Making Your Generating Unit More Grid-Friendly: Check the Air Quality Box

Posted to POWER Engineers—Environmental in the Utility Management Group
image credit: Grid of the future. Changes to the U.S. electricity industry are forcing coal-fired power plants to make modifications in order to meet the needs of an evolving power grid.
Brian Petermann's picture
Senior Project Manager - Environmental, POWER Engineers, Inc.

  40 years of experience mostly as a consultant in field of electric utility and energy production air quality permitting, compliance, testing, monitoring, and reporting. Tackling hydrogen and...

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  • Feb 15, 2023

The industry of generating and delivering electric power is undergoing dramatic and rapid change. Renewable energy, decreasing coal-fired capacity and changing demand patterns are increasing the complexities of operating the power grid.

In response, utilities are wisely making changes to their generating units to make them more “likeable” by the grid and to improve their economics. The number and range of these projects have steadily increased as utility generating units are looking for ways to operate at lower loads, improve load change response times and lower operating costs.

Achieving these goals will likely require one or more plant modifications. But before moving forward with a plan, you should first determine if there is an air permitting requirement.

Why Check the Air Quality Box?

Projects at a generating unit that result in an increase in pollutant emissions may require a permit before those changes can be made. Utilities have suffered significant enforcement actions when state and federal agencies found out and concluded that modification projects took place without a permit.

This is not a good situation for an offending utility because of the potential monetary penalties, retrofit of costly new emission controls and negative public perception. This can be avoided by performing certain assessments, and maybe simple permitting, prior to approval and initiation of the desired generating unit changes.

What Are the Rules?

At an existing plant, only those projects considered a “modification” may need a permit. A modification is any physical change, or even an operational change, that results in an emission increase.

Some changes are exempt, such as routine maintenance repair and replacement (RMRR) projects. Based on this, plant changes that are either RMRR or do not result in an emission increase generally do not require a permit. 

Do I Need a Permit or Not?

Assessing plant projects for permitting requirements is a process. Of course, each project is unique and requires a tailored approach with much more detail than we’ve provided here, but these basic steps provide a good framework for performing your assessment.

1. Define the ProjectAir permitting

Defining the project is critically important to the assessment of potential air permitting requirements. This includes collecting information and data necessary to not only describe the project itself but also its potential interrelated effects on the plant.

How this is communicated is key. Information can be collected through written requests, but a face-to-face meeting with all applicable plant staff is far more effective, especially with regard to interactive operational and emission effects. This is where you clearly define the purpose, schedule, specific plant changes and impact on the generating unit operation.

2. Determine If Emissions Are Affected

This is a key step because it can determine if the project assessment can be ended at this stage or not. You must determine if your project is:

  • Not a modification
  • Possibly a modification, but does not affect emissions.

If it is not a physical change or change in the method of operation, if it is RMRR, or if the change has no impact on emissions, then the assessment can stop at this point.

RMRR determination considers project nature, extent, purpose, frequency and cost. A complete and accurate project definition is important to make a confident determination. Plant projects that have no tie to emissions are not considered a modification. This assessment and its conclusions need to be fully documented for the utility’s files. Depending on the state air agency, some utilities may also need to submit a project notification to validate why a permit is not required.

3. Define the Emission Increase

If you have determined that the proposed plant project cannot be exempted, the next step is to understand the extent of the emission change.

The trigger for potential major permitting at a generating unit is either:

  • Any increase in the maximum hourly emission rate of sulfur dioxide, nitrogen oxides, or particulate
  • significant increase in annual emissions.

An increase in maximum hourly emission rate is typically governed by whether there is an increase in maximum fuel burn rate.

Assessing the increase in annual emission is more involved and considers past actual emissions and future “projected” emissions based on assumptions. These assumptions may be considered limitations after permit issuance, so this should be approached in a strategic, holistic way.

4. Document and Decide

If the project is considered a modification with an emission increase, a decision is made at this point whether the benefits of the desired plant project are worth the cost of getting a permit. This is an important decision for the utility and a thorough, accurate and creative assessment of the project and its costs is critical.

Three Tips for Success

1. Get Management Buy-In

The requirement for a permit assessment of proposed projects must come from senior management. If top management is convinced of the need, then the directive to conduct these assessments will be taken seriously.

Educating management on the risks of regulatory fines, resulting capital costs and negative public perception is key to convince them of the importance of this process.

 2. Bring Your Environmental Staff in Early

If you have an active capital project approval process, consider incorporating a required review step performed by key environmental staff.

If your environmental staff is experienced in permitting assessment techniques, they may be able to review most, if not all, of the proposed projects without a need for additional assistance. Make sure their process includes documentation of the assessment for corporate files for future reference and support in case of inquiry.

For more complicated projects, your staff may need the services of a specialized environmental consultant. This is someone who can perform more in-depth analysis and calculations. They can draw on deeper resources and apply successful approaches from other projects for estimating costs and assessing the project’s impact on emissions.

Incorporating a process flow diagram can bring consistency and confidence to the effort and is useful as an education tool. The overall process creates documentation needed for the utility files.

3. Get Out on the Plant Floor

One-on-one discussions with generating plant staff will go a long way to gaining buy-in at the plant operations level. They need to see environmental staff and consultants as part of the plant team working for a common cause, not a roadblock to moving forward with a desired project.

When the plant staff understand the need to consider the permitting aspects of their proposed project, they can provide better information for the assessment process. 

Following these general steps and with these tips in mind, you can more confidently check that air quality box when planning your next plant modification.

Article originally published in the Winter 2020 issue of Currents. Subscribe today to stay current on environmental insights and regulatory updates that impact your projects. 

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Jim Stack's picture
Jim Stack on Feb 16, 2023

Not using diesel generators can help. It is a problem taking gas to each generator so NG cost more can have a pipe right to you generator saving refueling and they run cleaner that diesel. Not perfect but better.

   The best is a large solar generator with battery storage. They also helps remore locations with no refueling. It can pay for itself. 


Brian Petermann's picture
Brian Petermann on Feb 16, 2023


Thanks for the comments. I presume you are referring to the development of scenarios at a utility plant to be more responsive to the grid demands while still reducing emissions and carbon. I totally agree that use of natural gas fired engines instead of diesel oil fired is a cost-effective strategy to provide fast grid response and the emissions are much lower than diesel such that permitting any additional hours would be simplified. As for your stated option of solar with battery energy storage system (BESS), this too is a great option for a number of reasons; 1)air permitting of the solar system and batteries is not applicable, 2)the BESS has very fast response to changing grid demands, 3)the BESS recharges during periods of low grid demand and high solar collection, and 4)there are tax credits available for the installation of solar/BESS.

So, good comments and good thinking!

Brian Petermann's picture
Thank Brian for the Post!
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