EMISSIONS STANDARDS FOR MUNICIPAL WASTE COMBUSTORS:
Discussion and Critique about Recently Proposed Standards
Marjorie J. Clarke
Fellow, Center for Applied Studies of the Environment
1995 International Conference on Solid Waste Management:
Thermal Treatment and Waste-to-Energy Technologies
Emissions Standards For Municipal Waste Combustors:
Discussion and Critique about Recently Proposed Standards
Marjorie J. Clarke
Center for Applied Studies of the Environment
Over the last several years the EPA and a number of states have been working to develop and modify standards for emissions from Municipal Waste Combustors (MWCs). In the 1980s, when EPA did not act to enact national standards, some forward-looking states did so, establishing benchmarks, which, along with European standards which were becoming more stringent with time, could serve as models for EPA. As a result of legal action and requirements in the 1990 Clean Air Act Amendments, EPA, in 1991 and again during this last year, has moved to recommend standards for MWCs.
This paper discusses and evaluates the proposed federal MWC standards in light of emissions data from new and retrofitted MWCs in this country and abroad. Two interpretations of Section 129 of the Clean Air Act Amendments and their effects on calculation of the Maximum Achievable Control Technology (MACT), and therefore the standards, will be discussed. The effect on emissions of different emission control designs will be explored briefly. Particular attention will be paid to the effect of operations (e.g., flue gas temperature, injection rates for reagents such as lime and activated carbon) and maintenance of the MWC on emissions, and the role of optimizing operations as part of standards. An alternative set of MWC standards, based on EPA’s dataset, additional data, and an alternative MACT interpretation will be presented.
Recently EPA and a number of states have been working to develop and modify standards for emissions from MWCs. In the 1980s, when EPA did not enact national standards, some forward-looking states did so, establishing benchmarks, which, along with European standards which were becoming more stringent with time, could serve as models for EPA. As a result of legal action and requirements in the 1990 Clean Air Act Amendments (CAAA), EPA, in 1991 and again during this last year, recommended standards for MWCs.
This paper critiques the proposed federal MWC standards in light of alternative interpretations of Part 129 of the CAAA and emissions data from new and retrofitted MWCs in this country and abroad which EPA excluded from its analysis. Particular attention will be paid to the effect of operations (e.g., flue gas temperature, injection rates for reagents such as lime and activated carbon) and maintenance of the MWC on emissions, and the role of requiring optimization of operations in the standards. Alternative emissions standards are proposed.
EPA’S REVISION OF LIMITS ACCORDING TO MACT
For new plants EPA interprets MACT to equal the performance level of the average plant in the top 12%-ile in their database of existing US plants, instead of the performance level of the best plant, as Sec. 129 stipulates. EPA's argument is that the best plant's performance varies over time, and therefore, the basis for this best plant's performance, and therefore, the NSPS, should be based on a range representing the best plant's performance, and the numerical value chosen should be less than the reported performance of the best plant in the database. This assumes that the all the figures in EPA’s database represent the best possible emission for each plant listed. But there is no evidence to support this assumption. In fact, a more supportable assumption is that each emissions database as a whole is based on data from different plants operating under a range of operations, some plants operated well, most average, and some poorly, such as in a normal distribution (bell curve). Additionally, one would expect that any plant at the top of a performance database would have relatively optimal operations and maintenance, and therefore would have less variation in performance. Thus, any individual datum in a database such as EPA’s is most likely to represent the middle of a distribution of operations for that plant, than one end or the other. So it is not at all clear, as EPA contends, that the best datum in each of EPA’s emission databases does not represent a typical emission for that plant. Further, it is certainly not clear that the average of the upper 12%ile of a bunch of different plants is an accurate representation of the emissions from the best plant.
Even if it were a correct interpretation of Sec. 129, to place a NSPS limit at a level less stringent than the performance level of the best plant in a database, variation of an order of magnitude by one plant surely would not reflect the performance of the best plant. But, including data which EPA excluded, it will be shown that EPA’s proposed NSPS is often an order of magnitude higher than their databases’ best plant’s emissions.
For existing plants EPA is interpreting MACT to equal the average of the top 12%-ile of permits issued over many years by many states. Part 129 (a) (2) clearly requires EPA to derive floors from lower actual emissions, when data is available: “Emissions standards for existing units in a category may be less stringent than standards for new units in the same category but shall not be less stringent than the average emissions limitation achieved by the best performing 12 percent of units in the category...” The statute emphasizes achievement (i.e. performance), not permitted levels, which are considerably higher. In contrast, for the most part, the states based their permitted emission levels on the capability of older plant designs and older concepts of optimal operating practice. Just as the older designs alone are not nearly as efficient at removing pollutants as EPA’s current design basis for controlling emissions of organics, metals, and acid gases (i.e., activated carbon, scrubbing, efficient particulate removal), previous concepts of good operating practice are incomplete, and in some cases inaccurate in the light of current experience. Following are additional reasons why permits should not serve as a basis for establishing emission guidelines for existing plants.
