Zhuojin Pipe Fitting Co., LtdFlow Field Measurement of a Three-Channel Burner for Cement Kilns
Literature Overview
This research, conducted by Zhang Hongqiang, He Dexin, Zhu Minghong, and Yin Dengao from the China Aerodynamics Research and Development Center, was published in Experiments and Measurements in Fluid Mechanics (2001, Vol. 15, No. 1, pp. 64–69). The study investigates the flow field characteristics of a three-channel burner used in cement rotary kilns. The primary objective was to measure and analyze the jet flow patterns within the coal injection tubes of the burner, evaluate the design of a new coal injection tube, and determine the optimal swirl angle for the tube geometry.
Technical Background
Three-Channel Burner Configuration
A three-channel burner is a specialized combustion device used in cement rotary kilns to deliver fuel, combustion air, and secondary air (or fuel gas) through separate channels. The coal injection tube is responsible for conveying pulverized coal into the kiln flame zone, and its internal flow characteristics directly influence fuel dispersion, combustion efficiency, and flame stability. The design of the coal injection tube must balance several competing requirements: sufficient jet velocity to penetrate the kiln atmosphere, adequate turbulence for fuel-air mixing, and manageable pressure drop to minimize fan power consumption.
Experimental Methodology
The authors employed flow field measurement techniques, likely including hot-wire anemometry or Pitot tube traverses, to characterize the velocity profiles within the coal injection tube. The measurements were taken at multiple axial stations to capture the development of the jet from the inlet to the exit. The swirl angle, defined as the helical angle of the internal guide vanes or spiral geometry within the tube, was varied to study its effect on the longitudinal velocity decay profile.
Key Findings and Analysis
Longitudinal Velocity Decay Characteristics
The experimental results demonstrated that the longitudinal velocity decay of the coal injection jet follows a reasonable and predictable pattern. This finding is significant because it confirms that the jet maintains sufficient momentum over the required transport distance to deliver coal effectively into the kiln flame. The decay rate is governed by the jet's initial momentum flux, the density ratio between the jet and ambient gas, and the turbulence intensity. A well-designed injection tube should produce a jet with a decay profile that ensures complete fuel penetration without excessive momentum that could cause flame instability or refractory damage.
| Design Parameter | Effect on Flow Field |
|---|---|
| Swirl angle | Influences turbulence intensity and radial velocity components |
| Tube diameter | Affects jet exit velocity and momentum flux |
| Guide vane geometry | Controls swirl number and jet spreading rate |
| Inlet flow uniformity | Determines baseline turbulence level |
Optimal Swirl Angle Determination
The study concluded that a swirl angle of 45 degrees represents an optimal parameter for the new coal injection tube design. This finding is consistent with established principles in combustion engineering, where moderate swirl promotes effective fuel-air mixing while maintaining sufficient axial momentum for jet penetration. At angles below 45 degrees, the jet may lack sufficient radial turbulence for complete mixing, leading to incomplete combustion and increased NOx formation. At angles above 45 degrees, excessive swirl can cause flow separation within the tube, increased pressure drop, and potential flame instability.
Design Validation
The authors concluded that the new coal injection tube design is reasonable and suitable for internal flow characteristic analysis. This conclusion implies that the measured flow field data align with expected theoretical behavior, validating both the design geometry and the measurement methodology.
Engineering Practice Implications
Application to Cement Kiln Operations
For cement kiln operators, the internal flow characteristics of the coal injection tube directly impact several operational parameters:
- Combustion efficiency: Proper jet velocity and swirl ensure complete fuel combustion, reducing unburned carbon losses and improving thermal efficiency.
- NOx emissions: The swirl angle influences the flame temperature distribution and residence time, which are key factors in thermal NOx formation.
- Refractory life: Excessive jet momentum directed at refractory surfaces can cause erosion and premature failure.
- Fan power consumption: The pressure drop across the injection tube must be minimized to reduce auxiliary power costs.
Measurement Technique Considerations
The flow field measurement approach used in this study provides a baseline for evaluating burner performance during commissioning or after maintenance. Engineers should consider implementing similar measurement protocols for their own burner systems, particularly when troubleshooting combustion instability or efficiency degradation. The key is to measure at multiple axial stations and at various radial positions to capture the full three-dimensional flow structure.
Study Insights and Outlook
This paper, while focused on a specific industrial application, demonstrates fundamental aerodynamic principles that are broadly applicable to jet flow design in industrial burners. The determination of an optimal swirl angle of 45 degrees is a practical result that can be directly applied to burner design and optimization. For engineers working on combustion systems, the study reinforces the importance of empirical flow field measurement in validating theoretical design assumptions. Future research could extend this work by incorporating computational fluid dynamics (CFD) simulations to predict flow field characteristics for a wider range of swirl angles and tube geometries, and by studying the interaction between the jet flow and the kiln's internal gas dynamics to optimize overall combustion performance.