills, mercury sorbents, combustion technology, combustion, flue gas emissions, incineration, air emissions, municipal solid waste, combustion contaminants, heavy metalsSBIR Phase I:
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.