1) Since there are no MWC permits in this country for facilities having EPA’s design basis, the database of current permits cannot come anywhere close to the eventual performance of existing MWCs when retrofitted with activated carbon as well as efficient scrubbers and particulate removal devices.
2) EPA's own BID document  prepared in support of the 1991 MWC standards show that model plants, equipped with "good combustion and temperature control with best acid gas control and best PM control" would perform better than the currently proposed standards for existing MWC's for almost all types and sizes of plants. (EPA’s definition of these operating practices include: "exhaust gas temperature control to 300oF", "best acid gas control - spray dryer", and "best PM control (0.01 gr/dscf)".) (Note that these model operating conditions do not include activated carbon injection.) Even without carbon injection, there is considerable disparity between the EPA model plant retrofit achievement levels and EPA's proposed guidelines for large and small existing MWC's (see Figure 1).
It is clear that the EPA model plant retrofits can achieve far lower emissions levels than the proposed guidelines. The addition of activated carbon to the model retrofit should serve to reduce the model emissions even further than the levels in Figure 1 would indicate. For this reason alone EPA's proposed guidelines for existing large and small plants are insupportable and should be lowered considerably.
3) EPA in its draft MWC emission guidelines report
states that the
4) NOx control has usually not been required at all on MWC's in
5) EPA has promulgated a single set of hazardous waste incineration requirements to apply to facilities regardless of their size, type of waste burned, or age. Since hazardous waste and the incinerators designed to burn it can vary even more than MWC's, EPA should, likewise, not choose to subdivide the universe of MWC's by age, combustor type, and size, or to devise different measures for good combustion practice and emission limit for each.
RECOMMENDED INTERPRETATION OF MWC MACT FLOORS
A more straightforward and accurate
interpretation of Sec. 129 as regards the MACT level for new plants is
warranted. The performance datum for the
best performing plant in the world should be the basis for the MACT floor for
new plants. It is necessary to enlarge EPA’s database to include MWC’s outside
For the reasons stated above, EPA's reliance on permitted values for regulating emissions from existing facilities is not warranted. Since permitted values are such a poor approximation of the likely performance of MWC's retrofitted with activated carbon, scrubbers, efficient particulate controls, and NOx controls, a more supportable basis for guidelines for all existing MWC's would be the average of the top 12%-ile performance data for existing facilities in this country. This level of performance has already been achieved by 12% of the plants in EPA's database, most of which don’t use activated carbon injection or NOx controls, and it should certainly be achievable by existing plants once they are retrofitted with these more advanced controls, scrubbers, and efficient particulate control.
The MACT database is incomplete
Part 129 directs EPA to revise all of
the numerical limits proposed prior to the 1990 CAAA, plus propose some
numerical limits for additional pollutants, calculated according to MACT. EPA compiled emissions databases for all the
pollutants they were supposed to revise, except carbon monoxide and PM10. So MACT was not calculated for these two
required parameters. Further, EPA
ignored much relevant data from new and retrofitted European plants with
advanced, state-of-the-art mercury, dioxin, and NOx control technologies, by
assembling a strictly U.S. database. In addition, EPA’s
In addition to leaving out data from
many plants in the
Though operating conditions are one of the largest determinants of environmental performance, EPA did not include in its database information about the extent to which the all of the operating conditions at the front and back end of each plant were optimized at the time of testing. Some of the data in EPA's databases may be reflective of reasonably good operating practice at the plants from which the data were taken. But it is also true that much of the data in EPA's databases are from older plants whose operators do not always carry out one or more of the following operating practices, which used together result in optimal environmental performance:
1. Screen wastes at the plant to reduce incineration of pollutant precursor-bearing items
2. Optimize mixing of waste in pit or on tipping floor (to homogenize moisture and BTU content).
3. Optimize furnace operation (e.g., optimized grate speeds, underfire and overfire air injection rates, locations, and directions, and operation of auxiliary burner)
4. Survey combustion equipment regularly to ensure it continues to be properly sealed and operative
5. Optimize type of nitrogen-reducing reagent used
6. Optimize injection location and rate for nitrogen-reducing reagent
7. Control water injection rate to optimize flue gas temperature in control devices (to maximize condensation and capture of pollutants on particulate and reagent)
8. Optimize type of alkaline reagent used (to maximize absorptive capacity)
9. Optimize injection location and rate for alkaline reagent
10. Optimize type of carbon used (to maximize adsorptive capacity)
11. Optimize injection location and rate for carbon
12. Optimize voltage and other electrical parameters of an ESP (to maximize capture of particulate)
13. Control ID fan speed to optimize residence time of flue gases within combustor and control devices (e.g., fabric filters, scrubbers, furnace)
14. Inspect and calibrate CEMS frequently
15. Survey Emission Control Devices to ensure they are/ continue to be properly sealed, insulated, and operative
16. Operate the plant using certified operators at all times.
If any of these are not optimized when emissions data are sampled (and most plant operators do not optimize all of these simultaneously at all times), then it is likely that measurements in EPA's database reflect less than optimal environmental performance. Since it is known that variation in application of the techniques, practices, and conditions listed above will result in variation in environmental performance, EPA should base its standards on data reflecting known good operating practices, and not on emissions from plants which do not follow optimal operating practices, for to do otherwise encourages less than optimal operations.
