Section 5: Emission Limits (Comments and Responses)

• 5.1 General Comments on Emission Limits
• 5.2 SO₂ Emission Limits
• 5.3 NO_x Emission Limits
• 5.4 Particulate Matter Emission Limits
• 5.5 Opacity Emission Limit
• 5.6 Output Basis
• 5.7 Thermal Efficiency/Heat Rate

• The Guidelines should implement the most stringent emission limits which can be technologically achieved. At present, this would most likely be equivalent to emissions from a natural gas combined cycle (NGCC) plant.

As stated previously, Environment Canada has committed to basing the Guidelines on emissions performance consistent with Best Available Technologies that are economically feasible, in accordance with the "keeping clean areas clean" commitments made by Ministers of the Environment under the Canada-wide Standards for PM and Ozone.

Emission limits equivalent to those from a natural gas combined cycle plant are not economically feasible with current BAT for coal-fired plants. However, Environment Canada agrees that performance "as clean as gas" is an appropriate long-term objective for fossil fuel-fired power plants, and would like to engage Canadians in a discussion on this.

• Emission limits, more stringent than the U.S. New Source Performance Standards (NSPS), should be implemented and companies should be encouraged to strive to reach these levels.
• It is not appropriate to use the U.S. NSPS as a basis for establishing Canadian emission limits. The NSPS are generally not the standards required for new facilities. In the U.S., a Best Available Control Technology (BACT) or Lowest Achievable Emission Rate (LAER) analysis is used to select appropriate emission limits. Canadian facilities should also be required to go through a similar process in addition to meeting the national standards. Details of a BACT/LAER process could be put in an appendix to the Guidelines, setting out air quality conditions under which LAER should apply.
• The review of U.S. BACT requirements, which are more stringent than the U.S. NSPS, as a basis for determining Canada's emission limits is supported.
• Emission limits should accommodate all standard modes of operations, the aging of equipment, technological upgrades, fuel diversity and regional needs. They need not specify the most stringent, site specific case since jurisdictional processes will reflect appropriate regional inputs. In the U.S., the NSPS, in conjunction with the New Source Review (NSR) process, operate in this manner.

The Guidelines present Environment Canada's expectations for appropriate performance standards at the national level for emissions from new plants, and the federal Minister of the Environment recommends that jurisdictional air pollution control agencies adopt the Guidelines as practical baseline standards for their regulatory programs. It is recognized that local conditions may necessitate the adoption of more stringent standards.

Similarly, in the U.S., the NSPS are the baseline national standards, accommodating a range of fuel types and regional circumstances. Individual plants may be required to meet more stringent local standards. This suggests that the U.S. NSPS are an appropriate reference point for the Guidelines. Where emission limits for recent new plants in the U.S. are consistently more stringent than NSPS across a range of fuel types and regional circumstances, this suggests that it is reasonable to select more stringent emission limits for the Guidelines. Therefore, the revised emission limits for the Guidelines have been selected based on a review of both the U.S. NSPS and consistent trends in recent permits for new plants which are based on BACT assessments. The following sections explain the basis for selection of limits for each pollutant addressed in the Guidelines.

A process for site-specific assessment and application of BAT to each new unit would fit best within the jurisdictional environmental assessment and permitting processes. Federal guidance on such a process would require further consultation and is not planned at this time.

• Clarification is needed for the phrase "... when determined over successive averaging periods as previously defined..." from Section 4 of the proposed Guidelines.

According to Section 3 of the proposed Guidelines (Section 4 of the revised Guidelines to be gazetted in 2002), under the heading "Interpretation", "averaging period" means a period for determining emission rates based on 720 operating hours. Also in Section 3, "720 hour rolling average" means for each pollutant, the average of the consecutive hourly mean emission rates, determined for the preceding 720 hours of operation.

In practice, this means that for each pollutant and each hour, a new emission rate must be calculated as the average of the hourly mean emission rates for the preceding 720 hours of operation. It is this 720 hour average that should not exceed the emission limit.

