Final Report: An Improved Sorbent for Mercury Abatement

EPA Contract Number: 68D99071
Title: An Improved Sorbent for Mercury Abatement
Investigators: Bell, William L.
Small Business: TDA Research Inc.
EPA Contact:
Phase: I
Project Period: September 1, 1999 through March 1, 2000
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (1999) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , SBIR - Air Pollution , Small Business Innovation Research (SBIR)

Description:

Coal-fired electric utilities produce the majority of the electric power generated in the U.S. and are also the largest single source of anthropogenic mercury emissions. The 1990 Clean Air Act amendments require the EPA to investigate whether mercury emissions from these utilities should be regulated, with a decision deadline of 15 December 2000. Dry sorbent injection is an attractive approach to mercury abatement that would be easy to retrofit into existing electric utilities. The dry sorbent is injected into the flue gas and removed with the fly ash in the particulate control module (PCM). Since the sorbent injection equipment is inexpensive and the sorbent recovery is carried out with unmodified, pre-existing equipment, the capital investment required is very low. However, because the sorbent is used only once and then disposed of, a low-cost sorbent is essential.

Most sorbents currently being evaluated for this use are carbon-based, such as lignite activated carbon (LAC). Carbon sorbents, in addition to having a higher cost than is desired, can cause problems with current uses of the fly ash. A large proportion of fly ash is currently sold as an extender for Portland cement in concrete; however, if the carbon content of the fly ash is too high, it cannot be used in this market. The problem is much more serious than the loss of revenue from sales: if the large quantities of fly ash produced by a utility are not salable for concrete, then they have no market at all, and immediately become an expensive waste problem. This research effort identified and tested a new, low-cost method to produce sorbents for mercury abatement from non-carbon feedstocks.

Summary/Accomplishments (Outputs/Outcomes):

The project goal is to produce new, low-cost sorbents for mercury abatement in coal-fired electric utility flue gases, that have a mercury uptake performance equal to activated carbon, but a lower cost. A baseline cost for activated carbon is $0.50/lb, or $1,000/ton, although some studies project that activated carbons for mercury abatement could cost as little as $0.25/lb or $500/ton. The specific objectives of Phase I were to demonstrate the feasibility of a new process to modify non-carbon feedstocks and estimate the cost of sorbents prepared with the new process. To achieve these objectives we prepared samples using a variety of additives and combinations of additives on several different non-carbon feedstocks. We then tested these sorbents using a packed bed mercury breakthrough apparatus. Finally, we carried out an engineering and economic analysis to estimate the cost and effectiveness of the mercury removal process.

TDA identified several combinations of additives that were effective in improving the mercury removal properties of the feedstocks. In some cases the performance of the modified non-carbon feedstock, as measured on the packed bed apparatus, was equivalent to lignite activated carbon, even though the new sorbent had a lower surface area than the LAC. TDA further demonstrated a very simple and inexpensive sorbent production method. It will be necessary to test the new materials in sorbent injection mode to accurately assess their potential. We did not carry out sorbent injection tests in Phase I due to time and budget limitations, but such tests are planned for Phase II.

Conclusions:

The key findings were: (1) Some of the new materials were as effective in mercury removal as activated carbon in our packed bed tests. These results must be confirmed by sorbent injection tests. (2) The simple production method TDA identified was effective on all feedstocks tested. (3) The engineering analysis indicated that the new sorbents could be produced for $160 to $230/ton, compared with $500 to $1,000 per ton for activated carbon. If the new sorbents prove to be as effective in sorbent injection as the current data indicate, then the new system has the potential to greatly reduce the cost of mercury abatement in coal-fired electric utilities.

Supplemental Keywords:

Waste incineration., RFA, Scientific Discipline, Toxics, Air, Waste, Sustainable Industry/Business, particulate matter, air toxics, cleaner production/pollution prevention, Chemistry, HAPS, Technology for Sustainable Environment, Incineration/Combustion, Engineering, 33/50, Engineering, Chemistry, & Physics, direct injection , combustion byproducts, particulates, air pollutants, coal fired utility boiler , emission control technologies, mercury, electric utilities, air pollution control, combustion emissions, emissions, air pollution, sorbents, combustion technology, mercury & mercury compounds, Mercury Compounds, coal combustion, coal fired power plants, cost effective, air emissions, power generation , removal

SBIR Phase II:

An Improved Sorbent for Mercury Abatement