CO -- Good Combustion Practice
EPA has not gathered a database of CO emissions as it has for the other pollutants of concern, and has thereby not complied with the requirements of CAAA Sec. 129; instead it is relying on its 1989 BID document. In the current proposal, EPA has again recommended a triple standard (50, 100, 150 ppm) for new plants and a quintuple standard (50, 100, 150, 200, 250 ppm) for existing plants depending on type of combustor. And yet in the BID document, EPA states that the first goal of good combustion practice (maximization of in-furnace destruction of trace organics) is accomplished by optimizing waste feeding procedures, achieving adequate combustion temperatures, providing the proper amount and distribution of combustion air, and optimizing the mixing process. A failure in any one of these components will be accompanied by spikes or bulk increases in flue gas CO concentrations.” Further EPA states, "Failure to achieve the necessary temperatures and residence times will result in the escape of organics from the furnace, which will lead to elevated concentrations of CO in flue gases", "CO emissions typically increase when insufficient O2 is available to complete combustion, or when excessive amounts of O2 quench combustion reactions", and "Failure to distribute combustion air in the correct proportions to primary and secondary supplies can result in elevated organics and CO emissions". It is clear from these statements that EPA considers that it is the combustion practices which govern CO emissions. Allowing some plants to have 150 or 250 ppm CO emissions would indicate that these plants receive deferential treatment, and can fail to distribute combustion air in correct proportion, or provide insufficient O2 or too much O2, or fail to achieve satisfactory combustion temperatures, whereas other plants would be required to conform to the good combustion practices mentioned, and consistently achieve 50 ppm. These triple and quintuple standards are inherently unfair, and makes a mockery of the term "good combustion practice", since it gives the operators at certain plants latitude in the monitoring and optimization of their combustion operations. In order to demonstrate that good combustion practice is being achieved at all plants, all plants should be held to the 50 ppm CO emissions level.
In the proposed standards and guidelines, RDF plants are permitted to average 150 ppm, and existing RDF plants to average 200 ppm. As argued above, good combustion practices, such as correct combustion air, mixing, and temperature, should not be required for some plants and not for others. That higher CO emissions are permitted from RDF plants means that these plants are not required to achieve as good combustion as some others. In addition, there is no evidence in the aforementioned background document used to devise these CO standards for RDF plants that concerted attempts were typically made to zero-in on those operating practices which optimized combustion. In fact, the Penobscot, ME plant, discussed in connection with good combustion at RDF plants in the BID, has no impetus to optimize combustion such that it operates any more efficiently than its 400 ppmv/4 hour permit requires. How can a standard of good operating practice be based on operations at such a plant?
Based on information relating
combustion efficiency and emissions of PICs to a number of incinerator
performance criteria, EPA, in 1987 issued its first good combustion practice
which flatly stipulated one CO limit, an O2 limit, and other firm
limitations for all plants. This
guidance, advising the states regarding good combustion practices, indicated
that carbon monoxide emissions of 50 ppm over a four-hour averaging time, along
with 6-12% oxygen after combustion, among other requirements, were indicators
of good combustion practice in a municipal waste combustor. Environment
As important as the level of CO
emissions maintained in a MWC is the averaging time over which these emissions
are evaluated. It is important to note,
in this regard, that the ASME/NYSERDA Pittsfield combustion tests
showed that CO levels above 100 ppm were associated with higher dioxin
levels. If several types of new and
existing MWC's are permitted to exceed this 100 ppm level routinely, then EPA
is not attempting to minimize dioxin emissions in certain combustor
Good Combustion Recommendations
Since "Good Combustion Practices" (GCP) are, ostensibly, practices which, when utilized, result in good combustion, the more reasonable approach would be to reestablish an across-the-board standard which is reflective of good combustion practices. Though EPA’s previous guidance stipulated this figure as 50 ppm, a recalculation of the MACT floor for CO shows that this figure is higher than MACT. In addition to using CO as an indicator of good combustion, EPA's original GCP's included a range of oxygen content (6-12%). EPA should reinstate this requirement defining good combustion, since it has been demonstrated that lower oxygen values increase the formation of PICs and higher oxygen values result when there is too much excess air, resulting in cool spots and reduced flue gas residence time in the furnace. Thus, it is recommended that good combustion practices for all incinerators require not only a minimum temperature of 1800oF across the furnace to ensure destruction of PICs as was recommended by EPA but also a maximum temperature of 2000oF at fully mixed height to minimize formation of NOx, as well as the requirement that flue gases remain at such high temperatures for two seconds.