• The proposed Guidelines penalize low-sulphur coal by imposing lowest emission limits on these coals, while less stringent emission limits are proposed for higher sulphur coals. The Guidelines would allow greater mass emissions in areas with significant air quality and acid deposition problems, simply because the coal used contains more sulphur. Yet, in places like Alberta, where there are few air quality problems, the emission limits are more stringent. The Guidelines should give credit for, or in some way recognize, the environmental benefits of the use of low sulphur coal.
• The sliding scale proposed in the revised Guidelines encourages blending with high sulphur fuels such as petroleum coke and discourages blending with lower sulphur fuels such as natural gas and biomass. It is recommended to utilize the current form of the sulphur emission limits with lower values considered in conjunction with stakeholder input.
• The upper limit of 520 to 400 ng/J is regionally restrictive where indigenous coals contain high sulphur. An appropriate percent reduction (70-90%) should be applied evenly across the country.
• Regional coal sulphur contents have to be accommodated. An increase from 90% to 95% reduction required for high sulphur coals would reduce emissions by half. For the Atlantic region, where the electric power sector is the overwhelming contributor to acid rain, this could be an important difference.

The proposed emission limits are based on the application of Best Available Technology that is economically feasible. Because the fuels (coal and oil) used in Canada vary widely in sulphur content, application of BAT for control of SO₂ emissions will achieve different results for fuels of different quality. Therefore, the approach proposed results in emission limits being lower for lower sulphur fuels. This is consistent with the U.S. EPA's NSPS for electric power generating units and also with the results of the U.S. BACT/LAER permitting process for new plants. The 1993 Guidelines already contain provision for varying SO₂ emission limits with the sulphur content of fuel. To do otherwise, for example to establish one emission limit for all fuels, would result in an emission limit that was either not economically feasible for higher sulphur fuel, or was not consistent with BAT for low sulphur fuel. The latter would be inconsistent with the Canada-wide Standards for PM and Ozone commitment to keeping clean areas clean, which is based on the recognition that there is no observable threshold for the health effects of pollutants associated with PM and ozone.

However, the proposed emission limits do in fact give a credit for the use of lower sulphur fuels in that the degree of emission reduction required declines as fuel sulphur content declines. To use the more stringent of the proposed emission limits as an example, emission reductions of 80% or less may be required for low sulphur fuel whereas reductions of 95% or more may be required for high sulphur fuel. This discourages blending with higher sulphur fuel and encourages blending with lower sulphur fuel. This is also consistent with the application of BAT that is economically feasible in that SO₂ removal is more difficult, and hence potentially more costly, at low flue gas SO₂ concentrations.

Therefore, the Guidelines will continue to contain SO₂ emission limits that vary with the sulphur content of fuel.

• Allowing new power plants to burn 7%, or even 3.5%, sulphur coal is environmentally irresponsible. Lowering the emission limit for SO₂ would ensure that high sulphur coal is not used.

The Guidelines attempt to strike a balance between accommodating the use of a wide range of fuels, and protecting the environment. Like the U.S. NSPS, it does this by establishing an upper limit on SO₂ emissions. Very high sulphur fuels may still be burned, but SO₂ emission reductions may have to be more than 95%.

• The range of SO₂ emission limits proposed by Environment Canada is very wide. The most stringent standard of 50 ng/J proposed by Environment Canada is supported.

The 50 ng/J emission limit was proposed by Environment Canada as a lower limit below which no further emission reduction would be required, for example where very low sulphur fuel was being used and further emission reductions might not be economically feasible. The use of this limit for high sulphur fuels is judged to be not economically feasible.

• The SO₂ limits are too complicated. They should be simplified, if possible, to one number or a simple equation which removes subjectivity and at the same time is representative of a variety of fuels.
• It is not clear how the reference emission rates based on uncontrolled emissions would be applied.

