Industrial Boiler MACT
Industrial Boiler MACT
Industrial Boiler MACT
6 minute read

The EPA has released a new draft of the Boiler MACT rule, affecting thousands of boilers at universities and manufacturing facilities. The Industrial Boiler Maximum Achievable Control Technology standard effects mainly coal-fired and biomass-fired boilers.

Owners of industrial, commercial or institutional boilers will soon be required to comply with new, stricter U.S. Environmental Protection Agency (EPA) air emissions requirements. The new regulation, known as the National Emission Standard for Hazardous Air Pollutants for Industrial, Commercial and Institutional Boilers, was issued in draft form by EPA on April 29, 2010, and is expected to be finalized later this year. The regulation will affect thousands of boilers at facilities deemed major sources of hazardous air pollutants (HAPs).


Section 112 of the Clean Air Act (42 U.S.C. § 7412) requires that national emission standards for HAPs be established that reflect Maximum Achievable Control Technology (MACT). As a result, the EPA is tasked with developing the MACT emission requirements for specific industry groups, including the industrial, institutional and commercial boiler group.

Commonly referred to as the Industrial Boiler MACT Rule, these requirements were first finalized by EPA in February 2004. Three years later, however, a U.S. appellate court issued a decision to vacate the Industrial Boiler MACT Rule. It took EPA three more years to rewrite the newly released draft rule. The EPA is taking comments on the rule, which must be finalized by Dec. 16, 2010.

Summary of the Rule

The Industrial Boiler MACT Rule applies to industrial, commercial or institutional boilers or process heaters at facilities deemed a major source of HAP emissions. That includes any facility with operations that collectively emit more than 10 tons per year of any single HAP or 25 tons per year of any combination of HAPs. The rule requires each boiler at a facility to meet emission limits or work-practice standards, meet operating limits, and demonstrate compliance on both an annual and a continuous basis.

Emission Limits and Work Practice Requirements — For all natural gas- and refinery gas-fired units and all existing units with a heat input capacity of less than 10 million British thermal units per hour (MMBtu/hour) — which account for roughly 85% of the affected boilers — the rule establishes a work-practice standard instead of emission limits. In other words, natural gas- and refinery gas-fired boilers are required to undergo an annual tune-up; for boilers with a heat input capacity of less than 10 MMBtu/hour, tune-ups are required every two years.

For virtually all other boilers, the rule sets emission limits for the following HAPs or HAP surrogates:

  • Particulate matter (PM), as a surrogate for non-mercury metallic HAPs
  • Mercury (Hg)
  • Hydrogen chloride (HCl), as a surrogate for acid gas HAPs
  • Carbon monoxide (CO), as a surrogate for non-dioxin organic HAP
  • Dioxin/furan

Emission limits are based on boiler status (existing or new), fuel type and boiler type. There are approximately 2,000 existing boilers that will be Boiler MACT affected and must meet the emissions limits shown in Table 1.

Emission limits apply at all times, including startup and shutdown — even during times of malfunction. Facilities are allowed to comply with PM, HCl and Hg limits by using emissions averaging, provided the average emissions are within 90% of the emission limit.

It is worth noting that this new Industrial Boiler MACT Rule is significantly more stringent than the 2004 rule. The PM, HCl and Hg emission limits proposed in the new rule, for example, are significantly more stringent than those in the original rule. The new rule also establishes emission limits for carbon monoxide and dioxin/furan that were not required in the original rule. In addition, the new rule does not contain the Health-Based Compliance Alternatives included in the original rule, which were key to compliance for many facilities.

In addition to setting emission limits for HAPs, the Industrial Boiler MACT Rule also sets standards for facilities to demonstrate compliance with the rule. That can be accomplished through annual stack testing, continuous monitoring of operating limits and record keeping/reporting.

Stack Testing — To demonstrate compliance with the emission limits and establish each boiler’s operating limits, facilities will be required to conduct initial and annual stack emissions tests on each boiler for PM, HCl, Hg, CO and dioxin/furan. A facility can conduct the stack tests less often for a given pollutant if the facility can demonstrate that it emits 75% of the emission limit or less for three consecutive years. In this case, a facility can conduct the stack test every three years. If a stack test shows emissions greater than 75% of the applicable emission limit, then the facility must revert to annual performance testing. The reduced testing frequency does not apply to the dioxin/furan emission limit and cannot be used if the facility is averaging emissions.

As an alternative, a facility can demonstrate Hg and/or HCl compliance by fuel analysis testing. A fuel analysis would be required for each type of fuel burned, with calculations performed to demonstrate that the pollutant concentration in the fuel is less than the emission limit.