Exclusion of Startup, Shutdown, and Upsets
Since it is during these times that extremely poor emissions occur, the exclusion of startup, shutdown, and periods, during which time the plant is malfunctioning, from measurement via CEM or stack testing for purposes of compliance is a huge loophole which winks at suboptimal operations and bad operating practices. Such a provision does not penalize a poorly maintained or operated plant which is often down, even though the air quality in the plant vicinity is certainly adversely affected by such inconsistent operations. Since it is assumed that, for good combustion practice, auxiliary burners are required in the furnace to keep temperatures to the correct level, avoiding upsets, there should be no need for EPA to exclude periods of startup, shutdown and upset from compliance monitoring and testing. Therefore, in keeping with the above recommendations regarding good combustion practice, it is further recommended that there be no exclusion in either stack sampling or CEM measurements, and that CEM measurements be required at all times a MWC is in operation in order to stay in compliance.
Flue Gas Temperature
This is the single most important short-term improvement to maximizing environmental performance at many MWC's operating today. Maintaining low flue gas temperature will have the dual effects of improving reagent (lime) utilization and increase removal of volatile trace elements, such as mercury and dioxin/furan as well as acid gas emissions (HCl and SO2) as described below.
In the 1991 MWC standards EPA was only interested in outlet temperature being below 450oF to avoid secondary formation of dioxins in the emissions control devices. But in EPA's 1989 BID document, p. 3-2), EPA's two most effective emissions control options, both require a temperature of 300oF. EPA mentions temperature control as one of the best technologies for retrofit for each type of MWC. But in the current proposal, there is no specific back-end temperature requirement. Data produced by Environment Canada showed that temperatures around 285oF were optimal for plants using both spray dryers and sorbent injection. Wet scrubbers lower the temperature much more than this, with as good or better results. Permitting MWC's to maintain high flue gas temperatures at MWC's is at odds with efforts to lower most emissions of concern and should be addressed in the new standards and guidelines.
In fact, MWC's can be successfully
operated at outlet temperatures of 240-260oF. In fact, in pilot plant tests, spray dryer
absorber outlet temperatures as low as 200oF have been tested while
maintaining a free flowing residue product according to Joy/NIRO. During start-up and testing of the Zurich SDA
Reagent Injection Rates
There are also significant
improvements to be gained by optimizing the injection rate for activated carbon
as shown by Kane (Ref. 14). At the
Kassel MWC the polishing effect of the activated carbon for decreasing dioxin
emissions increased from 78% to 98% as carbon feed rate increased from 25
mg/dscm to 137 mg/dscm while holding flue gas temperature constant at 275oF. This effect was also shown at the Zurich MWC
and the Borgess MWI. At several European
plants Brown and Felsvang showed the same effect for mercury. For example, at the Kassel MWC, an increase
in carbon injection rate from 9 to 64 mg/m3, while temperature was
held constant at 279oF, resulted in an increase in removal from 48%
to 82%. At the Amager plant in
Similarly, the injection rate for alkaline reagents affects the emission of acid gases, and probably also mercury and dioxin. EPA's aforementioned model emission control systems assume a 2.5 sorbent-to-acid gas stoichiometric ratio. The location of alkaline reagent injection is also critical to emissions control as seen below.
In 1989 EPA conducted a large test program on the 1970-vintage Montgomery County South incinerator. Six different operating conditions were tested, three runs apiece, and most of the major pollutants of concern were tested for each operating condition. All but the sixth were at a furnace mixing chamber temperature of 1750oF. The operating conditions were:
1. ESP inlet setpoint 575oF, no sorbent injection
2. ESP inlet setpoint 400oF, no sorbent injection
3. ESP inlet setpoint 400oF, furnace sorbent injection 500 lb/hr
4. ESP inlet setpoint 300oF, furnace sorbent injection 500 lb/hr
5. ESP inlet setpoint 300oF, duct sorbent injection 300 lb/hr
6. ESP inlet setpoint 525oF, no sorbent injection; 1500 mixing temp
The results were striking. The best condition is #5 for most pollutants.
For dioxin the differences between conditions are dramatic. At condition 5, two of the three runs for toxic
equivalents are quite low -- 1/5 the level of the European dioxin standard,
with the third reading twice that standard.
Considering this finding it is strange that the
The results of the testing were
clear. The downstream flue gas
Good Operating Practice -- Recommendations
The data presented above (Joy/NIRO,
Environment Canada) argues for institution of an operations requirement similar
to the one promulgated by the New Jersey Department of Environmental Protection
in September, 1994, as part of
Since good operating practice can be quantified, EPA should include in its NSPS and Guidelines for MWC’s some of the same provisions requiring optimization of operations that it included in its Medical Waste Incinerator standards:
· Initial optimization of reagent injection rates for lime, carbon, and other reagents for all plants,
· Continued observance of optimized injection rates in order for a plant to stay in compliance with the standard, and
· Optimization at all times of flue gas temperatures at the particulate control device inlets of all plants in order to maintain compliance. A good maximum target level for this flue gas temperature level would be 250oF.
