Affordable Clean Energy (ACE) Rule

What is the Affordable Clean Energy (ACE) Rule? 

The EPA’s recently published Affordable Clean Energy (ACE) Rule identifies heat rate improvements as the Best Source for Emissions Reductions (BSER) to control CO2. ACE does not set any emissions limits, rather it outlines the framework for states to use to set achievable unit level heat rate improvements (HRI) at the plants.

The ACE Package includes three distinct, separate, and independent actions:

  1. Repeal of the Clean Power Plan (CPP)
  2. ACE Rule – Emission Guidelines for Greenhouse Gas Emissions from Existing Electric Utility Generating Unit
  3. Revisions to Clean Air Act section 111(d) Emission Guidelines Implementing Regulations

States must set source-specific standards of performance - based only on emissions limitations achievable by six candidate technologies and best O&M practices. See the chart below:

Most Impactful HRI Measures and Range of their HRI Potential (%) by EGU Size

HRI Measure   <200 MW  200-500 MW  > 500 MW
 Min  Max  Min  Max  Min  Max
 Neural Network /
 Intelligent Sootblowers
 0.5  1.4  0.3  1.0  0.3  0.9
 Boiler Feed Pumps  0.2  0.5  0.2  0.5  0.2  0.5
 Air Heater & Duct
 Leakage Control
 0.1  0.4  0.1  0.4  0.1  0.4
 Variable Frequency
 0.2  0.9  0.2  1.0  0.2  1.0
 Blade Path Upgrade
 (Steam Turbine)
 0.9  2.7  1.0  2.9  1.0  2.9

 Redesign / Replace

 0.5  0.9  0.5  1.0  0.5  1.9
 Improved Operating &
 Maintenance (O&M)
 Can range from 0 to > 2.0% depending on the
 O&M practices

Source: EPA

EPA ACE Fact Sheet

EPA ACE Presentation Overview

ACE Timeline

2018 – EPA published proposed ACE Rule

2019 – EPA published final ACE Rule

2022 – States are required to establish standards of performance for each designated facility within their jurisdiction and submit state plans to EPA for approval

2019 to 2024 – Compliance schedules for designated facilities must initiate within 24 months after a state plan submission. If completeness schedule initiates beyond 24 months, increments of progress must be included for those designated facilities.

ACE-Designated Facilities

  • Coal-fired electric utility steam generating units (EGUs) with nameplate capacity greater than 25 MW-net and commenced construction on or before January 8, 2014
  • EPA is evaluating information for other fossil fuel-fired EGUs

Babcock & Wilcox Competencies to Support ACE

  • B&W has a core competency of three of the six BSER candidate technologies listed in the final rule.
  • Additionally, we can provide field engineering services and performance testing to identify other potential O&M and efficiency improvements.
  • Steam turbine upgrades may require reheater modifications, another B&W core competency.

Plant owners may choose any means to improve heat rate, not just the State’s recommendations, nor the six listed Best System of Emissions Reduction (BSER) technologies. B&W can help you support ACE Rule requirements and other efficiency improvements with the technologies shown below.

Units that are cycled or operate under low load conditions present unique challenges in optimizing plant heat rate. Retrofits and modifications are available to minimize the impacts of cycling on boiler systems.

B&W Competencies for ACE-Defined BSER Technologies

Neural Network / Intelligent Sootblowing

Check B&W Primary Technology

Optimizes boiler heat absorption and sootblower steam consumption; minimize exit gas temperature and stack losses

Redesign / Replace Economizer

Check B&W Primary Technology

Reduces boiler exit gas temperature; may affect SCR operation

O&M Improvements

Check B&W Primary Technology

Check B&W Supplied Technology

Performance testing can identify various O&M improvements at the plants

Blade Path Upgrade (Steam Turbine)

Requires boiler heating surface modifications (B&W technology) to match the boiler to the revised turbine conditions

Air Heater & Duct Leakage Control

 Check B&W Supplied Technology

Air heater and boiler setting leakage degrades AH performance, increases UBC, and requires operation at higher total excess air

Variable Frequency Drives

Check B&W Supplied Technology

Allows fans to operate more efficiently; most significant efficiency gain potential during low load operation

Boiler Feed Pumps

Check B&W Supplied Technology

Reduces power consumption


Contact us to speak with an expert or request an inspection. B&W can help you support ACE Rule requirements and other efficiency improvements.

B&W Competencies for Improved Heat Rate/Efficiencies

Pulverizer Performance

Check B&W Primary Technology

Improves coal fineness, reduces motor power consumption

Split /Sliding Pressure Operation

Check B&W Primary Technology

Permits increased load change rate capability; extends reheat steam temperature control range (better low load heat rate)

Flue Gas Recirculation

Check B&W Primary Technology

Extends steam temperature control range and fuel flexibility

Burners and Overfire Air Systems

Check B&W Primary Technology

Reduces total excess air and unburned carbon levels; maintains or reduces NOx and CO emissions