Research on and Design of a Self-Propelled Nozzle for the Tree-Type Drilling Technique in Underground Coal Mines
Abstract
:1. Introduction
2. Preliminary Design
3. Drilling Speed Tests
3.1. Test Apparatus and Method
- The high-pressure pump; rated pressure 32.5 MPa, rated flow rate 200 L/min.
- The jet generator; main components include the hose connector, the pressure gauge, high-pressure hose, and the nozzle connector.
- The drilling console mounted on tracks. There is a removable steel bar for fixing the nozzle to the steel pipe connected to the drilling console. When measuring the self-drilling speed, the bar is removed freeing the nozzle to move forward. When conducting the rock breaking tests and studying the pattern of broken holes, the bar is replaced to fix the nozzle to the drilling console so that the two will move together. The rate at which the drilling console can move is controlled by an electric motor and ranges from 0.01 to 100 mm/s.
- The nozzle. Using the control variable method to design experiments, the influence law of each forward orifice configuration on rock breaking efficiency of the nozzle was studied. Thirteen different self-propelled nozzles were designed and machined for testing. The nozzles, shown in Figure 5, all have the same backward orifices axial angle (25°). The specifications for the forward orifices are shown in Table 1. According to previous research, the optimal axial angle for a nozzle orifice is about 20° for rock breaking [20]. Therefore, the values of axial angle in the nozzles used for this study are around 20° and 5° as a research level considering machining limits. The values of radial angle cover the whole range from 0° to 90°. The values of center distance are limited by the diameter of the nozzle, so the maximum is 1.8 mm (±0.1 mm as a level also due to machining limits).
- Experimental coal sample. Coals from different mines in different regions can have very different physical properties. In order to test drilling in different kinds of coal and determine if the technique is broadly applicable, large blocks of coal were collected from three coal mines for drilling tests. The mines were the Songzao mine in southwest China, the Pingdingshan mine in central China, and the Tashan mine in northwest China. The coal ranks are from high volatile bituminous to anthracite and their hardnesses range from low to high. The experimental coal block sample from the Pingdingshan mine is shown in Figure 6.
Number | Forward Orifice Structure Parameters | ||
---|---|---|---|
Axial Angle α/° | Radial Angle β/° | Center Distance l/mm | |
1# | 15 | 0 | 1.5 |
2# | 20 | 0 | 1.5 |
3# | 25 | 0 | 1.5 |
4# | 30 | 0 | 1.5 |
5# | 35 | 0 | 1.5 |
6# | 25 | 25 | 1.5 |
7# | 25 | 45 | 1.5 |
8# | 25 | 65 | 1.5 |
9# | 25 | 90 | 1.5 |
10# | 25 | 90 | 1.4 |
11# | 25 | 90 | 1.6 |
12# | 25 | 90 | 1.7 |
13# | 25 | 90 | 1.8 |
3.2. Experimental Results and Discussion
3.2.1. The Effect of the Forward Orifice Axial Angle on Self-Drilling Speeds
3.2.2. The Effect of the Forward Orifice Radial Angle on Self-Drilling Speeds
3.2.3. The Effect of Forward Orifice Center Distance on Self-Drilling Speeds
4. Self-Propelling Force Measurement
4.1. Test Apparatus and Method
- The high-pressure pump and jet generator. The performance parameters are the same as those described in Section 3.1.
- A through-hole load cell. A load cell, model number LC8200-625-50 (from Omega Engineering Company, Stamford, CT, USA) was used to measure the forces. The load cell has a ~5 cm (2-inch) outer diameter and ~16 mm (0.625-inch) inner diameter and can measure forces in the 0–222 N range accurately.
- A glass pipe. The glass pipe was used to simulate a gas drainage borehole in a coal seam. The pipe’s inner diameter was 50 mm.
- Self-propelled nozzles. To analyze the total self-propelling force of the nozzle, five self-propelled nozzles with different backward orifice structures were machined. The nozzles are shown in Figure 12. These five nozzles all have the same forward orifice configuration (axial angle 25°; radial angle 90°; center distance 1.5 mm). The specifications for the backward orifices on the nozzles are shown in Table 2.
Number | Backward Orifice Axial Angle/° |
---|---|
1# | 10 |
2# | 15 |
3# | 20 |
4# | 25 |
5# | 30 |
4.2. Experimental Results and Discussion
4.2.1. The Effect of Backward Orifice Axial Angle on Total Self-Propelling Force
4.2.2. The Effect of the Backward Orifice Axial Angle on the Diameter of the Self-Drilled Borehole
5. Conclusions
Acknowledgments
Author Contributions
Conflicts of Interest
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Lu, Y.; Zhou, Z.; Ge, Z.; Zhang, X.; Li, Q. Research on and Design of a Self-Propelled Nozzle for the Tree-Type Drilling Technique in Underground Coal Mines. Energies 2015, 8, 14260-14271. https://doi.org/10.3390/en81212426
Lu Y, Zhou Z, Ge Z, Zhang X, Li Q. Research on and Design of a Self-Propelled Nozzle for the Tree-Type Drilling Technique in Underground Coal Mines. Energies. 2015; 8(12):14260-14271. https://doi.org/10.3390/en81212426
Chicago/Turabian StyleLu, Yiyu, Zhe Zhou, Zhaolong Ge, Xinwei Zhang, and Qian Li. 2015. "Research on and Design of a Self-Propelled Nozzle for the Tree-Type Drilling Technique in Underground Coal Mines" Energies 8, no. 12: 14260-14271. https://doi.org/10.3390/en81212426