The USAà¢€â„¢s Clean Air Mercury Rule requires utilities to dramatically reduce mercury emissions from coal fired power plants. Some may achieve this by adapting existing emission control technologies, while others will look to new, multi-pollutant control technologies that offer protection against future emission standards.
Douglas C. Comrie, vice president and principal inventor, Chem-Mod LLC, USA
Coal fired power plants are the largest, human-caused source of mercury emissions to the air in the USA. For years, mercury emissions from coal utilities remained unchecked due to lack of US legislation aimed at reducing emissions, but that changed in March 2005 when the Environmental Protection Agency (EPA) issued the Clean Air Mercury Rule (CAMR). The rule will soon require coal companies to dramatically reduce their mercury emissions from 48 to 38 tonnes by 2010 and eventually cap emissions at 15 tonnes by 2018.
Following this federal mandate of cutting mercury emissions by 70 per cent by 2018, more than 15 states including Pennsylvania, New York, Illinois, Michigan, Georgia, Montana and Oregon have begun to develop their own policy initiatives that push emissions reductions even further. Since March 2005, several states have passed mercury policies that are stricter than the federal guidelines, instituting emissions standards that call for reductions of 90 per cent by 2015 in Minnesota and 90 per cent by 2013 in Maryland. The introduction of new legislation at both the federal and state levels has applied new pressure to the utility industry, which now must determine the most cost effective and efficient means to reach these lower emission levels.
Utilities are now looking to new technologies to achieve higher reduction levels without negatively impacting their bottom lines. It was in response to this demand that the Chem-Mod Solution was developed. Chem-Mod is a multi-pollutant control technology that is emerging as a leading option for coal fired energy companies, due to its low cost and easy integration with existing scrubber technology.
Figure 1. Test results showing maximum mercury and sulphur dioxide reductions
The Chem-Mod Solution was first introduced to the US market in February 2006. The company, Chem-Mod, is a privately owned environmental services company based in Stow, Ohio. Chem-Modà¢€â„¢s system uses an innovative sorbent-based technology to significantly reduce mercury, sulphur dioxide, arsenic, other heavy metals and chloride emissions.
Chem-Modà¢€â„¢s dual injection sorbent system applies two sorbents before, during or after the coal combustion process to dramatically reduce toxic emissions. The powder sorbent, known as S-Sorb, is generally applied at a rate of 3-6 per cent by weight of fuel, and the liquid component, or Mersorb, is usually applied at an average rate of 0.2 per cent.
Once in the furnace, the sorbents mix with the furnace gases and form particulate compounds that are bound together in a fine-grained, ceramic-like matrix. These compounds form to complex with mercury, sulphur, heavy and light metals, fluorine and chlorine and report with the fly ash in the particulate control device.
The footprint for the system is generally considered to be 30 m by 30 m for a 200-400 MW facility. All raw materials for the system can be transported to the energy facility either by pneumatic rail car or pneumatic truck, and can be blended on site and applied by the utility directly to the fuel or into the furnace.
In December 2005, Chem-Mod concluded a series of successful commercial-scale tests of the Chem-Mod Solution at three full-scale coal fired power plants owned by three separate major US energy companies. Prior to its commercial tests, Chem-Mod conducted pilot testing of the system at the Energy and Environmental Research Center (EERC), an independent research laboratory specializing in clean coal technology.
Commercial and pilot testing, which was overseen by the EERC, was done on a variety of coal types including Powder River Basin, Illinois Basin, Appalachian, Pittsburgh Seam, and mixed fuel blends. These tests showed reductions in mercury of up to 98 per cent, and of sulphur dioxide emissions of up to 97 per cent, as well as dramatic reductions in arsenic, other heavy and light metals, and chloride emissions. These tests were not optimized at the time due to time constraints on testing, but it was concluded during testing that the duration and the quantity of the raw materials applied in the Chem-Mod process can be modified to influence the resulting effect on a particular pollutant and the amount of its related reduction.
The use of Chem-Modà¢€â„¢s sorbents during the commercial testing phase was also found to increase fuel efficiency by up to 5.5 per cent, measured by British Thermal Units (BTU) per kWh. This increased efficiency translated to 5.5 per cent less fuel used by the utility, an additional cost saving mechanism provided by the system. A portion of the efficiency gain is achieved through improved heat transfer in the furnace due to mechanisms such as reductions in slagging and more efficient fuel combustion. Helping efficiency, the sorbents chemically react to remove slag build-up from the boiler tubes.
