Fox Valley Glass Aggregate Plant Virtual Tour
Sludge Material Handling and Storage
Wet sludge is transported to the facility in self-dumping trailers. Truck scales at the plant allow actual sludge deliveries to be measured. The sludge is dumped in a receiving building, either onto the floor or directly into a live bottom pit. From this pit, wet sludge is transported using conveyors into a 2,600 wet ton capacity storage silo.
The sludge is reclaimed at the bottom of the wet storage silo using a live bottom sweep auger that discharges onto a series of screw and belt conveyors to transport the wet sludge to the drying system.
Sludge Drying and Wastewater Recovery
A closed-loop drying system recovers water vapor from the wet sludge driven off in the dryers. This water vapor is condensed in a packed tower wet scrubber, while the remaining noncondensable gases are directed to the boiler for destruction.
To maximize the facility’s thermal efficiency, steam is used to dry the sludge. The facility has two 85-foot-long rotary steam tube dryers that can dry 1,400 tpd of 60% moisture sludge down to 10% moisture.
From the dryers, sludge is again conveyed to the dry sludge storage silo. This silo has about eight hours of storage at full rated capacity.
Dry Sludge Firing
From the dry sludge storage silo, a system of screws and a pneumatic system transports the dry sludge to the cyclone boiler. The boiler has two 7-foot-diameter cyclone furnaces where dry sludge is fired.
The key to dry sludge firing in cyclone furnaces is to ensure adequate temperatures to facilitate molten slag formation and tapping. The lower furnace of the steam generator is specially designed to maintain high temperatures to allow the molten glass to run down the lower furnace walls and through the discharge opening in the lower furnace floor.
To lower the melting point of the raw material, a fluxing agent is added. Proper sludge/flux mixing is attained while the material is transported in the blow lines to the cyclones.
Steam Production and Distribution
The steam generator is a field-erected, top-supported, two-drum boiler of single pass design. The boiler is capable of generating 300,000 pounds/hour of steam at 350 psig/600 degree Fahrenheit superheated steam temperature.
Up to 180,000 pounds/hour of 350 psig/575 degree Fahrenheit steam is exported to a neighboring paper mill through a 2,500-foot-long steam distribution piping system. This steam is used to drive an existing paper mill backpressure steam turbine-generator, producing about 4 MW of power.
In addition, the plant uses any excess steam beyond the requirements of the paper mill in a full-condensing steam turbine generator. This system is rated 6,500 kW at 82,000 pounds/hour steam flow.
Glass Aggregate Processing
Once the molten glass discharges through the lower furnace opening, it falls into a quench tank filled with water that is maintained at a temperature of 140 degrees Fahrenheit. The molten glass fractures into pieces about 1/2 inch in diameter and smaller. The bottom of the quench tank is equipped with a wet drag conveyor that removes the glass aggregate while simultaneously dewatering the product on the wet drag upslope. The glass aggregate is discharged into a loadout area and loaded onto trucks.
The plant features Best Available Control Technology for all plant emissions. Particulate emissions are controlled through the use of a mechanical cyclone collector and fabric filter baghouse.
The facility is equipped with a selective non-catalytic reduction (SNCR) system that uses urea as the reagent to control NOx emissions.
Potential VOC emissions were addressed in the design phase of the project by installing a closed-loop drying system. Any potential VOC emissions generated in the drying process are carried to the cyclone furnaces in the combustion makeup air and are destroyed in the cyclone furnaces which have operating temperatures that are in excess of 1,700 degrees Fahrenheit.
The fuel receiving building is designed so that trucks are inside while unloading sludge. The combustion air is pulled from the sludge receiving building by a large odor-control air duct system. This system has other pickup points in critical areas of the facility. Odor levels have actually decreased in the area because sludge does not accumulate at the local paper mills, but instead is delivered to the facility 24 hours per day.
The facility was designed to operate very quietly. Essentially, all equipment is enclosed in buildings or galleries, which effectively reduces any fugitive noise emissions.
With our aggregate technologies, Minergy is helping paper mills meet their long-term sludge disposal and environmental goals. The plant has the capacity to process all the paper sludge produced in Winnebago County — which accounts for two-thirds of the entire waste stream in the county, and represents more recycled material than handled by the combined municipal recycling programs in the entire state of Wisconsin. By recycling the sludge into a useable product instead of placing it in a landfill, the Fox Valley Glass Aggregate Plant preserves 10 acres of green space per year. The plant’s steam production has allowed the adjacent mill to reduce operation of older, less efficient boilers, which have higher emissions levels. In addition, truck traffic and the resulting emissions have been reduced by about 450,000 miles per year.
Empowered Work Culture
We recognize that the integrity of our company depends on the talent and skills of our team members. Key to sustaining profitable operations is a lean staff of just 27 people. Four self-directed work teams draw on the skills of four cross-functional team members. Each team identifies and uses problem-solving skills to make day-to-day business decisions. Four technicians, three engineers and four administrative office personnel complement the operation teams. We are committed to finding and retaining those with the highest skills. The result is a work force that is committed to excellence by providing beneficial recycling of paper mill sludge through an environmentally safe process.