Environment Canada agrees that the proposed SO₂ limit is complicated and has changed the process to determine the limit while retaining the concept of basing the limit on the uncontrolled emission rate.

The application of emission rates based on uncontrolled emissions requires a decision to be made on the period of time required to sample the fuel to determine average sulphur content and heat content in order to estimate the uncontrolled emissions. For example, a very short averaging period would require very frequent analyses of fuel sulphur content which would have cost implications. A very long averaging period could lead to the emission limit at any time being more or less stringent than intended. The choice of averaging period is left to the implementing regulatory authority.

• The emission limit for SO₂ should be equivalent to that of natural gas combined cycle (NGCC) (i.e. approximately 0 ng/J). If this is too stringent, a limit of 50 ng/J should be set.

Environment Canada does not agree with the use of a single emission limit in the range of 0 - 50 ng/J because this would not be consistent with BAT that is economically feasible.

• The proposed emission limits of 50 to 520 ng/J allows for an increase in SO₂ emissions from the current emission limits of 258 ng/J. This will continue the use of 'dirty' coal and not provide incentive to reduce emissions.

The conclusion that the proposed emission limits would allow an increase in SO₂ emissions is a misinterpretation of the emission limits currently in the Guidelines. The current Guidelines call for 258 ng/J or 90% reduction, whichever is less stringent. This means that there is effectively no upper limit to SO₂ emissions, for example from high sulphur fuels, as long as a 90% reduction is achieved. The proposed emission limits contain an upper bound (eg. 520 ng/J) which may mean that emission reductions of greater than 90% are required for high sulphur fuels.

• A 70% reduction in uncontrolled emission limits is inadequate for new plants. An emission limit of 35-135 ng/J with specific reduction of 80-95% is proposed.
• Emission limits equivalent to natural gas combined cycle (NGCC) are desirable. If sEPArate limits for fuel type are required then an emission limit of 50 ng/J or 98% removal for high sulphur coals is proposed.

In reviewing U.S. data, it was found that the SO₂ emission limits for recently permitted plants across various regions and fuel sulphur contents were consistently more stringent than the U.S. NSPS. This suggests that the NSPS are out-of-date with respect to BAT. Based on consistent trends in the emission rates for recently permitted plants, the final emission limits for the revised Guidelines will reflect the following limits in the input-based format:

The emission rate for each plant should be equal to or less than:

1. 400 ng/J of heat input and 8 percent of uncontrolled emissions (92% reduction), or
2. 250 ng/J of heat input and 25 percent of uncontrolled emissions (75% reduction), or
3. 50 nanograms per joule

• Wording should be inserted in the Guidelines that endorses a flexible interpretation of the SO₂ standard formula so that it can be expressed as either a fixed or variable standard.

This comment is understood to request that the uncontrolled SO₂ emission rate can be either fixed or variable with the sulphur content of the fuel. A fixed standard would greatly simplify the emission limit but would require a decision as to whether the fixed standard was based on the minimum, maximum or average fuel sulphur content. This would mean that the standard would be more or less stringent than a BAT-based standard. A variable standard would most closely follow the guiding principle that the emission limits are based on BAT but, as indicated above, such a standard would require a decision as to the period of time required to sample the fuel to determine average sulphur content and heat content in order to estimate the uncontrolled emission rate. This decision is left to the implementing regulatory authority.

• The stringent emission limits for low sulphur coals would require scrubbers to operate at very low flue gas SO₂ concentrations where the incremental removal efficiency is very poor.

The lower SO₂ removal efficiency at lower flue gas SO₂ concentrations is accounted for in the "sliding scale" nature of the limits, whereby lower SO₂ removal efficiencies are required as the uncontrolled SO₂ emissions decrease. Data from the U.S. indicates that the SO₂ emission limits are technically and economically feasible for plants burning very low sulphur coal.

