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HomeMy WebLinkAboutSupplemental application to AEAApplication from the City of Craig Supplemental Information December 8, 2009 On December 7, 2009 the City of Craig received a request for additional information from staff at the AEA regarding the city’s application to AEA for project funding from the Renewable Energy Fund. The request asked that the city “explain the issues with the current walking floor dryer and why an additional dryer is needed.” Current Drying Capacity The Craig wood boiler facility does have a system to dry wood fuel once that fuel is delivered into the boiler building. The system consists of steel ducts cast into the concrete floor of the wood storage bin. These ducts transmit air heated by the wood boiler from a 20 horsepower electric fan into the chip pile within the storage bin. The heated air, typically about fifty degrees higher than the ambient air temperature, is forced through the chip pile through perforated plates that cover the top of the ducts. Moisture evaporated from this process is removed from the storage area by an exhaust fan. In short, this chip drying system works well up to a point. The system can dry wood that enters the building at up to about 50 percent moisture content. Between the time that wood is delivered and the time it ends up in the wood boiler, the in-floor duct system can usually dry the wood fuel to between about 30 and 35 percent moisture content. For green wood that has not been exposed to the precipitation—i.e. wood chips that are brought to the wood boiler from fresh off the chipping line—the installed drying system is functional. However, for wood that is more saturated, whether from whole logs that are particularly wet when chipped or from chips that are exposed to precipitation before they are delivered to the wood boiler, the installed system is unable to dry that wood to moisture content levels within the operational range of the Craig boiler. The issue of highly saturated wood chips was a chronic problem during the winter of 2008-2009. At those times when the mill supplying the chips had not chipped logs for an extended period of time, the chips delivered to the Craig boiler were remarkably wet from rain and snow, well in excess of 50 percent moisture content. While the wet chips were enough to create combustion problems, the matter was made worse during the deep winter months when layers of snow clumped together into large chunks of ice and imbedded in the chip pile. These deliveries of particularly wet wood chips could not be adequately dried by the in-floor system. The result was poor combustion efficiency in the boiler, and the loss of heating capacity from the wood boiler, meaning that the adjacent school buildings and the Craig Aquatic Center were forced to rely on diesel and propane fossil fuels at a time when the wood boiler would have otherwise provided the maximum benefit to the community. Proposed Wood Drying Alternative With the volume of wood chips at the mill that supplies the Craig wood boiler, it is not practical for the mill to attempt to cover the large area to shelter green wood chips from precipitation. Given that there appear to be markets for dried wood chips, hog fuel, and Renewable Energy Fund Round 3 Grant Application Application from the City of Craig Supplemental Information December 8, 2009 Page 2 sawdust for use as biomass fuel beyond what is demanded by the Craig wood boiler project, it is likely more efficient to dry large volumes of biomass, some of which can be used by the Craig project, and have sufficient quantities of properly dried wood fuel available to encourage other biomass projects in Alaska. A related benefit from bulk drying of biomass is a readily available supply of biomass that is already dried to a moisture content of between 25-35 percent, the ideal range of moisture content for commercial and industrial combustion. This would allow the City of Craig to avoid having to dry chips after delivery to the boiler building, meaning that the energy that the city now uses to dry out wood chips can instead be used to provide more heat to the Craig school and Aquatic Center buildings, which in turns means even less reliance on fossil fuels. The biomass drying project proposed here by the City of Craig will have still another tangible near-term benefit. Currently the city is working with the Craig Community Association (CCA, the federally-recognized Tribe in Craig) to connect the CCA Tribal Hall to the wood boiler facility. So long as the wet wood fuel issue is unresolved, the ability of the wood boiler to provide reliable energy to other public buildings is uncertain. However, the reliable supply of properly dried wood fuel would have such a beneficial effect on boiler operations that adding a substantial additional load to the boiler, such as one that would come with a connection between the boiler and the CCA Tribal Hall, can be done with a high level of confidence that the boiler can meet the additional load demand. If all the wood burned at the Craig boiler project were delivered to the facility within the 25-35 moisture content range, the quality of that fuel would eliminate the single greatest operational difficulty with the wood boiler—managing fuel that is too wet to burn properly.