Power Engineering

Preparing for HAPs Compliance

Power generators face their first mercury and hazardous air pollutant rules.

By Lindsay Morris, Associate Editor

The president of Southern Co. has called it the trigger that will “cause reserve capacity to plummet.” It has been pegged one of the most expensive rules in Environmental Protection Agency history by numerous industry groups, including the Clean Energy Group. Some, like Carl Weilert of Burns & McDonnell, believe it is a violation of the law.

Whether or not the Environmental Protection Agency’s (EPA’s) proposed Air Toxics Rule will cause a financial and retrofitting catastrophe for the power industry is yet to be seen. What is clear is that the rule will mark the first federal limits on hazardous air pollutants (HAPs) — including mercury — in U.S. history.

The HAPs to be controlled include mercury, lead, arsenic, hydrogen chloride (HCl), hydrogen fluoride (HF), dioxins/furans and other toxic substances identified by Congress in the 1990 amendments to the Clean Air Act (CAA). The rule establishes “maximum achievable control technology” (MACT) limits for many of these and has therefore adopted the nickname “Utility MACT.”

This isn’t the first time EPA has tried to regulate HAP emissions. On Feb. 8, 2008, a federal court ruled that EPA violated the CAA by trying to regulate mercury-emitting power plants through the Clean Air Mercury Rule (CAMR). The court said the EPA failed to make a specific health-based finding in relation to mercury. So on March 16, 2011, EPA proposed the replacement for CAMR, establishing a numerical MACT emission limit for new and existing coal-fired power plants. EPA estimates the proposed rule will reduce mercury emissions from covered power plants by 91 percent, acid gas emissions by 91 percent and SO2 emissions by 55 percent (see Table 1). A consent decree with public health and environmental groups requires EPA to finalize the standards by Nov. 16, 2011.

Activated carbon injection system provided by ADA Environmental Solutions at Basin Electric Power Cooperative’s 422 MW Dry Fork Station. Photo courtesy Basin Electric.
Activated carbon injection system provided by ADA Environmental Solutions at Basin Electric Power Cooperative’s 422 MW Dry Fork Station. Photo courtesy Basin Electric.

Good, Bad and Ugly

So what exactly will the Utility MACT do? According to Carl Weilert, principal air pollution control engineer at Burns & McDonnell, said Utility MACT presents “good, bad and ugly” scenarios for the power industry. The good? Utility MACT does not require emission limits for organic HAPs or dioxins/furans. The rulemaking also allows SO2 as a surrogate option for acid gas HAPs, which means most power producers that already have scrubbers for SO2 control will not need additional controls for acid gas HAPs. Utility MACT also allows for alternative compliance by averaging among similar units within one plant.

Some of the challenges Utility MACT presents—or “the bad” in Weilert’s view—include mandatory performance testing for both the surrogate and the pollutant. Also, “operating limits” on control equipment must be continuously monitored and maintained within “tight constraints,” even if continuous emissions monitoring systems (CEMS) are used to demonstrate compliance.

What about “the ugly”? Weilert said that total particulate matter (PM)—filterable plus condensable—selected as the surrogate for non-mercury metallic HAPs is sure to cause a number of challenges. For one, no CEMS currently exist for total PM. Also, the true “operating limit” for PM emissions is to be set based on the PM CEMS data collected during the performance test and it must be met on a 30-day rolling average.

This poses a problem for two reasons, Weilert said. First, the “operating limit” will be based only on the PM CEMS reading, which is correlated to filterable PM emissions but is not a direct measurement of filterable PM emissions.

Second, because every unit will have a different operating limit, this could create a difficult situation in which the operator will not know the numerical value of the effective filterable PM emission limit (which is to be based on PM CEMS data collected during the performance test) until the test is completed. Some comments to EPA have expressed this may be illegal since there will not be one consistent filterable PM limit that must be met by all sources subject to the MACT, Weilert said.

