MUNICIPAL HDPE RECYCLING PLANT DESIGN

Abstract

The objective of this project was to design a high-density polyethylene (HDPE) recycling facility located in Tucson, Arizona that processes HDPE derived from Pima County municipal recycling programs into two streams: low purity, dyed HDPE flakes and food-grade clear HDPE pellets. The dyed HDPE flakes are sold at $0.55/lb to construction material manufacturers, and clear pellets are sold at $0.75/lb to food and beverage companies. The purity specification of the food-grade product is 99.999% HDPE, determined from FDA guidelines on recycled plastics for food and beverage use, while the purity specification for dyed HDPE is 99%, as deemed acceptable for construction use. An economic analysis has been performed to show that assuming that it takes three years to construct the plant, the plant will be profitable just one year after construction is completed. The overall process of this facility is outlined by a bottle wash, grinder, flotation tank, sorter, flake wash, flake rinse, and extruder. The bottle wash step applies hot water, detergent, and caustic to remove the majority of contaminants including food residue, labels, and adhesives. The grinder granulates the plastic bottles into 5-10mm flakes using a wet grinding process to suppress dust emissions and prevent the plastic from melting. The flotation tank separates HDPE from contaminants by density. The sorter then optically sorts the dyed and clear HDPE, where dyed flakes are removed and sold while clear flakes are conveyed for further processing. The flake wash cleans the clear HDPE to food grade purity while the flake rinse removes residual detergent and contaminants. Finally, the extruder processes the flakes into pellets. Additionally, the plant includes an on-site water treatment facility to recycle 65% of the water consumed.