In the 1990s, the Clean Air Act cracked down on major air pollutants like nitrogen and sulfur compounds, ultimately leading to dramatic improvements in air quality in the United States. Now the EPA has implemented new Mercury and Air Toxics Standards (MATS). MATS requires, for the first time ever, that U.S. utilities operating oil and coal plants must reduce their dangerous mercury emissions.
It is estimated by the EPA that the new MATS rule will apply to around 1,100 coal-fired units and 300 oil-fired electric generating units (EGUs) in the U.S., which have until April 16, 2015 to comply with the new emissions restrictions – unless they are granted a one-year extension due to undue hardship in meeting the deadline.
Three basic forms of mercury can be emitted from the stacks of coal-fired power plants: elemental mercury (Hg0), oxidized mercury (Hg2+), and particulate-bound mercury (Hgp), with all three making up the total mercury (Hg) that must be reduced for utilities to be in compliance with MATS. Elemental mercury is the most difficult to remove, as it is not easily eradicated by standard sorbents and is also not removed in scrubbers due to being quite insoluble.
For utilities to meet the 90 percent reduction goal stipulated by MATS they must utilize technologies that can effectively remove elemental mercury. Many are looking at low-cost options like sorbent injection to achieve MATS compliance. Unfortunately, removing elemental mercury by injecting sorbents, such as activated carbon (AC), has proven to be a challenge.
Activated carbon injection (ACI) has been shown to be only somewhat effective at capturing mercury in early tests; in most cases, only about 60 percent removal was achieved no matter how much AC was injected. For several plants with high levels of Hg0, less than 50 percent removal was achieved using standard ACs – even at injection rates exceeding 10 lb/Macf (pounds/million actual cubic feet) of flue gas, which is a level most utilities consider to be uneconomical and unacceptable.
Fortunately, Midwest Energy Emissions Corp. (MEEC) has the solution.
In conjunction with the University of North Dakota’s Energy & Environmental Research Center (EERC), ME2C has been developing, testing, and successfully demonstrating a new technology that offers utilities a low-cost option for achieving MATS compliance. Through extensive research over the last several years, the company has developed a complex sorbent-flue gas interaction model that led to the development of Sorbent Enhancement Additive (SEATM), its revolutionary new mercury-controlling technology.
Capturing mercury using sorbents is very complex, involving many forms of mercury, oxidation, and the role and impact of various flue gas components on chemisorption. SEATM technology involves using a relatively small amount of halogen to promote catalytic oxidation as well as a small amount of proprietary material to protect the sites from competing adsorption by other flue gas components. Both of these make the sorbent much more reactive and able to more effectively capture mercury. SEATM technology can be implemented at a particular power plant in several ways, depending on the coal type being burned, the operational parameters, and the arrangement of emission control equipment that is installed.
SEATM technology offers many key advantages, such as improved mercury oxidation and enhancement of sorbent reactivity, which can improve capture in downstream equipment. SEATM technology improves mercury capture while using much less sorbent; it allows the use of sorbent supplies that are more abundantly available; it improves mercury capture efficiencies – in some cases to more than 90 percent; and it allows for performance and cost optimization of SEATM and sorbent at each site. By using lower amounts of sorbent, SEATM technology minimizes ESP particulate and opacity problems; it also minimizes fabric filter particulate emissions and pressure drop while allowing units to operate at maximum load by using lower amounts of sorbent. Furthermore, MEEC’s Sorbent Enhancement Additive reduces concerns associated with carbon oxidation, self-igniting, and heating in hoppers.
Through continued development, testing, and demonstration, commercialization has been achieved for the multi-patented SEATM technology, and MEEC believes this revolutionary technology is the best approach from the perspectives of maximum mercury capture, flexibility, and cost. In a case study utilizing SEATM technology, commercial equipment achieved greater than 90 percent mercury removal, which not only met but exceeded MATS requirements. Based on parametric testing and commercial performance, the power plant that was tested achieved EPA MATS compliance for around 65 percent less in annual costs than the leading brominated activated carbon (BAC) program. The tested power station will also require only 25 percent of the amount of material added to the flue gas, which will reduce potential balance-of-plant effects without hindering fly ash sales. Flyash, a byproduct of coal combustion, is often sold by utilities for use in making concrete and is often rendered useless by some of the BAC based solutions.
MEEC’s SEATM technology offers a second-generation approach to reducing mercury from power plants using much less sorbent, lessening the overall cost of mercury reduction and minimizing many of the balance-of-plant issues resulting from using large amounts of more traditional mercury-reducing sorbents, like AC or BAC.
Searching for cost effective solutions, multiple utilities have completed or contracted demonstrations of Midwest Energy Emissions’ mercury removal technology. These demonstrations are performed by MEEC on site at active utilities, under real world circumstances, and have produced promising results. As the EPA’s MATS compliance deadline looms, utilities have no choice but consider advanced mercury reducing technologies such as the one offered by MEEC.
For more information, visit MEEC online at www.midwestemissions.com
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