Air Pollution has Become a Major Lifestyle and Political Issue for the American Public. The Public demands both an ample supply of available electricity and a clean environment. To achieve this, the federal government over the past three decades has passed increasingly stringent legislation requiring, in many cases, state-of-the-art air pollution controls on new projects. The cost of obtaining permits to construct new plants or modify existing plants has risen substantially over the years. Staying abreast of current air quality rules, therefore, can save a plant owner or developer much money and time
Ambient Air Quality Standards
In the 1960s, the federal government recognized that pollutants found naturally in the ambient air could become a threat to public health at elevated concentrations. The U.S. Environmental Protection Agency (EPA) developed maximum allowable ambient concentrations for these “criteria” pollutants. Table 1 summarizes the current National Ambient Air Quality Standards (NAAQS) for criteria pollutants. Note that a federal appeals court recently issued a stay on the PM-2.5 ambient air quality standard, remanding it to EPA. The court left the revised one-hour ozone standard in place, but as non-enforceable.
A proposed new cogeneration or utility facility or one undergoing a major modification causing a significant increase in emissions must comply with a number of air quality regulations concerning the achievement or maintenance of attainment with the NAAQS. The goal of the federal rule called Prevention of Significant Deterioration (PSD) is to maintain areas currently in attainment with an ambient air quality standard. A facility must obtain a PSD permit if it is “major” and plans to increase emissions by more than a certain threshold. For each affected pollutant, the applicant must install best available control technology (BACT), which is defined as the most stringent control technology taking into consideration economic, energy and environmental factors. The PSD application must contain a BACT analysis, analyzing the most stringent applicable control technology. Table 2 lists common available air pollution control technologies for criteria pollutants emitted from combustion equipment. An actual BACT analysis should consider compatibility of control equipment with the specific combustion equipment utilized.
An important issue to consider when designing control equipment to meet BACT or any other air quality requirement is that the desired technology may have an adverse effect on other pollutants. For example, technologies to reduce volatile organic compounds (VOC) and CO by oxidizing these pollutants to CO2 will cause nitrogen compounds to form more NOx, potentially exacerbating a problem with that pollutant. Careful planning and communication with regulatory agencies is the key to not being caught in a position of good faith undercontrolling of a pollutant by implementing technology to reduce another, which can hold up permit issuance. A facility in Maryland recently had its construction permit revoked-after construction had begun-because of this issue.
In addition, the PSD application must contain an impact study using dispersion modeling to show that the net increase in emissions proposed, together with existing facility emissions and existing background concentration of the pollutant, will not cause its NAAQS to be exceeded or exceed a fraction of the remaining impacts.
For example, a power plant proposed in an attainment area that has the potential to emit a high quantity of NOx, SO2, PM-10 or CO must first demonstrate that the ground-level impact of each pollutant, together with the impacts from other nearby combustion sources, will not exceed each NAAQS. But this is not sufficient. PSD discourages a location from reaching the NAAQS quickly. Therefore, regulatory agencies do not want to see a rise in the total impact of a pollutant in an area by more than a fraction or “PSD increment” of the NAAQS over a period of time. To achieve this, regulatory agencies often restrict each applicant for a new facility or major plant modification to a given fraction of the PSD increment.
This has many implications for new power plants, particularly in areas where deregulation is occurring and where building new plants is economically feasible. In Maricopa County, Ariz., near Phoenix, as many as 11 new power plants are in the development stages. The applicants are rushing to obtain their PSD permits because those that apply later may have an unacceptably small fraction of the PSD increments available for the project as designed and sited. Competition for fractions of PSD increments has influenced power plant planners in other states, including New York and Connecticut.
Because of the time to address these requirements and to accommodate agency and public comment, PSD permits often take one to two years to be issued. Firms should plan to invest the time and effort necessary to obtain a PSD permit or consider appropriate strategies and emission controls in order to avoid its requirements.
New facilities or expansions causing increases in emissions that already exceed NAAQS undergo even greater scrutiny. Such situations are covered by New Source Review (NSR) regulations found at the state level. While similar to PSD in structure, the net proposed increase in annual emissions of the nonattainment pollutant that would draw a facility into NSR is lower than that for triggering PSD. Instead of installing BACT, a facility must install technology to achieve the lowest achievable emission rate (LAER). LAER is the most stringent regulatory standard or demonstrated lowest emission rate regardless of cost or other considerations. In some states, an impact study is required to predict how high the ground-level concentration of the pollutant will rise. Finally, facilities in many states must purchase emission offsets representing the proposed net annual emissions increase of the pollutant plus additional credits to show a net benefit to the environment.
