Entrance velocity optimization for modified dust cyclones.
2000; Volume: 4; Issue: 3 Linguagem: Inglês
ISSN
1524-3303
AutoresPaul Funk, S. E. Hughs, Gregory Holt,
Tópico(s)Cyclone Separators and Fluid Dynamics
ResumoEntrance air velocity affects both the fan energy consumption and the dust collection efficiency of cotton gin cyclones. Recent findings have resulted in changes in cyclone design recommendations. Entrance air velocity was varied on both conventional and modified cyclones to determine whether air velocity recommendations need to be updated for the new designs. High efficiency cyclones were constructed 30 cm (12 in) in diameter (D). The cyclone body was one D high, the cone section 3D high (1D3D). The cyclones either had a standard entrance D/8 wide by D tall, or a 2D2D-style entrance D/4 wide and D/2 tall. Trash outlets at the terminus of the cone section were either a standard D/4 or a modified D/3 wide. Four levels of entrance air velocity were tested from 13.2 to 17.8 m s (2600 to 3500 ft min). Dust collection efficiency was determined by weighing filters through which cyclone exhaust air had passed. There was not a statistically significant difference in dust collection due to entrance air velocity, but cyclone modifications clearly improved performance. Pressure drop, which relates to fan energy requirements, increased 20% with both modifications. Pressure drop was observed to increase linearly with entrance air velocity. There is insufficient evidence based on dust collection efficiency to change design velocity recommendations for either standard or modified 1D3D cyclones. However, the potential exists to save energy by reducing entrance velocity since the pressure drop in modified cyclones is 30% lower at 13.2 m s (2600 ft min) entrance velocity compared to 16.3 m s (3200 ft min). Dust cyclones are the most cost-effective technology available to control dust emissions from cotton gins (Flannigan et al., 1998). Meeting increasingly stringent state and county air quality regulatory agency requirements with cyclones alone is, therefore, desirable. Recent research indicates a significant improvement in the collection efficiency of the widely used 1D3D cyclone may be realized by modifying the 1D3D design to employ a 2D2D-style entrance (Hughs and Baker, 1997). Improvements P.A. Funk and S.E. Hughs, Southwestern Cotton Ginning Res. Lab., USDA-ARS, Mesilla Park, NM; and G.A. Holt, Cropping Systems Research Lab., USDA-ARS, Lubbock, TX. *Corresponding author (pfunk@nmsu.edu). Abbreviations: 1D3D, A cyclone of diameter D with the body height 1 x D and the cone height 3 x D; 2D2D, A cyclone of diameter D with the body height 2 x D and the cone height 2 x D; D/3, A cyclone of diameter D with the cone bottom terminating at diameter D/3; D/4, A cyclone of diameter D with the cone bottom terminating at diameter D/4. 179 FUNK ET AL.: CYCLONE VELOCITY OPTIMIZATION Figure 1. 1D3D cyclones of diameter D including a) standard entrance (D/8 wide), standard trash outlet (D/4); b) modified entrance (D/4 wide), standard trash outlet (D/4); c) standard entrance (D/8 wide), modified trash outlet (D/3); d) modified entrance (D/4 wide), modified trash outlet (D/3). also were observed when the D/4 trash exit was enlarged to D/3 (Baker and Hughs, 1999). In the above studies the 1D3D cyclone was modified but the standard entrance velocity of 16.3 m s (3,200 ft min) from the Cotton Ginners Handbook (Parnell et al., 1994) was not altered when the dust collection effectiveness was being measured. The study herein attempts to find the optimum entrance velocity for the 1D3D cyclone modified according to current design recommendations (Green et al., 2000). Four 1D3D cyclones were tested over a range of entrance velocities from 13 to 18 m s (2600 to 3500 ft min). Dust collection efficiency was measured by weighing fiberglass filters through which all the exhaust air had passed. Pressure drop also was recorded. MATERIALS AND METHODS The four cyclones constructed for this study were 30 cm (12 in) in diameter. The upper (body) sections and the lower (cone) sections of each cyclone were 30 and 90 cm (12 and 36 in) high, respectively. Two cyclones had the standard 3.75 x 30 cm (1.5 x 12 in) inlets. Two had the recommended modification (called a 2D2D inlet) that was 7.5 x 15 cm (3 x 6 in). The clean air outlet duct extended 3.75 cm (1.5 in) below the bottom of each inlet (Fig. 1). Trash outlets were 7.5 cm (3 in) and 10 cm (4 in) in diameter, so both inlet styles were tested with a standard D/4 and a new (currently recommended) D/3 outlet. Trash material that had passed through the unloading separator screen of a cotton gin was used for two reasons. It contained lint fiber, leaf trash and fine dust typical of the dust burden handled by cotton gin cyclones. Also, the particle size distribution (Table 1) was appropriate for 30 cm diameter test cyclones. Previous experiments with this trash material in 30 cm cyclones have indicated that results thus obtained are representative of results obtained with regular gin trash in full-size cyclones (Holt et al., 1999). A cloth conveyor belt dropped 1.66 g s (13 lb h) of trash material into the suction side of a variable speed fan drawing from 0.153 to 0.207 m s (324 to 438 ft min) air, resulting in a 10.9 to 8.02 g m (4.7 to 3.5 grains ft) trash loading rate. This rate corresponds to more heavily loaded exhausts in a cotton gin. A constant speed fan propelled the dust-laden air into the test cyclones. Transducers connected to a data logger recorded pressure drop. Material caught by the cyclone was collected in an airtight bucket attached below the trash outlet for later weighing. Material escaping with the clean air was collected on a 60 x 60 cm (24 x 24 in) Hi-vol fiberglass filter (Hi-Q Environmental Products, San Diego, CA). Filters were weighed to Table 1. Sieve analysis of trash material†. Sieve Size range Average Standard deviation
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