Operating a Wood-Fired Boiler

An area or major source of Hazardous Air Pollutants (HAP) utilizing a wood-fired boiler may be subject to the Boiler Maximum Achievable Control Technology (MACT) rules which may require stack testing, energy assessments, and boiler tune-up requirements.

A permitted source should evaluate the Potential to Emit (PTE) that was utilized to establish their air permit as it may need to be altered depending on the type of wood products combusted. The emission factor established for clean wood was most likely used to determine the PTE for an air permit issued to a facility utilizing a wood-fired boiler. Therefore, if a permitted source has been approved to combust clean wood but would like to combust or is combusting wood waste, the PTE should be re-evaluated to assist in gaining approval from the Indiana Department of Environmental Management (IDEM) and to update the air permit with correct information.

What is the difference between clean wood and wood waste?

Clean wood consists of uncoated, unpainted, and untreated wood scrap, sawdust, chips, millings or shavings, and natural growth wood materials. Clean wood does not include wood products that have been painted, pigment-stained, or pressure treated by compounds such as chromate copper arsenate, pentachlorophenol, and creosote, or manufactured wood products containing adhesives or resins (e.g., plywood, particle board, flake board, and oriented strand board).

Wood Waste consists of coated, painted, and treated wood scrap. Wood waste includes wood products that have been painted, pigment-stained, or pressure treated by compounds such as chromate copper arsenate, pentachlorophenol, and creosote, or manufactured wood products that contain adhesives or resins (e.g., plywood, particle board, flake board and oriented strand board).

How do I gain approval to combust wood waste if I am a permitted source eligible to combust clean wood?

The type(s) of fuel a source is permitted to combust within their wood-fired boiler(s) can be found within the wood-fired boiler description in Section D of an air permit.

If a source desires to combust wood waste such as laminated, resonated, coated, treated, glued or otherwise modified wood waste products, they will need to fulfill three (3) requirements before being considered for approval. The requirements include, in the order given:

  1. Provide a demonstration of the emissions from the wood combusted.
  2. Evaluate if the addition of wood waste increases the PTE.
  3. Apply for a modification, revision or administrative amendment
    • based on a change in PTE, if applicable.
    • to indicate that clean wood and/or waste wood is being combusted.

What are my responsibilities to update my air permit so it specifies approval to combust Wood Waste?

1) Provide a representative stack test or pertinent information to IDEM.

A stack test representing combustion of the clean wood as well as the wood waste requesting to be combusted should be submitted to the Office of Air Quality (OAQ). If a permitted source has a previous air stack test representative of their combusted wood, that stack test will be considered.

If a previous stack test is not available, the source will need to provide information on the type of wood waste they are requesting to combust with the appropriate stack test protocol. The constituents of concern are:

  • Particulate Matter (PM)
  • Volatile Organic Compounds (VOC)
  • Hazardous Air Pollutants (HAP)

The type of wood waste requesting to be combusted will determine the required stack test.

2) Evaluate the PTE from the wood waste desired to be combusted.

The permitted source should demonstrate whether the wood waste that is desired to be combusted alters the PTE that was utilized to establish their air permit. (Most likely, the emission factors for clean wood were utilized to determine this PTE.) The permitted source should then evaluate how the PTE is altered with the new emission factors provided from the stack test.

3) Apply for a permit modification, revision or administrative amendment.

In the event the emission factors significantly alter the PTE, the permitted source should apply for a source modification and/or permit revision to update the PTE and the description of the fuel type for the wood-fired boiler within their air permit. Air permitting application information can be obtained directly from the Office of Air Quality, or from the Compliance and Technical Assistance Program (CTAP).

In the event the emission factors do not significantly change the PTE, the permitted source may apply for an Administrative Amendment to update the description of the fuel type for the wood-fired boiler within their air permit. (The stack testing results and modified PTE calculations should be submitted when applying.)