21-0226 Biofuel Boiler



The project team at [project] (WRELC) would like to propose a biofuel system to be considered for an exception. The existing district energy system (DES) at WRELC serves the heating needs of the campus along with the West Dorm renovation project. There are two (2) large boilers, with the following capacities:

  •         Heating capacity of 1,210 KBtu
  •         Heating capacity of 2,610 kBtu
  • Due to the densely wooded and extreme weather of this project location, the DES is the most environmentally preferred and reliable option for the project. Even though there is combustion at the DES, care has been taken from the Wolf Ridge team to ensure advantageous biofuel sourcing without negative environmental impacts, as demonstrated in the following narrative.

    Exception 18-0625 Principles Outlined by ILFI

    To comply with the biofuel exception, the ILFI has provided the following guidance, with a response by WRELC, under the two main principles: Advantageous Biofuel Sourcing, Biofuel and Combustion Impacts


    Sourcing of biofuel should be from available, long term, sustainable (e.g. closed-loop) sources, such as:

  •  Local waste products. Any biofuel should be a local waste product, ideally associated with the project or project area, which will be readily available for the lifetime of the project.
  • o    WRELC Response: The biofuel used at WRELC is locally sourced from 100% post- consumer waste wood fiber. The factory that produces the wood pellets is located within the state of Minnesota and made from wood pallets that have reached the end of their useful life and otherwise would be landfilled.

  • Beneficial combustion. Consumption of detrimental global warming gas emissions is desirable. In particular, sources of anaerobic digestion (such as landfills) produce methane, a powerful greenhouse gas, and consumption of the methane can result in net positive emissions.
  • o    WRELC Response: No gas collection occurs as part of the WRELC biofuel system. All energy is sourced from waste wood fiber.

  • Net zero annual emissions. Rapidly renewable resources can have a net zero grow/burn/release annual emissions cycle, which may be acceptable, if they are not causing environmental degradation.
  • o    WRELC Response: Rapidly renewable resources are not used as part of the WRELC biofuel system. The waste wood used is a key piece to the net positive annual emissions and does not cause environmental degradation. Refer to the additional documentation demonstrating net positive emissions.


    Projects should avoid biofuel sources and systems that cause environmental degradation or reinforce other negative impacts, such as:

  • Displacement of beneficial land uses. Biofuel comes in many forms. Biofuel that is grown (rather than a waste product) displaces food production, and in some cases, wild areas, which is not acceptable.
  • o    WRELC Response: The WRELC biofuel source is 100% waste fiber, thus is not grown. The waste fiber, sourced from wood pallets, is at the end of useful life and would have been landfilled if not diverted into a source for biofuel. Because of this, the biofuel at WRELC does not displace beneficial land use or promote wasteful practices.

  • Depletion of advantageous biomass. Use of biofuels should not displace other environmental benefits, such as biomass. Much biomass plays an otherwise important role, in terms of habitat, soil and biotic health, etc.
  • o    WRELC Response: The biofuel at WRELC is waste wood sourced from pallets that are at the end of their useful life. These pallets are repaired an average of five (5) times before being considered waste and are diverted from the landfill to be made into the biofuel used at WRELC. This focus to reuse the pallets before obtaining new ones ensures there is no promotion of wasteful practices and no depletion of advantageous biomass.

  • Negative externalities. Sources of biofuel with potential additional negative externalities, such as animal waste, should be carefully considered to avoid reinforcement of negative environmental impacts.
  • o    WRELC Response: The only additional potential negative externalities that have been carefully avoided to limit the environmental impacts is the transportation of the biofuel to the site. The WRELC biofuel is sourced from 100% waste fiber as close to the site as possible, which is within the community (state). Additionally, the biofuel is sourced only in bulk, via 23-ton truck loads and stored in a 34-ton grain bin. By transporting only in bulk, the impacts of transportation and packaging are minimized along with the associated emission and carbon footprints respective to the system.

