Economic evaluation of a hypothetical integrated energy recovery system for trommel fines

Abstract

Trommel fines are a high-ash aggregate waste derived from material recycling facilities (MRFs) and are usually disposed in landfill. Increasing UK landfill tax and environmental concerns, however, calls for a flexible technology that can effectively process and extract valuable energy from trommel fines at high efficiencies. One possible technology is fast pyrolysis coupled to a combined heat and power (pyro-CHP) plant. To determine the feasibility of such technology, an understanding of its economic characteristics is required, in addition to the technical details. This study presents an economic evaluation of a pyro-CHP plant processing three pre-treated trommel fines feedstocks for energy recovery over a 20-year period. The three feedstocks were designated as DPT (from initial separation/size reduction), AW (from ash reduction by washing DPT with water) and AWS (from ash reduction by washing DPT with aqueous surfactant solution). Under all processing capacities (200 kg/h to 2000 kg/h) total revenues from the pyro-CHP system were higher than landfill costs, but only became profitable at 2000 kg/h processing capacity for the DPT feedstock. Further analysis showed positive net present values (NPV) only for AW and AWS, e.g. at 2000 kg/h capacities, with payback periods of about 14 years compared to 35 years for DPT at a fixed CHP efficiency of 60% and 20% internal rate of return (IRR). Sensitivity analysis carried out using different values of IRR and CHP efficiencies, confirmed the superior economic performance of the washed feedstocks over DPT, with payback periods reducing to about 6 years in some cases.