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A novel machine to produce fuel nuggets from non-recyclable plastics

by Lawrence, Matthew J.

Abstract (Summary)
The potential for energy reclamation from non-recyclable plastics is significant and particularly timely. A plastic-derived fuel production process was developed and has been shown to be effective for non-recyclable plastics that are normally discarded. A machine was designed, constructed and evaluated with regard to energy balance and fuel nugget production. The hydraulically driven machine processed dirty, non-recyclable plastics by first compacting and then extruding them through four internal channels of a heated die. The process produced plastic fuel nuggets with a thin, melted exterior which trapped unmelted plastic in the interior. The plastic nuggets, called Plastofuel™, were 3.8 cm (1.5 in) wide, 3.8 cm (1.5 in) high, and were cut to a length of 5.1 cm (2 in). All aspects of machine operation, with the exception of feedstock loading, were automated and controlled by an onboard microprocessor. The machine was equipped with two data loggers to collect hydraulic system metrics and electrical energy usage. Component positions, electric power consumption, and hydraulic system pressure were recorded and converted to total energy consumption for all production runs. Energy content of the Plastofuel™ formed using clean household plastic and unused mulch film was 45.5 MJ/kg (19500 BTU/lb). Plastofuel™ formed with used mulch film and used plastic pots and trays had an energy content of 38.8 MJ/kg (16700 BTU/lb). The average density of the individual PlastofuelTM nuggets formed was 708 kg/m3 (44.1 lb/ft3). The bulk density of PlastofuelTM was 378 kg/m3 (23.6 lb/ft3). An energy ratio was determined by dividing the combined hydraulic and electric energy used for PlastofuelTM formation into the potential energy stored in all plastic nuggets formed for a single test run. The highest energy ratio (Eout/Ein) from all test runs iv was 47. During this test run, the electrical system consumed 30% of the total input energy to melt the PlastofuelTM perimeter, and the hydraulic system consumed 70% of the total input energy to process the plastic feedstock. The maximum Plastofuel™ production rate achieved with the machine was 27.6 kg/hr (61 lbs/hr). A mathematical model was derived to predict a relationship between the die surface temperature, the plastic residence time in the die, and melt depth achieved around the PlastofuelTM exterior. The 99% confidence interval on the mean difference between actual and predicted melt depth was -0.08 mm (-0.003 in) to 0.1 mm (0.004 in) (P = 0.8). Twelve additional test runs were run to isolate the effect of temperature and residence time on melt depth. Both factors significantly affected (P < 0.05) melt depth. Increasing die residence time with a fixed temperature was shown to increase melt depth, and increasing die temperature with a fixed residence time was shown to increase melt depth. A theoretical analysis of electrical energy used to heat the unmelted interior of each nugget was performed and indicated that 18% of the total electrical energy consumed by the machine was used to heat the nugget interior. v
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School:Pennsylvania State University

School Location:USA - Pennsylvania

Source Type:Master's Thesis

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