• The Guidelines should not be more stringent than the N305 emission Guidelines, as of 2005. The least stringent emission limits proposed by Environment Canada should be effective not sooner than 2010.
• The emission limit should be a single number applicable to all fuels.
• A range of 30-45 ng/J should be used for the emission limits. This would be consistent with more stringent limits in the U.S. and some of the European countries.
• The range of emission limits (50 to 70 ng/J) proposed by Environment Canada is supported, but the most stringent (50 ng/J) is preferred.
• An emission limit of 50 ng/J is recommended as this limit is easily achievable with existing technology.
• Emission limits equivalent to natural gas combined cycle (NGCC) (i.e. approximately 20 ng/J) is desirable. If sEPArate limits for fuel type are required then an emission limit of 50 ng/J for coal and 20 ng/J for natural gas is recommended.
• An average of the opposing ends of the proposed range would be adequate.
• It is inappropriate to apply the more stringent NO_xstandards of the U.S. NSPS to a new coal-fired station in Alberta. These limits were a result of serious airshed and regional haze issues which do not exist in Alberta.
• The emission limits in the Guidelines should be based on the Alberta standard of 125 ng/J.

Of the above comments, the first is understood to refer to a NO_x emission limit of 100 ng/J proposed as a starting point for initiative N305 of the 1990 CCME NO_x/VOC Management Plan. This is judged to be out of date with respect to BAT that is now economically feasible.

A single NO_x emission limit for all fuels is in fact what is being proposed for the Guidelines.

As was the case for the SO₂ emission limits, it was judged appropriate to base the NO_x emission limit on what has been demonstrated to have been achieved across various regions and fuel types. A limit of 65 ng/J on an input basis fits this selection criterion. More stringent limits are being achieved at some plants in the U.S., but not on a consistent basis across regions and fuel types. The level of 65 ng/J on an input basis is equivalent to the U.S. NSPS, which is the minimum standard for all new plants in the U.S. regardless of regional airshed issues.

A NO_x emission limit equivalent to the performance of natural gas combined cycle plants was judged not achievable by BAT that is economically feasible for coal-fired power plants. However, Environment Canada agrees that performance "as clean as gas" is an appropriate long term objective for fossil fuel-fired power plants, and would like to engage Canadians in a discussion on this.

Based on the above, a NO_x limit of 65 ng/J on an input basis is appropriate for the revised Guidelines.

• The most stringent emission limit of 8 ng/J proposed by Environment Canada is supported.
• Emission limits equivalent to natural gas combined cycle (NGCC) (i.e. approximately 0 ng/J) is desirable. If sEPArate limits for fuel type are required then an emission limit of 8 ng/J for coal is acceptable. Since PM emissions from a natural gas plant are negligible, it may not be necessary to set a specific standard for this fuel.
• An average of the opposing ends of the proposed range would be adequate is suggested.
• The emission limits in the Guidelines should be set at 13 ng/J, based on the Alberta standard and the output from the Strategic Options Process.
• A promising control for mercury, especially for lignite, is activated carbon injection into a baghouse is noted. However, one study appears to indicate that a reduction in PM removal efficiency is required with activated carbon injection. Further work is required in understanding the simultaneous removal of mercury and PM before proposing a more strict PM emission limit.
• It is understood that although the U.S. NSPS of 13 ng/J for PM is expressed as total particulate matter, recent permit standards for comparable units are generally expressed as PM₁₀. A speciation test by Natural Resources Canada on one of Canada's existing coal-fired power plants showed that, when total PM emissions were near 13 ng/J, less than 70% of the total PM was in the form of PM₁₀. Consequently, it cannot be concluded that total particulate matter emissions as low as 8 ng/J are achievable or reasonable based on U.S. information.

A PM emission limit equivalent to the performance of natural gas combined cycle plants was judged not achievable by Best Available Technology that is economically feasible for coal-fired power plants. However, Environment Canada agrees that performance "as clean as gas" is an appropriate long-term objective for fossil fuel-fired power plants, and would like to engage Canadians in a discussion on this.