Operating Limits — Facilities will be required to demonstrate continuous compliance. To do so, they must monitor and comply with any site-specific operating limits established during the performance tests or fuel analysis. These operating limits will vary, depending on the type of pollution control equipment a facility employs. But they could include everything from maintaining opacity of less than 10% to a sorbent injection rate of at least 90% of that recorded during the stack test.

Notification, Recordkeeping and Reporting Requirements — Facilities will be required to keep records and submit notifications and reports related to their emissions. The EPA must be notified:

  • Within 180 days of the rule being published of any existing sources that are subject to the rule, and within 15 days of the startup for new sources
  • At least 30 days prior to conducting performance tests
  • Within 60 days of completing an initial compliance demonstration
  • Within 48 hours if a natural gas fired-unit intends to fire an alternative fuel during a curtailment period or supply interruption

Facilities are required to keep records that: 

  • Demonstrate compliance with emission requirements
  • Document deviations
  • Deport monthly fuel use
  • Document that they are not burning solid waste

Beyond-the-Floor Requirement — Facilities will be required to perform a one-time energy assessment on the affected boilers and facility to identify any energy conservation measures with a payback period of two years or less. Facilities must also implement energy management programs.

Industry Impact

EPA estimates there are more than 13,500 boilers and process heaters that will be subject to the Industrial Boiler MACT Rule. A majority of these boilers, approximately 11,500, fire natural gas or refinery gas and, therefore, will only be subject to the work-practice standards of the rule. That leaves approximately 2,000 boilers that will have to comply with the emission limits of the rule.

The rule is expected to have the most significant impact on facilities that have boilers that burn coal or biomass. EPA estimates there are approximately 600 coal-fired boilers and 400 biomass-fired boilers affected by the rule. Many of the solid fuel-fired boilers that were in compliance with the original 2004 rule will not be in compliance with the new rule’s more stringent emission limits. Table 2 compares the solid fuel boiler emission limits of the vacated 2004 rule and new proposed rule.

The stringent new emission limits may force owners of these solid fuel-fired boilers to upgrade their existing pollution control equipment significantly or consider switching to natural gas to fire their boilers. The PM limit will require most boilers to add a fabric filter as the particulate control device. Of the approximately 600 coal-fired boilers affected, less than 200 currently use fabric filters.

The HCl limit will require many solid-fuel fired boilers to install scrubbers or inject an alkaline sorbent (hydrated lime, trona, etc.) ahead of the particulate control device. The Hg limit will also require many boilers to install powdered activated carbon sorbent injection systems ahead of the particulate control device.

The CO and dioxin/furan limits will pose additional challenges for most boiler owners, since very little emissions testing has been conducted historically to understand the magnitude of these emissions or how best to control them.

Total air pollution control upgrades for solid fuel-fired boilers could take many different forms, including the retrofit of sorbent injection systems, a fabric filter or a scrubber, at minimum. The cost for these modifications will vary greatly, depending on boiler size, fuel type, the extent and condition of existing pollution control equipment and retrofit complexity. Capital costs could range from $1 million or less for a sorbent injection system, to $5 million to $10 million or more for a fabric filter or scrubber. EPA estimates that the average capital cost for retrofitting a coal-fired boiler with pollution control equipment to meet the emission limits will be nearly $8 million, and the average capital cost for a biomass-fired boiler will be nearly $5 million.

Compliance Planning is Key

Each compliance situation is unique. The only way to know what modifications might be necessary is to conduct a compliance study that establishes baseline emissions information and compares it against the Industrial Boiler MACT Rule emission limits. Because many facilities do not understand the magnitude of their emissions, compliance studies will likely include stack testing to establish baseline emissions, which a facility can use to assess compliance and, if necessary, develop a corrective plan of action.

Facilities must begin planning now to meet the expected late 2013 or early 2014 Industrial Boiler MACT Rule compliance date. In general, a compliance study may take six months to complete, and air pollution control retrofit projects or fuel switching projects can be expected to take from 18 months to three years from the start of compliance planning, through engineering and construction, to startup.


In a related rulemaking, the EPA also proposed a rule on April 29, 2010, that would reduce emissions of toxic air pollutants from industrial boilers located at area source facilities.

An area source facility emits or has the potential to emit less than 10 tons per year of any single air toxic or less than 25 tons per year of any combination of air toxics.

The rule would cover boilers that burn coal, oil or biomass and would establish standards to address emissions of Hg, PM (as a surrogate for non-mercury metals) and CO (as a surrogate for organic air toxics).

About the Author

Don Wolf, PE, is a Burns & McDonnell principal with 16 years of experience. He specializes in air pollution control technologies and heads the Energy Group at the Burns & McDonnell St. Louis office.

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