COMPARISON OF THE COMBUSTION BEHAVIOR OF PULVERIZED WASTE TIRES AND COAL

Comparative combustion studies were performed on particles obtained fr om pulverized bituminous coal and waste automobile tyres (rubber). Par ticle size cuts of 75-90 and 180-212 mu m were burned in a thermogravi metric analyser, at low heating rates, and in an electrically heated d rop-tube furnace, at high heating rates. The combustion of individual particles in the drop-tube furnace was observed with three-colour pyro metry, to obtain time-temperature histories and with high-speed cinema tography to record flame-particle size histories. Combustion was condu cted at a gas temperature of 1450 K, in air. Upon pyrolysis, the pheno mena of melting, swelling and formation of large blowholes were observ ed only in the case of the coal particles. The tyre particles formed c hars with rough surfaces and smaller blowholes. Separate volatile and char combustion phases were detected for the coal particles studied. T yre particles experienced an intense primary volatile combustion phase , followed by a phase of simultaneous secondary volatile combustion, o f lesser intensity, and char combustion. During the initial volatile p hase combustion, the peak flame temperatures were comparable for both materials, in the range 2200-2400 K. The secondary volatile/char combu stion phase, observed for the tyre particles, was cooler? i.e. 2000-21 00 M. The coal chars burned with temperatures of 1850-2000 K. Combusti on was diffusionally controlled (regime III) for coal chars of both si zes and for tyre chars of the larger size cut only. Char burnout times were considerably shorter for tyre particles than coal, which can be attributed to the secondary devolatilization and the lower density of the former.