As indicated in the comments, further work may be necessary to determine the impacts of future mercury emission standards on PM emission rates. It is judged premature at this time to base the PM limit on potential mercury control measures. Future revisions to the Guidelines can deal with this issue if/as appropriate.

Environment Canada has reviewed the level and form of the PM limits for recently permitted U.S. plants, and found that the majority of these plants have a permitted PM limit of 8 or 9 ng/J (input) in the form of total suspended particulate (TSP). In some cases, the plant permits specify a limit of 9 ng/J as TSP together with a limit of 8 ng/J as PM₁₀. Therefore, the revised Guidelines will contain a PM limit equivalent to 9 ng/J (input) as TSP. Given the current air quality focus on PM₁₀ and PM_2.5, it is considered likely that future updates to the Guidelines will deal with these PM size fractions.

• The normal operating opacity limit of 20% seems a little generous. However, with the new PM limit, this should be irrelevant.

Environment Canada is not at this time proposing changes to the opacity limit.

• The output-based approach proposed in the Guidelines is supported, in that it would reward energy efficiency. Potential problems identified with the output-based standard included:
  • With both deregulation and increased competition, reporting emissions using this form could potentially disclose sensitive information about the utility.
  • With the output-based standards being reported on a 'net' basis, there is no allowance for station service. This may act as a disincentive for utilities to implement appropriate control technology. Since the best available technology requires additional energy, utilities could elect to not add on the appropriate controls on the basis that their emission limits would have no allowance for such equipment. It was noted that the U.S. EPA uses a gross heat rate for conversion of emission limits to an energy output basis.
  • Monitoring, reporting and regulating on an energy output basis may be of concern.
• Emission limits in the Guidelines should continue to use an energy input basis until these issues are better understood.

Environment Canada has received no information that indicates the manner in which emission rate data reported on an output basis would be sensitive in a competitive electricity market. In fact, in competitive electricity markets in the U.S., very detailed data on emissions and other information is readily available to the public. If concerns were to be identified, Environment Canada believes that provisions are available to protect commercially sensitive information.

On the question of gross versus net energy output as the basis for the emission rates, the key consideration is that the same basis (gross or net) is used for both the derivation of the limit and the reporting of emissions. Either option (gross or net) would achieve the objective of having efficiency contribute to meeting the emission limits.

Environment Canada's rationale for using a net energy output basis for emission limits is that it considers the overall efficiency of the plant and therefore provides an incentive for the full range of measures that may contribute to this, including minimization of station service demands, in the sense that all these measures can contribute to meeting the emission limits. If gross energy output was used as the basis, minimization of station service demands would not contribute to meeting the emission limits.

Given that decisions of control technology will be based on the need to meet the applied emission limits, Environment Canada does not accept that the net basis will act as a disincentive to implement appropriate control technology.

Environment Canada does not agree that there will be serious problems with monitoring, reporting or regulating on an energy output basis.

• Concern was expressed with the applicability of 9.4 GJ/MWh, proposed in the Guidelines, as the heat rate for converting emission limits to an output basis. This value is not representative of today's commonly available technology. This value does not accommodate all fuels, technologies, operating regimes (i.e. load) and decrease in efficiency with age. Additionally, the proposed heat rate is approximately 30% higher on a gross basis, than that used by the U.S. Environmental Protection Agency (EPA).
• Environment Canada should either increase the reference heat rate or develop a staged approach if the output basis is to be used. A heat rate of 11 GJ/MWh is recommended.
• An efficiency of 34% (i.e. 10.6 GJ/MWh) is suggested.
• Additional provisions are requested for a unit which deviates from optimum operating conditions, and incorporates additional pollution control equipment.
• It was recommended to continue to use the energy input basis but allow an adjustment based on a unit design efficiency compared with the efficiency of typical subcritical units recently approved in North America.
• The heat rate of 9.4 GJ/MWh is a positive step and industry has not presented adequate arguments for an alternative. Since the Guidelines address new plants, they should not aim for anything less than what has been proposed at the new Genesee 3 plant, and should aim even higher.
• Other facilities, such as pressurized fluidized bed, supercritical, integrated gasification combined cycle and natural gas combined cycle plants, are operating with lower heat rates of 7 to 8.6 GJ/MWh.
• If 9.4 GJ/MWh is selected for the Guidelines, this value should be re-evaluated on a timely basis.