It is important that operators easily
monitor all devices and parameters of concern.
Continuous emission and process monitors are designed to assist in this,
and as soon as new technology is developed to monitor continuously pollutants
of concern, EPA should require their use.
At present EPA does not yet require HCl monitors even though they have
been in use in
OPERATOR TRAINING AND CERTIFICATION
In the 1991 NSPS EPA required that chief facility operators (CFO) and shift supervisors (SS) be certified to the first level of the ASME Operator Certification (OC) program, and that each plant have a plant operations manual that each employee was to "review". In this NSPS EPA has additionally required that the CFO's and SS's be certified to the second, site-specific, level of ASME's OC program, and that control room operators who are to take over for a CFO or SS should also be certified to the first level (optional). Also, with regard to operator training, the new standard would require that all CFOs, SS and control room operators complete an MWC operator training course approved by EPA within 2 years. These additions are definite improvements, but more is needed.
EPA has a minimal role in developing the questions for the provisional and site-specific exams. At present, the ASME QRO committee, many of whom represent the resource recovery industry and its training programs, derives its questions in hodgepodge fashion just from committee members and any others who happen to hear about it through word-of-mouth. In fact, ASME frequently states at QRO meetings that there is a shortage of questions in several categories. As a result, the questions on the exams may not be as rigorous or as varied as they should be. The first two times that the provisional test was given over 90% passed. Subsequent tests were passed by fewer applicants, but more of these were repeating the test because they had failed it before. Enough provisional exams have now been given that most of the existing CFOs and SSs have already taken it, so the only way to rectify possible flaws in testing would be recertification testing. At the present time, no recertification testing has to take place at specified intervals. Recommendations are detailed below.
Operator Training and Certification Recommendations
1. Limit frequency/period of time that control room operators can fill in for Chief Facility Operators and Shift Supervisors. Require all control room operators to have full certification if they are to substitute for Chief Facility Operators or Shift Supervisors;
2. Require operators to take tests on new regulations and new technologies every five years; this would ensure that operators stay up-to-date with the constantly changing technologies and regulations in the field;
3. Require that no employee of a firm which designs, operates, or constructs municipal waste combustors either create exam questions or have access to exam questions (currently there are potential conflicts of interest on the QRO);
4. Requirement that no employee of a firm which has designed, operated, or constructed the specific municipal waste combustor at which an applicant is taking a site-specific exam, be permitted to sit on the examining board (this would prevent future conflicts of interest); and
5. Require a minimum educational requirement for taking the certification exams: either a technical baccalaureate degree or 60 credits in physical science and/or engineering at an accredited institution. (Currently the minimum qualification requirement is a high school diploma or equivalent.)
6. EPA’s Air Pollution Training Institute should be heavily involved in developing questions for the provisional exams, and staff from this Institute should be involved in administering the site-specific exam as well. This should be done quickly, since ASME is scheduling exams at a fast pace.
7. Require that EPA's Training Institute approve the operation and training manuals at each incinerator site and that these manuals include specific directions for proper screening of waste, and for AVOIDING and not just dealing with upsets. In this NSPS, each plant is responsible for designing its own manual according to general guidelines. This will most certainly result in little uniformity in plant operations manuals across the country. Employees are only asked to "review" the manual annually. This lack of implied or enforced rigor will also ensure lack of uniformity in employee training and preparedness. EPA does not appear to have oversight either in approving the manuals or in making sure operators review these manuals adequately or are properly trained.
NUMERICAL LIMITS VS. PERCENTAGE CONTROL
Part 129 requires numerical limits for all the pollutants of concern. However, in contradiction of this
requirement, the current proposal lists numerical limits for some, and for
three pollutants, gives a choice of numerical or percentage reduction --
whichever is LESS stringent. Practically
speaking, the standards for HCl, SO2, and now, mercury are not
numerical standards, since the alternative percentages specified for each are
so lax, it is, in practical terms, the percentages that are governing for the
acid gases, and will be so for mercury. EPA says it chose the 85% number for Hg
because 85% control is still possible even when there is a spike in the Hg
inlet value due to a battery or similar.
But this dual standard could discourage active efforts to limit
batteries and other items with concentrated levels of pollutant precursors from
entering the waste stream. The remedy here is to require application of
pollution prevention measures to ensure that those waste items which typically
cause the spikes never enter the incinerator in the first place, not to assume
that they will always be there and relax the standard to accommodate them. Pollution prevention measures to address the
mercury spike problem are an integral part of
The effect of a dual standard is similar for acid gases. With respect to SO2, the uncontrolled emissions would have to be less than 150 ppm for 80% control to be less stringent. Many uncontrolled emissions of SO2 range as high as 500 ppm. As for HCl, the uncontrolled emissions would have to be less than 500 ppm in order for 95% reduction to be less stringent. The range of uncontrolled HCl is closer to 500 to over 1000 ppm.
