What Boiler MACT Means to an Energy Engineer

Boiler MACT is one of the first federal environmental regulations that have specifically called for conducting an energy assessment as a compliance activity. Energy assessments are nothing new; but how does integrating them into an environmental compliance activity impact the assessment process? As energy engineers, what can we learn from this new frontier?

The Boiler MACT regulations require energy assessments of two major energy systems found at many manufacturing plants and commercial/institutional facilities: boiler (steam) and process heater systems and their major end-uses. The rule specifies different compliance requirements depending upon the equipment type, size, fuel and total site emissions.

Hudson Global Energy Services (GES) specializes in conducting Boiler MACT energy system assessments at large complex sites such as refineries and petrochemical plants. These types of sites bring challenges, both in the identification of affected sources under the rule, as well as which end uses of energy to include in the assessment.

Some of the major differences we’ve observed between an assessment conducted to comply with the Boiler MACT regulations and one conducted at a facility’s discretion are summarized below:

  1. Work Processes
  2. Boiler MACT specifies what’s involved in a compliant assessment. These requirements are spelled out in Work Practice Standards §63.7500 (40 CFR Part 63, Subpart DDDDD – Table 3). These requirements range from completing visual inspection of the affected equipment to producing a comprehensive report identifying energy-efficiency measures. For a discretionary assessment, there are no work practice requirements that would necessarily apply across the board. Rather, the assessment scope and work practices will depend upon assessment best practices, the purpose of the assessment as defined by the facility, as well as any other legal requirements that apply.

    The American Society of Mechanical Engineers (ASME) has published standards for conducting assessments of boiler and process heating systems and these are often used by Hudson energy engineers when conducting discretionary steam or process heating assessments2. In fact, work practices identified in the ASME standards form an excellent foundation for a Boiler MACT assessment. An example of an ASME standard requirement that Hudson engineers have used in Boiler MACT assessments is the use of a year of operating data for system assessment. The Boiler MACT regulations do not address this topic.

  3. Drawing the Boundaries for the Assessment:
  4. Affected Sources and End Uses
    This is where it gets challenging! The Boiler MACT regulations define both what is an affected source and which end users of energy must be included in the assessment process These boundaries may seem a bit arbitrary from the perspective of energy use; however, they are being driven by the emissions reductions at the heart of the Boiler MACT rule. Viewed from that lens, they come to make more sense.

    But from an energy perspective, the Boiler MACT assessment may not deliver the value that a site’s energy manager might expect, due to the omission of certain energy sources. The cost of a boiler MACT assessment can be almost as much as an assessment conducted according to the ASME standard; but in the latter case, the site will have a comprehensive assessment of the plant’s energy system which will ALSO satisfy boiler MACT. From an energy management perspective, an ASME assessment may be the most cost-effective. This is not true across the board however; sites with a large amount of waste heat recovery or exothermic reactions may find significant differences in cost and coverage when evaluating an assessment conducted under the ASME standard versus the Boiler MACT regulations.

  5. Who’s at the Table
  6. Because the Boiler MACT assessment requirement is driven by environmental compliance, the environmental staff is a part of the process from the beginning. Hudson energy engineers have found the environmental staff to be a valuable addition to the assessment team in general, due to the interplay between energy use and emissions for combustion units. In the long run, this saves time because energy conservation measures can be eliminated early in the process if they will negatively impact environmental compliance.

So what’s been the biggest surprise that has come out of the Boiler MACT assessments? The process industries have made significant investments in instrumentation in the last decade, but turning this monitoring data into useful information, recommendations, and actions has not kept up. An example of this is the measurement of excess oxygen and stack temperature in combustion flue gas. This monitoring data can be used to calculate furnace efficiency, yet often it is not. Information on furnace efficiency could be a valuable addition to a process unit’s dashboard and training for operators on recommended actions. Hudson engineers have used the Boiler MACT assessment process to raise awareness of this lost opportunity to optimize the combustion process, save money and cut emissions.

(This article is offered as general information and guidance only, and is not intended to be, and does not represent, a complete analysis, review and discussion of the requirements of the National Emission Standards for Hazardous Air Pollutants (NESHAP) for Major Sources: Industrial, Commercial, and Industrial Boilers and Process Heaters, 40 CFR Part 63, Subpart DDDDD. This article is based on interviews with energy engineers Riyaz Papar, PE, CEM, and Subodh Chaudhari, EIT, EnMS, and CEM and does not reflect official opinions, views or policy of Hudson Technologies.)


1Boiler MACT in this article refers to the National Emission Standards for Hazardous Air Pollutants (NESHAP) for Major Sources: Industrial, Commercial, and Industrial Boilers and Process Heaters, originally published on March 21, 2011 and amended in 2013. 40 CFR Part 63, Subpart DDDDD.
2 See Energy Assessment for Process Heating Systems (ASME EA-1-2009) and Energy Assessment for Steam Systems (ASME EA-3-2009).


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