Environment Canada has reviewed information on the heat rates that can realistically be achieved for currently available pulverized coal technology considering the range of fuel types used in Canada and accounting for operating regimes, emission control technologies and the effects of plant age. This analysis indicated that a net heat rate of 10.6 GJ/MWh is currently achievable across all the above considerations. Key considerations in making this determination were that, as indicated in the comments, the originally proposed heat rate of 9.4 GJ/MWh could be difficult to achieve consistently for certain coal types, for part load operation and considering the decrease in efficiency with plant age .

Environment Canada believes that an output-based emission limit is preferable to an input-based limit adjusted to unit design efficiency because the output-based limit will encourage continual attention to the actual efficiency of unit operation as a means of meeting the limit. An input-based limit adjusted to unit design efficiency would not do this.

It should be noted that the much lower heat rates (higher efficiencies) achievable for pressurized fluidized bed and integrated gasification combined cycle plants are not appropriate for use here because such plants have not yet been demonstrated to be best available technology that is economically feasible in the manner that this term is used for the revision of the Guidelines.

• The terms 'gross' and 'net' should be defined in terms consistent with those used in the electrical generation sector. Also it should be stated that any potential efficiencies or heat rates referred to in the Guidelines are based on Higher Heating Value.

Environment Canada accepts that the terms 'gross energy output' and 'net energy output' should be defined in the Guideline for purposes of clarity. Consultation with authoritative sources in industry has resulted in the following definitions:

Gross energy output means the gross useful work performed by the steam generated. For units generating only electricity, the gross useful work performed is the gross electrical output from the turbine/generator set. For cogeneration units, site-specific provisions for accounting for any useful thermal energy output supplied by the plant may be specified by the appropriate regulatory authority.

Net energy output means gross energy output minus unit service power requirements.

Environment Canada agrees that it should be stated in the Guidelines that the heat rate is based on the Higher Heating Value of the fuel.

• The output-based standard, calculated using efficiency, may be inappropriate for plants which are not conventional fossil fuel-fired boilers. This would include combined cycle gas-fired units or plants with cogeneration. These facilities have substantially different efficiencies from conventional plants. Also, cogeneration facilities produce steam in addition to, or in place of, electricity.

As indicated in Section 3 of the proposed Guidelines (Section 4 of the revised Guidelines to be gazetted in 2002), under the heading "Interpretation", the Guidelines do not apply to plants which are not conventional fossil fuel-fired steam boilers, and this includes combined cycle gas-fired units. It is believed that new cogeneration plants will generally be of this type and therefore would not be subject to this Guideline. In the case where a new conventional fossil fuel-fired steam boiler was proposed as a cogeneration unit, site-specific provisions for accounting for any useful thermal energy output supplied by the plant would be up to the implementing jurisdiction.

• Since no existing Canadian units achieve the heat rate of 9.4 GJ/MWh, there is no opportunity for the Guidelines to apply to existing plants with major modifications.

As indicated previously, there are no provisions in the proposed Guidelines that apply the quantitative emission limits in Sections 4 and 5 (Sections 5 to 7 of the revised Guidelines to be gazetted in 2002) to existing or modified units. Although the emission limits in the Guidelines are not intended for application to modified units, they can be a source of direction for assessments of the feasibility of emissions reduction measures for modified units.