Boiler MACT and your boiler

The U.S. EPA’s National Emission Standards for Hazardous Air Pollutants, generally known as the “Boiler MACT Rule,” was issued in January, 2013. MACT stands for “maximum achievable control technology.”


A high percentage of owners of Major Source MACT boilers burning oil, coal or other fuels are replacing these with gas-fired packaged boilers, such as this vertical unit. A side benefits is often a reduced floor space requirement. Courtesy:Clayton BoilersThe U.S. EPA's National Emission Standards for Hazardous Air Pollutants, generally known as the "Boiler MACT Rule," was issued in January, 2013. MACT stands for "maximum achievable control technology." Affected facilities must be in compliance by Jan. 31, 2016. Most affected boiler operators know this. Many have already modified their facilities or made other operational decisions in order to remain in compliance. The Boiler MACT Rule is separate from New Source Performance Standards (NSPS), which are another part of EPA's Clean Air Plan.

New Emission Limitations

Boiler MACT requires industrial, commercial and institutional boilers across the nation to meet new emission limits and to follow revised work practices, including a boiler tune-up or energy assessment requirement. Boilers at major electric utility generating facilities are treated separately from industrial or institutional boilers.

The rules were originally issued in proposed form in 2003. An agonizingly long process included revision, litigation, vacation of the proposed rules, reissuance, more litigation, reissuance, and more litigation, and still more reconsideration. However, it is generally believed that the 2013 rules currently in place will remain, with few if any additional revisions. The 2016 compliance date still stands.

Size of Source Makes a Difference

The Boiler MACT rules divide the affected boilers into two groups: "Major Sources" and "Area Sources." Major Sources are those boilers that emit more than 10 million tons per year of any individual hazardous air pollutant (HAP) or 25 tons per year of all HAPs. Area Sources are those that emit less. Area Source facilities do not include commercial and residential sources or sources burning natural gas. They typically include: apartment buildings, hospitals, nursing homes, schools, churches, prisons, and some small manufacturing plants burning oil, coal and other solid fuel.

Under the Rule, all existing Major Source units that burn natural gas or other clean gas fuels are required only to do an annual tune-up. Major Source units that use other than clean gas fuels are required to do a one-time energy assessment and to demonstrate compliance with emission limits on a list of Hazardous Air Pollutants (HAPs). This includes most industrial boilers that use coal, coke, petroleum, biomass or gases that are not classified as "clean gases." These boilers can continue to operate only if they can meet specific emission limits for carbon monoxide, particulate matter, mercury and hydrogen chloride.

Compliance Choices

According to Bob Bessette, President of the Council of Industrial Boiler Owners, the owners of Major Source boilers were presented with a range of compliance options:

1. Install dry sorbent injection technology (promising, but still uncertain performance).

2. Install another proven control technology for all the HAP categories.

3. Reduce boiler operation to "Area Source" levels, thus eliminating the HAP emission restrictions.

4. Convert the existing boiler to natural gas or another clean gaseous fuel.

5. Replace the existing boiler with a new natural gas boiler.

6. Do nothing and shut down the boiler permanently.

Bessette indicates that the potential of dry sorbent injection technology for meeting HAP emission restriction is promising, but there is still an element of uncertainty, plus the potential that the emission restriction levels might change in the future, possibly taking these boilers again out of compliance.

Shift to "Area Source" Status

For some non-compliant Major Source boiler operators, it is possible to reduce boiler output to "Area Source" status. This might be possible when other plant operations can be done by other energy technologies. Large manufacturing facilities that rely on steam or hot water for manufacturing or site heating purposes will typically need to remain in the Major Source category.

Conversion to Gas Can Be Complicated

Bessette notes that some boilers are being converted to natural gas operation. In these cases, it is sometimes also necessary to make significant changes in the boiler tube layout in order to efficiently extract as must heat from combustion as the boiler had previously generated. This option would most logically be done with boilers that otherwise were in sound operating condition and were not approaching the end of their life cycle.

Bessette explains that the option that many owners are taking is to replace existing liquid or solid fuel boilers with new, packaged natural gas boilers with the appropriate steam or hot water output. The challenge here is for owners that delayed making that decision, and are now encountering production backlogs at some boiler manufacturers, or with qualified installation contractors.

Trend toward Natural Gas

Bessette indicated that the choice that the majority of owners are taking is to convert to natural gas, either with an existing boiler or a new unit. He feels that this choice is being taken because the current and even the projected price of natural gas is stable and comparatively low. Owners are generally reluctant to adopt a control technology that is not completely proven, even if the resulting fixed cost is less than a gas conversion?n. And they are wary of possible future additions to the list of HAPs and other emission limits to be set by EPA in the future.

Moving Into the New Era

Bessette points out that for owners that have not had access to bulk delivery of natural gas, a considerable expenditure may be required for a gas line extension. Many installations have also made provision for firing a standby fuel such as light oil as a backup boiler fuel. This is allowable under the MACT Rule. The new age of more natural gas-fired industrial boilers will result in lower HAP emissions, reduced greenhouse gas emissions, and continuing operation of essential industrial boilers.

This article originally appeared in the Gas Technology Winter 2015 issue.

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