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Fluid flow and combustion in rotary kiln

University of British Columbia

Thermal processing of minerals and materials within rotary kilns involves energy generation by combustion and its subsequent heat transfer (by turbulent diffusion and radiation) to the charge (the bed) and refractory walls. Thus, by influencing heat transfer, flame behavior and the combustion process can significantly influence processing conditions. Proper burner design and flame control ensure high fuel utilization efficiency, long life time of the refractory lining.(kiln walls), low pollutant emissions and high product quality. In the current work, a simplified computational fluid dynamics model of combustion aerodynamics and heat transfer within rotary kilns was developed and validated against thermal measurements from a 0.41 m I.D. by 5.5 meter long pilot rotary kiln. The validation program demonstrate the model's ability to capture the flame phenomena at the pilot scale. From this basis, the model was applied to simulate flame conditions for a 4 m I.D. by 40 m long kiln, which is more typical of the industrial scale. The effects of burner configuration and primary air ratio on the flame shape and heat transfer were investigated. These results suggest that flame length may be effectively increased by reducing the momentum of the fuel jet. The results suggest that, the primary air ratio will have marginal effect on flame behavior which is more strongly influenced by the momentum of the primary jet. Results are presented which demonstrate the effect of firing conditions; e.g. momentum of the primary jet and primary air ratio, on flame characteristics and, more importantly the axial distribution of heat transfer to both the bed and kiln refractory. From this basis, operators are given guidance on how the controllable burner parameters might be adjusted to reduce wall "hot spots"; and alleviate product quality and control of agglomeration/ringing problems. The work also indicates that for typical gas-fired operations, buoyancy effects should have little influence on flow and combustion within the hot-end of the kiln.

Thesis/Dissertation

application/pdf

2009-05-28

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http://hdl.handle.net/2429/8426

Materials Engineering

University of British Columbia

UBCV

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