The USA is on the brink of introducing legislation to control mercury emissions from power plants. This has obvious cost implications for utilities, and could spur other countries in the same direction.
Dr Anupam Sanyal, International Environmental and Energy Consultants, Inc., Florida, USA
On December 14, 2000, the US Environmental Protection Agency (EPA) announced its intent to regulate mercury emissions from coal fired generators under Title 3 of the Clean Air Act of 1990. EPA plans to issue final regulation by December 15, 2004, which is expected to require compliance by December 2007.
In 1999, EPA initiated the Mercury Information Collection Request (MICR) to 84 plants to provide new information to assist in making future regulatory determinations on controlling mercury emissions from coal fired plants.
Figure 1. Share of electric utilities in emissions of SOx, NOx and mercury in the USA
Based on these data, under the President’s Clear Skies Act of 2003, mercury emissions from industry is planned to be limited in two phases – 26 tons by 2010 and a cap of 15 tons by 2018, corresponding to a 47 per cent and 69 per cent reduction respectively.
In addition to the Clear Skies Act, a multi-pollutant control legislation was proposed by Senator Jeffords on March 15, 2001 and adopted by the Senate on June 27, 2002, called Clean Power Act of 2002. This calls for a 90 per cent reduction in mercury emissions below 1999 levels by 2008. This corresponds to an annual emission cap of 5 tons.
Under the Clear Skies Act, mercury allowances would be allocated based on the ratio of a unit’s heat input to the total baseline heat input of all affected units. This is coal dependent, since the heating value is determined by the type of coal.
As the total heat input of all affected units is not known (no data are available for units not yet constructed, but may be subjected to the Act), it is not possible to precisely determine the number of mercury allowances which would be allocated to an individual unit.
The Clean Power Act does not have any provision for mercury allowances. It calls for a mercury emission limitation for individual units of no more that 2.48 grams/1000 MWh, and does not differentiate by coal type.
Currently mercury is set to be regulated according to Clean Air Act Amendments (CAAA) of 1990, which mandates that Maximum Achievable Control Technology (MACT) must be applied. This requires that the emissions standard cannot be less stringent than the average emissions limitations achieved by the best performing 12 per cent of existing sources in the category or sub-category.
Trading of mercury emissions would be prohibited under the MACT. The uncertainty about MACT is whether mercury will be regulated under a single category of all utilities or if it will be regulated under sub-categories such as boiler type (e.g. cyclone) and/or fuel type (e.g. lignite). Mercury speciation and hence its control are affected by boilers, coal and ash quality. If mercury MACT is not sub-categorized and 90 per cent reduction is required for all utilities, compliance will be much more difficult than if MACT is sub-categorized by fuel type and only 50 per cent removal is required.
The Clear Skies Act would repeal the upcoming mercury MACT rule. Instead the Bill proposes a mercury cap and trade programme. This would give more allowances to units from which mercury removal is more difficult such as burning lignite or sub-bituminous coal.
The affected units under the Clear Skies Act would be exempt from the New Source Review if they comply with the NSPS emission limit of 0.015 lb/GWh (6818 mg/GWh).
In the Clean Power Act, there are no provisions for mercury allowances and trading. But emissions averaging between units in a single facility will be allowed. The Act will not allow a differentiation of mercury emission limits by coal type. Therefore lignite fired units will be subject to the same limit as units burning bituminous coal. Since mercury control depends on the type of coal, some power plants may find it difficult to meet the proposed emission regulations without the use of a trading programme.
Both the Clear Skies and Clean Power Acts contain provisions that might affect the developing mercury regulations. It is believed that neither of these two Acts are likely to pass in their current forms. The multi-pollutant control legislation that will actually be adopted is likely to be a compromise between these two. Since they vary greatly it is difficult to predict what provisions future legislation will actually contain.
There are over 1100 coal fired utility boilers that are likely to be impacted by the mercury legislation.
There is no dedicated mercury control appliance in use in any US coal fired utility. There is neither any proven mercury control technology yet. The US Department of Energy (DOE) has estimated that at 90 per cent mercury removal, the control cost may range between $25 000 and $70 000 per lb ($55 556 and $155 556 per kg) of mercury removed. At this rate mercury control could cost the coal fired utility industry some $2500-7300 million per year.
Mercury control projects
The DOE and the Electric Power Research Institute (EPRI) have initiated extensive mercury control technology programmes in the USA. These are co-funded by utilities and other allied industries. Since 1991, the DOE is reported to have invested some $35 million, closely followed by EPRI.
Figure 2 shows the mercury control technologies under development – wet scrubbing, sorbent injection, corona discharge, catalyst, fixed/fluid beds and precombustion coal cleaning.
In addition to full scale testing, numerous laboratory, bench and pilot scale efforts are underway for improved understanding of mercury emission and control mechanisms.
Figure 2. Power plant mercury control options
In addition to mercury, both the Clear Skies and Clean Power Acts also call for control of multi-pollutants – oxides of sulphur and nitrogen as well as fine particulates. (Control of CO2 is an additional requirement of the Clean Power Act). Additional development programmes have therefore been initiated for multi-pollutant control.
Some of the major development projects underway include:
- Full scale testing of enhanced mercury control in wet FGD by Babcock and Wilcox
- Full scale testing of mercury control by sorbent injection by ADA-ES.
- Pilot scale study of non-thermal plasma based technology by Powerspan Corporation.
- Pilot scale study of mercury removal in ESP at lower temperature by Consol Coal.
- Mercury removal by an advanced hybrid particulate collector (AHPC) – combination of ESP and baghouse by Energy and Environmental Research Center (EERC).
- Development of cost effective carbon and other chemical based sorbents for mercury removal in ESP or baghouse.
- Development and improvement of effectiveness of calcium based sorbents and oxidizing catalysts. The developers include URS Group, Southern Research Institute, and Arcadis.
- Pre-combustion mercury removal from low-rank coals privately funded by KFx Inc. & Associates. This novel and cost-effective technology also achieves multi-pollutant control.
At present, there are no regulatory limits for mercury emission from coal fired power plants in any other countries. There are also no proposals in any country besides the USA for mercury control from coal fired power plants.
The only mercury emission regulation in force is in the EU countries for MSW plants: 0.05 mg/Nm3 at 11 per cent oxygen dry.
© Figure 3. Fate of mercury (Hg) in power plants
It should be noted, however, that mercury regulations exist in the USA for MSW plants, medical incinerators and cement plants. The regulatory limit for MSW is 80 microgram of mercury per dry standard cubic meter (µg/dscm) or 85 per cent reduction of potential emissions; 550 µg/dscm or 85 per cent reduction for medical incinerators and 120 µg/dscm for existing and 56 µg/dscm for new cement plants.
The US DOE, EPRI and the power industry have been aggressively developing technologies to address the challenge of the proposed mercury legislation in the USA. While the exact limit is yet to be determined and will depend where the level is set between the President’s Clear Skies Act and Senator Jeffords’ Clean Power Act, the utilities have to remove mercury to a significantly high level.
It appears that technologies are going to be available to meet the challenge. The cost is still not known and will depend not only on the compliance level but also on coal quality and numerous plant parameters.
For municipal waste incinerators, as in the US, the European Union countries has had mercury legislation for some time. For coal fired power plants there does not seem to be any great concern at this stage. This may change, however, once the US legislation is in place.