CO-COMBUSTION OF PULVERIZED COAL, PINE SHELLS, AND TEXTILE WASTES IN A PROPANE-FIRED FURNACE: MEASUREMENTS AND PREDICTIONS

Abstract

This paper describes an experimental and numerical investigation on the co-combustion of propane with pulverized coal, pine shells, and textile wastes. Measurements have been performed in a large-scale laboratory furnace fired by an industrial-type swirl burner. Data are reported for in-flame major gas-phase species concentration, including NO_x, in-flame gas temperature, and overall char burnout for three flames: a propane/coal flame, a propane/pine shells flame, and a propane/textile wastes flame. For comparison purposes, data are also reported for a pure propane flame. The experimental results show that CO and unburned hydrocarbon emissions from propane cofiring with pine shells and textile wastes can be important due to the relatively large sizes of the solid particles and that NO_x emissions data reproduce the impact on them of the fuel nitrogen content via fuel-NO formation for the three solid fuels studied. Also, the cofiring of propane with pine shells and textile wastes yields particle burnout values much higher than that of the propane/coal flame despite the similarities of the three flames revealed by the in-flame data. This is because of the higher volatile matter content of the pine shells and textile wastes, in spite of their much larger particle sizes, compared with coal. The experimental conditions were then simulated numerically. For the numerical predictions, gas-phase calculations were based on the Eulerian approach whereas the particulate phase predictions were based on a stochastic Lagrangian approach. The turbulence model used herein was the standard two-equation eddy viscosity model. The gaseous fuel and volatiles oxidation was assumed to be controlled by both turbulent mixing and chemical kinetics. Radiation was accounted for. The biomass/waste devolatilization was simulated by a single-reaction, first-order decomposition model. Thermal-NO, prompt-NO, and fuel-NO mechanisms were all considered as potential contributors to the NO formation. From the comparisons of the predictions with the experimental data, a good agreement was generally found, except in the near-burner region close to the furnace symmetry axis. The discrepancies are due to the limitations of the k–ε turbulence model to simulate high swirling flows. Moreover, the simplified fuel-NO model used herein requires further improvements to yield more accurate results.

Keywords:

• cofiring
• pulverized coal
• pine shell
• textile wastes
• propane
• in-flame data
• measurements
• predictions

Acknowledgments

Financial support for this work was provided by the European Commission under the project “Fuel Blends—Production and Utilization of High Quality Fuel Blends from Industrial Wastes and Coal for Heat and Power Generation—Textile Waste Co-processing,” contract number JOF3-CT95-0010, and is acknowledged with gratitude. The first and second authors (T.H. Ye and J. Azevedo) are pleased to acknowledge the Fundação para a Ciência e Tecnologia for the provision of scholarships (SFRH/BPD/1561/2000 and PRAXIS XXI BM/10565/97).