Boilers

Boilers burn fuel to generate steam for space heating, hot water, and generating electric power.  The environmental impact of boilers can arise from air emissions from fuel combustion, wastewater from cooling and cleaning, and solid waste from ash disposal.  This page describes the potential impacts, the rules that have been developed to deal with the impacts, and the associated compliance requirements.

In addition to verifying compliance with the regulations, facilities are advised to implement a comprehensive energy audit.  Finding opportunities to minimize energy requirements will in turn minimize the load on boilers, leading to lower fuel consumption and minimizing waste generation.

• What goes in; what comes out
  • Fuels
  • Pollutants
  • Pollutant Releases by Fuel Type
• Compliance Requirements
  • Clean Air Act
  • Clean Water Act
  • Waste Ash
• More resources

What goes in; what comes out

Fuels

Boilers commonly use gas, oil, coal, solid waste, or a combination of these depending on fuel availability, price and when the units were installed.

Pollutants

• Air Emissions from boilers include

• Smog producing compounds:
  • nitrogen oxides
  • volatile organic compounds

In the presence of sunlight, these materials combine to produce ground-level ozone, which can:

• exacerbate asthma
• cause lung damage
• irritate eyes
• damage plant life

• Particulate matter:  Fine particles can lodge in the lungs and cause respiratory difficulties.
• Carbon monoxide:  combines with hemoglobin and prevents oxygen transport.
• Sulfur dioxide:  a component of acid rain
• Air Toxins (Toxics): Air toxics are known to cause or are suspected of causing adverse health effects in humans and the environment
• Greenhouse Gases: Carbon dioxide, a product of combustion sources, is a greenhouse gas that contributes to global warming.

• Wastewater

Non-combustion wastes are generated from activities related to operating boilers and are typically released to water. Non-combustion wastes include:

• once-through cooling water
• cooling system blowdown
• boiler blowdown
• water-side boiler cleaning
• demineralizer regenerant

• Waste Ash

Bottom and fly ash and flue gas desulfurization (FGD) wastes result from combustion but are not released through the stack. Ash is typically a solid waste and FGD waste can either be a solid waste or a slurry. Because ash can contain heavy metals and other hazardous components it should be disposed of properly

Pollutant Releases by Fuel Type

Compliance Requirements

Please note:  Your facility may be covered by state and local regulations that may involve additional requirements or more stringent standards than the federal standards summarized here.

EPA has compiled a list of state air pollution agency contacts as part of a recent effort to develop National Emissions Standards for Hazardous Air Pollutants (NESHAP) rules for boilers.  This list is not comprehensive or updated, but may help you locate further information for your state.

In general, to minimize adverse environmental impacts and ensure operator safety, boilers must be operated and maintained by trained staff in accordance with the manufacturers' specifications.  In addition, there are a number of federal standards and regulations that apply to boiler operations.  The rest of this section contains a summary of the applicable rules.

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Clean Air Act (CAA)

New Source Performance Standards

Boilers at veterinary facilities, especially those with heat input capacities equal to or greater than 2.9 megawatts or 10 million Btu/hr may be subject to one of the New Source Performance Standards (NSPS) for steam generating units:

• NSPS Subpart Dc applies to smaller boilers (between 10 and 100 million BTU/hr) constructed modified or reconstructed after June 8, 1989.
• NSPS Subpart Db applies to larger boilers (greater than 100 million BTU/hr) constructed modified or reconstructed after June 19, 1984.

Depending on the type of fuel combusted, the regulations have emission standards for sulfur dioxide, nitrogen oxides and particulate matter.

Owners and operators of boilers subject to Subparts Db and Dc may be required to install:

• pollutant control devices, such as fabric filters
• monitoring equipment, such as opacity monitors or NOx continuous emission control monitors

Boilers subject to these standards will also be required to:

• submit notifications prior to construction and operation
• conduct initial performance tests
• maintain records, e.g. fuel usage and monitoring system operations

To check on the latest new source performance standards regulations see the NSPS boiler page.  

Citation	Applicability	Pollutants Addressed
40 CFR Part 60 subpart Db	Steam generating unit constructed, modified or reconstructed after 6/19/84 heat input capacity > 100 million Btu per hour	PM SO2 NOx
40 CFR part 60 subpart Dc	Steam generating unit constructed, modified or reconstructed after 6/9/89 heat input capacity between 10 million and 100 million Btu per hour	PM SO2
40 CFR Part 60 Subpart A	Note that if an NSPS standard applies, facilities must comply with the NSPS General Provisions in Subpart A

National Emission Standards for Hazardous Air Pollutants

Boilers. Boilers at medical facilities that are major sources for Hazardous Air Pollutants under the Clean Air Act (potential to emit 10 tons/yr of a HAP or 25 tons/yr of a combination of HAPs) may be subject to the Industrial, Commercial and Institutional boilers and process heaters standard, if another NESHAP standard doesn't already apply. Facilities that are part of a larger entity, such as a university, prison or military base would be the most likely facilities to be major HAP sources under the CAA .

