Increasing the Reactivity of Solid Fuel with Liquid Hydrocarbons from the Pyrolysis of Waste Tires

Utilization of waste tires via pyrolysis is a promising solution. The liquid hydrocarbons generated during this process could be used for enhancing low-reactivity coals for energy application. Current study investigates oxidation and combustion characteristics (including composition of gaseous combustion products) of low-reactivity coal mixed with liquid hydrocarbons from pyrolysis of waste tires with a concentration up to 20%wt at 700 °C. The oxidation tests via TG-analyzer revealed that at heating rates up to 10 °C/min, the process had one stage, associated with combined oxidation of coal-liquid hydrocarbons mixture. Starting from 10 °C/min the second stage occurred at temperature ~400 °C due to evaporation of light components of the mixture. Combustion tests at experimental setup at 700 °C revealed almost linear increase in fuel reactivity, expressed into decline in ignition delay time of mixtures (up to 71.6%) with increasing concentration of liquid hydrocarbons, while flame and diffusion combustion times were, in contrast, increasing (by up to 69.5%). Increasing concentration of additives from 2.5 to 20%wt resulted not only in change in the form of obtained mixture but also changed the combustion mechanism from predominantly heterogeneous smoldering to majorly homogeneous gas-phase ignition and combustion. Gas-phase combustion products concentration curves generally complimented previously observed peculiarities of combustion. Increased CO and NOx concentrations in combustion products of coal mixed with liquid hydrocarbons revealed necessity in additional tailoring of burner characteristics for mitigating these effects. The compromise composition of mixture was found to include 10%wt of liquid hydrocarbons for enabling quick gas-phase ignition while maintaining moderate level of combustion products emissions.