Combustion characteristics of aromatic-enriched oil droplets produced by pyrolyzing unrecyclable waste tire rubber

Abstract

The purpose of this work is to study the combustion characteristics of aromatic-enriched tire pyrolysis oil (TPO) produced from typical small vehicles and truck tires. Pyrolysis oils (NRTO: natural rubber tire oil and SRTO: synthetic rubber tire oil) from two raw radial tire materials were produced and condensed at 25 °C and 130 °C in a three-stage auger pyrolysis reactor under negative pressure. Combustion particularities were acquired using a single-droplet suspension combustion device and evaluated by five different indicators: kinetics, flame shape, burning rates, flame stand-off ratio (FSR) and mass transfer parameters. It was found that TPO was a potential fuel with higher calorific value (40–44 MJ/kg) and lower combustion apparent activation energy (10–40 MJ/mol) than that of bio-oil and solid fuels. Oil produced from synthetic rubber and condensed at 25 °C exhibited higher stable burning rate (1.93 ± 0.03 mm2/s) than that of nature rubber pyrolysis oil. Comparing with traditional fuels, tire oil droplets displayed higher surface local heat transfer coefficient, but the mass transfer number (B ≈ 2.5) and FSR (<3.1) under stable combustion conditions were much lower. The combustion behavior of TPO has partial similarity with unsaturated hydrocarbons and ester biofuels. The reported results support the well-characterized TPO condensates for subsequent atomized combustion in realistic industrial burners.