  • Short term impacts. Burning of wood and wood waste balanced with replanting has a negative short and mid-term emissions cycle, with CO2  being released and proportionate removal occurring on a multi-decadal cycle, which is not acceptable.
  • o    WRELC Response: Similar to the response to the depletion of advantageous biomass, the waste wood is sourced from pallets that are repaired, on average, five (5) times before being considered waste. Because of this, the demand for products from the forest is lowered and, therefore, the need for replanting is also reduced.

    The included carbon analysis demonstrates that the WRELC district energy system, with use of 100% waste fiber, to be net positive carbon. There are no short-term impacts.

  • Fossil fuel replacement. Many biofuels systems, such as combined heat and power plants, or generators, can easily switch from grown biofuels to natural gas. Teams should avoid biofuel source that are easily replaced with fossil fuels and must show how an easy switch is not probable.
  • o    WRELC Response: The WRELC biofuel district energy heating system has two (2) large biofuel boilers, one being redundant. There is no Gas or Electric capacity to meet the heating needs of the facility. Two large biofuel boilers create the hot water. The biofuel boilers cannot be converted or modified to function as gas or electric boilers. Additionally, there is a small, 750 kBtu, propane boiler within the district energy plant used solely for emergency backup. See the following narrative that addresses requirements for exception I06-E6 v3.1 Emergency Power Systems.

    Exception I06-E6 v3.1 Emergency Power Systems

    Propane backup boilers are acceptable in harsh climates for non-grid-tied projects. WRELC is a 2,000-acre environmental learning center where school children, teachers, parents, and other adults participate in programs centered on learning about nature and conservation in northern Minnesota. These programs occur in the coldest months of the year, where the ASHRAE design heating temperature is -19.5ºF. It is imperative that the West Dorm and other buildings on campus maintain a minimum heating temperature in an emergency if the main biomass boilers go down. WRELC has a small, 750 Btu, propane boiler within the district energy plant used solely for emergency situations, including to safely evacuate the buildings and to prevent pipes from freezing. The backup boiler does not have the capacity to adequately heat any of the buildings on campus and has not been used since completion of the project in 2016.

    During the design process of the district energy system, the 1,210 kBtu boiler was sized to maintain comfortable space temperatures throughout the facility down to 10ºF outside temps. The 2,610 kBtu boiler maintains building temps down to - 50ºF. At 750 kBtu, the propane boiler was sized to the smallest possible size, just keep the building water lines from freezing in northern Minnesota mid-winter temperatures.

  • Air Quality Impacts. Unrefined biofuel can have many impurities which when burned can create negative air quality impacts, which may not be acceptable.
  • o    WRELC Response: By using post-consumer waste fiber, the material is already dry and lack any other impurities. The pallets are raw wood, with no paint or sealants.

    During the manufacturing process, the pallets that cannot be refurbished are sorted into quality pellet material and sent through the “grinding” process where it is converted into a wood chip. These wood chips are then dumped into the hammer mill where they are converted into what is very close to sawdust.  The sawdust is then sent into the pelletizer where it reaches over 180ºF and formed into a wood pellet. This temperature kills unwanted bacteria that was not pulled during the sort prior to the grind.

    The WRELC boilers, of European design, meet or exceed the US EPA guidelines for emissions. The boilers are sophisticated, computer-controlled combustion units.

    Combustion is computer controlled via sensors placed throughout the unit that drive variable speed feeds of primary and secondary combustion air into the combustion chamber, along with variable speed fed biofuel. These computer- controlled inputs work in concert with computer controlled variable speed exhaust fans and a cyclone particulate collector to meet maximum efficiency of combustion via oxygen sensor monitoring in the exhaust piping of the boilers. Ash is very minimal and as it is basic in pH it is used for soil amendments to very acidic soils at the organic vegetable farm on site.


    The information provided in the post, along with additional detail from the project team affirming that there are no toxic additives in the particular pellet-making process, substantiate that the proposed biofuel, made locally of material that would otherwise be landfilled, as used in the particular project application, meets the criteria in the 18-0625 v3.1 Biofuel Guidance for advantageous biofuel sourcing and avoidance of combustion and ancillary impacts. The Institute is granting a project-specific exception for its use as a renewable fuel.

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