Recommendation against Dual Standards
Considering that the CAAA requires numerical, not percentage standards, as well as the adverse effects of having a dual standard both on emissions when pollutant precursor content is high or on operations when they aren’t, it is recommended that the percentage control numbers be dropped entirely from the NSPS and Guidelines for HCl, SO2 and mercury, and that the numerical limits be operative at all times. A more protective method would be to have a dual standard which chooses the most stringent option. In this way if the waste stream is high in pollutant precursors the numerical limit would ensure that high levels of the pollutant are not emitted. If the waste stream is low in pollutant precursors, then the minimum percentage control requirement would be operative, ensuring that the plant operators must remain alert and operations and maintenance continue to be optimized.
DIFFERENT STANDARDS FOR SMALLER PLANTS
Since the 1991 NSPS, EPA decided that
there was no reason to subdivide the standards for new MWC’s, perhaps because it saw no difference in the emission
control technologies available to and already used on large and small
plants. However, for purposes of this
rulemaking, EPA divided the universe of existing
MWC plants into three size categories: large (over 250 tons per day), small (25
- 250 tons per day), and too small to be regulated (under 25 tons per
day). But, as successful retrofits on
small MWC’s in this country and
That EPA's small MWC database is full of small plants which do not perform well is not due to the inherent inability of small plants to perform well. It is more a consequence of low expectations by regulators, followed by very lax standards and permits, which encourage plant design using less advanced, cheaper technology. Permits for small plants have often included no requirements for control of emissions. There is no technological basis for continuing to forgive smaller plants for having higher emissions. And there is certainly no reason for EPA to excuse the smallest plants (i.e., 25 Mg/day or less, such as apartment incinerators, the new wave of residential MSW incinerators, and other very small units) from adhering to any standards at all.
In its currently proposed Guidelines,
(pp. 87-88) EPA states that many of the small plants don't have permits. For some pollutants, less than 11 small MWC
permits were identified, so in those cases, typical uncontrolled emission levels for that pollutant were used for determining
the average of the top 12% of emission limitations. The Clean Air Act Amendments did not specify
that a minimum number of plants have to be included in a database for a
standard to be set, and it certainly did not contemplate the standard being set
at an uncontrolled level. EPA has
claimed that smaller and older plants should not be held to the same standards
as new and larger plants. The basis for
this seems to be cost and paperwork. But
there are a number of exemplary MWC’s in
But EPA has indicated before that it sees no difference in the capability of smaller existing plants to be retrofit and perform as well as larger plant retrofits. In its 1989 BID document cited above, EPA states that model plant retrofit emission figures in Figure 1 all apply equally to large plants as well as to small plants. For example, Modular Excess-air units of 100 tpd and of 140 tpd, Modular starved-air reciprocating grate units of 25 tpd and of 50 tpd, as well as small mass burn waterwall units of 100 tpd. Furthermore, using permits as a basis for the small plants guidelines results in limits anywhere from 3 to 16 times what EPA said in 1989 that these small plants could achieve with the best technology for CO, particulates, dioxin, and acid gases. These facts argue against the need for special treatment for smaller MWC's.
EPA has decided that smaller plants don't need to have NOx controls at all (i.e. emission limit of 500 ppm, which is quite a bit higher than any uncontrolled NOx level). This is such a high emissions level that it invites the plant operators to become careless in regulating temperature and oxygen conditions in the furnace. EPA's decision could have been based on the fact that permit levels are uncontrolled for NOx, and control technology has not been required in the past. But EPA also claims, erroneously, that SNCR is incompatible with smaller, modular combustors. Enercon, which has always included flue gas recirculation in its incinerators, and which has comparatively low emissions of NOx as a result, indicates that SNCR is very compatible with its system because of the flue gas recirculation. The latter technology results in a stabilization of the temperature in the furnace at the level correct for SNCR injection of ammonia or urea. So by mischaracterizing SNCR’s wide applicability, and by not even considering flue gas recirculation and other technologies, EPA has mistakenly excluded smaller plants from NOx control requirements.
EPA has also used the argument that a 250 ton per day cutoff is needed to separate large from small plants because the cost of air pollution control devices is increasingly more expensive for smaller plants. But activated carbon injection is an inexpensive retrofit since it only involves duct work and silo. The European database is replete with examples of small plants successfully retrofitted and performing well with not only activated carbon injection, but also dual stage wet scrubbing and other technologies (see Ref. 3).