“EPA followed the law when developing standards for non-metallic HAPs and acid gas HAPs, but ignored the law when developing standards for mercury,” Weilert said. The law requires EPA to base the MACT on the top 12 percent of units “for which the Administrator has data.” However, Weilert said EPA’s December 2009 Information Collection Request plan for the MACT reported that it “knew” which units represented the top 15 percent—approximately 175 units—and that it was requiring those units to conduct tests and would subsequently use a slightly smaller subset—12 percent of all units—to develop the MACT limits.

The 12 percent of units equaled 131 units by EPA’s count. Consequently, EPA used data from 131 units to develop the proposed MACT limits for non-metallic HAPS and HCl. However, EPA used a smaller subset of the units (about 40) to develop mercury limits, Weilert said. “The issue is that EPA deviated significantly from its own plan as stated in the December 2009 ICR, and it did so only for mercury.”

Utility MACT Debacles

Some would argue the power industry will be able to easily meet HAPs compliance. According to the study “Control Technologies to Reduce Conventional and Hazardous Air Pollutants from Coal-Fired Power Plants” by the Northeast States for Coordinated Air Use Management (NESCAUM), emissions controls that significantly reduce mercury emissions from coal-fired power plants have already been installed, demonstrated and put into operation at a “significant number of facilities in the U.S.” The report said about 25 units representing some 7,500 MW are using commercial technologies for mercury control.

Mercury control regulations enforced by many states already require 80 to 95 percent mercury capture rates. Power plants in many of these states are therefore already operating at mercury control rates that meet the reduction levels sought in the Air Toxics Rule, according to NESCAUM.

“The states that are already prepared for meeting stringent mercury standards would have less challenge in meeting Utility MACT, because mercury emissions reduction has typically included PM emissions reduction,” said Anand Mahabaleshwarkar, senior project manager for Kiewit.

But because Utility MACT covers more than just mercury, even a power plant that has technology for a state mercury regulation may still need to install additional control technology in order to capture another emissions type.

“You can’t look at one pollutant in a vacuum. They all seem to be interrelated. The fact that a state has a mercury rule in place doesn’t mean they have all the other pieces to the regulations the federal government is proposing,” said Sharon Sjostrom, chief technology officer for ADA Environmental Solutions.

Cost vs. Benefit

Ultimately, what is most important is that benefits generated by Utility MACT outweigh compliance costs. EPA estimates the Utility MACT would generate $140 billion in annual health and welfare benefits in 2016. EPA also admits the ruling would impose costs of about $11 billion a year on the U.S. economy.

However, EPA’s number crunching has been questioned by a number of industry groups, including the Electric Reliability Coordinating Council (ERCC). According to Scott Segal, director of the ERCC, analysis of EPA’s data gathering shows that EPA’s contractors “allowed statistical transcription errors that overestimated removal efficiencies by a factor of one thousand.” However, Segal said, EPA has since contended that such large errors are still within its acceptable margin of error for variability. “We believe these and other errors, coupled with the general complexity and cost of the proposal, at least justify additional time for the comment period of the proposal,” Segal said.

According to data by ICF International, the result of EPA’s regulations will force plants to retire or retrofit at a cost of about $300 billion over the next five years.

A number of power companies and utilities have submitted commentary to the EPA regarding the Air Toxics rule. Exelon expressed support of the proposed rule, stating in a press release that industry “can comply with the Air Toxics Rule within the three-year period while maintaining the reliability of the nation’s electric grid.” Joseph Dominguez, Exelon’s senior vice president of federal regulatory affairs, said compliance will be possible “without steep rate increases” and will create “badly needed jobs at the same time.”

On June 9, 2011, American Electric Power announced the retirement of up to one-fourth of its coal-fired generation. Michael Morris, AEP’s chairman and CEO, said in a statement, “We support regulations that achieve long-term environmental benefits while protecting customers, the economy and the reliability of the electric grid, but the cumulative impacts of the EPA’s current regulatory path have been vastly underestimated, particularly in Midwest states dependent on coal to fuel their economies.”