Citation	Applicability	Regulated Pollutants
40 CFR 63 Subpart DDDDD	Industrial, commercial and institutional boilers and process heaters with heat input capacity greater than 10 million Btu/hour electric power generators burning materials other than fossil fuels (e.g., wood waste) Major HAP source, not subject if other NESHAP applies	PM arsenic cadmium chromium HF lead magnesium mercury nickel
40 CFR Part 63 Subpart A	Note that if an NESHAP standard applies, facilities must comply with the NESHAP General Provisions in Subpart A

More information, including an explanatory brochure, applicability flowchart and rule language, is available from the boiler NESHAP development page on the EPA website.

Boilers that burn alternative fuels other than fossil fuels, including solid waste, may be subject to additional combustion regulations. 

Boilers and Industrial Furnaces (BIF) that use or burn fuel containing hazardous waste must comply with design and operating standards. BIF regulations (40 CFR part 266, Subpart H) address unit design, provide performance standards, require emissions monitoring, and in some cases, restrict the type of waste that may be burned.

Asbestos

Any facility that contains asbestos, often used in insulation for boilers and pipes, is subject to the Asbestos National Emission Standard for Hazardous Air Pollutants (NESHAP). The Demolition and Renovation standard stipulates EPA notification and proper handling and disposal when asbestos containing material is disturbed.

Title V of the Clean Air Act mandates that states compile all applicable standards, such as those that apply to boilers, into a single permit for each major source.

Find more information on asbestos on the Asbestos page, and find information for your state on the Asbestos State Regulation Locator.

NOx SIP Call

On September 24, 1998, EPA finalized a "Finding of Significant Contribution and Rulemaking for Certain States in the Ozone Transport Assessment Group Region for Purposes of Reducing Regional Transport of Ozone" (commonly known as the "NOx SIP Call") requiring 22 States and the District of Columbia to submit State implementation plans that address the regional transport of ground-level ozone. The rule requires emission reduction measures to be in place by May 1, 2003. These measures will include controls on ozone precursors, such as NOx, emitted by fossil fuel-fired boilers and power generation units.

Boilers with a rated capacity over 250 million BTUs that are located in the eastern half of the US should be in contact with their state permitting agencies to see how this may apply.

More information is available on an information page on the NOx SIP Call provided by EPA.

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Clean Water Act (CWA)

Water used to maintain boilers, which can contain contaminants like those listed below, must be managed in accordance with the facility's pretreatment program if, as in most cases, the facility discharges to a Publicly Owned Treatment Works. Likewise, if the facility is a direct discharger the effluent standards for contaminants would be addressed in the CWA National Pollutant Discharge Elimination System (NPDES) permit.

Waste Streams and Effluent Limitations

Waste Stream	BAT Effluent Limitation Guidelines
All discharges	pH, poly-chlorinated biphenyls (PCBs)
Bottom ash transport waters and low volume waste sources	TSS, oil and grease
Chemical boiler metal cleaning wastes	TSS, oil and grease, iron, copper
Non-chemical metal cleaning wastes	Reserved (low volume wastewater limits apply)
Fly ash transport water (including economizer ash)	No discharge allowed (based on availability of dry disposal methods and the potential for reuse of fly ash transport water)
Once-through cooling water	Total residual chlorine (TRC) of free available chlorine (FAC), depending on facility's generating capacity
Cooling water blowdown	FAC, chromium, zinc, other 126 priority pollutants where they are found in chemicals used for cooling tower maintenance
Coal pile runoff	TSS

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Waste Ash

Ash from boilers fueled strictly by oil and coal may be subject to disposal requirements at the state level. It is not regulated as hazardous waste at the federal level.

Note that oil combustion wastes managed in unlined settling basins may pose potential ground-water pathway risks for three pollutants: arsenic, nickel, and vanadium. EPA determined, however, that oil combustion wastes do not warrant regulation as hazardous wastes under RCRA Subtitle C (65 Federal Register 32213, May 22, 2000).

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More resources

The EPA Air Toxics website provides a convenient index page for all combustion-related rules.