EMISSIONS OF BATCH COMBUSTION OF WASTE TIRE CHIPS: THE PYROLYSIS EFFECT

ABSTRACT

Staged pyrolysis and combustion of waste tire chips was investigated as a technique to minimize emissions of pollutants. Fixed quantities of chips were introduced to a furnace under pyrolytic conditions (in nitrogen) and devolatilized at furnace temperatures in the range 500–1000°C. The pyrolyzate gases were then mixed with additional streams of either nitrogen or oxygen in a venturi mixer, placed in-side the furnace. In the oxygen case, a nominally premixed flame occurred at the exit of the venturi, still inside the furnace. The effluent of either case was channeled to a secondary furnace for further treatment at 1000°C for a duration of 0.6 s. Sampling for combustion emissions, including products of incomplete combustion (PIC), took place at the exits of both furnaces. Sampled species included CO₂, CO, polynuclear aromatic hydrocarbons (PAHs), particulates, as well as nitrogen and sulfur oxides. Results showed that under inert conditions in both furnaces (pyrolysis–pyrolysis case) the emissions of PAHs and particulates from the primary furnace were high and drastically increased by the secondary furnace treatment. To the contrary, in the pyrolysis-oxidation case, when the pyrolyzates ignited and formed a flame at the exit of the venturi, the particulate and PAH emissions were low at the exit of the primary furnace. PIC were further reduced in the secondary furnace as oxidative conditions prevailed therein. As these experiments measured the PAH and soot amounts in the tire pyrolyzates before and after the flame, they illustrated the effectiveness of a nominally premixed flame for oxidizing such species. They also illustrated that a sequential pyrolysis–oxidation approach has the potential for low emissions in waste tire-to-energy plants.

Keywords:

• waste tires
• tire chips
• pyrolysis
• combustion
• emissions
• PAH
• soot

Acknowledgments

The authors would like to thank Mr. Eric Wisnaskas for assistance with the chromatographic analysis. The authors would also like to acknowledge the São Paulo Research Foundation, FAPESP, for financing Dr. Jefferson Caponero (No. 99/000375-5). Partial support was also provided by US NSF via grant CTS-9908962.

Notes

*Calculated.