Southern Co., which owns and operates a number of older coal-fired units throughout the Southeast, expressed opposition to the rulemaking. “This unprecedented and ill-timed transformation of the nation’s electricity infrastructure will only impede the U.S. economic recovery, reduce our ability to create jobs and add to the economic burdens of our customers,” wrote Thomas Fanning, Southern Co. president, chairman and CEO in the utility’s commentary letter to EPA.

Industry Upheaval

Whether or not Utility MACT will impede economic recovery as some allege, the rule is certain to bring some degree of upheaval to the power industry. The final rulemaking comes in the wake of a host of rules that EPA has released for the power industry, including the Cross-State Air Pollution Rule and the National Ambient Air Quality Standards. The power industry will also be competing for control technology installations. For example, the cement industry will be installing technology for Industrial MACT compliance over the same timetable as Utility MACT.

Babcock & Wilcox designed the MercPlus system for mercury capture at power plants that use low chlorine coals. Photo courtesy Babcock & Wilcox.
Babcock & Wilcox designed the MercPlus system for mercury capture at power plants that use low chlorine coals. Photo courtesy Babcock & Wilcox.

“There will be a substantial amount of equipment that needs to be online in a short period of time,” said Sjostrom. The finalized dates for Utility MACT and other rulemaking will partially determine what type of technology utilities are able to install, she said. “We expect delivery times to increase and potential price instability as utilities meet these deadlines.”

The challenge to produce high-quality equipment in a timely manner is obvious for equipment vendors. But there will also be a rush for operators to find enough craft labor to implement the equipment, Sjostrom said.

Many utilities have already turned to the guidance of engineering consultants to navigate through the various compliance solutions and to make sense of Utility MACT. “Whether the U.S. engineering fleet or OEMs will have the capability to deliver the equipment in time will be questionable,” Mahabaleshwarkar said. In light of a possible equipment shortage and/or increased prices, consultants will advise that some older and smaller coal plants be replaced by gas combustion turbines, he said.

Mercury Control

The technologies available for controlling HAPs are numerous. Since mercury is to be controlled for the first time, it may require the most in-depth control of any hazardous air pollutant. Mercury-specific control technologies include Activated Carbon Injection (ACI), halogen addition, and co-benefit methods of control, such as PM controls, dry sorbent injection (DSI) and dry and wet scrubbers (see Table 2).

ACI and halogen addition are the preferred methods for controlling mercury, said Brandy Johnson, manager of FGD project development at Babcock & Wilcox. ACI is essentially the injection of powdered activated carbon. The injected carbon is then captured using a downstream PM capture device (an electrostatic precipitator (ESP) or a baghouse). An ACI system is usually relatively simple and cost-effective, and consists of storage equipment, a pneumatic conveying system and injection hardware.

ACI systems cost approximately $5/kW and can be installed in 12 months or less, according to NESCAUM. ACI can also be used to reduce other HAPs, such as dioxins and furans.

ACI is typically effective at removing mercury except if high sulfur coals are used, or if SO3 is injected for flue gas conditioning for ESPs. SO3 interferes with mercury capture by ACI; however, upstream capture of SO3 by dry sorbent injection (DSI) can enable ACI to more effectively capture mercury.

In low chlorine coal cases, halogen addition can be used to enhance the mercury removal process. However, downsides exist to adding halogens, Mahabaleshwarkar said. “Halogen addition in coal is not well-controlled; not a well-monitored process. It can increase the corrosion potential in duct work or air heaters and downstream AQC equipment.”

Many technologies provide co-benefit methods of control for mercury. Baghouses (or fabric filters) typically provide a higher co-benefit mercury capture than ESPs. According to data collected by the EPA during its information gathering period for the development of Utility MACT, bituminous coal-fired boilers with fabric filters can have high rates of mercury capture.