PSD and NSR are of great concern to existing facilities in light of the legal actions EPA initiated against 32 “grandfathered” plants late last year. EPA contends that certain plant owners implemented modifications of combustion equipment, resulting in significant air emission increases, without first obtaining proper permits and review through the PSD and NSR programs. The facilities believe that the modifications were the result of necessary routine maintenance needed for aging equipment and should be exempt from PSD and NSR requirements. Notwithstanding a court’s final ruling on the definition of routine maintenance and modification, power generating facilities should review records of historic changes to combustion equipment and assess the impact of the change on air emission rates. Similarly, each future planned change should be investigated for its air emission consequences (Table 3).
In the 1970s, EPA began promulgating New Source Performance Standards (NSPS) containing specific emission and monitoring standards for a new installation or a modification of equipment capable of emitting air pollutants from different types of source categories. Contained in 40 CFR Part 60, there are three major NSPS standards that affect the energy community, Subparts Da, Db, and Dc. Emission standards are provided in NSPS for particulate matter (PM), SO2, opacity and NOx, depending on the fuel combusted and size of unit (Table 4). States are instructed not to issue any permits to construct or operate a new or modified source unless it meets NSPS requirements.
Reviewing emission permits is the principal means of enforcing air pollution regulations. Historically, however, permitting programs have varied widely from state to state. Title V of the 1990 Clean Air Act Amendments developed minimum national air permitting standards. All major sources (facilities) must prepare and submit a Title V permit. Major is defined as having the potential to emit at least 100 tpy of a criteria pollutant (except lead), 10 tpy of any single hazardous air pollutant (a list of 188 compounds deemed hazardous to public health) or 25 tpy of all hazardous air pollutants.
The Title V Operating Permit is meant to be an “umbrella” permit, covering all operations at a major facility. In some states, it will replace all existing individual permits. In others, however, facilities will still be required to prepare and submit individual permit applications for new or modified sources and, if applicable, modify the Title V Operating Permit.
Title V permits undergo stringent agency review and public comment. It is likely that enforcement of air quality rules will be more stringent for facilities with Title V Operating Permits. Most power plants likely exceed at least one major applicability threshold and are subject to the program.
Facilities must meet the terms of the Title V Operating Permit, including all emission and operating limitations. Because it is difficult for a facility to plan for future activities during application preparation, in most states the Title V application contains the opportunity to define Alternate Operating Scenarios (AOS) to anticipate future growth or changes to operation. If emission rates listed in a proposed AOS (due to new equipment, a change in fuel, etc.) comply with all applicable air quality regulations, then a facility can switch to that AOS without pre-approval from the agency. AOSs may be interpreted differently by different states. Site selection criteria for a prospective new facility should include a state with a less bureaucratic permitting approach.
The goal for a facility permitting a new or modified combustion source is to be allowed to construct or modify and operate the equipment as soon as possible with as few operating constraints as possible for the lowest cost of add-on air pollution control equipment. As an example, the following illustrates a successful strategy to modify a cogeneration facility.
A facility in the Northeastern U.S. had been combusting natural gas and waste gas from its processes in several engine generators for many years to supply electricity and steam. The engines, however, were aging and the plant’s electrical demands were growing beyond their capacity, causing the facility to purchase more power from the local utility. The facility decided to purchase new, larger engine generators to meet projected demand 20 years into the future. Since this represented a potential major net increase in emissions of regulated pollutants, the facility, which is in a severe ozone nonattainment region, would have been required to meet LAER restrictions, delaying the project one to two years.
To avoid LAER and speed up the permitting process, the facility agreed to temporary, enforceable usage restrictions on the new engines so that the net emissions increases of the new units would not exceed the applicable PSD or NSR significance limits. The facility still had to purchase energy from the local utility, but a smaller quantity. This underutilization of the new engines was also acceptable because the projected growth in demand had not yet occurred. As a result, the facility received its air permits much faster. The permits contained recordkeeping conditions, such as 12-month rolling average emission limits to demonstrate that in any given period net emission increases did not rise to levels that would trigger PSD or NSR.
Finally, after the engines were in operation, the facility and its engineer were able to design, install and operate appropriate air pollution control equipment to enable total energy independence and greater use of the units while still not exceeding the significance levels. The technologies chosen were less expensive than LAER or BACT. In fact, an additional benefit of this strategy was that while initial permitting was based on conservative vendor guarantees of emission rates, testing under actual conditions showed measured emission rates much lower than the guarantees. This gave the facility more information to design appropriate air pollution control equipment and to re-permit based on more realistic conditions.
Marc Karell, P.E., is a Senior Project Engineer at Malcolm Pirnie Inc. in White Plains, N.Y. He has more than 15 years of experience in all areas of air quality engineering, including emissions inventories, audits, permitting and design of air pollution control equipment. Karell has two masters degrees, one in biochemistry from the University of Wisconsin and one in chemical engineering from Columbia University.