A case in point demonstrates the capacity of small plants in achieving reduced emissions. A small modular MWC in Pittsfield, Massachusetts (3 x 120 tons per day) was retrofitted with the following equipment: a steaming economizer and a trim economizer (reduce flue gas temperature), 4-field ESPs (for particulate removal), condensate economizer (further reduces flue gas temperature -- to 160oF), wet scrubber (packed tower absorbers for acid removal), multi-cyclone/recirculating flue gas (for combustion air and NOx control, and CEMS for CO, NOx, SO2, and O2 (for improvement of combustion and emissions control). This retrofit was completed in 18 days, during a scheduled shutdown for maintenance. Emissions were reduced for all pollutants of concern by as much as three orders of magnitude, and often more than one order of magnitude due to this retrofit. These results show impressive improvements in performance not reflected in EPA's guidelines. It also demonstrates the viability of wet scrubbing technology for small as well as large MWC’s.
Exempting plants <25 Mg/Day
The NSPS exempts very small
incinerators from these emissions and siting requirements, even though it has
been shown that the smallest plants can be responsible for the worst ambient
impacts (e.g., in New York City -- apartment house incinerators were antiquated,
uncontrolled, badly operated, and emitted at roof level). Excusing these plants from standards
encourages more of them. An inventor in
Recommendation Regarding Plant Size
All guidelines should apply across-the-board to all sizes of MWC just as do standards for all sizes of hazardous and medical waste incinerators. The full range of emission control and combustion control technology is available and has been retrofitted on large and small MWC’s alike, and smaller MWC’s, particularly those under 25 tons per day, can produce a disproportionate effect because of short stack height and smaller dispersion. Excluding these smallest MWC’s just encourages construction of new ones, and should be avoided.
Recommendations From the Emission Control Industry
It is of interest that the Institute for Clean Air Companies (ICAC) stated in its testimony to the docket that EPA’s proposed standards and guidelines are too lax in a number of areas.
Acid Gases. For example, among the recommendations are that “on small plants the required removals could be increased to perhaps 70% for SO2 and 85% for HCl without making scrubber cost exorbitant.”
Mercury. And recognizing that EPA’s design basis for mercury
includes activated carbon in tandem with convention technology (SD/FF), ICAC
has stated that the “proposed limit on mercury emissions of 0.090 mg/dscm or
85% reduction from both new and existing units can be met using current
technology” and that lower limits have been set in
Dioxin. With respect to dioxins, ICAC states that “in many cases, use of a dry scrubber ...without carbon injection will be sufficient to meet the proposed limits”. Thus, even the industry agrees that EPA has underestimated the capability of its own technology design basis in setting its mercury and dioxin standards. NOx. Insofar as NOx is concerned, ICAC states “EPA’s proposed limit of 180 ppm is neither a technical limit to the capabilities of NOx control technologies, nor is it a minimum in the cost-effectiveness/removal efficiency curve for these technologies. In fact, a lower limit can be met comfortably and cost-effectively. We thus recommend that the Agency promulgate a limit of 150 ppm, with an alternative of a 50% reduction in emissions”. In addition to these recommendations regarding NOx, ICAC states: “EPA’s analysis of SNCR costs neglects economics of scale at plants with multiple combustors.”
HCl CEMS. Regarding continuous monitoring, ICAC recommends EPA
require CEMS for HCl since “CEM for HCl are in use at 15 municipal waste
combustion plants in the
Compliance Schedule. Finally, ICAC suggests “that EPA reduce the length of time afforded sources to come into compliance with the limits specified in the emissions guidelines. A three year timetable to reach compliance might make sense if owners and operators of combustors had no forewarning of impending regulation. In fact, these owners and operators have the additional two years between proposal of the guidelines and their implementation by the states, and further should have been aware of the order of magnitude of the standards since at least 1991.”
RECOMMENDATIONS FOR NUMERICAL NSPS AND GUIDELINES FOR EXISTING MWC’S
EPA’s proposed NSPS and guidelines for existing MWC's are founded on incomplete databases which are biased towards poorer performing plants, older plant designs, and less than optimal operation and maintenance, as a result of excluding some of the newest, best plants in this country and abroad. EPA should investigate all the best current technologies and current database worldwide, just as it requires of applicants for PSD permits, update its databases, and promulgate standards for new and existing MWC's which are supported by those databases. As it proposes for medical waste incinerators, EPA should also stipulate and require at all times observation of criteria representing Good Operating Practice, practices which result in efficient combustion and optimized air pollution control operations such as reagent injection rates and low flue gas temperature operation, as well as good maintenance and close monitoring of emissions and process parameters, at all times to maintain compliance.