Wet scrubbers with SCR controls upstream have also proven to be effective at removing oxidized mercury. Since eastern bituminous coals have higher levels of chloride, a wet scrubber is preferable for removing the oxidized mercury, Johnson said.

One downside to this option is that a wet scrubber will take mercury emissions out of the air, but can leave mercury emissions in water, said Weilert. The most direct way to eliminate mercury in wastewater would be to eliminate the wastewater discharge completely by choosing a dry scrubber instead.

Plants that only have an ESP may find it challenging to meet Utility MACT compliance, Mahabaleshwarkar said, because “ESPs remove limited mercury and HCl even with carbon/sorbent injection.” A plant that has an ESP and a wet scrubber installed will be more likely to meet compliance, while a plant with a dry scrubber and fabric filter will likely meet full compliance.

“Currently, more than 50 to 60 percent of coal-fired power plants have only ESPs installed,” Mahabaleshwarkar said. With this in mind, fabric filter retrofits may become higher in demand than ESPs, since they are capable of removing more emissions, such as mercury, HCl and PM.

The addition of a co-benefit method like a wet scrubber or SCR can help remove oxidized mercury in medium to high sulfur content coals with chlorine present, Mahabaleshwarkar said. Dry scrubbers used in conjunction with a fabric filter can also help remove mercury, but the activated or halogen impregnated carbon and lime must be injected at an optimum upstream location accounting for the competing presence of SO3 and loss of chlorine via a dry scrubber, he said.

Acid Gas Control

Strong acids like HCl and HF are formed as a result of the inherent halogen content in coal that is released during combustion to form acids as the flue gas cools. The proposed Utilty MACT rule sets a numerical emissions limit for HCl. This limit also functions as a surrogate limit for other acid gases, which are not given individual emission limits under the proposed rule.

In principle, wet and dry SO2 scrubbers can be used for controlling HCl and HF on plant boilers, but lower cost methods are available. Facilities that already have wet or dry scrubbers for SO2 control will likely be able to meet the requirements for HCl capture.

“If a facility already has a scrubber installed, they likely won’t need to worry about HCl because that will meet the alternative SO2 requirement,” Johnson said.

Units that are unscrubbed, however, may be adequately controlled through the installation of a DSI and a fabric filter. DSI has not yet experienced a wide deployment for acid gas controls, but data suggests that it is an effective technology for controlling HCl and HF, according to NESCAUM.

Dioxin/Furan Control

Under Utility MACT, EPA has proposed a work practice standard for organic HAPs, which includes the emissions of dioxins and furans. Under the proposed standard, power plants would be required to undergo an annual tune-up rather than meet a specific emission limit. EPA proposed this method after discovering that most organic HAP emissions are below current detection levels of EPA test methods.

Dioxins and furans are generally not present in coal, but can be formed during the molecular rearrangement of compounds and reactions of fly ash involving carbon, oxygen, hydrogen, chlorine and a transition metal catalyst. Because dioxins are formed through organic precursors, installing combustion controls or oxidation catalysts can help prevent or lower their formation. SCRs have also been proven to lower emissions of dioxins and furans. DSI upstream of the air preheater of a coal boiler may also be a way to reduce dioxin and furan formation.

Shop ‘Til You Drop

Searching for control solutions for mercury and other HAPs can be overwhelming. Selecting the right technology requires significant research and often the assistance of an engineering consultant. The following are a few of the many products available for coal and oil-fired plants seeking HAPs compliance.

Babcock & Wilcox offers a number of mercury-specific control options to meet various power plant needs. Its MercPlus System enhances mercury capture through halogen addition to the fuel to promote oxidation and minimizes powdered activated carbon usage at power plants that use low chlorine coals, such as PRB. The Absorption Plus (Hg) system is designed to inhibit mercury re-emission and to increase the total mercury captured and retained in a wet FGD system. Essentially, Absorption Plus maintains the Hg in the scrubber solution and prevents the mercury from changing back into elemental mercury and emitting from the stack. Babcock & Wilcox also offers powdered ACI, sorbent injection, baghouses and more.

