We were recently introduced to a commercial application of biomass gasification during our visit the Deep Portage Learning Center in Hackensack, Minnesota. What we learned surprised us.
Biomass gasification relies on renewable energy sources such as cord wood, wood pellets, and agricultural crop wastes. The technology is relatively simple, efficient, and utilizes the secondary burning of gaseous compounds that are otherwise lost to the atmosphere. The process of gasification occurs in two phases. The first occurs in what is essentially a conventional fuel chamber where temperatures in excess of 400°F results in combustion products such as charcoal, carbon dioxide, carbon monoxide, hydrogen, methane, various phenols, acetone and acetic acid. High-temperature refractory liners in the primary chamber minimize the buildup of ash. Downward induction utilizing controlled air flow then directs fine ash particulates and syngas into the secondary chamber where they are combusted at temperatures in excess of 2,000°F. Overall, the process is efficient (87-93%) and significantly reduces emissions associated with less complete, lower-temperature combustion.
The ecology purest may at first cringe at the idea of punctuated carbon release, but closer analysis reveals that carbon emissions compare favorably with natural gas and propane – especially when considering emissions and embodied energy associated with production and distribution. Other potential drawbacks include higher particulate emissions in congested areas or regions prone to thermal inversions. Although gasification is efficient, some unburned ash is produced and requires adequate considerations for safe disposal. Logistical requirements for fuel access, transport, and storage may also pose obstacles to facility operations.
The costs of high efficiency gasification systems are only slightly higher than comparable natural gas-fired furnaces and high efficient hot water tanks. Heat distribution utilizes conventional systems including radiant and forced air ducts. Efficient, controllable storage systems provide around the clock demand without continual combustion. The real benefits become apparent when comparing gasification costs to those of electric and propane heat. Vast rural areas in cold climates are not served by natural gas and are therefore reliant on propane as the primary heating fuel. Regions having less than 5,400 heating degree days are typically reliant on either propane or electric grids – resulting in exorbitant energy costs proportional to relatively short periods of heating demands.
Case Study: Deep Portage Learning Center
The Deep Portage Learning Center, a 60,450 sf facility in Hackensack, Minnesota, has recently integrated several renewable initiatives, including two cord wood gasification systems, a wind turbine, solar PVC solar hot water heating, and modest building envelope improvements. Prior to 2010, propane represented the center’s primary heating fuel with an average annual use of 30,000 gallons at $2.00/gallon. Through gasification of 70 cords of wood annually at an average cost of $160/cord, the center has reduced energy costs by approximately $40,000 annually. Although their local cord wood supply is plentiful, they are already experimenting with local brush species and non-conventional cord wood that may further reduce costs and environmental impacts.
Deep Portages’s creative energy plan serves as a good example of why biomass gasification deserves a seat at the table when evaluating alternative energy sources. Given its advantages and disadvantages, the greatest benefits are realized by residential and light commercial buildings that are reliant on propane or electric grids but are located near reliable biomass sources.