A concrete solution
In the Chem-Mod process, more fly ash is generated as a result of the addition of the S-Sorb sorbent to the coal. Fly ash created using the Chem-Mod Solution underwent TCLP testing by a third party independent lab and the results of these acid leach tests showed that the fly ash met Resource Conservation and Recovery Act (RCRA) regulated limits and was determined to be non-leachable. Furthermore, in most cases the fly ash passed drinking water standards as well. Chem-Modà¢€â„¢s fly ash was also found to be stronger than other fly ash types, and can be sold to concrete companies as a partial replacement to Portland cement. Chem-Modà¢€â„¢s safe sorbents encapsulate harmful pollutants within a ceramicized chemical structure that becomes part of the resulting high-grade fly ash produced by the system. The sale of Chem-Modà¢€â„¢s fly ash offers utilities an immediate and long-term way to realize revenue gains that offset the cost of the system and transfer a system byproduct into a readily useable product rather than one that must be disposed at landfills, as is the case with other lower grades of fly ash.
Concrete strength studies showed that when replacing a portion of Portland cement with fly ash generated using Chem-Modà¢€â„¢s proprietary sorbents, the resulting concrete is up to 60 per cent stronger than a pure Portland cement mix. Results of acid leach tests (conducted by EERC) verified that the resulting fly ash is safe to recycle and has met Resource Conservation and Recovery Act (RCRA) standards.
The ash produced by the Chem-Mod Solution also leads to a reduction in landfill waste by reducing the amount of ash that is disposed of in landfills, and reduces the amount of carbon dioxide emitted into the air, since less Portland cement is used in producing concrete when fly ash is included in the process. For every tonne of Portland cement replaced by fly ash, there is a corresponding 1 tonne reduction in carbon dioxide emissions into the air.
Wet scrubber comparision
Only 30 per cent of US coal fired power plants currently have scrubbers installed and it is estimated that the US utility industry will spend approximately $17 billion on scrubber technologies between 2005 and 2010 and approximately $1 billion specifically on mercury control technology from 2005 through 2010 in order to meet new compliance standards. This does not include the cost of replacing older plants that cannot be retrofitted with scrubbers, or utility sites that are too small for scrubbers.
Coal companies now have a choice – either enrich their existing emission control technologies, like wet scrubbers, or install new, technologically advanced reduction systems. Utilities that have chosen to upgrade their existing emission control systems through the application of new technologies, like Chem-Mod, have found a way to meet new emissions standards without the cost of buying additional wet scrubbers. While the Chem-Mod Solution can be used on a stand-alone basis, it can also be used in tandem with scrubbers to greatly reduce the cost of emissions reductions, or to allow the use of higher sulphur coals. Alternatively, the technology can extend the life of older or land-locked plants with minimal capital investment.
Figure 2. Normal slag buildup on boiler tubes
Utilities that have chosen to buy new scrubbers to meet stricter emissions standards must bear the high capital and operational costs of this technology and also must manage the limited ability of scrubbers to effectively reduce mercury emissions and heavy metals, since scrubbers can only reduce oxidized forms of mercury, but not elemental mercury, which is the most harmful form of mercury to humans.
While the Chem-Mod Solution requires minimal expertise in terms of required engineering and construction other than an understanding of boiler operations, scrubbers require specialized personnel to install and operate them, which adds significant costs. Initial implementation of Chem-Modà¢€â„¢s technology costs approximately $1.5-$5.0 million for a 200 MW plant, based on the size and complexity of the facility. The average cost of installing a wet scrubber at a similar capacity facility could range from $35-$65 million, representing a substantial cost differential.
Figure 3. Slag buildup removed with Chem-Mod sorbents
Chem-Modà¢€â„¢s system is easily installed and requires very little physical space – approximately 465 to 2044 m2 for equipment for a 100 MW to 1200 MW plant – unlike scrubber systems, which generally require thousands of square metres for a similar sized facility. The technology requires little expertise in terms of required engineering and associated costs. Utilities should be able to install the à¢€Ëœoff-the-shelfà¢€â„¢ equipment within 30 days and be operational soon thereafter.
The Chem-Mod Solution also does not require the assistance of specialized personnel, due to the non-hazardous nature of the raw materials used in the system. The increase in fuel efficiency created by the system also allows coal fired plants to burn less coal while producing the same amount of energy. This is in sharp contrast to the parasitic load created when using scrubbers. Finally, the fly ash created by the process can be sold for use in concrete production as a replacement to Portland cement, which provides an environmentally sound way to effectively recycle the byproduct produced and serves to offset the low capital and operational costs of the technology. This compares with the disposal cost of scrubber sludge.
Emissions standards will continue to evolve at both the state and federal levels, and will ultimately become more stringent over time. Utilities that adopt new technologies early on to meet emissions compliance will benefit from these technologies today and in the future due to the multi-pollutant controls that are offered with these cost effective systems. As standards increase, it will become imperative for all emission control systems to reduce multiple pollutants effectively.