Skyonic’s SkyMine was listed by EPA as an advanced combustion control technology for fossil fuel power plants. Photo courtesy Skyonic.
Skyonic’s SkyMine was listed by EPA as an advanced combustion control technology for fossil fuel power plants. Photo courtesy Skyonic.

ADA Environmental Solutions has been providing ACI systems for the coal-fired market over the past 10 years and has participated in more than 60 full-scale demonstrations and tests. ADA’s ACI systems can be tailored to meet specific requirements. Operators can choose between options like PLC or DCS controls, gravimetric or volumetric feeders, ladders or stairs, and standard or deluxe instrument packages. If an operator chooses ADA’s standard ACI system design, the engineering time is reduced considerably, resulting in cost savings and shorter delivery time, Sjostrom said.

ADA also offers Dry Sorbent Injection (DSI) systems that use alkaline materials (hydrated lime, trona, sodium bicarbonate) to reduce SO2, SO3 and HCl from stack gases.

Instead of installing mercury-specific solutions like ACI or halogen addition, some utilities may choose multi-pollutant solutions that capture mercury, SO2, NOx and CO2. While this form of compliance comes with a price tag, it could be more beneficial long-term, preventing the implementation of multiple technologies in order to comply with all of the EPA rules in the mix.

Skyonic has also produced a multi-pollutant control technology to help plants comply with HAPs regulations. The SkyMine emissions removal technology has 99 percent efficiency removal of SOx, NO2, mercury and other heavy metals. The technology is also capable of capturing carbon from flue gas stacks. Skyonic CEO Joe Jones said SkyMine offers a 50 percent cost savings over scrubbing methods such as wet-limestone scrubbers (SCR). SkyMine can be used on 50 MW plants where traditional technologies, such as wet-limestone-scrubbers and SCR, are typically not feasible.

SkyMine was listed as an advanced combustion control technology for fossil fuel power plants as part of EPA’s Commercial Demonstration Permit Program. The program was outlined in the proposed revisions to the New Source Performance Standards (NSPS) published in the Federal Register on May 3 in conjunction with the National Emission Standards for Hazardous Air Pollutants.

The technology produced by Eco Power Solutions, Comply 2000, is a multi-pollutant removal system that was selected by EPA to be included on a list of technologies that “offer the potential of reduced compliance costs and improved overall environmental performance” of the New Source Performance Standards and MACT.

The Comply 2000 reduces SO2 emissions through injecting a fogging spray mixed with a hydrogen peroxide solution that is condensed concurrently with other pollutants over coils to remove all combustion emissions from the exhaust gas stream. This process converts NOx and SO2 to nitric and sulfuric acid in the wastewater stream, resulting in 99 percent removal of SO2, mercury, halogens including fluoride, chlorine and bromide, heavy metals include arsenic and cadmium, 2.5 and 10-micron PM, as well as 20 percent removal of CO2. Tom Thompson, CEO of Eco Power Solutions, said that almost 100 percent of the utility generators Eco Power Solutions works with have SOx concerns, either SO2, SO3, or both. “We’ve seen an uptake inbound in our activity.”

In addition to reducing multiple emissions types, the Comply 2000 also generates supplemental energy by recovering waste heat that normally escapes into the atmosphere, reducing a plant’s operating costs significantly.

While a number of technologies for HAPs controls exist, it will be up to each power plant to decide what retrofits are necessary. The finalized Utility MACT rule, to be released no later than Nov. 16, will determine the scope of compliance. Whether embraced or begrudgingly accepted, the Utility MACT, along with other regulations in EPA’s mix, will affect the power industry in a profound way over the coming years.

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