If I Knew Then What I Know Now: Air Emissions Permitting Considerations for Biomass Boilers

Addressing major questions early on the biomass boiler development process can help save valuable time and money.
By John Hinkley | July 29, 2021

“If I knew then what I know now, then I would have done things much differently.” One of the most standout observations in my past two decades of assisting clients is that project developers who ask the right questions early in the project planning process enjoy the process the most, and are the ones who are happiest with the outcomes. In this article, I will address questions that commonly occur when an air emissions permit is required for a new biomass-fired boiler.

When do I need an air emissions permit? An air permit is intended to protect human health and the environment and is a legally binding document that includes enforceable limits on air pollutant emissions (e.g., particulate matter (PM) nitrogen oxides, sulfur dioxide and carbon monoxide) that a facility can release to ambient air. Air permits specify how facilities must design and operate pollution control equipment, how emissions must be vented (i.e., how exhaust stacks should be designed), air pollutant limits that must be met, as well as how to monitor, record keep and report aspects of their operations related to their emissions.

Assuming an air emissions permit is required, it is important to anticipate the timeframe for when it will be issued, because very little construction is typically permitted before an air permit is issued. In my experience, air permit applications can generally take from three weeks to three months to prepare, depending on the size and complexity of the proposed project. Following application submittal to a state agency, it can typically take between two and 18 months for the agency to issue the permit, again depending on the project. Given these timeframes, it may be necessary to start work on an application up to two years before commencing construction for a complex project.

Am I subject to federal requirements? Permits are issued by state agencies, and in some cases, not all federal requirements are included in the air permit. For example, not all state agencies enforce the federal rule that many refer to as the “Area Source Rule” (40 CFR Part 63, Subpart JJJJJJ—National Emission Standards for Hazardous Air Pollutants for Industrial, Commercial and Institutional Boilers) and therefore do not include that rule’s requirements in the air permits they issue. Further, there are some cases in which a boiler may not trigger air permitting in a particular state, but the rule still applies, so its requirements still have to be met.

Are there new state or federal regulations on the horizon? Regulations impact the design, operation and therefore cost of facilities. Consequently, it is imperative to perform due diligence to determine if there are new regulations that could be promulgated at a time that could impact your project. For example, the New York State Department of Environmental Conservation recently changed Title 6, Part 227-1 of the New York Codes, Rules and Regulations (6 NYCRR 227-1) for stationary combustion installations, which significantly reduced the allowable PM emissions limit for biomass boilers. This change means that many small biomass boilers, or boilers with a heat input less than 10 million British thermal units per hour (MMBtu/hr), will likely have to be permitted with an advanced form of emissions control such as a high-efficiency multicyclone, electrostatic precipitator (ESP) or fabric filter baghouse in lieu of a cyclone or conventional multicyclone. This significantly increases capital and operating costs of a constructing and operating a biomass boiler.  

Am I subject to air toxics regulations? Air toxics regulations in some states require that air permit applications for biomass boilers include an evaluation of air toxics that would be emitted from the combustion process. In my experience, this has triggered evaluating best management practices (BMP, measures that can be implemented upstream of, and within the biomass combustion chamber) and add-on pollution controls that can reduce the level of emissions released. A few BMP examples include performing regular tune-ups, periodic monitoring of carbon monoxide with a combustion analyzer, and performing visual observations of stack exhaust. Add-on controls can include conventional and high-efficiency multicyclones, ESPs or fabric filter baghouses.

What do I need for emissions control? Emissions, specifically PM, typically need to be controlled with add-on controls for biomass projects. The type of add-on control typically depends on applicable state or federal emissions limits, the expected level of annual emissions, the need to construct a shorter exhaust stack, and existing ambient (outdoor) pollutant concentrations. The capital and operating costs of pollution control equipment can vary widely (from $15,000 for a cyclone to $350,000 for an ESP), so it is imperative to identify early in the planning process which level of control is necessary (i.e., what level of reduction of a pollutant must be achieved).  

How tall does my stack need to be? Emissions are typically vented to ambient air with a vertical stack that extends some height above the building it is associated with. Simply put, taller stacks are more expensive than shorter ones. Also, taller stacks can make facilities more visible, which may not be desirable for aesthetic reasons. Some state regulatory agencies have rule-of-thumb formulas for establishing stack heights. In some cases, air quality dispersion modeling (air quality modeling) may be required, or can be voluntarily performed to establish the stack height. The next question describes air quality modeling.

Do I need to perform air quality modeling? Air quality modeling is a computer-based technique for evaluating how emissions from biomass combustion disperse in ambient air. The triggers for modeling vary from state to state and depend on the size of a boiler, the quantity of estimated annual emissions, and state modeling requirements. Modeling is performed to determine whether a proposed emissions source will be designed to provide the dispersion needed to meet air quality standards that are intended to protect human health. Modeling is often performed even when not required, in cases where project developers want to ensure that the design (i.e., height and inside diameter) and location of a stack will be adequate to protect human health. In cases where a rule-of-thumb requirement by a state would require building a significantly tall stack, air quality dispersion modeling can be performed to demonstrate that a shorter stack will meet air quality standards.

Do I have to do anything after my permit has been issued? The party is not over when you receive your air permit. Air permits include state and federal requirements that apply after an air permit has been issued. The type and degree of requirements depend on the size of the biomass boiler, the type of biomass burned (i.e., all natural biomass and waste wood), and whether there are other emissions sources being permitted for the same project. Compliance requirements following air permit issuance can   include submitting notifications (for commencing construction and commencing operation), performing source emissions testing (i.e., measuring the rate of pollutant emissions released from the stack), submitting electronic reports to state and federal agencies, preparing an air permit compliance certification, performing boiler efficiency testing, and preparing and submitting emissions fee reports.  

Hopefully, this article has helped shed some light on what needs to be considered when planning to construct a biomass boiler. While there are many more questions that should be asked, beginning with asking the ones described in this article as soon as possible is a great start. There is no better time than the present.  


Author: John Hinckley
QEP, Senior Managing Consultant, ALL4 LLC
jhinckley@all4inc.com
802.359.7294