Swirl burner

Swirling flow, or vortex flow, occurs in different types of equipment, such as cyclones, hydrocyclones, spray dryers and vortex burners. Swirling flow also plays a central role in the developing fields of fluidics and process intensification. It is also the basis for the operation of foam-breaking or defoaming separators that have received significant industrial attention in recent years. 

The circular burner shown in Fig. 27-17 is widely used in horizontally fired furnaces and is capable of firing coal, oil, or gas in capacities as tigh as 174 GJ/h (1.65 X 10 Btii/h). In such burners the air is often swirled to create a zone of reverse flow immediately downstream of the burner centerline, which provides for combustion stability. 

Oil Burners The structure of an oil flame is shown in Fig. 27-28, and Fig. 27-29 illustrates a conventional circiilar oil burner for use in boilers. A combination of stabilization techniques is used, typically including swirl. It is important to match the droplet trajectories to the combustion aerodynamics of a given burner to ensure stable ignition and good turndown performance. 

Gas Burners Gas burners may be classified as premixed or non-premixed. Many types of flame stabilizer are employed in gas burners (see Fig. 27-32). Bluff body, swirl, and combinations thereof are the predominant stabilization mechanisms. 

The burner should be so arranged that the flame impinges upon the side of the flask in such a way as to dissolve the sodium iodide from the top downward. The flask should be shaken or swirled frequently during the onset of boiling. A small amount of white solid remains undissolved even at reflux. 

A two-color pyrometer has been used along with the phase-Doppler anemometer to simultaneously measure the local velocity and size of kerosene droplets and the temperature of burning soot mantle in a swirl burner.[648] The measurements were conducted within the flame brush that develops in the shear layer of a swirl-stabilized, gas-supported kerosene flame with a swirl number of about 0.19 and potential heat releases of 10.6 and 15.5 kW, respectively. The results showed that the maximum burning fraction of the droplets occurs adjacent to the region denoted as gas flame but the value ranges from 20 5 to 40 5% depending on the axial station, and decreases sharply across the shear layer. The flame mantle temperature was found to be independent of droplet diameter, which agrees with previous results in the literature. 

Swirl Since swirl is present in many propulsion burners, studies were undertaken to test the robustness of the control system by imposing swirl in the central air flow. Another objective of these studies was to see if added swirl could improve the operation of the controller. The swirl was introduced by letting the airflow into the central tube from two off-axis 90-degree inlets. The percent swirl quoted here is the percent of the total central air flow that entered from these swirl inlets as opposed to the nonswirling inlets. The average axial velocity radial profile showed a strong minimum on the centerline, and at higher levels of swirl the flame could actually be sucked back into the airflow. 

Figure 17.1 (a) Countercurrent Swirl Combustor experimental facility (6) isometric view of the burner and (c) cross-sectional view of the burner indicating relevant parameters... 

The swirl number, a dimensionless ratio of the angular momentum to the product of the axial momentum and the radium of the burner, can be varied through separate control of the two secondary air streams in order to study various burner designs. The air flows were measured using sharp edged orifices. Control of the air flows and calibration of the coal feeder made it possible to duplicate combustion conditions as determined both by exhaust gas analysis (CO, CO2, O2, NO, NOx) and aerosol characteristics. 

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