## 6 Conclusions  
A kind of swirling curtain dust collector (SCDC) was designed for removing dust produced in a metal mine. This dust collector consists of a dust collector box, a spray device, a bidirectional swirling-dedusting-dewatering device and a dust slurry collector. The performance of the SCDC was studied under different operating parameters. The main conclusions are as follows:  
1. The proposed device is a kind of comprehensive wet dust collector. After the dust airflow entered the dust collector, it was mixed with the water curtain produced by ultrasonic nebulizer and pressure sprayer. A mixture of dust and water was formed after collision, interception and diffusion. Finally, the dust-water mixture was thrown onto the cylinder wall and removed under the centrifugal action of the cyclone.
2. The optimum working conditions of the device were as follows: air pressure: 0.35 MPa, water volume: 30 L/h; liquid-gas ratio: 0.15 L/m3; wind speed: 14-16 m/s. Under the above conditions, the suppression efficiency of total dust and respirable dust were over 99.8% and 97%, respectively.
3. The proposed device was applied in Luohe Iron Mine located in China. It was installed on transfer station and the dust removal effect was evaluated comparatively. The results of the application measurements indicated that the mean dust concentration decreased from 32.7 mg/m3 to 4.3 mg/m3 when the SCDC was used. The dust removal efficiency was over 99.8%. The average dust concentration at the outlet of SCDC was less than 20 mg/m3, which is stipulated by Chinese standard GB 28661-2012. Based on the above discussion, the proposed device was an ideal device with which to replace the traditional Venturi wet scrubber. It is also suitable for a wider utilization.  
Conceptualization, G.L.; methodology, G.L.; investigation, G.L.; writing--original draft preparation, G.L. and J.H.; writing--review and editing, J.H. and X.H.; supervision, H.Q.; project administration, X.H. and H.Q. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Key R&D Program of China \"Physicochemical dust removal technology and equipment in mining and transportation of metal and nonmetallic mines during the 13 th Five-year Plan Period\" (grant number 2017 YFC0805204), the Science research project of Hunan Provincial Department of Education of China (grant number 18C0322) and the Doctoral Scientific Research Foundation of Hunan University of Science and Technology (grant number E51853).  
Figure 14: Comparison of dust distribution before/after SCDC used in transfer station.  
**Acknowledgments:** This research was funded by the \"Physicochemical dust removal technology and equipment in mining and transportation of metal and nonmetallic mines during the 13 th Five-year Plan Period\" (grant number 2017 YFC0805204), the Science research project of Hunan Provincial Department of Education of China (grant number 18C0322) and the Doctoral Scientific Research China National Key R&D Program for the Foundation of Hunan University of Science and Technology (grant number E51853).  
**Conflicts of Interest:** The authors declare no conflict of interest.