This is where the woody biomass is held until it is needed to fuel the boiler. The storage building can hold up to 9 days of biomass fuel. The facility is completely enclosed to contain dust, noise, and odor. Conveyors bring fuel in to storage just below the roofline, and the fuel for the boiler is reclaimed just above the floor, to regularly turnover the inventory.
The completely enclosed fuel conveyors transport the woody biomass from the truck unloading- station to the storage building and from the storage building to the boiler building. Having the conveyors enclosed keeps dust and sound inside.
When trucks bring biomass fuel to the plant, they unload their shipment at the truck-unloading station. Trucks will back into the covered truck tipper and are tilted to release the biomass onto the conveyor system. The air in the unloading station is drawn under vacuum to a filter to minimize and suppress airborne dust. Filtered air is vented through the 110-foot chimney attached to the truck-unloading baghouse filter. On average, 75 truckloads per day of fuel will be delivered to the facility.
The boiler building is where the boiler is housed and biomass fuel is combusted to convert it to energy. The boiler will be a Circulating Fluid Bed (CFB) design, which has the highest efficiency and lowest emissions of boiler designs suitable for combusting biomass. This boiler will be equipped with state-ofthe- art air quality control equipment, including a high efficiency baghouse for particulate control.
With the combination of the biomass facility's air quality technology and the retirement of Domtar's existing boilers, we anticipate that the new facility will reduce the overall emissions from the mill site by about 30 percent.
The chimney on the boiler building is approximately 265 feet tall. The height is driven by several factors, including the surrounding terrain and the height of the boiler building. Like most plant matter, woody biomass has entrained water. As a result, an occasional water vapor plume may be visible from the chimney. This would be more prevalent or noticeable during colder weather.
The chimney lighting requirements will be determined by the Federal Aviation Administration (FAA).
The cooling towers are used to condense the steam exiting the turbine/generator back to water, so it can be sent back to the boiler and reused. Water is circulated between the tower and the steam turbine condenser, where it is heated as it condenses the steam. The hot water is then cooled in the cooling tower by mixing with air. The use of cooling towers eliminates a separate discharge of heated water to the Wisconsin River. We've selected cooling towers with plume abatement technology to minimize water vapor. At above freezing temperatures, the plume normally will not be visible – or only visible as a fine mist and will usually dissipate within 30 feet of the top of the tower.
To ensure the paper mill always has steam for its papermaking process, the new facility will be equipped with a natural gas auxiliary boiler that only will be used when the biomass boiler is not operating (i.e. down for scheduled maintenance or other repairs). This back-up boiler will include a 210-foot chimney.