Recalculation of NSPS for New and Existing Plants
Based on the aforementioned arguments,
the top 12% performance average on which EPA has based MACT for new plants,
underestimates the performance capability of the best plants currently existing
(even those without activated carbon injection). But Sec. 129 of the Clean Air Act requires
that the NSPS be set at the level achieved by the best plant. Therefore, EPA's NSPS for all parameters
should be more stringent. As EPA did,
our MACT calculations involve ranking the performances of plants for each
pollutant, resulting in different plants achieving the lowest emission
limitations for different pollutants. To
attempt to choose a single plant as best for all parameters would involve
subjective judgements. Tables 1-10 present,
for each pollutant, data from U.S. MWC’s not in EPA’s databases, interspersed
with EPA’s data in numerical order, with EPA’s original data in bold for the
top 12%ile of plants. Also in these tables EPA’s proposed NSPS is contrasted
with the average data for the best plant in the combined U.S./European
database, which includes EPA’s database plus additional plants. It is this performance average which is
recommended as the NSPS level for each pollutant. Also presented in each table is the number of
plants represented by 12% of the number of plants in the revised database. MACT
for existing plants is calculated by averaging the emissions from top 12%-ile
of small and large domestic plants,
using our list and EPA’s list combined. (Please see this reference for a full
enumeration of the
Figure 1. Proposed Guidelines for Small and Large Existing MWC’s vs. EPA Model Retrofit Data
Figure 2. Adverse Effects of a Dual Standard
Figure 3. Current NSPS Proposal vs. The Best Plant in each Database
(Note: the NSPS for CO is represented as the average of the 50 - 150 ppm range)
Figure 4. Guidelines for Large MWC’s vs. Average 12%-ile Performance Level for Existing Database
(Note: The CO Guideline is represented as an average of the 50 - 250 ppm range)
Marjorie J. Clarke
Municipal Solid Waste
 "Municipal Waste Combustors -- Background Information for Proposed Guidelines for Existing Facilities" USEPA, EPA-450/3-89-27e, August, 1989. Table 4.1-12, Table 4.2-12, Table 4.3-10, Table 5-1-11, Table 5.2-9, Table 5.3-12, Table 7.2-11, and Table 10.1-9.
 USEPA 40 CFR Part 60,
Emission Guidelines: Municipal Waste
 Clarke, Marjorie J., “The Development of New Jersey’s Mercury Emissions Standards for Municipal Waste Combustors”, Third International Conference on Municipal Waste Combustion, Williamsburg, VA, March 30-April 2, 1993.
 Fischer, James and Randy
Pasek, "Air Pollution Control at Resource Recovery Facilities, 1991
 "Municipal Waste Combustion Assessment: Technical Basis for Good Combustion Practice", EPA-600/8-89-063, August, 1989.
 "Operational Guidance on Control Technology for New and Modified
Municipal Waste Combustors", USEPA Office of Air Quality Planning and
 Waste on
Municipal Waste Combustion, Volume I,
 "Air Pollution Aspects of Incineration Facilities
for Household Waste and Comparable Commercial Waste", Ministry of Public
Housing, Urban Planning and Environmental Management, Kingdom of the
 "Results of the Combustion and Emissions Research Project at the Vicon Incinerator Facility in Pittsfield, Massachusetts -- Final Report", #87-16, prepared for New York State Energy Research and Development Authority by Midwest Research Institute, June 1987.
 "Municipal Waste Combustors Assessment: Combustion Control at New Facilities", USEPA, August, 1989
 "Municipal Waste Combustors -- Background Information for Proposed Guidelines for Existing Facilities" USEPA, EPA-450/3-89-27e, August, 1989.
 The National
Incinerator Testing and Evaluation Program:
Air Pollution Control Technology", Report EPS 3/UP/2, Environment
James R., and Karsten Felsvang, "Low Outlet Temperature Operation for
Resource Recovery SDA Emission Control Systems", Proceedings of the
82nd Annual Meeting and Exhibition,
Colleen, "Activated Carbon Injection for Supplemental Dioxin/Furan Control
at Municipal Waste Combustors", Memorandum from Radian Corp. to Walt
 Brown, B.
and K. Felsvang, "Control of Mercury and Dioxin Emissions from United
States and European Municipal Solid Waste Incinerators by Spray Dryer
Absorption Systems", Conference Papers and Abstracts from the Second
Annual International Specialty Conference,
Karsten and O. Helvind, "Results of Full Scale Dry Injection Tests at
MSW-Incinerators Using a New Active Absorbent" Municipal Waste
Combustion, Conference Papers and Abstracts from the Second Annual
International Specialty Conference,
 EPA's Draft
Emissions Test Report at South Incinerator - Unit 3,
 Personal communication. David Hoecke, President, Enercon Systems, Inc., August, 1994
 Smith, Jeffrey, and Michael Wax, Testimony
for Docket A-90-45, Institute of Clean Air Companies,
David and Marjorie Clarke, “Comments of the Natural Resources Defense Council
upon Proposed New Source Performance Standards and Emissions Guidelines for
Municipal Waste Combustors”, 59 Fed. Reg. 48198 and 59 Fed. Reg. 48228 (