PNNL

Abstract

Municipal solid waste (MSW)’s 40–60% carbon content makes it a feedstock for biofuel production via pyrolysis. One challenge in the conversion process is MSW fouling due to thermal decomposition. The accumulated deposit on the injection screw eventually leads to plugging and constriction. This study examined the morphology and composition of the MSW fouling deposit on a used injection screw and conducted a thermal simulation to understand the temperature gradience of the injection screw. Surface modifications including smoothening and coating were proposed for the injection screw to address the deposit problem. For evaluating the candidate mitigations, a bench-scale fouling test was developed with the gas environment, temperature, and sliding speed relevant to the contact interface between the MSW particles and an actual screw surface. Results suggested that a smoother screw surface finish and an anti-sticking coating could be effective mitigations. Specifically, reducing the roughness from 2 to 0.6 and then to 0.2 mm proportionally decreased fouling, and the diamond-like-carbon, CrN, and CrC/NiCr composite coatings all effectively hindered the deposit accumulation. This study provides fundamental insights into the MSW fouling and proof-of-concept of potential mitigations through the screw surface modification.